Regional partition coefficient of water in patients with cerebrovascular disease and its effect on rCBF assessment.

OBJECTIVE Cerebral blood flow (CBF) estimation with C15O2 PET usually assumes a single tissue compartment model and a fixed brain-blood partition coefficient of water. However, the partition coefficient may change in pathological conditions. The purpose of this study was to investigate the changes in the partition coefficient of water in pathological regions and its effect on regional CBF assessment. METHODS The study protocol included 22 patients with occlusive cerebrovascular disease to compare the partition coefficients among three regions (infarction area, noninfarct hypoperfusion area, and contralateral area) in the pathological brain (analysis A), and to compare the CBF estimated by using a fixed partition coefficient and CBF estimated using floating partition coefficients (analysis B). RESULTS The partition coefficient in the infarction area (0.55±0.07 ml/g) was lower than that in the contralateral normal cortex (0.68±0.05 ml/g), whereas noninfarct hypoperfusion area did not show a significant change (0.67±0.06 ml/g). As a result, the use of a fixed partition coefficient of normal volunteers (0.70 ml/g) resulted in an underestimation in regional CBF by 12% in infarction area (P<0.05), whereas the estimation errors were smaller and induced no significant difference in the noninfarct hypoperfusion area or in contralateral areas. CONCLUSION The partition coefficient is stable except for the infarction area, and CBF estimation using a fixed partition coefficient of normal volunteers provides clinically appreciable information in patients with cerebrovascular disease.