Graphical evaluation of blood-to-brain transfer constants from multiple-time uptake data. Generalizations

Diagnosis of cardiac sarcoidosis using glucose metabolic rate from four-dimensional 18F-FDG PET/CT

OBJECTIVE

18F-Fludeoxyglucose (FDG) PET/CT is an effective tool for detecting active cardiac sarcoidosis (CS), but often has difficulty distinguishing CS lesions from physiological myocardial accumulation. We investigated the potential of the glucose metabolic rate (MRglc, mg/min/100mL) from four-dimensional FDG PET/CT in distinguishing between CS and physiological accumulation. Additionally, we compared CS delineation between MRglc and standardized uptake value (SUV).

METHODS

A total of 192 individuals with CS or suspected CS who underwent four-dimensional FDG PET/CT after 18 h fasting was enrolled. Ultimately, 45 individuals with CS and 14 patients with physiological accumulation, with SUVmean ≥ 2.7 accumulation in the left ventricular myocardium, were analyzed. The SUV, MRglc, and the ratio of MRglc to SUV (MRglc/SUV) were calculated for each lesion with SUVmean ≥ 2.7 using data acquired between 30 and 50 min on four-dimensional FDG PET/CT. In the CS group, lesion-to-normal myocardium contrast ratios on MRglc and SUV images were compared.

RESULTS

A total of 127 lesions from 45 individuals with CS and 43 physiological accumulations from 14 individuals were analyzed. The SUV, MRglc, and MRglc/SUV for CS lesions were significantly lower than those for physiological accumulations (SUV, 4.26±1.35 vs. 6.06±3.28; MRglc, 1.91 ± 1.02 vs. 3.78 ± 2.11; MRglc/SUV, 0.43 ± 0.14 vs. 0.63 ± 0.14; p < 0.0001). Receiver operating characteristic analysis revealed that the ability to discriminate CS lesions from physiological accumulations yielded areas under the curves of 0.656, 0.808, and 0.849; sensitivities of 68, 76, and 73%; and specificities of 61, 72, and 84%, for SUV 4.525, MRglc 2.41, and MRglc/SUV 0.518. In the CS group, the contrast ratio of lesions was significantly greater on MRglc images than on SUV images (6.36 ± 6.17 vs. 2.54 ± 1.03, p < 0.0001).

CONCLUSIONS

MRglc from four-dimensional FDG PET/CT is a useful quantitative measure to distinguish CS lesions from physiological accumulation and enables better visualization of CS lesion contrast than SUV.

Genetic risk for treatment resistant schizophrenia and corresponding variation in dopamine synthesis capacity and D2/3 receptor availability in healthy individuals

Dysfunction of dopamine systems has long been considered a hallmark of schizophrenia, and nearly all current first-line medication treatments block dopamine D2 receptors. However, approximately a quarter of patients will not adequately respond to these agents and are considered treatment-resistant. Whereas abnormally high striatal presynaptic dopamine synthesis capacity has been observed in people with schizophrenia, studies of treatment-resistant patients have not shown this pattern and have even found the opposite - i.e., reductions in striatal presynaptic dopamine synthesis capacity. Whether such reductions in fact represent clinical epiphenomena such as medication or other treatment effects or whether they rather represent neurobiological differences related to etiology has been unclear. To understand the dopaminergic implications of genetic liability for treatment-resistant schizophrenia without the confound of clinical epiphenomena, we studied a cohort of healthy individuals without neuropsychiatric illness using [18F]-FDOPA positron emission tomography (PET) and found that striatal presynaptic dopamine synthesis capacity showed an expected direct association with cumulative genetic risk burden for general schizophrenia but an inverse association with specific polygenic risk for treatment-resistant schizophrenia. Subsequent evaluation of D2/3 dopamine receptor availability in an overlapping cohort using [18F]-fallypride PET did not identify any effects of genetic risk in the striatum but found an association with treatment-resistant schizophrenia polygenic risk in the thalamus. Overall, these results align with prior PET studies in patients and implicate, at least with respect to the dopamine system, fundamentally distinct molecular mechanisms in the unique genetic liability for treatment-resistant schizophrenia.

Effects of reducing sedentary behavior on liver insulin sensitivity, liver fat content, and liver enzyme levels: a six-month randomized controlled trial

Metabolic syndrome increases the risk of developing noncommunicable diseases such as metabolic dysfunction-associated steatotic liver disease. The aim was to investigate the effects of sedentary behavior (SB) reduction on liver glucose uptake (LGU), endogenous glucose production (EGP), liver fat content (LFC), and liver enzyme levels [alanine aminotransferase (ALT), aspartate aminotransferase, and γ-glutamyltransferase]. Forty-four sedentary (daily SB time ≥ 10 h), physically inactive middle-aged adults with metabolic syndrome were randomized into intervention (INT; n = 23, 21 completed) and control (CON; n = 21, 19 completed) groups. For 6 mo, INT aimed to limit SB by 1 h/day, whereas CON aimed to maintain usual habits. SB and physical activity (PA) were measured continuously with hip-worn accelerometers. Before and at the end of the intervention, LGU was measured using positron emission tomography during the hyperinsulinemic-euglycemic clamp. EGP was calculated, and LFC was measured by magnetic resonance spectroscopy. INT reduced SB by 51 [95% confidence interval (CI): 22, 78] min/day and increased moderate-to-vigorous physical activity (MVPA) by 22 (95% CI: 12, 33) min/day, with no significant change in CON. Differences in liver health markers between the groups were not significant. However, according to the exploratory analyses among participants who successfully reduced SB, ALT decreased (-1.1 [95% CI: 0.93, 1.36] U/L) compared with the continuously sedentary participants (+0.8 [95% CI: 0.65, 1.05] U/L) (group × time, P = 0.006). To enhance liver health, reducing SB for longer durations and/or increasing the intensity of PA may be necessary. However, successfully reducing SB may lead to better levels of circulating ALT liver enzymes.NEW & NOTEWORTHY Aiming to reduce sedentary behavior (SB) by 1 h/day did not significantly influence liver health markers, suggesting that more substantial reductions or a different approach might be necessary to see improvements. However, achieving the desired behavioral change could lead to improvements in ALT levels. This study is the first to analyze how reducing SB and replacing it with nonguided physical activity impacts liver health in adults with metabolic syndrome, offering insights for future intervention strategies.

Feasibility of simplified Patlak parametric imaging with scaled population-based input function on pancreatic cancer

BACKGROUND

This study evaluates the feasibility of using a simplified Patlak parametric imaging technique with a scaled population-based input function (sPBIF) in pancreatic cancer.

METHODS

Twenty-six patients underwent multi-bed, multi-pass [18F]FDG PET/CT scans, from which both dynamic and static PET images were reconstructed. Patlak parametric images were generated from the dynamic PET series using both the image-derived input function (IDIF) and the sPBIF. The consistency between IDIF and sPBIF was evaluated by comparing the area under the curve (AUC) and Patlak parameters derived from both input functions. The detectability of pancreatic lesions, assessed by tumor-to-background ratio (TBR) and contrast-to-noise ratio (CNR), was compared between SUV and Patlak parametric images. Additionally, the correlation between clinicopathological features and PET parameters, including SUV and Patlak values, was analyzed.

RESULTS

We found good agreement between the AUC for IDIF and sPBIF with correlation coefficients of 0.87 and 0.93 for the 0-30 min and 0-50 min intervals, respectively. The Patlak parameters from IDIF and sPBIF presented correlation coefficients higher than 0.94. The SUV and Patlak Ki exhibited correlation coefficients greater than 0.92 and 0.73 in malignant and benign pancreatic lesions, respectively. The SUV and Patlak V0 correlated with correlation coefficients higher than 0.75 in benign lesions, but exhibited only a weak correlation in malignant lesions. The TBR of Patlak Ki was significantly higher in malignant lesions compared to SUV. However, the CNR of Patlak Ki was lower due to increased noise in the parametric images. Most clinicopathological features showed weak correlation with PET parameters, except for a marginal classification of lesion differentiation by the maximum Ki value.

CONCLUSIONS

The sPBIF approach enables the acquisition of additional Patlak parametric images alongside static SUV imaging in pancreatic cancer patients. Ki parametric imaging provided higher contrast than static imaging for detecting pancreatic lesions.

Amyloid beta peptides inhibit glucose transport at the blood-brain barrier by disrupting the insulin-AKT pathway

Molecular mechanisms underlying disruptions in brain glucose uptake and metabolism, linked with cognitive decline in Alzheimer's disease (AD) patients, are only partially understood. This study investigated how soluble amyloid beta (sAβ) peptides affect glucose transport at the blood-brain barrier (BBB), the primary portal for glucose entry into the brain. We demonstrated that [18F]-fluorodeoxyglucose (18FDG) uptake is reduced in sAβ overproducing APP,PS1 transgenic mice compared to wild-type mice. Moreover, the influx rate of 18FDG decreased in sAβ40 or sAβ42 pre-infused mice, highlighting the inhibitory effect of sAβ peptides on glucose transport at the BBB. Consistently, the expression of GLUT1, the primary glucose transporter at the BBB, is reduced in polarized human cerebral microvascular endothelial cell (hCMEC/D3) monolayers upon exposure to sAβ peptides and in Aβ-laden cerebral vasculature in vivo. The study further examined the influence of sAβ on the insulin-AKT pathway, known to regulate glucose uptake through modulation of thioredoxin-interacting protein (TXNIP) expression. Results showed that sAβ peptides suppress AKT phosphorylation and reduce GLUT1 expression by upregulating TXNIP levels in hCMEC/D3 monolayers. Co-incubation of resveratrol with sAβ peptides reduced TXNIP expression and rectified reductions in GLUT1 expression. In summary, toxic sAβ impairs BBB glucose transport by disrupting the insulin/AKT/TXNIP axis.

Test-retest repeatability of quantitative organ and tissue uptake using 20-minute dynamic multiparametric whole-body [18F]FDG PET/CT in patients with type 2 diabetes

BACKGROUND

Recently developed dynamic whole-body PET/CT (D-WB PET/CT) protocols allow for measurements of potentially more precise metabolic parameters than the commonly used semiquantitative SUV. Most notable is the metabolic rate of FDG uptake (MRFDG), which reflects quantitative glucose uptake into tissues and organs. However, data on the reproducibility of MRFDG measurements are scarce, particularly in patients with perturbed glucose homeostasis such as type 2 diabetes. We therefore aimed to evaluate the test-retest repeatability of both MRFDG and SUV in these patients.

