Magnetic Resonance Imaging In Rectal Cancer Research Articles

Survey of rectal cancer MRI technique and reporting tumour descriptors in the UK: a multi-centre British Society of Gastrointestinal and Abdominal Radiology (BSGAR) audit

To evaluate variation in magnetic resonance imaging (MRI) technique and reporting of rectal cancer staging examinations across the UK. A retrospective, multi-centre audit was undertaken of imaging protocols and information documented within consecutive MRI rectal cancer reports between March 2020 and August 2021, which were compared against American and European guidelines. Inclusion criteria included histologically proven rectal adenocarcinoma and baseline staging MRI rectum only. Fully anonymised data from 924 MRI reports by 78 radiologists at 24 centres were evaluated. Thirty-two per cent of radiologists used template reporting, but these reports offered superior documentation of 13 out of 18 key tumour features compared to free-text reports including T-stage, relation to peritoneal reflection and mesorectal fascia (MRF), nodal status, and presence of extramural venous invasion (EMVI; p<0.027 in each). There was no significant differences in the remaining five features. Across all tumour locations, the tumour relationship to the MRF, the presence of EMVI, and the presence of tumour deposits were reported in 79.5%, 85.6%, and 44% of cases, respectively, and tumour, nodal, and distant metastatic stage documented in 94.4%, 97.7%, and 78.3%. In low rectal tumours, the relationship to the anal sphincter complex was reported in only 54.6%. Considerable variation exists in rectal cancer MRI acquisition and reporting in this sample of UK centres. Inclusion of key radiological features in reports must be improved for risk stratification and treatment decisions. Template reporting is superior to free-text reporting. Routine adoption of standardised radiology practices should now be considered to improve standards to facilitate personalised precision treatment for patients to improve outcomes.

Application of natural language processing to post-structuring of rectal cancer MRI reports

To evaluate a natural language processing (NLP) system for extracting structured information from the free-form text of rectal cancer magnetic resonance imaging (MRI) reports written in Chinese. A rule-based NLP model that could extract 11 key image features of rectal cancer was constructed using 358 MRI reports of rectal cancer written between 2015 and 2021. Fifty reports written before 2015 and 50 written after 2021 were used as test datasets, and the reference standard was determined by manual extraction of information by two radiologists. The length and reporting rate of image features in pre-2015 and post-2021 datasets, as well as the accuracy, precision, recall, and F1 score of feature extraction by the NLP system, were compared. The time required for the NLP to extract data was compared with that required by the radiologists. Reports written after 2021 had longer diagnostic impression sections than reports written before 2015. The reporting rate of key imaging features of rectal cancer was 36.55% before 2015 and 79.82% after 2021. The accuracy, precision, recall, and F1 score of NLP for correct extraction of values from reports were 93.82%, 95.63%, 87.06%, and 91.15%, respectively, for pre-2015 reports, and 92.55%, 98.53%, 94.15%, and 96.29%, respectively, for post-2021 reports. NLP generated all the structured information in <1 second. The NLP system with rule-based pattern matching achieved rapid and accurate structured processing of rectal cancer MRI reports. MRI reports with structured templates are more suitable for NLP-based extraction of information.

The importance of MRI for rectal cancer evaluation

Magnetic resonance imaging (MRI) has gained increasing importance in the management of rectal cancer over the last two decades. The role of MRI in patients with rectal cancer has expanded beyond the tumor-node-metastasis (TNM) system in both staging and restaging scenarios and has contributed to identifying “high” and “low” risk features that can be used to tailor and personalize patient treatment; for instance, selecting the patients for neoadjuvant chemoradiation (NCRT) before the total mesorectal excision (TME) surgery based on risk of recurrence. Among those features, the status of the circumferential resection margin (CRM), extramural vascular invasion (EMVI), and tumor deposits (TD) have stood out. Moreover, MRI also has played a role in surgical planning, especially when the tumor is located in the low rectum, when the relationship between tumor and the anal canal is important to choose the best surgical approach, and in cases of locally advanced or recurrent tumors invading adjacent pelvic organs that may require more complex surgeries such as pelvic exenteration. As approaches using organ preservation emerge, including transanal local excision and “watch-and-wait”, MRI may help in the patient selection for those treatments, follow up, and detection of tumor regrowth. Additionally, potential MRI-based prognostic and predictive biomarkers, such as quantitative and semi-quantitative metrics derived from functional sequences like diffusion-weighted imaging (DWI) and dynamic contrast-enhanced (DCE), and radiomics, are under investigation. This review provides an overview of the current role of MRI in rectal cancer in staging and restaging and highlights the main areas under investigation and future perspectives.

