Background Photon-counting CT (PCCT) offers improved spatial resolution, contrast to noise ratio, and dose efficiency, but its clinical utility remains incompletely defined for breast cancer. Purpose To evaluate the feasibility of PCCT for pretreatment breast cancer assessment through comparisons with MRI, full-field digital mammography (FFDM), and fluorine 18 (18F) fluorodeoxyglucose (FDG) PET/CT. Materials and Methods In this prospective study (March-May 2025), female participants with breast lesions categorized as Breast Imaging Reporting and Data System 4C or higher at US or FFDM underwent breast MRI and multiphasic contrast-enhanced PCCT. 18F-FDG PET/CT was performed in a subset with locally advanced disease. Four radiologists independently evaluated lesion morphologic characteristics, additional findings, and clinical TNM stage. Agreement was analyzed using intraclass correlation coefficients (ICCs) and κ statistics. The diagnostic performance for additional lesions and nodal metastasis was compared with the reference standard (pathologic examination). Results Among 126 participants (mean age, 58.1 years ± 12.3 [SD]), interreader agreement across PCCT, MRI, and FFDM was good to excellent. PCCT agreed with MRI for lesion characterization (κ = 0.57-0.96) and clinical T categorization (κ = 0.86-0.88), with highest agreement with pathologic size (ICC, 0.70-0.81). For 46 pathologically confirmed additional lesions, PCCT was more sensitive than FFDM (difference, 44% [95% CI: 19, 66]) and similar to MRI (difference, 7% [95% CI: -5, 21]). Additionally, 44% (95% CI: 27, 52) of microcalcifications were missed at PCCT versus FFDM. For pathologically confirmed nodal metastasis, PCCT was more sensitive (difference, 10% [95% CI: 1, 20]) and accurate (difference, 6% [95% CI: 1, 11]) than MRI. For clinical N category, PCCT agreed with PET/CT (κ = 0.82 [95% CI: 0.62, 0.96]; n = 19). Two distant metastases identified at PCCT were consistent with 18F-FDG PET/CT and pathologic findings. Conclusion PCCT demonstrated similar performance to MRI for lesion characterization and detection of additional lesions, with better performance for nodal metastasis evaluation; however, detection of microcalcifications was limited. © RSNA, 2026 Supplemental material is available for this article.

Rationale and Objectives To evaluate the feasibility of dual-energy cardiac computed tomography (DE-CCT) in detecting left atrial fibrosis (LAF), atrial fibrillation (AF) classifications, and postablation recurrence, using left atrial cardiac magnetic resonance (LA-CMR) as reference. Materials and Methods This retrospective study included 81 pre-ablation AF patients without concomitant other arrhythmia or prior cardiac surgery. DE-CCT (utilizing dark-blood images with 5-minute post-injection iodine quantification) was quantitatively compared to concurrent LA-CMR to assess LAF, AF types, and recurrence risk. Results For LAF detection, dark-blood images manifested high specificity (100%, 253/253 segments), moderate sensitivity (77.07%, 242/314 segments), and satisfactory accuracy (87.30%, 495/567 segments) compared with LA-CMR. Increased iodine ratio of LAF to blood pool (OR = 1.214, p = 0.041), incremental LAF segments in DE-CCT (OR = 1.739, p = 0.050), elevated brain natriuretic peptide (BNP), higher body mass index, and worse degree of left atrial volume index (LAVI) were significant risk indicators for PeAF (AUC=0.965, p<0.001). Concerning LA-CMR, independent risk factors for PeAF were also elevated LAF segments in CMR (OR = 2.108, p = 0.008), BNP levels, and LAVI grades (AUC=0.954, p<0.001). Cumulatively, 59 patients completed 1-year follow-up postablation, with 30.5% experiencing recrudescence. Significant predictors for 1-year relapse included increased LAF segments in DE-CCT (OR = 2.130, p = 0.009) or LA-CMR (OR = 1.740, p = 0.039), PeAF, thyrotoxicosis, and larger CHA2DS2-VASc scores, yielding AUCs of 0.895 (p<0.001) and 0.869 (p<0.001), respectively. No significant differences were found between DE-CCT and LA-CMR in discerning PeAF (p = 0.451) and early relapse (p = 0.114). Conclusions DE-CCT is a viable alternative for evaluating LAF, AF subtypes, and high-risk recurrence, comparable to LA-CMR, potentially enabling personalized therapy and guiding further studies on higher-resolution multi-energy CT.

