Journal of Cerebral Blood Flow & Metabolism

This study presents a novel in vivo neuroimaging approach using dynamic single photon emission computed tomography (SPECT/CT) to investigate cerebrospinal fluid (CSF) dynamics in pigs, a translationally relevant model due to their human-like brain structure. The distribution, brain penetration of [99mTc]-DTPA and subsequent clearance were followed by brain SPECT for three hours after injection into the cisterna magna of anesthetized pigs and rats. To investigate the effects of anesthesia and across-species effects, we examine CSF dynamics under two types of anesthesia, propofol and ketamine/dexmedetomidine (K/D), and compare the outcome in pigs to that of rats, in which we also compared isoflurane. Propofol and K/D produced largely similar tracer distribution patterns across both pigs and rats: In both species, K/D was associated with higher tracer penetration into the dorsal striatum compared to propofol while neither species showed a tracer accumulation difference in the thalamus. K/D also increased intracranial radiotracer retention and reduced urinary tracer clearance in rats, but not in pigs. In rats, propofol and isoflurane showed similar tracer distribution, reflecting their shared GABAergic mechanism of action. The differences observed between pigs and rats may reflect species-specific physiology, differences in anesthesia dosing, or methodological factors. The work demonstrates the feasibility of using SPECT/CT to study CSF transport in the large gyrencephalic pig brain to advance understanding of human brain fluid dynamics.

BackgroundApolipoprotein E (APOE) has been implicated in blood-brain barrier (BBB) dysfunction and may influence ischaemic cerebrovascular disease and cerebral small-vessel disease (cSVD). This study examined associations between APOE genotype, BBB permeability, and infarct distribution in patients with mild ischemic stroke. MethodsWe recruited patients with mild ischemic stroke who underwent structural and dynamic contrast-enhanced MRI (DCE-MRI) and APOE genotyping. Infarct type and location, white matter hyperintensities (WMH), and perivascular spaces (PVS) were assessed. BBB-related metrics were quantified using fractional plasma volume (vP) and permeability-surface area product (PS) across five brain regions of interest: deep grey matter (DGM), hippocampus, thalamus, normal-appearing white matter (NAWM), and WMH. Associations between genotype, BBB metrics, vascular risk factors, and age were evaluated using linear mixed-effects models. Binary logistic regression was also applied to assess the association between APOE status and infarct location by vascular territory (anterior vs posterior circulation). ResultsAmong 147 patients with APOE genotype and BBB measures, APOE4 carriers (n=44) demonstrated a greater proportion of posterior circulation infarcts than E3/E3 individuals (n=80; 56.4% versus 32.9%), including higher frequencies of posterior cerebral artery cortical, posterior borderzone, and thalamic infarcts. Mean PS and vP did not differ significantly by genotype. Increasing age was associated with lower PS across multiple regions and lower vP in WMH, while higher vascular risk burden was associated with lower vP in NAWM and WMH. Inclusion of regional BBB metrics did not substantially alter APOE4 effect estimates in infarct-location models. ConclusionsAPOE4 carriers showed a posterior-predominant infarct distribution despite similar BBB permeability and vascularity measures. Age and vascular risk burden were more strongly associated with BBB-related imaging metrics than APOE genotype. These findings add to evidence suggesting that APOE genotype may influence regional cerebrovascular vulnerability and that this effect is unlikely to be fully explained by DCE-MRI-derived measures of BBB permeability and vascularity alone.

Accurate assessment of cerebral hemodynamics impairment traditionally relies on arterial metrics, yet often overlooks venous drainage and arteriovenous dynamics, thereby limiting the evaluation of ischemia-induced microvascular dysfunction. To address this limitation, we implemented a signal-averaging framework, combined with co-fluctuation analysis, to extract predominantly arterial and venous hemodynamic signals and construct a dynamic arteriovenous co-fluctuation index that quantifies frame-by-frame coordination between arterial inflow and venous outflow activity. This time-resolved index enables spatial characterization of large-scale cortical arteriovenous coordination beyond conventional static correlation-based analyses. Comparative analyses between healthy controls and acute ischemic stroke mice demonstrated that the arteriovenous co-fluctuation index sensitively detects disruption of vascular coordination, revealing a slower state transition that occurs alongside distinct temporal abnormalities and regional heterogeneity between ischemic core and penumbral regions. These findings underscore the utility of arteriovenous coordination as a sensitive indicator of microcirculatory dysfunction, offering a practical analytical tool for assessing stroke-induced microvascular impairment.

