High-Resolution T2-Weighted MRI to Evaluate Rectal Cancer: Why Variations Matter.

Abstract

MRI has been used to image rectal cancer for over two decades and there is extensive research on this imaging technique. The 1999 seminal paper by Brown et al. [1] demonstrated the accuracy of thin-slice MRI in identifying the depth of extramural tumor in 28 patients with rectal cancer. MRI has also been shown to predict involvement of the circumferential resection margin in total mesorectal excision surgery, which is extremely useful to surgeons who may otherwise have produced an R2 resection [2,3]. MRI has enabled the stratification of patients into high- and low-risk and the selection of appropriate patients for neoadjuvant chemoradiotherapy. It has previously been demonstrated that the thin section, or high-resolution (HR) T2 imaging provided promising results in the assessment of lymph nodes, detection of extramural venous invasion, and differentiation of tumors from fibrosis on post-treatment imaging, which continue to be extensively studied [4,5,6]. The majority of publications assessing MRI in rectal cancer describe the use of HR T2 sequences, and the term ‘HR T2’ has been generally accepted to represent HR imaging. There have been a variety of results regarding the accuracy of rectal MRI, particularly the T2 sequence alone, and it has been regularly assessed against other techniques including diffusion, post-contrast, and radiomics. On more in-depth methodological assessment, there is significant heterogeneity in the resolution of the HR T2 sequences across many publications, and this may have an impact on the results.