Concurrent functional and metabolic assessment of brain tumors using hybrid PET/MR imaging

Abstract

To evaluate diagnostic accuracy of perfusion weighted imaging (PWI) and positron emission tomography (PET) using an integrated PET/MR system in tumor grading as well as in differentiating recurrent tumor from treatment-induced effects (TIE) in brain tumor patients. Twenty patients (Group A: treatment naïve, 9 patients with 16 lesions; Group B: post-therapy, 11 patients with 18 lesions) underwent fluorine 18 ((18)F) fluorodeoxyglucose (FDG) brain PET/MR with PWI. Two blinded readers predicted low versus high-grade tumor (for Group A) and tumor recurrence versus TIE (for Group B) based solely on tumor rCBV (regional cerebral blood volume) and SUV (standardized uptake values). Tumor histopathology at resection was the reference standard. Using rCBV(mean) ≤ 1.74 as a cut-off, 100% sensitivity and 74% specificity were observed, whereas 75% sensitivity and 89.7% specificity were observed with SUV(mean) ≤ 4.0 as a cut-off to classify patients as test positive for low-grade tumors (Group A) and TIE (Group B). Diagnostic accuracy for detection of low-grade tumors was 90% using PWI and 40% using PET in Group A (p = 0.056); for detection of TIE in Group B, diagnostic accuracy was 94.1% using PWI and 55.6% using PET (p = 0.033). No significant correlation was demonstrated between rCBV parameters and SUV in Group A (mean values: p > 0.403), Group B (p > 0.06) and in the entire population (p > 0.07). Best overall sensitivity and specificity were obtained using rCBV(mean) ≤ 1.74 and SUV(mean) ≤ 4.0 cut-off values. PWI demonstrated better diagnostic accuracy in both groups. Poor correlation was observed between FDG and rCBV parameters.

Magnetic Resonance Perfusion Imaging in the Diagnosis of High-Grade Glioma Progression and Treatment-Related Changes: A Systematic Review

“…Most other studies provided P values and reached statistical significance for the use of rCBV to distinguish true progression and treatment-related effects with sensitivities ranging from 63% [38] [39]. Among these studies however, optimum cut-off values ranged extensively from 0.71 according to Hu et al [24], to as high as 5.01 in Sacconi et al [33]. Unfortunately, the issue of wide variability in cut-off values is known to the literature because of a lack of standardisation in acquiring and processing rCBV values, including different scanner technologies, varying algorithms for processing, and at times, a lack of quantification.…”

“…[43], and 1 used ASL + DSC + DCE [34] adjunctive to other non-perfusion based techniques. In general, the composite measures exhibited greater diagnostic accuracy compared to single parameters, except for 3 studies which found no statistically significant difference for certain measures [19] [32] [33]. Further, studies utilising three or more parameters in a single measure had greater diagnostic accuracy when more imaging modalities were utilised compositely (see Table 4…”

Contribution of PET Imaging to Clinical Management of Gliomas

“…As previously stated, hybrid MRI/PET has great advantages in the differential diagnosis of brain tumors, grading of gliomas, assessment of progression, and the distinction between necrosis and recurrence of tumors [162][163][164][165][166]. Additionally, it is an important tool for the selection of sites for biopsies and in the evaluation of treatment effects [160,[167][168][169][170][171][172][173][174][175][176]. Adding diffusion tensor imaging/fiber tracking, fMRI, PWI, MRS, and activation-PET to multimodal imaging can enhance the assessment of a tumor on the functional networks in the brain [177][178][179][180][181] and show anaerobic changes as well as the effect on efferent and connecting fiber tracts and on task-related activation patterns.…”

Neurologic Applications of PET/MR Imaging

“…They found differing spatial distribution between regions of elevated rCBV and increased 18 F-FDG uptake. 69 Future challenges for the PET/MR community include defining the optimal set of MR imaging parameters and standardizing their acquisition and processing for reproducibility, identifying the best PET radiotracer for each clinical question, and justifying the clinical utility of multimodal imaging.…”