IntroductionChemogenetic tools such as Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) provide a powerful means to causally manipulate defined neuronal populations in vivo. While chemogenetic fMRI studies have consistently demonstrated robust hemodynamic responses following circuit perturbation, considerably less is known about the accompanying metabolic consequences. Functional magnetic resonance spectroscopy (fMRS) offers the potential to probe these neurochemical processes, yet the relationship between hemodynamic and metabolic responses remains poorly understood. Here, we combined chemogenetics, pharmacological fMRI (ph-fMRI), and proton magnetic resonance spectroscopy (1H-MRS/fMRS) at 7 T to investigate the temporal evolution of metabolic and hemodynamic responses in the rat motor cortex. MethodsFemale Fischer rats received viral injections in the motor cortex to express either a pan-neuronal hM3D(Gq) DREADD construct (hSyn-hM3Dq) or an interneuron-targeted construct (hDlx-hM3Dq). Ph-fMRI, fMRS, and 1H-MRS measurements were performed before, during, and following systemic administration of clozapine-N-oxide (CNO, 1 mg/kg). Functional MRS was acquired during the acute response phase (0-60 min post-injection), while conventional 1H-MRS measurements were obtained at a delayed time point (70 min post-injection). ResultsChemogenetic modulation produced robust and opposing hemodynamic responses. Pan-neuronal activation elicited focal positive BOLD responses (+3.5 {+/-} 1.5%), whereas interneuron-targeted activation generated significant negative BOLD responses (-3.3 {+/-} 0.8%). In contrast, acute fMRS measurements revealed no significant changes in Glx or GABA concentrations during the first hour following CNO administration, despite the presence of strong hemodynamic effects. However, delayed metabolic alterations were detected 70 min after CNO administration. Animals expressing the pan-neuronal construct exhibited significant increases in GABA (+14.4%) and total choline compounds (+57.8%), whereas interneuron-targeted animals displayed reductions in several metabolites, including Glx (-15.6%), total NAA (-16.9%), glucose (-25.9%), and total creatine (-25.4%). ConclusionChemogenetic perturbation of cortical circuits produced robust hemodynamic responses but more subtle and temporally complex metabolic effects. The absence of detectable acute changes in Glx and GABA despite strong BOLD responses, together with the emergence of delayed neurochemical alterations, highlights the challenges of interpreting metabolic signals in relation to circuit activity.

Cerebral blood flow (CBF) is a quantitative metric for mapping perfusion. While the prototypical MRI approach arterial spin labelling (ASL) is well-validated in humans, the reproducibility of rodent ASL mapping remains poor, limiting translational impact. To address this gap, we used both newly acquired and analysis of previously published data to illustrate biological and physical sources of variation in CBF measured with ASL. Via a meta-analysis, we quantified the variation in CBF reported from the cortex of healthy rodents. A total of 23 mouse studies (343 data points) and 5 rat studies (41 data points) met the inclusion criteria. We demonstrate that reported CBF values exhibit a broad variability (50-400 ml/100g/min) driven primarily by experimental confounds rather than physiological differences. Our meta-analysis explores which factors cause variance in perfusion rates measured. Our experimental data highlight biological factors, particularly the choice of anaesthesia (e.g., isoflurane vs. medetomidine) and strain variations, that alter baseline CBF. Our work, reflecting both state-of-the-art and conventional practice in preclinical imaging, highlights the need to account for multiple sources of variability. Establishing community guidelines for rigorous ASL calibration and physiological monitoring will support improved study design and accelerate translational alignment between rodent and human perfusion measurements.