RESULTS

Fifteen participants (mean age 71 ± 7 years; 2 females) with type 2 diabetes underwent a short 20-minute [18F]FDG D-WB PET/CT after 6 h fasting on two consecutive days. Both SUV and MRFDG images were reconstructed from D-WB PET/CT data obtained 60-80 min post-injection of [18F]FDG. MRFDG and SUV data were measured in organs and tissues, and repeatability was assessed with Bland-Altman analysis, intraclass correlation coefficients (ICC), repeatability coefficients (RPC) and coefficients of variation (wCV). There was high repeatability of both SUVmean and MRFDG-mean in all measured organs (ICC range: 0.65-0.95 for SUVmean and 0.66-0.94 for MRFDG-mean). SUVmean generally demonstrated higher reliability (ICC) and lower variability (%RPC and %wCV) when compared to MRFDG-mean. However, MRFDG test-retest variation was < 19% in most analysed tissues, demonstrating that MRFDG may be used as a precise marker of treatment response.

CONCLUSION

This study demonstrates that MRFDG calculated from D-WB PET/CT exhibit high repeatability, comparable to SUVs across most organs in patients with type 2 diabetes.

Phase I/II trial of iPS-cell-derived dopaminergic cells for Parkinson's disease

Parkinson's disease is caused by the loss of dopamine neurons, causing motor symptoms. Initial cell therapies using fetal tissues showed promise but had complications and ethical concerns1-5. Pluripotent stem (PS) cells emerged as a promising alternative for developing safe and effective treatments6. In this phase I/II trial at Kyoto University Hospital, seven patients (ages 50-69) received bilateral transplantation of dopaminergic progenitors derived from induced PS (iPS) cells. Primary outcomes focused on safety and adverse events, while secondary outcomes assessed motor symptom changes and dopamine production for 24 months. There were no serious adverse events, with 73 mild to moderate events. Patients' anti-parkinsonian medication doses were maintained unless therapeutic adjustments were required, resulting in increased dyskinesia. Magnetic resonance imaging showed no graft overgrowth. Among six patients subjected to efficacy evaluation, four showed improvements in the Movement Disorder Society Unified Parkinson's Disease Rating Scale part III OFF score, and five showed improvements in the ON scores. The average changes of all six patients were 9.5 (20.4%) and 4.3 points (35.7%) for the OFF and ON scores, respectively. Hoehn-Yahr stages improved in four patients. Fluorine-18-L-dihydroxyphenylalanine (18F-DOPA) influx rate constant (Ki) values in the putamen increased by 44.7%, with higher increases in the high-dose group. Other measures showed minimal changes. This trial (jRCT2090220384) demonstrated that allogeneic iPS-cell-derived dopaminergic progenitors survived, produced dopamine and did not form tumours, therefore suggesting safety and potential clinical benefits for Parkinson's disease.

A positron emission tomography tracer for the imaging of oxidative stress in the central nervous system

Reactive oxygen and nitrogen species (RONS) contribute to the pathogenesis of neurodegeneration, but the inability to detect RONS in vivo in the central nervous system has confounded the interpretation of results of clinical trials of antioxidants. Here we report the synthesis and characterization of a positron emission tomography (PET) probe, [18F]fluoroedaravone ([18F]FEDV), for the in vivo quantification of oxidative stress. Derived from the antioxidant edaravone, the probe can diffuse through the blood-brain barrier and is stable in human plasma. In mice, PET imaging with [18F]FEDV allowed for the detection of RONS after intrastriatal injection of sodium nitroprusside, in the middle cerebral artery after stroke by photothrombosis, and in brains with tauopathy. When using dynamic PET imaging coupled with parametric mapping, the sensitivity of [18F]FEDV-PET to RONS allowed for the detection of increased oxidative stress. [18F]FEDV-PET could be used to quantify RONS longitudinally in vivo and to assess the results of clinical studies of antioxidants.

Measuring hypoxia in chronic limb-threatening ischemia using 18F-FAZA kinetic modelling - a pilot study

BACKGROUND

Chronic limb- threatening ischemia (CLTI) is a serious condition that can lead to amputation, and in some cases, it can be associated with mortality. Current clinical evaluation methods have several limitations. Therefore, new methods to assess CLTI are needed to better understand and measure underlying causes and functionality, and hence potentially improve the treatment. In this study, we use dynamic 18F-FAZA PET-imaging as a method of measuring hypoxia as a marker associated with CLTI, on twelve patients identified with CLTI who underwent 18F-FAZA PET-MR imaging.

RESULTS

The kinetic modelling goodness-of-fit metrics using AIF from independent limb with the irreversible-2TC3K model distinguished between index and contralateral limbs better than the reversable-2TC4K model. The Spearman correlation coefficients between the standardized uptake value (SUV) SUV-to-SUVmed ratio and the perfusion parameter, [Formula: see text], was rs = -0.07 for index and rs = 0.22 for contralateral limbs. For the SUV-to-SUVmed ratio correlation with diffusion parameter, [Formula: see text], it is found to be negative for both index (rs = -0.16) and contralateral (rs = -0.11).

CONCLUSIONS

The kinetic modelling of 18F-FAZA dynamic PET-MR was able to differentiate between index and contralateral limbs in CLTI patients, and the diffusion metric from the kinetic modelling can potentially be used as a metric to measure hypoxia in CLTI.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04054609. Registered 20,190,611, https//clinicaltrials.gov/study/NCT04054609.

Hippocampal perineuronal net degradation identifies prefrontal and striatal circuits involved in schizophrenia-like changes in marmosets

In schizophrenia, anterior hippocampus (aHipp) overactivity is associated with orbitofrontal cortex (OFC) dysfunction, but the contribution to symptomatology is unknown. In rodents, degradation of the hippocampal perineuronal net (PNN) replicates this overactivity, but uncertainty over rodent/human prefrontal homology limits translation to humans. Here, we test the hypothesis that aHipp PNN degradation in a species with a human-like prefrontal cortex, the marmoset, alters aHipp-striatal and aHipp-OFC circuitry. Microdialysis and [18F]-fluoro-l-dihydroxyphenylalanine positron emission tomography identified increased dopamine synthesis in the associative striatum, but not the nucleus accumbens, as is seen in schizophrenia, and elevated dopamine and noradrenaline in the OFC. Behaviorally, activity was elevated in a marmoset version of the amphetamine-induced activity test, and impaired probabilistic discrimination learning was seen in an OFC/striatum-dependent task that computational modeling suggests was due to loss of goal-directed behavior. Together, these findings demonstrate that a loss of primate aHipp PNNs is sufficient to induce striatal and prefrontal dysfunction consistent with that observed in humans with schizophrenia.

Characterizing the evolution of lesion, penumbra and blood-brain barrier permeability in a photothrombotic juvenile rat stroke model using MRI and histology

Pediatric stroke is a significant cause of childhood mortality and morbidity. The clinical research in this field bears certain limitations that do not exist in the pre-clinical setting. Experimental models of ischemic stroke show differences in lesion evolution and blood-brain barrier (BBB) permeability between adult and neonatal rats. However, little is known about these factors in the juvenile stage. Here, we characterize the evolution of the lesion, penumbra and degree of BBB permeability in a photothrombotic ring model of juvenile stroke using a mixed longitudinal and cross-sectional study. Fourteen Sprague Dawley juvenile rats (weight 130-189 g), lesion, penumbra volume and blood-brain barrier (BBB) leakage were measured longitudinally on days 0, 2, and 7 following photothrombotic stroke. Magnetic resonance imaging (MRI) techniques were used to measure lesion and penumbra volumes (T2-weighted imaging [T2]), water restriction (diffusion-weighted imaging [DWI]) and BBB leakage (with dynamic contrast-enhanced imaging [DCE]). To confirm stroke, histology was performed (n = 9) with Triphenyltetrazolium chloride staining (TTC) (n=9), (Haemotoxylin and Eosin (H&E) staining (n=3); andn Evans Blue (EB) staining to assess BBB permeability (n=9). We found the volume of the penumbra to be larger and better delineated on MRI and histology in the acute compared to the subacute and chronic stages. The lesion was smaller in volume and increased over time following same time trajectory. The BBB was most compromised at the hyperacute stage (day 0) and decreasingly, yet persistently, disrupted to day 7. Our in vivo and ex vivo findings provide insight into the evolution of stroke and could serve as a study model to test blood-brain barrier stabilization agents in the pediatric setting.

Total-Body Parametric Imaging Using Relative Patlak Plot

The standard Patlak plot, a simple yet efficient model, is widely used to describe irreversible tracer kinetics for dynamic PET imaging. Its widespread application to whole-body parametric imaging remains constrained because of the need for a full-time-course input function (e.g., 1 h). In this paper, we demonstrate the relative Patlak (RP) plot, which eliminates the need for the early-time input function, for total-body parametric imaging and its application to 20-min clinical scans acquired in list mode. Methods: We conducted a theoretic analysis to indicate that the RP intercept b' is equivalent to a ratio of the SUV relative to the plasma concentration, whereas the RP slope Ki ' is equal to the standard Patlak Ki (net influx rate) multiplied by a global scaling factor for each subject. One challenge in applying RP to a short scan duration (e.g., 20 min) is the resulting high noise in the parametric images. We applied a self-supervised deep-kernel method for noise reduction. Using the standard Patlak plot as the reference, the RP method was evaluated for lesion quantification, lesion-to-background contrast, and myocardial visualization in total-body parametric imaging in 22 human subjects (12 healthy subjects and 10 cancer patients) who underwent a 1-h dynamic 18F-FDG scan. The RP method was also applied to the dynamic data reconstructed from a clinical standard 20-min list-mode scan either at 1 or 2 h after injection for 2 cancer patients. Results: We demonstrated that it is feasible to obtain high-quality parametric images from 20-min scans using RP parametric imaging with a self-supervised deep-kernel noise-reduction strategy. The RP slope Ki ' was highly correlated with the standard Patlak Ki in lesions and major organs, demonstrating its quantitative potential across subjects. Compared with conventional SUVs, the Ki ' images significantly improved lesion contrast and enabled visualization of the myocardium for potential cardiac assessment. The application of the RP parametric imaging to the 2 clinical scans also showed similar benefits. Conclusion: Using total-body PET with the RP approach, it is feasible to generate parametric images using data from a 20-min clinical list-mode scan.

Dynamic 18 F-FDG PET to detect differences among patients with progressive and relapsing multiple sclerosis: a pilot study

BACKGROUND

Patients with multiple sclerosis (MS) may remain in a relapsing-remitting (RRMS) course despite long-standing disease, while others will develop secondary progression (SPMS). Chronic inflammation and changes in the blood-brain barrier resulting in perturbed glucose metabolism may account for these differences. PET-MRI with kinetic analysis of 2-deoxy-2(18 F)fluoro-d-glucose (18 F-FDG) provides insight into glucose metabolism and has proven useful in several chronic inflammatory diseases. However, to our knowledge, it has never been studied in MS.

OBJECTIVE

To explore potential differences in glucose distribution kinetics among individuals with long-standing SPMS and RRMS using dynamic 18-F-FDG PET-MRI.

METHODS

Dynamic 18-F-FDG PET-MRI scans were obtained in 11 patients with long-standing MS: 4 with RRMS and 7 with SPMS. Kinetic analysis of PET data was performed using a three-compartment model equation that represents plasma, tissue and 18 F-FDG phosphorylation. Individual rate constants of 18-F-FDG across the compartments were calculated.

