Cavum septum pellucidum (CSP) is a common neuroimaging finding linked to repetitive head trauma, yet its relationship to blast exposure among the military population remains elusive. Here, we investigated whether lifetime exposure to different types of blast is associated with CSP morphology among Special Operations Forces (SOF) personnel. We retrospectively analyzed 323 SOF members from the Comprehensive Brain Health and Trauma Program at Home Base who completed high-resolution 3T MRI and the Blast Exposure Threshold Survey (BETS), which quantifies lifetime exposure to explosive weapons across five blast exposure count categories (BEC1-BEC5). CSP grade and length were assessed using validated criteria on coronal 3D T1-weighted Magnetization Prepared Rapid Gradient Echo scans. A CSP length-to-septum length ratio (CSP ratio) was calculated to adjust for anatomical variation. BEC1-BEC5 were log-transformed to correct skewness and are referred to as log-BEC1-5.Variance inflation factor analysis indicated low multicollinearity among predictors (log-BEC1-5 and age), and variable selection using Least Absolute Shrinkage and Selection Operator regression identified log-BEC5 (exposure to large explosives) as the only retained predictor. In fully adjusted models, only log-BEC5 remained significantly associated with CSP measures and was therefore the focus of subsequent analyses.Participants were stratified by BEC5 = 0 vs. BEC5 > 0, and associations with CSP measures were assessed using group comparisons, multivariable regression, and dose-response models.Among 323 participants (mean age 42.7 ± 8.8 years), 273 (84%) reported any BEC5 exposure. SOF members with BEC5 > 0 had significantly greater CSP presence (42.1% vs. 22.0%, p = 0.007) and longer CSP length (median 3 mm vs. 2 mm, p = 0.002). In age-adjusted models, BEC5 > 0 was associated with greater odds of CSP presence (OR = 2.58, 95% CI 1.26-5.25, p = 0.009) and a 1.45 mm increase in CSP length (p = 0.004). In continuous models, each one-unit increase in log-BEC5 was associated with a 0.31 mm increase in CSP length (p = 0.008) and a 0.0059 increase in CSP ratio (p = 0.008).These findings indicate a statistically significant association between cumulative exposure to heavy explosives and CSP enlargement, suggesting that CSP may serve as a potential imaging marker of blast-related neurotrauma.

BACKGROUND AND PURPOSE:Low-level light therapy (LLLT) has been shown to modulate recovery in patients with traumatic brain injury (TBI). However, the longitudinal impact of LLLT on brain metabolites has not been studied. The purpose of this study was to use MR spectroscopic imaging to assess the metabolic response of LLLT in patients with moderate TBI at acute (within 1 week), subacute (2-3 weeks), and late-subacute (3 months) recovery phases. MATERIALS AND METHODS:This is a secondary analysis of a prospective single-site double-blind sham-controlled study conducted in patients with moderate TBI. Participants were randomized for LLLT and sham treatment. Three-Tesla 2D MR spectroscopic imaging was acquired. Our focus of investigation was the metabolic change in the corpus callosum (CC) and the changes in mIns/NAA, representing the combined effect of elevated neuroinflammation (mIns) and decreased neuronal/axonal health (NAA). A linear mixed-effects model was constructed to quantify the association between mIns/NAA and treatment, scan, and the interaction between treatment and scan. RESULTS:Thirty-four participants (18 men, age 49 ± 17 [range, 20-79]; 15 LLLT, 19 sham) were included in the final data set and were scanned at the following time points: acute (n=24), subacute (n=27), and late subacute (n=23). The mIns/NAA ratio in the CC of the sham-treated participants increased over time. Sham-treated participants revealed a significant increase in mIns/NAA from the acute to the late subacute phases (0.19; 95% CI, 0.09-0.29; P Holm = .005). mIns/NAA stayed relatively stable in participants undergoing LLLT treatment (all P Holm > .64). Consequently, mIns/NAA was significantly higher in the sham-treated participants compared with the LLLT-treated participants during the late subacute phase of recovery (-0.31; 95% CI, -0.50 to -0.12; P Holm = .019). CONCLUSIONS:Despite the small sample size, MR spectroscopic imaging indicates a metabolic response in participants treated with LLLT compared with those receiving sham treatment. This potentially suggests a neuroprotective and anti-inflammatory effect from the acute administration of LLLT in individuals with moderate TBI.