Traumatic brain injury (TBI) is the main cause of death and disability in the United States in people younger than 35 years old and is a common cause of wartime injuries. Mild TBI (mTBI) is a predisposing factor for later development of dementia and cerebrovascular disease. Aerobic exercise was reported to improve cognitive function in chronic TBI through improved vascular function. The aims of the study are to characterize and correlate the subacute (10 weeks) and chronic (12 months) cognitive and cerebrovascular functional impairment following mTBI and evaluate the modulating effect of exercise early or late following mTBI on these changes. Sprague-Dawley rats received midline fluid percussion injury or sham procedure and followed for 10 weeks or 12 months with a subgroup of mTBI rats undergoing 5-week treadmill aerobic exercise 2 weeks (early) or 10 months (late) post-injury for 6 weeks. Cognitive function was assessed using novel object recognition (NOR) and novel object location (NOL) tests. Regional cerebral blood volume (CBV) and cerebrovascular reactivity following hypercapneic stimulation (CVR) using contrast magnetic resonance imaging (MRI) and ex vivo pial artery vasoreactivity to intraluminal pressure, angiotensin II and diethylenetriamine NONOate (DETA NONOate) were measured. There was no difference in NOR or NOL at 10 weeks between mTBI and sham. NOR, but not NOL, was reduced in mTBI rats at 12 months. CBV at 10 weeks was higher in the primary somatosensory trunk cortex (trunk) and dentate gyrus regions in mTBI, but not at 12 months. CVR was lower in the trunk region of mTBI rats at 12 months. Compared to sham response at 10 weeks, there was impaired arterial constriction response to 90 mm Hg intraluminal pressure in mTBI rats at 10 weeks and in sham and mTBI rats at 12 months, with no difference seen in response to angiotensin II or DETA-NONOate exposure. There was no correlation between cognitive and vascular outcomes at 10 weeks or 12 months. Early or late exercise did not affect 12-month cognitive or vascular function following mTBI. The study showed chronic impairment in short-term memory cognitive function, regional cerebrovascular reactivity and early onset of impaired cerebrovascular myogenic response in rats subjected to mTBI. The findings of persistent cognitive and cerebrovascular impairment in this animal model enhance our understanding of the long-term consequence of mTBI.

This study tests the hypothesis that vasomotion, an [~] 0.1 Hz oscillation in arteriole diameter, is generated by intrinsic oscillations within the arterioles that perfuse the brain, and not by external drive from systemic blood pressure oscillations (Mayer waves). During cardio-pulmonary bypass that transiently eliminated systemic blood pressure oscillations in 14 patients, we observed that vasomotor oscillations persist with normal amplitudes and frequencies over the one- to three-hour time course of surgery. In contrast, [~] 0.1 Hz oscillations in peripheral blood pressure were predominantly absent. This implies that cerebral arterioles generate their own rhythmic vaso-dynamics, although we cannot discount that vasomotion can phase-lock with [~] 0.1 Hz systemic physiological rhythms in the awake, healthy state. We discuss the impact of this finding on the role of vasomotion in modulating the perfusion of blood and the transport of interstitial fluid in the brain.

Sex differences in brain disorders span age at onset, symptom profiles, disease course and treatment response, and may partly reflect underlying differences in cellular metabolism. Indeed, in vivo evidence of sex-related neurometabolic variation remains sparse, with heterogenous and conflicting findings. Using fast high-resolution whole-brain three-dimensional magnetic resonance spectroscopic imaging, we mapped five brain metabolites in three independent cohorts of healthy participants (total n = 114). In a discovery sample of adolescents scanned at 3 Tesla (3T) (n = 61), males showed higher total N-acetylaspartate (tNAA) across widespread gray matter regions. Regional analyses further revealed opposing sex patterns with a complementary higher total creatine (tCr) observed in females, motivating examination of their ratio as an integrative metabolic index. The tNAA/tCr ratio was consistently higher in males in the discovery sample and this finding was replicated across two independent young-adult samples (3T, n = 26; 7T, n = 27), with a widespread gray and white matter distribution. This tNAA/tCr ratio may link neuronal mitochondrial metabolism with cellular energy buffering, positioning it as a potential index of bioenergetic balance relevant for conditions showing both sex differences and altered neurometabolism, notably multiple sclerosis, Alzheimer disease, and psychosis. Together, these findings reveal a reproducible, distributed metabolic sexual dimorphism in the human brain, and underscore the importance of accounting for sex-specific neurometabolic profiles in studies of brain health and disease.

