MR SAR B1+ RMS SED

Replace with image Continue Continue Continue Continue Continue Continue Continue Continue Continue Continue Continue Continue Continue Continue Continue Continue Continue MRI SAR B1+RMS SED Numaris X MRI SAR, B1+RMS, & SED - Numaris X online training Welcome This online training focuses on Specific Absorption Rate, B1+RMS, and Specific Energy Dose (SED) for Siemens Healthineers Numaris X MR systems. MRI SAR, B1+RMS, & SED Table with 4 columns and 5 rows At the end of this training, you should be able to: Define Specific Absorption Rate (SAR) Specify SAR operating modes and limitations Describe B1+RMS Explain Specific Energy Dose (SED) Navigate myExam User Interface for SAR, B1+RMS, and SED Identify Potential SAR/SED reduction techniques Disclaimers Disclaimers Objectives At this end of this module, you should be able to: Define Specific Absorption Rate (SAR) Specify SAR operating modes and limitations Define B1+RMS Define Specific Energy Dose (SED) Navigate myExam User Interface for SAR, B1+RMS, and SED Identify Potential SAR/SED reduction techniques Please review disclaimers by selecting the button. Please review disclaimers before proceeding. Siemens Healthineers Disclaimers Siemens Healthineers MAGNETOM MR systems are not labeled for use with implantable medical devices. FDA has not evaluated the safety and effectiveness of these systems for use with implantable medical devices. Siemens Healthineers does not assume any responsibility or liability for the operation of a MAGNETOM MR System with any implantable device. Please direct any safety related questions to your facility’s MR Safety Officer (MRSO), MR Medical Director (MRMD), or Directing Radiologists. The information presented in the MRI SAR, B1+RMS, and SED module is for illustration only and is not intended to be relied upon by the reader for instruction as to the practice of medicine. Any health care practitioner reading this information is reminded that they must use their own learning, training, and expertise in dealing with their individual patients. This material does not substitute for that duty and is not intended by Siemens Healthineers to be used for any purpose in that regard. Please refer to a contrast agent manufacturer's labeling, and instructions for use, for use of that contrast agent with an MRI exam. Disclaimers ? Specific Absorption Rate SAR is defined as the Radiofrequency (RF) power absorbed per unit of mass of an object when exposed to a radio frequency (RF) electromagnetic field. RF Exposure Application of time varying electromagnetic fields with frequencies in MHz range generating heat within tissue being exposed. Heating is a major effect of RF exposure. Safety considerations focus on temperature increases. SAR = Specific Absorption Rate Specific to the tissue (per kilogram) Absorption of the RF into the body and tissue Rate of RF exposure and absorption Unit of Measure = Watts per kilogram (W/kg) SAR Specific Absorption Rate is defined as the R-F power absorbed per unit of mass of an object when exposed to a radio frequency electromagnetic field. It is measured in Watts per kilogram. SAR is Specific to the mass of tissue, the absorption of the R-F into the body and tissue, and the rate of R-F exposure and absorption. R-F exposure is an application of time varying electromagnetic fields with frequencies in the Mega Hertz range, generating heat within tissue that is exposed. Heating is a major effect of R-F exposure and safety considerations focus on temperature increases. ? Safety Aspects of SAR Various MR Safety aspects must be considered. These include: Capacity of the patient's thermo-regulation to dissipate heat is respective to global RF load If not limited to tolerable values, life-threatening episodes could be a consequence Localized high SAR values in excess could lead to local burns Guidelines are issued that set limits for SAR to limit RF load to tolerable values Safety aspects of SAR There are various safety aspects that must be considered, theses include: the capacity of the patient's thermo-regulation to dissipate heat is respective of global radio frequency load. If this is not limited to tolerable values, life threatening episodes could be a consequence. Localized high SAR values in excess could also lead to localized burns. Therefore, guidelines have been issued by the F-D-A and the I-E-C that set limits for SAR to limit the Radiofrequency load to tolerable values for patients. ? FDA & IEC guidelines The FDA and IEC provide guidelines that issue limits on Radiofrequency (RF) exposure during an MR examination. United States Food & Drug Administration (FDA) International Electrotechnical Commission (IEC) is accepted in most countries (including US) FDA & IEC guidelines The Food and Drug Administration and the International Electrotechnical Commission provide guidelines issuing limits respective of Radiofrequency exposure during an M-R examination. The I-E-C guidelines are accepted in most countries including the United States. International Electrotechnical Commission (IEC) Footnote Normal & first level mode Normal & first level mode Normal & first level mode Normal & first level mode Guidelines & SAR limits Guidelines & SAR limits Guidelines & SAR limits Guidelines & SAR limits SAR SAR SAR SAR IEC Base layer The I-E-C provides guidelines and limits for M-R equipment. Select each tab to discover more about each of the topics shown. Normal and first level mode tab The SAR monitor on Siemens Healthineers M-R equipment provides two operating modes that fall within the guidelines for the I-E-C. These include, normal operating mode which only requires routine monitoring of the patient. The first level-controlled mode requires medical supervision. Medical supervision requires a positive assessment by a qualified medical practitioner of the risk versus benefit for the scan, or a decision by a qualified surrogate of the practitioner that the patient satisfies a set of objective criteria formulated by the medial practitioner. Formulation of this set of objective criteria is the responsibility of the medical practitioner. Medical practitioners may have different criteria based on the risks and benefits to their specific patient population. SAR Tab In accordance with the I-E-C standard and national regulations, our systems have SAR limits. These SAR limits apply to examinations with volume Radiofrequency transmit coils, for example, the body coil. They refer to an averaging time of six-minutes. To protect against too high short-time SAR exposures, the I-E-C guidelines requires additional limits, which are set with respect to any ten-second averaging interval. These ten-second limits are twice as high as those issued for the six-minute averaging time For the SAR aspects “Whole Body” and “Head”, the system calculates how much SAR will be applied to the head and to the whole body of the patient, dependent on the position of the patient relative to the transmit coil, patient height, and patient weight. For the aspect “Exposed Body”, SAR is derived by the ratio of the mass of the exposed part of the body and the whole-body mass. For example, an infant at the isocenter of the system will have its complete mass within the volume that is excited by the body coil, so that the ratio of exposed body mass, to whole body mass is one. Hence the “Exposed Body” aspect will be at its minimum limit of two-Watts-per-kilogram, which also matches the “Whole Body” limit. A tall patient positioned with the feet at isocenter, will have a small ratio of an exposed part of the body to the whole-body mass. The “Exposed Body” limit will therefore be close to the maximum of 10 W/kg. The system derives the patient position with respect to the patient table from the patient orientation entered, for example, Head-First-Supine, patient height, and the standard positioning of the head. In patient setups where the head positioning is not standard, for example, if the patient orientation is feet-first, the system follows a conservative approach to estimate the patient position. This situation usually results in stricter SAR limitations. The SAR limit values are also a function of the ambient temperature. At a room temperature of greater than, twenty-five-degrees-Celsius, or, greater than Seventy-Seven degrees Fahrenheit, the permitted SAR limits decrease. Guidelines and limits slide I-E-C guidelines also differentiate between two groups of SAR limits: Global and Local. -Global SAR-Limits include: whole body, exposed part of the body, and head. -Local SAR-Limits include: the Head, Trunk, and Extremities These guidelines specify rules, regarding when to observe which limits, depending on the type of transmit coil, or, whether it is a volume, or local R-F transmit coil. The Volume Transmit coils observe Global SAR limits only, and Local Transmit coils observe Local SAR limits, plus whole-body SAR limits. Let’s review the I-E-C, SAR limits. -Whole-Body SAR limit averages the patient’s total body mass over specified time. -Partial body SAR limits, (or the exposed part), is averaged over the patient’s body mass, exposed by the volume of the Radio Frequency transmit coil, over a specified amount of time. -Head SAR limits are averaged over the mass of the patient's head over a specified amount of time, and -Local SAR, is the maximum amount of SAR averaged over any 10-grams of tissue of a patient's body over a specified time . Tab Slide Please click on one of the tabs to display the corresponding content on this page. IEC Guidelines differentiate two groups of SAR limits Global SAR-Limits – Whole Body, exposed part of Body, Head Local SAR-Limits – Head, Trunk, Extremities Guidelines specify rules on when to observe which limits depending on the type of transmit coil, volume, or local RF transmit (Tx) coil Volume Tx coils > Global SAR limits only Local Tx coils > Local SAR limits + whole-body SAR limit Whole body SAR The SAR is averaged over the patient’s total body mass over a specified time. Partial body SAR (Exposed Part) The SAR is averaged over the patient’s body mass that is exposed by the volume of the RF transmit coil over a specified time. Head SAR The SAR is averaged over the mass of the patient's head over a specified time. Local SAR The SAR is the maximum amount of SAR averaged over any 10 grams of tissue of a patient's body over a specified time. Specific Absorption Rate (SAR) SAR limits: In accordance with the IEC 60601-2-33 standard and national regulations, our systems are limited to: Table with 3 columns and 4 rows SAR Aspect Limits in Normal Operating Mode [W/kg] Limits in First