Perfusion patterns in CT transit studies

Transit studies consist of a rapid sequence of single cross-section CT scans performed during and following the bolus injection of contrast medium into the venous system. The low vascular volume of the brain leads to small changes in attenuation thereby reflecting the perfusion of vasculature. Studies were carried out following 45 examinations on 24 stroke patients and 15 tumor patients. Hypo-, normo- and hyperperfusion were observed in different tissue categories and related to specific tissue elements. The comparison of perfusion patterns with pre-contrast CT values and enhancement after 5 min elucidates cerebral hemodynamics in hypodense to hyperdense lesions with or without damage of the blood-brain barrier (BBB). Cystic lesions and edema were found to have slight damage of the BBB and markedly reduced perfusion. Infarcts demonstrated, depending on their state of evolution to cystic defects or recovery to normal, hypoperfusion and extravasation of contrast medium or hyperperfusion with or without damage of the BBB. A diagnostically valuable difference between edema and infarcts was seen in the phase of stable distribution after 5 min. In most tumors hypervascularity and pathological extravasation were seen, whereby the cause of enhancement could be differentiated. Owing to the properties of the contrast medium used, and to the fact that transit times can not yet be measured, quantification of CBV and CBF was not possible. Definition of large cerebral vessels, especially in the neighbourhood of brain tumors, and the improvement in detectability of small lesions by low dose contrast injection, will be demonstrated as a spin-off of CT transit studies. (orig.)