BackgroundPreexisting factors are among the strongest predictors of recovery following traumatic brain injury (TBI), with chronic stress closely associated with permanent disability and worse long-term outcomes. While chronic cerebrovascular dysfunction is linked to these poor trajectories, as impaired blood flow regulation drives secondary disease progression, the mechanisms regulating this vascular failure remain incompletely understood. Crucially, how premorbid chronic stress and TBI disrupt the fundamental coordination of the cerebrovascular network post-injury remains unknown. MethodsTo elucidate this coordination at rest and in response to increased neuronal activity, we used a model of three repeated moderate closed cortical impacts comorbid with chronic stress induced by social isolation (SI) post-weaning. Our previously developed vascular analysis pipeline (NOVAS3D) was employed to estimate changes in vascular radii across cerebrovasculature proximal to neuronal activation. Arteries and veins were annotated in the imaged volumes to allow for blood flow simulations. ResultsUsing graph-based network analysis, we demonstrate that TBI, when compounded with chronic stress, critically disrupts the long-range coordination of the capillary network. Specifically, the functional coordination of radius changes between nearby, non-adjacent capillaries was reduced by 40{+/-}20% in TBI+SI mice relative to controls. Consequently, simulations estimated that the vascular networks in TBI+SI mice experienced a 68{+/-}7% reduction in arterial red blood cell velocity (VRBC) responses to neuronal activation. These network-wide impairments were fundamentally driven by severely blunted vessel reactivity, including a 28{+/-}7% decrease in the magnitude of arteriolar dilations and a 47{+/-}7% decrease in the magnitude of arteriolar constrictions. ConclusionThese findings provide a mechanistic foundation for worse clinical outcomes seen in TBI patients with comorbid chronic stress, identifying arteriolar reactivity and long-range capillary coordination as critical therapeutic targets to mitigate secondary injury and improve long-term recovery.

Background Mitochondrial dysfunction and abnormal cerebral energy metabolism are implicated in many neuropsychiatric and neurodegenerative disorders. 13C magnetic resonance spectroscopy (MRS), combined with 13C-labeled substrate infusion, offers a non-ionizing, minimally invasive method for assessing fluxes through the main cerebral energy metabolism pathways. However, its human application at 7 T has not been fully established, especially within the frontal lobe. Purpose To explore a clinically translatable interleaved 1H/13C MRS protocol for quantification of cerebral glucose uptake and downstream metabolism at 7 T, and to estimate the tricarboxylic acid (TCA) cycle flux (VTCA) for validation. Study Type Prospective. Population Three young healthy volunteers. Field Strength/Sequence 7T; ACE-STEAM (indirect 1H-[13C]) and ISIS-DEPT (direct 13C-[1H]). Assessment ACE-STEAM and ISIS-DEPT were applied to acquire the time-resolved spectra in the frontal lobe. 13C-labeled glucose, glutamate, and glutamine fractional enrichment time courses were quantified to estimate VTCA through the one-compartment model. Statistical Tests The relative estimated fitting uncertainties (EFUs) were reported for the processed spectra. Nonlinear least squares minimization was used for flux fitting of 13C traces. Uncertainty of the estimated metabolic fluxes was evaluated using Monte-Carlo simulations. Results [1-13C]-glucose (GlcC1) was detected immediately on 13C MR spectra, followed by 13C-labeled GluH4 and GlnH4 and then GlxH3 can be quantified on 1H MR spectra. End-of-infusion mean enrichments were 17% (GluH4), 13% (GlnH4), and 7% (GlxH3). Brain glucose concentration ranged 1.86-2.94 mM, with 61% of the mean enrichment in C1. Group-average VTCA was 0.66 {+/-} 0.07 mol/g/min. Data Conclusion This interleaved 1H/13C MRS protocol enables minimally invasive quantification of cerebral metabolic fluxes, may provide a useful framework for investigating neuropsychiatric and neurodegenerative diseases at 7 T. Evidence Level 1. Technical Efficacy Stage 1.