Level Operating Mode [W/kg] Whole Body 2.0 4.0 Exposed Body 2.0 – 10.0 2.0 – 10.0 Head 3.2 3.2 Infant Whole body vs. Exposed Body SAR aspect = 1:1 > 25 0 C or > 77 0 F SAR limits decrease Tab instructional statement(s). Normal Operating Mode – requires routine monitoring of the patient First Level Mode – requires medical supervision Info: A positive assessment by a qualified medical practitioner of the risk versus benefit of the scan, or a decision by a qualified surrogate of the practitioner that the patient satisfies a set of objective criteria formulated by the medical practitioner. ? Estimating SAR SAR and core temperature RF Power in RF Power out Cooling RF power absorbed = RF power in – RF power out As RF power is introduced into the body, some power is reflected out of the body while some is absorbed. RF Power Absorbed = Power in and power out. As RF power is absorbed, heating occurs, and the core temperature rises. This absorbed RF power is measured with directional couplers (DICO) and is what we utilize to estimate SAR. Note: The body’s own mechanisms creates and dissipates heat (cooling), and time for cooling to occur is considered during SAR estimation. SAR and core temperature How do we estimate SAR, and core body temperature? As the R-F power is introduced into the body, some power is reflected out of the body while some is absorbed. R-F Power Absorbed equals Power in minus Power Out. As the Radiofrequency power is absorbed, heating occurs, and the core temperature rises. This absorbed R-F power is measured with directional couplers, and this is what we utilize to estimate SAR. Please Note: The body’s own mechanisms create and dissipates heat or cooling, and the time for cooling to occur is considered during the SAR estimation. ? Estimating SAR Look-Ahead monitor & SAR-man Look-Ahead Monitor During Patient Registration, the system estimates the body part volume and mass. The system then determines the position of body parts relative to transmission field volume based on the table landmark and then calculates how much RF power the scan being programed will execute. An estimation is made regarding how much power is being absorbed by each body part (SAR) and it compares these estimates to the defined SAR limits. SAR Limits are Exceeded Look Ahead Monitor & SAR man The Siemens Healthineers M-R system has a Look-Ahead monitor. Prior to each measurement, the Look-Ahead monitor estimates the SAR values that are automatically calculated, which includes possible measurement errors. It then compares this with the prescribed limit values. If one of the calculated SAR values exceeds the corresponding limit, the measurement cannot be started. In this scenario, the following message appears in the dialog window of the M-R User interface: SAR Limit’s are Exceeded. During patient registration the system estimates the body part volume and mass, this is dependent on the data entered on the registration page (height, weight, age, and sex). The system then determines the position of body parts relative to transmission field volume, based on table landmark. It then calculates how much R-F power the scan being programmed executes. An estimation is then made regarding how much power is absorbed by each body part, (SAR), and then compares these estimates to define the SAR limits. ? Estimating SAR Body part estimation: SAR-man Select the tab arrows to learn more about body part estimation in estimating SAR. Body part estimation Head Torso Leg Thick vs. Thin Estimating SAR - Look-Ahead monitor & SAR man Base layer Select the tab arrows to learn more about body part estimation in estimating SAR. Tab 1 The M-R patient registration data entered, estimates the body part volume and mass when the user enters the height, weight, sex and age of the patient. The SAR-Man on a Siemens Healthineers MAGNETOM M-R system, breaks the body down into volumes represented geometrically as cylinders (length, radius and mass) as shown in this diagram. This model is used to determine kilograms, in the watts per kilogram measurement of S-A-R. As we already stated, during patient registration when entering the patient's weight, height, age and sex, the system estimates the body part volume and mass. The SAR-man breaks the body down into parts represented geometrically as cylinders. The dimensions of the cylinders are based on normal growth measurements determined by world statistics. These statistics are taken from the National Center for Health Statistics and the Center for Disease Control. These organizations obtained statistical data that was dependent on the age of the patient, up to eighteen years of age. The dimensions of the cylinders are derived from statistical growth data. For patients over eighteen years of age, the values are extrapolated assuming that the body measurements are constant. Head tab When looking at the cylinders independently, the Head cylinder volume looks at both the head circumference and the length of the head cylinder. The head circumference calculates the head cylinder radius based on the age and sex of the patient entered on the patient registration page. The head cylinder length is calculated from the determined radius and mass of the patient’s head. Torso tab The Torso cylinder looks at the torso cylinder length, mass and radius as show in the diagram. The torso cylinder length subtracts the head and leg cylinder length from the patient’s height. The torso cylinder mass is determined by the difference in the total patient’s body mass, and the head and leg cylinder masses. While the torso cylinder radius is determined by both the length and mass of the patient. As you can see in the previous illustrations, it is important to the enter the patient’s height, weight, sex and age correctly, so the M-R system can accurately determine the patient’s body habitus. Leg tab The leg cylinder looks at the calf radius, length of the leg cylinder, and the calf circumference as show in the diagram. The calf radius determines a reasonable value for the overall leg cylinder radius. While the length of the leg cylinder is determined based on a “Sitting Height” ratio, it is a function of the age and sex of the patient and is used with the overall height entered in the Patient Registration window. The calf circumference is a function of the age and sex of the patient and determines the leg cylinder radius. Thin vs thick tab Now let’s review how the SAR-Man looks at various body types, thin verses thick patients. Thin or thick patients are only considered for the torso cylinder, the system assumes that the head and leg circumference variance is smaller compared to the torso. So, the radius of torso cylinder varies based on the patient’s total weight. The head radius is not affected by the weight entered; however, the total weight is a function of the patients age and sex entered. Then the system checks the validity of the weight entered in Patient Registration window. Thin vs thick patients Thin versus Thick patients are only considered for the torso cylinder. The system assumes that the head and leg circumference variance is smaller compared to torso. So, the radius of torso cylinder varies based on total patient’s weight. The Head radius is not affected by weight entered during Patient Registration. Total weight is a function of age and sex entered The system checks the validity of weight entered in Patient Registration. Leg cylinder volume Calf radius determines a reasonable value for the overall leg cylinder radius. Length of leg cylinder is determined based on a sitting height ratio, which is a function of the age and sex of the patient. It is used with the overall height entered during Patient Registration. Calf circumference is a function of the age and the sex of the patient and determines the leg cylinder radius. Torso cylinder volume Torso cylinder length subtracts the head and leg cylinder length from the patient’s height. Torso cylinder mass is determined by the difference in the total patient’s body mass, and the head and leg cylinder masses. Torso cylinder radius is determined by both the length and mass of the patient. Head cylinder volume Head Circumference calculates the head cylinder radius based on the age and sex entered during Patient Registration. Head Cylinder Length is calculated from the determined radius and mass of the patient’s head. Body part estimation – SAR man Patient Registration input estimates the body part volume and mass.  Date of Birth (required) Age (required) Sex (required) Height (required) Weight (required) The SAR-Man breaks the body down into volumes that are represented geometrically as cylinders (length, radius, and mass). Patient Registration input estimates the body part volume and mass. Up to 18 years the dimensions of the cylinders are derived from statistical growth data. Adults (>18 years) the values are extrapolated assuming that body measurements are constant. Dimensions of the cylinders are based on Normal Growth Measurements. Organizations obtained statistical data with dependency on the age of the patient up to 18 years of age. World statistics are taken from NCHS/CDC – National Center for Health Statistics/Center for Disease Control. Body & table position Body & table position Body & table position Example 02 Example 02 Example 01 Example 01 Body part estimation – SAR man Body part estimation - SAR man Select the following buttons for examples of how the patient’s body size ultimately effects the calculation inside the cylinder. example 1 In this example, you can see how the patient’s body size ultimately effects the calculation inside the cylinder. For example, if the patient is seven-feet tall, and weighs three-hundred-pounds, a smaller amount of their body is within the torso cylinder, and the coverage area is not as large. example 2 However, if the patient is five-feet tall, and weighs three-hundred-pounds, then the torso cylinder model covers most of the torso. This helps to explain how a patient that is shorter, and heavier has different SAR tolerances than a thinner and taller patient. Body & table position The body and table position, determines the position of the body part relative to the transmission field volume, which is based on where the table landmark was made. These cylinders define the mass of the body part used to calculate the specific SAR value for each body part, this then defines the location of each body part on the table. The body and table position determines the position of body parts relative to transmission field volume based on where the table landmark is made. Cylinders define the mass of the body