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The aim of this study was to develop an efficient fully automated synthesis method to achieve a high radiochemical yield of [(18)F]FAZA with a small amount of precursor. A small cartridge containing 25mg of the QMA resin was prepared and evaluated to obtain [(18)F]F(-) in a small quantity of base (K(2)CO(3)), which might allow the use of a small amount of precursor. The labeling and hydrolyzing conditions for [(18)F]FAZA synthesis were also investigated manually. No-carrier-added [(18)F]F(-) was trapped on the small QMA cartridge and eluted with a mixture of Krytofix 222 (2.26 mg, 6.0 μmol) and K(2)CO(3) (0.69 mg, 5.0 μmol) in 70% MeCN (0.4 mL). The automated synthesis of [(18)F]FAZA was optimally performed with a modified NIRS original synthesis system for clinical use, by labeling 2.5mg (5.2 μmol) of the precursor in DMSO (0.4 mL) at 120°C for 10 min, and then by hydrolyzing the (18)F-labeled intermediate with 0.1M NaOH (0.5 mL) at room temperature for 3 min. Using the above condition, the [(18)F]FAZA injection was obtained with a high radiochemical yield of 52.4±5.3% (decay-corrected, n=8) within 50.5±1.5 min.

Although the progression of cancer is a leading cause of death, oncologic medicine is adapting its strategy regarding cancer therapy and contributing to a personalized medicine approach. Because of its ability to measure therapeutic efficacy in vivo rapidly, molecular imaging has received growing attention and has shed light onto new avenues for assessing the therapeutic effect and determining the progression of disease (1,2). Successful chemotherapy or radiotherapy induces apoptosis in neoplastic cells, which can be a predictive indicator of a good therapy outcome in oncology (3,4). An early hallmark of apoptosis is the externalization of anion phospholipids including phosphatidylserine and phosphatidylinositide (5,6). Noninvasive imaging of cell death has been successfully applied in tumor models and clinical trials to determine whether apoptosis imaging could be a surrogate marker for monitoring therapeutic efficacy (7–12). C2A domain of synaptotagmin I is an approximate 120–amino-acid segment with a common fold, an 8-strand anti-parallel β sandwich connected by variable loops. In many C2 domains, binding of 2 or 3 Ca2+ ions in the 3 variable loops creates a substantial electrostatic potential that accelerates a protein’s association. The C2A domain also binds anionic phospholipids with relatively high affinity (13). Our previous studies demonstrated that the technetium-labeled C2A-based molecular imaging probe 99mTc-C2A could target apoptotic cells not only in acute myocardial infarction but also in a tumor model (14–18). However, the biodistribution of 99mTc-C2A-glutathione-S-transferase (GST) is not optimal, and its main drawback is high uptake of radioactivity in the kidneys and abdomen, severely hampering its clinical application, especially for imaging of abdominal tumors. It has been reported that 18F-annexin V showed favorable characteristics of biodistribution and kinetics, compared with 99mTc-annexin V derivatives (19–21). Meanwhile, PET with higher spatial resolution and easily quantified calculation of standardized uptake value (SUV) may have more advantages in detecting apoptotic cells than other modalities including SPECT. The current study aimed to synthesize and develop 18F-labeled C2A-GST as a molecular imaging probe for detecting apoptosis and to assess the feasibility of early evaluation of paclitaxel chemotherapy outcome in a rabbit VX2 lung cancer model.

Introduction High specific radioactivity is preferable in the measurement of neuroreceptor bindings with positron emission tomography (PET) because receptor occupancy by mixed cold ligand hampers the accurate estimation of receptor binding. Recently, we succeeded in synthesizing [ 11 C]raclopride, a dopamine D 2 receptor ligand, with ultra-high specific radioactivity, i.e., several thousand GBq/μmol. In the present study, we compared the [ 11 C]raclopride bindings to dopamine D 2 receptors between radioligands with ultra-high specific radioactivity and ordinary high specific radioactivity in healthy human subjects. Methods Two PET studies using [ 11 C]raclopride with ultra-high specific radioactivity (4302–7222 GBq/μmol) or ordinary high specific radioactivity (133-280 GBq/μmol) were performed on different days in 14 healthy men. Binding potential (BP) was calculated by the simplified reference tissue method, peak equilibrium method, and area-under-the-curve method for each region-of-interest using time-activity data in the cerebellum as a reference brain region. Results BP values for radioligands with ultra-high specific radioactivity and ordinary high specific radioactivity calculated by the simplified reference tissue method were 4.06±0.29 and 4.10±0.25 in the putamen, 0.44±0.07 and 0.47±0.07 in the thalamus and 0.37±0.06 and 0.38±0.06 in the temporal cortex, respectively (mean±S.D.). No significant difference in BP was observed between ultra-high specific radioactivity and ordinary high specific radioactivity in any of the brain regions. Conclusion BP values of [ 11 C]raclopride with ultra-high specific radioactivity did not differ from those with ordinary high specific radioactivity in the measured brain regions, including striatal and extrastriatal regions.

An ultrafast and efficient high-performance liquid chromatographic (LC) method was developed to purify positron emission tomography (PET) radiopharmaceuticals as well as for metabolite analysis of the plasma sample. Chromatographic separation was achieved on a short (60 mm length) semipreparative (10 mm I.D.) column packed with 2.5-[mu]m particles using a mixture of acetonitrile and sodium phosphate buffer as the mobile phase at a flow rate of 8–10 ml/min. Under the optimum conditions, excellent separation of the target PET probe was obtained from chemical/radiochemical impurities or radioactive metabolites with a very short run time of 2 min. This characteristic enabled significant shortening of the purification and evaporation processes in the production of short-lived radiopharmaceuticals and highly sensitive radiometric analysis with good temporal resolution during the metabolism study.

[(18)F]FEAC ([(18)F]4a) and [(18)F]FEDAC ([(18)F]4b) were developed as two novel positron emission tomography (PET) ligands for peripheral-type benzodiazepine receptor (PBR). [(18)F]4a and [(18)F]4b were synthesized by fluoroethylation of precursors 8a and 8b with [(18)F]FCH(2)CH(2)Br ([(18)F]9), respectively. Small-animal PET scan for a neuroinflammatory rat model showed that the two radioligands had high uptakes of radioactivity in the kainic acid-infused striatum, a brain region where PBR density was increased.

