Faculty Bibliography

Background MR enterography (MRE) is increasingly used to guide treatment and improve outcomes in Crohn disease (CD). An abbreviated MRE (A-MRE) protocol-omitting contrast and antiperistaltic agents-may reduce scanning time and cost and improve compliance. Purpose To compare intrareader concordance and interreader agreement in detecting disease activity and disease-related complications using contrast-enhanced MRE (CE-MRE) versus an A-MRE protocol in participants with CD. Materials and Methods In this secondary analysis of a prospective study, 10 abdominal radiologists independently reviewed MRE examinations from a prospective study of participants with CD before and after treatment with biologics, using both A-MRE and CE-MRE protocols, at least 1 month apart. Interreader agreement and intrareader concordance were assessed using Gwet first agreement coefficient (AC1) at both the segment and participant levels for the presence of active inflammation, associated indicative features, and complications. Diagnostic accuracy of the simplified MR index of activity (sMaRIA) was evaluated against ileocolonoscopy when available. Results This study included 60 participants (median age, 36 years [IQR, 28-44 years]; 40 female; 80 examinations). Interreader agreement for detecting intestinal active disease was high and comparable between A-MRE and CE-MRE at the participant level (AC1, 0.87 [95% CI: 0.79, 0.95] vs 0.91 [95% CI: 0.85, 0.97]). For strictures, similar interreader agreement was observed between protocols (AC1: A-MRE, 0.61 [95% CI: 0.47, 0.74] vs CE-MRE, 0.50 [95% CI: 0.35, 0.65]). For penetrating complications, the interreader agreement was also similar between protocols (A-MRE, 0.71 [95% CI: 0.56, 0.86] vs CE-MRE, 0.76 [95% CI: 0.63, 0.90]). The intrareader concordance between protocols for detecting active inflammation and CD complications was almost perfect for all readers (AC1 range, 0.86-1.00). In the terminal ileum, sMaRIA showed high sensitivity (A-MRE, 96.4%; CE-MRE, 98.4%) and specificity (A-MRE, 68.1%; CE-MRE, 71.4%) for detecting inflammation. Conclusion An A-MRE protocol demonstrated comparable interreader agreement to conventional CE-MRE and high intrareader concordance for detecting active CD and related complications in participants with CD. © The Author(s) 2026. Published by the Radiological Society of North America under a CC BY 4.0 license. Supplemental material is available for this article. See also the editorial by Ohliger in this issue.

BACKGROUND & AIMS/OBJECTIVE:Perianal fistulising Crohn's disease (pfCD) affects one-fifth of patients with Crohn's disease (CD), significantly affecting their quality of life. Magnetic resonance imaging is the gold standard for evaluating fistula healing in pfCD, but variability in radiological definitions hampers meaningful clinical interpretation and consistent trial design. This study aimed to establish an international consensus on the definition of radiological healing in pfCD. METHODS:The study was conducted in 2 phases. Phase 1 involved a systematic review to identify magnetic resonance imaging-based variables and indices used to define healing in pfCD, assessing methodological quality using the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) framework. Phase 2 utilized a 2-round online Delphi consensus process with 84 international experts, followed by a stakeholder meeting to achieve consensus (agreement threshold >80%). Results were reported as per Accurate Consensus Reporting Document (ACCORD) guidelines. RESULTS:A radiologically healed fistula can be defined by the absence of T2-weighted hyperintensity, a completely fibrotic fistula tract and, when contrast is used, the absence of contrast enhancement on post-contrast T1-weighted images (95% consensus). Radiological improvement of a fistula can be defined (80% consensus) by the presence of a least one essential criterion: an increasingly fibrotic fistula tract, an unequivocal reduction in one or more of the following: T2-weighted hyperintensity, fistula diameter, fistula length, abscess size, or contrast enhancement of the fistula tract. CONCLUSION/CONCLUSIONS:This international Delphi consensus standardizes radiological endpoints in pfCD, improving consistency in clinical and research settings. Future studies will validate this definition and assess how radiological changes predict long-term clinical outcomes and quality of life improvements.