part used to calculate the specific SAR for each body part. Which then defines the location of each body part on the table. Patient is 300 lbs. and 5 feet tall then the torso cylinder model covers most of the torso. Patient is 300 lbs. and 7 feet tall a smaller part of their body will be within the torso cylinder and the coverage area is not as large. ? Dependencies of SAR SAR scales with square of the main magnetic field as well as with square of the flip angle assuming there is a constant pulse duration. SAR is mainly interested on the dependency of B1 field, since B1 rules the Flip Angle Doubling the main magnetic field strength and keeping the pulse Flip Angle the same quadruples the SAR Increasing the Field Strength from 1.5T to 3T increases SAR by a factor of 4 Dependencies of SAR SAR scales with the square of main magnetic field, and the square of the flip angle, assuming there is a constant pulse duration. SAR is mainly interested on the dependency of the B-one field, since B-one rules the flip angle. If we double the main magnetic field strength, going from one-point-five-Tesla to three-Tesla, SAR increases by a factor of four, provided, all other factors remain the same. ? RF power deposition SAR increases proportionally as B02 (field strength) increases or a2 (Flip Angle) increases. SAR µ B02 a2 B1 (RF Field) µ a Scenarios If you keep the Flip Angle (a) the same and double B0 (field strength) then SAR quadruples. If you keep the B0 the same and double the Flip Angle, then SAR quadruples. If you double both B0 and Flip Angle, then SAR goes up by a factor of 16! RF power deposition SAR is proportional to the Larmor frequency squared, and B-one squared. Typically, we think in terms of B-zero field strength, (what you buy), and the flip angle, (what you set). The Larmor frequency is proportional to the B-zero field strength, and B-one is proportional to the flip angle. So, SAR is proportional to B-zero squared, and the flip angle squared. So, if you keep flip angle (B-one), the same, and double B-zero (Larmor), then SAR quadruples. Or, if you keep B-zero the same, and double the flip angle, then SAR quadruples. If you double, both B-zero and the flip angle, then SAR goes up by a factor of sixteen! ? Rf power requirements RF power requirements are empirically determined by the RF Power for a 180˚ flip angle versus the field strength for whole body applications. Rf power requirements Audio The R-F power requirements are empirically determined by the Radiofrequency Power for a hundred eighty-degree flip angle, versus the field strength for whole body applications. In the illustration, you can appreciate, as the field strength increases the R-F power, (SAR) also increases. SAR operating modes SAR and stimulation monitoring can be operated in two modes which are set during patient registration. Select the icons below to learn more about these two modes. SAR operating modes Audio To prevent health risks during M-R examinations, several international organizations (for example, the I-E-C), and various national health organizations, have published guidelines and limit values. Compliance with country-specific approval guidelines are the basis for the monitoring functions integrated into the M-R system, with respect to stimulation and warming effects. Both stimulation and SAR levels are based on current scientific literature related to safety. Siemens Healthineers MAGNETOM M-R systems, has two operating modes, Normal and First Level mode. In Normal Mode, SAR and d-B-over-D-t limits are set to lower values. So, warming of the patient is kept to a minimum and stimulation is typically excluded. When using First Level Mode (controlled mode), the SAR and d-B-over-d-t limits are set to higher values. This increases the SAR values, which may cause the patient to experience an increase in heating, and/or some slight peripheral nerve stimulation. Please note, patient monitoring is always recommended when scanning in First Level Mode. Increasing SAR Tolerance – Caution First Level Controlled Operating Mode shouldn’t be used in these instances: General or local hyperthermia of patients Don’t examine patients with restricted thermoregulatory capability (e.g., small Children, elderly, sick, or medicated patients) Don’t examine patients unable to communicate potential overheating effects. (e.g., small children, seriously ill, paralyzed, unconscious, sedated, or handicapped patients) Ensure patients wear patient gowns or scrubs (e.g., no snaps, or any metallic objects) Remove all additional insulation (e.g., blankets that may interfere with heat dissipation Observe/Monitor patient and provide squeeze bulb First Level Mode SAR and dB/dt limits are set to higher values Increased SAR Values may cause patient to experience notable heat increases Increased dB/dt values may cause patient to experience slight peripheral nerve stimulation Normal Mode SAR and dB/dt limits are set to low values Warming of patient is kept to a minimum and stimulation can be excluded Default operating mode myExam UI Queue - Examination toolbar: SAR SAR icon – Opens/closes SAR information dialog window. Progress Bar indicates the current SAR operating mode. Fill Level Progress Bar indicates the highest SAR and Stimulation values of the current measurement and when they are getting to the critical limit. Percentage value displayed when moving mouse pointer over progress bar Red-100% = SAR Exceeded Green-100% = SAR is below or at 100% Click the Mode Indicator (down arrow) to switch from Normal to First Level Mode. Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 myExam UI: Queue - toolbar In the myExam User interface, under the Examination toolbar, you can find the SAR icon. The SAR icon Opens and Closes the SAR information window. The Progress Bar indicates the current SAR operating mode in use. The Fill Level Progress Bar indicates the highest SAR and Stimulation values of the current measurement and shows when it is reaching the critical limit. A Percentage value is displayed when you move the mouse pointer over the progress bar. When it’s Red, and at one-hundred-percent, then a SAR Exceeded window appears. If it’s Green, and at one-hundred-percent, then SAR is below, or at one-hundred-percent. To Switch from Normal to First Level Mode, click the Mode Indicator (down arrow). Progress Bar myExam UI SAR information When the SAR icon is selected in examination, the SAR Monitor Operating Mode window opens. The window displays a Prediction tab that can be viewed prior to scanning a sequence. Option to change the SAR Operating mode to either Normal Mode or First Level. Shows predicted SAR percentage of maximum value (dependent on SAR operating mode) and B1+RMS. Green bar shows the absolute values for the selected SAR aspect. (e.g., B1+RMS has been selected and its corresponding value is displayed). 1 2 3 myExam UI: SAR information When you click on the SAR icon, the SAR Information, monitor operating mode window opens. This window has a Prediction tab that can be viewed prior to scanning a sequence. Here you can set the SAR Operating mode to (Normal Mode or First Level). The mode selected, is active as soon the next measurement is started, and is retained either until another mode is set or a new patient is measured. The table shows the predicted SAR as a percentage of the maximum value for the selected SAR operating mode, and the predicted B-one-plus-r-m-s in micro-Tesla. The green bar shows the absolute values for the selected SAR aspect. In this example, B-one-plus-r-m-s, has been selected and its corresponding value is displayed. If the SAR value is selected, then the green bar indicates the SAR limits in watts per kilogram. ____________________________ CC info: Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 myExam UI Setting up a sequence to view the predicted SAR To set up sequences to view the predicted SAR value before running a sequence: Right-click on a Sequence > select Edit Properties. Select Execution. Click the check-box Wait for User to Start > select Single Measurement. Click OK. Play icon is next to sequence name in queue. After the scan preparation, it pauses (Exam Paused pop-up) > check Predicted Value before continuing by clicking on the SAR icon. Click Continue to run the sequence. Setting up a sequence to view the predicted SAR To set up, and view the predicted SAR value, before running a sequence: Right-click on a sequence, and select Edit Properties.... Next, click on Execution... Check-the-box, Wait for User to Start, and select Single Measurement..... Click, OK... The Play icon, is now seen next to the sequence name in the queue... After the scan preparation, it pauses. (Exam Paused pop-up)..... You can then check the predicted value before continuing by clicking on the SAR icon.... Click Continue, to run the sequence, if the predicted value is within allowed limits.... To view the changes during scanning: Select the Current tab – SAR monitor does not update the UI display of the Current tab automatically. To update, click on another tab, then click back on the Current tab to update the values. The time stamp of the values are displayed in the table. When scanning, the measured SAR values can vary from the prediction. myExam UI SAR information myExam UI: SAR information Audio The values given in the Current tab are averaged measured values which describe the real actual SAR burden of the patient. They depend both on the current measurement protocol and the history of protocols. All values are measured by the SAR supervision and averaged over their respective durations (for example, if you wait for six-minutes without scanning after the end of a sequence, the values shown in the Current tab all return to zero-percent. When scanning, the measured SAR values are monitored in real-time. These values can vary from the prediction for two reasons. First, they can vary because the prediction may be incorrect. Second, they may vary even with a correct prediction, if the sequence itself produces SAR values that fluctuate over time. To view the changes during scanning: Click on the Current tab. Please note that the SAR monitor does not update the user interface display of the Current tab automatically. To update the Current tab, click on another tab, then click back on the Current tab to update the display. The time-stamp of the values are displayed in the table. To view additional information regarding patient information utilized for the measurement or sequence specific information, click on the Status, Patient, or Protocol tabs CC info: Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 Examine the Status, Patient, or Protocol tabs to view additional information regarding patient information utilized for the measurement or sequence specific information. SAR limits exceeded Safety Aspects of SAR If SAR limits are exceeded, the system automatically tries to adapt the protocol by utilizing the tolerances (i.e., configured on the Sequence/Assistant parameter card) of protocol. SAR Limit(s) Exceeded window offers recommendations on how to avoid exceeding the SAR limit. Proposed changes apply to one parameters (TR, Slices, or Flip Angle), assuming the other two parameters are not changed. Change Operating Mode from Normal > First Level Change Protocol Parameters Hint: if an option is dimmed, no change is suggested for that parameter. 