title: Effects of centre-of-rotation shift on contrast and spatial resolution of the SPECT system.
abstract: The effects of centre-of-rotation (COR) shift of the rotating camera-based single photon emission commuted tomography (SPECT) system on tomographic images were investigated quantitatively. Contrast and spatial resolution variations as a function of COR shift were measured for all shifts less than 1 pixel, in steps of 0.1 pixels. This region encompasses the typical COR variations. The behaviour of these indices was analysed. In addition, the validity of the limit imposed on the allowable COR shift, as utilized in the current SPECT quality control protocols, was examined. The value of either +/- 0.5 or +/- 0.25 pixels is presently in use as the limit. From this study, both limits result in the loss of resolution. The resolution loss will increase the uncertainties of volume and concentration measurements. For a COR shift of 0.25 pixels, the spatial resolution loss is approximately 5%. This small spatial resolution loss may not affect the qualitative evaluation of tomographic images. However, any loss of resolution should be avoided. For a COR shift of 0.1 pixels, there is no observed loss of resolution. This value should be a desirable choice as the maximum allowable COR shift since it ensures the optimum performance of the SPECT system.
mesh_terms: D012399:Rotation; D014055:Tomography, Emission-Computed / Q000295:instrumentation