MR Safety Aspect Magnet, RF, and Gradient

SIEMENS Healthineers MR Safety Aspects : Magnet, RF, and Gradient Saturday, 5 March 2022 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 MRI Works MAGNETOM Sola 3 Restricted © Siemens Healthineers, 2022 How MRI works coronal N Y axial sagittal X VIL 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 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 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 3 mT a strong attraction on 5ml ferromagnetic objects. 10mT 20mT 200mT 40mT The most critical value is 5 Gauss Z (m) line (0.5 mT) -2 -1 1500 mT 3 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 Magnetom Essenza user manual Restricted © Siemens Healthineers, 2022 Static Magnetic Field (B0) Sometimes the 5 Gauss line extend beyond examination room Aera Skyra 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 magnetic fields are stronger in higher Tesla and heavier objects FxV(m-B)=+Fr < 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 20 • FIRST LEVEL 4 4 - 10 a 10b fever 3,2 10 CONTROLLED • impaired ability to perspire SECOND LEVEL > 4 > (4-10) a > 3,2 > 10º > 10 > 20 • pregnancy (risk for fetal heating) CONTROLLED • SHORT TERM SAR The SAR limits over any 10 s period shall not exceed 3 times the stated values drug regimes that may affect 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 21 Restricted © Siemens Healthineers, 2022 RF Deposition (B1) @ SAR Information 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 % been exceeded Legs Local 0 % 4. If any limit is reached, the monitor disables B1+ rms 36 % the RF transmission Calculation time: 11:48:20 26 Head 3.2 Close 22 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 23 Restricted © Siemens Healthineers, 2022 RF Deposition SARLimit(s) Exceeded I X Current operating mode: First level (FL) BORE temperature: 23.5ºC Solving strategy in case SAR monitor detects SAR 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 Sequence name Body SAR depend on the ambient temperature 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 d 24 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 25 Restricted © Siemens Healthineers, 2022 Specific Energy Dose (SED) D 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 26 Restricted © Siemens Healthineers, 2022 General MR safety measures Patient must not positioned as shown on the left picture Should use paper or cotton/linen to cover exposed skin No direct patient contact to magnet bore or electric cables 27 Restricted © Siemens Healthineers, 2022 MRI BURN PREVENTION Tips for Keeping Patients Safe Screen patients for implants, devices, and other metallic objects. Assume anything unknown is MR Unsafe. Screen objects to ensure that anything entering the scan room is MR Conditional MR or MR Safe. Match conditions on MR Conditional devices with your scanner. MR All metals, even non-ferromagnetic ones, have the potential to heat up and cause burns. Have patients change out of street clothes whenever possible. Position patients to avoid skin-to-skin contact (e.g. no hands on hips, no crossed arms, no crossed legs, etc.). Always use the manufacturer-provided padding to insulate the patient. Sheets and blankets may be added for patient comfort but are not a substitute for manufacturer-provided padding. Route cables out of the scanner in a straight line. Don't coil cables or allow them to touch the patient. Lowest Use only Normal Operating Mode and the lowest SAR, whenever possible. SAR Possible Keep your eyes and ears on the patient at all times. Stay In communication with patients to identify warming. Monitor sedated patients using MR Conditional monitoring equipment. FDA SMRT AWORLD 28 OF KNOWLEDGE Restricted © Siemens Healthineers, 2022 PROFISSIONAIS Time Varying Gradient (dB/dt) MAGNETOM Sola 29 Restricted © Siemens Healthineers, 2022 Time Varying Gradient (dB/dt) B B0 RF Z On GS Off Off Source : Siemens mri magnets spin resonances en. 30 Restricted © Siemens Healthineers, 2022 Time Varying Gradient (dB/dt) B Bo weaker field as before stronger field Source : Siemens mri magnets spin resonances en. 31 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 32 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 O ... LO PETRA conventional Quiet Suite Siemens 33 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) b C Tx Tx Tx Tx LACQ JACQ MACe MACe | T/RX Gradient Gx Gradient G, y,z 34 Restricted © Siemens Healthineers, 2022 Time Varying Gradient (dB/dt) Stimulation Monitor - Stimulation Limit Exceededl ? X Stimulation Monitor, will check the scanning Step 1 - TWIST_Head_ePAT2×3_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 35 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 36 Restricted © Siemens Healthineers, 2022 SIEMENS Healthineers Thank You SIEMENS Healthineers MAGNETOM Mini Magnetic Resonance 37 Unrestricted © Siemens Healthineers, 2019