1 2 3 SAR limits exceeded Audio If SAR limits are exceeded, the system automatically tries to adapt the protocol by utilizing tolerances (these are configured on the Sequence-Assistant parameter card). If the SAR prediction calculates that SAR limits are exceeded during an examination, the SAR limits exceeded window is displayed. The SAR Limit(s) Exceeded window offers recommendations on how to avoid exceeding the SAR limit. Proposed changes apply to one parameter (T-R, Slices, or Flip Angle), assuming the other two parameters have not changed. Hint, if an option is dimmed, no change has been suggested for that parameter modification. ____________________________ CC info: Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 What is B1+rms? B1+rms is defined as the root-mean-square average of the RF transmission field (B1+) intensity during a scanning procedure. Units of measure for B1+rms are in micro-tesla (μT). B1+ RMS Magnetic field generated by the RF coil The particular, (positively rotating) component of the B1 field is useful for imaging Root-mean-square (time average over all RF pulses) B1+rms Audio What is B-one, plus-r-m-s? R-F pulses can have varying shapes, so how do we account for these variances. B-one-plus-r-m-s provides us with a standard way of measuring the B-one-plus field utilized during scanning. B-one is the magnetic field generated by the Radiofrequency coil. The units of measure for B-one, are in micro-tesla. Plus, is the particular-positively rotating component of the B-one field useful for images. R-m-s, is the Root-mean-square, or the time average over all of the Radiofrequency pulses. The root mean-square is a specific type of average that is appropriate for R-F wave forms as both positive and negative B-one fields that contribute to the root-mean-square. To summarize, B-one-plus-r-m-s, is the average Radiofrequency transmission magnetic field during a scanning procedure, measured in micro-tesla. What is B1+rms? B1+ and RF Pulses RF Pulses of any shape Flip Angle q = g B1t = 180° t = 1 ms B1+ = 11.7 mT B1+ and RF pulses R-F pulses are used to excite hydrogen protons and cause the net magnetization to rotate it through a specific angle, which we typically refer to as the “flip angle”. These Radiofrequency pulses are electromagnetic waves which include an electric field that contributes to heating. The R-F pulses can come in many shapes and have positive and negative rotating components (sinusoidal). So, what is the best way to accurately provide measurements that can be utilized for safety purposes? Root Mean Square (RMS) When attempting to measure B1+ amongst variable RF pulse sequences that have both positive and negative variates, standard mean values (average) is not acceptable since they cancel each other out. Instead, we use the Root Mean Square (RMS) to convert the data into meaningful values. Root mean square (RMS) When attempting to measure B-one-plus, amongst variable Radiofrequency pulse sequences that have both positive and negative variates, standard mean values (average) is not acceptable since they cancel each other out. Instead, we use the Root Mean Square to convert the data into meaningful values. Root Mean Sauare (RMS) Using the RMS or quadratic mean allows us to take varying RF pulses and convert the data into a measure of the magnitude. To provide this meaningful information, we do three things in this order: Square the B1+ value to account for the positive and negative values (sinusoidal waves). Mean: find the average or mean value since we are not concerned with the pulse variations. Root: find the square root of the value to bring the units back into B1+ units. RMS Audio When looking at variable pulse sequences that have both positive and negative variates, mean value is not acceptable. So, to provide meaningful information we do three things: 1. Square the value to account for the positive and negative values (sinusoidal waves), 2. Mean, find the average or mean value since we are not concerned with the pulse variations, 3. Root, find the square root of the value to bring the units back into B-one-plus units. The Root-Mean-Square in this instance is best suited for dealing with these variates to acquire meaningful values. B1+ versus B1+RMS B1+ versus B1+RMS In this example, you see the varying R-F pulses (B-one-plus) that equate to a uniform B-one-plus-r-m-s value. SAR and B1+ s m SAR is inversely proportional to the tissue mass w 2 SAR is proportional to B02 (the main magnetic field) B1 2 SAR is proportional to B12 (the RF transmission field) SAR and B1+ SAR is dependent on numerous external variances, and many assumptions are made. This formula displays some of its reliance: B-zero Field, the (main magnetic field). B-one-plus Field, the (Radiofrequency transmission field). Tissue Conductivity, and Tissue Mass, these are both patient dependent. Why measure B1+rms? 1 Implant Disclaimer - The MRI restrictions (if any) of any implant must be considered prior to patient undergoing MRI exam. MR imaging of patients with implants brings specific risks. However, certain implants are approved by the governing regulatory bodies to be MR conditionally safe. For such implants, the previously mentioned warning may not be applicable. Please contact the implant manufacturer for the specific conditional information. The conditions for MR safety are the responsibility of the implant manufacturer and user, not of Siemens Healthineers. B1+rms is not patient-dependent, so implant manufacturers often use it as a more precise metric for tissue injury in the context of an implanted device1. SAR makes a lot of assumptions, but B1+rms does not. B1+rms is NOT to take place of other metrics for safety such as SAR and SED, as smaller mass of tissue increases risk of injury (patient dependent). Why measure B1+rms? B-one-plus-r-m-s, is a more precise Radiofrequency exposure metric than SAR because B-one-plus-r-m-s, is the fundamental Radiofrequency field parameter related to M-R image creation. The scanner calibrates the Radiofrequency pulse, B-one-plus field strength during the pre-scan and the B-one-plus-r-m-s value for an imaging sequence that is determined by the scan parameters needed to produce the desired tissue contrast. B-one-plus-r-m-s, for a scan protocol is a fundamental electromagnetic field parameter that is patient independent. In contrast, SAR is a conservative estimate of the Radiofrequency power deposited in a specific region of the patient under examination, (for example: head, whole-body, and partial-body) for a particular B-one-plus-r-m-s value. Predicting SAR from the known B-one-plus-r-m-s value is a complicated function of patient weight, morphology, tissue composition, posture, landmark location, and averaging time. It is important to note, that SAR is currently the best metric for patient safety in standard imaging scenarios. However, B-one-plus-r-m-s, has one use case where it is a good metric for tissue injury, and that is in the context of an implanted devices. If the patient has an implanted device, we can assume that the limiting factor is the interaction of the field with the device, and that the SAR delivered to the whole body will be reduced far below the standard limits. So why are some manufacturers using it for implant safety? The mass of tissue near the device is the mass of tissue at risk, in this scenario, not the overall patient mass. The mass of tissue near the device depends on the design of the device and is independent of the patient. So, it is OK to be independent of the patient mass here. The manufacturer of the device knows what type of tissues the device will be installed near, and therefore the manufacturer knows the susceptibility of that tissue to thermal injury and even other relevant properties like the conductivity and perfusion. The manufacturer can therefore account for the tissue sensitivity in their recommended limits. myExam UI - B1+rms and SAR monitor SAR information SAR information System operator manual System operator manual Tab 1 Tab 1 SAR menu B1+rms and SAR monitor B-one-plus-r-m-s, measurements are also located in the SAR menu. SAR information layer B-one-plus-r-m-s, values displayed in the SAR information window are Predicted values without a safety margin. Even on the Current tab, where the value is derived from simulation results and the timing of the measurement protocols. Please note, that the actual B-one-r-m-s, value can be much higher than the predicted B-one-r-m-s value, by a factor of up to ten. Both values B-one-r-m-s, and B-one-plus-r-m-s are not monitored. Exceeding the displayed B-one-plus-r-m-s value does not control or stop a scan. If there is a question of a potential injury to a patient due to an implant, and if the patient is not suitable for an MR examination. Do not use the displayed b-one-plus-r-m-s value, to decide whether an active or passive implant is suitable for an M-R examination. Please note that Siemens Healthineers will not accept responsibility for scanning a patient with active or passive implants. In addition, be aware that the I-E-C, six-zero, six-zero-one, dash, two-dash, thirty-three, standard, only requests that the b-one-plus-r-m-s, values are displayed, but it does not require supervision. Siemens MAGNETOM M-R systems must comply with the standard by showing the b-one-plus-r-m-s, values on the Prediction and Current tabs, but they do not provide any limitations. On both E-line and Numaris X software, the values between the predicted and current value are the same. System OM tab In total, three different components are used to describe the transmit field in M-R scanners: B-one-plus, B-one-minus, and B-one. B-one-plus is the effective component that affects spins in the rotating frame (rotating in synchronization with the spins), B-one-minus, is the component rotating in the opposite