Abstract
BackgroundDiffusion-weighted imaging (DWI) has shown great value in rectal cancer imaging. However, traditional DWI with echo-planar imaging (DW-EPI) often suffers from geometrical distortions. We applied a three-dimensional diffusion-prepared stimulated-echo turbo spin-echo sequence (DPsti-TSE), allowing geometrically undistorted rectal DWI. We compared DPsti-TSE with DW-EPI for locally advanced rectal cancer DWI.MethodsFor 33 prior-to-treatment patients, DWI images of the rectum were acquired with DPsti-TSE and DW-EPI at 3 T using b-values of 200 and 1000 s/mm2. Two radiologists conducted a blinded scoring of the images considering nine aspects of image quality and anatomical quality. Tumour apparent diffusion coefficient (ADC) and distortions were compared quantitatively.ResultsDPsti-TSE scored significantly better than DW-EPI in rectum distortion (p = 0.005) and signal pileup (p = 0.001). DPsti-TSE had better tumour Dice similarity coefficient compared to DW-EPI (0.84 versus 0.80, p = 0.010). Tumour ADC values were higher for DPsti-TSE compared to DW-EPI (1.47 versus 0.86 × 10-3 mm2/s, p < 0.001). Radiologists scored DPsti-TSE significantly lower than DW-EPI on aspects of overall image quality (p = 0.001), sharpness (p < 0.001), quality of fat suppression (p < 0.001), tumour visibility (p = 0.009), tumour conspicuity (p = 0.010) and rectum wall visibility (p = 0.005).ConclusionsDPsti-TSE provided geometrically less distorted rectal cancer diffusion-weighted images. However, the image quality of DW-EPI over DPsti-TSE was referred on the basis of several image quality criteria. A significant bias in tumour ADC values from DPsti-TSE was present. Further improvements of DPsti-TSE are needed until it can replace DW-EPI.
Highlights
Diffusion-weighted imaging (DWI) has shown great value in rectal cancer imaging
Echo-planar imaging (EPI)-based methods are sensitive to susceptibility differences near the gas-filled rectum, which may result in strong geometrical distortions [9]
The bar plot shows the scores for the DPsti-TSE and DWI with echo-planar imaging (DW-EPI) methods for the six image quality aspects and the three anatomical detail aspects, as well as the intraclass correlation coefficient (ICC) values for two radiologists
Summary
Diffusion-weighted imaging (DWI) has shown great value in rectal cancer imaging. traditional DWI with echo-planar imaging (DW-EPI) often suffers from geometrical distortions. Rectal tumours typically show restricted diffusion, which causes them to show distinctly high signal compared to the suppressed background on DWI at high b-values (> 800 s/mm2) [2, 5]. EPI-based methods are sensitive to susceptibility differences near the gas-filled rectum, which may result in strong geometrical distortions [9]. These image distortions can often lead to signal pileup and inaccurate ADC estimations [7]. Another difficulty for conventional rectal cancer DW-EPI is the low signal-to-noise ratio at high b-values, which may cause ADC underestimation and variation [7, 10]
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