The binding of two radiolabelled analogues (N-(5-[125I]Iodo-2-phenoxyphenyl)-N-(2,5-dimethoxybenzyl)acetamide ([125I]desfluoro-DAA1106) and N-(5-[125I]Fluoro-2-phenoxyphenyl)-N-(2-[125I]Iodo-5-methoxybenzyl)acetamide ([125I]desmethoxy-DAA1106) of the peripheral benzodiazepine receptor (PBR) (or TSPO, 18kDa translocator protein) ligand DAA1106 was examined by in vitro autoradiography on human post mortem whole hemisphere brain slices obtained from Alzheimer's disease (AD) patients and age-matched controls. Both [(125)I]desfluoro-IDAA1106 and [(125)I]desmethoxy-IDAA1106 were effectively binding to various brain structures. The binding could be blocked by the unlabelled ligand as well as by other PBR specific ligands. With both radiolabelled compounds, the binding showed regional inhomogeneity and the specific binding values proved to be the highest in the hippocampus, temporal and parietal cortex, the basal ganglia and thalamus in the AD brains. Compared with age-matched control brains, specific binding in several brain structures (temporal and parietal lobes, thalamus and white matter) in Alzheimer brains was significantly higher, indicating that the radioligands can effectively label-activated microglia and the up-regulated PBR/TSPO system in AD. Complementary immunohistochemical studies demonstrated reactive microglia activation in the AD brain tissue and indicated that increased ligand binding coincides with increased regional microglia activation due to neuroinflammation. These investigations yield further support to the PBR/TSPO binding capacity of DAA1106 in human brain tissue, demonstrate the effective usefulness of its radio-iodinated analogues as imaging biomarkers in post mortem human studies, and indicate that its radiolabelled analogues, labelled with short half-time bioisotopes, can serve as prospective in vivo imaging biomarkers of activated microglia and the up-regulated PBR/TSPO system in the human brain.

18F-fluoroethyl-SPA-RQ (18F-FE-SPA-RQ) was recently developed as a radioligand for the measurement of neurokinin 1 (NK1) receptor with PET. In this study, we used 18F-FE-SPA-RQ with PET to visualize and quantify NK1 receptor in the human brain. Methods: PET scans were performed on 7 healthy men after intravenous injection of 18F-FE-SPA-RQ. Binding potential (BPND) was calculated by the indirect kinetic, simplified reference tissue model (SRTM), and ratio methods. The indirect kinetic method was used as the gold standard method and was compared with the SRTM method, with scan times of 180, 270, and 330 min, and with the ratio method, with time integration intervals of 120–180, 210–270, and 300–330 min. The cerebellum was used as the reference brain region. Results: Regional radioactivity was highest in the caudate head and putamen; mid level in the parahippocampus, cerebral cortex, and thalamus; and lowest in the cerebellum. BPND values by the indirect kinetic method were 3.15 ± 0.36, 3.11 ± 0.66, 1.17 ± 0.25, and 0.46 ± 0.14 in the caudate, putamen, parahippocampal region, and thalamus, respectively. For cerebral cortical regions, BPND values by the indirect kinetic method were 0.94 ± 0.23, 0.82 ± 0.15, 0.76 ± 0.15, and 0.69 ± 0.16 in the occipital, temporal, frontal, and anterior cingulate cortices, respectively. BPND values by the SRTM and ratio methods were in good agreement with those by the indirect kinetic method (r = 0.94–0.98). Conclusion: The regional distribution of 18F-FE-SPA-RQ was in agreement with previous PET studies and postmortem studies of NK1 receptor in the human brain. The ratio method will be useful for clinical research of psychiatric disorders, for the estimation of NK1 receptor without arterial blood sampling and long dynamic PET.

Fluorine-18 ((18)F, beta(+); 96.7%, T(1/2)=109.8 min) is of considerable importance for developing positron emission tomography (PET) ligands for imaging receptor, enzyme, gene expression etc. in brain, tumor, myocardium and other regions or organs due to its optimal decay characteristics. To synthesize (18)F-labeled PET ligands, reliable labeling techniques inserting (18)F into a target molecule are necessary. [(18)F]Fluoroalkylation is a useful way of introducing (18)F into target molecules containing amino, phenol, thiophenol, and amide functional groups. Here, we review the preparation, reactivity and application of [(18)F]fluoroalkyl agents for the development of (18)F-labeled PET ligands in molecular imaging. [(18)F]Fluoroalkyl agents have been synthesized by reacting [(18)F]F(-) with the corresponding alkyl derivatives containing halogen and sulfonate as leaving groups. After the fluorination reaction, the radiolabeled products with relatively low boiling points were distilled from the reaction mixtures, sometimes added by Sep-Pak or gas chromatography separation. The [(18)F]fluoromethyl agents have high reactivity with nucleophilic substrates, but many [(18)F]fluoromethylated compounds are in vitro unstable. To increase the efficiency of [(18)F]fluoroethylation, [(18)F]FCH2CH2Br, the most frequently used [(18)F]fluoroethyl agent, was converted into [(18)F]FCH2CH2I or [(18)F]FCH2CH2OTf in situ. Most [(18)F]fluoromethylated ligands were found to be in vivo unstable due to defluorination. Deuterium substitution for the fluoromethyl group reduced defluorination to an extent. A number of [(18)F]fluoroethylated PET ligands have been developed for animal evaluation and clinical investigation.

The lung is one of the key organs for determining the distribution of drugs in the human body. Various factors influence the accumulation of drugs. In this study, we investigated the effects of smoking on drug distribution to the lung using radiolabeled drugs. We measured the lung uptake of [11C](+)McN5652, a radioligand for serotonin transporter (5-HTT), and inactive enantiomer [11C](−)McN5652 in 19 healthy men (12 nonsmokers and 7 smokers) using positron emission tomography. Pretreatment study was performed by the administration of clomipramine (50 mg), a potent 5-HTT inhibitor. The mean lung uptake of [11C](+)McN5652 and [11C](−)McN5652 was significantly higher in smokers than in nonsmokers. The lung uptake of [11C](+)McN5652 decreased after pretreatment with clomipramine, whereas that of [11C](−)McN5652 was not affected by clomipramine. Lung uptake of [11C](−)McN5652 was influenced by smoking, possibly because the probable nonspecific binding accumulation was changed as [11C](−)McN5652 was reported to have negligible affinity to 5-HTT. Smoking might be one of the important factors when distribution of radioligands is considered.

