Job AId MR Safety Aspect Magnet, RF and Gradient

SIEMENS Healthineers MR Safety Aspects : Magnet, RF, and Gradient Wahyu Widhianto Magnetic Resonance Restricted © Siemens Healthineers, 2022 Outline ▪How MRI Works ▪Static Magnetic Field (B0) ▪Radio Frequency Deposition (B1) ▪Time-varying Gradient Magnet (dB/dt) 2 Restricted © Siemens Healthineers, 2022 How MAGNETOM Sola MRI Works 3 Restricted © Siemens Healthineers, 2022 How MRI works coronal N Y axial sagittal X N External Magnetic Field Radiofrequency Gradient Coils Inside a strong magnetic field, Exposing the proton with a “match” To obtain a “slice” image from proton in our body will pointing frequency (Resonance) will change various angle, gradient coils are either parallel or anti parallel. its rotation angle which generating activated electric current. This is our signal 4 Restricted © Siemens Healthineers, 2022 New body coil How MRI Works 5 Restricted © Siemens Healthineers, 2022 SIEMENS MAGNETOM Skyra B O. Bo N Source : Siemens mri magnets spin resonances en. Source : https://directmedparts.com/all-about-gradient-coils-in-magnetic-resonance-imaging-mri/ 6 Restricted © Siemens Healthineers, 2022 Static Magnetic Field (B0) MAGNETOM Sola 7 Restricted © Siemens Healthineers, 2022 Static Magnetic Field (B0) MRI incident at Long Island imaging center spurs legal action January 23, 2014 by Lauren Dubinsky , Staff Writer Courtesy Zwanger-Pesiri Radiology On July 15, 2009, Daniel Mahony, 79, stepped U into the Zwanger-Pesiri Radiology center in Medford, N.Y. to get an MRI. But things didn't go exactly as planned. He walked into the MRI room with his metal walker and the magnetic field pulled it from his hand, causing him to fall and hit his head. Boy, 6, Killed in Freak MRI Accident July 31 A 6-year-old boy died after undergoing an MRI exam at a New York-area hospital when the machine's powerful magnetic field jerked a metal oxygen tank across the room, crushing the child's head. The force of the device's 10-ton magnet is about 30,000 times as powerful as Earth's magnetic field, and 200 times stronger than a common refrigerator magnet. The canister fractured the skull and injured the brain of the young patient, Michael Colombini, of Croton-On-Hudson, N.Y ., during the procedure Friday. He died of the injuries on Sunday, the hospital said. 8 Restricted © Siemens Healthineers, 2022 Static Magnetic Field (B0) X (m)_+ 3 Magnetic fields extend outside 0.5mT the magnet housing, it called ImT “Stray/fringe Field” and will exert 3mT a strong attraction on 5ml ferromagnetic objects. 10mT 20mT 200mT 40mT The most critical value is 5 Gauss Z (m) line (0.5 mT) 1500 mT -2 -1 The picture shows a stray field map of 1.5T Magnetom Essenza, where the 5 Gauss line extend to 4 m in Z direction and 2.5 m in X/Y direction 9 Source : Siemens MagnetomEssenza user manual Restricted © Siemens Healthineers, 2022 Static Magnetic Field (B0) Sometimes the 5 Gauss line extend beyond examination room Aera n Skyra AA FH4-16 10 Source : Siemens Training Material Restricted © Siemens Healthineers, 2022 Static Magnetic Field (B0) Magnetic Minimum distances flux density Devices affected Magnetic fields can adversely (x = y = radial, z = axial) affect the functions of 3 mT x = 1.8 m Small motors, watches, cameras, mechanical and electrical z = 2.7 m credit cards, magnetic media components 1 mT x = 2.2 m Oscilloscopes, computers, disk drives, z = 3.4 m shielded color monitors 0.5 mT x = 2.5 m B/W monitors, magnetic media, z = 4.0 m cardiac pacemakers, insulin pumps 0.2 mT x = 3.0 m Siemens CT systems z = 4.9 m 0.1 mT x = 3.4 m Siemens linear accelerators z = 5.8 m 0.05 mT x = 4.1 m X-ray I.I ., gamma cameras, z = 6.9 m third party linear accelerators 11 Source : Siemens Magnetom Essenza user manual Restricted © Siemens Healthineers, 2022 12 Restricted © Siemens Healthineers, 2022 Magnetic Field The force resulted from the M DERLO MAGN magnetic fields are stronger in higher Tesla and heavier objects FxV(m-B)=FcV.B.V8. 