[Evaluation of partial volume effect in quantitative measurement of regional cerebral blood flow in single photon emission computed tomography--effects of limited spatial resolution and first-pass extraction fraction].

Two numerical brain phantoms were generated in order to investigate errors which might be included in the quantitative measurement of regional CBF with use of single photon emission computed tomography (SPECT). The first phantom simulated the normal brain, and effects of the limited spatial resolution of the SPECT scanner were evaluated for 4 tracer kinetic models of the conventional microsphere model, the intra-carotid bolus injection technique of 133Xe, 133Xe Kanno-Lassen method, and the IMP-autoradiography (IMP-ARG) method. The second phantom simulated the diseased brain with middle-carotid artery (MCA) occlusion, and effects of the limited first-pass extraction fraction were investigated for the microsphere model with various permeability-surface area products. The limited spatial resolution caused systematic underestimation of the radioactivity concentration in the gray matter regions, and systematic overestimation in the low CBF regions. These errors in the original radioactivity distribution were found to cause further systematic errors in the calculated regional CBF images. It was also found that these errors were highly dependent on the tracer kinetic model employed, e.g., regional CBF values were overestimated in the clearance and the Kanno-Lassen methods compared with the conventional microsphere method, whereas values were underestimated in the IMP-ARG method. It was also shown in this study that the limited first-pass extraction fraction caused significant underestimation in the calculated rCBF values. In addition, regional contrast can be reduced when using a tracer with small PS product.(ABSTRACT TRUNCATED AT 250 WORDS)