The pharmacokinetics of drugs with specific binding sites in the brain needs to be evaluated at these sites. In this study, we measured the time course of the selective serotonin reuptake inhibitor fluvoxamine in the human brain based on serotonin transporter (5-HTT) occupancy by positron emission tomography. Consecutive positron emission tomography scans were performed using [11C]3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile before, 5 hours, 26 hours, and 53 hours after 50 mg of fluvoxamine administration in 6 healthy male volunteers (mean, 24.3 +/- 4.8 years). Quantification was performed using the multilinear reference tissue model 2. Mean 5-HTT occupancies were 72.9% +/- 4.9% at 5 hours, 50.3% +/- 11.0% at 26 hours, and 24.7% +/- 15.3% at 53 hours, and plasma concentrations were 13.9 +/- 5.5 ng/mL at 5 hours, 5.1 +/- 3.2 ng/mL at 26 hours, and 1.5 +/- 1.7 ng/mL at 53 hours. The relationship between the plasma concentration of fluvoxamine and 5-HTT occupancy at these different time points was fitted to the law of mass action.

The usefulness of high-performance liquid chromatography with electrochemical detection (HPLC/ECD) in the quality control of positron emission tomography (PET) radiopharmaceuticals was evaluated for a number of substances. Chromatographic separation was performed using a reversed phase column and acetonitrile or 20 mM sodium phosphate buffer as the mobile phase. The effluent from the column was introduced into an electrochemical detector equipped with a glassy carbon electrode versus Ag/AgCl electrode operated in the direct current mode. In 19 of 21 PET radiopharmaceuticals studied, the compounds and corresponding precursors used in the synthesis of the radiopharmaceuticals could be successfully detected by the HPLC/ECD method. For 17 compounds with electroactive functional groups, such as aliphatic amines, phenols and aromatic amines, the detection limits were ppb levels for a 20-mul injection volume; this was significantly better compared with ultraviolet (UV) detection. This method could be applied to the analysis of [11C]MP4A, useful PET radiopharmaceutical for measuring acetylcholinesterase activity in the brain with no available UV absorbance.

Conventional antipsychotics tend to elicit extrapyramidal symptoms at clinical doses, but dose optimization could reduce the risk of such side-effects. In-vivo receptor-binding studies have suggested that 70-80% of dopamine D2 receptor occupancy provides the desired antipsychotic effects without extrapyramidal symptoms. In terms of dose optimization based on the occupancy, there has not been enough supporting data regarding the clinical doses of the respective antipsychotics. In this study, we measured dopamine D2 receptor occupancy of two conventional benzamide antipsychotics, sulpiride and sultopride, using positron emission tomography, to investigate the rationale of their clinical dose. Although they are prescribed at similar doses (300-1200 mg), the doses required to obtain similar receptor occupancy (70-80%) were quite different: 1010-1730 mg for sulpiride but 20-35 mg for sultopride. In terms of dose, sultopride has about 50 times greater potency than sulpiride based on dopamine D2 receptor occupancy. Evidence for the optimal doses of conventional antipsychotics based on dopamine D2 receptor occupancy would be helpful for rational antipsychotic therapy.

Objective Chordoma is a rare malignant bone tumor that arises from notochord remnants. This is the first trial to investigate the utility of 11C-methionine(MET) positron emission tomography(PET) in the imaging of chordoma before and after carbon-ion radiotherapy(CIRT). Design and patients Fifteen patients with chordoma were investigated with MET-PET before and after CIRT and the findings analyzed visually and quantitatively. Tumor MET uptake was evaluated by tumor-to-nontumor ratio(T/N ratio). Results In 12(80%) patients chordoma was clearly visible in the baseline MET-PET study with a mean T/N ratio of 3.3±1.7. The MET uptake decreased significantly to 2.3±1.4 after CIRT(P＜0.05). A significant reduction in tumor MET uptake of 24% was observed after CIRT. Fourteen (93%) patients showed no local recurrence after CIRT with a median follow-up time of 20 months. Conclusion This study has demonstrated that MET-PET is feasible for imaging of chordoma. MET-PET could provide important tumor metabolic information for the therapeutic monitoring of chordoma after CIRT.

The authors developed and applied two new linearized reference tissue models for parametric images of binding potential ( BP) and relative delivery ( R1) for [11C]DASB positron emission tomography imaging of serotonin transporters in human brain. The original multilinear reference tissue model (MRTMO) was modified (MRTM) and used to estimate a clearance rate ( k′2) from the cerebellum (reference). Then, the number of parameters was reduced from three (MRTM) to two (MRTM2) by fixing k′2. The resulting BP and R1 estimates were compared with the corresponding nonlinear reference tissue models, SRTM and SRTM2, and one-tissue kinetic analysis (1TKA), for simulated and actual [11C]DASB data. MRTM gave k′2 estimates with little bias (O from 12–70% to 1–4% at the expense of somewhat increased variability. MRTM2 substantially reduced BP variability by a factor of two or three over MRTM or SRTM. MRTM2, SRTM2, and 1TKA had R1 bias 11C]DASB positron emission tomography studies.

Recent studies have indicated that the serotonergic (5-HT) system plays important roles in memory function. However, the specific relationship between 5-HT(1A) receptors and memory function is not clear in the human brain. To clarify this relationship, the authors determined the availability of 5-HT(1A) receptors in the human brain and the relationship between regional receptor binding and memory function.Using positron emission tomography (PET) with [(11)C]WAY-100635, the authors examined 5-HT(1A) receptors and assessed their relationship with memory function. The 5-HT(1A )agonist tandospirone was then administered to investigate the effect of 5-HT(1A) receptor stimulation on cognitive function and neuroendocrinological response.There was a significant negative correlation between explicit memory function and 5-HT(1A) receptor binding localized in the bilateral hippocampus where the postsynaptic 5-HT(1A) receptors are enriched. Furthermore, the administration of tandospirone dose-dependently impaired explicit verbal memory, while other cognitive functions showed no significant changes. The change in memory function paralleled those of body temperature and secretion of growth hormone, which were reported to be induced by the stimulation of postsynaptic 5-HT(1A) receptors.Postsynaptic 5-HT(1A )receptors localized in the hippocampal formation have a negative influence on explicit memory function, which raises the possibility that the antagonistic effect of postsynaptic 5-HT(1A) receptors in the hippocampus leads to improvement of human memory function. Drugs that work as antagonists on postsynaptic 5-HT(1A) receptors may be favorable for improved control of memory impairment.