OBJECTIVE:To determine the optimal iodine concentration (IC) to differentiate enhancing from nonenhancing renal lesions at venous phase photon-counting CT (PCCT). MATERIALS AND METHODS/METHODS:Sixty-seven patients [41 males, mean (SD) age: 68 (13) y] who underwent contrast-enhanced venous phase abdominal PCCT and contrast-enhanced MRI were retrospectively identified. MRI characterization of renal lesions as simple cysts, hemorrhagic/proteinaceous cysts or masses was the reference standard. Two radiologists, blinded to MRI characterization, independently drew region-of-interests (ROI) within each renal lesion and the aorta to determine IC, iodine concentration normalized to aortic enhancement (NIC), postcontrast and virtual noncontrast attenuation. These variables were compared using nonparametric tests, and intraclass correlation coefficient was assessed. ROC analysis for IC, NIC, and attenuation difference was performed using mean measurements. RESULTS:Median (IQR) IC was 0.015 (0.00 to 0.20) mg/mL for cysts (n = 41) and 3.00 (1.59 to 4.10) mg/mL for masses (n = 26; P < 0.001). NIC was 2 (-1 to 4)% for cysts and 58 (33 to 81)% for masses (P < 0.001). For differentiating cysts from masses, 0.6 mg/mL IC had 100% sensitivity and 95% specificity [AUC = 1.00 (0.99, 1.00)] and 14.1%. NIC had 100% sensitivity and 98% specificity [AUC = 1.00 (0.99, 1.00)]. For differentiating cysts from enhancing masses, a 20 HU attenuation change from VNC to postcontrast images demonstrated a sensitivity of 96% and specificity of 95% [AUC = 1.00 (0.99, 1.00)]. IC was 0.13 (-0.11 to 0.20) mg/mL for hemorrhagic cysts (n = 16) and 1.63 (1.31 to 1.89) mg/mL for papillary neoplasms (n = 8; P < 0.001). NIC was 2 (-1 to 5)% and 32 (22 to 40)%, respectively (P < 0.001). For differentiating hemorrhagic cysts from papillary neoplasms, 0.53 mg/mL IC had 100% sensitivity and 88% specificity [AUC = 0.98 (0.93, 1.00)] and 14.1% NIC had 100% sensitivity and 94% specificity [AUC = 0.98 (0.95, 1.00)]. A 20 HU change had 88% sensitivity and specificity. For differentiating hemorrhagic cysts from papillary neoplasms, a 20 HU attenuation change had 88% sensitivity and 88% specificity [AUC = 0.98 (0.93, 1.00)]. CONCLUSIONS:PCCT iodine concentration showed outstanding diagnostic performance to differentiate renal cysts from neoplasms. A 20 HU change in attenuation from VNC to postcontrast imaging on PCCT remains a reliable threshold for enhancing lesion, similar to conventional CT. Iodine concentration demonstrated superior sensitivity and specificity compared with 20 HU change when identifying renal cysts versus masses.

OBJECTIVE:To assess photon counting CT iodine density as a marker of histopathologic treatment response after neoadjuvant chemotherapy in patients with pancreatic ductal adenocarcinoma. MATERIALS AND METHODS/METHODS:A retrospective PACS search identified 21 pancreatic ductal adenocarcinoma patients [14 men; mean (SD) age: 64 (10) y] who underwent neoadjuvant chemotherapy and pancreatic photon counting CT 2 months before resection from April 11, 2022 to February 2, 2024. The histopathologic treatment response grade was the reference standard. Freehand regions-of-interest measurements were drawn independently by 2 radiologists as large as possible within the mass on pancreatic parenchymal phase images. Attenuation, iodine density, and iodine density normalized to the aorta were recorded. Mann-Whitney U test was used to compare attenuation, iodine density, and normalized iodine density for responders (pathologic grade 1, 2) versus nonresponders (grade 3). Receiver operating characteristic curves were created, and optimal thresholds were determined with Youden's index. A P<0.05 indicated statistical significance. RESULTS:Thirteen of 21 (61.9%) patients showed pathologic treatment response. Iodine density for nonresponders and responders was mean (SD) 0.47 (0.23) mg/mL and 1.20 (0.75) mg/mL, respectively (P=0.005). Normalized iodine density for nonresponders and responders was 7.6 (5.5)% and 22.5 (16.0)%, (P=0.006). Attenuation for nonresponders and responders was 56.5 (10.9) HU and 70.6 (17.7) HU, (P=0.04). Upon receiver operating characteristic analysis, an iodine density threshold of 0.65 mg/mL had 77% sensitivity and 88% specificity (AUC=0.86), and a normalized iodine density threshold of 10.1% had 77% sensitivity and 88% specificity (AUC=0.86) for treatment response. A 61.8 HU threshold had 77% sensitivity and 75% specificity (AUC=0.78). CONCLUSIONS:Elevated iodine density correlates with pancreatic ductal adenocarcinoma histopathologic treatment response with high specificity. Photon counting CT iodine density may be used as a marker of histopathologic treatment response.

