Objective: Despite viral suppression, HIV-associated cognitive impairment persists and may be partially due to persistent immune signalling by cells of the myeloid-lineage. Here, we aimed to understand the contribution of activated microglia located in vulnerable brain regions (e.g. frontal, subcortical) of HIV-infected, virally suppressed (HIV+VS) individuals in relation to cognitive and motor function. Design: Twenty-one HIV+VS individuals underwent PET with [11C]DPA-713 to image the translocator protein 18 kDa (TSPO), a marker of microglial activation, and completed a comprehensive neuropsychological test battery. Methods: Multivariable linear regressions were used to examine the contribution of [11C]DPA-713 binding to cognitive performance. Results: Higher [11C]DPA-713 binding was associated with lower cognition among HIV+VS individuals. [11C]DPA-713 binding in middle frontal gyrus/frontal cortex, hippocampus/temporal cortex and occipital cortex was inversely associated with performance on a number of cognitive domains, including verbal memory, processing speed/attention/concentration, executive function, working memory and motor function. [11C]DPA-713 binding in parietal cortex, cerebellum and thalamus was associated with only specific cognitive domains including visual construction and verbal memory. Binding was not associated with global cognitive performance. Conclusion: The findings add to the growing body of evidence that immune-mediated brain injury may contribute to domain specific, HIV-associated, cognitive vulnerabilities despite viral suppression.

Objective Inflammation secondary to autoantibody-mediated effects occurring in multiple organs is a hallmark of systemic lupus erythematosus (SLE). The inflammatory response to SLE-mediated damage in brain parenchyma has been postulated in both normal and cognitively impaired individuals. Our goal is to use molecular imaging to investigate the distribution within the brain of the mitochondrial translocator protein (TSPO) that is upregulated during glial cell activation, and is considered as a marker of brain injury and repair. Methods We sought to characterize TSPO distribution in the brain of SLE patients using positron emission tomography (PET) and [11C]DPA-713 (DPA), a radiopharmaceutical that targets TSPO. We imaged 11 healthy controls and 10 patients with SLE (years of diagnosis: 13.0 ± 7.7), all between the ages of 22 and 52.RESULTS:Among the nine brain regions studied, no statistically significant increases in DPA binding were observed in SLE. Instead, there was a significant decrease in TSPO distribution in the cerebellum and hippocampus of SLE patients, as compared to healthy controls. Such decreases were most significant in cognitively normal SLE subjects, but showed pseudo-normalization in those with cognitive impairment, due to higher cerebellar and hippocampal DPA binding in the cognitively impaired (versus normal) SLE brain. Conclusions Results from this pilot study suggest a link between diminished regional TSPO expression in the brain of patients with SLE, as well as possible glial cell activation within the cerebellum and hippocampus of cognitively impaired individuals with SLE. Further studies are needed to elucidate how mitochondrial dysfunction and glial cell activation may act together in SLE and SLE-mediated neurocognitive deficits.

assumed to be a true reference region, it has been previously shown to have low displaceable fraction of TSPO in rats [5]. In order to explore the association between specific binding and genetics independent of plasma variability, we estimated a pseudo binding potential (BPref) [4] using grey matter masked caudate as a reference region. The genotypic influence was not observed on the VT, but was seen on BPref and particularly evident in cortical regions. Conclusions: Binding of F-PBR111 can be quantified with a 2TC model in healthy subjects. When normalized by a pseudo reference region, there was evidence that the cortical binding was influenced by the status of the rs6971 polymorphism in the TSPO gene.

Ribavirin is used for the treatment of hepatitis C virus (HCV) infection. The equilibrative nucleoside transporter 1 (ENT1) expressed in hepatocytes transports ribavirin into the liver, the site of efficacy of the drug. However, it is still unclear whether ENT1 plays a dominant role in the hepatic distribution of the drug in vivo. In addition, due to fetal toxicity, administration of ribavirin to pregnant women with HCV infection is contraindicated. ENT1 might play a role in the fetal distribution and therefore the fetal toxicity of ribavirin. The aim of the present study was to investigate the in vivo contribution of ENT1 to the tissue distribution of ribavirin. When compared with that in Ent1(+/+) mice, the ribavirin tissue to plasma concentration ratio (including phosphorylated metabolites) in Ent1(-/-) mice at 15 min and 6 h after intravenous [(3) H]-ribavirin (3 mg/kg) administration was consistently and significantly decreased in the liver and the pancreas. Likewise, when compared with the Ent1(+/+) mice, the fetal distribution of ribavirin at 15 min after administration was significantly reduced in Ent1(-/-) fetuses and placenta. In contrast, there was no significant difference between Ent1(+/+), Ent1(+/-) and Ent1(-/-) mice in the fetal or placental to maternal plasma ribavirin concentration ratio at 2 h after ribavirin administration. The findings in the present study suggest that ENT1 plays a pivotal role in the distribution of ribavirin into tissues including the liver and pancreas, but affects only the rate, but not the extent, of ribavirin distribution into the fetus. Copyright © 2016 John Wiley & Sons, Ltd.