Mechanical stress is a fundamental aspect of soft tissues that influences cellular behavior and tissue integrity, yet noninvasive imaging of stress in vivo remains a major challenge. Conventional magnetic resonance elastography (MRE) measures tissue stiffness but not stress. Employing a physics-informed model, we analyze reverberant shear wave fields recorded by MRE to capture the 3D mapping of tissue stress. By decomposing reverberant waves into anisotropic traveling wave components, we establish a direct relationship between wave speed, polarization, and local stress, without requiring wave direction knowledge. This method was validated with numerical simulations and phantom experiments. Applied to patients with meningiomas and pituitary adenomas, it generated high-resolution stress maps consistent with anatomy and physiology. Cortical stress measurements enabled intracranial pressure estimation, uncovering trends related to patient age and pathology. Our results demonstrate that noninvasive stress imaging provides a novel quantitative biomarker for mechanobiological research and suggests new possibilities for clinical applications.

RATIONALE AND OBJECTIVES:To evaluate the robustness and grading performance of Photon-counting CT (PCCT)-derived fat fraction (CTFF) in liver fat quantification across different protocols and cohorts with varying liver conditions, using proton density fat fraction (PDFF) as the reference. MATERIALS AND METHODS:The prospective study enrolled 297 participants in the Volunteer cohort. Participants were randomly assigned to 120-kVp or 140-kVp groups and subdivided into high- and low-dose subgroups for technical validation. Clinical validation was performed in two cohorts: participants with metabolic dysfunction-associated steatotic liver disease (MASLD, n = 86) and heterogeneous liver diseases (HLD, n = 61). PCCT and PDFF (reference standard for grading) were performed within 1 month. Statistical analyses included intraclass correlation coefficients, Bland-Altman analysis, Mann-Whitney U and Kruskal-Wallis tests, and areas under the receiver operating characteristic (AUC-ROC) and precision-recall curves (AUC-PR). RESULTS:Overall, 444 participants were included (age 44.9 ± 14.3 years; 264 men). In the Volunteer cohort, CTFF showed excellent agreement with PDFF (all ICCs = 0.98; R2 ≥0.96) with a maximum bias of 0.80% (95% CI: 0.70-0.89%), across the whole-cohort and subgroups. No significant differences in the absolute error between PDFF and CTFF were observed across all subgroups (all p > 0.05). CTFF achieved high diagnostic accuracy for both the detection and grading of steatosis with all AUC-ROC and AUC-PR exceeding 0.99. The diagnostic accuracy of CTFF was verified in the MASLD and HLD cohorts. CONCLUSION:CTFF demonstrated excellent agreement with PDFF and consistent diagnostic performance across diverse scan settings and liver conditions.