Rationale. Tandospirone is a selective 5-hydroxytryptamine (HT)1A receptor agonist and is clinically used as an anxiolytic in Japan. However, there are no data concerning the occupancy of these receptors by tandospirone in the living human brain. Objectives. The aim of this study was to assess the effect of tandospirone on in vivo 5-HT1A receptor binding of [11C]WAY 100635 using positron emission tomography (PET) and the neuroendocrine effect. Methods. In the PET study, seven healthy volunteers were scanned three times following an oral dose of placebo or tandospirone (30 mg or 60 mg). The binding potential of [11C]WAY 100635 was estimated for six regions: prefrontal cortex, temporal cortex, anterior cingulate cortex, parietal cortex, hippocampus and dorsal raphe nucleus. In the neuroendocrine study, six volunteers received a single oral dose of tandospirone (60 mg) or placebo in a randomized double-blind, cross-over design, and then the plasma levels of growth hormone and cortisol and the body temperature were measured. Results. Tandospirone (60 mg) induced a significant decrease in body temperature and an increase in the plasma concentration of growth hormone. However, there was no significant reduction of [11C]WAY 100635 binding following the administration of 30 mg or 60 mg tandospirone. Conclusion. Despite the significant effect on growth hormone and body temperature, a clinical dose of tandospirone had a negligible effect on [11C]WAY 100635 binding. This indicates that the agonist produces a pharmacological effect without measurable occupancy, and a new index other than occupancy will be required for the in vivo evaluation of agonists.

Human personality has been considered to have a neurochemical background. We examined the relation between extrastriatal dopamine D2 receptor binding in living human brain and the personality trait of novelty seeking that has been proposed to be related to dopaminergic function in the brain. We measured extrastriatal dopamine D2 receptors of 24 healthy young male subjects using [(11)C]FLB 457 positron emission tomography. The personality trait of each subject was assessed by the Temperament and Character Inventory (TCI). Correlation of dopamine D2 receptor binding with novelty seeking was calculated using region-of-interest analysis and statistical parametric mapping based on the binding potential images generated using a reference tissue model. A significant negative correlation was observed between binding potential values and the novelty seeking scores on TCI in the right insular cortex. No significant correlation was observed in any other region. Our result indicates that there is a significant association between dopamine D2 receptor binding and the human novelty seeking trait in the right insular cortex.

For sensitive analysis of the radioactive-metabolite in human PET, a radio-HPLC system coupled to a newly designed positron detector was constructed. The detector had the advantages of low noise level(1.7+/-1.0cpm)and high sensitivity(32+/-1%)due to coincidence counting and large BGO crystals. Furthermore, the detector was easy to move,since a pair of the BGO housings coupled to photomultipliers was effectively arranged in parallel and a HPLC cell with different volume could be inserted between the BGO housing. This radio-HPLC system was useful for analyzing samples with low radioactivity. It was applied to the measurement of [11C]FLB457in plasma,having high affinity and high selectivity with dopamine D2 receptors. Extremely low radioactivity of [11C]FLB457(2500dpm)could be analzed by using the radio-HPLC system. The performance of this detector was compared with those of commercially available systems that had been used as sensitive detectors for HPLC. (C)2001 Elsevier Science Ltd. All rights reserved.

Using positron emission tomography (PET) and [11C]N-methylspiperone (NMSP), we examined 5-HT2 receptors in the cortex of schizophrenic patients in whom we previously observed decereased prefrontal D1 receptor binding. The subjects were 10 neuroleptic-naive schizophrenic patients, 7 schizophrenic patients who were drug-free but had previously been treated with neuroleptics, and 12 normal controls. A non-significant trend towards decreased prefrontal [11C]NMSP binding was observed in the neuroleptic-treated patients, suggesting a possible effect of previous neuroleptic treatment on the alteration in cortical 5-HT2 function. However, the neuroleptic-naive patients showed no noticeable difference in cortical [11C]NMSP binding compared to controls. Our results do not rule out the role of 5-HT2 function as a crucial site of therapeutic activity of schizophrenia, but they do suggest that cortical 5-HT2 receptors might not be primarily involved in the pathophysiology of schizophrenia.

Summary Background Although high-affinity imipramine binding sites have been reported in both rat and human lung, the role of the lungs in the pharmacokinetics of antidepressants has not received much attention. Substantial accumulation of selective serotonin-reuptake inhibitors (SSRIs) in the lungs has been reported. We have investigated the role of the lungs in pharmacokinetic drug interactions between tricyclic antidepressants and SSRIs. Methods We used a carbon-11-labelled form of the imipramine derivative cyanoimipramine to measure uptake in the lungs and brain of healthy volunteers by positron emission tomography. Clomipramine (50 mg) was administered to measure the effect of antidepressants with high affinity for the serotonin transporter on lung and brain uptake. Findings A large proportion of the injected 11 C-cyanoimipramine (68–86% in the four volunteers) was extracted by the lungs. Clomipramine decreased the lung uptake from 68% to 35% and from 81% to 54% in the two volunteers studied. By contrast, whole-brain uptake was low in control studies (1·7–2·0% in three volunteers) and increased after clomipramine administration (to 4·5–4·9%). Plasma radioactivity was also higher after clomipramine than in control studies. Interpretation The lungs may function as a reservoir for antidepressants with high affinity to the serotonin transporter. The accumulated antidepressants may be displaced by other antidepressants, and this displacement would substantially increase plasma concentrations and thus cause toxic effects.

Summary Background Acetylcholinesterase activity, a marker for degeneration of the central cholinergic system, has consistently been reported, in necropsy brain studies, to be reduced in the cerebral cortex of patients with Alzheimer's disease. We have shown regional acetylcholinesterase activity in vivo in rodent and primate brains with radioactive acetylcholine analogues. In the present study, we used one of the analogues to map acetylcholinesterase activity in the brains of living people. Methods Positron emission tomography (PET) and a radiolabelled acetylcholine analogue with high hydrolytic specificity to acetylcholinesterase [ 11 C]N-methyl-4-piperidyl acetate (MP4A), was used in eight elderly healthy controls and five patients with Alzheimer's disease who had mild dementia. All participants were given an intravenous injection of [ 11 C]MP4A and then sequential patterns of radioactivity in various brain regions were obtained by PET. Time courses of [ 11 C]MP4A concentration in arterial blood were also measured to obtain an input function. A three-compartment model was used to estimate regional acetylcholinesterase activity in the brain. Findings The estimated acetylcholinesterase distribution in the brain of the control participants agreed with the acetylcholinesterase distribution at necropsy. All patients with Alzheimer's disease had multiple cortical regions with a reduced estimated acetylcholinesterase activity in comparison with control participants. The reduction was more pronounced in the parietotemporal cortex, with an average reduction rate of 31% in temporal and 38% in parietal cortex, and less pronounced in other cortical lesions (19% in frontal, 24% in occipital, and 20% in sensorimotor cortex). Each patient was found to have at least two cortical regions with significantly reduced acetyl-cholinesterase activity. Interpretation The method we describe for non-invasive in-vivo detection of regional acetylcholinesterase changes in the living human brain that is feasible for biochemical assessment of Alzheimer's disease.