Background: [C]flumazenil (FMZ) PET images GABAA receptors. Various methods of data analysis are used in the literature, including simple summed radioactivity images (SRI) and parametric images, obtained via compartmental modelling with or without an arterial input function, or via spectral analysis. The Delforge partial saturation method (1997) has been used extensively but no test-retest data on the reliability of the various possible output images has been available. Methods: Ten healthy controls (22-47 years) were studied twice at one-week intervals. All had high resolution 1.5T MRI. After injection of 2.6 MBq/kg of [C]FMZ and 0.01 mg/kg of unlabeled FMZ, 3D data were acquired on a Siemens/CTI ECAT HR + over 55 m, corrected for attenuation and scatter, and rebinned into 12 time frames. SRIs were created over two published time intervals (10-20 m, SRI-10-20, and SRI-20-45). Both were also expressed as standardized uptake values (SUV; SUV-10-20; SUV-2045). The partial saturation model, based on a Scatchard plot, was used for the calculation of parametric Bmax images, with pons as a reference and with Kd either variable per voxel (BmaxKdvar) or using the same Kd throughout (BmaxKdfix). 83 regions were sampled with a frequency-based brain atlas (Hammers et al., 2003) warped onto each individual’s MRI scan using Statistical Parametric Mapping software (SPM5), thresholded at 50% grey matter probability, and then coregistered onto each individual PET. Image quality was assessed visually. Average percentage test-retest differences were calculated as the standard deviation of (test-retest)/ mean (test + retest) for all grey matter containing regions except pallidum and those under ten times scanner resolution (B4.1 mm). Reliability was assessed per region via the intraclass correlation coefficient (ICC). Results: Image quality was good for all types (Figure). The rank order of % test-retest differences (absolute values) was SUV-20-45 > SRI-20-45 > BmaxKdvar > SRI-10-20 > SUV-10-20 > BmaxKdfix. The rank order of ICCs was similar. Conclusions: Considering left and right regions separately and including some regions with low binding (e.g. basal ganglia) may explain somewhat worse values than in other test-retest studies. Bmax is in theory an attractive parameter to quantify, being directly related to receptor concentration. However, in our hands Bmax parametric maps had relatively high test-retest variability and low reliability, with hardly any regions achieving ICCs considered as good, i.e. > 0.70. We did, however, not test the reliability of measures of Bmax derived directly from less noisy time-activity curves at the ROI level. SRI and SUV images obtained between 20 and 45 m post injection performed best, with good ICCs despite relatively high average test-retest variability (B10%). SRI-10-20 and SUV-10-20 images had intermediate values, unlikely to be sufficient for most studies (compare e.g. Hammers et al. 2008).

Myocarditis is more severe in men than in women and difficult to diagnose due to a lack of imaging modalities that directly detect myocardial inflammation. Translocator protein 18 kDa (TSPO) is used extensively to image brain inflammation due to its presence in CD11b+ brain microglia. In this study, we examined expression of TSPO and CD11b in mice with coxsackievirus B3 (CVB3) myocarditis and biopsy sections from myocarditis patients in order to determine if it could be used to image myocarditis. We found that male mice with CVB3 myocarditis upregulated more genes associated with TSPO activation than female mice. TSPO expression was increased in the heart of male mice and men with myocarditis compared with female subjects due to testosterone, where it was expressed predominantly in CD11b+ immune cells. We show that TSPO ligands detect myocardial inflammation using microSPECT, with increased uptake of [125I]-IodoDPA-713 in male mice with CVB3 myocarditis compared with undiseased controls.

