99mTc-bicisate reliably images CBF in chronic brain diseases but fails to show reflow hyperemia in subacute stroke: report of a multicenter trial of 105 cases comparing 133Xe and 99mTc-bicisate (ECD, neurolite) measured by SPECT on same day

A multicenter study was performed in seven European centers comparing 99mTc-bicisate with 133Xe as a means of evaluating bicisate as a tracer of CBF distribution in humans. The same type of single photon emission computed tomography (SPECT) instrument (Tomomatic) was used in all centers. A total of 115 cases were collected, and of these 105 were considered technically adequate, comprising 18 normal subjects, 18 senile dementia, eight epilepsy, one brain tumor, eight chronic head trauma, and 52 stroke cases. As expected, bicisate gave better spatial resolution than Xe. Agreement between the results of the two methods was noted in 98 cases, but not in the remaining 7, all belonging to the stroke group. These seven all suffered from a subacute stroke (11-23 days after onset), and the disagreement in all cases consisted of bicisate showing low count rate in the area of the infarct and Xe a normal or elevated flow (luxury perfusion) as sign of spontaneous thrombolysis with reperfusion; in fact, these seven cases comprised all the reperfusion cases in the series. The results validate bicisate as a tracer of CBF in normal humans and in chronic brain diseases. Only in a subgroup of subacute stroke cases does bicisate not follow CBF, as it fails to show reperfusion hyperemia. This suggests the usefulness of bicisate in stroke cases, particularly in the subacute phase, where other SPECT methods often present difficulties due to reflow masking the size and the severity of the lesion.