Background The ischemic penumbra, a metabolically compromised yet potentially salvageable region surrounding the ischemic core, is a prime target for acute stroke intervention. Yet an objective molecular definition of the penumbra, particularly during the earliest stages of ischemia, remains lacking. Methods and Results We applied principal component analysis (PCA) followed by k-means clustering to high-resolution mass spectrometry imaging data covering multiple metabolic pathways to identify a metabolically defined penumbra in a mouse model of hyperacute stroke (45 min middle cerebral artery occlusion, MCAO). Targeted spatial metabolomic profiling by matrix-assisted laser desorption/ionization (MALDI) and desorption electrospray ionization (DESI) reveals a distinct penumbral metabolic profile, marked by relative preservation of high-energy phosphates, comparable lactate accumulation, and reduced succinate accumulation relative to the core. Spatial transcriptomics revealed selective induction of immediate-early genes, including Npas4, Fos and Junb, within the penumbra. Consistently, imaging mass cytometry shows enrichment of phospho-histone H3 (pHH3) within the penumbra, suggesting a chromatin-associated response potentially linked to immediate-early gene activation. Conclusion Together, these findings provide a multimodal molecular atlas of the hyperacute metabolically defined penumbra and reveal molecular features that facilitates its identification and inform future therapeutic strategies.

Moderate hypoxia is increasingly recognized as a physiological driver of neuroprotection and neuroregeneration. In this first randomised, double-blind, controlled, four-arm trial, we demonstrate the cognitive and neuroplastic effects of cognitive training under moderate inspiratory hypoxia in humans. Healthy volunteers underwent three weeks of either cognitive or sham training under normobaric hypoxia (12% O2) or normoxia (20% O2) for 3.5 hours daily, six days per week. Participants were assessed at baseline, treatment completion, and one-month follow-up. The primary outcome was change in a broad cognitive composite score. Additional cognitive, blood-based, and neuroimaging outcomes were assessed, including measurement of the presynaptic protein SV2A with [11C]UCB-J positron emission tomography (PET) and neural activity through functional magnetic resonance imaging (fMRI). In total, 126 participants were randomised to hypoxia-cognitive training (H-CT: n=36), hypoxia-sham training (H-ST: n=30), normoxia- cognitive training (N-CT: n=30), or normoxia-sham training (N-ST: n=30). Intention-to-treat analyses showed no effect of H-CT relative to N-ST in the primary outcome at treatment completion (primary endpoint; treatment effect=0.11, 95% CI=[-0.06;0.28], p=0.19), but improvements emerged at follow-up (treatment effect=0.17, 95% CI=[0.01;0.34], p=0.04). N-CT induced transient improvement in the primary outcome at treatment completion (treatment effect=0.20, 95% CI=[0.02;0.38], p=0.03), which rendered non-significant at follow-up. Finally, H-ST showed no significant cognitive change relative to N-ST. Moderate hypoxia was safe and well-tolerated. Cognitive benefits were accompanied by decreased hippocampal presynaptic density measured with [11C]UCB-J PET. In conclusion, three weeks of H-CT can enhance cognition with associated effects on neuroplasticity, although with a delayed onset of effects on cognition.