direction, and hence has no impact on spins, B-one is the vector sum of B-one-plus and B-one-minus. B-one-plus-r-m-s, is defined as the root mean square value of the spatial average B-one-plus field of the axial central slab. Like for the other SAR aspects, the temporal averaging intervals have durations of ten-seconds and six-minutes. The I-E-C, size-zero-six-zero-one, dash-two, dash-thirty-three, standard does not set a limit for B-one-plus-r-m-s, such that all given values are absolute numbers. B-one-r-m-s, is a metric sometimes used to measure the device temperature rise (for example, active or passive implants). The B-one-plus-r-m-s, value displayed in the SAR dialog box are predicted values without a safety margin. Even on the Current tab where the value is derived from simulation results and the timing of the measured protocols. _________________________________ CC info: Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 ____________________________ CC info: Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 Excerpts from Operating Manual – MR Examination Manual System operator manual Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 SAR menu SAR menu B1+RMS values displayed in the SAR dialog box are Predicted values without a safety margin. Even on the Current tab where the value is derived from simulation results and the timing of the measurement protocols. SAR information Warning The actual B1 RMS value can be much higher than the predicted B1+rms value, by a factor of up to 10. Both values B1 RMS and B1+rms are not monitored. Exceeding the displayed B1+rms value does not control or stop a scan. Injury of patient due to implants not suitable for MR examinations Do not use the displayed B1+ rms value to decide whether an active or passive implant is suitable for MR examinations. Please note that Siemens Healthineers will not accept responsibility for scanning a patient with an active or passive implant. Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 SAR menu SAR menu What is Specific Energy Dose (SED)? Specific Energy Dose (SED) is defined as the value of the accumulated whole-body SAR throughout the entire examination. RF Exposure Application of time varying electromagnetic fields with frequencies in MHz range generating heat within tissue being exposed. Heating is a major effect of RF exposure. Safety considerations focus on temperature increases. SED = Specific Energy Dose Specific to the Body Part and Tissue Energy of the RF Dose into the Body Unit of Measure = Joules per kilogram (Joules/kg) What is Specific Energy Dose (SED)? Now that we have covered SAR, and B-one-plus-r-m-s, what about SED? Specific Energy Dose is defined as the value of the accumulated whole-body SAR throughout the entire examination. It is expressed in Joules per kilogram. SED, is “Specific” to the body part and tissue. Energy, represents the energy of the R-F, and Dose, is the energy dose that is deposited into the body. Siemens Healthineers uses the term SED; however, it may also be referred to as “Specific Absorbed Energy”. SED = SAR x Time Joules/kg = Watts/kg x sec = Watt-sec/kg SED is the amount of energy that gets deposited in the body. Units = Joules/kg SED (Specific Energy Dose) SAR is the rate at which energy gets deposited in the body. Units = Watts/kg SAR (Specific Absorption Rate) SAR versus SED SAR vs. SED What is the difference between SAR and SED? While SAR is the rate at which energy gets deposited in the body, SED is the total accumulated amount of energy that gets deposited in the body. In other words, SED equals SAR multiplied by the duration of the R-F exposure. For a given scan with constant R-F power, SAR is the same throughout the scan, but SED steadily increases as the scan time progresses. In a worst-case scenario, if the patient cannot dissipate heat, then SED is proportional to the temperature increases. But even non-compromised patients can suffer if SED levels are too high. This can be better visualized if we plot temperature, or SED, over time. If we define some upper temperature threshold as the T-max, this represents, for example, the SED limit that is correlated to the maximum rise in core body temperature allowed for patient safety. Now for high R-F power, high SAR scan, the rate of temperature change (and SED) is fast, hitting T-max in a relatively short period of time. On the other hand, for low R-F power, low SAR scan, the increase is more gradual, taking a longer time to reach that same limit. SAR, SED, and core temperature rise Total temperature rise SAR, SED, and Core temperature Rise Most importantly, recall that since the rate of temperature rise over time is proportional to SAR, then means that SED, is proportional to the change in the temperature, or the total temperature rise in the body. SED Monitoring and limits As with SAR, the SED is monitored continuously. When the SED limit is reached, however, it is no longer possible to scan. The SED limit of 240 W-min/kg (14400 J/kg) is a requirement from IEC 60601-2-33 edition 3 (2010). Beginning with VE11A software, Siemens Healthineers introduced a pop-up warning at 100 W-min/kg (6000 J/kg). SED = 240 W-min/kg (14400 J/kg) is equivalent to: Scan continuously for 1 hr. at a SAR level of 4 W/kg Scan continuously for 2 hrs. at a SAR level of 2 W/kg SED = 100 W-min/kg (6000 J/kg) is equivalent to: Scan continuously for 25 mins at an SAR level of 4 W/kg Scan continuously for 50 mins at an SAR level of 2 W/kg SED monitoring and limits SED Warning dialog box, choose the following options: Do not proceed with the examination cancels the current measurement step. Confirm raising the energy dose to X J/kw (X corresponds to the displayed value): accepts the predicted SED values and continues the measurement If the SED limit has been reached and the next measurement will exceed it, the message SED Limit reached will be displayed. In this case, the measurement cannot be started. If the SED prediction exceeds 100 W-min/kg before the start of the measurement, a SED Warning is displayed. myExam UI SED Warning myExam UI - SED Base layer If the SED limit has been reached and the next measurement exceeds the limit, the message SED Limit Reached is displayed. In this case, the measurement cannot be started. If the SED prediction exceeds one-hundred-watts-per-minute-per-kilogram, before the start of the measurement, a SED Warning is displayed. In the SED Warning window, you can choose one of the following options: Do not Proceed with the examination, this cancels the current measurement step. Confirm raising the energy dose to X-joules per kilowatts, where X, corresponds to the displayed value. This accepts the predicted SED values and continues the measurement. if the measurement is continued, the patient must be closely monitored to avoid unacceptable thermal stress. layer Audio A SED Warning is received when a six-thousand Joules-per-kilogram is reached. Above this level, patients with compromised thermal regulation may suffer physiological stress or even experience tissue damage. A SED warning continues to be displayed before each sequence, until the maximum SED limit of fourteen-thousand-four-hundred Joules-per-kilograms is reached, or you end the exam. Once you reach the maximum of fourteen-thousand-four-hundred Joules-per-kilogram, the SED limit is reached, and the scanner will not allow you to continue the examination. Research has shown that this level produces a temperature rise to forty-three-degrees Celsius, above which patients with normal thermal regulation may suffer tissue damage. SED Warning = 100 W-min/kg (6000 J/kg) Above this level, patients with compromised thermal regulation may suffer physiological stress or even experience tissue damage. SED Limit = 240 W-min/kg (14400 J/kg) Research has shown that this level will produce a temperature rise to 43⁰C above which patients with normal thermal regulation may suffer tissue damage. myExam UI SAR Monitor and Accumulated SED SAR monitor and accumulated SED Audio The accumulated SED can be viewed under the Patient tab in the SAR information, Monitor Operating Mode at any point during the examination. Layer As previously stated, SED is monitored continuously during the exam and steadily increases. The cumulative value is monitored by the patient registration information and accumulates if the patient has multiple studies. The software has two ways it checks to make sure that a patient does not exceed the SED limits of safety.   First, the system checks to see if the patient was one of the last sixteen patients scanned and adds this to the previous value. Second, if the first condition is negative, then the system looks to see if the patient has been scanned on the same day, or in less than eight-hours. Again, it adds this to the previous value. If both conditions are negative, then the SED is reset to zero.   In other words, if a patient gets re-registered, and one of these two conditions are met, it will retain the last SED value and continue from there with the new scan. If the patient is re-registered the next day, or after eight-hours from the last scan that was completed, the SED value is “reset” back to a value of zero. If you are not able to scan and both conditions are negative, you may need to restart the system. Important note, never change the patient registration information to avoid this limit. In addition, for safety reasons do not place the patient on another MAGNETOM M-R system to continue the examination. You must wait the allotted time defined on the M-R system before rescanning the patient. SED is monitored continuously during the exam and steadily increases. Cumulative – monitored by patient registration information and accumulates if the patient has multiple studies. First, the system checks to see if the patient is one of the last 16 patients scanned (adds to the previous value). Second, if the 1st condition is negative, the system will look to see if they have been scanned on the same day, or less than 8 hours (Adds to previous value). If Both conditions are negative, then the SED is reset to 0. Note – If unable to scan and both conditions are negative, you may need to restart system. NEVER CHANGE PATIENT REGISTRATION INFORMATION TO AVOID THIS LIMIT!!! SED Siemens Healthineers Monitoring Overview Siemens Healthineers monitoring overview SAR & SED reduction techniques TR & Concatenations Increasing the TR from the minimum allows greater SAR recovery time. A buffer of 50-100ms can help prevent SAR warnings; however, this increases scan time. NOTE: Does NOT Affect SED, Only SAR Increasing the number of Concatenations