Biophysical diffusion MRI models such as Neurite Exchange Imaging (NEXI) are essential for probing gray matter microstructure, estimating compartment diffusivities (Di , De ), neurite fraction (f), and exchange time (tex ). However, NEXI multi-shell, multi-diffusion-time requirements lead to prohibitively long acquisitions. Leveraging the Connectome 2.0 ultra-high gradient scanner, we developed a time-efficient protocol using an Explainable AI (XAI) framework. Combining XGBoost, SHAP, and Recursive Feature Elimination trained on synthetic signals, XAI identified an optimal 8-feature subset, halving scan time from 27 to 14 minutes. Validated in vivo in 7 healthy participants, the XAI protocol was benchmarked against the full 15-feature acquisition, a Cramér-Rao Lower Bound (CRLB) theoretical optimum, and 2 expert-designed heuristics ("Mid-Range" and "Corner"). The XAI protocol robustly reproduced parameter estimates and maintained full protocol test-retest reproducibility. Remarkably, the data-driven XAI selection converged to the theoretical CRLB optimum. This validates XAI mathematical optimality while highlighting its primary advantage: achieving gold-standard optimization without requiring complex analytical Jacobians, making it effortlessly adaptable to numerically defined models or complex noise distributions where CRLB becomes intractable. Furthermore, XAI demonstrated superior in vivo robustness compared with heuristics: "Mid-Range" sampling yielded biased tex estimates due to insufficient temporal diversity, while "Corner" sampling yielded unstable Di estimates (fivefold higher coefficient of variation) due to noise sensitivity. Ultimately, this robust 14-minute NEXI protocol accelerates exchange-sensitive microstructural mapping, establishing a generalizable, model-agnostic optimization framework adaptable to future ultra-high gradient systems (e.g., Siemens Cima.X or GE MAGNUS) and existing clinical scanners.

The assessment of brain function using PET imaging has recently gained increasing interest due to several technical advancements, including bolus+infusion radiotracer administration protocols combined with hybrid PET/MR or high-sensitive PET/CT scanners. Functional PET (fPET) enables imaging of stimulation-induced changes in glucose metabolism and neurotransmitter action in a single scan as well as computation of molecular connectivity represented by temporal associations of PET signals between brain regions. In addition to methodological considerations, this work aims to highlight key advantages, limitations and future challenges of fPET and applications in multimodal imaging. Regional increases in glucose metabolism largely correspond to those observed with BOLD fMRI across a range of cognitive tasks, whereas divergence within the default mode network during internally directed attention seems to reflect active inhibitory processes. Extensions to radioligands beyond [18F]FDG demonstrated marked increases in dopamine and serotonin synthesis during reward processing, providing complementary insight into neurotransmitter action. Moreover, image reconstruction in the range of seconds facilitates extraction of moment-to-moment fluctuations in fPET signals for computation of molecular connectivity. The use of large axial field-of-view PET scanners for total-body imaging further enables inference on molecular interactions at the systems level. In sum, fPET imaging, particularly multimodal combinations, offers novel perspectives that cannot be obtained with either of these modalities alone. Future challenges include the detailed characterization of the relationships between neurovascular and neurometabolic coupling as well as the physiological underpinnings of rapid changes in fPET signals and the translation to clinical research settings.

This article outlines the evolving role of MRI in traumatic spinal cord injury (SCI) across acute to chronic stages. Conventional MRI remains indispensable for diagnosis and early prognosis, while quantitative morphometrics such as tissue bridges and spinal cord cross-sectional area provide robust and clinically applicable predictors of post-SCI recovery. Advanced techniques, including diffusion, myelin-sensitive, and functional MRI, enable the detection of microstructural damage, remote neurodegeneration, and functional reorganization. Ongoing advances in scan protocol standardization, automated image analysis, and AI-driven lesion segmentation are expected to improve reproducibility and facilitate the integration of imaging biomarkers into clinical practice and interventional trials.