Atrial fibrillation (AF) is associated with an increased risk of neurological morbidity, yet its impact on cerebral perfusion and neuro-cardiorespiratory regulation remains incompletely understood. We used arterial spin labeling, blood oxygenation level-dependent functional MRI (BOLD-fMRI), and a breath-hold challenge to characterize alterations in 14 AF patients compared with 14 age-matched healthy controls. We also examined the changes after catheter ablation with pulmonary vein isolation (PVI) in a subset of patients. Compared with controls, AF patients exhibited widespread reductions in basal cerebral perfusion, including in brainstem regions involved in cardiorespiratory regulation, and a higher prevalence of periodic breathing during wakeful rest. During breath-hold challenge, the coupling between heart rate and BOLD signal changes ({Delta}BOLD) was smaller in AF, whereas {Delta}BOLD coupling with breath-by-breath O2-CO2 exchange ratio was greater at rest within pontine respiratory centers, indicating altered cardiac and respiratory contributions to cerebral hemodynamic regulation. Follow-up MRI scans 1-6 months after PVI demonstrated that restoration of sinus rhythm was associated with stronger heart rate-{Delta}BOLD coupling during breath-hold challenge, whereas basal cerebral perfusion showed no significant change. This dissociation suggests distinct temporal responses of neuro-cardiorespiratory coupling and cerebral perfusion after sinus rhythm restoration, while the timing of cerebral perfusion recovery remains unresolved.

IntroductionReduced or absent capillary blood flow (termed no-reflow) even after arterial recanalization is associated with poorer neurological outcomes following ischemic stroke. The aim of the current study was to test whether acute administration of peptidylglycine -amidating monooxygenase (PAM) can increase capillary blood flow and improve brain recovery after ischemic stroke. MethodsA 60-minute ischemic stroke was induced using middle cerebral artery occlusion (MCAO) in rats. A modified, long-acting PAM enzyme was administered 30 minutes after induction of ischemia and rats were recovered for either 24 hours or 7 days. In all animals, real-time cerebral blood flow was assessed before, during and after MCAO using trasncranial contrast enhanced ultrasound (tCEU). For rats in the 7-day protocol, a modified neuroscore test was used to assess neurological deficit following MCAO. At the end of each experiment, a transcardiac perfusion was used to generate a fluorescent vascular cast and histology was used to examine capillary diameters and determine infarct volume. ResultsFollowing MCAO and arterial recanalization, untreated rats had reduced cerebral blood flow across brain regions affected by ischemia, indicative of no-reflow. PAM administration led to enhanced cerebral blood flow in affected regions, and this was associated with increased capillary diameters 24 hours after ischemic stroke. Although there was no difference in infarct volume at 24 hours, by day 7, infarct volume was markedly reduced in the PAM group and these animals exhibited improved neurological function compared to the untreated group. ConclusionAdministration of PAM improves capillary blood flow after ischemic stroke leading to enhanced neurological and brain recovery. This work highlights PAM as a novel theraputic approach to improve brain blood flow and recovery after ischemic stroke. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/732201v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@1637bdeorg.highwire.dtl.DTLVardef@59548aorg.highwire.dtl.DTLVardef@bd365borg.highwire.dtl.DTLVardef@3baf84_HPS_FORMAT_FIGEXP M_FIG C_FIG

Background: Mu-opioid receptors (MORs) are expressed throughout the body including in the brain and gastrointestinal (GI) tract. Total-body PET imaging of the brain and GI tract offers a promising approach for cross-sectional in vivo evaluation of the MOR brain-GI axis. However, intestinal motility and bladder filling introduce motion throughout the GI tract over the scan window. Here we establish analysis methodology to account for motion for dynamic imaging of the brain-GI axis, to further characterize peripheral MORs throughout the body and provide a framework for semi-automatic total-body PET modeling. Methods: 4 subjects underwent 90-min dynamic [11C]-carfentanil (cfn) total-body PET acquisitions at baseline, after intravenous naloxone (central antagonist) administration, and after orally administered loperamide (peripheral agonist and P-glycoprotein substrate). Thalamic MOR availability was measured using the Logan reference tissue model. Using CT-based segmentation, the GI tract was subdivided into anatomical segments, in addition to other peripheral organs (e.g., liver, psoas muscle). Frame-by-frame semi-automatic motion correction was performed with three distinct reference frames (11-14 min post-injection, p.i., 35-40 min p.i., and 85-90 min p.i.). The performance of these three were compared to manual correction. Compartment modeling and Logan graphical analysis were performed to estimate relevant kinetic parameters (K1, VT, VTLogan). Results: Across the 4 subjects and regions, kinetic parameter estimates were highly correlated (r>0.7) for K1, VT and VT Logan when comparing semi-automatic (reference frame at 35-40 min p.i.) and manual correction. With semi-automatic motion correction, graphical-based estimation of VTLogan in the gastrointestinal tract was significantly decreased with loperamide relative to baseline (p<0.05). As expected, naloxone decreased brain thalamic MOR availability but loperamide did not. Conclusions: With semi-automatic motion correction and [11C]-cfn total-body PET, pharmacologic perturbations of MOR brain-GI axis can be quantitatively characterized, reducing the burden of image analysis for these studies.

