Constrained Positron Flight in PET Imaging via Strong Magnetic Fields
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Physics Honors Theses; 2008
Positron Emission Tomography (PET) imaging is a noninvasive imaging technique that utilizes radioactive emissions to produce positron-electron annihilations. Annihilation events result in the production of a pair of detectable photons that travel anti-parallel to one another with a slight angle of acollinearity. PET imaging has found use in the field of medicine by attaching radiotracers to materials such as sugars and antibodies, where metabolizing these agents allows for the observation of specific internal regions of the patient. Dependent on the region to be observed, radioisotopes of varying energy spectra are attached to the appropriate agent and introduced to the patient. Higher-energy isotopes emit positrons that tend to travel further prior to annihilation, which correlates to poorer image resolution. This is because a higher-energy positron must scatter off of more electrons than a lower-energy positron in order to lose enough energy that an annihilation event is likely. Poor image resolution is also associated with imaging in less dense media, as the positron must travel further on average in order to collide with an electron. As the positron, the anti-particle of the electron, possesses the property of charge, the presence of a strong magnetic field can constrain the flight of the positron to a helical path. By constraining the flight of the positron, the average distance from the source to the annihilation point is reduced. While the positron travels the same distance overall, the displacement of the positron from its source is reduced, resulting in images with better resolution. Simulations of the imaging process in the absence and presence of strong, homogeneous magnetic fields have shown the theoretical effectiveness of performing PET scans in the presence of a strong magnetic field. In collaboration with the Ohio State University Medical Center, the laboratory of Dr. Klaus Honscheid has tested a novel silicon-silicon small-animal PET system in the presence of a 7 Tesla magnetic field. The experimental data agrees well with the predictions made by simulation.