A method for the quantitative measurement of cerebral vascular permeability using iodine contrast agent and X-ray CT scanner

It is important to know the vascular permeability quantitatively for the treatment of brain tumors. We developed a new method to measure the vascular permeability quantitatively by a conventional X-ray CT scanner and iodine contrast agent (delayed dynamic CT). Ki (influx transfer constant), Kb (outflux transfer constant), VP (plasma vascular volume) and λ (=Ki/Kb, the size of extracellular fluid space) were calculated according to the following equation constructed from 2 compartment model. CcT(t)=Ki {1-Vp/(1-b·Htc)} · ∫0tCp(s)e-kb(t-s)ds+Cp(t) · Vp. CcT(t); tracer concentration in the tissue measured by CT, b; tissue Htc (0.69), Cp(t); plasma tracer concentration. Iodine contrast agent was injected bolusly via the cubital vein in several seconds and serial CT scannings were performed in the interval of 0.1-5.0 minute till 40 minute. The concentration of the contrast agent in the tissue was calculated from the increment of CT attenuation value and that in the blood was from that in the superior sagittal sinus. The parameters mentioned above were calculated from the equation by Newton's method. Furthermore, functional maps of these parameters were made by calculating them for each pixel. These parameters were well correlated with histological findings of brain tumors and they were proved to be useful for the prediction of histological findings judging from 49 clinical cases. DDCT made it possible to quantify vascular permeability, vascular volume, and the size of extracellular fluid space, the factors that detertmine the contrast enhancement, using contrast media and a conventional X-ray CT scanner. Our method will give very useful information about histological findings as well as the chemotherapeutic plan for brain tumors. (author)