# 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

## TL;DR

This study compares brain tumor characterization using MR parameters from GE-SE EPIK with FET PET, finding that MR metrics like OEF and T2 can help distinguish tumor types.

## Contribution

GE-SE EPIK provides multiple MR parameters that can differentiate tumor types based on metabolic and vascular properties.

## Key findings

- GE-SE EPIK-derived parameters like OEF, T2, and vCBV showed significant differences in tumor regions compared to reference values.
- Oligodendrogliomas and astrocytomas showed distinct MR parameter profiles compared to glioblastomas.
- FET PET uptake correlated with T2/T2* values, suggesting a link between metabolic activity and MR parameters.

## Abstract

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.

To evaluate the potential of gradient‐echo spin‐echo echo‐planar imaging with keyhole (GE‐SE EPIK)‐derived parameters (OEF/T2/T2*/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.

Retrospective.

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)).

10‐echo GE‐SE EPIK sequence at 3 T.

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.

One/two‐sampled, two‐tailed t‐tests of mean relative MR‐derived parameters. p‐value < 0.05 was considered significant.

Significantly increased T2/T2* and decreased vCBV/OEF were found in FET‐PET and FLAIR‐derived VOIs. Latter showed decreased R2′. Significant correlation between FET uptake and T2/T2* was found in FET‐VOIs (Pearson correlation: 0.26/0.31, respectively). Oligodendrogliomas showed significant differences to glioblastomas (rR2′, rOEF) and astrocytomas (rR2′). Metastasis showed different rT2 values than suspected gliomas. Astrocytoma differed from gliomas in FET‐TBR. Susceptibility artifacts in T2* maps from air‐tissue interfaces limited qualitative data interpretation.

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 T2*/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.

3.

Stage 2.