Aim: To assess the potential diagnostic value of the low-dose computed tomography (CT) component of dual-examination single photon emission CT and CT (SPECTCT) cerebral perfusion studies.
Method and materials: Two hundred and forty consecutive 99 mTc hexamethylpropylene amine oxime (HMPAO) SPECTCT studies were considered for inclusion. The images were acquired on a hybrid dual-head gamma camera/low-dose CT system. The CT component had a fixed tube current of 2.5 mA. The CT section thickness was 5mm and total acquisition time approximately 7.5 min. Studies in which no CT images were acquired, or those excessively degraded by movement artefact were excluded. The CT images of each of the remaining studies were retrospectively reviewed and categorized as normal or abnormal. Details of the abnormalities were recorded.
Results: Fifteen of the 240 studies were excluded as no CT images were obtained. A further 14 were excluded as they were considered excessively degraded by movement artefact. A single abnormality was demonstrated on 48 (23%), and two abnormalities on four (2%) of the remaining 211 studies. The most common abnormal findings were low attenuation in the deep cortical white matter (n=22), infarcts (n=12), cerebral atrophy (n=7), dilated ventricles (n=5), basal ganglia calcification (n=4), and post-surgical change (n=3). Other findings included a chronic subdural haematoma, a meningioma, and a posterior fossa cyst. Previous cerebral imaging was available for comparison in 31% of cases. There was 85% concordance between previous imaging and the low-dose CT images.
Conclusion: Twenty-five percent of the low-dose CT images in this study demonstrated abnormalities. Therefore the CT component of cerebral perfusion SPECTCT investigations should be routinely reported in their own right.