OBJECTIVE:To evaluate the diagnostic performance of a 3-min ultrafast brain MRI and MRA protocol for screening of acute ischemic stroke. METHODS:This study involved 67 adult patients who underwent ultrafast and reference MRI and MRA scans from September 2023 to June 2024 for stroke evaluation. Two readers independently assessed the ultrafast and reference MRI and MRA images in a masked and randomized manner for acute and chronic infarct and hemorrhage as well as large-vessel occlusion and severe stenosis. A 3-point Likert scale was used to evaluate diagnostic quality of the ultrafast sequences and Cohen's κ was used to assess interrater agreement. RESULTS:The ultrafast MRI and MRA protocol showed high diagnostic quality, with 98% of sequences rated as diagnostic. Raters showed perfect agreement in identifying acute infarcts, aneurysms, and vascular occlusions using both ultrafast and reference protocols and near-perfect agreement (>95%) for detecting acute hemorrhage and severe stenosis. For chronic conditions such as chronic infarction and chronic hemorrhage, there was substantial agreement with κ values ranging from 0.73 to 0.76. DISCUSSION:The screening ultrafast MRI and MRA protocol can effectively identify acute ischemic stroke and intracranial large-vessel occlusion with high diagnostic accuracy while significantly reducing acquisition time, making it suitable for initial stroke triage. Evaluation for chronic pathologies on the ultrafast protocol is inferior compared with standard MRI and MRA imaging.

BACKGROUND AND PURPOSE:CTP is important for acute ischemic stroke imaging and treatment, but defining the ischemic penumbra and infarct core remains debated. This study examined the relationship between initial hypoperfused tissue and final infarct in patients with acute anterior circulation occlusion, stratified by reperfusion status, to assess CTP's predictive spatial and volumetric accuracy and re-evaluate its role in prognostication, nuanced clinical decision-making, and novel pathophysiology research in the new large core era. MATERIALS AND METHODS:This retrospective single-center study included patients diagnosed with anterior circulation acute ischemic stroke who underwent CTP between May 2021 and February 2024. Initial imaging and follow-up NCCT scans were automatically co-registered. CTP-derived ischemic core and penumbra segmentations were compared with manually segmented final infarcts on follow-up imaging. Groups with (endovascular thrombectomy [EVT] with modified TICI score ≥ 2b) and without successful reperfusion (no or unsuccessful EVT) were compared by using the Dice similarity coefficient (DSC) for spatial alignment and Spearman correlation for volumetric agreement. RESULTS:One hundred twenty-one patients were included (51% men, median age: 70 years, median NIHSS score: 14). Successful reperfusion was achieved in 37 patients, while 84 received no or unsuccessful EVT. Significant differences in regions of hypoperfusion were observed between the nonreperfusion and reperfusion groups concerning spatial alignment (median DSC: 0.52 versus 0.29; P < .001) and volumetric agreement (Spearman correlation between predicted and actual infarct volumes: 0.72 versus 0.07; P < .001). CONCLUSIONS:CTP offers valuable insights into salvageable tissue in acute ischemic stroke, guiding treatments, predicting infarct volumes, aiding in future stroke pathophysiology research in the large core era, and potentially improving prognostication.

