Application of Field-of-View Optimized and Constrained Undistorted Single Shot (FOCUS) with Intravoxel Incoherent Motion (IVIM) in 3T in Locally Advanced Rectal Cancer

Abstract

Purpose. To evaluate the efficacy of field-of-view (FOV) optimized and constrained undistorted single shot (FOCUS) with IVIM in 3T MRI in the grading of patients with locally advanced rectal cancer. Methods. From January 1st to December 31st, 2019, patients with locally advanced rectal cancer were retrieved. FOCUS DWI and FOCUS IVIM were obtained. Apparent diffusion coefficient (ADC) and IVIM parameters including mean true diffusion coefficient ( $D$ ), pseudodiffusion coefficient associated with blood flow ( $D\ast$ ), and perfusion fraction ( $f$ ) of the tumor parenchyma and normal rectal wall, as well as the normalized tumor parameters by corresponding normal intestinal wall parameters (ADCNOR, $D_{\text{NOR}}$ , $D\ast {}_{\text{NOR}}$ , and $f_{\text{NOR}}$ ), were compared between the well/moderately differentiated and poorly differentiated groups by Student’s $t$ -test. The relationship between the above parameters and the histologic grade was analyzed using Spearman’s correlation test, with the ROC curve generated. Results. Eighty-eight patients (aged 31 to 77 years old, $\text{mean}=56$ ) were included for analysis. $D_{\text{tumor}}$ and $f_{\text{tumor}}$ were positively correlated with the tumor grade ( $r=0.483$ , $p<0.001$ and $r=0.610$ , $p<0.001$ , respectively). All the normalized parameters (ADCNOR, $D_{\text{NOR}}$ , $D\ast {}_{\text{NOR}}$ , and $f_{\text{NOR}}$ ) were positively correlated with the tumor grade ( $r=0.267$ , $p=0.007$ ; $r=0.564$ , $p=0.001$ ; $r=0.414$ , $p=0.005$ ; and $r=0.605$ , $p<0.001$ , respectively). The best discriminative parameter was the $f_{\text{tumor}}$ value, and the area under the ROC curve was 0.927. With a cut-off value of 22.0%, $f_{\text{tumor}}$ had a sensitivity of 88.9% and a specificity of 100%. Conclusion. FOCUS IVIM-derived parameters and normalized parameters are useful for predicting the histologic grade in rectal cancer patients.