RESULTS

Patients with SPMS exhibited a trend towards an increased net influx rate of glucose (p = 0.059) and an increased rate constant representing glucose phosphorylation. Together, the data suggest increased uptake of glucose and glycolysis in these patients.

CONCLUSION

Dynamic 18 F-FDG PET-MRI is a feasible technique that may show information in vivo of glucose metabolism in MS. Although preliminary data suggest a potential radiological marker of progression in MS, further studies are required to confirm this hypothesis.

Exploring a Nitric Oxide-Releasing Celecoxib Derivative as a Potential Modulator of Bone Healing: Insights from Ex Vivo and In Vivo Imaging Experiments

The inducible enzyme cyclooxygenase-2 (COX-2) and the subsequent synthesis of eicosanoids initiated by this enzyme are important molecular players in bone healing. In this pilot study, the suitability of a novel selective COX-2 inhibitor bearing a nitric oxide (NO)-releasing moiety was investigated as a modulator of healing a critical-size bone defect in rats. A 5 mm femoral defect was randomly filled with no material (negative control, NC), a mixture of collagen and autologous bone fragments (positive control, PC), or polycaprolactone-co-lactide (PCL)-scaffolds coated with two types of artificial extracellular matrix (aECM; collagen/chondroitin sulfate (Col/CS) or collagen/polysulfated hyaluronic acid (Col/sHA3)). Bone healing was monitored by a dual-tracer ([18F]FDG/[18F]fluoride) approach using PET/CT imaging in vivo. In addition, ex vivo µCT imaging as well as histological and immunohistochemical studies were performed 16 weeks post-surgery. A significant higher uptake of [18F]FDG, a surrogate marker for inflammatory infiltrate, but not of [18F]fluoride, representing bone mineralization, was observed in the implanted PCL-scaffolds coated with either Col/CS or Col/sHA3. Molecular targeting of COX-2 with NO-coxib had no significant effect on tracer uptake in any of the groups. Histological and immunohistochemical staining showed no evidence of a positive or negative influence of NO-coxib treatment on bone healing.

The control costs of human brain dynamics

The human brain is a complex system with high metabolic demands and extensive connectivity that requires control to balance energy consumption and functional efficiency over time. How this control is manifested on a whole-brain scale is largely unexplored, particularly what the associated costs are. Using the network control theory, here, we introduce a novel concept, time-averaged control energy (TCE), to quantify the cost of controlling human brain dynamics at rest, as measured from functional and diffusion MRI. Importantly, TCE spatially correlates with oxygen metabolism measures from the positron emission tomography, providing insight into the bioenergetic footing of resting-state control. Examining the temporal dimension of control costs, we find that brain state transitions along a hierarchical axis from sensory to association areas are more efficient in terms of control costs and more frequent within hierarchical groups than between. This inverse correlation between temporal control costs and state visits suggests a mechanism for maintaining functional diversity while minimizing energy expenditure. By unpacking the temporal dimension of control costs, we contribute to the neuroscientific understanding of how the brain governs its functionality while managing energy expenses.

Permeability Benchmarking: Guidelines for Comparing in Silico, in Vitro, and in Vivo Measurements

Permeability is a measure of the degree to which cells can transport molecules across biological barriers. Units of permeability are distance per unit time (typically cm/s), where accurate measurements are needed to define drug delivery in homeostasis and to model dysfunction occurring during disease. This perspective offers a set of community-led guidelines to benchmark permeability data across multidisciplinary approaches and different biological contexts. First, we lay out the analytical framework for three methodologies to calculate permeability: in silico assays using either transition-based counting or the inhomogeneous-solubility diffusion approaches, in vitro permeability assays using cells cultured in 2D or 3D geometries, and in vivo assays utilizing in situ brain perfusion or multiple time-point regression analysis. Then, we demonstrate a systematic benchmarking of in silico to both in vitro and in vivo, depicting the ways in which each benchmarking is sensitive to the choices of assay design. Finally, we outline seven recommendations for best practices in permeability benchmarking and underscore the significance of tailored permeability assays in driving advancements in drug delivery research and development. Our exploration encompasses a discussion of "generic" and tissue-specific biological barriers, including the blood-brain barrier (BBB), which is a major hurdle for the delivery of therapeutic agents into the brain. By addressing challenges in reconciling simulated data with experimental assays, we aim to provide insights essential for optimizing accuracy and reliability in permeability modeling.

MR Imaging Indices for Brain Interstitial Fluid Dynamics and the Effects of Orexin Antagonists on Sleep

PURPOSE

The purpose of this study was to assess the extent to which improvement in sleep with lemborexant contributed to changes in interstitial fluid dynamics.

METHODS

The 3 methods including diffusion tensor image analysis along the perivascular space (DTI-ALPS), dynamic contrast-enhanced method to assess tissue vascular permeability (Ktrans), and choroid plexus volume (CPV) were used. Correlations between these imaging indices and sleep parameters (latency to persistent sleep [LPS], wake after sleep onset [WASO], total sleep time [TST], and sleep efficiency [SE]) were evaluated using Pearson correlation analysis. Additionally, multiple regression analysis and linear mixed model analysis were employed to assess the relationship between baseline sleep status and imaging parameter changes. MRI and sleep assessments were performed before treatment initiation (week 0, w0) and at 12 weeks after lemborexant administration (week 12, w12).

RESULTS

The ALPS-index was inversely correlated with LPS and positively correlated with TST and SE at w0. In multiple regression analysis, ALPS-index was lower when sleep parameters other than LPS were poor at w0. A linear mixed model analysis suggested that poor sleep status in LPS and SE at w0 may have an effect on greater ALPS-index. In the evaluation of Ktrans measurement, the single regression analysis showed a statistically significant correlation between the reduction in Ktrans and the shortening in LPS. Examination of CPV and sleep parameters showed a significant negative correlation between TST and CPV at w0 and w12. Multiple regression analysis also showed that TST of w12 had a significant effect on CPV at w12.

CONCLUSION

Our results suggested that poor sleep status is related to the greater change of ALPS-index and CPV improvement after lemborexant administration may be related to in part to sleep parameter improvement.

Glucose metabolic rate from four-dimensional [18F]FDG PET/CT to differentiate sarcoid lesions from malignant lesions

OBJECTIVES

On 18F-Fludeoxyglucose (FDG) PET/CT, active sarcoid lesions are often difficult to differentiate from malignant lesions. We investigated the potential of the glucose metabolic rate (MRglc, mg/min/100 mL), a new quantification of glucose metabolic kinetics derived from direct reconstruction based on linear Patlak analysis, to distinguish between sarcoidosis and malignant lesions.

MATERIALS AND METHODS

A total of 100 patients with cardiac sarcoidosis (CS) and 67 patients with cancer who underwent four-dimensional FDG PET/CT were enrolled. The lesions with a standardized uptake value (SUV) ≥ 2.7 on the standard scan were included as active lesions in the analysis. SUV and MRglc were derived using data acquired between 30 min and 50 min on four-dimensional FDG PET/CT. The mean value in the volume of interest (size 1.5 cm3) was measured. The diagnostic performance of sarcoidosis using MRglc and SUV was evaluated using receiver-operating-characteristic (ROC) analysis.

RESULTS

A total of 90 sarcoidosis lesions from 44 CS patients (18 males, 63.4 ± 12.2 years) and 87 malignant lesions from 57 cancer-bearing patients (32 males, 65 ± 14 years) were analyzed. SUV and MRglc for sarcoid lesions were significantly lower than those for malignant lesions (SUV, 4.98 ± 2.00 vs 6.21 ± 2.14; MRglc, 2.52 ± 1.39 vs 3.68 ± 1.61; p < 0.01). ROC analysis indicated that the ability to discriminate sarcoid patients from those with malignancy yielded areas under the curves of 0.703 and 0.754, with sensitivities of 64% and 77% and specificities of 75% and 72% for SUV 5.025 and MRglc 2.855, respectively.

CONCLUSION

MRglc was significantly lower in sarcoid lesions than malignant lesions, and improved sarcoid lesions identification over SUV alone.

CLINICAL RELEVANCE STATEMENT

MRglc improves sarcoid lymph node identification over SUV alone and is expected to shorten the examination time by eliminating delayed scans.

KEY POINTS

Active sarcoid lesions are sometimes associated with FDG accumulation and should be differentiated from malignant lesions. SUV and metabolic rate of glucose (MRglc) strongly positively correlated, and MRglc could differentiate sarcoid and malignant lesions. MRglc allows for accurate evaluation and staging of malignant lesions.

Probabilistic nested model selection in pharmacokinetic analysis of DCE-MRI data in animal model of cerebral tumor

Best current practice in the analysis of dynamic contrast enhanced (DCE)-MRI is to employ a voxel-by-voxel model selection from a hierarchy of nested models. This nested model selection (NMS) assumes that the observed time-trace of contrast-agent (CA) concentration within a voxel, corresponds to a singular physiologically nested model. However, admixtures of different models may exist within a voxel's CA time-trace. This study introduces an unsupervised feature engineering technique (Kohonen-Self-Organizing-Map (K-SOM)) to estimate the voxel-wise probability of each nested model. Sixty-six immune-compromised-RNU rats were implanted with human U-251 N cancer cells, and DCE-MRI data were acquired from all the rat brains. The time-trace of change in the longitudinal-relaxivity (ΔR1) for all animals' brain voxels was calculated. DCE-MRI pharmacokinetic (PK) analysis was performed using NMS to estimate three model regions: Model-1: normal vasculature without leakage, Model-2: tumor tissues with leakage without back-flux to the vasculature, Model-3: tumor vessels with leakage and back-flux. Approximately two hundred thirty thousand (229,314) normalized ΔR1 profiles of animals' brain voxels along with their NMS results were used to build a K-SOM (topology-size: 8 × 8, with competitive-learning algorithm) and probability map of each model. K-fold nested-cross-validation (NCV, k = 10) was used to evaluate the performance of the K-SOM probabilistic-NMS (PNMS) technique against the NMS technique. The K-SOM PNMS's estimation for the leaky tumor regions were strongly similar (Dice-Similarity-Coefficient, DSC = 0.774 [CI: 0.731-0.823], and 0.866 [CI: 0.828-0.912] for Models 2 and 3, respectively) to their respective NMS regions. The mean-percent-differences (MPDs, NCV, k = 10) for the estimated permeability parameters by the two techniques were: -28%, + 18%, and + 24%, for vp, Ktrans, and ve, respectively. The KSOM-PNMS technique produced microvasculature parameters and NMS regions less impacted by the arterial-input-function dispersion effect. This study introduces an unsupervised model-averaging technique (K-SOM) to estimate the contribution of different nested-models in PK analysis and provides a faster estimate of permeability parameters.

