Background: Pain assessment in animal models is challenging, as behavioral tests often lack sensitivity. Particularly under analgesia, it is unclear whether pain occurs without medication. Imaging of pain-associated pathways, such as σ1 receptor (σ1R) expression, offers a promising approach to better understand underlying mechanisms. Therefore, this study evaluated [¹⁸F]fluspidine positron emission tomography/computed tomography (PET/CT) imaging for detecting σ1R-mediated pain after partial liver resection in rats.
Materials and methods: Postoperative pain was assessed in eighteen female Wistar rats undergoing skin incision or partial liver resection. Nine untreated rats served as controls. Carprofen was administered for three consecutive days after surgery. PET/CT imaging was performed on postoperative days 1, 4, and 7. At each time point, organs and incision sites of three animals were harvested for histological analysis. Postoperative pain and welfare were monitored by observational score sheets, the Open Field test, Rat Grimace Scale, Von Frey test, fecal corticosterone metabolites, and hemograms.
Results: Despite analgesic treatment, PET/CT and immunohistochemistry revealed elevated σ1R expression at the abdominal incision site on day 1 after partial liver resection in comparison to the other groups, likely due to the additional peritoneal opening. σ1R expression normalized by day 4. No behavioral indicators of pain or distress were observed, though mechanical hypersensitivity was detected on day 4 in all groups, likely due to carprofen side effects.
Conclusion: [18F]Fluspidine PET/CT imaging sensitively detected postoperative pain-associated σ1R expression independent of analgesia. This imaging modality could remarkably refine pain monitoring, opening to further studies using different pain and analgesia models.
Relevance statement: [¹⁸F]Fluspidine PET/CT imaging demonstrates high sensitivity in detecting pain-associated σ1R upregulation despite non-steroidal anti-inflammatory drug administration. This approach offers valuable insights for refining pain assessment, improving severity grading, and enhancing the reliability and translational value of preclinical pain models.
Key points: PET/CT imaging with [18F]fluspidine sensitively detects pain-associated σ1R expression post-liver resection. Necessary analgesia interferes with some behavioral tests, limiting their reliability for pain assessment. [18F]Fluspidine detects peripheral σ1R upregulation despite non-steroidal anti-inflammatory drug analgesia. Imaging pain-associated receptors provides valuable insights for refining preclinical pain monitoring.
Phantom studies are essential in medical imaging, offering a controlled and reproducible framework for evaluating imaging technologies across all modalities. Phantoms, whether physical (synthetic, biological, or mixed) or computational, simulate human tissues or anatomical structures and serve roles in technology validation, performance benchmarking, protocol optimization, quality assurance, and artificial intelligence development. We provide recommendations for designing and conducting phantom studies in medical imaging (PSMI). Key aspects include phantom selection, image acquisition protocols, and analysis strategies, particularly when image quality is evaluated in relation to radiation dose or contrast agent optimization. Quantitative image analysis is considered with emphasis on signal-to-noise ratio, contrast-to-noise ratio, and spatial resolution (e.g., modulation transfer function). Qualitative assessment is addressed considering reader selection and training, blinding, randomization, and use of absolute or relative Likert scales. Brief recommendations for sample size calculation, data reporting, and statistical analysis are provided, covering continuous/ordinal data, inter-rater agreement, and group comparisons. A checklist is provided to allow authors to document adherence to these recommendations and to identify shortcomings, limitations, and weaknesses in their phantom studies. The PSMI checklist is proposed to promote transparency, reproducibility, and critical appraisal, containing 25 items regarding: title/abstract (1, 2); background/introduction (3); methods/study design (4); methods/phantom description (5-7); methods/imaging protocol (8, 9); methods/image analysis (10, 11); methods/statistics (12-15); results/quantitative analysis (16, 17); results/qualitative analysis (18); results/tables and figures (19); discussion (20-23); and conclusions (24, 25). Finally, the importance of maintaining a clinical perspective is underscored, highlighting how well-designed phantom studies can inform, but not replace, clinical validation. RELEVANCE STATEMENT: This paper provides comprehensive recommendations for designing and conducting PSMI. The use of the PSMI checklist may contribute to increasing the quality of phantom studies. KEY POINTS: Phantom studies provide controlled, reproducible evaluation of imaging technologies. Phantoms simulate human tissues for validation, optimization, and AI development. Good design includes proper phantom selection and analysis strategies. Clinical relevance must guide interpretation; phantoms cannot replace clinical validation. The proposed 25-item PSMI checklist supports transparent and reproducible phantom study reporting.
