Dr. Vaska’s PET Lab

The main thing I have been focusing on for this lab has been testing different geometrically simple scintillator crystal shapes using the GATE program. I used a flat 8×8 detector array that would go directly underneath the crystal and shot a 511KeV source directly into the center of the detector labeled E-4 in the following image.

I started by creating a squared off sphere STL file as shown below, that exactly matches the dimensions of the detector array it would be sitting upon. In this image, I exaggerated the size of the detector array in red so that it would be clear how the detectors and crystals would be placed relative to each other.

Using this STL file in the GATE software and using the single point source in the center of E-4, I obtained the x-y coordinates of each hit that took place on any of the 64 detectors. From here, a MATLAB code was created in order to sort each of these given hit-coordinates into bins for each detector to create an array that shows how the light distribution looked for each detector. Note that the Y axis of this image is flipped.

While this light distribution does have a hot spot located in E-4, it also has even darker hot spots located in other, farther locations. This data suggests that this is probably not an ideal shape for scintillator crystals.

Ideally, the light distribution should be localized around the same area the light source entered, which in this case is E-4.

From here, I looked into using different squared-off cone shapes.

The first STL file was a cone with 800 sides. This number was chosen as it seemed to be perfectly smooth.

Other “cones” were created with severely less sides in order to account manufacturing limitations, including:

The 4 sided cone (or a triangular pyramid)

The 8 sided cone

And lastly, the 16 sided cone

I plan to use some or all of these shapes in future tests where the position of the light source is moved and the accuracy of the light distribution for each movement is recorded.

Stay tuned for more fun updates!