Impact of relative head sensitivity differences in multi-head gamma cameras

Cerebral perfusion single photon emission computer tomography (SPECT) can be used to identify epileptogenic foci. A (99m)Tc ethyl cysteinate dimer SPECT of the brain showed clinically evident differences in uptake between the CT attenuation corrected image and the Chang attenuation corrected image. The upper right hemisphere of the brain showed apparent diffuse hyperperfusion in the CT attenuation corrected image while the Chang attenuation corrected image, after reconstruction that appears to average projections, showed symmetrical cerebral perfusion. On review of archived patient data, this artefact was also observed in multiple previous cerebral SPECT studies undertaken on the same camera. Phantom investigation was used to identify the cause of the artefact as a difference in relative head sensitivity. The investigation also characterised the extent and nature of this artefact for CT attenuation corrected images, Chang attenuation corrected images and non-attenuation corrected images.