Measurement of regional cerebral plasma pool and hematocrit with copper-62-labeled HSA-DTS

We developed copper-62-labeled human serum albumin-dithiosemicarbazone (62Cu-HSA-DTS) as a blood-pool imaging agent for PET. To evaluate 62Cu-HSA-DTS for plasma-pool imaging and to measure the regional cerebral hematocrit, 12 normal volunteers and 7 patients with cerebrovascular disease underwent PET studies with 62Cu-HSA-DTS and 15O-labeled carbon monoxide (C15O).

The normal subjects were studied with both C15O and 62Cu-HSA-DTS. All patients were examined by 15O-gas studies to measure cerebral perfusion and oxygen metabolism, followed by measurement of plasma volume with 62Cu-HSA-DTS for analysis of regional cerebral hematocrit. Regional cerebral hematocrit was calculated from regional cerebral red cell volume (rCRCV) measured by C15O and regional plasma volume (rCPV) measured by 62Cu-HSA-DTS in each subject, and the regional cerebral/large-vessel hematocrit ratio was obtained for both cerebral hemispheres in each subject.

Mean regional cerebral hematocrit and mean cerebral/large-vessel hematocrit ratio in the 12 normal volunteers were 38.3 +/- 3.45% and 0.88 +/- 0.06, respectively. In the seven patients with cerebrovascular disease, regional cerebral hematocrit was significantly lower on the hypoperfused side than the normal hemisphere. The images of rCPV and rCRCV from these patients demonstrated a greater increase in rCPV than rCRCV in the hypoperfused area.

These results suggest that 62Cu-HSA-DTS can be used for measurement of plasma volume and that regional cerebral hematocrit may provide valuable information regarding the microcirculation in the brain.