Development of an Online Curriculum for Surgeons on the Use of Pelvic Magnetic Resonance Imaging in Rectal Cancer and Results of a Pilot Study

High-resolution pelvic magnetic resonance imaging (MRI) is a critical tool in the management of patients with rectal cancer. An on-line curriculum was developed for surgical trainees on the interpretation of pelvic MRI in rectal cancer for clinical staging and surgical planning. The online curriculum was developed using the six-step approach to curriculum development for medical education. The curriculum incorporated case-based learning, annotated videos, and narrated presentations on key aspects of pelvic MRI in rectal cancer. A pilot study was conducted to assess curriculum effectiveness among Complex General Surgical Oncology (CGSO) fellows using pre- and post-intervention assessments. Of 15 eligible fellows, nine completed the pilot study (60%). The fellows' median confidence score after completing the online curriculum (40, IQR: 33-46) was significantly higher than their baseline median confidence score (23, IQR: 14-30), P=0.0039. The total practical assessment score significantly increased from a pre-median score of 9 (IQR: 8-11) to a post-median score of 14 (IQR: 13-14), P=0.0078. A subgroup analysis revealed a significant change in the knowledge assessment with a median score of 7 compared to a baseline median score of 4, Z=2.64, P=0.0078. However, the skills assessment showed no significant change. The case-based online curriculum had a positive impact on CGSO fellows' knowledge and confidence in the utilization of pelvic MRI for patients with rectal cancer. This unique on-line curriculum demonstrates a mechanism to enhance shared educational collaboration across CGSO fellowships and other surgical training programs.

Magnetic resonance imaging-based artificial intelligence model in rectal cancer.

Rectal magnetic resonance imaging (MRI) is the preferred method for the diagnosis of rectal cancer as recommended by the guidelines. Rectal MRI can accurately evaluate the tumor location, tumor stage, invasion depth, extramural vascular invasion, and circumferential resection margin. We summarize the progress of research on the use of artificial intelligence (AI) in rectal cancer in recent years. AI, represented by machine learning, is being increasingly used in the medical field. The application of AI models based on high-resolution MRI in rectal cancer has been increasingly reported. In addition to staging the diagnosis and localizing radiotherapy, an increasing number of studies have reported that AI models based on high-resolution MRI can be used to predict the response to chemotherapy and prognosis of patients.

Metastatic lymph node calcification in rectal cancer: comparison of CT and high-resolution MRI.

Calcification causes mixed signal intensity in the lymph node (LN) on high-resolution magnetic resonance imaging (MRI), which is a strong indicator of regional LN metastasis in rectal cancer. Calcified metastatic LNs in rectal cancer commonly display scattered fine punctate calcifications to varying degrees on computed tomography (CT). On high-resolution MRI, the calcifications manifest a patchy area of signal loss in corresponding calcified area that is larger than on CT. It is necessary to recognize the appearance of metastatic LN calcifications on high-resolution MRI in rectal cancer because it is the primary imaging method for local staging in rectal cancer. This pictorial essay aims to introduce an important imaging finding that can contribute to the diagnosis of LN metastasis by illustrating features and differences between CT and high-resolution MRI of metastatic LN calcifications in rectal cancer.

Association between high-resolution MRI-detected extramural vascular invasion and tumour microcirculation estimated by dynamic contrast-enhanced MRI in rectal cancer: preliminary results

BackgroundTo determine whether magnetic resonance imaging (MRI)-detected extramural vascular invasion (mrEMVI) status is associated with quantitative perfusion parameters derived from dynamic contrast-enhanced MRI (DCE-MRI) in rectal cancer.MethodsSeventy-two patients with rectal adenocarcinoma who underwent curative surgery alone within 2 weeks following rectal MRI were enrolled in this retrospective study. mrEMVI status was determined based on high-resolution MRI. The quantitative perfusion parameters (Ktrans, kep and ve) derived from DCE-MRI were calculated from all sections containing tumours. DCE-MRI parameters and clinicopathological variables in patients with different mrEMVI statuses were compared.ResultsFor patients who were mrEMVI positive, the tumours demonstrated significantly lower kep values (P = 0.012) and higher ve values (P = 0.021) than tumours of patients who were mrEMVI negative, while the Ktrans value displayed no significant difference (P = 0.390). The patients who were mrEMVI positive had larger tumour size, higher pathological tumour stage and increased regional nodal metastases compared to those who were mrEMVI negative (2.9 cm vs. 3.5 cm, P = 0.011; 63.8% vs. 92.0%, P = 0.010; 36.2% vs. 76.0%, P = 0.001; respectively).ConclusionsThis study demonstrated for the first time that tumour microcirculation is altered in mrEMVI-positive patients with rectal adenocarcinoma, as evidenced by significantly lower kep and higher ve values. In addition, these patients were more likely to have a larger tumour size, a higher pathological tumour stage and regional nodal metastases than mrEMVI-negative patients.