Imaging the brain distribution of translocator protein (TSPO), a putative biomarker for glial cell activation and neuroinflammation, may inform management of individuals infected with HIV by uncovering regional abnormalities related to neurocognitive deficits and enable non-invasive therapeutic monitoring. Using the second-generation TSPO-targeted radiotracer, [11C]DPA-713, we conducted a positron emission tomography (PET) study to compare the brains of 12 healthy human subjects to those of 23 individuals with HIV who were effectively treated with combination antiretroviral therapy (cART). Compared to PET data from age-matched healthy control subjects, [11C]DPA-713 PET of individuals infected with HIV demonstrated significantly higher volume-of-distribution (VT) ratios in white matter, cingulate cortex, and supramarginal gyrus, relative to overall gray matter VT, suggesting localized glial cell activation in susceptible regions. Regional TSPO abnormalities were evident within a sub-cohort of neuro-asymptomatic HIV subjects, and an increase in the VT ratio within frontal cortex was specifically linked to individuals affected with HIV-associated dementia. These findings were enabled by employing a gray matter normalization approach for PET data quantification, which improved test–retest reproducibility, intra-class correlation within the healthy control cohort, and sensitivity of uncovering abnormal regional findings.

We have developed a SPECT imaging system, AwakeSPECT, to enable molecular brain imaging of untrained mice that are conscious, unanesthetized, and unrestrained. We accomplished this with head tracking and motion correction techniques. Methods: The capability of the system for motion-corrected imaging was demonstrated with a 99mTc-pertechnetate phantom, 99mTc-methylene diphosphonate bone imaging, and measurement of the binding potential of the dopamine transporter radioligand 123I-ioflupane in mouse brain in the awake and anesthetized (isoflurane) states. Stress induced by imaging in the awake state was assessed through measurement of plasma corticosterone levels. Results: AwakeSPECT provided high-resolution bone images reminiscent of those obtained from CT. The binding potential of 123I-ioflupane in the awake state was on the order of 50% of that obtained with the animal under anesthesia, consistent with previous studies in nonhuman primates. Levels of stress induced were on the order of those seen in other behavioral tasks and imaging studies of awake animals. Conclusion: These results demonstrate the feasibility of SPECT molecular brain imaging of mice in the conscious, unrestrained state and demonstrate the effects of isoflurane anesthesia on radiotracer uptake.

Introduction: The alpha-7 nicotinic acetylcholine receptor (alpha 7 nAChR) is key in brain communication and has been implicated in the pathophysiology of diseases of the central nervous system. A positron-emitting radioligand targeting the alpha 7 nAChR would enable better understanding of a variety of neuropsychiatric illnesses, including schizophrenia and Alzheimer's disease, and could enhance the development of new drugs for these and other conditions. We describe our attempt to synthesize an alpha 7 nAChR-selective radiotracer for positron emission tomography (PET).Methods: We prepared the high-affinity (K-d = 0.2 nM) alpha 7 nAChR agonist, 5'-(2-[F-18]fluorophenyl)spiro[1-azabicyclo-[2.2.2]octane]-3,2'-(3'H)furo[2,3-b]pyridine, [F-18]AZ11637326, in two steps, a nucleophilic fluorination followed by decarbonylation. We studied [F-18]AZ11637326 in rodents, including mice lacking alpha 7 nAChR, and in non-human primates.Results: [F-18]AZ11637326 was synthesized in a non-decay-corrected radiochemical yield of 3% from the end of synthesis (90 min) with a radiochemical purity >90% and average specific radioactivity of 140 GBq/mu mol (3,781 mCi/mu mol). Modest rodent brain uptake was observed (2-5% injected dose per gram of tissue, depending on specific activity), with studies comparing CD-1 and alpha 7 nAChR null mice indicating an element of target-specific binding. Blocking studies in non-human primates did not reveal specific binding within the brain.Conclusion: Despite the high affinity and target selectivity of AZ11637326 for alpha 7 nAChR in vitro and encouraging rodent studies, receptor-mediated binding could not be demonstrated in non-human primates. Further structural optimization of compounds of this class will be required for them to serve as suitable radiotracers for PET. (C) 2013 Elsevier Inc. All rights reserved.

529 Objectives To facilitate personalized study of neuroinflammation by PET using the TSPO-targeted radiopharmaceutical 11C-DPA-713, we built a parametric image atlas based on healthy subjects and demonstrated its utility in brain mapping by voxel-level z-scoring of individuals with potential neuroinflammation. Methods Healthy volunteers (n = 12) were imaged with dynamic 11C-DPA-713 PET [1, 2] and parametric images of distribution volume (Vt) were generated applying the Logan method. A normalization approach was devised to compensate for the effects of TSPO gene polymorphism [3] and other factors [4] affecting intra-subject reproducibility and inter-subject variation. All normalized Vt images of healthy subjects were warped to a standard brain space, generating population mean and standard deviation (SD) images to complete the atlas. Utilizing this, the Vt images of several subjects suffering from putative neuroinflammation (former NFL players: N=4, HIV+ patients: N=7) were processed and analyzed by calculating voxel-level z-scores, providing individual whole brain mapping indicative of potential disease-related neuroinflammation. Results With the individual mean Vt value from gray matter used in normalization, the normalized Vt images demonstrated much improved intra-class correlation among healthy subjects, allowing generation of an atlas with reasonable SDs. Individuals with putative brain inflammation showed large z-scores (> 4) in various brain regions, indicating localized disease. Conclusions We have developed an approach that may enable construction of a normal brain atlas for TSPO PET imaging and improve the sensitivity of personalized imaging studies of neuroinflammation. We have demonstrated the utility of this method in 11C-DPA-713 PET imaging of both healthy subjects and those with putative neuroinflammation. Research Support We thank the support from NFL Charities and NIH Grant 5R21MH082277.