Impact of different parametric Patlak imaging approaches and comparison with a 2-tissue compartment pharmacokinetic model with a long axial field-of-view (LAFOV) PET/CT in oncological patients

AIM

The recently introduced Long-Axial-Field-of-View (LAFOV) PET-CT scanners allow for the first-time whole-body dynamic- and parametric imaging. Primary aim of this study was the comparison of direct and indirect Patlak imaging as well as the comparison of different time frames for Patlak calculation with the LAFOV PET-CT in oncological patients. Secondary aims of the study were lesion detectability and comparison of Patlak analysis with a two-tissue-compartment model (2TCM).

METHODOLOGY

50 oncological patients with 346 tumor lesions were enrolled in the study. All patients underwent [18F]FDG PET/CT (skull to upper thigh). Here, the Image-Derived-Input-Function) (IDIF) from the descending aorta was used as the exclusive input function. Four sets of images have been reviewed visually and evaluated quantitatively using the target-to-background (TBR) and contrast-to-noise ratio (CNR): short-time (30 min)-direct (STD) Patlak Ki, short-time (30 min)-indirect (STI) Patlak Ki, long-time (59.25 min)-indirect (LTI) Patlak Ki, and 50-60 min SUV (sumSUV). VOI-based 2TCM was used for the evaluation of tumor lesions and normal tissues and compared with the results of Patlak model.

RESULTS

No significant differences were observed between the four approaches regarding the number of tumor lesions. However, we found three discordant results: a true positive liver lesion in all Patlak Ki images, a false positive liver lesion delineated only in LTI Ki which was a hemangioma according to MRI and a true negative example in a patient with an atelectasis next to a lung tumor. STD, STI and LTI Ki images had superior TBR in comparison with sumSUV images (2.9-, 3.3- and 4.3-fold higher respectively). TBR of LTI Ki were significantly higher than STD Ki. VOI-based k3 showed a 21-fold higher TBR than sumSUV. Parameters of different models vary in their differential capability between tumor lesions and normal tissue like Patlak Ki which was better in normal lung and 2TCM k3 which was better in normal liver. 2TCM Ki revealed the highest correlation (r = 0.95) with the LTI Patlak Ki in tumor lesions group and demonstrated the highest correlation with the STD Patlak Ki in all tissues group and normal tissues group (r = 0.93 and r = 0.74 respectively).

CONCLUSIONS

Dynamic [18F]-FDG with the new LAFOV PET/CT scanner produces Patlak Ki images with better lesion contrast than SUV images, but does not increase the lesion detection rate. The time window used for Patlak imaging plays a more important role than the direct or indirect method. A combination of different models, like Patlak and 2TCM may be helpful in parametric imaging to obtain the best TBR in the whole body in future.

Total Body PET-CT Protocols in Oncology

Recently developed long axial field of view (LAFOV) PET-CT scanners, including total body scanners, are already in use in a few centers worldwide. These systems have some major advantages over standard axial field of view (SAFOV) PET-CT scanners, mainly due to up to 20 times higher sensitivity and therefore improved lesion detectability. Other advantages are the reduction of the PET acquisition time for a static whole-body measurement, the reduction of the administered radiotracer dose, and the ability to perform delayed scans with good image quality, which is important for imaging radionuclides with long half-lives and pharmaceuticals with long biodistribution times, such as 89Zr-labeled antibodies. The reduction of the applied tracer dose leads to less radiation exposure and may facilitate longitudinal studies, especially in oncological patients, for the evaluation of therapy. The reduction in acquisition time for a static whole body (WB) study allows a markedly higher patient throughput. Furthermore, LAFOV PET-CT scanners enable for the first-time WB dynamic PET scanning and WB parametric imaging with an improved image quality due to increased sensitivity and time resolution. WB tracer kinetics is of particular interest for the characterization of novel radiopharmaceuticals and for a better biological characterization of cancer diseases, as well as for a more accurate assessment of the response to new targeted therapies. Further technological developments based on artificial intelligence (AI) approaches are underway and may in the future allow CT-less attenuation correction or ultralow dose CT for attenuation correction as well as segmentation algorithms for the evaluation of total metabolic tumor volume. The aim of this review is to present dedicated PET acquisition protocols for oncological studies with LAFOV scanners, including static and dynamic acquisition as well as parametric scans, and to present literature data to date on this topic.

Assessment of dual time point protocols to produce parametric Ki images in FDG PET/CT: A virtual clinical study

PURPOSE

This simulation study investigated the feasibility of generating Patlak Ki images using a dual time point (DTP-Ki) scan protocol involving two 3-min/bed routine static PET scans and, subsequently, assessed DTP-Ki performance for an optimal DTP scan time frame combination, against conventional Patlak Ki estimated from complete 0-93 min dynamic PET data.

METHODS

Six realistic heterogeneous tumors of different characteristic spatiotemporal [18F]FDG uptake distributions for three noise levels commonly found in clinical studies and 20 noise realizations (N = 360 samples) were produced by analytic simulations of the XCAT phantom. Subsequently, DTP-Ki images were generated by performing standard linear indirect Patlak analysis with t*≥ 12 $ \ge 12$ -min (Patlakt* = 12) using a scaled population-based input function (sPBIF) model on 66 combinations of early and late 3-min/bed static whole-body PET reconstructed images. All DTP-Ki images were evaluated against respective DTP-Ki images estimated with Patlakt* = 12 and 0-93 min individual input functions (iIFs) and against gold standard Ki images estimated with Patlakt* = 12, 0-93 min iIFs and tissue time activity curves from all reconstructed WB passes 12-93 min post injection. The optimal combination of early and late frames, in terms of attaining the highest correlation between DTP-Ki with sPBIF and gold standard Ki was also determined from a set of 66 different combinations of 2-min early and late frames. Moreover, the performance of DTP-Ki with sPBIF was compared against that of the retention index (RI) in terms of their correlation to the gold standard Ki. Finally, the feasibility and practicality of DTP protocol in the clinic were assessed through the analysis of nine patients.

RESULTS

High correlations (>0.9) were observed between DTP-Ki values from sPBIF and those from iIFs for all evaluated DTP protocols while the mean AUC difference between sPBIF and iIFs was less than 10%. The percentage difference of mean values between DTP-Ki from sPBIF and from iIFs was less than 1%. DTP Ki from sPBIF exhibited significantly higher correlation with gold standard Ki, in contrast to RI, across all 66 DTP protocols (p < 0.05 using the two-tailed t-test by Williams) with the highest correlation attained for the 50-53-min early + 90-93-min late scan time frames (optimal DTP protocol).

CONCLUSION

Feasibility of generating Patlak Ki [18F] FDG images from an early and a late post injection 3-min/bed routine static scan using a population-based input function model was demonstrated and an optimal DTP scan protocol was determined. The results indicated high correlations between DTP-Ki and gold-standard Ki images that are significantly larger than those between RI and gold-standard Ki.

Cholinergic dysfunction in isolated rapid eye movement sleep behaviour disorder links to impending phenoconversion

BACKGROUND AND PURPOSE

Most patients with isolated rapid eye movement sleep behaviour disorder (iRBD) progress to a parkinsonian alpha-synucleinopathy. However, time to phenoconversion shows great variation. The aim of this study was to investigate whether cholinergic and dopaminergic dysfunction in iRBD patients was associated with impending phenoconversion.

METHODS

Twenty-one polysomnography-confirmed iRBD patients underwent baseline 11C-donepezil and 6-Fluoro-(18F)-l-3,4-dihydroxyphenylalanine (18F-DOPA) positron emission tomography (PET). Potential phenoconversion was monitored for up to 8 years. PET images were analysed according to patients' diagnoses after 3 and 8 years using linear regression. Time-to-event analysis was made with Cox regression, dividing patients into low and high tracer uptake groups.

RESULTS

Follow-up was accomplished in 17 patients. Eight patients progressed to either Parkinson's disease (n = 4) or dementia with Lewy bodies (n = 4), while nine remained non-phenoconverters. Compared with non-phenoconverters, 8-year phenoconverters had lower mean 11C-donepezil uptake in the parietal (p = 0.032) and frontal cortex (p = 0.042), whereas mean 11C-donepezil uptake in 3-year phenoconverters was lower in the parietal cortex (p = 0.005), frontal cortex (p = 0.025), thalamus (p = 0.043) and putamen (p = 0.049). Phenoconverters within 3 years and 8 years had lower 18F-DOPA uptake in the putamen (p < 0.001). iRBD patients with low parietal 11C-donepezil uptake had a 13.46 (95% confidence interval 1.42;127.21) times higher rate of phenoconversion compared with those with higher uptake (p = 0.023). iRBD patients with low 18F-DOPA uptake in the most affected putamen were all phenoconverters with higher rate of phenoconversion (p = 0.0002).

CONCLUSIONS

These findings suggest that cortical cholinergic dysfunction, particularly within the parietal cortex, could be a biomarker candidate for predicting short-term phenoconversion in iRBD patients. This study aligns with previous reports suggesting dopaminergic dysfunction is associated with forthcoming phenoconversion.

High-Density Lipoprotein Mimetic Peptide 4F Reduces Toxic Amyloid-Beta Exposure to the Blood-Brain Barrier Endothelium in Alzheimer's Disease Transgenic Mice

Aβ accumulation in the blood-brain barrier (BBB) endothelium, which lines the cerebrovascular lumen, is a significant contributor to cerebrovascular dysfunction in Alzheimer's disease (AD). Reduced high-density lipoprotein (HDL) levels are associated with increased AD risk, and the HDL mimetic peptide 4F has been developed as a promising therapeutic agent to improve cerebrovascular health in AD. In this study, we evaluated the impact of 4F on 125I-Aβ42 blood-to-brain distribution using dynamic SPECT/CT imaging in both wild-type and APP/PS1 transgenic mice. Graphical analysis of the imaging data demonstrated that 4F significantly reduced the blood-to-brain influx rate in wild-type mice and the distribution of 125I-Aβ42 in the BBB endothelium in APP/PS1 mice. To elucidate the molecular mechanisms underlying the effect of 4F, we evaluated its impact on the p38 pathway and its role in mediating Aβ42 trafficking in human BBB endothelial cell monolayers. Treatment with 4F significantly decreased Aβ42 induced p38 activation in BBB endothelial cells. Furthermore, inhibition of p38 kinase significantly reduced endothelial accumulation of fluorescence-labeled Aβ42 and luminal-to-abluminal permeability across the cell monolayer. While our previous publication has hinted at the potential of 4F to reduce Aβ accumulation in the brain parenchyma, the current findings demonstrated the protective effect of 4F in reducing Aβ42 accumulation in the BBB endothelium of AD transgenic mice. These findings revealed the impact of a clinically tested agent, the HDL mimetic peptide 4F, on Aβ exposure to the BBB endothelium and offer novel mechanistic insights into potential therapeutic strategies to treat cerebrovascular dysfunction in AD.