Background Photon-counting CT (PCCT) can theoretically be used to quantify extracellular volume fraction (ECV) for liver fibrosis assessment, but its performance remains unclear. Purpose To determine the feasibility of PCCT-derived ECV for staging liver fibrosis by assessing its correlation with MR elastography-derived liver stiffness measurement (LSM) and comparing their diagnostic performance, using histopathologic findings as the reference standard. Materials and Methods Between July 2024 and July 2025, 157 participants with suspected hepatic malignancies were prospectively enrolled and underwent PCCT and MRI at Ruijin Hospital. Intraparticipant comparisons of ECV and LSM were performed, and their diagnostic performance in staging liver fibrosis was evaluated using histopathologic findings as the reference standard. Subgroup analyses of fibrosis staging using ECV were performed among participants with coexisting steatosis or inflammation and participants with a body mass index of 25 or higher. Correlation, receiver operating characteristic, and equivalence analyses were performed. Results Ultimately, 139 participants (mean age, 62 years ± 8 [SD]; 114 male) were included. ECV was strongly correlated with LSM (Spearman ρ = 0.84; P < .001) in an intraparticipant-level comparison. When histopathologic examination was used as the reference standard, the area under the receiver operating characteristic curve (AUC) values for ECV were 0.99 (95% CI: 0.98, 1.00), 0.98 (95% CI: 0.96, 1.00), and 0.98 (95% CI: 0.96, 1.00) for participants with fibrosis stages F2 or higher, F3 or higher, and F4, respectively. Equivalence analysis revealed comparable diagnostic performance between ECV and LSM (95% CI differences in AUCs: 0.005, 0.055 for stage F2 or higher; -0.015, 0.027 for stage F3 or higher; and -0.021, 0.012 for stage F4). With use of the cutoffs derived from the whole-group analysis, ECV showed excellent agreement with histopathologic stage overall and across each subgroup (all weighted κ coefficients ≥0.86; P < .001 for all). Conclusion PCCT-derived ECV was strongly correlated with MR elastography-derived LSM and showed equivalent, clinically feasible performance for liver fibrosis staging. © RSNA, 2026 Supplemental material is available for this article. See also the editorial by Wu and Shi in this issue.

Disrupted midbrain energy homeostasis, derived from phosphorus 31 ( 31 P) MR spectroscopy, effectively differentiated early-stage Parkinson disease from its mimics, outperforming conventional hydrogen 1 MRI markers for iron and neuromelanin, establishing 31 P MR spectroscopy as a promising diagnostic tool.

BACKGROUND AND PURPOSE:The diagnostic performance of ultra-high-resolution (UHR) photon-counting detector (PCD) CTA for evaluating cerebral and carotid artery stenosis remains unclear. This study aimed to compare UHR PCD-CTA with standard resolution (SR) CTA for stenosis assessment, using DSA as the reference standard. MATERIALS AND METHODS:In this cohort study, participants with suspected cerebral and carotid artery stenosis, who were indicated for CTA examination were prospectively enrolled from September 2023 to April 2024. All participants were examined with a photon-counting CT scanner, and both UHR and SR-CTA reconstructions were generated from the same raw data. The quantitative diameter stenosis (DS) was computed for each lesion by blinded independent reading. The correlation and agreement analyses were performed using DSA as the reference standard. Stenosis was graded into 4 categories (<30%, 30%-50%, 50%-70%, ≥70%), with categoric agreement assessed using weighted κ statistics. RESULTS:Among 40 participants (age: 63.2 ± 9.2 years; 16 men), a total of 54 stenoses were recorded (DS: 44.1% ± 18.4%). Compared with SR-CTA, UHR PCD-CTA demonstrated significantly stronger correlation (r = 0.94 [95% CI, 0.90-0.97] versus r = 0.70 [95% CI, 0.54-0.82]; P < .001) and agreement (mean difference: -0.00 ± 0.06 versus 0.01 ± 0.14, variance difference test P < .001) with DSA in evaluating DS. Across 4 stenosis categories, UHR-CTA demonstrated significantly higher overall accuracy (77.8% versus 53.7%; P = .004) and stronger agreement with DSA (weighted κ = 0.79 versus 0.53; P = .004) compared with SR-CTA. In calcified lesions, UHR-CTA retained significantly higher agreement with DSA than SR-CTA (weighted κ = 0.76 versus 0.35; P = .001). In lesions with small residual lumen (minimum lumen diameter ≤2.0 mm), UHR-CTA showed no statistically significant deviation from DSA (-0.02 ± 0.06; P = .10), whereas SR-CTA significantly underestimated stenosis severity (-0.06 ± 0.12; P = .03). CONCLUSIONS:UHR PCD-CTA showed superior correlation and agreement with DSA compared with SR-CTA in the assessment of cerebral and carotid artery stenosis, with particular advantages in calcified lesions and vessels with small residual lumen. These findings support its role as a reliable noninvasive tool for cerebrovascular stenosis assessment, with direct implications for clinical management and treatment decisions.