Radiographic Staging of Colorectal Cancer

Imaging increasingly plays an important role in selecting the most optimal treatment for patients with colon and rectal cancer. While in colon cancer, computed tomography (CT) remains the modality of choice for local and distant staging, in patients with rectal cancer magnetic resonance imaging (MRI) is the main modality and mandatory for local staging. Endoluminal rectal ultrasound (ERUS) is the preferred staging method for superficial rectal tumors. This chapter addresses the current role of various imaging modalities in colorectal tumor staging. This review contains 4 figures and 50 references. Key words: Preoperative imaging, Colorectal cancer, Magnetic resonance imaging, Diffusion weighted MRI, Computed tomography, Mesorectal fascia, TNM staging, Treatment stratification

Radiographic Staging of Colorectal Cancer

Imaging increasingly plays an important role in selecting the most optimal treatment for patients with colon and rectal cancer. While in colon cancer, computed tomography (CT) remains the modality of choice for local and distant staging, in patients with rectal cancer magnetic resonance imaging (MRI) is the main modality and mandatory for local staging. Endoluminal rectal ultrasound (ERUS) is the preferred staging method for superficial rectal tumors. This chapter addresses the current role of various imaging modalities in colorectal tumor staging. This review contains 4 figures and 50 references. Key words: Preoperative imaging, Colorectal cancer, Magnetic resonance imaging, Diffusion weighted MRI, Computed tomography, Mesorectal fascia, TNM staging, Treatment stratification

Standardised reports with a template format are superior to free text reports: the case for rectal cancer reporting in clinical practice

PurposeRectal cancer staging with magnetic resonance imaging (MRI) allows accurate assessment and preoperative staging of rectal cancers. Therefore, complete MRI reports are vital to treatment planning. Significant variability may exist in their content and completeness. Template-style reporting can improve reporting standards, but its use is not widespread. Given the implications for treatment, we have evaluated current clinical practice amongst specialist gastrointestinal (GI) radiologists to measure the quality of rectal cancer staging MRI reports.Materials and methodsSixteen United Kingdom (UK) colorectal cancer multi-disciplinary teams (CRC-MDTs) serving a population over 5 million were invited to submit up to 10 consecutive rectal cancer primary staging MRI reports from January 2016 for each radiologist participating in the CRC-MDT. Reports were compared to a reference standard based on recognised staging and prognostic factors influencing case managementResultsFour hundred ten primary staging reports were submitted from 41 of 42 (97.6%) eligible radiologists. Three hundred sixty reports met the inclusion criteria, of these, 81 (22.5%) used a template. Template report usage significantly increased recording of key data points versus non-template reports for extra-mural venous invasion (EMVI) status (98.8% v 51.6%, p < 0.01) and circumferential resection margin (CRM) status (96.3% v 65.9%, p < 0.01). Local tumour stage (97.5% v 93.5%, NS) and nodal status (98.8% v 96.1%, NS) were reported and with similar frequency.ConclusionRectal cancer primary staging reports do not meet published standards. Template-style reports have significant increases in the inclusion of key tumour descriptors. This study provides further support for their use to improve reporting standards and outcomes in rectal cancer.Key Points• MRI primary staging of rectal cancer requires detailed tumour descriptions as these alter the neoadjuvant and surgical treatments.• Currently, rectal cancer MRI reports in clinical practice do not provide sufficient detail on these tumour descriptors.• The use of template-style reports for primary staging of rectal cancer significantly improves report quality compared to free-text reports.

An audit of performance, interpretation, and influence of pretherapeutic MRI in rectal cancer: a Swedish population-based cohort study.