The evaluation of patients with gastrointestinal (GI) bleeding is complicated due to the variety of tests available and the large number of potential causes of bleeding. MRI is less commonly used than computed tomography and endoscopy but it can diagnose disease that causes GI bleeding and serve as a complementary role to other tests. MRI is most often used in the form of magnetic resonance enterography (MRE) to assess patients with suspected bleeding from the small bowel. While CT enterography (CTE) and video capsule endoscopy (VCE) are the more commonly used tests in the setting of GI Bleeding, MRE has characteristics which may make it the more favorable modality for a given patient. Potential advantages of MRE, protocol considerations and the literature delineating its diagnostic performance for detecting pathology which can cause GI bleeding relative to CTE and VCE are reviewed here. MRI is uncommonly used to assess patients with upper GI bleeding, lower GI bleeding and patients with bleeding sites that remain undetected despite a formal evaluation of the GI tract, however it may add value in specific clinical scenarios. These uncommon scenarios and specific clinical examples are also presented to highlight the potential benefits of MRI.

Photon-counting CT (PCCT) offers new opportunities for abdominal imaging by enabling higher spatial resolution, improved image quality, and reduced radiation exposure compared with conventional energy-integrating detector CT systems. However, standardized PCCT protocols for abdominal imaging are lacking, which limits clinical adoption, comparability across institutions, and multicenter research studies. The Society of Abdominal Radiology (SAR) Photon-Counting Detector CT Emerging Technology Commission created a survey to achieve consensus on common adult abdominal PCCT protocols for the FDA-approved PCCT, including portal venous phase CT, multiphase aortic CTA, and multiphase pancreas CT protocols. The survey included the following items for each protocol: scan mode, tube potential, image quality level, primary viewing virtual monoenergetic imaging (VMI) level, reconstruction kernel, additional VMI or other spectral reconstructions sent to PACS, and details of archiving the special spectral image dataset. Consensus statements were generated based on the survey and voted upon by nine radiologists from nine institutions using the consensus-minus-one method. Consensus was reached for 20 protocol features, including that 70-keV VMI is recommended for primary interpretation of portal venous and multiphase pancreas PCCT and that, for multiphase aortic CTA, low virtual monoenergetic levels should be viewed. This multiinstitutional consensus endorsed by SAR establishes standardized abdominal PCCT protocols.

Dual-energy computed tomography (DECT) has been available for clinical use since 2006. Since its clinical debut, multiple different dual energy systems have been developed including sequential acquisition, rapid-switching, dual-source, and twin-beam, in addition to spectral imaging techniques such as dual-layer and photon counting CT. While the specifics of these techniques vary, the underlying principles remain the same; by acquiring at least two data sets, material specific information in each image voxel can be determined. Most commonly used to evaluate for the presence or absence of iodine, DECT has found clinical applications in the assessment of gastrointestinal bleeding, bone marrow edema, the characterization of renal stones, and the accurate evaluation of vascular stenosis, among other uses. This review aims to familiarize the radiologist with the theoretical basis underlying DECT, describe the different types of DECT including the relative strengths and weaknesses of each, and highlight specific clinical applications for which DECT may be valuable.

In rectal cancer, because of the need for high-resolution anatomic detail in determining local tumor extension, imaging for local staging and restaging of the primary tumor in the pelvis is considered separately from the evaluation of distant metastatic disease in the chest, abdomen, and pelvis, often resulting in the need for a combination of modalities to fully stage the patient. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.