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TU‐AB‐BRA‐07: Distortion‐Free 3D Diffusion MRI On An MRI‐Guided Radiotherapy System for Longitudinal Tumor Response Assessment
Author(s) -
Gao Y,
Yang Y,
Rangwala N,
Cao M,
Low D,
Hu P
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4957417
Subject(s) - nuclear medicine , imaging phantom , diffusion mri , effective diffusion coefficient , reproducibility , medicine , materials science , nuclear magnetic resonance , magnetic resonance imaging , biomedical engineering , physics , mathematics , radiology , statistics
Purpose: To develop a reliable, 3D distortion‐free diffusion MRI technique for longitudinal tumor response assessment and MRI‐guided adaptive radiotherapy(RT). Methods: A diffusion prepared 3D turbo spin echo readout (DP‐TSE) sequence was developed and compared with the conventional diffusion‐weighted single‐shot echo‐planar‐imaging (DW‐ssEPI) sequence in a commercially available diffusion phantom, and one head‐and‐neck and one brain cancer patient on an MRI‐guided RT system (ViewRay). In phantom study, the geometric fidelity was quantified as the ratio between the left‐right (RL) and anterior‐posterior (AP) dimension. Ten slices were measured on DP‐TSE, DW‐ssEPI and standard TSE images where the later was used as the geometric reference. ADC accuracy was verified at both 0°C (reference ADC available) and room temperature with a range of diffusivity between 0.35 and 2.0*10 −3 mm 2 /s. The ADC reproducibility was assessed based on 8 room‐temperature measurements on 6 different days. In the pilot single‐slice in‐vivo study, CT images were used as the geometric reference, and ADC maps from both diffusion sequences were compared. Results: Distortion and susceptive‐related artifact were severe in DW‐ssEPI, with significantly lower RL/AP ratio (0.9579±0.0163) than DP‐TSE (0.9990±0.0031) and TSE (0.9995±0.0031). ADCs from the two diffusion sequences both matched well with the vendor‐provided values at 0°C; however DW‐ssEPI fails to provide accurate ADC for high diffusivity vials at room temperature due to high noise level (10 times higher than DP‐TSE). The DP‐TSE sequence had excellent ADC reproducibility with <4% ADC variation among 8 separate measurements. In patient study, DP‐TSE exhibited substantially improved geometric reliability. ROI analysis in ADC maps generated from DP‐TSE and DW‐ssEPI showed <5% difference where high b‐value images were excluded from the latter approach due to excessive noise level. Conclusion: A diffusion MRI sequence with excellent geometric fidelity, accurate and highly reproducible ADC measurements was proposed for longitudinal tumor response assessment using an MRI‐guided RT system. Yu Gao acknowledges research support from ViewRay.