Background The performance of magnetic resonance imaging (MRI) interpretation and communication of findings and its implication on treatment decisions has not fully been explored in rectal cancer. Purpose To investigate in a region the adherence to MRI protocol standards and the relation between MRI interpretation and selection to preoperative therapy in rectal cancer. Material and Methods Data on consecutive patients who underwent elective rectal cancer surgery in the region from January to June 2010 were obtained from the National Colorectal Cancer Registry. Pretherapeutic MRI images were re-evaluated. Agreement between the original reports and the re-evaluation was compared using Cohen’s kappa coefficient. Results Among the 94 patients included, 81 (86%) had pretherapeutic MRI in accordance with defined imaging guidelines. In 34% of the original MR reports, data on extramural venous invasion (mrEMVI) and mrT category were not reported. Complete tumor staging was not possible because of missing data in 33 (35%) of the patients. The agreement between the original MR reports and the re-evaluation regarding tumor stage was moderate (κ = 0.48). For decided treatment compared to recommended preoperative treatment according to the re-evaluation, the agreement was fair (κ = 0.33). Conclusion Established MRI protocol standards were not universally applied. Missing data and inadequacies in original MRI reports resulted in moderate agreement between the original report and the re-evaluation indicating a risk of inappropriate treatment selection. The results call for further educational efforts in rectal cancer MRI acquisition and repeated audits of image protocol adherence and interpretation quality.

MR Imaging of Rectal Cancer: Radiomics Analysis to Assess Treatment Response after Neoadjuvant Therapy.

Purpose To investigate the value of T2-weighted-based radiomics compared with qualitative assessment at T2-weighted imaging and diffusion-weighted (DW) imaging for diagnosis of clinical complete response in patients with rectal cancer after neoadjuvant chemotherapy-radiation therapy (CRT). Materials and Methods This retrospective study included 114 patients with rectal cancer who underwent magnetic resonance (MR) imaging after CRT between March 2012 and February 2016. Median age among women (47 of 114, 41%) was 55.9 years (interquartile range, 45.4-66.7 years) and median age among men (67 of 114, 59%) was 55 years (interquartile range, 48-67 years). Surgical histopathologic analysis was the reference standard for pathologic complete response (pCR). For qualitative assessment, two radiologists reached a consensus. For radiomics, one radiologist segmented the volume of interest on high-spatial-resolution T2-weighted images. A random forest classifier was trained to separate the patients by their outcomes after balancing the number of patients in each response category by using the synthetic minority oversampling technique. Statistical analysis was performed by using the Wilcoxon rank-sum test, McNemar test, and Benjamini-Hochberg method. Results Twenty-one of 114 patients (18%) achieved pCR. The radiomic classifier demonstrated an area under the curve of 0.93 (95% confidence interval [CI]: 0.87, 0.96), sensitivity of 100% (95% CI: 0.84, 1), specificity of 91% (95% CI: 0.84, 0.96), positive predictive value of 72% (95% CI: 0.53, 0.87), and negative predictive value of 100% (95% CI: 0.96, 1). The diagnostic performance of radiomics was significantly higher than was qualitative assessment at T2-weighted imaging or DW imaging alone (P < .02). The specificity and positive predictive values were significantly higher in radiomics than were at combined T2-weighted and DW imaging (P < .0001). Conclusion T2-weighted-based radiomics showed better classification performance compared with qualitative assessment at T2-weighted and DW imaging for diagnosing pCR in patients with locally advanced rectal cancer after CRT. © RSNA, 2018 Online supplemental material is available for this article.

Histopathological and radiological reporting in rectal cancer: concepts and controversies, facts and fantasies.

In rectal cancer patients, the stage of the disease, local spread and distant metastases status drive the treatment decisions to be made. Histopathology remains the gold standard, but preoperative staging, particularly magnetic resonance imaging (MRI), is pivotal for defining surgical planes and finding patients who could potentially benefit from preoperative regimes. Unfortunately, due to a lack of awareness, expertise and practise the quality of rectal cancer MRI and histopathology reporting varies among centres. This paper highlights the most important and frequently occurring radiological and histopathological discrepancies/mistakes to be aware of.