1.5 T 2.5 N 3.0 T 6 N LO KIL 13 Restricted © Siemens Healthineers, 2022 Spatial Field Gradient (dB/dz) The magnetic field strength drop rapidly on the edge of the gantry. 0.1 T/m 0.5 T/m I 1.0 m- MR conditional label provide two Side view numbers 0.8 m : 10 T/m 1.0 T/m 1. the maximum static field (B0) 0.6 m/ 7 T/m 2. Maximum spatial field gradient 0.4 m 5 T/m (dB/dz) 3 T/m D.2 m |0.1 T/m 1.0 T/m 0.0 m 0.5 T/m 0.2 m- 0.4 m 0.6 m MR --- 0.8 m 10.m MR Conditional 1 T - 1.0 m 0.8m 06m 0.4 m 0.2 m 0.0 m 0.2 m 0.4 m 0.6m 0.8 m 1.0 m 1.2 m 1.4 m 1.6 m 1.8m Source : ACR Guidance Document on MR Safe Practices: Updates and Critical Information 2019 14 Restricted © Siemens Healthineers, 2022 Biological effect from Static Magnetic Field (B0) There are no findings to suggest any permanent adverse effect on human subjects when exposed net ionic current into hair cells to static magnetic fields in strengths up to 8T magnetic field Source : Symptoms And Cognitive Effects of Exposure to Magnetic Stray Fields of MRI Scanners A MHD fluid forces The biological effects most likely to occur in patients undergoing MRI procedures are production of vertigo-like sensations and these effects are associated with movement in the MRI field. "r Source : Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use B Left Ear Right Ear Source : Vestibular stimulation by magnetic fields 15 Restricted © Siemens Healthineers, 2022 RF Deposition (B1) MAGNETOM Sola 19 Restricted © Siemens Healthineers, 2022 RF Deposition (B1) The Radiofrequency power delivered to tissue during an MRI examination is referred to Ingoing RF power = Specific Absorption Rate (SAR), expressed as RF energy/ time watts per kg (W/kg) Radiofrequency power deposition results in heating of patient tissues Based on the equation : RF pulse • Proportional BO2 (4 times higher in 3T) • Proportional to B1 2 (flip angle) • Proportional to tissue conductivity • Inverse proportional to body mass • SAR oc Spatially varying caused by human anatomy m Source : AJR 20 Restricted © Siemens Healthineers, 2022 RF Deposition (B1) TABLE II. Thermal injury root cause categories. Category Description The thermal injury was attributed to contact with another object. Anything present within the bore of the MR system was considered an object (e.g ., accessory coils, ECG leads, patient headphones, patient implants, patient clothing). For attribution to an object as the root cause, the location of the thermal injury needed to match the location of the object Skin-to-skin A thermal injury attributed to skin-to-skin contact at two contact anatomic locations, or a report describing thermal injuries in two anatomical locations that are likely to have be in direct contact (e.g ., inner thighs, left and right calf, thumb, and ipsilateral hip) leading to a possible current loop Bore contact Thermal injury occurring at an anatomic site in contact with (or near) the bore of the MR system Not RF-related Thermal events that are clearly not RF-related, for example, fires and cryogen burns Unclear The root cause of the event was unknown or the event description includes insufficient detail to draw any conclusions. Reports for which multiple causes were possible were also placed in this category Source : MRI-related adverse event reports : A 10-yr review 21 Restricted © Siemens Healthineers, 2022 RF Deposition (B1) TABLE III. Breakdown of MRI adverse events. MRI adverse event category Number (%)ª Thermal 906 (59) Mechanical 170 (11) Projectile 133 (9) Miscellaneous 109 (7) Image quality 89 (6) Acoustic 86 (6) Unclear 55 (4) Peripheral nerve stimulation 0 (0) Total 1548 "Total percentage may not be 100 due to rounding. Source : MRI-related adverse event