Background: We aimed to evaluate longitudinal changes in ultrashort echo time (UTE) two-component biomarkers reflecting graft ligamentization after anterior cruciate ligament (ACL) reconstruction and to identify associated clinical factors.
Materials and methods: Patients who underwent ACL reconstruction were prospectively included to perform 3-T three-dimensional double-echo UTE sequence at 3, 6, and 12 months postoperatively. Mean values of short T2* (T2*s), long T2* (T2*l), and fast fraction (FF), i.e., the signal proportion attributed to the T2*s component, were calculated by fitting a biexponential model. Changes were analyzed using repeated measures analysis of variance-ANOVA. Multiple linear regression was used to assess associations between clinical factors and UTE parameters at 12 months.
Results: Forty-two patients (20 males), aged 32.7 ± 15.0 years (mean ± standard deviation), were enrolled. T2*s and T2*l increased from 3 to 6 months (T2*s, 5.3 to 5.7 ms; p = 0.017; T2*l, 21.1 to 23.3 ms; p < 0.001), then decreased from 6 to 12 months (T2*s, 5.7 to 5.0 ms; T2*l, 23.3 to 21.1 ms; both p < 0.001). FF followed the opposite trend, decreasing from 0.29 to 0.25, then increasing to 0.30 (both p < 0.001). At 12 months, a higher body mass index (BMI) was associated with elevated T2*s (p = 0.005), while semitendinosus-gracilis (STG) grafts (p = 0.018) and remnant preservation (p = 0.004) were associated with lower T2*s values.
Conclusion: UTE two-component analysis captures temporal changes in graft after ACL reconstruction, suggesting collagen regeneration. Higher BMI may hinder, while STG grafts and remnant preservation may promote ligamentization.
Relevance statement: UTE two-component analysis serves as an imaging biomarker for ACL graft ligamentization, with higher BMI being associated with impaired ligamentization, while the use of STG grafts and remnant preservation may be associated with more favorable graft maturation at 12 months as assessed by UTE two-component MRI. These findings may help tailor rehabilitation protocols and guide graft selection.
Trial registration: This study was prospectively registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) under the identification number UMIN000045710 in October 2021.
Key points: Ultrashort echo time two-component analysis noninvasively evaluates ligamentization of reconstructed ACL. Graft short T2* significantly decreased between 6 and 12 months postoperatively. Body mass index, graft type, and remnant status may influence graft maturation at 12 months.
Recent advances in magnetic resonance imaging (MRI) hardware and software have renewed interest in low-field MRI, challenging the long-held notion that such systems are inherently inferior to high-field counterparts. Traditionally dismissed due to lower signal-to-noise ratios and reduced image quality, low-field MRI was primarily relegated to cost-sensitive or resource-limited settings. However, modern low-field systems now integrate advanced reconstruction algorithms, refined imaging techniques, and improved hardware design, significantly narrowing the performance gap. In some scenarios, these systems offer distinct advantages, such as reduced susceptibility artifacts and improved safety of metallic implants. Their portability, lower operational costs, and reduced infrastructure demands make them especially valuable in point-of-care, remote, or intraoperative environments. This review examines the physical principles of low-field MRI, traces its technological evolution, and evaluates its current and emerging clinical applications. By highlighting both its strengths and limitations, we aim to clarify the growing role of low-field MRI in contemporary diagnostic imaging and underscore its potential in expanding global access to high-quality radiological care. RELEVANCE STATEMENT: Low-field and portable MRI systems offer a cost-effective, accessible, and safer imaging alternative that may expand diagnostic capabilities in underserved, point-of-care, and intraoperative settings, thereby improving global access to essential radiologic services. KEY POINTS: Advanced image reconstruction improves low-field MRI image quality and diagnostic utility. Reduced susceptibility artifacts enhance imaging near metallic hardware and air-tissue interfaces. Low-field systems enable cost-effective, portable imaging in constrained clinical environments.