Readout-segmented echo-planar imaging improves the image quality of diffusion-weighted MR imaging in rectal cancer: Comparison with single-shot echo-planar diffusion-weighted sequences

PurposeTo determine whether readout-segmented echo-planar imaging (rs-EPI) diffusion-weighted imaging (DWI) can improve the image quality in patients with rectal cancer compared with single-shot echo-planar imaging (ss-EPI) DWI using 3.0 T magnetic resonance (MR) imaging. Materials and methodsThis study was approved by the Institutional Review Board, and informed consent was obtained from all patients. Seventy-one patients with rectal cancer were enrolled in this study. For all patients, both rs-EPI and ss-EPI DWI were performed using a 3T MR scanner. Two radiologists independently assessed the overall image quality, lesion conspicuity, geometric distortion and distinction of anatomical structures. The signal-to-noise ratio (SNR), lesion contrast, contrast-to-noise ratio (CNR), and apparent diffusion coefficient (ADC) were also measured. Comparisons of the quantitative and qualitative parameters between the two sequences were performed using the paired t-test and the Wilcoxon signed rank test. ResultsThe scores of overall image quality, lesion conspicuity, geometric distortion and distinction of anatomical structures of rs-EPI were all significantly higher than those of ss-EPI (all p<0.05). The SNR and CNR were higher in rs-EPI than those in ss-EPI (all p<0.05). There was no significant difference between ss-EPI and rs-EPI with regard to ROI size and mean ADCs of the tumour (p=0.574 and p=0.479, respectively), but the mean ADC of the normal tissue was higher in rs-EPI than in ss-EPI (1.73±0.30×10−3mm2/s vs. 1.60±0.31×10−3mm2/s, p=0.001). ConclusionsDW imaging based on readout-segmented echo-planar imaging is a clinically useful technique to improve the image quality for the purpose of evaluating lesions in patients with rectal tumours.

Prospective Validation of a Low Rectal Cancer Magnetic Resonance Imaging Staging System and Development of a Local Recurrence Risk Stratification Model: The MERCURY II Study.

This study aimed to validate a magnetic resonance imaging (MRI) staging classification that preoperatively assessed the relationship between tumor and the low rectal cancer surgical resection plane (mrLRP). Low rectal cancer oncological outcomes remain a global challenge, evidenced by high pathological circumferential resection margin (pCRM) rates and unacceptable variations in permanent colostomies. Between 2008 and 2012, a prospective, observational, multicenter study (MERCURY II) recruited 279 patients with adenocarcinoma 6 cm or less from the anal verge. MRI assessed the following: mrLRP "safe or unsafe," venous invasion (mrEMVI), depth of spread, node status, tumor height, and tumor quadrant. MRI-based treatment recommendations were compared against final management and pCRM outcomes. Overall pCRM involvement was 9.0% [95% confidence interval (CI), 5.9-12.3], significantly lower than previously reported rates of 30%. Patients with no adverse MRI features and a "safe" mrLRP underwent sphincter-preserving surgery without preoperative radiotherapy, resulting in a 1.6% pCRM rate. The pCRM rate increased 5-fold for an "unsafe" compared with "safe" preoperative mrLRP [odds ratio (OR) = 5.5; 95% CI, 2.3-13.3)]. Posttreatment MRI reassessment indicated a "safe" ymrLRP in 33 of 113 (29.2%), none of whom had ypCRM involvement. In contrast, persistent "unsafe" ymrLRP posttherapy resulted in 17.5% ypCRM involvement. Further independent MRI assessed risk factors were EMVI (OR = 3.8; 95% CI, 1.5-9.6), tumors less than 4.0 cm from the anal verge (OR = 3.4; 95% CI, 1.3-8.8), and anterior tumors (OR = 2.8; 95% CI, 1.1-6.8). The study validated MRI low rectal plane assessment, reducing pCRM involvement and avoiding overtreatment through selective preoperative therapy and rationalized use of permanent colostomy. It also highlights the importance of posttreatment restaging.

Rectal Cancer Magnetic Resonance Imaging: Imaging Beyond Morphology

Magnetic resonance imaging (MRI) has in recent years progressively established itself as one of the most valuable modalities for the diagnosis, staging and response assessment of rectal cancer and its use has largely focused on accurate morphological assessment.The potential of MRI, however, extends beyond detailed anatomical depiction: aspects of tissue physiology, such as perfusion, oxygenation and water molecule diffusivity, can be assessed indirectly. Functional MRI is rapidly evolving as a promising non-invasive assessment tool for tumour phenotyping and assessment of response to new therapeutic agents. In spite of promising experimental data, the evidence base for the application of functional MRI techniques in rectal cancer remains modest, reflecting the relatively poor agreement on technical protocols, image processing techniques and quantitative methodology to date, hampering routine integration into clinical management. This overview outlines the established strengths and the critical limitations of anatomical MRI in rectal cancer; it then introduces some of the functional MRI techniques and quantitative analysis methods that are currently available, describing their applicability in rectal cancer and reviewing the relevant literature; finally, it introduces the concept of a multi-parametric quantitative approach to rectal cancer.