Recent advances in neurophysiology highlighted the potential of high temporal resolution in Blood-Oxygen Level Dependent (BOLD) functional MRI (fMRI), although it is not yet standard practice. We demonstrated that fast BOLD fMRI can detect single-subject, single-stimulus visually evoked responses to brief stimuli at 3T. We used fast fMRI in patients with Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL), a genetic form of cerebral small vessel disease (cSVD). Using 2- and 10-second visual stimuli, we probed different neurovascular coupling regimes and showed that different regions of interest detect different facets of vascular dynamics. CADASIL patients showed significant changes in the amplitude and timing of the BOLD response, indicating early-age neurovascular impairment unrelated to anatomical lesions, and providing strong discriminative and generalization performance. These findings resolve prior inconsistencies in fMRI studies of CADASIL, supporting the use of fast fMRI to develop non-invasive biomarkers for cSVD and other neurodegenerative disorders.

Purpose: {beta}-hydroxybutyrate (BHB), a ketone body and alternative cerebral energy substrate, can be measured in vivo using J-difference edited proton magnetic resonance spectroscopy (1H-MRS). Oral ketone supplementation with substrates such as the ketone monoester (R)-3-hydroxybutyl-(R)-3-hydroxybutyrate (KME) and 1,3-butanediol (BD) have gained attention as a mechanism to elevate circulating BHB and induce ketosis without dietary restrictions. Elevated brain ketone availability is of growing therapeutic interest as a strategy to support neuronal energetics in conditions such as epilepsy, neurodegenerative disease, and alcohol use disorder (AUD). However, both pathways introduce BD into the bloodstream, which crosses the blood-brain barrier. Critically, BD exhibits a spectral signature that closely resembles the prominent BHB peak in JDE-MR spectroscopic imaging (MRSI), identified in a pilot AUD study. Methods: Two separate JDE-MRSI acquisitions tailored for BHB and BD editing were implemented, exploiting frequency separation between the BHB (4.14ppm) and BD (3.95ppm) coupling partners of the observed 1.2ppm resonance to independently quantify each metabolite. Results: Brain BD concentrations (0.25-0.58mM) were comparable to or exceeded corresponding BHB concentrations (0.20-0.27mM) in all volunteers after consumption of a single dose of the KME, indicating that BD constitutes a major fraction of the signal conventionally attributed to BHB. Combined BHB+BD concentrations (~0.45-0.85mM) were consistent with brain BHB values reported in prior studies employing similar doses of the KME, indicating that those measurements likely reflect a combined BHB+BD signal. Conclusions: Separate quantification of the two metabolites is important for interpreting brain ketone studies and for understanding the full pharmacology of KME supplementation.

The development of digital twins in medicine, i.e., virtual replicas of human organs, offers a promising path toward precision medicine by enabling interpretable, mechanistic, and actionable insights. In the brain, cerebrovascular twins support individualized modeling of hemodynamics and bio-transport, with broad applications. A major bottleneck, however, is the lack of robust methods to transform in vivo cerebrovascular images into simulation-ready cerebrovascular meshes or graphs. Here, we present CerebroVascular Imaging to Graph reconstruction (CVIG), a robust and multiscale framework for reconstructing whole brain cerebrovascular graphs from in vivo cerebrovascular images. CVIG integrates vessel vectorization, with tolerance to discontinuity in vessel structures, using a topology-guided assembly of vessel trees to generate cerebrovascular graphs from medical images. We demonstrate the ability of CVIG to generate vascular graphs with improved vascular coverage and topological correctness, the capability essential for high fidelity brain biophysical simulations. This work establishes a vascular graph framework for individualized modeling and analysis, providing a key foundation for digital twins of the human brain.