A 28-year-old male patient without previously diagnosed systemic disease or any ocular history presented with 3 months of progressive blurred vision in both eyes. His ocular exam revealed bilateral vitreous hemorrhage, tractional retinal detachments (TRDs), and extensive retinal neovascularization (NV). His systemic workup revealed elevated angiotensin-converting enzyme, bilateral hilar, and mediastinal adenopathy on computed tomography (CT) chest scan, and extensive multifocal leptomeningeal-enhancing nodules within the posterior fossa on magnetic resonance imaging (MRI) brain scan, confirming sarcoidosis with neurologic and ocular involvement. Ocular complications of sarcoidosis predominantly involve the anterior segment, with anterior uveitis as the most common presentation overall. While posterior findings of ocular sarcoidosis are less common, these include but are not limited to retinal periphlebitis with candlewax drippings, choroidal granulomas, and optic nerve involvement, with cystoid macular edema representing the leading cause of vision loss. This report presents a unique case of bilateral TRDs and retinal NV as the initial manifestation of sarcoidosis. Improved awareness of atypical ocular presentations of sarcoidosis is critical for facilitating earlier diagnosis and timely intervention.

Hippocampal hyperactivity, detected with mnemonic similarity task (MST) fMRI, is both a promising marker of risk and a probable driver of degeneration in Alzheimer's disease (AD). However, implementation of such fMRI in interventional research is limited by long scan times and the absence of a framework for identifying prospective participants with hyperactivity who could be targeted with therapeutic approaches aimed at reducing this activity. We used multi-echo fMRI during the MST, an episodic memory task previously shown to engage hippocampal subfields CA3 and dentate gyrus (DG), to characterize activity profiles in 33 cognitively normal older adults. We compared MST-related CA3 and DG activation and behavioural performance across subsets of eight task runs. Behavioural and activation effects were equivalent for the first set of four runs (Runs-A) and the second set (Runs-B), suggesting that robust data can be obtained with four runs. Left and right CA3 + DG activation did not differ. We provide an exemplar framework for the derivation of a threshold for single-participant classification of elevated hippocampal activation as an indicator of AD risk in cognitively normal older individuals. Scalable (~22 min) multi-echo MST fMRI robustly captures hippocampal activation and provides a framework for individual-level characterization of hippocampal function in cognitively normal older adults. This enables individualized detection of elevated hippocampal activation as a modifiable risk factor and may guide enrolment into prevention trials targeting preclinical AD.

Bilateral subdural hematomas occurring simultaneously with subarachnoid hemorrhage in a traumatic context are rare and pose considerable diagnostic challenges. Comorbidities such as diabetes and HIV may further worsen prognosis and complicate management. This case underscores the vital importance of early diagnosis and multidisciplinary care in patients with subacute subdural hematomas and subarachnoid hemorrhage, particularly when compounded by comorbidities in resource‑limited settings. We report the case of a 44-year-old housewife who was diabetic and living with HIV. She presented with severe headaches followed by altered consciousness with severe coma, and Cushing's triad two weeks after a minor head trauma. Brain CT scan revealed a bilateral panhemispheric subacute subdural hematoma (SASDH) associated with subarachnoid hemorrhage. Management consisted of emergent bilateral burr hole craniotomy for drainage, combined with measures to reduce intracranial pressure and prevent secondary brain injury of systemic origin. Her course was complicated by infection and hypertensive crisis; both were successfully managed. Glycemic control was achieved and antiretroviral therapy optimized. Clinical and radiological outcomes were ultimately favorable. This case underscores the importance of early diagnosis and multidisciplinary management of subdural hematomas in patients with diabetes and HIV. Beyond timely surgical intervention with burr‑hole craniotomy, comprehensive intensive care - including vigilant monitoring, early detection, and prompt control of complications - can significantly improve survival and optimize neurological outcomes.

Face blindness, also called prosopagnosia, is the inability to recognize familiar faces and is often secondary to dysfunction of the fusiform gyrus. This symptom can be part of dementia or be related to a lesion in this anatomical structure. We present the case of a 78-year-old female patient, with a diagnosis of dementia without prosopagnosia, who developed an episode of transient loss of consciousness. A brain computed tomography scan revealed an extensive right hemispheric chronic subdural hematoma. Patient underwent urgent hematoma drainage after deterioration of the neurological condition, with sudden reduction of Glasgow Coma Scale. Postoperatively, patient developed inability to recognize the faces of family members for 48 hours. Transient prosopagnosia is an infrequent symptom in dementia. In this case, we hypothesized that, when involving right basal temporal structures, treatment of chronic subdural hematoma may determine a transient prosopagnosia. After hematoma drainage, the concavity of the fusiform gyrus and the inferior-medial surface of the temporal lobe might crush against the skull base, causing alterations of the microcirculation and temporary flow deficits at this level. We defined this phenomenon, onomatopoeically, "squash effect."

