Quantitative MRI relaxometry in brain tumor needle biopsies: Multimodal comparison with tissue fluorescence, radiology, and neuropathology

Abstract

Background

Quantitative MRI (qMRI) relaxometry holds potential for brain tumor identification beyond contrast enhancement on conventional images. However, clinical implementation is limited by long acquisition times, changing conditions between imaging and surgery, and lack of correlation with standard techniques.

Purpose

To extend a methodology for multimodal data analysis to relaxometry data. To integrate relaxometry into the burr hole needle biopsy procedure with optical guidance, setup a workflow for multimodal data processing and analysis, and apply the methodology in a clinical setting.

Methods

Multi-dimensional multi-echo relaxometry data (2x6 min) was acquired in addition to the clinical imaging protocol. Relaxation rate and proton density maps, as well as their differences were calculated before (R₁, R₂) and after gadolinium contrast-agent administration (R₁Gd, R₂Gd). Radiological volumes of interest (VOIs: tumor, edema, white matter, and biopsy) were defined on clinical images. Rate distribution changes were analyzed on three levels: the biopsied volume, along the needle trajectory (4x4x4 mm³ volumes), and VOIs. Increased R₁Gd and R₂Gd were compared to indications from 5-aminolevulinic acid-induced fluorescence and detailed neuropathological evaluation.

Results

Neuropathological analysis confirmed seven glioblastoma, one lymphoma, and one non-tumorous diagnosis. Increased R₁Gd was found in all biopsied volumes, although tumorous volumes presented larger R₁Gd increase (3–9 times) compared to volumes dominated by necrotic or non-tumorous tissue. Along the trajectory, increased R₁Gd and R₂Gd were not tumor-specific, however, the greatest R₁Gd shifts were found in or adjacent to radiologically defined tumorous tissue. Increased relaxation rates corresponded to 82% and 45% (R₁Gd: φ = 0.35, R₂Gd: φ = 0.27) of fluorescence peaks. In the radiological VOIs, increased R₁Gd and R₂Gd were found in tumorous tissue, a slight right shift in edematous tissue, and negligible changes in white matter.

Conclusion

Combined analysis suggests increased R₁Gd together with fluorescence peaks as a marker for tumor tissue. The presented multimodal approach provides a workflow toward clinical translation of relaxometry.