Computed Diffusion-Weighted Images of Rectal Cancer: Image Quality, Restaging, and Treatment Response after Neoadjuvant Therapy

Background: Computed diffusion-weighted images (cDWI) of random b value could be derived from acquired DWI (aDWI) with at least two different b values. However, its comparison between aDWI and cDWI images in locally advanced rectal cancer (LARC) patients after neoadjuvant therapy (NT) is needed.

Purpose: To compare the cDWI and aDWI in image quality, restaging, and treatment response of LARC after NT.

Study type: Retrospective.

Population: Eighty-seven consecutive patients.

Field strength/sequence: 3.0 T/DWI.

Assessment: All patients underwent two DWI sequences, including conventional acquisition with b = 0 and 1000 s/mm² (aDWI_b1000 ) and another with b = 0 and 700 s/mm² on a 3.0-T MR scanner. The images of the latter were used to compute the diffusion images with b = 1000 s/mm² (cDWI_b1000 ). Four radiologists with 3, 4, 14, and 25 years of experience evaluated the images to compare the image quality, TN restaging performance, and treatment response between aDWI_b1000 and cDWI_b1000 .

Statistical tests: Interclass correlation coefficients, weighted κ coefficient, paired Wilcoxon, and McNemar or Fisher test were used. A significance level of 0.05 was used.

Results: The cDWI_b1000 images were superior to the aDWI_b1000 ones in both subjective and objective image quality. In T restaging, the overall diagnostic accuracy of cDWI_b1000 images was higher than that of aDWI_b1000 images (57.47% vs. 49.43%, P = 0.289 for the inexperienced radiologist; 77.01% vs. 63.22%, significant for the experienced radiologist), with better sensitivity in determining ypT0-Tis tumors. Additionally, it increased the sensitivity in detecting ypT2 tumors for the inexperienced radiologist and ypT3 tumors for the experienced radiologist. N restaging and treatment response were found to be similar between two sequences for both radiologists.

Data conclusion: Compared to aDWI_b1000 images, the computed ones might serve as a wise approach, providing comparable or better image quality, restaging performance, and treatment response assessment for LARC after NT.

Level of evidence: 3 TECHNICAL EFFICACY STAGE: 2.