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The authors' hypothesis is that incorporating bidirectional contrast agent transport into the DSC MR imaging signal model will improve rCBV estimates in brain tumors. A unidirectional contrast agent extravasation model (Boxerman-Weisskoff) was compared with a bidirectional contrast agent exchange model. For both models, they compared the goodness of fit with the parent leakage-contaminated relaxation rate curves and the difference between modeled interstitial relaxation rate curves and dynamic contrast-enhanced MR imaging in 21 patients with glioblastoma. The authors conclude that the bidirectional model more accurately corrects for the T1 or T2* enhancement arising from contrast agent extravasation due to blood-brain barrier disruption in high-grade gliomas by incorporating interstitial washout rates into the DSC MR imaging relaxation rate model.

The authors assessed correlations among baseline perfusion and arterial transit time artifacts, cerebrovascular reactivity, and the presence of collateral vessels on digital subtraction angiography. Arterial spin-labeling MRI and DSA were compared with BOLD MR imaging measures of hypercapnic cerebrovascular reactivity in 18 patients with symptomatic intracranial stenosis. In regions with normal-to-high signal on ASL, collateral vessel presence on DSA strongly correlated with declines in cerebrovascular reactivity (as measured on BOLD MRI). These data support the use of ASL MR imaging rather than invasive DSA to assess the presence of collateralization, even for patients with internal carotid stenosis from nonatherosclerotic etiologies. Also, collaterals identified on ASL with arterial transit artifacts correlated with decreased CVR compared with regions not perfused via collaterals.