Absolute quantitative MR perfusion and comparison against stable‐isotope microspheres

Abstract

Purpose This work sought to compare a quantitative T1 bookend dynamic susceptibility contrast MRI based perfusion protocol for absolute cerebral blood flow (qCBF) against CBF measured by the stable‐isotope neutron capture microsphere method, a recognized reference standard for measuring tissue blood flow, at normocapnia, hypercapnia, and in acute stroke. Methods CBF was measured in anesthetized female canines by MRI and microspheres over 2 consecutive days for each case. On day 1, 5 canines were measured before and during a physiological challenge induced by carbogen inhalation; on day 2, 4 canines were measured following permanent occlusion of the middle cerebral artery. CBF and cerebrovascular reactivity measured by MRI and microsphere deposition were compared. Results MRI correlated strongly with microspheres at the hemispheric level for CBF during normo‐ and hypercapnic states (r2 = 0.96), for individual cerebrovascular reactivity (r2 = 0.84), and for postocclusion CBF (r2 = 0.82). Correction for the delay and dispersion of the contrast bolus resulted in a significant improvement in the correlation between MRI and microsphere deposition in the ischemic state (r2 = 0.96). In all comparisons, moderate correlations were found at the regional level. Conclusion In an experimental canine model with and without permanent occlusion of the middle cerebral artery, MRI‐based qCBF yielded moderate to strong correlations for absolute quantitative CBF and cerebrovascular reactivity measurements during normocapnia and hypercapnia. Correction for delay and dispersion greatly improved the quantitation during occlusion of the middle cerebral artery, underscoring the importance for this correction under focal ischemic condition.

QSM in canine model of acute cerebral ischemia: A pilot study

“…QSM was evaluated against quantitative perfusion in a controlled large animal MCAO model 4,5,39 . X‐ray angiography was used to quantify the degree of arterial collateralization, a known cofactor of infarction in selective occlusion models 40‐42 …”

“…This method has been directly compared to stable neutron microsphere deposition and found to have an error equal or less than 10% of true perfusion (mL/100 g/ min) in the setting of MCAO. 5 Finally, infarct volume was determined using a DWI scan. DWI was acquired using the following set of parameters: TR/ TE = 2993/83 ms, FA = 90°, BW = 1790 Hz/pixel, matrix size = 128 × 128 × 50, voxel size = 1.75 × 1.75 × 2 mm 3 , b values = 0, 800 s/mm 2 , and 33 directions.…”

“…The MRI perfusion images were postprocessed to create qCBF (in mL/100 g/min) parametric images using custom software created for MatLab v9.3 (The Mathworks, Natick, MA). 5 Quantitative susceptibility mapping is a widely used technique for the determination of local magnetic fields and has been discussed widely in the literature. [46][47][48] In the following, we present only those details germane to the current work.…”

“…3 Although DWI is closely reflective of tissue damage, estimates of perfusion do not accurately reflect tissue at imminent risk. 4,5 Furthermore, traditionally used diffusion-perfusion mismatch might overestimate the extent of tissue at risk due to oligemia. 6 Therefore, the availability of an additional MRI marker of metabolic activity that is independent of assumption in blood flow could be used to identify functioning but hypoperfused (ie, above the perfusion threshold for neuronal cell death 7,8 ) and severely ischemic tissues and potently improve the clinical definition of the ischemic penumbra.…”

“…Using DWI and perfusion imaging (ie, dynamic susceptibility contrast perfusion or arterial spin labelling), MRI can define tissue that has succumb to cytotoxic edema as well as hemodynamically unstable tissue that may or may not be at risk for tissue death 3 . Although DWI is closely reflective of tissue damage, estimates of perfusion do not accurately reflect tissue at imminent risk 4,5 . Furthermore, traditionally used diffusion‐perfusion mismatch might overestimate the extent of tissue at risk due to oligemia 6 .…”