can reduce SAR. Divides slices acquired into groups Amount of SAR reduction is dependent on TR as well Increases scan time NOTE: Does NOT Affect SED, Only SAR TR & Concatenations Audio There are different techniques you can utilize to reduce SAR and SED, lets review some of these alternatives. When you set the T-R to the minimum on a Turbo Spin Echo-based sequence, the user is only allowing enough time for all the pulses to be played out, and no time for SAR recovery. If a small cushion can be added to the minimum T-R, this may allow for SAR recovery and prevent the SAR limits exceeded warning. The user must also be conscious and ensure by increasing the T-R, the weighting of the pulse sequence is not affected by the amount of (T-one, proton density, or T-two weighting), otherwise the weighting of the sequence could be modified. Concatenations is another way to reduce SAR, by increasing the number of concatenations (for example, from one to two) the system divides the slices into two groups, and collects half of the slices with one concatenation, and the second half of the slices with the next concatenation. Number of slices Number of slices Reducing slices may reduce SAR/SED Reduction is also dependent on TR Coverage of anatomy is reduced Number of slices Audio Number of Slices can also affect SAR depending on how many total slices are needed to cover the anatomy of interest, and the minimum T-R used. By either reducing the total number of slices or increasing the T-R, SAR can be reduced. Reducing the number of slices also decreases the SED, but increasing the T-R does not. Resolution and Phase Encoding Resolution/Phase Encoding steps Reducing the amount of acquired lines of k-space reduces SED. (e.g., Phase Resolution, FOV Phase, Partial Fourier, etc.). Coverage of anatomy is reduced May indirectly reduce SAR, but is dependent on other parameters Resolution and Phase Encoding Audio As you increase the base and phase resolution the system acquires more lines of k-space which may also increase SAR. Reducing phase encoding steps reduces SED but may or may not indirectly affect SAR. This reduction can be invested in either decreasing the total acquisition time or increasing the time between R-F pulses. If used without minimizing the T-R to reduce time, the SAR of the sequence can be reduced since fewer R-F pulses are played out per unit of time. If the T-R is minimized and the total acquisition time is reduced with the reduction in steps, the SAR remains the same, but the total amount of energy deposited (SED) is reduced. iPAT (Integrated Parallel Acquisition Techniques) iPAT techniques GRAPPA mSENSE CAIPIRINHA Compressed Sensing iPAT Effects Reduces number of phase lines Scan time reduction Decreases SNR Reduces SED May indirectly reduce SAR, but is dependent on other parameters iPAT Checklist Array or Matrix coils Array or Matrix coil elements must be aligned in phase encoding direction More than 1 coil element must be used Number of coil elements must be ≥ Accel. factor PE Sufficient SNR – SNR is reduced when iPAT is used and PAT factor is increased iPAT Audio Another reduction technique is i-PAT. i-PAT stands for Integrated Parallel Acquisition Techniques, it is another way to indirectly reduce SAR. There are different types of i-PAT reconstruction algorithms, GRAPPA, m-SENSE, CAIPIRINHA, and Compressed Sensing. i-PAT reduces SED but may or may not directly affect SAR. i-PAT can be invested in either decreasing the total acquisition time or increasing the time between the R-F pulses. If i-PAT is used without minimizing the T-R to reduce time, the SAR of the sequence can be reduced as fewer R-F pulses are played out per unit time. If the T-R is minimized, and the total acquisition time reduced with i-PAT, the SAR will remain the same, and only the total amount of energy deposited (SED) is reduced. There are some to things that should be considered when using i-PAT. You must use Array or Matrix coils. The Array or Matrix coil elements must be aligned in phase encoding direction. More than one coil element must be used, and the Number of coil elements must be equal-to-or-greater-than the Acceleration factor in the Phase-Encoding direction. You should also ensure you have sufficient signal-to-noise ratio in the initial sequence before implementing i-PAT, since the signal-to-noise ratio is reduced when i-PAT is implemented, or when the PAT factor is increased. SAR Assistant – TR Set individually per sequence in the Sequence > Assistant parameter card. Allows the user to set a Maximum TR value. This grants the system pre-approval to increase the TR up to the maximum value in cases of exceeding SAR. It will only raise as high as it needs to remain in current SAR Mode (Normal/First). Note – TR Does not affect SED, only SAR SAR Assistant - TR Audio In the Sequence, Assistant parameter card you can set-up the SAR assistant for each sequence. If T-R is selected the user can set a maximum T-R value. This grants the system pre-approval to increase the T-R up to the maximum value entered, in case SAR is exceeded. However, the system will only raise the T-R as high as needed to remain in the current SAR Mode (Normal or First) Level. Note, T-R does not affect SED, only SAR. Flip Angle & SAR Higher the Flip Angle the higher the SAR. t = 0 M q B1 t = t M Flip Angle & SAR Audio The flip angle used also matters. Recall that the flip angle is directly proportional to the B-one transmission field. Since the R-F power goes as the square of the B-one field, the SAR goes up with the square of the flip angle. This is important to keep in mind when trying to minimize SAR and patient heating. For example, reducing the one-hundred-eighty-degree refocusing flip angle to one-hundred-twenty-degrees reduces the contribution to the overall SAR of each refocusing pulse by nearly sixty-percent. Doing this, however, may also compromise the signal-to-noise ratio, so this may not always be wise to do. Flip Angle Rotation of magnetization from a direction (e.g., longitudinal, transverse, etc.) at end of RF Pulse. The Flip Angle affects amount of contrast and signal in image. Spin Echo – Flip Angle refers to initial RF pulse (i.e., Flip 90˚). Turbo Spin Echo – Flip Angle refers to refocusing pulses (i.e., Flip 180˚). Flip Angle Audio The Flip Angle is the rotation of magnetization from a direction (e.g., longitudinal, transverse, etc.) at end of the R-F Pulse. Flip angles affect the amount of contrast and signal in an image. When we refer to a Spin Echo pulse sequence the flip angle refers to the initial R-F pulse which is ninety-degrees When referring to a Turbo Spin Echo pulse sequence the flip angle refers to refocusing pulses or the one-eighty-degree pulse. Flip Angle (Spin Echo with Reduced Refocusing Pulse @ 3T) Example refocusing Flip Angle: ≥160°. SAR is reduced by ~ 20%, signal reduction is ~ 3%. Change in SAR and SNR dependent on T1 and the TR specified. Flip Angle (Spin Echo with Reduced Refocusing Pulse @ 3T) Audio When working on three-Tesla systems, if a spin echo sequence is selected, it is recommended to reduce the refocusing pulse. This example shows a flip angle equal to one hundred sixty degrees. This provides a SAR reduction of approximately twenty percent with a signal reduction of approximately three percent. Lower flip angles are also possible, for corresponding lower SAR and lower signal. The change in SAR and signal-to-noise-ratio is dependent on the T-one and the T-R specified. SAR Assistant Sequence > Assistant parameter card set the SAR Assistance individually per sequence. SAR Assistant parameter defines the strategy to avoid exceeding the SAR limit. The system manipulates the selected parameter defined by the User. The SAR Assistant parameter list defines whether a parameter is used at all and in what order. It allows a combination of up to 3 parameters that can be modified: Flip Angle TR RF Pulse Type SAR Assistant Audio As previously stated, in the Sequence, Assistant parameter card you can set the SAR assistant individually per sequence. The SAR Assistant parameter defines the strategy to avoid exceeding the SAR limit. The system therefore manipulates the selected parameter defined by the user. The SAR Assistant parameter list defines whether a parameter is used and in what order. It allows you to select a combination of up to three parameters that can be modified. For example, Flip Angle, T-R, and R-F Pulse Type. SAR Assistant – Flip Angle Modification Limits are set by the User depending on the selection made in the SAR Assistant pulldown. If the Flip Angle is selected, the maximum possible value for the modification is defined by the minimum value entered in the field. User sets minimum Flip Angle (e.g., 150°) Grants the system pre-approval to decrease the Flip Angle down to the minimum value in cases of exceeding SAR Flip Angle decreases only as much as it needs to remain in current SAR Mode (Normal/First). SAR Assistant – Flip Angle Audio These modification limits are set by the user and depend on the choice made in the SAR Assistance pull-down. If Flip angle is selected, the maximum possible value for the modification corresponds to the defined minimum flip angle entered in the minimum flip angle field. This grants the system pre-approval to decrease the Flip Angle down to the minimum value in cases where SAR would be exceeded. The Flip Angle decreases only as much as needed to remain in the current SAR Mode: Normal or First Level. SAR Assistant – TR options SAR Assistant > TR Maximum possible value for the modification corresponds to the defined maximum TR. TR options: TR TR > Flip Angle TR > Flip Angle > RF Pulse Type TR > RF Pulse Type TR > RF Pulse Type > Flip Angle SAR Assistant – TR options Audio If T-R is selected in the SAR Assistant pulldown, the maximum possible value for the modification corresponds to the defined maximum T-R. There are some options available under the SAR Assistant for T-R. Increasing T-R reduces SAR but does not affect SED SAR Assistant – RF Pulse Type options SAR Assistant > RF Pulse Type A limit for the RF pulse type cannot be specified. Possible settings (Fast, Normal, or Low SAR) will depend on the sequence selected. Maximum TR is also relevant for the RF pulse type. If the RF Pulse Type is changed, then the TR can also be changed automatically to the maximum. SAR Assistant – RF Pulse Type options Audio If R-F Pulse Type is selected in the SAR Assistant pulldown, then a limit for the R-F pulse type cannot be specified. The possible settings (Fast, Normal, or Low SAR) depend on the sequence selected. The maximum T-R is also