Exogenous free radicals oxidize and damage tumor proteins, but their non-specific reactivity also causes unintended harm to tumor-suppressive proteins, which compromises the therapeutic efficacy. Here we show a nanosystem that generates in-situ radical-conjugated species with predefined targeting capability toward oncogenic protein. This nanosystem consists of lipid nanoparticles encapsulating polyphenolic tannic acid and hydrophobic calcium peroxide nanoparticles in spatially segregated compartments. Upon cellular uptake, the components are released into the cellular membrane through membrane fusion. Consequently, calcium peroxide nanoparticles act as oxidizing agents, radicalizing tannic acid, which generates gallic acid species conjugated with phenoxyl radicals. Since gallic acid confers specific binding affinity for the oncogenic GPC-3 protein in hepatocellular carcinoma, the radical-conjugated species integrate dual functionalities: a targeting module that binds to the oncogenic GPC-3 protein, and a stabilized phenoxyl radical inducing site-specific oxidative damage. These species direct to GPC-3 and induce localized disruption of critical peptide segments and lipid domains, triggering protein cleavage and membrane shedding, which suppresses downstream signaling including the canonical Wnt/β-catenin pathway and finally inhibits hepatocellular carcinoma progression. By enabling site-specific radical delivery, this strategy achieves precise inactivation of predefined oncogenic targets and establishes a framework for molecularly free-radical-mediated antitumor therapy. Exogenous free radicals oxidize and damage proteins of tumor cells but the lack of specificity compromises the therapeutic efficacy. Here this group reports a nanosystem enabling the in-situ generation of radical-conjugated species targeting oncogenic GPC-3 in hepatocellular carcinoma (HCC), thereby achieving targeted free radical-mediated anti-HCC therapy.

This case report describes a patient with left-sided weakness following transient ischemic attacks who underwent external carotid angioplasty based on findings from ultrahigh-resolution photon-counting computed tomographic angiography (CTA).

Background Whether phosphorus 31 (31P) MR spectroscopy outperforms or complements conventional hydrogen 1 (1H) MRI biomarkers in the differential diagnosis of early-stage Parkinson disease (PD) remains unclear. Purpose To evaluate 31P MR spectroscopy and its integration with conventional 1H MRI for discriminating early-stage PD from mimics. Materials and Methods This prospective study consecutively enrolled participants with early-stage PD, participants with PD mimics, and controls (November 2023 to October 2024). Participants underwent 31P MR spectroscopy for inorganic phosphate (Pi), phosphocreatine (PCr), and adenosine triphosphate (ATP); quantitative susceptibility mapping for iron; and neuromelanin-sensitive MRI. Intergroup imaging differences were assessed using multivariable general linear models, and partial correlations with clinical scores were analyzed. A penalized logistic regression classifier evaluated discrimination performance of energy metabolites, alone and combined with iron and/or neuromelanin. Results Seventy-two participants with early-stage PD (mean age, 60.1 years ± 6.8 [SD]; 44 male participants), 34 with PD mimics (mean age, 62.1 years ± 7.9; 18 male participants), and 46 controls (mean age, 56.3 years ± 9.6; 33 female controls) were included. Early-stage PD showed a decreased Pi/PCr ratio (mean, 0.47 [95% CI: 0.44, 0.50] vs 0.57 [95% CI: 0.52, 0.63]) and an increased total ATP/Pi ratio (mean, 4.89 [95% CI: 4.57, 5.24] vs 4.06 [95% CI: 3.50, 4.68]) in the left midbrain compared with participants with PD mimics (both Bonferroni-corrected P < .05). The Pi/PCr ratio correlated with nonmotor symptom scores (r = 0.42; 95% CI: 0.12, 0.69; P = .008) and autonomic symptom scores (r = 0.60; 95% CI: 0.34, 0.80; P < .001) in PD. Energy metabolites outperformed both iron (area under the receiver operating characteristic curve [AUC], 0.90 vs 0.50; P < .001) and neuromelanin (AUC, 0.90 vs 0.64; P = .04) in differentiating PD from mimics. There was no evidence that combining iron and/or neuromelanin improved AUC over energy metabolites alone (0.90 vs 0.90 with the addition of iron [P > .99] vs 0.91 with the addition of neuromelanin [P = .70] vs 0.93 with the addition of both [P = .42]). Conclusion 31P MR spectroscopy revealed disrupted midbrain energy homeostasis in early-stage PD and effectively helped differentiate it from mimics. © RSNA, 2026 Supplemental material is available for this article.

