Gamma cameras contain energy discriminators that allow only those photons within a specified energy range to be recorded. The process of setting this energy window is called “peaking" the camera. A spontaneous shift in the peak of one head of a triple-head gamma camera was reported to cause an artifact that mimicked ischemia on 201Tl-chloride myocardial SPECT. The characteristic energy distribution results from the collection of total photon energy absorbed by the detector. Physically peaked detectors will center the energy window on the photo peak of selected isotope. Aim of the study: Our aim is to evaluate the effect of energy peak drifting for both imaging heads on the image contrast in SPECT. Materials and methods: Using a dual head gamma camera, the SPECT phantom with its inserts was scanned using a fixed acquisition protocol and image reconstruction parameters but with changing the energy peak window adjustment which was operated for both heads at different values starting from 120 KeV up to 160 KeV with incremental step of 5 KeV, and the window width was adjusted to be 15% as used in the clinical applications.
Results: Our results shows a fluctuation in the image contrast, as there was a gradual increase in the contrast value from 120 KeV setting up to 140 KeV by 31 % and also there was a gradual decrease in the contrast value from 140 KeV setting up to 160 KeV setting by 15 %. The clinical verification for these results was done on cardiac patient who underwent a cardiac scan twice with the normal gamma camera peak setting and then with off-peak setting at 120 KeV (which gives the lowest contrast value for the phantom study). And the case interpretation results confirm the phantom results as there was a significant change in the uptake in the left ventricle wall, with also a verification from the quantitative results by the Quantitave comparison using the quantitative gated SPECT data, that shows a 9% difference in the EF calculated value from the normal to the off-peak setting, which may affect the interpretation and in consequence the further treatment of the patient.
Conclusion: The energy window peaking for the gamma camera has a proven effect on the planar images, and this was explained and proved in our study to have a significant effect on the contrast of the SPECT images which will affect the interpretation of the clinical results.