A CT method to measure hemodynamics in brain tumors: Validation and application of cerebral blood flow maps

BACKGROUND AND PURPOSE: CT is an imaging technique that is routinely used f or evaluating brain tumors. Nonetheless, imaging often cannot show the dist inction between radiation necrosis and neoplastic growth among patients wit h recurrent symptoms after radiation therapy. In such cases, a diagnostic t ool that provides perfusion measurements with high anatomic detail would sh ow the separation between necrotic areas, which are characterized by low pe rfusion, from neoplastic areas, which are characterized by elevated CBF, We attempted to validate a dynamic contrast-enhanced CT method for the measur ement of regional CBF in brain tumors, and to apply this method by creating CBF maps. METHODS: We studied nine New Zealand White rabbits with implanted brain tum ors, We obtained dynamic CT measurements of CBF, cerebral blood volume (CBV ), and permeability surface (PS) from the tumor, peritunor, and contralater al normal tissue regions. In all nine rabbits (two studies per rabbit), we compared CT-derived CBF values with those simultaneously obtained by the st andard of reference ex vivo microsphere technique. Using CT, we examined th ree rabbits to assess the variability of repeated CBF and CBV measurements; we examined the other six to evaluate regional CBF reactivity to arterial carbon dioxide tensions. Finally, CT CBF maps were obtained from a rabbit w ith a brain tumor during normocapnia and hypocapnia, RESULTS: We found a significant linear correlation (r = 0.847) between the regional CT- and microsphere-derived CBF values, with a slope not significa ntly different from unity (0.99 +/- 0.03, P > .01), The mean difference bet ween regional CBF measurements obtained using both methods did not signific antly deviate from zero (P > .10), During normocapnia, tumor had significan tly higher CBF, CBV, and PS values (P < .05) than did peritumor and normal tissues. The variability in CT-derived CBF and CBV measurements in the repe ated studies was 13% and 7%, respectively. CT revealed no significantly dif ferent CBF CO2 reactivity from that determined by the microsphere method (P > .10). The CBF map of tumor regions during normocapnia showed much higher how than normal regions manifested, and this difference was reduced on the hypocapnia CBF map. CONCLUSION: The dynamic CT method presented herein provides absolute CBF me asurements in brain tumors that are accurate and precise. Preliminary CBF m aps derived with this method demonstrate their potential for depicting area s of different blood flow within tumors and surrounding tissue, indicating its possible use in the clinical setting.