Relative Cerebral Blood Volume Maps Corrected for Contrast Agent Extravasation Significantly Correlate with Glioma Tumor Grade, Whereas Uncorrected Maps Do Not
J.L. Boxermana,
K.M. Schmaindab and
R.M. Weisskoffc
a Department of Radiology, Rhode Island Hospital and Brown University Medical School, Providence, RI
b Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wis
c Massachusetts General Hospital NMR Center, Charlestown, Mass
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Fig 1. Typical corrected and uncorrected  R2* curves are shown. Note that even the first-pass curve is shifted to account for early leakage occurring during this segment. Without correction, the area under the curve (relative cerebral blood volume [rCBV]) is underestimated, even for integration techniques that stop at zero crossing or use gamma fitting.
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Fig 2. Typical case (grade IV glioma) demonstrating post-Gd T1, uncorrected relative cerebral blood volume (rCBV) map with artificially low tumor blood volume, the K2 parameter map from our fitting algorithm showing areas of greatest correction, and the corrected rCBV map highlighting a focus of corrected very high blood volume. On the bottom are sample tumor and normal brain regions of interest based on the corrected rCBV map.
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Fig 3. A, rCBV estimates corrected for contrast agent extravasation correlate significantly with glioma grade by using a Spearman rank correlation, whereas uncorrected relative cerebral blood volume (rCBV) does not. The disparity is due primarily to artificially low uncorrected blood-volume estimates in high-grade tumors that arises from the competing T1 effects of Gd leaking through disrupted blood-brain barrier.
B, Despite significant correlation, there exists moderate corrected rCBV variability within each grade and intergrade overlap. This supports the notion that glioma grading remains controversial and that multiple parameters, including vascular permeability and vessel size distribution, will probably be required in aggregate for accurate prognostication.
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Fig 4. Percentage difference between corrected and uncorrected relative cerebral blood volume (rCBV) for each of the 43 gliomas separated by grade. For all 3 grades, there were several cases in which correction made no difference (shown in white), probably because of a combination of low vascular permeability (possibly from steroids) and the Gd preload. Most of the high-grade tumors, however, had >10% difference, with 6 cases differing by at least a factor of 2.
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