[Dynamic computed tomography of brain tumor]

Dynamic computed tomography (CT) has been widely used because of its simplicity, but regional cerebral perfusion of brain tumors has not critically been evaluated. This study was conducted to evaluated parameters obtained from the dynamic perfusion study in brain tumors and to clarify the usefulness of the dynamic CT comparing with Xe-enhanced CT. Dynamic CT was performed on 20 patients with brain tumor (three meningiomas, one pineal tumor, three metastatic brain tumors, thirteen gliomas). Dynamic CT consisted of performing six rapid sequential scans after a bolus intravenous injection of 40 ml of iodinated contrast medium. In this study, five parameters (corrected first moment, area, peak, time to peak, percent terminal height) were obtained from computer analysed curve fit on time density curve profile of serial scanning. In Xe-enhanced CT, serial CT was taken every three or five minutes during inhalation of 40 to 50 percent stable xenon. Flow rate constant (K), partition coefficient (lambda) and cerebral blood flow (CBF) for each pixel were calculated from delta HU (Hounsfield unit) and end-tidal air curve and displayed on CRT as images. In patients with meningioma, values of area and percent terminal height of the tumor were much higher than those of contralateral gray matter, and these findings show excessive increase of the intratumoral blood volume and extreme extravasation of iodinated contrast medium respectively. In patients with metastatic brain tumor or malignant glioma, which were enhanced by contrast medium, the values of all parameters of the tumors were higher than contralateral gray matter. Increase of intratumoral blood volume and destruction of blood brain barrier are suggested in these tumors. In the remaining patients with glioma, which was not enhanced, the values of corrected first moment and time to peak of the tumors were higher but area and peak were lower than contralateral gray matter. These findings show decrease of intratumoral blood volume and delay of mean transit time and arrival time of the bolus. Compared with CBF measured by Xe-enhanced CT, it was suggested that high density area of metastatic brain tumor or malignant glioma consisted of viable tumor cells, and in patients with glioma, low density area adjacent to the tumor with contrast enhancement was the invasive site of the tumor. Using dynamic CT, we were also able to distinguish the tissue contains viable tumor cells from the other part of brain by the differences in the parameter value.