Ronnie Wirestam

Background: Attempts to retrieve absolute values of cerebral blood flow (CBF) by dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) have typically resulted in overestimations. Purpose: To improve DSC-MRI CBF estimates by calibrating the DSC-MRI-based cerebral blood volume (CBV) with a corresponding T1-weighted (T1W) steady-state ( ss) CBV estimate. Material and Methods: 17 volunteers were investigated by DSC-MRI and Xe-133 SPECT. Steady-state CBV calculation, assuming no water exchange, was accomplished using signal values from blood and tissue, before and after contrast agent, obtained by T1W spin-echo imaging. Using steady-state and DSC-MRI CBV estimates, a calibration factor K=CBV(ss)/CBV(DSC) was obtained for each individual. Average whole-brain CBF( DSC) was calculated, and the corrected MRI-based CBF estimate was given by CBF(ss)=KxCBF(DSC). Results: Average whole-brain SPECT CBF was 40.1 +/- 6.9 ml/min . 100 g, while the corresponding uncorrected DSC-MRI- based value was 69.2 +/- 13.8 ml/min . 100 g. After correction with the calibration factor, a CBF( ss) of 42.7 +/- 14.0 ml/min . 100 g was obtained. The linear fit to CBF( ss)-versus-CBF( SPECT) data was close to proportionality (R=0.52). Conclusion: Calibration by steady-state CBV reduced the population average CBF to a reasonable level, and a modest linear correlation with the reference Xe-133 SPECT technique was observed. Possible explanations for the limited accuracy are, for example, large-vessel partial-volume effects, low post-contrast signal enhancement in T1W images, and water-exchange effects.