Purpose: In ischemic stroke, MRI and CT are both utilized to estimate lesion progression distinguishing reversible from irreversible tissue injury and are therefore used for acute treatment decision-making. On MRI, relative increase of fluid-attenuated inversion recovery signal (rFLAIR) is thought to represent vasogenic edema indicating irreversible tissue injury. On CT, progressing hypoattenuation is the imaging correlate of ischemic net water uptake (NWU), which can be quantified by densitometry and may reflect both ionic edema, which is potentially reversible, and irreversible vasogenic edema following blood-brain barrier breakdown. The relationship of rFLAIR and NWU has not been compared directly. We hypothesized that the degree of early CT-based NWU is directly linked to rFLAIR in patients undergoing both modalities on admission. Methods: Observational retrospective study of patients with acute anterior circulation ischemic stroke undergoing both CT and MRI on admission with visible core lesion on diffusion-weighted imaging. DWI-FLAIR mismatch was rated on MRI and quantitative NWU was measured on admission-CT. Multiparametric MRI signal changes were measured including rFLAIR and correlated to CT-based NWU with respect to time from symptom onset-admission. Results: 53 patients were included. The median NWU was 7.7% (IQR: 4.9-13.0) and the median rFLAIR 1.38 (IQR: 1.21-1.72). There was no correlation between NWU and rFLAIR (r=0.15, p=0.48); however, NWU was significantly higher in FLAIR-positive versus FLAIR-negative cases (11.2% versus 5.5%, p<0.0001) and NWU significantly correlated with time (r=0.62, p<0.0001), while rFLAIR did not (r=0.1, p=0.73). In logistic regression analysis, higher NWU was significantly associated with FLAIR-positivity (OR: 1.31, 95%CI:1.11-1.56,p=0.001), and the optimal cut-off for NWU to classify FLAIR-positivity was 7.4% (AUC: 0.82, 95%CI: 0.70-0.94). Conclusion: CT-based quantitative NWU distinguished FLAIR-positive from FLAIR-negative cases, significantly correlating with progressing time from onset while rFLAIR showed no correlation to time. Hence, NWU and rFLAIR might depict a different early lesion pathophysiology. A low degree of NWU without a correlate on FLAIR might represent early ionic edema, which is potentially reversible and could therefore explain cases of reversible lesion hypodensity.

The aim of this study was to assess the number of foot/ankle computed tomography (CT) exams ordered per encounter for patients presenting to the emergency department (ED) with foot and ankle trauma over a 5-year period. Secondary aims included evaluating the positivity rate of foot/ankle CT exams and identifying factors associated with receiving a CT foot/ankle. This retrospective study analyzed data from a large urban Level-1 trauma center between 2016 and 2021. Patients were identified by charted chief complaints related to foot and ankle trauma. The primary outcome was the number of CT foot/ankle exams ordered per patient in a given period. A univariate chi-square analysis was conducted to evaluate differences in patient presentations and imaging rates across the study period. Over the 5-year span, there were 9,845 patient encounters, with a significant increase in CT foot/ankle orders from 2.4 % to 6.6 % (p < 0.001). The CT positivity rate, defined as CTs with positive findings, declined from 95.2 % in 2016 to 84.1 % in 2021 (p < 0.001). Black patients had lower odds of receiving CT scans compared to White patients, as did Medicare recipients compared to Medicaid recipients (p < 0.001). Factors such as age (OR: 1.02 per year), year of visit (OR: 2.66 for 2021), time of day (OR: 1.62 for evening arrivals), and arrival by EMS (OR: 5.60) were significantly associated with higher CT order rates. This study highlights a marked increase in CT utilization for foot and ankle trauma with a corresponding decline in the rate of positive findings. Further research is necessary to explore the reasons behind this trend and to identify potential workflow or protocol adjustments to improve imaging efficacy.