Background: Aortic dissection (AD) is a life-threatening condition. We developed an artificial intelligence (AI) algorithm capable of robust, accurate, and automated AD detection and sub-classification.
Materials and methods: Based on 2010-2023 data from Mannheim University Medical Centre, heterogeneous internal training cases with confirmed AD (n = 70) were manually segmented and, together with non-AD cases (n = 87), used for training of a convolutional neural network (CNN; U-Net architecture) configured using the nnU-Net framework. Internal test dataset was composed of 106 cases. The external test was performed on a public dataset: 100 AD cases from ImageTBAD, Guangdong Provincial People's Hospital, China, and 38 non-AD cases from the AVT dataset (multiple sources). Model performance was evaluated by area under the receiver operating characteristic curve (AUROC), area under the precision-recall curve (AUPRC), sensitivity, specificity, precision, and F1-score, and by investigating performance on different subsets of cases. Confidence intervals were determined using DeLong's method and bootstrapping.
Results: The best-performing algorithm achieved an AUROC of 98.7% (95% CI: 96.1-100.0%) and an AUPRC of 98.9% (96.0-100.0%) on the internal test dataset, 97.0% (94.7-99.3%) and 99.06% (98.0-99.7%) on the external test datasets, respectively. In the internal test dataset, of 15 unsuspected AD cases, 14 (93.3%) were successfully detected by the algorithm. On the external test dataset, sensitivity, specificity, precision, and F1-score were 92.0%, 100.0%, 100.0%, and 95.8%, respectively.
Conclusion: The developed AI pipeline highlighted the capability of optimized CNNs to reliably detect AD across heterogeneous multicenter datasets. The resulting tool will be made publicly available for further scientific evaluation.
Relevance statement: Artificial Intelligence demonstrated promising potential to detect AD on heterogeneous thoracic CT imaging data.
Key points: Early detection of aortic dissection (AD) is crucial for timely treatment. A modern convolutional neural network (CNN) achieved 93.5% sensitivity and 100.0% specificity for AD detection on multicenter, heterogeneous CT data. These results demonstrate the potential of streamlined, optimized CNNs for robust AD detection on CT, supporting fast clinical response.
Background: Computed tomography (CT) is widely used to diagnose peritoneal metastases (PM), with debated accuracy. Dual-energy CT (DECT) may improve accuracy, yet its diagnostic performance is still unknown. We explored the potential of DECT for PM detection and quantification.
Materials and methods: We retrospectively included patients undergoing staging DECT for cancers with a high risk of peritoneal involvement, followed by staging laparoscopy/laparotomy, which served as the reference standard. Nine readers with varying experience levels (three expert, three intermediate, and three inexpert) reviewed two sets of images, separated by ≥ 60 days, considering the presence/absence of PM, abdominal region(s) involved, and calculated the radiological peritoneal cancer index (PCI). The first set included contrast-enhanced delayed-DECT scans reconstructed as virtual 120-kVp images; the second set also included virtual monoenergetic, 40-keV images and iodine maps. Performance metrics, receiver operating characteristic (ROC) analysis, McNemar, DeLong, and Wilcoxon tests were applied.