Whole-Body Multiparametric PET in Clinical Oncology: Current Status, Challenges, and Opportunities

The interpretation of clinical oncologic PET studies has historically used static reconstructions based on SUVs. SUVs and SUV-based images have important limitations, including dependence on uptake times and reduced conspicuity of tracer-avid lesions in organs with high background uptake. The acquisition of dynamic PET images enables additional PET reconstructions via Patlak modeling, which assumes that a tracer is irreversibly trapped by tissues of interest. The resulting multiparametric PET images capture a tracer's net trapping rate and apparent volume of distribution, separating the contributions of bound and free tracer fractions to the PET signal captured in the SUV. Potential benefits of multiparametric PET include higher quantitative stability, superior lesion conspicuity, and greater accuracy for differentiating malignant and benign lesions. However, the imaging protocols necessary for multiparametric PET are inherently more complex and time intensive, despite the recent introduction of automated or semiautomated scanner-based reconstruction packages. In this Review, we examine the current state of multiparametric PET in whole-body oncologic imaging. We summarize the Patlak method and relevant tracer kinetics, discuss clinical workflows and protocol considerations, and highlight clinical challenges and opportunities. We aim to help oncologic imagers make informed decisions about whether to implement multiparametric PET in their clinical practices.

Neuroinflammation in Parkinson's disease: A study with [11C]PBR28 PET and cerebrospinal fluid markers

OBJECTIVE

To investigate neuroinflammation in Parkinson's disease (PD) with [11C]PBR28 positron emission tomography (PET) and cerebrospinal fluid (CSF) biomarkers, and the relationship to dopaminergic functioning measured with 6-[18F]-fluoro-L-dopa ([18F]FDOPA) PET.

METHODS

The clinical cohort consisted of 20 subjects with PD and 51 healthy controls (HC). All HC and 15 PD participants underwent [11C]PBR28 High Resolution Research Tomograph (HRRT) PET for the quantitative assessment of cerebral binding to the translocator protein (TSPO), a neuroinflammation marker. CSF samples were available from 17 subjects with PD and 21 HC and were examined for soluble triggering receptor expressed on myeloid cells 2 (sTREM2), chitinase 3-like 1 protein (YKL-40), neurogranin (NG), alpha-synuclein (aSyn) and oligo-alpha-synuclein. All subjects with PD underwent [18F]FDOPA HRRT PET.

RESULTS

While the subjects with PD and HC did not differ in the total volume of distribution (VT) of [11C]PBR28 in any studied brain regions, higher levels of neuroinflammation and neurodegeneration CSF biomarkers sTREM2 and NG, respectively were associated with more severe motor symptoms evaluated by The Unified Parkinson's Disease Rating Scale motor part (UPDRS-III) (r = 0.52, p = 0.041 and r = 0.59, p = 0.016 respectively). Additionally, in the PD group increased [11C]PBR28 VT in the basal ganglia and substantia nigra (SN) was related to higher levels of neuroinflammation biomarker YKL-40 (p < 0.01).

CONCLUSION

Associations between CSF biomarkers, motor disability and [11C]PBR28 VT in the striatum and SN may support a role for neuroinflammation in PD.

Current trends in the characterization and monitoring of vascular response to cancer therapy

Tumor vascular physiology is an important determinant of disease progression as well as the therapeutic outcome of cancer treatment. Angiogenesis or the lack of it provides crucial information about the tumor's blood supply and therefore can be used as an index for cancer growth and progression. While standalone anti-angiogenic therapy demonstrated limited therapeutic benefits, its combination with chemotherapeutic agents improved the overall survival of cancer patients. This could be attributed to the effect of vascular normalization, a dynamic process that temporarily reverts abnormal vasculature to the normal phenotype maximizing the delivery and intratumor distribution of chemotherapeutic agents. Longitudinal monitoring of vascular changes following antiangiogenic therapy can indicate an optimal window for drug administration and estimate the potential outcome of treatment. This review primarily focuses on the status of various imaging modalities used for the longitudinal characterization of vascular changes before and after anti-angiogenic therapies and their clinical prospects.

Ultrashort Oncologic Whole-Body [18F]FDG Patlak Imaging Using LAFOV PET

Methods to shorten [18F]FDG Patlak PET imaging procedures ranging from 65-90 to 20-30 min after injection, using a population-averaged input function (PIF) scaled to patient-specific image-derived input function (IDIF) values, were recently evaluated. The aim of the present study was to explore the feasibility of ultrashort 10-min [18F]FDG Patlak imaging at 55-65 min after injection using a PIF combined with direct Patlak reconstructions to provide reliable quantitative accuracy of lung tumor uptake, compared with a full-duration 65-min acquisition using an IDIF. Methods: Patients underwent a 65-min dynamic PET acquisition on a long-axial-field-of-view (LAFOV) Biograph Vision Quadra PET/CT scanner. Subsequently, direct Patlak reconstructions and image-based (with reconstructed dynamic images) Patlak analyses were performed using both the IDIF (time to relative kinetic equilibrium between blood and tissue concentration (t*) = 30 min) and a scaled PIF at 30-60 min after injection. Next, direct Patlak reconstructions were performed on the system console using only the last 10 min of the acquisition, that is, from 55 to 65 min after injection, and a scaled PIF using maximum crystal ring difference settings of both 85 and 322. Tumor lesion and healthy-tissue uptake was quantified and compared between the differently obtained parametric images to assess quantitative accuracy. Results: Good agreement was obtained between direct- and image-based Patlak analyses using the IDIF (t* = 30 min) and scaled PIF at 30-60 min after injection, performed using the different approaches, with no more than 8.8% deviation in tumor influx rate value (Ki ) (mean difference ranging from -0.0022 to 0.0018 mL/[min × g]). When direct Patlak reconstruction was performed on the system console, excellent agreement was found between the use of a scaled PIF at 30-60 min after injection versus 55-65 min after injection, with 2.4% deviation in tumor Ki (median difference, -0.0018 mL/[min × g]; range, -0.0047 to 0.0036 mL/[min × g]). For different maximum crystal ring difference settings using the scan time interval of 55-65 min after injection, only a 0.5% difference (median difference, 0.0000 mL/[min × g]; range, -0.0004 to 0.0013 mL/[min × g]) in tumor Ki was found. Conclusion: Ultrashort whole-body [18F]FDG Patlak imaging is feasible on an LAFOV Biograph Vision Quadra PET/CT system without loss of quantitative accuracy to assess lung tumor uptake compared with a full-duration 65-min acquisition. The ultrashort 10-min direct Patlak reconstruction with PIF allows for its implementation in clinical practice.

Pathological and neurochemical correlates of locus coeruleus functional network activity

The locus coeruleus (LC) produces the neuromodulators norepinephrine and dopamine, and projects widely to subcortical and cortical brain regions. The LC has been a focus of neuroimaging biomarker development for the early detection of Alzheimer's disease (AD) since it was identified as one of the earliest brain regions to develop tau pathology. Our recent research established the use of positron emission tomography (PET) to measure LC catecholamine synthesis capacity in cognitively unimpaired older adults. We extend this work by investigating the possible influence of pathology and LC neurochemical function on LC network activity using functional magnetic resonance imaging (fMRI). In separate sessions, participants underwent PET imaging to measure LC catecholamine synthesis capacity ([18F]Fluoro-m-tyrosine), tau pathology ([18F]Flortaucipir), and amyloid-β pathology ([11C]Pittsburgh compound B), and fMRI imaging to measure LC functional network activity at rest. Consistent with a growing body of research in aging and preclinical AD, we find that higher functional network activity is associated with higher tau burden in individuals at risk of developing AD (amyloid-β positive). Critically, relationships between higher LC network activity and higher pathology (amyloid-β and tau) were moderated by LC catecholamine synthesis capacity. High levels of LC catecholamine synthesis capacity reduced relationships between higher network activity and pathology. Broadly, these findings support the view that individual differences in functional network activity are shaped by interactions between pathology and neuromodulator function, and point to catecholamine systems as potential therapeutic targets.

Quantitative Assessments of Tumor Activity in a General Oncologic PET/CT Population: Which Metric Minimizes Tracer Uptake Time Dependence?

In oncologic PET, the SUV and standardized uptake ratio (SUR) of a viable tumor generally increase during the postinjection period. In contrast, the net influx rate (Ki ), which is derived from dynamic PET data, should remain relatively constant. Uptake-time-corrected SUV (cSUV) and SUR (cSUR) have been proposed as uptake-time-independent, static alternatives to Ki Our primary aim was to quantify the intrascan repeatability of Ki , SUV, cSUV, SUR, and cSUR among malignant lesions on PET/CT. An exploratory aim was to assess the ability of cSUR to estimate Ki Methods: This prospective, single-center study enrolled adults undergoing standard-of-care oncologic PET/CT. SUV and Ki images were reconstructed from dynamic PET data obtained before (∼35-50 min after injection) and after (∼75-90 min after injection) standard-of-care imaging. Tumors were manually segmented. Quantitative metrics were extracted. cSUVs and cSURs were calculated for a 60-min postinjection reference uptake time. The magnitude of the intrascan test-retest percent change (test-retest |%Δ|) was calculated. Coefficients of determination (R 2) and intraclass correlation coefficients (ICC) were also computed. Differences between metrics were assessed via the Wilcoxon signed-rank test (α, 0.05). Results: This study enrolled 78 subjects; 41 subjects (mean age, 63.8 y; 24 men) with 116 lesions were analyzed. For both tracers, SUVmax and maximum SUR (SURmax) had large early-to-late increases (i.e., poor intrascan repeatability). Among [18F]FDG-avid lesions (n = 93), there were no differences in intrascan repeatability (median test-retest |%Δ|; ICC) between the maximum Ki (Ki ,max) (13%; 0.97) and either the maximum cSUV (cSUVmax) (12%, P = 0.90; 0.96) or the maximum cSUR (cSURmax) (13%, P = 0.67; 0.94). For DOTATATE-avid lesions (n = 23), there were no differences in intrascan repeatability between the Ki ,max (11%; 0.98) and either the cSUVmax (13%, P = 0.41; 0.98) or the cSURmax (11%, P = 0.08; 0.94). The SUVmax, cSUVmax, SURmax, and cSURmax were all strongly correlated with the Ki ,max for both [18F]FDG (R 2, 0.81-0.92) and DOTATATE (R 2, 0.88-0.96), but the cSURmax provided the best agreement with the Ki ,max across early-to-late time points for [18F]FDG (ICC, 0.69-0.75) and DOTATATE (ICC, 0.90-0.91). Conclusion: Ki ,max, cSUVmax, and cSURmax had low uptake time dependence compared with SUVmax and SURmax The Ki ,max can be predicted from cSURmax.

