Brain Tumor Characterization Using Multiple MR Parameters From Multi-Contrast EPI With Keyhole (GE-SE EPIK) Including Oxygen Extraction Fraction: A Comparison to O-(2-[18F]Fluoroethyl)-L-Tyrosine (FET) Positron Emission Tomography

Background: Tumor characterization and treatment efficacy are associated with tissue hypoxia. MR-derived oxygen extraction fraction (OEF) may offer valuable tumor insights but depends on multiple measurement parameters, often requiring multiple sequence acquisitions. Specific multi-parametric sequences offer direct access to MR parameter sets within short acquisition times. Purpose: To evaluate the potential of gradient-echo spin-echo echo-planar imaging with keyhole (GE-SE EPIK)-derived parameters (OEF/T ₂/T ₂*/venous cerebral blood volume (vCBV)) to characterize increased metabolic activity tissue identified in [ ¹⁸F]fluoroethyl-L-tyrosine (FET) PET, serving as a surrogate for neoplastic tissue. Study Type: Retrospective. Population: Fifty-seven brain tumor patients (female/male:31/26; age 27–73 years) with 66 histologically confirmed lesions (suspected glioblastoma (16), glioblastoma (28), astrocytoma (11), metastasis (6), oligodendroglioma (5)). Field Strength/Sequence: 10-echo GE-SE EPIK sequence at 3 T. Assessment: GE-SE EPIK data were acquired in a hybrid MR PET scanner during FET PET acquisitions. Two tumor segmentations based on FET-PET uptake and FLAIR hyperintensities were manually created. Mean GE-SE EPIK-derived parameters were calculated within tumor regions and compared to contralateral reference values. Relative tumor-to-reference parameters were compared across tumor types. Statistical Tests: One/two-sampled, two-tailed t-tests of mean relative MR-derived parameters. p-value < 0.05 was considered significant. Results: Significantly increased T ₂/T ₂* and decreased vCBV/OEF were found in FET-PET and FLAIR-derived VOIs. Latter showed decreased R2′. Significant correlation between FET uptake and T ₂/T ₂* was found in FET-VOIs (Pearson correlation: 0.26/0.31, respectively). Oligodendrogliomas showed significant differences to glioblastomas (rR ₂′, rOEF) and astrocytomas (rR ₂′). Metastasis showed different rT ₂ values than suspected gliomas. Astrocytoma differed from gliomas in FET-TBR. Susceptibility artifacts in T ₂* maps from air-tissue interfaces limited qualitative data interpretation. Data Conclusion: GE-SE EPIK provides multiple MR parameters that are sensitive to expected changes in tumor regions obtained from FET and FLAIR thresholds. Susceptibility artifacts in T ₂*/OEF maps made the differentiation between tumor relapse and treatment-related changes challenging. However, certain MR-derived parameters showed the ability to distinguish tumor types. Evidence Level: 3. Technical Efficacy: Stage 2.