reports : A 10-yr review 22 Restricted © Siemens Healthineers, 2022 RF Deposition (B1) Averaging time 6 min Considerations for increases in body temperature should be made for patients with : WHOLE BODY PARTIAL HEAD SAR LOCAL SAR SAR BODY SAR • cardiovascular disease Body region -> Whole body Exposed Head Head Trunk Extremities • hypertension body part • Operating diabetes (W/kg) (W/kg) (W/kg) (W/kg) (W/kg) (W/kg) Mode + • increased age NORMAL 2 2 - 10 a 3,2 10 10 20 • obesity • FIRST LEVEL fever 4 4 - 10 a 3,2 10 10 20 CONTROLLED • impaired ability to perspire SECOND LEVEL > 4 > (4-10) a > 3,2 > 10b > 10 > 20 • CONTROLLED pregnancy (risk for fetal heating) • drug regimes that may affect SHORT TERM SAR The SAR limits over any 10 s period shall not exceed 3 times the stated values thermoregulatory capabilities (e.g. diuretics, a The limit scales dynamically with the ratio "exposed PATIENT mass / PATIENT mass": tranquillizers, vasodilators) - NORMAL OPERATING MODE : PARTIAL BODY SAR = 10 W/kg - (8 W/kg * exposed PATIENT mass / PATIENT mass) • extensive tattoos FIRST LEVEL CONTROLLED OPERATING MODE : PARTIAL BODY SAR = 10 W/kg - (6 W/kg " exposed PATIENT mass / PATIENT mass) • implanted organ devices b In cases where the orbit is in the field of a small LOCAL RF TRANSMIT COIL, care should be taken to ensure that the temperature rise is limited to 1 ºC. Source : radiopedia 23 Restricted © Siemens Healthineers, 2022 RF Deposition (B1) SAR Information ? X SAR Monitor Operating Mode SAR Monitor Current measurement Normal Function as patient safety monitoring by Next measurement . Normal mode measuring the SAR of the power being irradiated First Level into the patients. Prediction Status Patient Protocol Current The monitor will do following steps : Displayed values belong to the current patient! 1. quantify the amount of heat-causing energy Whole Body 76 % being applied to the patient Exposed Body 54 % 2. Calculate the distribution of these energy Head 83 % throughout the body Head Local 0 % 3. Check the irradiation limits which may have Torso Local 0 % been exceeded Legs Local % 4. If any limit is reached, the monitor disables B1+ rms 36 % the RF transmission Calculation time: 11:48:20 2.6 Head 0.0 3.2 W/kg Close 24 Restricted © Siemens Healthineers, 2022 RF Deposition Head cylinder SAR Calculation Factors Cylindrical Model, the Body is broken down into parts. The percentage of each cylinder in the RF field is applied to the formula. Torso cylinder • Mass • Age • Height Height is needed to calculate the diameter and actual location of the head when patient positioned “Feet First” Leg cylinders 25 Restricted © Siemens Healthineers, 2022 RF Deposition SARLimit(s) Exceeded ! X Solving strategy in case SAR monitor detects SAR Current operating mode: First level (FL) BORE temperature: 23.5ºC a limit exceeded Operating mode for the next measurement Normal mode First level b a. Bore temperature may affect SAR limits. Whole Program step tse Body SAR depend on the ambient temperature Sequence name tse and humidity, and SAR limit is de-rated ¼ W/kg for every degree room temperature above 25° CURRENT PROPOSALS b. First Level mode will increase our SAR Limit Slices 33 O Reduce Slices to 27 c. Parameter adaptation proposed by SAR c TR 3000 [ms] O Increase TR to 3550 [ms] Monitor to reduce SAR value of sequence Flip angle 180 [deg] O Decrease Flip angle to 163 [deg] d. Adapt parameter manually OK Cancel Open Protocol Help d 26 Restricted © Siemens Healthineers, 2022 Specific Energy Dose (SED) SED limit is correlated to a maximum rise in core body temperature, Tmax SED is the total accumulated Tmax amount of energy that gets deposited in the body SED = SAR x time energy Joules/kg = Watts/kg x sec (SED) low RF power or temp, T (low SAR) high RF power (high SAR) scan time 27 Restricted © Siemens Healthineers, 