Importance:Overuse of advanced imaging in the emergency department (ED) contributes to higher costs, reduced efficiency, and crowding. Computed tomographic angiography (CTA) is a recommended first-line diagnostic for acute gastrointestinal bleeding (GIB), yet its increasing use may not always improve detection of active bleeding. Objective:To evaluate recent trends in CTA use for suspected GIB in the ED and assess changes in diagnostic yield. Design, Setting, and Participants:This retrospective cohort study included all adult patients who underwent CTA of the abdomen and pelvis for suspected GIB at a 1011-bed urban academic medical center between January 2017 and December 2023. Exposure:Suspected GIB prompting a CTA order in the ED. Main Outcomes and Measures:The primary outcome was the annual number and proportion of GIB-related CTAs among all ED computed tomography (CT) examinations. The secondary outcome was the test-positive proportion (diagnostic yield), defined as the percentage of CTAs showing active bleeding or evidence of hemorrhage. All CTAs were interpreted by board-certified emergency radiologists and reviewed by a fellowship-trained emergency radiologist. Results:Among 954 ED patients (mean [SD] age, 66.7 [6.3] years; 427 female [44.8%]), the number of GIB-related CTA examinations increased from 30 of 32 197 ED CT examinations (0.09%) in 2017 to 288 of 44 423 (0.65%) in 2023. Over the same period, the test-positive proportion declined from 6 of 30 (20.0%) in 2017 to 18 of 288 (6.3%) in 2023. Multivariable analysis showed that more recent calendar year was associated with lower odds of a test-positive examination (OR, 0.84; 95% CI, 0.73-0.96; P = .01), older age with higher odds (OR, 1.02; 95% CI, 1.00-1.04; P = .02), and active cancer with lower odds (OR, 0.35; 95% CI, 0.12-1.00; P = .05). Conclusions and Relevance:CTA use increased substantially over 7 years while diagnostic yield declined. This trend highlights the need to balance the diagnostic benefit of CTA with interpretation time, radiation exposure, and operational strain. These findings support a need for evidence-based ordering criteria and decision-support tools to help guide CTA use in the ED evaluation of gastrointestinal bleeding.

Emergency/trauma radiology artificial intelligence (AI) is maturing along all stages of technology readiness, with research and development (R D) ranging from data curation and algorithm development to post-market monitoring and retraining. To develop an expert consensus document on best research practices and methodological priorities for emergency/trauma radiology AI. A Delphi consensus exercise was conducted by the ASER AI/ML expert panel between 2022-2024. In phase 1, a steering committee (7 panelists) established key themes- curation; validity; human factors; workflow; barriers; future avenues; and ethics- and generated an edited, collated long-list of statements. In phase 2, two Delphi rounds using anonymous RAND/UCLA Likert grading were conducted with web-based data capture (round 1) and a bespoke excel document with literature hyperlinks (round 2). Between rounds, editing and knowledge synthesis helped maximize consensus. Statements reaching ≥80

Photon-counting CT (PCCT) has emerged as a transformative technology, with the potential to herald a new era of clinical capabilities. This review provides an overview of the current status and potential future developments of PCCT, including basic physics principles and technical implementation by different vendors, with special attention to applications that have not, to date, been emphasized in the literature. The technologic underpinnings that distinguish PCCT scanners from traditional energy-integrating detector (EID) CT scanners with dual-energy capability are discussed. The inherent challenges of PCCT and the innovative breakthroughs that have enabled key PCCT features, such as enhanced image resolution, material discrimination, and radiation dose efficiency, are reviewed. Two categories of clinical applications are considered: (a) applications that are possible with current-generation EID CT but may be improved with the higher spatial, temporal, and contrast resolution of PCCT (eg, CT angiographic vasculitis imaging with high spatial, contrast, and temporal resolution and ultra-high-spatial-resolution "opportunistic" osseous imaging) and (b) potential future applications that are not currently feasible with EID CT but that may become possible and practical with PCCT (eg, reduced need for serial follow-up imaging with advanced CT or MRI because of more complete, definitive imaging evaluation with PCCT at first presentation).

