1. 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

2. 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

3. 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
Do this before inducred heating
Induced heating here

4. 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

5. 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

6. 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

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

8. 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

9. 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

10. 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

11. 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

12. 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

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

14. Questions?