Dynamic susceptibility contrast MRI calibrated using T1-based steadystate CBV and vascular space occupancy (VASO) Comparison with model-free arterial spin labelling

Abstract: IntroductionThe perfusion-related parameters cerebral blood flow (CBF) and cerebral blood volume (CBV) can be measured using dynamic susceptibility-contrast magnetic resonance imaging (DSC-MRI). However, absolute values of CBF and CBV are often overestimated and quantification of these parameters is challenging. By acquiring an independent absolute CBV estimate, a calibration factor can be obtained by comparing these values with CBV values estimated with DSC-MRI. This calibration factor is theoretically applicable both to CBV and CBF obtained from the same DSC-MRI measurement. In this study, DSC-MRI-based CBV and CBF were calibrated using steady-state T1-based CBV (called Bookend) and vascular space occupancy (VASO) techniques, and calibrated CBF values were compared with CBF values obtained by arterial spin labelling (ASL) MRI.Material and MethodsFifteen subjects were investigated using 3T MRI (Philips Achieva). For estimation of absolute CBV values, T1 measurements (for the Bookend technique) and VASO experiments were performed before and after a DSC-MRI experiment with administration of 0.1 mmol/kg b.w. contrast agent. Arterial spin labelling (ASL) was performed before the other measurements. The calibration factors were obtained by comparing CBV values from Bookend and VASO with DSC-MRI CBV values in the same region. Calibration factors were estimated from both white and grey matter regions and both CBV and CBF maps from DSC-MRI were calibrated using the retrieved calibration factors. Grey-matter CBF values in calibrated DSC-MRI images were compared to the corresponding values from ASL.ResultsThe mean value of CBF in grey matter obtained by DSC-MRI was 313 ml/(min 100 g) before any calibration. After applying calibration factors from Bookend, the mean value reduced to 33 ml/(min 100 g) and 29 ml/(min 100 g) using calibration factors from grey and white matter, respectively. Calibration factors obtained from VASO resulted in mean values of 42 ml/(min 100 g) and 38 ml/(min 100 g) using calibration factors based on grey and white matter, respectively. These estimates can be compared to the ASL-based mean CBF value of 44 ml/(min 100 g). The correlation between CBF estimates in grey matter obtained by DSC-MRI and ASL was improved when calibration factors from Bookend were used and when grey-matter based calibration factors from VASO were applied.ConclusionBookend and VASO techniques can be used for calibration of CBV and CBF estimates from DSC-MRI. The values obtained after calibration were more reasonable and the correlation with ASL improved for most of the calibration factors used. However, there is a need for further investigation of the methods, including optimization of the