BACKGROUND:Observational studies have suggested that brain imaging-derived phenotypes (IDPs) may serve as specific markers of pain-related phenotypes and severity. However, the shared genetic architecture between pain and brain IDPs and their potential causal relationships remains unclear. METHODS:We applied linkage disequilibrium score regression and Mendelian randomization (MR) analyses to uncover genetic correlations and potential causal links of brain structural (33,224 UK Biobank participants) and functional (47,276 UK Biobank participants) changes with site-specific pain phenotypes (approximately 500,000 Finngen participants). The scoping literature review was conducted to compare current findings with previous observational studies. RESULTS:In this study, we identified 559 significant genetic correlations between 587 structural IDPs and 13 pain-related phenotypes. Using MR analyses, we found that genetic liability to headache, migraine, joint pain, and sciatica was causally associated with alterations in 15 structural IDPs. Additionally, changes in the surface area of three brain regions were linked to a lower risk of sciatica, low back pain, and overall pain. Among the six pain-related phenotypes associated with structural IDPs, further analyses demonstrated putative causal relationships between functional IDPs and these conditions. Notably, headache exhibited both significant structural and functional changes across three key brain regions: the superior frontal gyrus, lingual gyrus, and paracentral lobule. CONCLUSIONS:These findings provide novel insights into the genetic correlations and genetically inferred associations between pain and neurobiological abnormalities from neuroimaging perspectives, with structural alterations as the primary findings and functional changes as complementary exploratory evidence, advancing the understanding of pain-related mechanisms.

Substantial asymmetries of motor dysfunction are evident in patients with Parkinson’s disease (PD), the mechanisms of which remain largely unexplored. This study investigated how deep brain stimulation (DBS) targeting the globus pallidus interna (GPi) and subthalamic nucleus (STN) modulates characteristics of hemispheric lateralization in PD patients, with particular emphasis on motor asymmetries and hemispheric integration (via homotopic functional connectivity) and segregation (via hemispheric asymmetry in connectivity). Resting-state functional magnetic resonance imaging (fMRI) and Unified Parkinson’s Disease Rating Scale (UPDRS) III scores were analyzed from 55 PD patients who underwent either bilateral GPi- or STN-DBS. Both targets produced significant improvements in motor function. Notably, stimulation effects on motor asymmetry depend on patients’ baseline asymmetry direction (DBS OFF): STN-DBS consistently reduced asymmetry in the leftward-asymmetry patients, whereas GPi-DBS has stronger effects in rightward patients. In both cases, stimulation led to a more symmetric pattern. Beyond motor outcomes, motor gains were associated with changes in homotopic connectivity in the lateral occipital region, overlapping the extrastriate body area, suggesting a compensatory role of visual networks. These findings highlight the contribution of the visual networks to motor improvement and reveal target-dependent effects of DBS on both motor asymmetry and non-motor cognitive domains.

