A preliminary investigation of dynamic transmission computed tomography for measurements of arterial flow and tumour perfusion.

An assessment of the meaning and accuracy of CT numbers in dynamic CT has been made using data obtained from both phantom and patient investigations. Following an injection of contrast material, a series of 5-s scans (at 125 kVp, 230 mAs) were taken of the same slice at a rate of 6 scans min-1 using a Siemens Somatom 2 scanner. In order to study rapid changes of CT number, each 5-s scan was split into three segmented and overlapping images of 3-s duration. The variation of the mean CT number within small regions of interest (ROIs) were displayed as density-time curves and the errors associated with the artery and tumour curves were studied. In order to investigate the errors in the arterial curve which are associated with the timing sequence, blood flow through a large vessel was simulated in an experimental model. The results show that the largest error is associated with the peak CT value but this error can be reduced by a factor of approximately 2 if the images are split. Dynamic CT has been carried out on six patients with retroperitoneal or pelvic lesions in a preliminary study to investigate its use as a tool for monitoring the effectiveness of therapy. The results demonstrate that this technique can provide useful information regarding tumour vascularity and perfusion. In the studies on patients, a large spread in the CT numbers within a ROI was found to be a useful indicator of an uneven iodine distribution. For example, in two tumours, necrotic centres which were not apparent on the pre-contrast scan were identified from the dynamic study.