Results: Twenty patients (mean age 64.2 years; 12 females) were included, 10 with PM. At per-patient analysis, the addition of monoenergetic 40-keV images and iodine maps slightly increased the performance and improved inter-reader agreement, with significant benefit for inexperienced readers only (p = 0.010). Per-region analysis demonstrated a significant advantage with an area under the ROC curve ranging from 0.709 to 0.766 (p < 0.001), confirmed for each reader group; in addition, the inter-reader agreement significantly improved. Quantitative analysis showed a reduction in the differences between CT results and surgical PCI by DECT (4 ± 12 versus 2 ± 9, p < 0.001).
Conclusion: DECT-derived reconstructions in the delayed-phase enhanced PM detection and quantification.
Relevance statement: Delayed-phase DECT reconstruction showed superior accuracy over conventional CT in detecting and quantifying peritoneal metastases. These findings could help establish a new standard CT protocol for malignancies with peritoneal tropism.
Key points: CT is the most widely used technique for assessing peritoneal metastases. The accuracy of CT for peritoneal metastases is debated; dual-energy CT shows promise. In our study, delayed-phase dual-energy CT provided significant advantages for all readers.
Background: To determine the feasibility of diffusion-relaxation correlation spectroscopic imaging in identifying tumoral differentiation profile and predicting cervical lymph node metastasis (CLNM) in oral tongue squamous cell carcinoma (OTSCC).
Materials and methods: This prospective study enrolled fifty-seven OTSCC patients who underwent preoperative head and neck magnetic resonance imaging (MRI). Scans with multi b-values (0-1500 s/mm2) and multi-echo times (7-150 ms) were performed to generate normalized diffusion-T2 spectra. Tumor maximal diameter and depth of invasion were measured. Tumors were segmented into five compartments (VA to VE) with metrics compared across normal controls, CLNM-, and CLNM+ groups. Pathological parameters such as tumor-stroma ratio (TSR), perineural invasion, Ki-67, tumor p53 protein, and cyclin-dependent kinase inhibitor p16 were evaluated. Correlations between MRI metrics and pathological parameters were assessed. Predictors of CLNM+ were identified using logistic regression analysis, and the predictive performance was evaluated using receiver operating characteristic analysis.
Results: Thirty-four patients were assigned to the CLNM+ group and 23 to the CLNM- group. CLNM+ patients showed larger tumor maximal diameters, deeper invasion, increased VB and VD, and decreased VA compared to CLNM- patients. VB exhibited strong positive correlations with perineural invasion and depth of invasion, while VD correlated positively with TSR. Moreover, VB and depth of invasion were independent prognostic factors for CLNM+, and their combined model achieved the highest predictive performance.
Conclusion: Diffusion-relaxation correlation spectroscopic imaging marked a significant advancement in the diagnostic and prognostic assessment of OTSCC, offering detailed tumor characterization and improving CLNM+ prediction, with great potential for accurate and non-invasive evaluation.
Relevance statement: Diffusion-relaxation correlation spectroscopic imaging metrics (VB and VD) characterized tumor heterogeneity and correlated with pathological biomarkers, making it a promising non-invasive tool for enhancing preoperative decisions and reducing unnecessary lymph node dissections in clinical workflows.
Key points: Tumoral components and heterogeneity of oral tongue cancer were investigated on MRI. Advanced diffusion-relaxation imaging delineated the tumoral differential profile and predicted metastasis. We provided a non-invasive tool for preoperative decision-making in clinical workflows.
Background: Maximum intensity projections (MIPs) facilitate rapid lesion detection both for contrast-enhanced (CE) and diffusion-weighted imaging (DWI) breast magnetic resonance imaging (MRI). We evaluated the feasibility of AI-based virtual CE subtraction MIPs as a reading approach.