Abstract Objectives This study aimed to develop and validate a fat-corrected virtual magnetic resonance elastography (FC-vMRE) framework based on diffusion-weighted imaging (DWI) to assess liver fibrosis in patients with metabolic dysfunction-associated steatotic liver disease (MASLD). Materials and methods A total of 463 MASLD patients underwent multi-b-values (0–1500 s/mm²) DWI acquisition, proton density fat fraction (PDFF), and conventional magnetic resonance elastography (MRE). Apparent diffusion coefficient (ADC) parameters were calculated with or without fat correction (based on PDFF). Using the training cohort (n = 361), ADC-to-MRE formulas were derived to compute virtual MRE (vMRE) and FC-vMRE. In the validation cohort (n = 102, with biopsy), the diagnostic performance of vMRE, FC-vMRE, and MRE for fibrosis staging was compared. Results ADC200-1200 demonstrated the strongest correlation with MRE values (R = −0.706, p < 0.001), yielding the formula: FC-vMRE = 6.50 − 3.13 × ADCw. Compared with vMRE, FC-vMRE showed superior agreement with MRE (bias: −0.001 kPa vs 0.469 kPa; intraclass correlation coefficient: 0.666 vs 0.381). In staging performance, FC‑vMRE significantly outperformed vMRE across all fibrosis stages. FC-vMRE showed promising diagnostic performance to MRE in detecting ≥ F2 fibrosis (AUC: 0.761 vs 0.848, p = 0.053), ≥ F3 fibrosis (AUC: 0.756 vs 0.818, p = 0.066), and cirrhosis (AUC: 0.838 vs 0.914, p = 0.065). Conclusion FC-vMRE provides a clinically promising alternative requiring only standard MRI equipment, effectively correcting for fat-related confounding in MASLD, and demonstrating encouraging diagnostic concordance with MRE and histology. This approach shows potential for broader clinical implementation. Critical relevance statement Fat-corrected virtual MRE using diffusion-weighted imaging provides promising fibrosis staging accuracy to conventional magnetic resonance elastography in metabolic dysfunction-associated steatotic liver disease patients without requiring specialized hardware. Key Points Fat infiltration confounds diffusion measurements in metabolic steatotic liver disease. Fat-corrected virtual MRE showed superior agreement with standard MRE. Hardware-free fibrosis assessment enables accessible liver stiffness measurement. Graphical Abstract

REM sleep behavior disorder (RBD) in Parkinson's disease (PD) marks a more aggressive subtype. While mitochondrial dysfunction, iron deposition, and neuromelanin loss are central to PD pathobiology, their contributions to RBD in PD remain unclear. This study noninvasively compared brain bioenergetics, phospholipid metabolism, iron accumulation, and neuromelanin integrity across PD patients with RBD (PD-RBD), without RBD (PD-noRBD), and healthy controls (HCs) to identify RBD-related metabolic alterations. Twenty-six PD-RBD, 46 PD-noRBD, and 48 HCs were recruited consecutively. All participants underwent 3T MRI, including phosphorus-31 MR spectroscopic imaging (31P-MRSI), quantitative susceptibility mapping (QSM), and neuromelanin-sensitive MRI (NM-MRI), all acquired in a standardized OFF-medication state (≥12 h withdrawal). Phosphorus metabolites included phosphoethanolamine (PE), total adenosine triphosphate (tATP), phosphodiester (PDE), and others. Group differences and associations with clinical scales were analyzed, and PD subtype discrimination performance was assessed using ROC analysis. PD-RBD patients demonstrated right basal ganglia metabolic alterations characterized by elevated α-ATP/Pi (p = 0.003 vs HCs) and PCr/Pi ratios (p = 0.001 vs HCs), together with reduced PE-related phospholipid turnover indices, including lower PE/tATP relative to PD-noRBD (p = 0.003). In contrast, PD-noRBD showed milder alterations primarily involving high-energy phosphate metabolism compared with HCs, whereas phospholipid turnover remained relatively preserved. No significant differences in iron or neuromelanin measures were observed between PD-RBD and PD-noRBD groups. However, both PD subgroups showed significantly reduced neuromelanin-related contrast in the substantia nigra compared to HCs. PE/tATP (R = -0.350, p < 0.01) and PE/PDE ratios (R = -0.441, p < 0.001) were negatively correlated with RBD symptom severity across the PD cohort. 31P-MRSI demonstrated superior discrimination performance (AUC = 0.80) compared with QSM (AUC = 0.72) or NM-MRI (AUC = 0.69), while multimodal integration achieved the highest diagnostic accuracy (AUC = 0.86). These findings support a role for altered bioenergetic and membrane phospholipid metabolism in PD-RBD and highlight 31P-MRSI as a promising imaging approach for characterizing PD heterogeneity.