Dantrolene (1) is a substrate for breast cancer resistant protein, which is widely distributed in the blood-brain-barrier, intestine, gall bladder, and liver. PET study with 1 labeled with a positron emitter can be used to visualize BCRP and to elucidate the effect of BCRP on the pharmacokinetics of drugs. The objective of this study was to label 1 using nitrogen-13 ((13)N, a positron emitter; half-life: 9.9min). Using no-carrier-added [(13)N]NH(3) as the labeling agent, we synthesized [(13)N]dantrolene ([(13)N]1) for the first time. The reaction of carbomyl chloride 2b with [(13)N]NH(3) gave an unsymmetrical urea [(13)N]3, followed by cyclization of [(13)N]3 to afford [(13)N]1. Due to its instability, 2b was prepared in situ by treating amine 5 with triphosgene in a ratio of 4 to 1 and used for subsequent [(13)N]ammonolysis without purification.

Positron emission tomography (PET) was used to assess the role of dopamine D2 receptors in the striatum and serotonin S2 receptors in the frontal cortex in the susceptibility to methamphetamine-induced psychosis. Subjects were six men who had previously experienced methamphetamine psychosis (methamphetamine subjects) and 10 age- and sex-matched control subjects. The radiotracer used was 11C-N-methylspiperone. Although binding availability, assessed by dynamic analysis, in the two regions did not differ between the two groups, the ratio of binding availability in the striatum to that in the frontal cortex significantly decreased in the methamphetamine subjects as compared with the control subjects. These findings suggest that an imbalance in the activity of these two receptors may be related to the susceptibility to methamphetamine psychosis.

The effects of age on the binding of [11C]Ro 15-4513, a partial inverse agonist of the central benzodiazepine receptor, were studied. Sixteen healthy male volunteers (21–78 years old) participated. REgional radioactivity in the brain was followed for 45 min by positron emission tomography after a bolus injection of [11C]Ro 15-4513. Similar tracer kinetics were observed in both young and old subjects. For the quantification of receptor binding in vivo, a compartment model, in which radioactivity in the pons was used as an input function, was applied. There were no significant changes in the binding potentials with age (P > 0.1) in ten brain regions. These observations delineate an interesting difference between central benzodiazepine (BZ) receptors and other neurotransmitter receptors in the human brain measured by PET that have been shown to have a reduction with age.

The effects of age on the binding parameters of [11C]N- methyl-4-piperidylbenzilate ([11C]NMPB), a specific muscarinic cholinergic receptor ligand, were studied. Eighteen healthy male volunteers (18-75 years old) participated. Regional radioactivity in the brain was followed for 60 min by positron emission tomography (PET). Uptake of [11C]NMPB continuously increased in all brain areas with the exception of the cerebellum. For the quantification of receptor binding, a compartment model, in which radioactivity in the cerebellum was used as an input function, was used. The binding parameter, K3, of muscarinic acetylcholine receptors in eight brain regions (pons, hippocampus, frontal cortex, striatum, temporal cortex, thalamus, occipital cortex, parietal cortex) showed an age-related decrease of about 45% over the age range.

OBJECTIVE: Dopamine transporter (DAT) is a reuptake carrier of dopamine at presynapse that regulates dopaminergic neural transmission. [(11)C]PE2I is a cocaine analog developed as a potent positron emission tomography (PET) ligand for DAT with high selectivity. The aim of this study was to evaluate the applicability of quantification methods using reference tissue models for [(11)C]PE2I. METHODS: Dynamic PET scans were performed in 6 young healthy male volunteers after an intravenous bolus injection of [(11)C]PE2I. Metabolite-corrected arterial plasma-input functions were obtained. Compartment model analysis and plasma-input Logan analysis were performed to determine the kinetic parameters and distribution volume (V (T)). The distribution volume ratio (DVR) was calculated as the ratio of V (T) in the cerebral region to that in the cerebellum. DVRs were also determined by the original multilinear reference tissue model method (MRTMo) and the simplified reference tissue model method (SRTM), comparing the results with those obtained from graphical analysis using arterial input function. To estimate errors in DVR calculated using the reference tissue model, a simulation study that focused on cerebellar kinetics and scan duration was performed. RESULTS: The highest [(11)C]PE2I binding was observed in the striatum, followed by the midbrain and thalamus. The 2-tissue model was preferable to the 1-tissue model for describing the [(11)C]PE2I kinetics in the cerebellum. Both the measured and 90-min simulated data showed that reference tissue models caused an underestimation of DVR in the striatum. The simulation showed that 90-min scan duration was insufficient when cerebellar kinetics was described as a 1-tissue model. Nevertheless, DVR values determined by MRTMo and SRTM were in good agreement with those by the graphical approach in other lower binding regions. CONCLUSION: Due to the [(11)C]PE2I kinetics in the cerebellum and limited scan duration for (11)C, MRTMo and SRTM underestimated the striatal DVR. Despite this limitation, the present study demonstrated the applicability of reference tissue models. Since DAT in the midbrain and thalamus is of interest in the pathophysiology of neuropsychiatric disease, this noninvasive quantitative analysis will be useful for clinical investigations.

The aim of this study was to assess the feasibility of MET-PET as an evaluation method of the therapeutic effect of carbon ion beam radiotherapy.Twenty-four choroidal melanoma patients who were treated with a carbon ion beam underwent at least three MET-PET scans before and after therapy. The uptake was visually and semiquantitatively evaluated on the basis of the tumor-to-brain ratio (TBR).The accumulation was significantly decreased at 6 months or more after therapy and disappeared in 50% of the patients at 12 months after therapy. The baseline TBR, 1, 6, 12 and 24 months after therapy averaged 1.88+/-0.65, 1.73+/-0.52, 1.08+/-0.42, 0.67+/-0.27 and 0.65+/-0.30, respectively. TBR was significantly decreased at 6 months or more after therapy.MET-PET may be an alternative method for evaluating the effect of radiotherapy.