MR imaging of rectal cancer before and after chemoradiation therapy

This study was done to determine the diagnostic accuracy of magnetic resonance (MR) imaging in patients with rectal carcinoma by comparing post-chemoradiation MR imaging with pathological specimens. We enrolled 39 patients with locally advanced rectal cancer. All patients received chemoradiation therapy before surgery and neoadjuvant chemoradiation therapy followed by MR imaging. MR images were analysed by a team of two expert radiologists unaware of the clinical and histopathological findings. Following neoadjuvant chemoradiation therapy, the analysis of MR images showed 23 (59%) patients with a rectal disease staged ≤T2 and 16 (41%) with a disease staged >T2. Post-treatment histological staging (TNM) revealed 13 patients with a disease >T2 and 26 patients with a disease ≤T2. Cohen's kappa to measure concordance between post-chemoradiation MR staging and histological response showed 83.6% concordance for disease confined to the serosa (≤T3): concordance was 97.22% for disease ≤N1 and 33.33% for disease >N1. MR imaging is critical for discovering T3 disease; moreover, morphological MR imaging does not always provide the opportunity to discern small residual cancer cells hidden in fibrotic tissue that could cause involvement of circumferential resection margin (CRM) on histology.

Diagnostic Sequence of MRI and PET/CT in a Case of Bone Metastases by Hypopharyngeal Squamous Cell Carcinoma

Magnetic resonance imaging (MRI) has gained increasing importance in the management of rectal cancer over the last two decades. The role of MRI in patients with rectal cancer has expanded beyond the tumor-node-metastasis (TNM) system in both staging and restaging scenarios and has contributed to identifying “high” and “low” risk features that can be used to tailor and personalize patient treatment; for instance, selecting the patients for neoadjuvant chemoradiation (NCRT) before the total mesorectal excision (TME) surgery based on risk of recurrence. Among those features, the status of the circumferential resection margin (CRM), extramural vascular invasion (EMVI), and tumor deposits (TD) have stood out. Moreover, MRI also has played a role in surgical planning, especially when the tumor is located in the low rectum, when the relationship between tumor and the anal canal is important to choose the best surgical approach, and in cases of locally advanced or recurrent tumors invading adjacent pelvic organs that may require more complex surgeries such as pelvic exenteration. As approaches using organ preservation emerge, including transanal local excision and “watch-and-wait”, MRI may help in the patient selection for those treatments, follow up, and detection of tumor regrowth. Additionally, potential MRI-based prognostic and predictive biomarkers, such as quantitative and semi-quantitative metrics derived from functional sequences like diffusion-weighted imaging (DWI) and dynamic contrast-enhanced (DCE), and radiomics, are under investigation. This review provides an overview of the current role of MRI in rectal cancer in staging and restaging and highlights the main areas under investigation and future perspectives.

Local staging of rectal cancer: A review of imaging

During the past decades the management of patients with rectal cancer has substantially changed, with a significant reduction in local recurrence rates following the introduction of better imaging, better surgery, and more efficient neoadjuvant therapy. This review discusses the clinically relevant information radiologists should know on staging of rectal cancer patients. The crucial role of the radiologist in patient management is explained. Furthermore, the evidence for the use of magnetic resonance imaging (MRI) in staging and restaging of rectal cancer patients as well as the main features that need to be evaluated when interpreting rectal cancer MRI are given. New diagnostic challenges as a result of new treatment options are also discussed.

Magnetic Resonance Imaging of Rectal Cancer

Magnetic resonance imaging (MRI)is a useful modality for the evaluation of rectal cancer, providing superior anatomic/pathologic visualization when compared with endorectal ultrasound (EUS) and computed tomography (CT). Preoperative MRI is useful for tissue characterization and tumor staging, which determines the surgical approach and need for neoadjuvant/adjuvant therapy. Important prognostic factors include the circumferential resection margin (CRM), T and N stages, and extent of local invasion. Postoperative MRI to assess the extent of tumor recurrence enables early resection, which can greatly prolong survival. MRI criteria for local recurrence include T2 hyperintensity, early dynamic rim enhancement, and nodular morphology. Future research in MRI of rectal cancer is geared toward developing optimal imaging techniques including high-resolution MRI, whole-body scans, and parallel imaging; imaging of lymph nodes by MR lymphography; and response to therapy using diffusion/perfusion-weighted MR and functional imaging.