Background: Asymptomatic structural joint abnormalities are prevalent among athletes, yet studies on their multi-joint distribution and comparisons with low-activity controls remain lacking. This article evaluated the prevalence and characteristics of asymptomatic structural abnormalities across joints in collegiate athletes compared with controls using 3.0-T MRI. Methods: The cross-sectional study enrolled 53 asymptomatic elite collegiate athletes (high physical activity, HPA) and 84 healthy volunteers (low physical activity, LPA) aged 18-25 years. All participants were asymptomatic with no history of joint trauma or surgery. Generalized estimating equation (GEE) logistic regression was employed to identify independent risk factors for joint abnormalities after evaluation. Results: A total of 666 joints were analyzed. Participants with at least one joint abnormality were significantly more common in the HPA group than LPA group (49.1% vs. 6.0%, p < 0.001). At the joint level, overall abnormality prevalence was 13.5% versus 2.2%, respectively. In the HPA group, knee joints were the most frequently affected (24.2%), predominantly involving meniscal lesions. Shoulder pathologies consisted exclusively of supraspinatus tendon lesions (6.8%), while ankle abnormalities were primarily bone marrow edema (5.9%). GEE analysis identified high physical activity (adjusted OR = 5.23; 95% CI: 1.55-17.71; p = 0.008) and elevated BMI (adjusted OR = 1.09 per kg/m2; 95% CI: 1.03-1.15; p = 0.001) as independent risk factors. Conclusions: Asymptomatic abnormalities are highly prevalent and demonstrate intra-individual clustering across multiple joints. MRI-based surveillance represents a promising strategy for early risk identification and injury prevention.

Background Accurate detection and morphology evaluation of unruptured intracranial aneurysms (UIAs) are essential for patient management. This study aimed to assess the efficacy of ultra-high-resolution (UHR) photon-counting detector-CT angiography (PCD-CTA) in detecting UIAs and characterizing their morphological features. Methods This prospective study recruited consecutive participants suspected of cerebral vascular diseases who underwent PCD-CTA and subsequent digital subtraction angiography (DSA) within 1 month from September 2023 to May 2024. Performance of UIA diagnosis using UHR PCD-CTA images (slice thickness 0.2 mm) and standard resolution (SR, reflecting clinical protocols) reconstructed images were compared with DSA as reference on a per-participant, per-vessel, and per-aneurysm basis. The inter-rater agreement for UIA detection and aneurysm morphology characterization using UHR/SR PCD-CTA was also evaluated. Results Among 95 participants, 50 UIAs were confirmed in 42 participants using DSA. The inter-rater agreement for UIA detection was: kappa 0.95 for UHR and 0.89 for SR (p<0.05). On a per-aneurysm basis, the sensitivity, specificity, and diagnostic accuracy of UHR (98.0%, 96.7%, 97.3%) were all significantly higher than SR (72.0%, 86.7%, 80.0%) (p<0.05). UHR PCD-CTA accurately identified 13 of the 14 aneurysms (93%) missed by SR PCD-CTA, including 3 cases (21%) larger than 3 mm. Furthermore, UHR identified more aneurysm irregularity (18/50, 36%) than SR (5/50, 10%) (p=0.004). UHR also revealed 4 (8.0%) more cases with wall calcification and 3 (6.0%) more cases with intra-aneurysmal hypointensity (possible thrombus) than SR. Conclusions The advantages of UHR PCD-CTA, including enhanced reliability, improved diagnostic accuracy, and more comprehensive information, have the potential to significantly optimize UIA management.