Whole-body PET/CT was used to characterize the radiation dosimetry of 11C-DPA-713, a specific PET ligand for the assessment of translocator protein. Methods: Six healthy control subjects, 3 men and 3 women, underwent whole-body dynamic PET scans after bolus injection of 11C-DPA-713. Subjects were scanned from head to mid thigh with 7 passes performed, with a total PET acquisition of approximately 100 min. Time–activity curves were generated in organs with visible tracer uptake, and tissue residence times were calculated. Whole-body dosimetry was calculated using OLINDA 1.1 software, assuming no voiding. Results: The absorbed dose is highest in the lungs, spleen, kidney, and pancreas. The lungs were determined to be the dose-limiting organ, with an average absorbed dose of 2.01 × 10−2 mSv/MBq (7.43 × 10−2 rem/mCi). On the basis of exposure limits outlined in the U.S. Food and Drug Administration Code of Federal Regulations (21CFR361.1), the single-dose limit for 11C-DPA-713 radiotracer injection is 2,487.6 MBq (67.3 mCi). Conclusion:11C-DPA-713 has an uptake pattern that is consistent with the biodistribution of translocator protein and yields a dose burden that is comparable to that of other 11C-labeled PET tracers.

Prostate-specific membrane antigen (PSMA) is a type II integral membrane protein expressed on the surface of prostate cancer (PCa) cells, particularly in androgen-independent, advanced, and metastatic disease. Previously, we demonstrated that N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-4-18F-fluorobenzyl-l-cysteine (18F-DCFBC) could image an experimental model of PSMA-positive PCa using PET. Here, we describe the initial clinical experience and radiation dosimetry of 18F-DCFBC in men with metastatic PCa. Methods: Five patients with radiologic evidence of metastatic PCa were studied after the intravenous administration of 370 MBq (10 mCi) of 18F-DCFBC. Serial PET was performed until 2 h after administration. Time–activity curves were generated for selected normal tissues and metastatic foci. Radiation dose estimates were calculated using OLINDA/EXM 1.1. Results: Most vascular organs demonstrated a slow decrease in radioactivity concentration over time consistent with clearance from the blood pool, with primarily urinary radiotracer excretion. Thirty-two PET-positive suspected metastatic sites were identified, with 21 concordant on both PET and conventional imaging for abnormal findings compatible with metastatic disease. Of the 11 PET-positive sites not identified on conventional imaging, most were within the bone and could be considered suggestive for the detection of early bone metastases, although further validation is needed. The highest mean absorbed dose per unit administered radioactivity (μGy/MBq) was in the bladder wall (32.4), and the resultant effective dose was 19.9 ± 1.34 μSv/MBq (mean ± SD). Conclusion: Although further studies are needed for validation, our findings demonstrate the potential of 18F-DCFBC as a new positron-emitting imaging agent for the detection of metastatic PCa. This study also provides dose estimates for 18F-DCFBC that are comparable to those of other PET radiopharmaceuticals such as 18F-FDG.

375 Objectives To investigate the use of anatomy-assisted PET image reconstruction using modalities of MRI and diffusion tensor imaging (DTI) as applied to parametric imaging for clinical research. Methods PET images continue to be affected by noise and the partial volume effect (PVE). An approach to reduce simultaneously both effects is to incorporate anatomical information within the PET image reconstruction task. Our extensive simulations of Bayesian PET reconstructions incorporating an anato-functional joint entropy (JE) prior have revealed considerable promise, moving beyond conventional approaches that assume over-simplified correlations between anatomy and radiopharmaceutical uptake. We applied this technique to [11C]DPA-713 PET and MRI imaging studies of healthy control subjects (n=3). DTI imaging was additionally performed on each subject (as the study aims to also investigate changes in white matter tract in controls vs. schizophrenic patients). We hypothesized that utilization of MRI and/or DTI images within PET reconstruction could impact and enhance PET imaging. Eighteen regions-of-interest (ROIs) were considered. Parametric K1 and distribution volume (DV) images were generated using a standard 2-tissue 5-parameter compartmental model and a linear regression with spatial constraint (LRSM) algorithm, and were statistically compared. Results In comparison to standard 3D-OSEM reconstructed images, MRI- and DTI-guided PET images depicted significant qualitative differences, demonstrating considerably sharper distinction between various regions. Ongoing quantitative analysis has revealed increases in nearly all regions of the parametric images for both DV (by 17%; P Conclusions Anatomy-guided image reconstruction can substantially impact quality and quantification of PET images, and have the potential to enhance parametric PET imaging significantly