Advances in PET Imaging of Large Vessel Vasculitis: An Update and Future Trends

Systemic vasculitides are autoimmune diseases characterized by inflammation of blood vessels. They are categorized based on the size of the preferentially affected blood vessels: large-, medium-, and small-vessel vasculitides. The main forms of large-vessel vasculitis include giant cell arteritis (GCA) and Takayasu arteritis (TAK). Depending on the location of the affected vessels, various imaging modalities can be employed for diagnosis of large vessel vasculitis: ultrasonography (US), magnetic resonance angiography (MRA), computed tomography angiography (CTA), and [18F]-fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG-PET/CT). These imaging tools offer complementary information about vascular changes occurring in vasculitis. Recent advances in PET imaging in large vessel vasculitis include the introduction of digital long axial field-of-view PET/CT, dedicated acquisition, quantitative methodologies, and the availability of novel radiopharmaceuticals. This review aims to provide an update on the current status of PET imaging in large vessel vasculitis and to share the latest developments on imaging vasculitides.

Characterization of a Syngeneic Orthotopic Model of Cholangiocarcinoma by [18F]FDG-PET/MRI

Cholangiocarcinoma (CCA) is a type of primary liver cancer originating from the biliary tract epithelium, characterized by limited treatment options for advanced cases and low survival rates. This study aimed to establish an orthotopic mouse model for CCA and monitor tumor growth using PET/MR imaging. Murine CCA cells were implanted into the liver lobe of male C57BL/6J mice. The imaging groups included contrast-enhanced (CE) MR, CE-MR with static [18F]FDG-PET, and dynamic [18F]FDG-PET. Tumor volume and FDG uptake were measured weekly over four weeks. Early tumor formation was visible in CE-MR images, with a gradual increase in volume over time. Dynamic FDG-PET revealed an increase in the metabolic glucose rate (MRGlu) over time. Blood analysis showed pathological changes in liver-related parameters. Lung metastases were observed in nearly all animals after four weeks. The study concludes that PET-MR imaging effectively monitors tumor progression in the CCA mouse model, providing insights into CCA development and potential treatment strategies.

Noninvasive Quantification of Glucose Metabolism in Mice Myocardium Using the Spline Reconstruction Technique

The spline reconstruction technique (SRT) is a fast algorithm based on a novel numerical implementation of an analytic representation of the inverse Radon transform. The purpose of this study was to compare the SRT, filtered back-projection (FBP), and the Tera-Tomo 3D algorithm for various iteration numbers, using small-animal dynamic PET data obtained from a Mediso nanoScan® PET/CT scanner. For this purpose, Patlak graphical kinetic analysis was employed to noninvasively quantify the myocardial metabolic rate of glucose (MRGlu) in seven male C57BL/6 mice (n=7). All analytic reconstructions were performed via software for tomographic image reconstruction. The analysis of all PET-reconstructed images was conducted with PMOD software (version 3.506, PMOD Technologies LLC, Fällanden, Switzerland) using the inferior vena cava as the image-derived input function. Statistical significance was determined by employing the one-way analysis of variance test. The results revealed that the differences between the values of MRGlu obtained via SRT versus FBP, and the variants of he Tera-Tomo 3D algorithm were not statistically significant (p > 0.05). Overall, the SRT appears to perform similarly to the other algorithms investigated, providing a valid alternative analytic method for preclinical dynamic PET studies.

Non-invasive assessment of stimulation-specific changes in cerebral glucose metabolism with functional PET

PURPOSE

Functional positron emission tomography (fPET) with [18F]FDG allows quantification of stimulation-induced changes in glucose metabolism independent of neurovascular coupling. However, the gold standard for quantification requires invasive arterial blood sampling, limiting its widespread use. Here, we introduce a novel fPET method without the need for an input function.

METHODS

We validated the approach using two datasets (DS). For DS1, 52 volunteers (23.2 ± 3.3 years, 24 females) performed Tetris® during a [18F]FDG fPET scan (bolus + constant infusion). For DS2, 18 participants (24.2 ± 4.3 years, 8 females) performed an eyes-open/finger tapping task (constant infusion). Task-specific changes in metabolism were assessed with the general linear model (GLM) and cerebral metabolic rate of glucose (CMRGlu) was quantified with the Patlak plot as reference. We then estimated simplified outcome parameters, including GLM beta values and percent signal change (%SC), and compared them, region and whole-brain-wise.

RESULTS

We observed higher agreement with the reference for DS1 than DS2. Both DS resulted in strong correlations between regional task-specific beta estimates and CMRGlu (r = 0.763…0.912). %SC of beta values exhibited strong agreement with %SC of CMRGlu (r = 0.909…0.999). Average activation maps showed a high spatial similarity between CMRGlu and beta estimates (Dice = 0.870…0.979) as well as %SC (Dice = 0.932…0.997), respectively.

CONCLUSION

The non-invasive method reliably estimates task-specific changes in glucose metabolism without blood sampling. This streamlines fPET, albeit with the trade-off of being unable to quantify baseline metabolism. The simplification enhances its applicability in research and clinical settings.

Endocannabinoid levels in plasma and neurotransmitters in the brain: a preliminary report on patients with a psychotic disorder and healthy individuals

BACKGROUND

Interactions between the endocannabinoid system (ECS) and neurotransmitter systems might mediate the risk of developing a schizophrenia spectrum disorder (SSD). Consequently, we investigated in patients with SSD and healthy controls (HC) the relations between (1) plasma concentrations of two prototypical endocannabinoids (N-arachidonoylethanolamine [anandamide] and 2-arachidonoylglycerol [2-AG]) and (2) striatal dopamine synthesis capacity (DSC), and glutamate and y-aminobutyric acid (GABA) levels in the anterior cingulate cortex (ACC). As anandamide and 2-AG might reduce the activity of these neurotransmitters, we hypothesized negative correlations between their plasma levels and the abovementioned neurotransmitters in both groups.

METHODS

Blood samples were obtained from 18 patients and 16 HC to measure anandamide and 2-AG plasma concentrations. For all subjects, we acquired proton magnetic resonance spectroscopy scans to assess Glx (i.e. glutamate plus glutamine) and GABA + (i.e. GABA plus macromolecules) concentrations in the ACC. Ten patients and 14 HC also underwent [18F]F-DOPA positron emission tomography for assessment of striatal DSC. Multiple linear regression analyses were used to investigate the relations between the outcome measures.

RESULTS

A negative association between 2-AG plasma concentration and ACC Glx concentration was found in patients (p = 0.008). We found no evidence of other significant relationships between 2-AG or anandamide plasma concentrations and dopaminergic, glutamatergic, or GABAergic measures in either group.

CONCLUSIONS

Our preliminary results suggest an association between peripheral 2-AG and ACC Glx levels in patients.

Daily standing time, dietary fiber, and intake of unsaturated fatty acids are beneficially associated with hepatic insulin sensitivity in adults with metabolic syndrome

Background

Obesity is associated with impaired glucose metabolism and hepatic insulin resistance. The aim was to investigate the associations of hepatic glucose uptake (HGU) and endogenous glucose production (EGP) to sedentary behavior (SB), physical activity (PA), cardiorespiratory fitness, dietary factors, and metabolic risk markers.

Methods

Forty-four adults with metabolic syndrome (mean age 58 [SD 7] years, BMI ranging from 25-40kg/; 25 females) were included. HGU was measured by positron emission tomography during the hyperinsulinemic-euglycemic clamp. EGP was calculated by subtracting the glucose infusion rate during clamp from the glucose rate of disappearance. SB and PA were measured with hip-worn accelerometers (26 [SD3] days). Fitness was assessed by maximal bicycle ergometry with respiratory gas measurements and dietary intake of nutrients by 4-day food diaries.

Results

HGU was not associated with fitness or any of the SB or PA measures. When adjusted for sex, age, and body fat-%, HGU was associated with whole-body insulin sensitivity (β=0.58), water-insoluble dietary fiber (β=0.29), energy percent (E%) of carbohydrates (β=-0.32), saccharose (β=-0.32), mono- and polyunsaturated fatty acids (β=0.35, β=0.41, respectively). EGP was associated with whole-body insulin sensitivity (β=-0.53), and low-density lipoprotein cholesterol [β=-0.31], and when further adjusted for accelerometry wear time, EGP was associated with standing [β=-0.43]. (p-value for all< 0.05).

Conclusions

Standing more, consuming a diet rich in fiber and unsaturated fatty acids, and a lower intake of carbohydrates, especially sugar, associate beneficially with hepatic insulin sensitivity. Habitual SB, PA, or fitness may not be the primary modulators of HGU and EGP. However, these associations need to be confirmed with intervention studies.

Evaluation of [11C]UCB-A positron emission tomography in human brains

BACKGROUND

In preclinical studies, the positron emission tomography (PET) imaging with [11C]UCB-A provided promising results for imaging synaptic vesicle protein 2A (SV2A) as a proxy for synaptic density. This paper reports the first-in-human [11C]UCB-A PET study to characterise its kinetics in healthy subjects and further evaluate SV2A-specific binding.

RESULTS

Twelve healthy subjects underwent 90-min baseline [11C]UCB-A scans with PET/MRI, with two subjects participating in an additional blocking scan with the same scanning procedure after a single dose of levetiracetam (1500 mg). Our results indicated abundant [11C]UCB-A brain uptake across all cortical regions, with slow elimination. Kinetic modelling of [11C]UCB-A PET using various compartment models suggested that the irreversible two-tissue compartment model best describes the kinetics of the radioactive tracer. Accordingly, the Patlak graphical analysis was used to simplify the analysis. The estimated SV2A occupancy determined by the Lassen plot was around 66%. Significant specific binding at baseline and comparable binding reduction as grey matter precludes the use of centrum semiovale as reference tissue.

CONCLUSIONS

[11C]UCB-A PET imaging enables quantifying SV2A in vivo. However, its slow kinetics require a long scan duration, which is impractical with the short half-life of carbon-11. Consequently, the slow kinetics and complicated quantification methods may restrict its use in humans.

Probabilistic Nested Model Selection in Pharmacokinetic Analysis of DCE-MRI Data in Animal Model of Cerebral Tumor

Purpose

Best current practice in the analysis of dynamic contrast enhanced (DCE)-MRI is to employ a voxel-by-voxel model selection from a hierarchy of nested models. This nested model selection (NMS) assumes that the observed time-trace of contrast-agent (CA) concentration within a voxel, corresponds to a singular physiologically nested model. However, admixtures of different models may exist within a voxel's CA time-trace. This study introduces an unsupervised feature engineering technique (Kohonen-Self-Organizing-Map (K-SOM)) to estimate the voxel-wise probability of each nested model.

Methods

Sixty-six immune-compromised-RNU rats were implanted with human U-251N cancer cells, and DCE-MRI data were acquired from all the rat brains. The time-trace of change in the longitudinalrelaxivityΔ R 1 for all animals' brain voxels was calculated. DCE-MRI pharmacokinetic (PK) analysis was performed using NMS to estimate three model regions: Model-1: normal vasculature without leakage, Model-2: tumor tissues with leakage without back-flux to the vasculature, Model-3: tumor vessels with leakage and back-flux. Approximately two hundred thirty thousand (229,314) normalized Δ R 1 profiles of animals' brain voxels along with their NMS results were used to build a K-SOM (topology-size: 8×8, with competitive-learning algorithm) and probability map of each model. K-fold nested-cross-validation (NCV, k=10) was used to evaluate the performance of the K-SOM probabilistic-NMS (PNMS) technique against the NMS technique.

