Radio Frequency Induced Heating Near Medical Devices During MRI Justin Peterson University of Western Ontario Medical Biophysics March. 23, 2011

MR System Components Main Magnet (3 T) Gradient Coils RF Coils (64 or 127 MHz) y x B0B0 z  Applied Field B0B0 BzBz z ∆ z Radio- frequency signals

MR Induced Heating Factors affecting rate of heating: Strength of magnet Geometry Composition Position in bore

Device Stainless steel pins connected by a carbon fiber/fiberglass hybrid bar Stainless steel pins connected by a carbon fiber/fiberglass hybrid bar Used to brace damaged joints while healing Used to brace damaged joints while healing Simple configuration shown: Simple configuration shown:

Objectives Determine the relationship between radial position and rate of temperature change in the device Determine the relationship between radial position and rate of temperature change in the device Determine the ideal “worst case scenario” for future testing Determine the ideal “worst case scenario” for future testing

Methods Phantom resembles human head and torso Phantom resembles human head and torso Fill with gel made of NaCl, Polyacrylic acid and distilled water Fill with gel made of NaCl, Polyacrylic acid and distilled water Gel has conductivity similar to human tissue (4.80 mS/cm) Gel has conductivity similar to human tissue (4.80 mS/cm) Brace device and attach optical temperature sensors Brace device and attach optical temperature sensors

Methods

Methods -240 mm-210 mm-160 mm 0 mm+230 mm

Results

Results

Discussion Strong trend showed an increased rate of temperature change as radial distance from the centre increases Strong trend showed an increased rate of temperature change as radial distance from the centre increases electric field associated with gradient coils electric field associated with gradient coils Ideal “worst case scenario” for radial position: Ideal “worst case scenario” for radial position: Along the edge of the bore Along the edge of the bore Device pin closest to the ‘head’ of the phantom has the highest rate of temperature change Device pin closest to the ‘head’ of the phantom has the highest rate of temperature change

Conclusion/Future Studies Highest rate of temperature change along edge of bore Highest rate of temperature change along edge of bore Higher sample size for each group Higher sample size for each group Different heating of two pins Different heating of two pins Tests down the length of the bore Tests down the length of the bore

Acknowledgements Blaine Chronik, PhD Blaine Chronik, PhD Ian MacDonald, PhD Ian MacDonald, PhD Baraa Al-Khazraji Baraa Al-Khazraji Nicole Niovielli Nicole Niovielli