BACKGROUND: Understanding how mechanical properties relate to functional changes in glioblastomas may help explain variation between patients. PURPOSE: To map differences in biomechanical and functional properties between tumor and healthy tissue, to study their spatial distribution, and to assess any relationship between biomechanical and functional properties. STUDY TYPE: Prospective. SUBJECTS: Nine patients with glioblastoma, 17 healthy subjects FIELD STRENGTH/SEQUENCE: 3T, MRE, DSC, DTI, ASL ASSESSMENT: Stiffness and viscosity measurements G′ and G″, cerebral blood flow (CBF), apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were measured in patients′ contrast-enhancing tumor, necrosis, edema, and gray and white matter, and in gray and white matter for healthy subjects. STATISTICAL TESTS: Voxel-wise regression analysis using a linear and a random forest model for CBF as a function of ADC, FA, G′ and G″. Model performance was evaluated by root-mean-square error with a leave-one-patient-out cross-validation strategy. A paired Wilcoxon signed-rank test was used for comparisons of different regions and models. A significance level of P<0.05 was assumed for all tests. RESULTS: Median G′ and G″ in contrast-enhancing tumor were 15 % and 39 % lower than in normal-appearing white matter (cNAWM), respectively (P<0.01). FA was 53 % lower in tumor compared to cNAWM (P<0.01). ADC and CBF were 50 % and 2.9 times higher in tumor than in cNAWM, respectively (P<0.01). For both models, prediction of CBF was improved by adding MRE measurements to the model, compared to a baseline model with ADC and FA as predictors (P<0.05). DATA CONCLUSION: Tumors differed from healthy tissue with regard to G′ and G″, CBF, ADC and FA, with heterogeneity both between patients and within tumors. Measurements approached values in normal-appearing tissue when moving outward from the tumor core, but abnormal tissue properties were still present in regions of normal-appearing tissue. The inclusion of MRE measurements in statistical models helped predict perfusion, with stiffer tissue associated with lower perfusion values.
Relative cerebral blood volume (rCBV) from dynamic susceptibility contrast (DSC)-MRI is a valuable biomarker in patients with glioblastoma for assessing treatment response and predicting overall survival. DSC-MRI based on echo planar images (EPI) may possess severe geometric distortions from magnetic field inhomogeneities up to the order of centimeters. The aim of this study is to assess how much two readily available EPI-based geometric distortion correction methods, FSL TOPUP and EPIC, affect rCBV values from DSC-MRI in patients with confirmed glioblastoma. Method: We used a combined single-shot 2D gradient-echo (T2*), spin-echo (T2) EPI sequence to estimate both T2* and T2-weighted rCBV from the same contrast agent injection. Effects of distortion correction on the positive phase-encoded T2-and T2*-images were assessed in healthy anatomical brain regions in terms of Wilcoxon signed rank tests on median rCBV change and on Dice coefficients, as well as in tumor lesions in terms of Wilcoxon signed rank tests on median rCBV change. Results: Our results show that following distortion correction, both gradient-echo and spin-echo rCBV increased in cortical areas of the frontal, temporal and occipital lobe, including the posterior orbital gyri in the frontal lobe and middle frontal gyri (p < 0.0008). Similar, improved Dice coefficients were observed for gradient-echo EPI in temporal, occipital and frontal lobe. Only spin-echo rCBV in enhancing lesion increased with correction (p = 0.0002). Conclusion:Our study sheds light on the importance of performing geometric distortion correction on EPI-based MRI data before assessing functional information such as rCBV values. Our findings may indicate that uncorrected rCBV values can be underestimated from positive phase-encoding EPI and that geometric distortion correction is warranted when comparing EPI-based data to conventional MRI.
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