Oncocytic (Hurthle cell) carcinoma is an uncommon thyroid malignancy that tends to spread through the bloodstream and often concentrates radioactive iodine poorly. Spread to the brain is rare, and a solitary cerebellar deposit is rarer still. We describe a 44-year-old man who presented with neck swelling and was found to have a widely invasive oncocytic carcinoma with extensive vascular invasion and a minor classic papillary component (5%). He underwent total thyroidectomy with central neck dissection followed by radioactive iodine ablation with 150 mCi of iodine-131. The post-therapy scan showed uptake confined to the thyroid bed. Over the next 18 months, his serum thyroglobulin climbed steadily from 1.5 µg/L to 11.6 µg/L even though the thyroid-stimulating hormone (TSH)-stimulated diagnostic whole-body iodine scan remained negative. Fluorodeoxyglucose positron emission tomography/computed tomography then showed multiple hypermetabolic bilateral pulmonary nodules suspicious for metastases. Roughly 22 months after thyroidectomy, he developed progressive dizziness and headache. Magnetic resonance imaging (MRI) revealed a 3.3 × 3.2 × 3.1 cm mixed cystic and solid left cerebellar mass with surrounding vasogenic edema and mass effect on the brainstem. The mass was resected through a left suboccipital craniotomy. Histology showed a malignant epithelioid neoplasm with nested and trabecular growth, abundant granular eosinophilic cytoplasm, prominent nucleoli, scattered bizarre giant nuclei, and 8 mitoses per 2 mm[2] without necrosis. The tumor cells expressed cytokeratin AE1/AE3, CK7, TTF-1, and PAX-8 and were negative for CK20, CDX-2, synaptophysin, chromogranin, and S100, confirming thyroid origin. The metastasis fulfilled criteria for high-grade differentiated thyroid carcinoma with oncocytic features. His symptoms resolved after surgery, and stereotactic radiosurgery for the resection cavity was recommended. A rising thyroglobulin with negative iodine imaging represents a biochemical incomplete response and should prompt a search for structural disease recurrence. Because the brain lesion in our patient came to light only when symptoms appeared, brain MRI may be worth considering in patients with radiodiodine-refractory distant metastases.

Brain-based prediction of behavioral phenotypes is promising for precision medicine. However, predictive models in the field have commonly shown limited accuracy and individual bias. For instance, participants of ethnic/racial minority (e.g., African Americans) are more likely to be misclassified or show larger prediction errors, compared to white American participants. Addressing these limitations requires a better understanding of the sociodemographic and scan-related factors related to prediction biases. Here, we investigated the association between the prediction errors of brain-based models predicting over 100 behavioral measures and eight variables capturing sociodemographic and scan-related individual characteristics. These associations were examined in two developmental and one young adult cohorts (sample size = 4278, 432, and 784 respectively). We found that socioaffective and mental health phenotypes in developmental cohorts were particularly susceptible to bias associated with individual characteristics. In particular, head motion, head morphology, and sex/gender are consistently related to the machine learning biases in multiple behavioral measures. Our work highlights the multifactorial nature of the prediction errors generated by the brain-based predictive models. Overall, our results call for greater attention to model bias in developmental populations, particularly in the context of AI-based approaches for psychiatric risk prediction and early diagnosis.

Anorexia nervosa (AN) has been linked to both impaired and improved whole-body insulin sensitivity, but tissue-specific metabolic alterations remain unexplored. To address this gap, we studied 12 female volunteers with recently diagnosed AN and 13 healthy, lean female controls in a cross-sectional design using positron emission tomography (PET) imaging with the glucose analogue [[18]F]FDG tracer under hyperinsulinemic conditions. We show that tissue-specific glucose uptake during hyperinsulinemia was higher only in the duodenum of individuals with AN, but comparable in other tissues, possibly indicating altered intestinal glucose handling and nutrient sensing in reduced energy intake. In five participants with AN, glucose uptake was elevated despite reduced skeletal muscle glucose utilization. In controls, growth hormone (GH) levels correlated with skeletal muscle, liver, and brain insulin sensitivity, but these associations were absent in AN, suggesting disrupted endocrine regulation of glucose metabolism. Overall, whole-body insulin sensitivity was not altered, yet tissue-specific glucose metabolism exhibited greater variability in AN. These differences were not directly explained by disease duration or weight loss severity, suggesting contributions from individual genetic background and behavioral patterns.