Faculty Bibliography

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.

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.

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.

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.

As photon-counting CT (PCCT) gains wider clinical acceptance and is implemented in more practice settings, guidance for implementing this cutting-edge imaging modality in its currently clinically available form (NAEOTOM Alpha; Siemens Healthineers) is needed. Understanding the core physics of PCCT, particularly the nuances in detector technology, is paramount for achieving optimal imaging system setup and proficient image acquisition. Through a comprehensive overview of PCCT physics and real-life case examples to highlight the technologic differences from conventional energy-integrating detector CT systems, the radiologist will be able to effectively implement PCCT in clinical practice. The key steps taken when starting a successful PCCT imaging practice across radiology subspecialties includes (a) imaging system setup; (b) protocol development, emphasizing the critical role of tailored protocols in achieving diagnostic precision and radiation dose optimization and introducing new terminology; (c) the imaging process, highlighting the importance of optimizing scan modes to suit clinical requirements; and (d) postimaging considerations, including the interpretation of system outputs and the judicious selection of images for routine transmission to the picture archiving and communication system. This article serves as a reference for radiologists, technologists, medical physicists, and informatics teams seeking to harness the full potential of PCCT. By optimizing workflow and facilitating adept image interpretation, this guidance aims to augment diagnostic capabilities and elevate the standard of patient care in the era of PCCT. ^©RSNA, 2025 An earlier incorrect version of this article appeared online. This article was corrected on February 5, 2025.

Background Osteoporosis is underdiagnosed and undertreated, prompting the exploration of opportunistic screening using CT and artificial intelligence. Purpose To develop a reproducible convolutional neural network to automatically identify a three-dimensional (3D) region of interest (ROI) in trabecular bone, develop a correction method to normalize attenuation values across different CT protocols and scanner models, and establish thresholds for diagnosing osteoporosis in a large diverse population. Materials and Methods In this retrospective study, a deep learning-based method was developed to automatically quantify trabecular attenuation of the thoracic and lumbar spine on CT images with use of a 3D ROI. A statistical method was developed to adjust for different tube voltages and scanner models. Normative values and diagnostic thresholds for trabecular attenuation of the spine for osteoporosis were established based on the reported prevalence of osteoporosis by the World Health Organization. Differences between groups were assessed using the Student t test. Results A total of 538 946 CT examinations from 283 499 patients (mean age, 65 years ± 15 [SD]; 145 021 [51.2%] female; 157 457 [55.5%] White patients) were analyzed, representing 43 scanner models and six different tube voltages. The attenuation values at 80 kVp and 120 kVp differed by 23%, and different scanner models resulted in differences in values of less than 10%. The automated ROI placement of 1496 vertebrae was validated by manual radiologist review and demonstrated greater than 99% agreement. Trabecular attenuation was greater in young women (age <50 years) than in young men (P < .001) and decreased with age, with a steeper decline in postmenopausal women. In patients older than 50 years, trabecular attenuation was greater in male than in female patients (P < .001). Trabecular attenuation was highest in Black patients, followed by Asian patients, and lowest in White patients (P < .001). Conclusion Deep learning-based automated opportunistic osteoporosis screening can identify patients with low bone mineral density using CT scans obtained for clinical purposes with use of different scanners and protocols. © RSNA, 2025 Supplemental material is available for this article. See also the editorial by Feuerriegel and Sutter in this issue.

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.

The role of imaging in initial staging of colon cancer, and in posttreatment restaging or surveillance, is most beneficial in identifying distant metastases in the chest, abdomen, and pelvis, regardless of primary T or N stage. Appendiceal cancers are classified separately and managed differently than colon cancer; however, initial staging and postoperative surveillance is also primarily focused on detection of distant metastatic disease, usually in the abdomen and pelvis. 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.

Obesity is an increasing worldwide epidemic. Bariatric procedures are safe and effective in the treatment of obesity and obesity-related comorbidities. There are numerous different bariatric procedures ranging from less-invasive procedures to more invasive surgeries. This document discusses the guidelines for the appropriate use of imaging in the preoperative and postoperative evaluation of adult bariatric patients, as well as after surgery when a complication is suspected. 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.

In this article, we briefly summarize the technological differences between conventional energy-integrating detector computed tomography and photon-counting computed tomography (PCCT). With an eye on genitourinary (GU) applications, we discuss current literature on the development and optimization of clinical PCCT protocols, including the selection of kilovoltage peaks, ultra-high-resolution mode, and generation of spectral data sets such as virtual non-contrast series. Then, we review the current literature regarding applications in the GU system, including the differentiation of benign renal cysts from renal masses, the characterization of adrenal masses without the use of follow-up imaging, and the improved detection of renal stones.