Local cerebral blood flow and oxygen metabolism in aneurysmal cases studied by positron CT

Changes in local cerebral blood flow and oxygen metabolism in cases of ruptured aneurysm were studied by positron CT using 15O as a positron emitter. During continuous inhalation of C15O2 and 15O2 gases, seven slices (16 mm in thickness) were simultaneously obtained by positron CT. Based on the data from the C15O2 study, images of cerebral blood flow (CBF) were obtained. Further, the data from both the C15O2 and 15O2 studies were used to obtain images of oxygen extraction ratio (OER) and cerebral metabolic rate for oxygen (CMRO2). Six cases of ruptured aneurysm were studied, and, among them, two cases were studied two or more times. In normal cases, images of CBF and CMRO2 were quite similar, indicating a coupling of flow and metabolism. In cases of ruptured aneurysm, the area of decreased blood flow was wider than that shown on X-ray CT. A mild decrease in flow was noted even in cases that showed minimal or no change on X-ray CT. Asymmetry of cerebellar blood flow between the two hemispheres was noted in large supratentorial infarction or hematoma. In one case of focal increase in OER, neurological abnormalities disappeared after several days, whereas in a case of focal decrease in OER, deficits did not improve. Thus, OER might be a good indicator of neurological recovery. However, movements of patients, which must be overcome through proper positioning, sometimes created artifacts that did not allow for precise assessment. (author)