Background: The deployment of black-box AI models in medical imaging presents significant challenges, especially in maintaining reliability across different clinical settings. These challenges are compounded by distribution shifts that can lead to failures in reproducing the accuracy attained during the AI model's original validations. Method: We introduce the conformal triage algorithm, designed to categorize patients into low-risk, high-risk, and uncertain groups within a clinical deployment setting. This method leverages a combination of a black-box AI model and conformal prediction techniques to offer statistical guarantees of predictive power for each group. The high-risk group is guaranteed to have a high positive predictive value, while the low-risk group is assured a high negative predictive value. Prediction sets are never constructed; instead, conformal techniques directly assure high accuracy in both groups, even in clinical environments different from those in which the AI model was originally trained, thereby ameliorating the challenges posed by distribution shifts. Importantly, a representative data set of exams from the testing environment is required to ensure statistical validity. Results: The algorithm was tested using a head CT model previously developed by Do and colleagues [9] and a data set from Massachusetts General Hospital. The results demonstrate that the conformal triage algorithm provides reliable predictive value guarantees to a clinically significant extent, reducing the number of false positives from 233 (45%) to 8 (5%) while only abstaining from prediction on 14% of data points, even in a setting different from the training environment of the original AI model. Conclusions: The conformal triage algorithm offers a promising solution to the challenge of deploying black-box AI models in medical imaging across varying clinical settings. By providing statistical guarantees of predictive value for categorized patient groups, this approach significantly enhances the reliability and utility of AI in optimizing medical imaging workflows, particularly in neuroradiology. ### Competing Interest Statement M.H.L. is a consultant at GE Healthcare and at Takeda/Seagen/Roche-Genentech Pharmaceuticals. ### Funding Statement This study did not receive any funding. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: IRB of Massachusetts General Hospital gave ethical approval of this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced are available online at https://github.com/aangelopoulos/conformal-triage .

Prudent imaging use is essential for cost reduction and efficient patient triage. Recent efforts have focused on head and neck CTA in patients with emergent concerns for non-focal neurological complaints, but have failed to demonstrate whether increases in utilization have resulted in better care. The objective of this study was to examine trends in head and neck CTA ordering and determine whether a correlation exists between imaging utilization and positivity rates. This is a single-center retrospective observational study at a quaternary referral center. This study includes patients presenting with headache and/or dizziness to the emergency department between January 2017 and December 2021. Patients who received a head and neck CTA were compared to those who did not. The main outcomes included annual head and neck CTA utilization and positivity rates, defined as the percent of scans with attributable acute pathologies. Among 24,892 emergency department visits, 2264 (9.1

BACKGROUND AND PURPOSE:The use of MR imaging in emergency settings has been limited by availability, long scan times, and sensitivity to motion. This study assessed the diagnostic performance of an ultrafast brain MR imaging protocol for evaluation of acute intracranial pathology in the emergency department and inpatient settings. MATERIALS AND METHODS:Sixty-six adult patients who underwent brain MR imaging in the emergency department and inpatient settings were included in the study. All patients underwent both the reference and the ultrafast brain MR protocols. Both brain MR imaging protocols consisted of T1-weighted, T2/T2*-weighted, FLAIR, and DWI sequences. The ultrafast MR images were reconstructed by using a machine-learning assisted framework. All images were reviewed by 2 blinded neuroradiologists. RESULTS:The average acquisition time was 2.1 minutes for the ultrafast brain MR protocol and 10 minutes for the reference brain MR protocol. There was 98.5% agreement on the main clinical diagnosis between the 2 protocols. In head-to-head comparison, the reference protocol was preferred in terms of image noise and geometric distortion (P < .05 for both). The ultrafast ms-EPI protocol was preferred over the reference protocol in terms of reduced motion artifacts (P < .01). Overall diagnostic quality was not significantly different between the 2 protocols (P > .05). CONCLUSIONS:The ultrafast brain MR imaging protocol provides high accuracy for evaluating acute pathology while only requiring a fraction of the scan time. Although there was greater image noise and geometric distortion on the ultrafast brain MR protocol images, there was significant reduction in motion artifacts with similar overall diagnostic quality between the 2 protocols.

Objective. Combining magnetic resonance imaging (MRI) and electroencephalography (EEG) provides a powerful tool for investigating brain function at varying spatial and temporal scales. Simultaneous acquisition of both modalities can provide unique information that a single modality alone cannot reveal. However, current simultaneous EEG-fMRI studies are limited to a small set of MRI sequences due to the image quality and safety limitations of commercially available MR-conditional EEG nets. We tested whether the Inknet2, a high-resistance polymer thick film based EEG net that uses conductive ink, could enable the acquisition of a variety of MR image modalities with minimal artifacts by reducing the radiofrequency-shielding caused by traditional MR-conditional nets. Approach. We first performed simulations to model the effect of the EEG nets on the magnetic field and image quality. We then performed phantom scans to test image quality with a conventional copper EEG net, with the new Inknet2, and without any EEG net. Finally, we scanned five human subjects at 3 Tesla (3 T) and three human subjects at 7 Tesla (7 T) with and without the Inknet2 to assess structural and functional MRI image quality. Main results. Across these simulations, phantom scans, and human studies, the Inknet2 induced fewer artifacts than the conventional net and produced image quality similar to scans with no net present. Significance. Our results demonstrate that high-quality structural and functional multimodal imaging across a variety of MRI pulse sequences at both 3 T and 7 T is achievable with an EEG net made with conductive ink and polymer thick film technology.

