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 [ 18 F]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.