It has been demonstrated in vitro that the dopamine D(2) receptor has 2 interconvertible affinity states for endogenous dopamine, referred to as the high- and the low-affinity states. (11)C-(R)-2-CH(3)O-N-n-propylnorapomorphine ((11)C-MNPA) is a new agonist radioligand for in vivo imaging of the high-affinity state of dopamine D(2) receptors using PET. In the present study, the kinetics of (11)C-MNPA were examined for the first time, to our knowledge, in the human brain and analyzed using quantitative approaches with or without an arterial input function.A 90-min dynamic PET scan was obtained for 10 healthy men after an intravenous injection of (11)C-MNPA. The binding potential (BP(ND)) was calculated using the indirect kinetic method, a kinetic compartment analysis with a metabolite-corrected arterial input function. BP(ND) was also calculated by the simplified reference tissue model (SRTM) and transient equilibrium methods, both with the cerebellum as the reference brain region. The results of the quantitative methods were compared in a cross-validation approach.The highest regional radioactivity was observed in the putamen. BP(ND) values obtained by kinetic analysis were 0.82 +/- 0.09, 0.59 +/- 0.11, and 0.28 +/- 0.06, respectively, in the putamen, caudate, and thalamus. BP(ND) values obtained by the SRTM and transient equilibrium methods were in good agreement with those obtained by the indirect kinetic method (r = 0.98 and r = 0.93, respectively). For all quantification methods, the BP(ND) values based on data acquired from 0 to 60 min were in good agreement with those based on data acquired from 0 to 90 min (r = 0.90-0.99).The regional distribution of (11)C-MNPA binding was in good agreement with previous PET studies of dopamine D(2) receptors in the human brain using antagonist radioligands. The results support routine use of the SRTM and transient equilibrium methods, that is, methods that do not require an arterial input function and need a scan time of only about 60 min. (11)C-MNPA should thus be useful for clinical research on the pathophysiology of neuropsychiatric disorders and estimation of dopamine D(2) receptor occupancy by dopaminergic drugs.

Central-type benzodiazepine binding sites were characterized in a single normal human subject, using positron emission tomography (PET) and the radiolabelled benzodiazepine antagonist, carbon-11 labelled flumazenil ([11C] Ro 15-1788). The subject was scanned using tracer alone and tracer plus 4 different concentrations of unlabelled Ro 15-1788, including one concentration of unlabelled Ro 15-1788, chosen to produce maximum displacement of [11C] Ro 15-1788 from specific binding sites. Concentrations of free, unmetabolized [11C] Ro 15-1788 in plasma were estimated using a simple extraction and ultrafiltration method. Radioactivity in the regional exchangeable pool in brain was estimated under non-saturation conditions from the ratio of radioactivity in brain to plasma, under saturation conditions and the kinetics of free ligand in plasma. The specific binding was, then, estimated by the difference between the total radioactivity in brain and exchangeable pool radioactivity. Scatchard analyses were performed to yield Bmax and Kd values under pseudo-equilibrium conditions, which was observed as an increase of specific binding/free with reduction in specific binding. In cerebral cortex and cerebellum, the Bmax values were about 62-73 nmol/l and the Kd values were 3.6-6 nM in the estimation of free ligand in plasma and 12-15 nM in the estimation of exchangeable pool in brain, as free in brain.

The effects of age on the binding parameters of 11C-SCH23390, the highly selective ligand for central D1 dopamine receptors, at specific binding sites in the brain were studied. Seventeen healthy male volunteers (20-72 years old) participated. Regional radioactivity in the brain was followed for 40 min by positron emission tomography (PET). A high accumulation of radioactivity was observed in the striatum and there was a conspicuous accumulation in the neocortex. A two-compartment model was used to obtain quantitative estimates of rate constants of association (K3) and dissociation (k4). The binding potential (k3/k4) of the dopamine D1 receptors in the striatum and frontal cortex decreased by 35% and 39%, respectively, with age. The value of k3 decreased by 58% in the striatum and 83% in the frontal cortex, whereas the value of k4 decreased by 35% in the striatum and 72% in the frontal cortex with age.

Introduction Malignant mesothelioma is a highly aggressive tumor originating in the pleura, peritoneum and pericardium, and the prognosis of patients undergoing current treatment remains poor. To develop new therapies, it is important to have a noninvasive imaging system for evaluating the efficacy of such prospective treatments. We have established clinically relevant mouse models and evaluated conventional and novel positron emission tomography (PET) tracers. Methods Epithelioid and sarcomatoid mesothelioma cells were inoculated subcutaneously and intrapleurally into nude mice. Biodistribution and PET imaging studies were conducted by injecting [ 18 F]fluoro-2-deoxy-d-glucose (FDG), 3′-[ 18 F]fluoro-3′-doxythymidine (FLT) or 4′-methyl-[ 11 C]thiothymidine (S-dThd) into the mouse models. In vitro cellular uptake of [ 14 C]FDG and [ 3 H]FLT and thymidine kinase 1 (TK 1 ) activity in both cell lines were measured. Expression of glucose transporter 1 (GLUT-1) and Ki-67 in xenografted tumors was evaluated by immunohistochemical staining. Results In epithelioid mesothelioma models, biodistribution experiments showed that tumor uptake of [ 11 C]S-dThd was significantly higher than that of [ 18 F]FDG. On the other hand, in sarcomatoid models, [ 18 F]FDG showed significantly higher accumulation than the other two tracers. These differential uptakes of the three tracers were confirmed by PET imaging. The cellular uptake of [ 14 C]FDG and [ 3 H]FLT and TK 1 activity in sarcomatoid cells were higher than those of epithelioid cells. GLUT-1 protein was strongly expressed in sarcomatoid but not in epithelioid tumor. We observed a high percentage of Ki-67-positive cells in both epithelioid and sarcomatoid tumors. Conclusions We established nude mouse models of epithelioid and sarcomatoid subtypes of mesothelioma. PET tracers applicable for the evaluation of epithelioid and sarcomatoid mesothelioma would vary: [ 18 F]FLT and [ 11 C]S-dThd seemed suitable for the epithelioid subtype and [ 18 F]FDG seemed suitable for the sarcomatoid subtype in our mouse models. Our results indicated that cellular uptake and TK 1 activity in vitro are not always consistent with tracer uptake of [ 18 F]FLT and [ 11 C]S-dThd in vivo. These mouse models and PET imaging might be useful tools for evaluating new and effective treatments in mesothelioma.