Results

The K-SOM PNMS's estimation for the leaky tumor regions were strongly similar (Dice-Similarity-Coefficient, DSC=0.774 [CI: 0.731-0.823], and 0.866 [CI: 0.828-0.912] for Models 2 and 3, respectively) to their respective NMS regions. The mean-percent-differences (MPDs, NCV, k=10) for the estimated permeability parameters by the two techniques were: -28%, +18%, and +24%, forv p , K trans , andv e , respectively. The KSOM-PNMS technique produced microvasculature parameters and NMS regions less impacted by the arterial-input-function dispersion effect.

Conclusion

This study introduces an unsupervised model-averaging technique (K-SOM) to estimate the contribution of different nested-models in PK analysis and provides a faster estimate of permeability parameters.

MINocyclinE to Reduce inflammation and blood-brain barrier leakage in small Vessel diseAse (MINERVA): A phase II, randomized, double-blind, placebo-controlled experimental medicine trial

INTRODUCTION

Cerebral small vessel disease (SVD) is a common cause of stroke/vascular dementia with few effective treatments. Neuroinflammation and increased blood-brain barrier (BBB) permeability may influence pathogenesis. In rodent models, minocycline reduced inflammation/BBB permeability. We determined whether minocycline had a similar effect in patients with SVD.

METHODS

MINERVA was a single-center, phase II, randomized, double-blind, placebo-controlled trial. Forty-four participants with moderate-to-severe SVD took minocycline or placebo for 3 months. Co-primary outcomes were microglial signal (determined using 11C-PK11195 positron emission tomography) and BBB permeability (using dynamic contrast-enhanced MRI).

RESULTS

Forty-four participants were recruited between September 2019 and June 2022. Minocycline had no effect on 11C-PK11195 binding (relative risk [RR] 1.01, 95% confidence interval [CI] 0.98-1.04), or BBB permeability (RR 0.97, 95% CI 0.91-1.03). Serum inflammatory markers were not affected.

DISCUSSION

11C-PK11195 binding and increased BBB permeability are present in SVD; minocycline did not reduce either process. Whether these pathophysiological mechanisms are disease-causing remains unclear.

INTERNATIONAL CLINICAL TRIALS REGISTRY PORTAL IDENTIFIER

ISRCTN15483452 HIGHLIGHTS: We found focal areas of increased microglial signal and increased blood-brain barrier permeability in patients with small vessel disease. Minocycline treatment was not associated with a change in these processes measured using advanced neuroimaging. Blood-brain barrier permeability was dynamic but MRI-derived measurements correlated well with CSF/serum albumin ratio. Advanced neuroimaging is a feasible outcome measure for mechanistic clinical trials.

Mechanism of Action and Translational Potential of (S)-Meclizine in Preemptive Prophylaxis Against Stroke

BACKGROUND

Mild chemical inhibition of mitochondrial respiration can confer resilience against a subsequent stroke or myocardial infarction, also known as preconditioning. However, the lack of chemicals that can safely inhibit mitochondrial respiration has impeded the clinical translation of the preconditioning concept. We previously showed that meclizine, an over-the-counter antivertigo drug, can toggle metabolism from mitochondrial respiration toward glycolysis and protect against ischemia-reperfusion injury in the brain, heart, and kidney. Here, we examine the mechanism of action of meclizine and report the efficacy and improved safety of the (S) enantiomer.

METHODS

We determined the anoxic depolarization latency, tissue and neurological outcomes, and glucose uptake using micro-positron emission tomography after transient middle cerebral artery occlusion in mice pretreated (-17 and -3 hours) with either vehicle or meclizine. To exclude a direct effect on tissue excitability, we also examined spreading depression susceptibility. Furthermore, we accomplished the chiral synthesis of (R)- and (S)-meclizine and compared their effects on oxygen consumption and histamine H1 receptor binding along with their brain concentrations.

RESULTS

Micro-positron emission tomography showed meclizine increases glucose uptake in the ischemic penumbra, providing the first in vivo evidence that the neuroprotective effect of meclizine indeed stems from its ability to toggle metabolism toward glycolysis. Consistent with reduced reliance on oxidative phosphorylation to sustain the metabolism, meclizine delayed anoxic depolarization onset after middle cerebral artery occlusion. Moreover, the (S) enantiomer showed reduced H1 receptor binding, a dose-limiting side effect for the racemate, but retained its effect on mitochondrial respiration. (S)-meclizine was at least as efficacious as the racemate in delaying anoxic depolarization onset and decreasing infarct volumes after middle cerebral artery occlusion.

CONCLUSIONS

Our data identify (S)-meclizine as a promising new drug candidate with high translational potential as a chemical preconditioning agent for preemptive prophylaxis in patients with high imminent stroke or myocardial infarction risk.

Dopamine signaling enriched striatal gene set predicts striatal dopamine synthesis and physiological activity in vivo

The polygenic architecture of schizophrenia implicates several molecular pathways involved in synaptic function. However, it is unclear how polygenic risk funnels through these pathways to translate into syndromic illness. Using tensor decomposition, we analyze gene co-expression in the caudate nucleus, hippocampus, and dorsolateral prefrontal cortex of post-mortem brain samples from 358 individuals. We identify a set of genes predominantly expressed in the caudate nucleus and associated with both clinical state and genetic risk for schizophrenia that shows dopaminergic selectivity. A higher polygenic risk score for schizophrenia parsed by this set of genes predicts greater dopamine synthesis in the striatum and greater striatal activation during reward anticipation. These results translate dopamine-linked genetic risk variation into in vivo neurochemical and hemodynamic phenotypes in the striatum that have long been implicated in the pathophysiology of schizophrenia.

Patlak Slope versus Standardized Uptake Value Image Quality in an Oncologic PET/CT Population: A Prospective Cross-Sectional Study

Patlak slope (PS) images have the potential to improve lesion conspicuity compared with standardized uptake value (SUV) images but may be more artifact-prone. This study compared PS versus SUV image quality and hepatic tumor-to-background ratios (TBRs) at matched time points. Early and late SUV and PS images were reconstructed from dynamic positron emission tomography (PET) data. Two independent, blinded readers scored image quality metrics (a four-point Likert scale) and counted tracer-avid lesions. Hepatic lesions and parenchyma were segmented and quantitatively analyzed. Differences were assessed via the Wilcoxon signed-rank test (alpha, 0.05). Forty-three subjects were included. For overall quality and lesion detection, early PS images were significantly inferior to other reconstructions. For overall quality, late PS images (reader 1 [R1]: 3.95, reader 2 [R2]: 3.95) were similar (p > 0.05) to early SUV images (R1: 3.88, R2: 3.84) but slightly superior (p ≤ 0.002) to late SUV images (R1: 2.97, R2: 3.44). For lesion detection, late PS images were slightly inferior to late SUV images (R1 only) but slightly superior to early SUV images (both readers). PS-based TBRs were significantly higher than SUV-based TBRs at the early time point, with opposite findings at the late time point. In conclusion, late PS images are similar to early/late SUV images in image quality and lesion detection; the superiority of SUV versus PS hepatic TBRs is time-dependent.

Protein restriction during pregnancy alters Cdkn1c silencing, dopamine circuitry and offspring behaviour without changing expression of key neuronal marker genes

We tracked the consequences of in utero protein restriction in mice throughout their development and life course using a luciferase-based allelic reporter of imprinted Cdkn1c. Exposure to gestational low-protein diet (LPD) results in the inappropriate expression of paternally inherited Cdkn1c in the brains of embryonic and juvenile mice. These animals were characterised by a developmental delay in motor skills, and by behavioural alterations indicative of reduced anxiety. Exposure to LPD in utero resulted in significantly more tyrosine hydroxylase positive (dopaminergic) neurons in the midbrain of adult offspring as compared to age-matched, control-diet equivalents. Positron emission tomography (PET) imaging revealed an increase in striatal dopamine synthesis capacity in LPD-exposed offspring, where elevated levels of dopamine correlated with an enhanced sensitivity to cocaine. These data highlight a profound sensitivity of the developing epigenome to gestational protein restriction. Our data also suggest that loss of Cdkn1c imprinting and p57KIP2 upregulation alters the cellular composition of the developing midbrain, compromises dopamine circuitry, and thereby provokes behavioural abnormalities in early postnatal life. Molecular analyses showed that despite this phenotype, exposure to LPD solely during pregnancy did not significantly change the expression of key neuronal- or dopamine-associated marker genes in adult offspring.

Deep-learning-derived input function in dynamic [18F]FDG PET imaging of mice

Dynamic positron emission tomography and kinetic modeling play a critical role in tracer development research using small animals. Kinetic modeling from dynamic PET imaging requires accurate knowledge of an input function, ideally determined through arterial blood sampling. Arterial cannulation in mice, however, requires complex, time-consuming and terminal surgery, meaning that longitudinal studies are impossible. The aim of the current work was to develop and evaluate a non-invasive, deep-learning-based prediction model (DLIF) that directly takes the PET data as input to predict a usable input function. We first trained and evaluated the DLIF model on 68 [18F]Fluorodeoxyglucose mouse scans with image-derived targets using cross validation. Subsequently, we evaluated the performance of a trained DLIF model on an external dataset consisting of 8 mouse scans where the input function was measured by continuous arterial blood sampling. The results showed that the predicted DLIF and image-derived targets were similar, and the net influx rate constants following from Patlak modeling using DLIF as input function were strongly correlated to the corresponding values obtained using the image-derived input function. There were somewhat larger discrepancies when evaluating the model on the external dataset, which could be attributed to systematic differences in the experimental setup between the two datasets. In conclusion, our non-invasive DLIF prediction method may be a viable alternative to arterial blood sampling in small animal [18F]FDG imaging. With further validation, DLIF could overcome the need for arterial cannulation and allow fully quantitative and longitudinal experiments in PET imaging studies of mice.

Increased lesion detectability in patients with locally advanced breast cancer-A pilot study using dynamic whole-body [18F]FDG PET/CT

BACKGROUND

Accurate diagnosis of axillary lymph node (ALN) metastases is essential for prognosis and treatment planning in breast cancer. Evaluation of ALN is done by ultrasound, which is limited by inter-operator variability, and by sentinel lymph node biopsy and/or ALN dissection, none of which are without risks and/or long-term complications. It is known that conventional 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) has limited sensitivity for ALN metastases. However, a recently developed dynamic whole-body (D-WB) [18F]FDG PET/CT scanning protocol, allowing for imaging of tissue [18F]FDG metabolic rate (MRFDG), has been shown to have the potential to increase lesion detectability. The study purpose was to examine detectability of malignant lesions in D-WB [18F]FDG PET/CT compared to conventional [18F]FDG PET/CT.