Background: Competition between neurotransmitter and radioligands has provided a very useful method to assess synaptic changes in dopamine, but this approach has been slow to extend to other neurotransmitter system. Previously, Fujita and colleagues showed that the high affinity beta2-nicotinic acetylcholine receptor (b2-nAChR) radioligand [I]5-IA85380 (5-IA) may be sensitive to extracellular increases in ACh in baboons; 1 however, such an examination in humans has lagged. Given that acetylcholine is one of the major neurotransmitters in the brain and has been implicated in the psychiatric and medical illnesses, we developed a paradigm to interrogate the ACh system in vivo via use of 5-IA SPECT imaging and physostigmine, a centrally-acting acetylcholinesterase inhibitor. Methods: Six healthy subjects (3 men, 3 women; 31±4.1 yrs) participated in one 5-IA SPECT study. 5-IA was administered as a bolus plus constant infusion (B/I 7.0 h); total injected dose was 390.2±13.2 MBq. After three 30-min baseline scans at 6-8 h post infusion, physostigmine (1-1.5 mg) was administered IV over 60 min, and nine additional 30-min scans were collected during the next 6 h. The outcome measure was BPF (specific volume of distribution), calculated as VT/fp (estimated receptor availability) minus VND/fp (nondisplaceable binding; previously estimated in a smoking to satiety paradigm). Results: We observed a significant reduction in BPF after physostigmine administration (25±15% reduction in cortical regions, 15±11% thalamus (Figure 1), 16±14% in striatum, and 35±34% in cerebellum; p < .05). This effect reflected a combination of a significant decrease in tissue concentration of 5-IA (7-16% region specific, p < .05) and a significant increase in plasma parent concentration (8%, p < .05). Conclusions: These data suggest that physostigmineinduced increases in extracellular ACh might compete with 5-IA for binding to b2-nAChRs in humans, although other mechanisms, such as a direct effect of physostigmine on nicotinic acetylcholine receptors, should be ruled out. Additional validation of this paradigm is warranted, but we suggest that nicotinic imaging could be used to interrogate changes in synaptic ACh.

Ribavirin is frontline treatment for hepatitis C virus infection. To determine the role of nucleoside transporters in the intestinal absorption of orally administered ribavirin, we perfused the intestines of Ent1(-/-) and wild-type mice, in situ, with [(3)H] ribavirin (20, 200, and 5000 μM) in the presence and absence of sodium. The decrease in luminal ribavirin concentration over 30 min was measured at 5 min intervals. Blood samples were collected approximately every 10 min. Ribavirin plus phosphorylated metabolite concentrations (hereafter referred to as ribavirin) were determined in tissue, blood, and plasma by HPLC fractionation and scintillation counting. There was no significant difference between wild-type and Ent1(-/-) mice in intestinal loss of ribavirin at any ribavirin concentration studied. Perfusions without sodium drastically reduced the intestinal loss of ribavirin in both wild-type and Ent1(-/-) mice. After 20 μM ribavirin perfusions, Ent1(-/-) intestinal tissue contained 8-fold greater ribavirin than wild-type mice (p < 0.01). Ribavirin concentrations in the wild-type intestinal tissue were 70-fold higher after 200 vs 20 μM perfusions (p < 0.001), indicating saturation of intestinal ribavirin efflux and possibly other processes as well. Ribavirin plasma concentrations were significantly higher in wild-type mice (2.7-fold) vs Ent1(-/-) mice at 30 min after the 20 μM perfusion (p < 0.01). These results suggest that, at lower intestinal concentrations of ribavirin, concentrative and equilibrative nucleoside transporters are important in the intestinal absorption of ribavirin. At higher intestinal concentrations, these transporters are saturated and other processes in the intestine (transport and/or metabolism) play an important role in the absorption of ribavirin.