The impact of partial-volume effects in dynamic susceptibility contrast magnetic resonance perfusion imaging.

PURPOSE

To demonstrate the degree of the cerebral blood flow (CBF) estimation bias that could arise from distortion of the arterial input function (AIF) as a result of partial-volume effects (PVEs) in dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI).

MATERIALS AND METHODS

A model of the volume fraction an artery occupies in a voxel was devised, and a mathematical relationship between the amount of PVE and the measured baseline MR signal intensity was derived. Based on this model, simulation studies were performed to assess the impact of PVE on CBF. Furthermore, the effectiveness of linear PVE compensation approaches on the concentration function was investigated.

RESULTS

Simulation results showed a nonlinear relationship between PVE and the resulting CBF measurement error. In addition to AIF underestimation, PVE also causes distortions of AIF frequency characteristics, leading to CBF errors varying with mean transit time (MTT). An uncorrected AIF measured at a voxel with a partial-volume fraction of <or=50% could produce a CBF overestimation of more than fourfold. Linear compensation of the concentration curves did not produce correct CBF estimates.

CONCLUSION

PVE can induce significant CBF estimation biases. In addition, the MTT dependence of CBF accuracy raises doubts of the validity of adopting a single cross-calibration factor (i.e., setting normal white matter to 22 mL minute(-1) (100 g)(-1)) to obtain CBF values with absolute units. The impact of PVE may be reduced by decreasing the maximum arterial signal drop in the perfusion images. To correct the AIF distortions introduced by PVE, the nonlinear relationship between the impact of PVE on MR signal intensity and contrast concentration function must be considered.