Materials and methods: This Institutional Review Board-approved retrospective study includes 540 multi-parametric breast MRI examinations (performed from 2017 to 2020), including multi-b-value DWI (50, 750, and 1,500 s/mm²). A 2D U-Net was trained using unenhanced (UnE) images as inputs to generate virtual abbreviated CE (VAbCE) subtractions. Two radiologists evaluated lesion suspicion, image quality, and artifacts for UnE, VACE, and abbreviated CE (AbCE) images. Lesion conspicuity was compared between VAbCE and AbCE MIPs.
Results: Cancer detection rates for UE, VAbCE, and AbCE MIPs were 90.0%, 91.4%, and 94.3%, respectively. Single-slice reading demonstrated sensitivities of 88.6% (UnE), 91.4% (VAbCE), and 94.3% (AbCE). Inter-rater agreement (Cohen κ) for lesion suspicion scores was higher for VAbCE (0.53) than UnE alone (0.39) and comparable to AbCE (0.58). No significant difference in mean lesion conspicuity was observed for VACE MIPs compared to ACE (p ≥ 0.670). No significant difference could be observed for quality (p ≥ 0.108), and reading time (p = 1.000) between methods. Fewer visually significant artifacts could be observed in VAbCE than in AbCE MIPs (p ≤ 0.001).
Conclusion: VAbCE breast MRI improved inter-rater agreement and allowed for slightly improved sensitivity compared to UnE images, while AbCE still provided the overall highest sensitivity. Further research is necessary to investigate the diagnostic potential of VAbCE breast MRI.
Relevance statement: VAbCE breast MRI generated by neural networks allowed the derivation of MIPs for rapid visual assessment, showing a way for screening applications.
Key points: Virtual abbreviated contrast-enhanced (VAbCE) MIPs provided comparable sensitivity to MIPs of unenhanced high b-value DWI and were slightly lower than AbCE MIPs. Adding VAbCE to unenhanced high b-value DWI significantly improved interrater agreement for lesion suspicion scoring. Single-slice evaluation of VAbCE MIPs provided a sensitivity comparable to unenhanced high b-value DWI MIPs.
The study aimed to evaluate the feasibility of using cone-beam computed tomography (CBCT) for gastric volume assessment before and after endoscopic sleeve gastroplasty (ESG), focusing on patient radiation dose. Ten patients scheduled for ESG were prospectively enrolled. Each patient underwent three CBCT scans under anesthesia: two scans following CO2 insufflation of the gastric lumen-one pre-ESG and one post-ESG-and a third scan post-ESG after gastric distension with Gastrografin. Image quality was evaluated for its adequacy in generating three-dimensional reconstructions and calculating gastric volumes. Dose-area product was recorded for each scan and used to estimate the effective dose (ED) via Monte Carlo simulations using the PCXMC rotational model. Although image quality did not match conventional computed tomography (CT), it was sufficient for three-dimensional reconstruction and gastric volume measurements. The median ED was 4.2 mSv for pre-ESG scans with CO2 insufflation, 4.2 mSv for post-ESG scans with CO2 insufflation, and 4.8 mSv for post-ESG scans with Gastrografin. CBCT provided satisfactory image quality for gastric volumetry at relatively low radiation doses, with ED being approximately 50% of that of conventional CT. This preliminary feasibility study suggests that CBCT could be a useful tool for planning ESG and assessing post-procedural outcomes. RELEVANCE STATEMENT: Low-dose CBCT provided sufficient image quality for gastric volumetry in a small cohort of patients undergoing ESG, reducing radiation exposure by approximately 50% compared to conventional CT. This investigational technique enables seamless intraoperative imaging that could improve planning and evaluation of endoscopic bariatric procedures. KEY POINTS: CBCT allowed gastric volumetric assessment at a relatively low radiation dose. Scans with CO2 insufflation delivered lower radiation doses than scans with Gastrografin. Scans with CO2 insufflation showed superior image quality compared to scans with Gastrografin. CBCT could be a valuable tool for planning ESG and evaluating outcomes.
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