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High Fidelity, Low Distortion Tetrahedral Diffusion-Weighted MRI for Radiation Treatment Planning

E Paulson

E Paulson*, Radiation Oncology and Radiology, Medical College of Wisconsin, Milwaukee, WI

MO-G-BRA-5 Monday 5:15:00 PM - 6:00:00 PM Room: Ballroom A

Purpose: Diffusion-weighted (DW) MR imaging provides supplemental information that may aid in target delineation during radiation treatment planning. However, geometric distortion artifacts and the inability to acquire higher b-value DW images in tissues with short T2s have encumbered the utilization of DW MRI in radiation treatment planning. To rectify these issues, we present here a novel DW imaging approach that combines tetrahedral diffusion encoding and a multi-shot, variable-density spiral (MS-VDS) acquisition.

Methods: A custom MS-VDS pulse sequence with Stejkal-Tanner (ST) and twice refocused spin echo (TRSE) excitation schemes was implemented on a Siemens 3T scanner. For comparison to current state-of-the-art, orthogonal and tetrahedral DW images were acquired in the brains of three healthy volunteers (FOV: 220mm², matrix: 1282, interleaves: 16, TR: 3000ms, TH: 3mm, b-values: 0/1000 s/mm²). Self-navigated phase correction was applied during reconstruction to correct each spiral interleaf for eddy current and motion-induced phase errors.

Results: The MS-VDS acquisition was effective at diminishing geometric distortion artifacts. The minimum echo times for the orthogonal ST, tetrahedral ST, and tetrahedral TRSE acquisitions were 79 ms, 56 ms, and 71 ms, respectively. Although the inherent self-navigating capability of VDS was effective at diminishing eddy current and motion-induced phase errors in the orthogonal ST images, the tetrahedral ST images were contaminated by residual eddy current-induced blurring. However, the tetrahedral TRSE images exhibited quality similar to the orthogonal ST images, indicating that the TRSE sequence provided effective compensation of residual eddy currents.

Conclusions: Tetrahedral encoding results in a reduction in minimum echo time for a given b-value, facilitating acquisition of DW images in tissues with shorter T2s. A TRSE excitation is required to provide eddy current compensation in tetrahedral DW acquisitions. The combined MS-VDS TRSE tetrahedral DW imaging method permits acquisition of high fidelity, low distortion DW images suitable for radiation treatment planning.

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