Objective Gefitinib (N-(3-chloro-4-fluorophenyl)-7-methoxy-6-[3-(morpholin-4-yl)propoxy]quinazolin-4-amine, Iressa) is an approved anticancer drug. In this study, we labeled gefitinib with carbon-11 and evaluated [11C]gefitinib to explore its specific binding in intact fibrosarcoma (NFSa)-bearing mice. Methods [11C]Gefitinib was synthesized by the reaction of desmethyl precursor (1) with [11C]CH3I. In vitro uptake of [11C]gefitinib into NFSa, human-A431 epidermoid carcinoma, and Jurkat T cells was determined. Positron emission tomography (PET) imaging using [11C]gefitinib was performed for NFSa-bearing mice. Results [11C]Gefitinib accumulated into NFSa cells with 2.1 uptake ratio (UR)/mg protein in cells. Addition of nonradioactive gefitinib decreased uptake in a concentration-dependent manner. [11C]Gefitinib also had high uptake (2.6 UR/mg protein) into epidermal growth factor receptor/tyrosine kinase (EGFR/TK)-rich A431 cells but low uptake (0.2 UR/mg protein) into EGFR/TK-poor Jurkat cells. In vivo distribution study on NFSa-bearing mice by the dissection method revealed that [11C]gefitinib specifically accumulated into the tumor. The ratio of radioactivity in tumors to that in blood and muscle as two comparative regions increased from 0.4 to 6.0 and from 0.6 to 5.0 during this experiment (0–60 min), respectively. PET for NFSa-bearing mice produced a clear tumor image, although high radioactivity was distributed throughout the body. Treatment with nonradioactive gefitinib (100 mg/kg) decreased uptake in the tumor. In vivo metabolite analysis demonstrated that [11C]gefitinib was stable in the tumor, liver, kidney, and blood. Conclusion These results demonstrated the promising potential of [11C]gefitinib to serve as a PET ligand for in vivo imaging of NFSa-bearing mice. Key words Iressa - Gefitinib - Positron emission tomography - Carbon-11 - Carbon-ion radiotherapy - CIRT - Fibrosarcoma

(S,S)-18F-FMeNER-D2 was recently developed as a radioligand for the measurement of norepinephrine transporter imaging with PET. In this study, a norepinephrine transporter was visualized in the human brain using this radioligand with PET and quantified by several methods. Methods: PET scans were performed on 10 healthy men after intravenous injection of (S,S)-18F-FMeNER-D2. Binding potential relative to nondisplaceable binding (BPND) was quantified by the indirect kinetic, simplified reference-tissue model (SRTM), multilinear reference-tissue model (MRTM), and ratio methods. The indirect kinetic method was used as the gold standard and was compared with the SRTM method with scan times of 240 and 180 min, the MRTM method with a scan time of 240 min, and the ratio method with a time integration interval of 120–180 min. The caudate was used as reference brain region. Results: Regional radioactivity was highest in the thalamus and lowest in the caudate during PET scanning. BPND values by the indirect kinetic method were 0.54 ± 0.19 and 0.35 ± 0.25 in the thalamus and locus coeruleus, respectively. BPND values found by the SRTM, MRTM, and ratio methods agreed with the values demonstrated by the indirect kinetic method (r = 0.81–0.92). Conclusion: The regional distribution of (S,S)-18F-FMeNER-D2 in our study agreed with that demonstrated by previous PET and postmortem studies of norepinephrine transporter in the human brain. The ratio method with a time integration interval of 120–180 min will be useful for clinical research of psychiatric disorders for estimation of norepinephrine transporter occupancy by antidepressants without requiring arterial blood sampling and dynamic PET.

Purpose: Progress of the novel carbon ion radiotherapy (CIRT) in the treatment of cancers has created the need for a method to accurately evaluate the response. We investigated whether L-[11C]methyl-methionine (11C–methionine) uptake at pre- and post-CIRT could be an early response predictor in patients with pelvic recurrence of rectal cancer. Patients and Methods: 11C–methionine positron emission tomography (PET) was performed prospectively in 53 patients with pelvic recurrence of rectal cancer before and 1 month after CIRT. 11C–methionine tumor uptake was measured by the tumor to muscle ratio (T/M ratio). The T/M ratios were evaluated in relation to clinical outcomes such as local re-recurrence, distant metastasis and survival. The response to CIRT was also judged by computed tomography (CT) and magnetic resonance imaging (MRI). 11C–methionine PET judgment was compared with CT/MRI judgment regarding the relevance to clinical outcome. Results: Baseline T/M ratio was 5.27±1.90 (mean±SD) in patients without developing local re-recurrence and 7.66±3.17 in patients with local re-recurrence (P=0.023, Mann-Whitney U test). Post-CIRT T/M ratios were 3.10±1.28 in patients without local re-recurrence and 6.15±2.98 in patients with local re-recurrence (p=0.006, Mann-Whitney U test). By Kaplan-Meier analysis with log-rank test, patients with a baseline T/M ratio of ≦7.6 or a post-CIRT T/M ratio of ≦5.0 had significant lower pelvic re-recurrence. However, the % change (reduction rate) from baseline to post-CIRT T/M ratio did not have significant relation to pelvic re-recurrence. There were no significant differences between 11C–methionine results (baseline T/M ratio, post-CIRT T/M ratio and % change) and other clinical parameters (distant metastasis and survival). Conclusion: 11C–methionine PET can be used for early prediction of local re-recurrence after CIRT. Because CIRT is local therapy, 11C–methionine PET cannot predict distant metastasis or survival after CIRT.

