Preliminary results of Tc-99m ECD SPECT to evaluate cerebral collateral circulation during balloon test occlusion

The authors obtained noninvasive quantitative measurements of regional cerebral blood flow using Tc-99m L,L-ethyl cysteinate dimer (Tc-99m ECD) SPECT to evaluate cerebral collateral circulation during balloon test occlusion (BTO) of the internal carotid artery and vertebral artery (VA).

Five cases associated with an aneurysm and a brain tumor were investigated. After 10 minutes of BTO, a bolus of Tc-99m ECD was injected intravenously and radionuclide angiography was performed. The balloon remained inflated for an additional 5 minutes. After radionuclide angiography was completed, brain SPECT imaging was performed. For quantitative analysis, regions of interest were defined on the transverse images on each side of the anterior cerebral artery and middle cerebral artery territories in cases of occlusion of the internal carotid artery. Regions of interest were defined for the posterior cerebral artery territory and cerebellum in cases of occlusion of the VA. The percentage activity change during BTO was calculated.

In two of the three patients in whom BTO of the internal carotid artery was performed, the percentage activity reduction of more than 30% was noted in the anterior cerebral and middle cerebral artery territories. These two patients underwent bypass grafting before carotid occlusion. In one of the two patients in whom BTO of the VA was performed, the percentage activity reduction of 16% was noted in the posterior cerebral artery territory. This patient underwent bypass grafting before occlusion of the VA.

This noninvasive and quantitative method of cerebral blood flow measurement using Tc-99m ECD during BTO appears to have the potential to help select patients who may tolerate temporary or permanent arterial occlusion.