Utility of relative cerebral blood volume mapping derived from perfusion magnetic resonance imaging in the routine follow up of brain tumors

Abstract

It was recently demonstrated that imaging of brain tumors by relative cerebral blood volume (CBV) maps reconstructed from dynamic magnetic resonance (MR) data provide similar diagnostic information compared to positron emission tomography (PET) or 201Tl single-photon emission computerized tomography (201Tl-SPECT) scans. The authors used relative CBV mapping for routine follow-up evaluation of patients with brain tumors and compared its sensitivity to diagnostic MR imaging, 201Tl-SPECT and clinical assessment. Fifty-nine patients were prospectively followed using 191 concomitant studies of dual section relative CBV maps, MR imaging, 201Tl-SPECT, and neurological evaluations. Studies were repeated every 2 to 3 months (median three evaluations/patient). The relative CBV maps were graded as relative CBV 0 to 4, where Grades 3 and 4 are indicative of proliferating tumors (four = rapid leak). There were 44 high-grade and 15 low-grade tumors followed during treatment. During the follow-up period a change in relative CBV grade was observed in 56% of the patients, revealing an increasing grade in 72% of them. The rapid leak phenomenon was detected in 35% of all studies and in 81% of those with a worsening relative CBV grade. Tumor progression was detected earlier by relative CBV maps as follows: earlier than MR imaging in 32% of the studies (earlier by a median of 4.5 months; p < 0.01); earlier than 201Tl-SPECT in 63% (median 4.5 months; p < 0.01), and earlier than clinical assessment in 55% (median 6 months; p < 0.01). In 82% of studies with positive MR imaging but negative 201Tl-SPECT, the lesions were smaller than 1.5 cm. The relative CBV maps clearly delineated the appearance of rapid leak in these lesions. Routine use of relative CBV maps that can be implemented on any high-field MR unit and added to the regular MR evaluation provides useful functional information in patients with brain tumors. When used as an adjunct follow-up evaluation it proved more sensitive than the other modalities for early prediction of tumor growth. It is very sensitive to small regional changes, unlike functional imaging such as PET or SPECT scans. Based on previous experience with 76 regional CBV studies, the authors conclude that regional CBV mapping correlates with active tumor and it may separate enhancing scar and radiation injury from infiltrative tumor. A new effect named the rapid leak phenomenon was also observed; this phenomenon, as identified on the regional CBV maps, correlates with high malignancy.

Role of Perfusion CT in Glioma Grading and Comparison with Conventional MR Imaging Features

“…8,[29][30][31][32] Even in the high-grade gliomas with pathologic contrast enhancement, the enhancement may not reflect the areas of neovascularity and angiogenesis. 33,34 Thus radiologic grading of tumors with conventional MR imaging is not always accurate, with sensitivity in identifying high-grade gliomas ranging from 55.1% to 83.3% in various studies 8,14,17,18,31 and 85.7% in our study. Finally, conventional MR imaging does not provide information on tumor physiology, which is also an important factor in determining the tumor grade.…”

Comparison of dynamic contrast-enhanced MRI with WHO tumor grading for gliomas

“…Good correlation between histologically and radiologically determined tumor grades has been achieved [38,39,40]. However, the procedure applied here, based on histograms, is more reliable than the use of mean values or regions of interest (ROIs) [38,39,40,41,42]. Unfortunately, only the data from a single slice can be used with the measuring technique applied here and the histogram may vary according to the MRI slice in which the measurement is performed, but the variation should be relatively small compared to the variation with the ROI 6 Representation of the fractional tumor volume with a vascular volume V b above a threshold vs. the threshold.…”

Comparison of Dynamic Susceptibility-weighted Contrast-enhanced MR Methods: Recommendations for Measuring Relative Cerebral Blood Volume in Brain Tumors

“…The feasibility and relevance of using dynamic susceptibility-weighted contrastenhanced MR imaging to measure rCBV in brain tumors has been supported with studies that show that rCBV may help in better differentiation of histopathologic tumor types than conventional MR imaging, may provide information to help predict tumor grade (6-11), and may better help to predict survival than histopathologic findings (12). In addition, rCBV maps may aid in the differentiation of posttreatment changes from tumor recurrence (13,14) and may be predictive of early local recurrence or malignant transformation (15,16).Despite these promising results, it has long been known that use of dynamic susceptibility-weighted contrast-enhanced methods for the determination of rCBV can be complicated by a leaky blood-brain barrier, as is often present with brain tumors. Under these conditions, contrast agent leaks out of the vessels into the extravascular-extracellular space, which can result in shortening of the tissue water T1.…”

“…The feasibility and relevance of using dynamic susceptibility-weighted contrastenhanced MR imaging to measure rCBV in brain tumors has been supported with studies that show that rCBV may help in better differentiation of histopathologic tumor types than conventional MR imaging, may provide information to help predict tumor grade (6-11), and may better help to predict survival than histopathologic findings (12). In addition, rCBV maps may aid in the differentiation of posttreatment changes from tumor recurrence (13,14) and may be predictive of early local recurrence or malignant transformation (15,16).…”