relevant for the R-F pulse type, that is, if the R-F pulse type is changed, then the T-R can also be changed automatically to the maximum. Allowed Delay Maximum Delay time after the end of the measurement. Exceptions when Allowed Delay shouldn’t be used: Studies using contrast agents where timing is critical Dynamic imaging where timing is critical Setting up protocols to adhere to specific B1+RMS values NOTE: Allowed Delay Does Not Affect SED, only SAR Allowed delay Audio Allowed Delay is the maximum delay time that is added after the end of the measurement prior to the next sequence running, when the pulse sequences are queued. If thirty seconds is entered for the allowed delay, and the system adds time at the end of the sequence prior to starting the next sequence, for SAR recovery, the system only uses the amount of time needed. If only ten-seconds of the allowed delay is needed of that thirty-seconds entered, this is the time utilized. If no allowed delay is needed, none of the thirty seconds allocated is used. (Note: Allowed Delay should not be used when setting up protocols for B-one-plus-r-m-s limitations). There are other exceptions when the allowed delay should never be used, these include studies using contrast agents, dynamic imaging, where timing is critical, and when setting up protocol to adhere to specific B-one-plus-r-m-s, values. Saturation Bands Number of Saturation Bands Reducing the number of sat bands reduces SAR. But may increase artifacts dependent on sat band usage. Shape Standard is a regular saturation region that is numbered and may be positioned freely Asymmetric has a sharp edge that allows the saturation region to be positioned closer to the anatomy of interest Note: use Standard over Asymmetric if SAR issues. Saturation Bands Audio Saturation bands also affect SAR and SED, within a range the frequency bandwidth is constant, and the slice gradient strength is variable. Across a range the frequency bandwidth is variable. In addition, when the saturation band is thicker, edge blurring also increases. If the number of saturation bands is increased, SAR and SED also increase. By keeping the saturation band thickness smaller (forty to fifty milli-seconds) and using only one saturation band, SAR and SED can be reduced compared to sequences with more or thicker saturation bands. However, in certain types of examinations multiple sat bands may be required on a sequence (for example, spectroscopy). Shape, allows you to select either the standard Saturation pulse, or an Asymmetric Saturation Pulse. Standard, is a regular saturation region that is numbered and may be positioned freely. Asymmetric has a sharp edge, this allows the saturation region to be positioned closer to the anatomy of interest. However, if there are SAR issues, use the Standard Saturation Pulse would be ideal. Turbo Factor (TF) or Echo Train Length (ETL) Reducing Turbo Factor or Echo Train Length reduces the number of refocusing pulses, so it typically reduces SAR. This changes the available TE values and may change contrast Scan time is increased Very limited affect on SED Turbo Factor (TF) or Echo Train Length (ETL) Audio When the turbo factor is increased the number of one-hundred-eighty-degree refocusing pulses, per T-R increases, which increases SAR. Since the total number of ninety-degree excitation pulses decreases, SED is slightly decreased. If a lower turbo factor is used, then the number of one-hundred-eighty-degree refocusing pulses per T-R decreases, and SAR is also reduced. The total number of ninety-degree pulses increases, so SED increases slightly. RF Pulse Type Normal RF Pulse with good slice profile with optimal SAR. Low SAR Extended RF Pulse duration with reduced SAR. Fast Short RF Pulse duration with higher SAR. 3 Tesla VERSE used when Fast RF is selected VERSE used when Low SAR is selected RF Pulse Type Audio There are three different R-F Pulse types available on the system that can affect SAR: Normal, Low SAR, and Fast. Normal uses an R-F Pulse type with good slice profile and provides optimal SAR. Low SAR uses an extended R-F Pulse type duration, so SAR is reduced. Fast uses a short R-F Pulse duration with higher SAR. However, when using the Fast R-F, or the Low SAR pulse type on a three-Tesla system, the VERSE pulse is implemented, and SAR increase is mitigated. RF Pulse Type & VERSE @ 3T Available at 3T and the Aera 1.5 T MAGNETOM MR Systems. Reduces SAR by changing the shape of excitation and refocusing RF Pulses. The VERSE pulse reduces SAR. VERSE pulses are implemented on both: RF Pulse Type – Fast RF Pulse Type – Low SAR Table with 2 columns and 4 rows Pulse Type VERSE Fast ON Normal OFF Low SAR ON* *Uses a shorter RF pulse with less perfect slice profile *Replaced with standard RF pulse if IR is selected RF Pulse Type & VERSE @ 3T Audio VERSE is also available on a Siemens MAGNETOM MR three-Tesla, and on the Aera one-point-five Tesla system. VERSE reduces SAR by changing the shape of the excitation and refocusing R-F pulses. VERSE has the potential to reduce SAR by up to forty-five percent. The term VERSE is not displayed on the parameter cards, only in literature. However, when using Fast or the Low SAR, R-F Pulse types, the VERSE pulse is implemented. RF Pulse Type & VERSE Standard RF Pulse 75% 70% time Gs RF 75% 70% time Gs RF Fast / High Power Slow / Low Power VERSE Pulse - reduces SAR by changing the shape of excitation and refocusing RF pulses. 3 RF 75% 70% time Gs 70% 70% VERSE RF Pulse -> Fast and Low Power RF Pulse Type & VERSE Audio In this illustration a standard R-F pulse is displayed with the R-F Pulse type-Fast. which has higher power. The R-F Pulse type Low SAR, is slow and has lower power. The VERSE pulse shown, is a fast but low powered R-F pulse which aids in reducing SAR. It changes the shape of the excitation and the R-F refocusing pulses, resulting in a SAR reduction of up to forty-five percent. Special RF Pulses & SAR Table with 4 columns and 7 rows Special RF Pulses Duration Bandwidth SAR Spectral Suppression (FatSat) pulses long duration low bandwidth low SAR Adiabatic (Dark-Fluid TIRM) pulses long duration moderate bandwidth moderate SAR Spatial Saturation (SAT) pulses short duration high bandwidth high SAR Magnetization Transfer (MT) pulses long duration high flip angle high SAR VERSE (Variable Rate Selective Excitation) pulses low power low bandwidth low SAR Binomial Composite (water excitation) pulses short collective bursts low bandwidth moderate SAR Special RF Pulses & SAR Audio It should also be noted that different applications may require a special type of R-F pulse, each of which contributes in their own way to the overall SAR of the scan. Spectral suppression fat-sat pulses for example, contribute very little to the overall SAR, but spatial sat bands typically contribute a lot to the SAR. These things should be kept in mind when scanning. Hyperecho TSE Hyperecho varies the refocusing Flip Angle to reduce the overall SAR. When activated, Flip Angle parameter indicates the minimum value (maximum will be 180⁰). The contrast portion of k-space (center) is acquired when using the peak Flip Angle Refocusing pulse (180⁰). Hyperecho TSE Audio Another parameter that can be used to reduce SAR at three-Tesla is Hyper-echo. Hyper-echo, varies the refocusing Flip Angle to reduce the overall SAR. When activated on a turbo spin echo sequence, the Flip Angle parameter indicates the minimum value, the maximum value is one-hundred-eighty-degrees. The contrast portion of k-space (center) is acquired when using the peak Flip Angle, Refocusing pulse, which is one-hundred-eighty-degrees. There is also a Hyperecho HASTE sequence available on some software versions, where the user interface parameter defines the flip angle at the center of k-space and the periphery is always sixty-degrees. Hyperecho TSE Hyperecho TSE – 3T   Turbo Spin Echo Hyperecho TSE Audio These sequence diagrams displays a Hyper-echo Turbo Spin Echo pulse sequence compared to the standard Turbo Spin Echo pulse sequence. When looking at the turbo spin echo sequence it shows the initial ninety-degree R-F pulse, with the center R-F pulse constant at one hundred and eighty degrees. However, on the hyper-echo sequence, after the initial ninety-degree R-F pulse, the center R-F pulses vary in amplitude resulting in SAR reduction. The contrast portion of k-space (center) is acquired when using the peak flip refocusing pulse, at one-hundred-eighty-degrees. Sequence types Replacing higher SAR sequences with lower SAR sequences may be an option. Contrast and diagnostic differences are potential risks, so decision must be decided by individual facility. Examples: TSE > SE TSE/SE > GRE STIR > T2 FS 90 180 SE (low SAR) 90 180 180 180 180 180 TSE (high SAR) Sequence types Audio Now let’s look at some additional techniques that can be used to help reduce SAR. Pulse sequence types: using a spin echo or gradient echo-based pulse sequence, versus a turbo spin echo pulse sequence, can also reduces SAR These partial sequence diagrams show the difference in the number of pulses between a Spin Echo and a Turbo Spin Echo sequence. Since SAR is calculated from the sum of the energy of the pulses divided by time, it is easy to see why the Turbo Spin Echo sequence releases more R-F energy since it has a series of one-eighty-degree pulses after the original ninety-degree pulse. Spin echo only has one, one-eighty-degree pulse, that transmits energy. Assuming both sequences have the same scan time, this Turbo Spin Echo sequence transmits five, one-eighty-degree R-F pulses with high energy during the same time as the Spin Echo transmits one, one-eighty-degree R-F pulse, making the Turbo Spin Echo sequence, a higher SAR sequence. Gradient echo-based pulse sequences use flip angles less than ninety-degrees, so these sequences also have lower SAR. Sequence types Table with 3 columns and 7 rows Sequence RF Pulse/Echo Train/Flip Angle/TR SAR EPI (Perfusion, diffusion) Single Shot low SAR GRE (2D T1 weighting, SWI) low flip angle low SAR SE, TSE (T1 weighting) many slices with short TR moderate SAR GRE (3D breathhold, DCE) very short TR moderate SAR FSE, TSE (T2 weighting) long echo trains high SAR HASTE, RARE (MRCP) long echo trains low SAR Sequence types Audio Different sequences and their applications vary greatly in terms of SAR. For example, most E-P-I-based applications, for example, perfusion and diffusion have very low SAR, since they are “single shot” techniques, meaning, the R-F pulsing is only done once to acquire a complete image. At the other end of the spectrum, Fast Spin Echo, or Turbo Spin Echo sequences, used for T-two weighting, have additional, one-eighty-degree refocusing pulses, so these tend to have higher SAR. Tx/Rx coils Specialized local transmit/receive coils minimize RF exposure to the patient and can therefore reduce SAR and the risk of RF heating. Knee 18 Tx/Rx coil Head CP Tx/Rx coil Only Knee Tx/Rx and Head Tx/Rx coils are currently available for Numaris X systems Tx/Rx coils Audio Although the body coil integrated into the magnet bore is typically used for transmission, it exposes most of the human body to R-F even though the scanning may be highly localized. Local transmit coils are tuned to the body’s region of interest, and therefore can help to control the R-F exposure, reduce SAR, and minimize the risk of heating. Only the Knee and Head Transmit and Receive coils are currently available for Siemens Healthineers, Numaris-X, M-R, Systems. Room temperature Ambient temperature SAR limit values are also a function of the ambient temperature. At a room temperature of > 25°C (>77 °F), the permitted SAR limits are decreased. Siemens Healthineers recommends setting the temperature of the examination room to 21°C (70 °F), . Since a higher ambient temperature may lead to lower SAR limits. Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 Note: Does NOT affect SED, Only SAR limits Room temperature Audio Another important consideration is the Ambient temperature. Since the core body temperature rise depends on cooling, as well as heating, the ambient temperature in the exam room is also monitored. If it goes above twenty-four-degrees-Celsius, the SAR limits become progressively reduced since body cooling at higher temperatures is more difficult. In the Siemens Healthineers manual, it recommends that the temperature in the examination room is set to twenty-one-degrees-Celsius, since higher ambient temperatures may lead to lower SAR limits. ______________ CC info: Reference: 10VA60A_OM_MR_Examination_ER1_MR-05061G.630.15.01.02 Overview Table with 2 columns and 13 rows SAR Reduction Cost ↑ TR and/or Concatenations ↑ Scan Time ↓ Phase Encoding Steps or Slices ↓ Anatomy Coverage, ↑ SNR (PE) ↓ Flip Angle ↓ SNR, Contrast Variance ↑ Allowed Delay ↑ Overall Study Time iPAT ↓ SNR, ↓Visual Resolution, ↑ Artifacts(possibly) ↓ # of Saturation Bands or Thickness ↑ Artifacts (flow, breathing, phase wrap, etc.) RF Mode: Fast(High SAR)  Normal(Optimal)  Low SAR ↑ Echo Spacing (↓ Slice Profile/↑ Distortions) ↑ Scan Time ↓ Additional Pulses (Restore, MTC, inversions, etc.) Varying Effects (↑ Scan Time, Contrast Change, etc.) Hyperecho Contrast Variance, ↑ Slice Distortion, & ↑ Blurring ↓ Turbo Factor/ETL Contrast Variance, ↑ Scan Time Use Spectral FS (Standard) over SPAIR Contrast Variance, ↑ B1 Susceptibility, ↓ FatSat Uniformity Replace High SAR Sequence with Lower SAR Sequence (e.g., STIR  T2 FS, 2D  3D, or TSE/SE  GRE) Change of Contrast, Sequence Inherent Issues Overview Audio This table summarizes various SAR reduction techniques and the results when these parameters and sequences are modified. Course Review Congratulations. You have completed the MRI SAR, B1+rms, and SED Numaris X online training course. Select the numbered buttons below to review the material before proceeding to the final assessment. SAR & SED reduction techniques Specific Energy Dose (SED) B1+RMS Specific Absorption Rate (SAR) 1 1 2 2 2 3 3 3 4 4 4 Course Review SAR & SED reduction techniques Increasing the TR from the minimum allows greater SAR recovery time. Increasing the number of Concatenations can reduce SAR Reducing slices may reduce SAR/SED Resolution/Phase Encoding steps reduces the amount of acquired lines of k-space reducing SED iPAT techniques SAR Assistant Flip Angle Allowed Delay Number and type of Saturation Bands Turbo Factor or Echo Train Length RF Pulse Type VERSE (3T and Aera 1.5T) Special RF Pulses & SAR Hyperecho TSE (3T only) Sequence types Tx/Rx Coils Room Temperature Specific Energy Dose (SED) Specific Energy Dose (SED) is defined as the value of the accumulated whole-body SAR throughout the entire examination. SED = Specific Energy Dose Specific to the Body Part and Tissue Energy of the RF Dose into the Body Unit of Measure = Joules per kilogram (Joules/kg) B1+rms B1+rms is defined as the root-mean-square average of the RF transmission field (B1+) intensity during a scanning procedure. Units of measure for B1+rms are in micro-tesla (μT). B1+rms is not patient dependent, so it is often used by implant manufacturers as a more precise metric for tissue injury in the context of an implanted device. Specific Absorption Rate(SAR) SAR is defined as the Radiofrequency (RF) power absorbed per unit of mass of an object when exposed to a radio frequency (RF) electromagnetic field. SAR has two (2) Operating Modes: Normal Operating Mode – requires routine patient monitoring First Level Mode – requires medical supervision The SAR-Man breaks the body down into volumes that are represented geometrically as cylinders (length, radius, and mass). SAR limits are exceeded, the system automatically tries to adapt the protocol by utilizing the protocol tolerances (i.e., configured on the Sequence/Assistant parameter card) of protocol. SAR = Specific Absorption Rate Specific to the tissue (per kilogram) Absorption of the RF into the body and tissue Rate of RF exposure and absorption Unit of Measure = Watts per kilogram (W/kg) Disclaimer Please note that the learning material is for training purposes only. For the proper use of the software or hardware, please always use the Operator Manual or Instructions for Use (hereinafter collectively “Operator Manual”) issued by Siemens Healthineers. This material is to be used as training material only and shall by no means substitute the Operator Manual. Any material used in this training will not be updated on a regular basis and does not necessarily reflect the latest version of the software and hardware available at the time of the training. The Operator Manual shall be used as your main reference, in particular for relevant safety information like warnings and cautions. Please note: Some functions shown in this material are optional and might not be part of your system. Certain products, product related claims or functionalities (hereinafter collectively “Functionality”) may not (yet) be commercially available in your country. Due to regulatory requirements, the future availability of said Functionalities in any specific country is not guaranteed. Please contact your local Siemens Healthineers sales representative for the most current information. The reproduction, transmission or distribution of this training or its contents is not permitted without express written authority. Offenders will be liable for damages. All names and data of patients, parameters and configuration dependent designations are fictional and examples only. All rights, including rights created by patent grant or registration of a utility model or design, are reserved. © Siemens Healthcare GmbH 2023 Siemens Healthineers Headquarters\Siemens Healthcare GmbH\Henkestr. 127\ 91052 Erlangen, Germany\Telephone: +49 9131 84-0\siemens-healthineers.com Disclaimer Assessment Assessment Welcome to the assessment. For each question, select the button to the left of your answer, and then select Submit. You will have 3 attempts to take this assessment and to successfully pass this course, you must receive a score of 80% or higher. You will receive your score when you have completed the assessment. Note: If you close the learning activity at any time before you have finished the quiz, your answers will not be saved. Select Start to begin. Start Assessment Select the best answer. ? First Level Second Level Second Level Second Level Question 1 of 10 SAR and Stimulation monitoring can be operated in normal or _____ mode that is set during patient registration. Primary Level Primary Level Primary Level Predominate Level Predominate Level Predominate Level Multiple Choice Select the best answer. ? Specific Energy Dose (SED) Specific Absolute Reference (SAR) Question 2 of 10 _____ is defined as the Radiofrequency (RF) power absorbed per unit of mass of an object when exposed to a radio frequency (RF) electromagnetic field. Specific Absorption Rate (SAR) B1+rms Multiple Choice Select the best answer. ? Specific Energy Dose (SED) Specific Absolute Reference (SAR) Specific Absorption Rate (SAR) Question 3 of 10 _____ is defined as the root-mean-square average of the RF transmission field (B1+) intensity during a scanning procedure. B1+RMS Multiple Choice Select the best answer. ? Specific Energy Dose (SED) Specific Absolute Reference (SAR) B1+RMS Question 4 of 10 _____ is defined as the value of the accumulated whole-body SAR throughout the entire examination. Specific Absorption Rate (SAR) Multiple Choice Select the best answer. ? 210C 310C 350C Question 5 of 10 Siemens Healthineers recommends setting the temperature of the examination room to _____. 250C Multiple Choice Select the best answer. ? Compensate T2 Decay Hyperecho Question 6 of 10 _____ varies the refocusing Flip Angle to reduce the overall SAR. Motion Correction Reduce Motion Sensitivity Multiple Choice Select the best answer. ? Medium Boost Question 7 of 10 The VERSE pulse is implemented on the RF Pulse Type Fast and _____ on a 3T and Aera 1.5T MAGNETOM MR system. Low SAR Normal Multiple Choice Select the best answer. ? SAR Assistant SAD Assistant Question 8 of 10 The _____________ defines the strategies to avoid exceeding the SAR limit. SED Assistant B1+RMS Assistant Multiple Choice Select the best answer. ? SAR Specific Absorption Rate (SAR) Specific Absolute Reference (SAR) Question 9 of 10 _____ is not patient dependent, so it is often used by implant manufacturers as a more precise metric for tissue injury in the context of an implanted device. SED B1+RMS Multiple Choice Select the best answer. ? True Question 10 of 10 The FDA and IEC provide guidelines that issue limits respective of Radiofrequency (RF) exposure during a MR examination. False Multiple Choice Retry Assessment Results %Quiz1.ScorePercent%% %Quiz1.PassPercent%% Continue YOUR SCORE: PASSING SCORE: Results Slide You have exceeded your number of assessment attempts. Exit You did not pass the course. Select Retry to continue. Congratulations. You passed the course. Exit To access your Certificate of Completion, select the Certificates tab from the learning activity overview page. You can also access the certificate from your PEPconnect transcript. You have completed the MRI SAR B1+RMS SED Numaris X assessment. Completion MRI SAR B1+RMS SED Numaris X