Comparison of Computed and Acquired DWI in the Assessment of Rectal Cancer: Image Quality and Preoperative Staging

OBJECTIVE: The aim of the study was to evaluate the computed diffusion-weighted images (DWI) in image quality and diagnostic performance of rectal cancer by comparing with the acquired DWI. METHODS: A total of 103 consecutive patients with primary rectal cancer were enrolled in this study. All patients underwent two DWI sequences, namely, conventional acquisition with b = 0 and 1,000 s/mm(2) (aDWI(b1,000)) and another with b = 0 and 700 s/mm(2) on a 3.0T MR scanner (MAGNETOM Prisma; Siemens Healthcare, Germany). The images (b = 0 and 700 s/mm(2)) were used to compute the diffusion images with b value of 1,000 s/mm(2) (cDWI(b1,000)). Qualitative and quantitative analysis of both computed and acquired DWI images was performed, namely, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and signal intensity ratio (SIR), and also diagnostic staging performance. Interclass correlation coefficients, weighted κ coefficient, Friedman test, Wilcoxon paired test, and McNemar or Fisher test were used for repeatability and comparison assessment. RESULTS: Compared with the aDWI(b1,000) images, the cDWI(b1,000) ones exhibited significant higher scores of subjective image quality (all P <0.050). SNR, SIR, and CNR of the cDWI(b1,000) images were superior to those of the aDWI(b1,000) ones (P <0.001). The overall diagnostic accuracy of computed images was higher than that of the aDWI(b1,000) images in T stage (P <0.001), with markedly better sensitivity and specificity in distinguishing T1–2 tumors from the T3–4 ones (P <0.050). CONCLUSION: cDWI(b1,000) images from lower b values might be a useful alternative option and comparable to the acquired DWI, providing better image quality and diagnostic performance in preoperative rectal cancer staging.