University of Western Ontario Relationship between Insertion Depth and MRI Induced Heating of External Stabilizing Brace Brett Empringham University of Western Ontario Medical Biophysics March. 22, 2011

Overview MRI is a leading Imaging Modality Can be dangerous for several reasons Experiment involves investigating induced heating MRI is a relatively new imaging modality Discuss evolution of technology excellent for soft tissue imaging Often times MRI is used by professional athletes to determine tendo and muscle damage around a joint One problem is heating of tissue, especially with devices- this experiment is designed to investigate MRI compatibility of a specific prosthesis and how we can minimize this heating

Background Information MRI consists of three components Primary magnet Gradient coils Radio frequency coil Induced heating Discuss the purpose of each coil and how MRI works Primary magnet causes homogeneous magnetic field Gradient coil causes the magnetic field to be dependant upon position in the bore of the magnet RF coil causes the precession that can be detected by RF detectors Note like 127 MHz I think http://www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/ Do this before inducred heating Induced heating here

Objectives Study the effect of intrusion into the tissue on induced heating of medical device Possible future benefits From determining this Talk about worst worst case scenario This sort of data will help us understand ways to minimize induced heating on this and other devices in the future Talk about motivation

Approach MRI scans were done on the device inserted to different depths of the phantom and the increase in temperature at various places within the phantom were measured

Making the Phantom Material that resembles human tissue in certain traits NaCl, Poly-acrylic acid, distilled water Shape similar to human torso Distilled water Nacl PAA poly acrylic acid Batches of 10 L

Methods Temperature probes Record temperatures before, during and after radio frequency exposure Adjust Insertion depth and repeat Where are the probes format better

Results Discuss axes Discuss what is happening- basically the probes on the tips of the pins are the only ones heating up and the one closer to the heat is the hottest This is at minimum insertion See if I can figure out how to change location of probe 2 Discuss why error bars unneccessary

Results Discuss what this is saying Ie the deeper the thing is in the phantom the less heating there is Discuss axes and error bars This is the hottest probe, or probe 1

Results Bar Location dT/dt (oC/s) 78 mm from phantom surface 0.756 0.6460 58 mm from phantom surface 0.478 48 mm from phantom surface 0.334 38 mm from phantom surface 0.2715 Discuss why no statistical analysis

Discussion Factors that decrease MRI induced heating Smaller loop causes less magnetic flux More insertion exposes the pin to more gel Moving further away from the side of the bore

Conclusion and Future Research Appears as though as insertion depth increases, rate of temperature rise decreases Research is needed to characterize the effect on induced heating of different variables

I would like to thank… Dr. Blaine Chronik Baraa Al-Khazraji Nicole Novielli Dr. Ian Macdonald

Questions?