Repeatability quantification of brain diffusion-weighted imaging for future clinical implementation at a low-field...

Area of Science:

• Medical Imaging
• Radiotherapy Physics
• Neuroimaging

Background:

• Diffusion-weighted imaging (DWI) can assess tumor response during radiotherapy by measuring apparent diffusion coefficients (ADCs).
• DWI is not yet clinically available on low-field magnetic resonance imaging-guided linear accelerators (MR-linacs).
• Assessing the repeatability of ADC measurements is essential for clinical implementation of DWI on low-field MR-linacs.

Purpose of the Study:

• To evaluate the repeatability of apparent diffusion coefficient (ADC) measurements using diffusion-weighted imaging (DWI) on a 0.35 T MR-linac.
• To compare two DWI sequence variants: one optimized for high resolution (highRes) and one for high signal-to-noise ratio (highSNR).
• To assess the feasibility of using DWI for early treatment response assessment in clinical settings.

Main Methods:

• A diffusion phantom and eleven volunteers were scanned on a 0.35 T MR-linac using two echo-planar imaging DWI sequences.
• Test-retest scans with an intermediate break were performed to assess repeatability.
• Mean ADCs were calculated for phantom vials, cerebrospinal fluid (CSF), and brain tissue regions; repeatability coefficients (RC) and relative RCs (relRCs) were determined.

Main Results:

• Both DWI sequences showed high repeatability in the diffusion phantom (absolute relative deviations < 1%).
• In vivo, the highSNR sequence demonstrated better repeatability (relRCs: 6% for brain tissue, 12% for CSF) and accuracy compared to the highRes sequence (relRCs: 9% for brain tissue, 7% for CSF).
• The highRes sequence systematically underestimated ADC values compared to literature.

Conclusions:

• Apparent diffusion coefficient (ADC) measurements are highly repeatable on a low-field MR-linac.
• The high signal-to-noise ratio (highSNR) DWI sequence offers superior accuracy and repeatability over the high-resolution (highRes) sequence.
• These findings support the clinical utility of DWI on low-field MR-linacs for early treatment response monitoring.