RESULTS

This study prospectively included ten women with locally advanced breast cancer who were referred for an [18F]FDG PET/CT as part of their diagnostic work-up. They all underwent D-WB [18F]FDG PET/CT, consisting of a 6 min single bed dynamic scan over the chest region started at the time of tracer injection, a 64 min dynamic WB PET scan consisting of 16 continuous bed motion passes, and finally a contrast-enhanced CT scan, with generation of MRFDG parametric images. Lesion visibility was assessed by tumor-to-background and contrast-to-noise ratios using volumes of interest isocontouring tumors with a set limit of 50% of SUVmax and background volumes placed in the vicinity of tumors. Lesion visibility was best in the MRFDG images, with target-to-background values 2.28 (95% CI: 2.04-2.54) times higher than target-to-background values in SUV images, and contrast-to-noise values 1.23 (95% CI: 1.12-1.35) times higher than contrast-to-noise values in SUV images. Furthermore, five imaging experts visually assessed the images and three additional suspicious lesions were found in the MRFDG images compared to SUV images; one suspicious ALN, one suspicious parasternal lymph node, and one suspicious lesion located in the pelvic bone.

CONCLUSIONS

D-WB [18F]FDG PET/CT with MRFDG images show potential for improved lesion detectability compared to conventional SUV images in locally advanced breast cancer. Further validation in larger cohorts is needed.

CLINICAL TRIAL REGISTRATION

The trial is registered in clinicaltrials.gov, NCT05110443, https://www.

CLINICALTRIALS

gov/study/NCT05110443?term=NCT05110443&rank=1 .

Validation of image-derived input function using a long axial field of view PET/CT scanner for two different tracers

BACKGROUND

Accurate image-derived input function (IDIF) from highly sensitive large axial field of view (LAFOV) PET/CT scanners could avoid the need of invasive blood sampling for kinetic modelling. The aim is to validate the use of IDIF for two kinds of tracers, 3 different IDIF locations and 9 different reconstruction settings.

METHODS

Eight [18F]FDG and 10 [18F]DPA-714 scans were acquired respectively during 70 and 60 min on the Vision Quadra PET/CT system. PET images were reconstructed using various reconstruction settings. IDIFs were taken from ascending aorta (AA), descending aorta (DA), and left ventricular cavity (LV). The calibration factor (CF) extracted from the comparison between the IDIFs and the manual blood samples as reference was used for IDIFs accuracy and precision assessment. To illustrate the effect of various calibrated-IDIFs on Patlak linearization for [18F]FDG and Logan linearization for [18F]DPA-714, the same target time-activity curves were applied for each calibrated-IDIF.

RESULTS

For [18F]FDG, the accuracy and precision of the IDIFs were high (mean CF ≥ 0.82, SD ≤ 0.06). Compared to the striatum influx (Ki) extracted using calibrated AA IDIF with the updated European Association of Nuclear Medicine Research Ltd. standard reconstruction (EARL2), Ki mean differences were < 2% using the other calibrated IDIFs. For [18F]DPA714, high accuracy of the IDIFs was observed (mean CF ≥ 0.86) except using absolute scatter correction, DA and LV (respectively mean CF = 0.68, 0.47 and 0.44). However, the precision of the AA IDIFs was low (SD ≥ 0.10). Compared to the distribution volume (VT) in a frontal region obtained using calibrated continuous arterial sampler input function as reference, VT mean differences were small using calibrated AA IDIFs (for example VT mean difference = -5.3% using EARL2), but higher using calibrated DA and LV IDIFs (respectively + 12.5% and + 19.1%).

CONCLUSIONS

For [18F]FDG, IDIF do not need calibration against manual blood samples. For [18F]DPA-714, AA IDIF can replace continuous arterial sampling for simplified kinetic quantification but only with calibration against arterial blood samples. The accuracy and precision of IDIF from LAFOV PET/CT system depend on tracer, reconstruction settings and IDIF VOI locations, warranting careful optimization.

Dynamic whole-body [18F]FES PET/CT increases lesion visibility in patients with metastatic breast cancer

BACKGROUND

Correct classification of estrogen receptor (ER) status is essential for prognosis and treatment planning in patients with breast cancer (BC). Therefore, it is recommended to sample tumor tissue from an accessible metastasis. However, ER expression can show intra- and intertumoral heterogeneity. 16α-[18F]fluoroestradiol ([18F]FES) Positron Emission Tomography/Computed Tomography (PET/CT) allows noninvasive whole-body (WB) identification of ER distribution and is usually performed as a single static image 60 min after radiotracer injection. Using dynamic whole-body (D-WB) PET imaging, we examine [18F]FES kinetics and explore whether Patlak parametric images ( K i ) are quantitative and improve lesion visibility.

RESULTS

This prospective study included eight patients with metastatic ER-positive BC scanned using a D-WB PET acquisition protocol. The kinetics of [18F]FES were best characterized by the irreversible two-tissue compartment model in tumor lesions and in the majority of organ tissues. K i values from Patlak parametric images correlated with K i values from the full kinetic analysis, r2 = 0.77, and with the semiquantitative mean standardized uptake value (SUVmean), r2 = 0.91. Furthermore, parametric K i images had the highest target-to-background ratio (TBR) in 162/164 metastatic lesions and the highest contrast-to-noise ratio (CNR) in 99/164 lesions compared to conventional SUV images. TBR was 2.45 (95% confidence interval (CI): 2.25-2.68) and CNR 1.17 (95% CI: 1.08-1.26) times higher in K i images compared to SUV images. These quantitative differences were seen as reduced background activity in the K i images.

CONCLUSION

[18F]FES uptake is best described by an irreversible two-tissue compartment model. D-WB [18F]FES PET/CT scans can be used for direct reconstruction of parametric K i images, with superior lesion visibility and K i values comparable to K i values found from full kinetic analyses. This may aid correct ER classification and treatment decisions. Trial registration ClinicalTrials.gov: NCT04150731, https://clinicaltrials.gov/study/NCT04150731.

Advances and challenges in measuring hepatic glucose uptake with FDG PET: implications for diabetes research

The liver plays a crucial role in the control of glucose homeostasis and is therefore of great interest in the investigation of the development of type 2 diabetes. Hepatic glucose uptake (HGU) can be measured through positron emission tomography (PET) imaging with the tracer [18F]-2-fluoro-2-deoxy-D-glucose (FDG). HGU is dependent on many variables (e.g. plasma glucose, insulin and glucagon concentrations), and the metabolic state for HGU assessment should be chosen with care and coherence with the study question. In addition, as HGU is influenced by many factors, protocols and measurement conditions need to be standardised for reproducible results. This review provides insights into the protocols that are available for the measurement of HGU by FDG PET and discusses the current state of knowledge of HGU and its impairment in type 2 diabetes. Overall, a scanning modality that allows for the measurement of detailed kinetic information and influx rates (dynamic imaging) may be preferable to static imaging. The combination of FDG PET and insulin stimulation is crucial to measure tissue-specific insulin sensitivity. While the hyperinsulinaemic-euglycaemic clamp allows for standardised measurements under controlled blood glucose levels, some research questions might require a more physiological approach, such as oral glucose loading, with both advantages and complexities relating to fluctuations in blood glucose and insulin levels. The available approaches to address HGU hold great potential but await more systematic exploitation to improve our understanding of the mechanisms underlying metabolic diseases. Current findings from the investigation of HGU by FDG PET highlight the complex interplay between insulin resistance, hepatic glucose metabolism, NEFA levels and intrahepatic lipid accumulation in type 2 diabetes and obesity. Further research is needed to fully understand the underlying mechanisms and potential therapeutic targets for improving HGU in these conditions.

Immune regulation and blood-brain barrier permeability in cerebral small vessel disease: study protocol of the INflammation and Small Vessel Disease (INSVD) study - a multicentre prospective cohort study

INTRODUCTION

The INflammation and Small Vessel Disease (INSVD) study aims to investigate whether peripheral inflammation, immune (dys)regulation and blood-brain barrier (BBB) permeability relate to disease progression in cerebral small vessel disease (SVD). This research aims to pinpoint specific components of the immune response in SVD relating to disease progression. This could identify biomarkers of SVD progression, as well as potential therapeutic targets to inform the development and repurposing of drugs to reduce or prevent SVD, cognitive decline and vascular dementia.

METHODS AND ANALYSIS

INSVD is a prospective observational multicentre cohort study in individuals with symptomatic SVD. This longitudinal study combines comprehensive immunophenotyping of the peripheral blood immune compartment with advanced neuroimaging markers of SVD and BBB permeability. The main SVD marker of interest is white matter microstructure as determined by diffusion tensor imaging, a valuable marker of disease progression owing to its sensitivity to early alterations to white matter integrity. The research is being conducted in two sites-in the UK (Cambridge) and the Netherlands (Nijmegen)-with each site recruiting 100 participants (total n=200). Participants undergo clinical and cognitive assessments, blood draws, and brain MRI at baseline and 2-year follow-up.

ETHICS AND DISSEMINATION

This study received ethical approval from the local ethics boards (UK: East of England-Cambridge Central Research Ethics Committee (REC) ref: 22/EE/00141, Integrated Research Application System (IRAS) ID: 312 747. Netherlands: Medical Research Ethics Committee (MREC) Oost-Nederland, ref: 2022-13623, NL-number: NL80258.091.22). Written informed consent was obtained from all subjects before the study. Any participant-derived benefits resulting from this research, such as new insights into disease mechanisms or possible novel therapies, will be disseminated to study participants, patient groups and members of the public.

TRIAL REGISTRATION NUMBER

NCT05746221.

Propofol anesthesia improves stroke outcomes over isoflurane anesthesia-a longitudinal multiparametric MRI study in a rodent model of transient middle cerebral artery occlusion

General anesthesia is routinely used in endovascular thrombectomy procedures, for which volatile gas and/or intravenous propofol are recommended. Emerging evidence suggests propofol may have superior effects on disability and/or mortality rates, but a mode-of-action underlying these class-specific effects remains unknown. Here, a moderate isoflurane or propofol dosage on experimental stroke outcomes was retrospectively compared using serial multiparametric MRI and behavioral testing. Adult male rats (N = 26) were subjected to 90-min filament-induced transient middle cerebral artery occlusion. Diffusion-, T2- and perfusion-weighted MRI was performed during occlusion, 0.5 h after recanalization, and four days into the subacute phase. Sequels of ischemic damage-blood-brain barrier integrity, cerebrovascular reactivity and sensorimotor functioning-were assessed after four days. While size and severity of ischemia was comparable between groups during occlusion, isoflurane anesthesia was associated with larger lesion sizes and worsened sensorimotor functioning at follow-up. MRI markers indicated that cytotoxic edema persisted locally in the isoflurane group early after recanalization, coinciding with burgeoning vasogenic edema. At follow-up, sequels of ischemia were further aggravated in the post-ischemic lesion, manifesting as increased blood-brain barrier leakage, cerebrovascular paralysis and cerebral hyperperfusion. These findings shed new light on how isoflurane, and possibly similar volatile agents, associate with persisting injurious processes after recanalization that contribute to suboptimal treatment outcome.