Background. Ortho-positronium (o-Ps) lifetime, now measurable in vivo on long-axial-field-of-view (LAFOV) PET/CT, has been proposed as a biomarker of tissue oxygenation and hypoxia. Because o-Ps lifetime is dominated by tissue free-volume structure while the oxygen- specific contribution is small, whether an in-vivo lifetime contrast reflects oxygenation rather than anatomy is an open, identifiability-limited question. Aim. To test the oxygenation hypothesis directly using the heart's natural arterial/venous oxygenation contrast, with a built-in anatomical control. Methods. We re-analysed a public [82Rb]Cl human cardiac LAFOV PET/CT dataset (5.30 x 10^8 evaluated three-photon events). Per-compartment o-Ps lifetimes were extracted with a background-plus-two-component exponentially-modified-Gaussian (EMG) model. The list-mode to image mapping and right/left ventricle (RV/LV) identity were established lifetime-free (the mapping reproduces the provider's reconstructed image at block-correlation 0.998 and wins a joint multi-organ alignment panel). We applied a confound battery: registration stress test, blood-core vs wall, lung-air and wall-myocardium partial-volume, tissue density; and a structure/position-matched control (pulmonary artery, deoxygenated, vs aorta, oxygenated). An isotope-matched 82Rb uniform-quartz reference bounded the instrument's positional behaviour. All results were produced by two independent analysis pipelines. Results. RV o-Ps lifetime exceeded LV by delta tau = +0.304 ns (RV 1.700 +/- 0.172, LV 1.396 +/- 0.130 ns; about 1.4 sigma), in the oxygen-expected direction; the contrast was stable across +/-16 mm registration perturbation (sign preserved in 100% of 342 shifts) and resided in the blood core, not the wall. However, the matched-vessel control was null: pulmonary artery minus aorta = -0.011 +/- 0.344 ns. Lung-air and wall-myocardium partial-volume were disfavoured, and the effect fell within the isotope-matched 82Rb instrumental positional envelope (about 0.1-0.35 ns over 40 mm in uniform material). Conclusion. On this single subject, the cardiac o-Ps lifetime contrast does not provide a clean readout of blood oxygenation: an oxygenation effect of the observed (about 0.3 ns) magnitude is ruled out by the matched control, while a small physiological effect cannot be excluded. We provide a reusable confound-control battery for evaluating future in-vivo o-Ps oxygenation claims. Multi-subject replication with anatomy decoupled from oxygenation is required.

Cerebral small vessel disease and neurodegenerative disorders have been associated with increased cerebrovascular pulsatility. Recently, BOLD fMRI-based methods have emerged for assessing pulsatility, however their interpretability is limited because the relation between estimated pulsatility indices (PI) and vascular anatomy and physiology remains poorly understood. To improve interpretability, we introduce a cardiac-specific BOLD fMRI- based PI, investigate its relationship to the cortical vasculature, and validate its sensitivity by introducing the known physiological vascular modulation of hypercapnia. Using high-resolution 7T BOLD fMRI with gradient-echo (GE) and spin-echo (SE) sequences, we disentangled macro- and microvascular contributions to the PI and quantified it across cortical depth. PI maps revealed anatomically plausible patterns, with elevated GE-PI near large veins and in white matter while SE-PI remained largely constant across cortical depth. GE-PI decreased during hypercapnia consistent with altered vascular tone, SE-PI on the other hand did not. PI correlated with cerebrovascular reactivity and venous blood volume suggesting sensitivity to vascular density and vessel mechanics. Our findings demonstrate that BOLD-derived PI provides a spatially and physiologically specific measure of vascular pulsatility. The BOLD fMRI-based PI method is readily applicable to existing datasets and has potential for assessing potential microvascular damage in cerebrovascular and neurodegenerative disease.