2022 Specific Energy Dose (SED) SED Warning ? x SED limit is 14400 J/kg, equivalent to continuous SAR level of 2W/kg for 2 hours or 4 The patient has been exposed to an accumulated energy dose of: W/kg for 1 hour 0.00 J/kg SED warning will pop up when it’s reached 6000 J/kg, equivalent to continuous SAR level of 2 The next measurement will rise the energy dose to: W/kg for 50 mins or 4 W/kg for 25 mins. 91.62 J/kg To avoid harm to the patient it is strongly recommended to stop the examination now. If you nevertheless decide to continue the examination the patient must be closely monitored to avoid unacceptable thermal stress. (For further details please consult the operator manual: Specific energy dose) Do you really want to continue the examination? Yes No 28 Restricted © Siemens Healthineers, 2022 Time Varying Gradient (dB/dt) MAGNETOM Sola 31 Restricted © Siemens Healthineers, 2022 Time Varying Gradient (dB/dt) B B0 RF Z On Gs Off Off Source : Siemens mri magnets spin resonances en. 32 Restricted © Siemens Healthineers, 2022 Time Varying Gradient (dB/dt) B B BO Bo N weaker field as before stronger field Source : Siemens mri magnets spin resonances en. 33 Restricted © Siemens Healthineers, 2022 Time Varying Gradient (dB/dt) Rapid changing of gradient magnet (dB/dt) produce a strong air pressure which generate the sounds that we normally hear during image acquisition. Thinner the slices, smaller the FOV, higher the resolution will lead to stronger noise. Another effect which may occur is Peripheral Nerve Stimulation. It’s monitored by stimulation monitor. The stimulation occur because development of electrical fields whiting patient’s nerve fibers which are induced by the dynamic magnetic field 34 Restricted © Siemens Healthineers, 2022 Time Varying Gradient (dB/dt) Localizer, 99 dBA, TA 0:11 T2 TSE, 91 dBA, TA 3:37 T2 TSE DarkFluid, T1 SE, 93 dBA, TA 3:07 MPRAGE, 0.9 iso, 100 88 dBA, TA 4:32 SWI, 88 dBA, TA 5:51 dBA, TA 4:59 99% reduction* 1 3D PETRA, 0.9 iso 100 dBA 110 dBA 61 dBA, TA 5:57 80 dBA 90 dBA 64 dBA 65 dBA LO ... O Siemens PETRA Quiet Suite conventional 35 Restricted © Siemens Healthineers, 2022 *Reduction in sound pressure. 1Decibel measurements and images acquired on MAGNETOM Aera, November 2014. Data on file. Results may vary. Time Varying Gradient (dB/dt) 1 Stimulation Monitor - Stimulation Limit Exceededl ? x Stimulation Monitor, will check the scanning Step 1 - TWIST_Head_ePAT2x3_iso parameter before execution. Stimulation occurs when a characteristic threshold of Unable to start the measurement. electrical field is exceeded, its depend on The stimulation monitor indicates that the sequence will patient anatomy and physiology, geometrical exceed the stimulation limit. and physical attributes of the gradient coil and position of the patient within this coil. Open Protocol Calculate Cancel dB/dt is determined by the amplitude and rise time of gradient, sequence type and (1) (2) (3) parameter. When the monitor detect stimulation limit exceeded : 1. Open protocol for modification 2. Start calculation 3. Cancel respective protocol 37 Restricted © Siemens Healthineers, 2022 Time Varying Gradient (dB/dt) Stimulation Monitor - Recommendations ? X Some parameter modification Step 5 - ep2d_diff_3scan_trace_p2 recommendation will be proposed when the stimulation level is Protocol Parameters exceeded, • current recommended Increase FOV read • Increase slice thickness Change FoV read 240 320 mm • Change gradient mode (from fast Change Slice thickness to slow) but will affecting the TE O Change Gradient Mode or TR Additional changes required by changing Gradient Mode TE 98.0 100.0 ms Open protocol OK Skip 38 Restricted © Siemens Healthineers, 2022 SIEMENS Healthineers Thank You SIEMENS Healthineers O MAGNETOM Mini -- Magnetic Resonance 39 Unrestricted © Siemens Healthineers, 2019