Accurate quantification of arterial blood T2 can be useful for non-invasive assessment of blood oxygenation and blood-brain barrier (BBB) function. While arterial spin labeling (ASL) combined with multi-echo readouts offers a contrast-agent-free approach to map arterial blood T2, in vivo applications remain challenging due to rapid signal decay and low signal-to-noise ratio (SNR) at longer echo times (TEs), likely leading to overestimation of T2 values. We propose a novel temporal evolution acquisition based ASL (TEA-ASL) sequence incorporating an optimized variable refocusing flip angle (RFA) train to preserve signal across all TEs. Data were acquired on a 5T MRI system combining a pseudo-continuous ASL (pCASL) with the proposed TEA readout with 12 echo times (32-384 ms). The variable RFA scheme significantly improved signal stability across the echo train compared to conventional acquisition with constant RFAs. Accuracy and clinical feasibility of the proposed method was validated by simulations, phantom scans, in-vivo test/retest experiments and in a patient with middle cerebral artery stenosis. The proposed TEA-ASL technique provides robust arterial T2 mapping at ultra-high field, offering a promising tool for probing oxygenation-related hemodynamics and BBB-associated pathophysiology. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Our institute receives funding from United Imaging Healthcare Co., Ltd. ### 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: This study was approved by the Ethics Committee of Ruijin Hospital, Shanghai Jiao Tong University (IRB number: RJ2025300). Informed consent was obtained from all participants. 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 Data and code used in this paper can be shared upon request to the corresponding author.

Objectives To compare the performance of low-dose (LD) ultrahigh-resolution (UHR) photon-counting detector (PCD) CT with energy-integrating detector (EID) CT for sacroiliac joint assessment in axial spondyloarthritis (axSpA). Materials and Methods This was a prospective randomized study. AxSpA patients were enrolled and assigned to LD or clinical dose (CD) groups. Patients underwent UHR PCD-CT of the sacroiliac joints at low radiation dose (IQ level, 30), followed by EID-CT scanning using either LD (matched to PCD-CT dose) or CD protocols (108 quality reference mAs). Image noise, signal-to-noise ratio, interobserver reproducibility, subjective image quality, diagnostic confidence, and structural damage scores were evaluated by two radiologists and compared. Results In total, 40 patients were enrolled (LD group: n = 20, 36.5 ± 9.8 years, 8 females; CD group, n = 20, 35.5 ± 8.8 years, 8 females). Compared with CD EID-CT, PCD-CT delivered lower effective dose (0.63 ± 0.23 mSv vs. 1.79 ± 1.05 mSv, p < 0.001), and exhibited higher image noise (p < 0.001) and lower SNR (p < 0.001). Interobserver reproducibility of subjective image quality and diagnostic confidence on PCD-CT (substantial to almost perfect) was higher than LD EID-CT. PCD-CT provided better subjective image quality, diagnostic confidence, and structural lesion scores than LD EID-CT. PCD-CT showed higher subjective image quality for erosions and joint space changes while yielding higher erosion and sclerosis scores than CD EID-CT. Conclusion LD UHR PCD-CT reduced radiation dose by 65% compared with CD EID-CT, and improved structural lesion visualization and diagnostic confidence compared with both LD and CD EID-CT.