Split dose iodine-123-IMP SPECT: sequential quantitative regional cerebral blood flow change with pharmacological intervention.

Unlabelled: At least two quantitative rCBF measurements are needed to evaluate rCBF changes with pharmacological intervention. We have developed the split dose 123I-IMP SPECT method, which enables measurement of rCBF to be repeated in a short time.

Methods: Thirty-one cerebrovascular disease patients were investigated to assess reproducibility and vasoreactivity to acetazolamide. During 44-min dynamic SPECT imaging, 123I-IMP injection and respective arterial sampling were performed twice at an interval of about 25 min. The rCBF values were calculated using a microsphere model in which the washout of 123I-IMP from the brain can be negligible in the first several minutes after injection. For the second rCBF measurement, the remaining activity due to the first 123I-IMP injection was estimated and subtracted from the total brain activity.

Results: In ten patients, two consecutive resting mean rCBF values in the MCA territory (CBF1 and CBF2) had good correlation (CBF1 = 47.4 +/- 4.0 (ml/min/100 ml: mean +/- s.d.), CBF2 = 45.2 +/- 8.2, CBF2 = 0.900*CBF1 + 2.9, r = 0.915). In 11 patients with occlusive lesions in the unilateral ICA system, mean rCBF in the MCA territory was increased by only 27.7% +/- 14.0% in the affected side by a 1-g intravenous acetazolamide injection, while 44.5% +/- 12.3% increase was found in the nonaffected side. In 10 patients without a major arterial lesion, a 49.7% +/- 17.0% increase of rCBF was demonstrated.

Conclusions: This split dose method 123I-IMP SPECT can be useful to estimate vascular reserve.