BACKGROUND AND PURPOSE:Imaging stewardship in the emergency department (ED) is vital in ensuring patients receive optimized care. While suspected cord compression (CC) is a frequent indication for total spine MR imaging in the ED, the incidence of CC is low. Recently, our level 1 trauma center introduced a survey spine MR imaging protocol to evaluate for suspected CC while reducing examination time to avoid imaging overutilization. This study aims to evaluate the time savings, frequency of ordering patterns of the survey, and the symptoms and outcomes of patients undergoing the survey. MATERIALS AND METHODS:This retrospective study examined patients who received a survey spine MR imaging in the ED at our institution between 2018 and 2022. All examinations were performed on a 1.5T GE Healthcare scanner by using our institutional CC survey protocol, which includes sagittal T2WI and STIR sequences through the cervical, thoracic, and lumbar spine. Examinations were read by a blinded, board-certified neuroradiologist. RESULTS:A total of 2002 patients received a survey spine MR imaging protocol during the study period. Of these patients, 845 (42.2%, mean age 57 ± 19 years, 45% women) received survey spine MR imaging examinations for the suspicion of CC, and 120 patients (14.2% positivity rate) had radiographic CC. The survey spine MR imaging averaged 5 minutes and 50 seconds (79% faster than routine MR imaging). On multivariate analysis, trauma, back pain, lower extremity weakness, urinary or bowel incontinence, numbness, ataxia, and hyperreflexia were each independently associated with CC. Of the 120 patients with CC, 71 underwent emergent surgery, 20 underwent nonemergent surgery, and 29 were managed medically. CONCLUSIONS:The survey spine protocol was positive for CC in 14% of patients in our cohort and acquired at a 79% faster rate compared with routine total spine. Understanding the positivity rate of CC, the clinical symptoms that are most associated with CC, and the subsequent care management for patients presenting with suspected cord compression who received the survey spine MR imaging may better inform the broad adoption and subsequent utilization of survey imaging protocols in emergency settings to increase throughput, improve allocation of resources, and provide efficient care for patients with suspected CC.

Endovascular thrombectomy (EVT) has revolutionized large vessel occlusion (LVO) stroke management, but often requires advanced imaging. The collateral pattern on CT angiograms may be an alternative because a symmetric collateral pattern correlates with a slowly growing, small ischemic core. We tested the hypothesis that such patients will have favorable outcomes after EVT. Consecutive patients (n = 74) with anterior LVOs who underwent EVT were retrospectively analyzed. Inclusion criteria were available CTA and 90-day modified Rankin Scale (mRS). CTA collateral patterns were symmetric in 36%, malignant in 24%, or other in 39%. Median NIHSS was 11 for symmetric, 18 for malignant, and 19 for other (p = 0.02). Ninety-day mRS ≤2, indicating independent living, was achieved in 67% of symmetric, 17% of malignant, and 38% of other patterns (p = 0.003). A symmetric collateral pattern was a significant determinant of 90-day mRS ≤2 (aOR = 6.62, 95%CI = 2.24,19.53; p = 0.001) in a multivariable model that included age, NIHSS, baseline mRS, thrombolysis, LVO location, and successful reperfusion. We conclude that a symmetric collateral pattern predicts favorable outcomes after EVT for LVO stroke. Because the pattern also marks slow ischemic core growth, patients with symmetric collaterals may be suitable for transfer for thrombectomy. A malignant collateral pattern is associated with poor clinical outcomes.