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Advancing free-breathing liver diffusion-weighted imaging with Propeller-EPI: Improved image quality and ADC
Liyuan Liang1,2,3, Lu Wang4,5, Qiting Wu1
1Department of Biomedical Engineering, The Chinese University of Hong Kong, Hong Kong SAR, China.
Background:
Liver diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) measurement has proven valuable in diagnosing liver diseases. In certain patient populations, a free-breathing (FB) liver DWI approach is desirable to improve patient comfort and broaden clinical applicability. However, maintaining high image quality under FB conditions and achieving satisfactory ADC repeatability can be challenging when using routine diffusion-weighted single-shot echo-planar imaging (DW-ss-EPI).
Purpose:
This study aimed to develop an advanced FB liver DWI technique based on diffusion-weighted Propeller echo-planar imaging (DW-Propeller-EPI) to achieve motion compensation, and to prospectively evaluate its performance in terms of image quality and ADC repeatability compared to standard DW-ss-EPI.
Methods:
A DW-Propeller-EPI pulse sequence and reconstruction pipeline was developed on a 1.5T MRI system. The pipeline incorporated a reference-free Nyquist ghost correction method and motion compensation using correlation weighting during data reconstruction. For in vivo evaluation, participants prospectively underwent two repeated liver DWI scans using four techniques: three routine DW-ss-EPI sequences with different breathing controls (breath-holding, BH; respiratory-triggering, RT; and FB), and one FB DW-Propeller-EPI sequence. The raw data from the FB DW-Propeller-EPI scans were processed offline with the developed motion-compensated reconstruction. Two radiologists independently rated the image quality on a 5-point scale across five aspects (signal homogeneities in the left lobe, geometric fidelity, liver edge sharpness, vessel clarity, and overall image quality). Mean scores were compared among the four techniques using the Friedman test. The repeatability of ADC measurements was evaluated with Bland-Altman analysis, and differences in ADC values between liver lobes and techniques were analyzed using two-way repeated measures ANOVA.
Results:
35 participants were enrolled, with twenty completing repeated scans. FB DW-Propeller-EPI demonstrated significantly higher ratings than the three routine DW-ss-EPI sequences across all aspects (all P < 0.001), with good interobserver agreements (ICC ranging from 0.80-0.88). The mean geometric fidelity score of FB DW-Propeller-EPI was rated the highest (4.86 ± 0.33). FB DW-Propeller-EPI also exhibited superior ADC repeatability in both the left and right liver lobes (LOA: 0.212 × 10-3 mm2/s versus 0.255 × 10-3 mm2/s). ADC measurements were comparable between FB DW-Propeller-EPI and both RT or FB DW-ss-EPI techniques.
Conclusions:
The proposed FB DW-Propeller-EPI technique enables high-quality FB liver DWI with satisfactory ADC repeatability, outperforming conventional DW-ss-EPI in image quality and ADC repeatability. This advancement addresses the limitations of routine DW-ss-EPI in FB scenarios, offering a promising solution for clinical applications in challenging population.
