Ok I stole these pictures off Dale's home computer but just so that you can see the people that I am talking about and staying with. This one is of Dale, Laura, and the 2 little ones, Luke is 3 and Loni is 2 and they are both very cute, and this one is of Ed, Dale and Luke.
So I spent some time editing Laura's page so that all the links and pictures in her gallery would work and so if you want to see some of Laura's work go there.
A little add in about what I am doing here, if you don't care about physics, have a strong distaste for math and graphs, or you are just uninterested skip this little paragraph. So what I am doing is looking at the attenuation (weakening) of gamma ray signals from Gallium 67 imaging. In nuclear medicine one of the ways they take a scan is to put a radionuclide, in this case Gallium 67, in you and depending on what is going on in your body different organs and such will take that tracer up in different amounts and then as it breaks down it releases gamma rays which the gamma camera pics up to give a picture of your insides and what is going on. The thing is that as the gamma rays travel through your tissue some of them are scattered via the photo electric effect, Compton scattering, and coherent scattering, and so those gamma rays now appear as though they have come from a different place in the body than they actually did. So the gamma camera is set to reject some of the gamma rays it receives but this results in a fainter image, especially from deeper tissues. This loss of signal strength is called attenuation and it follows an exponential decay equation. So there is an attenuation correction that is applied to account for this loss of signal. The thing is that attenuation coefficients, which are used for the attenuation correction, are dependent on energy and so for Ga67 (which has 3 windows of photon energy that are used for imaging, three different attenuation corrections have to be applied to the three energies before the images can be summed. So what I am looking at is whether it can all sort of be averaged and a single effective attenuation coefficient can be used in the correction. I got my first set of data and the first linear attenuation coefficients that I found are, 0.1544cm-1 for 93.3keV, 0.1049cm-1 for 184.6keV, 0.0861cm-1 for 300.2keV, and 0.1236cm-1 for the sum of the three (which I am trying to determine if it can be used as an effective average).Ok sorry one more quick dorky physicsy thing, so we had a little excitement here but it looks like it is just turning out to be some contamination, but still an important thing to notice. So I was saying above that they do things to reduce the amount of scattered photons that end up being viewed on the final image. The gamma camera is set so that it will only receive gamma rays that are moving perpendicular to the face of the camera, this way it can determine where the gamma ray came from and make a 2D picture. However it is still possible that a gamma ray could be deflected so that it is headed perpendicular to the camera face, however when gamma rays are scattered they lose some of their energy so the gamma camera is set up to only image gamma rays that fall into certain energy windows. These windows are chosen to isolate the energies of gamma rays that have gone through no scattering, and therefore are around the "photopeaks" of the energy graph. Well so the excitement, while showing me the photopeaks of a gallium scan of a patient on his 9th day after receiving the injection of the gallium tracer an extra peak (the peak that is not highlighted is the extra one) was noticed. We couldn't figure out why there was an extra peak but Dale and my self did some calculations and we figured out that the peak was in the range of 180 degree compton backscattering from the 300.2keV photons. If that peak was caused by 180 degree backscattering than despite the fact that the photons were deflected they would still give an accurate position reading and could be used to improve the resolution of the images. However when we looked to see the peak again a couple days later, it was not there, it appears that there may have been contamination in the room that caused that peak and it stuck out because it was the patients 9th day and so the camera had to be exposed for longer to get a good reading and so the contamination peak became more prominent. Its still an imortant find though because now they have some contamination problems that they are going to try to fix.
