Vasodilatation and disruption of the blood brain barrier determine hyperfixation with 99mTc-HMPAO brain SPECT in subacute stroke

Hyperfixation characterized by excess tracer activity compared with cerebral blood flow (CBF) using 99mTc-d, l-hexamethylpropyleneamine oxime (HMPAO) brain single photon emission tomography (SPECT), has not been measured in terms of cerebral metabolic rate of oxygen consumption (CMRO2) oxygen extraction fraction (OEF) and cerebral blood volume (CBV). We studied four patients with subacute stroke who showed hot uptake in infarct areas with 99CTc-HMPAO brain SPECT. We performed positron emission tomography (PET) and magnetic resonance (MR) imaging. Regions of interest (ROIs) were drawn in the same hot uptake areas in SPECT and PET images. The average counts per pixel of 99mTc-HMPAO and the absolute values of CBF, CMRO2 OEF and DBV with PET were then obtained. The hyperfixation rate with 99mTc-HMPAO is expressed as the surplus rate compared with PET-CBF. PET parameters in the hot uptake area were compared with those of 5 normal controls. OEF and CMRO2 at the hot uptake areas in the 4 patients were significantly lower than those of normal controls (P<0.01), but CBF and CBV were not significantly different between patients and normal controls (ns). The hyperfixation rate of 4 patients was 0.30±0.15, which correlated well with CBV (r=0.97, y=11.75 + 0.42 ; P<0.05). The hyperfixation rate by 99mTc-HMPAO brain SPECT correlated with CBV in the PET study and reflected Gd-DTPA enhancement by MR imaging. Therefore, 99mTc-HMPAO hyperfixation in the infarct area might be caused by vascular dilatation and disruption of the blood brain barrier in terms of an increased capillary permeability-surface product