Brain perfusion SPECT with 99mTc-bicisate: comparison with PET measurement and linearization based on permeability-surface area product model.

To characterize a recently introduced cerebral perfusion tracer, 99mTc-bicisate, single photon emission computed tomography (SPECT) images of 99mTc-bicisate were compared with CBF images obtained by positron emission tomography (PET) using the 15O steady-state method in 10 cases of cerebrovascular disease and dementia. 99mTc-Bicisate SPECT and PET CBF images showed a similar distribution pattern except for two cases with subacute stroke, in which 99mTc-bicisate showed less uptake than CBF in the infarcted area where oxygen metabolism was severely diminished. Comparison of 99mTc-bicisate uptake and CBF in the other eight cases showed less contrast between high- and low-flow regions in 99mTc-bicisate SPECT. Although the SPECT count ratio of cerebral structures to cerebellum showed a good correlation with CBF ratio, it gradually deviated from the linear relationship in the high-flow range. Assuming this nonlinear relationship is due to the limited extraction of the tracer, we estimated the permeability-surface area product (PS) value by a nonlinear least-squares curve-fitting procedure. The correction of the nonlinear relationship using the estimated PS value and a table lookup method resulted in an excellent linear relationship between corrected SPECT counts and CBF.