Evaluation of lymph node metastases: Comparison of gadofluorine M‐enhanced MRI and diffusion‐weighted MRI in a rabbit VX2 rectal cancer model

Abstract

Purpose: To compare the diagnostic performance of a diffusion-weighted imaging (DWI) dataset and a gadofluorine M-enhanced imaging dataset for identifying lymph node (LN) metastases in a rabbit rectal cancer model. Materials and Methods:VX2 carcinomas were injected into the rectum of 26 rabbits. Four weeks later, T2-weighted imaging (T2WI), pre-T1WI, DWI, and post-T1WI were performed. Two radiologists independently reviewed the DWI set (T2WI, pre-T1WI, DWI) and the gadofluorine M set (T2WI, pre-and post-T1WI) and recorded their confidence scores for LN metastasis on a per-LN basis. Receiver operating characteristic (ROC) analysis was performed to compare the area under the ROC curve (A z ) of the two imaging sets. Histopathologic results were used as the reference standard.Results: The A z and sensitivity of the gadofluorine M set were comparable to those of the DWI set (A z , for reader 1, 0.849, 0.829, P ¼ 0.571; for reader 2, 0.923, 0.876, P ¼ 0.212; sensitivity, for reader 1, 97%, 97%; for reader 2, 97%, 92%, P ¼ 0.304). The specificity of the former was greater than that of the latter (for reader 1, 65%, 53%, P ¼ 0.0003; for reader 2, 81%, 68%, P ¼ 0.01).Conclusion: Gadofluorine M-enhanced images provided greater specificity than DWI for identifying LN metastases, whereas the A z and sensitivity of the former were comparable to those of the latter. COLORECTAL CANCER is the third most common cancer and the third leading cause of cancer-related death in the United States, with a 5-year survival rate reported to be %66% (1). In its treatment, neoadjuvant chemoradiation therapy (CRT) has been considered the standard of care for locally advanced rectal cancer (!T3 stage, which is defined as tumor invades through the rectal wall into perirectal soft tissues or lymph node [LN] metastasis), since several investigators demonstrated that neoadjuvant CRT was able to significantly decrease the local recurrence rate (2,3). As LN metastasis has been singled out to be an important prognostic factor related to disease-free survival and to the local recurrence rate (4), accurate preoperative diagnosis of LN metastasis in patients with rectal cancer is crucial not only for obtaining the optimal prognosis but also for appropriate selection of patients who will derive the most benefit from neoadjuvant CRT. However, although magnetic resonance imaging (MRI) is an excellent diagnostic tool for tumor-staging due to its excellent soft-tissue contrast and ability to depict all mesorectal structures (5-7), its accuracy for LN-staging has been reported to be in the range of 43%-85% (6-8). This wide range of accuracy and relatively poor sensitivity of 66% suggest that the MR criterion for the detection of LN metastases, ie, LN size, is not a reliable discriminator for metastatic LNs (8-11). Although several attempts have been made to increase the poor sensitivity of MR for LN metastases by adding morphologic criteria such as border and internal signal intensity (11), these morphologic criteria seem to have intrinsic limitations in sma...

Diffusion-weighted imaging in rectal cancer: current applications and future perspectives

“…59,66,74 Altogether, the majority of studies that investigated ADC as a biomarker to assess or predict response to treatment found significant results at one or more time points, although a subgroup (21%) of studies could not produce any statistically significant results. 49,51,75,76,[85][86][87]89,90 As a critical note, most study cohorts presented so far are small and single centre, and reported ADC and cut-off values show large variation and overlap between studies and have never been validated in prospective study cohorts. This stresses the need for standardization and multicentre validation studies.…”