Tensor-valued diffusion magnetic resonance imaging in a radiotherapy setting

Patrik Brynolfsson; Minna Lerner; Pia C Sundgren; Christian Jamtheim Gustafsson; Markus Nilsson; Filip Szczepankiewicz; Lars E Olsson

doi:10.1016/j.phro.2022.11.005

Tensor-valued diffusion magnetic resonance imaging in a radiotherapy setting

Phys Imaging Radiat Oncol. 2022 Nov 10:24:144-151. doi: 10.1016/j.phro.2022.11.005. eCollection 2022 Oct.

Authors

Patrik Brynolfsson^{1

2

3}, Minna Lerner^{1

4}, Pia C Sundgren⁵, Christian Jamtheim Gustafsson^{1

4}, Markus Nilsson⁵, Filip Szczepankiewicz⁵, Lars E Olsson¹

Affiliations

¹ Dept. of Translational Medicine, Division of Medical Radiation Physics, Lund University, Malmö, Sweden.
² Random Walk Imaging AB, SE-22002 Lund, Sweden.
³ NONPI Medical AB, SE-90738 Umeå, Sweden.
⁴ Dept. of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden.
⁵ Dept. Diagnostic Radiology, Clinical Sciences Lund, Lund University, Lund, Sweden.

Abstract

Background and purpose: Diagnostic information about cell density variations and microscopic tissue anisotropy can be gained from tensor-valued diffusion magnetic resonance imaging (MRI). These properties of tissue microstructure have the potential to become novel imaging biomarkers for radiotherapy response. However, tensor-valued diffusion encoding is more demanding than conventional encoding, and its compatibility with MR scanners that are dedicated to radiotherapy has not been established. Thus, our aim was to investigate the feasibility of tensor-valued diffusion MRI with radiotherapy dedicated MR equipment.

Material and methods: A tensor-valued diffusion protocol was implemented, and five healthy volunteers were scanned with different resolutions using conventional head coil and radiotherapy coil setup with fixation masks. Signal-to-noise-ratio (SNR) was evaluated to assess the risk of signal bias due to rectified noise floor. We also evaluated the repeatability and reproducibility of the microstructure parameters. One patient with brain metastasis was scanned to investigate the image quality and the transferability of the setup to diseased tissue.

Results: A resolution of 3 × 3 × 3 mm³ provided images with SNR > 3 for 93 % of the voxels using radiotherapy coil setup. The parameter maps and repeatability characteristics were comparable to those observed with a conventional head coil. The patient evaluation demonstrated successful parameter analysis also in tumor tissue, with SNR > 3 for 93 % of the voxels.

Conclusion: We demonstrate that tensor-valued diffusion MRI is compatible with radiotherapy fixation masks and coil setup for investigations of microstructure parameters. The reported reproducibility may be used to plan future investigations of imaging biomarkers in brain cancer radiotherapy.

Keywords: ADC, apparent diffusion coefficient; Brain tumors; DIVIDE, Diffusional Variance Decomposition; FA, fractional anisotropy; GTV, gross tumor volume; MD, mean diffusivity; MKA, anisotropic diffusional variance; MKI, isotropic diffusional variance; MRI in radiotherapy; MRI, magnetic resonance imaging; Quantitative imaging; RT, radiotherapy; SNR, signal to noise ratio; Tensor-valued diffusion; µFA, microscopic fractional anisotropy.