Ultra-high b-value DWI in rectal cancer: image quality assessment and regional lymph node prediction based on radiomics.

Abstract

This study aims to evaluate image quality and regional lymph node metastasis (LNM) in patients with rectal cancer (RC) on multi-b-value diffusion-weighted imaging (DWI). This retrospective study included 199 patients with RC who had undergone multi-b-value DWI. Subjective (five-point Likert scale) and objective assessments of quality images were performed on DWI_b1000, DWI_b2000, and DWI_b3000. Patients were randomly divided into a training (n = 140) or validation cohort (n = 59). Radiomics features were extracted within the whole volume tumor on ADC maps (b = 0, 1000 s/mm²), DWI_b1000, DWI_b2000, and DWI_b3000, respectively. Five prediction models based on selected features were developed using logistic regression analysis. The performance of radiomics models was evaluated with a receiver operating characteristic curve, calibration, and decision curve analysis (DCA). The mean signal intensity of the tumor (SI_tumor), signal-to-noise ratio (SNR), and artifact and anatomic differentiability score gradually were decreased as the b-value increased. However, the contrast-to-noise (CNR) on DWI_b2000 was superior to those of DWI_b1000 and DWI_b3000 (4.58 ± 0.86, 3.82 ± 0.77, 4.18 ± 0.84, p < 0.001, respectively). The overall image quality score of DWI_b2000 was higher than that of DWI_b3000 (p < 0.001) and showed no significant difference between DWI_b1000 and DWI_b2000 (p = 0.059). The area under curve (AUC) value of the radiomics model based on DWI_b2000 (0.728) was higher than conventional ADC maps (0.690), DWI_b1000 (0.699), and DWI_b3000 (0.707), but inferior to multi-b-value DWI (0.739) in predicting LNM. DWI_b2000 provides better lesion conspicuity and LNM prediction than DWI_b1000 and DWI_b3000 in RC. DWI_b2000 offers satisfactory visualization of lesions. Radiomics features based on DWI_b2000 can be applied for preoperatively predicting regional lymph node metastasis in rectal cancer, thereby benefiting the stratified treatment strategy. Lymph node staging is required to determine the best treatment plan for rectal cancer. DWI_b2000 provides superior contrast-to-noise ratio and lesion conspicuity and its derived radiomics best predict lymph node metastasis. DWI_b2000 may be recommended as the optimal b-value in rectal MRI protocol.