Validation to eliminate vascular activity on 99Tcm-HMPAO brain SPECT for regional cerebral blood flow (rCBF)...

Since more than 15% of the injected dose of 99Tcm-HMPAO 10 min after injection labels plasma or red blood cells (RBC), the elimination of vascular activity from actual brain activity is mandatory to evaluate accurately regional cerebral blood flow (rCBF) with 99Tcm-HMPAO brain SPECT. The late image (4 h post-injection) will show a reduced vascular activity of approximately 30% compared to the initial image (30 min post-injection), due principally to a plasma fraction reduction of 54%, and an insignificant reduction of activity in the RBC fraction. The circulating RBC count can then be normalized for both the injected dose and total blood volume, because the entrapment mechanism of 99Tcm-HMPAO with RBC is the same as that with brain retention. After elimination of the vascular contribution using the RBC activity the mean counts in the 14 middle cerebral artery areas from seven cases on 99Tcm-HMPAO SPECT showed a good correlation (r = 0.85) with the initial slope index of 133Xe cerebrography. It was concluded that the elimination of the vascular activity on 99Tcm-HMPAO brain SPECT is needed to quantify rCBF accurately.