3-N-[11C]methylspiperone(11C-NMS, molecular weight = 409 for 12C-NMS) has been prepared automatically with high specific activity (37 ± 18 GBq/μmol at EOS) for the measurement of dopamine D2 receptors in the human brain with a positron camera. It was observed that the radiochemical purity of 11C-NMS decreased from 97.8% (in HPLC eluate) to 83.5% (in saline, after the dispensing procedure, at 29 min from EOS), and to 79.9% in a further 59 min and that another 11C-labelled compound with a molecular weight of 425 (as a 12C-labelled compound) was formed. It was also observed that an aqueous solution of carrier methylspiperone (NMS) decomposed on 60Co irradiation and, using the same analytical conditions, gave the compound with the same retention time and the same molecular weight as 11C-NMS gave. The G-value of NMS decomposition by 60Co irradiation was estimated to be about two in an aqueous solution. The decomposition of 11C-NMS was suppressed remarkably by the addition of hydroxyl radical scavengers such as potassium iodide, and accelerated slightly by a hydrated electron scavenger such as sodium nitrate. Therefore, it was assumed that the hydroxyl radical generated by the radiolysis of water played an important role in the decomposition of 11C-NMS in the aqueous solution. Polysolvate-80 and ethyl alcohol were used as i.v. injectable additives to protect 11C-NMS against decomposition. In 47 routine productions, 2.7 ± 1.7 GBq of 11C-NMS aqueous solutions ready for i.v. injection have been produced at 98.3 ± 1.0% radiochemical purity using an automated synthesis apparatus. The products were used for clinical purposes with a positron camera and animal experiments.

N-methyl-D-aspartate (NMDA) receptors are of major interest in brain functions and neuropsychiatric disorders. However, at present there are few suitable radioligands for in vivo imaging of NMDA receptors. 7-choloro-4-hydroxy-3-[3-(4-methoxybenzyl) phenyl]-2(1H)-quinolone (L-703,717) is one of the potent ligands for the glycine-binding site of NMDA receptors. 4-Acetoxy derivative of L-703,717 (AcL703) is a candidate, as a positron emission tomography (PET) ligand for NMDA receptors, because of its better permeability at the blood-brain barrier compared with L-703,717. After intravenous injection of 624-851 MBq of [11C]AcL703, dynamic PET scan was performed on six healthy males for 90 min. Regions-of-interest were located on the cerebral cortices, cerebellar cortex, and cerebral white matter. The binding potential (BP) was calculated from the ratio of the area under the curve (AUC) of radioactivities from 40 to 90 min in the target region to that in white matter. Regional radioactivities reached close to equilibrium in all regions after about 40 min postinjection. Regional brain uptake of [11C]AcL703 at 40 min after injection was 0.00028-0.00065% of the injected dose/milliliter. Radioactivity concentration of [11C]AcL703 was highest in the cerebellar cortex and lowest in white matter. AUC in the cerebellar cortex was higher than those of cerebral cortices, thalamus, striatum, and white matter. BP in the cerebellar cortex was twofold higher than in the cerebral cortices (cerebellar cortex: BP=2.20+/-0.72; cerebral cortices: BP=1.05+/-0.45). Despite the low brain uptake of [11C]AcL703, regional distributions were in good agreement with our previous studies of rodents. This indicates the possibility of in vivo evaluation of NMDA receptors using PET with [11C]AcL703 in living human brain.

We evaluated 4'-[methyl-11C]thiothymidine ([methyl-11C]S-dThd) to obtain a thymidine analog that might prove simpler to use for imaging DNA synthesis and that might follow the same biochemistry as its surrogate.[Methyl-14C]S-dThd was synthesized by rapid methylation of 5-trimethylstannyl-4'-thio-2'-deoxyuridine via a palladium-mediated Stille coupling reaction with 14C-methyl iodide. Degradation of [methyl-14C]S-dThd, when incubated in human blood, was analyzed by high-performance liquid chromatography (HPLC). The in vivo potential of [methyl-14C]S-dThd was evaluated by studying its distribution in EMT-6 mammary carcinoma-bearing mice. 2-Fluoro-2'-deoxycytidine, a potent inhibitor of DNA synthesis, was used to modulate cell proliferation. Tissue extraction was also performed to investigate the incorporation of [methyl-14C]S-dThd into DNA.[Methyl-14C]S-dThd was obtained in a 31%-41% radiochemical yield (calculated from 14C-methyl iodide) at 130 degrees C, 5-min reaction in N,N-dimethylformamide followed by semipreparative HPLC purification. The radiochemical purity of [methyl-14C]S-dThd was99% and the specific activity was 2.04 GBq/mmol (according to the specific activity of 14C-methyl iodide). [2-14C]Thymidine, when incubated with human blood, demonstrated rapid degradation. In contrast, [methyl-14C]S-dThd was stable with3% degradation at 60 min. An in vivo distribution study showed the accumulation of radioactivity in proliferating tissues (spleen, thymus, duodenum, and tumor). On the other hand, the radioactivity of nonproliferating tissues (lung, liver, kidney, and muscle) was rapidly cleared in parallel with the clearance of blood radioactivity. The tumor uptake of [methyl-14C]S-dThd was high (8.8 percentage injected dose per gram at 60 min) and selective (tumor-to-blood ratio, 12.2 at 60 min). 2-Fluoro-2'-deoxycytidine pretreatment significantly reduced the tumor uptake of [methyl-14C]S-dThd. Relative blood flow as measured by the uptake of 4-[N-methyl-14C]iodoantipyrine was similar between the treated and untreated groups. Tissue extraction studies showed that most of the total tissue radioactivity of rapidly proliferating tissues was recovered in the DNA fraction at 60 min after [methyl-14C]S-dThd injection.The labeling procedure is rapid and suitable for 11C labeling. Positron-labeled 4'-thiothymidine should be useful for imaging DNA synthesis by PET.

P-glycoprotein in the blood-brain barrier (BBB) has been found to be associated with several types of neurologic damage. (11)C-Verapamil has been used for in vivo imaging of P-glycoprotein function in the BBB by PET, but metabolites in plasma complicate the quantitative analysis of human studies. In this study, we validated the quantification methods of (11)C-verapamil transfer from plasma to the brain in humans.The transfer rate constant from plasma to the brain, K(1), was estimated by nonlinear least squares (NLS) with a 2-input compartment model, including the permeation of the main metabolite in plasma at the BBB, and with a 1-input compartment model using only 15-min data that contained little metabolite in plasma. K(1) was also estimated by graphical analysis of an integration plot that uses only early-time data, before the appearance of metabolites, and the estimated K(1) was compared with that obtained by the NLS method. In the simulation study, the reliability of parameter estimates in the graphical analysis method was investigated for various values of rate constants, time ranges of parameter estimations, and noise levels.(11)C-Verapamil in plasma gradually converted to its metabolites, and about 45% of the radioactivity in the plasma specimen was associated with (11)C-verapamil metabolites at 30 min after injection. Although K(1) estimated from graphical analysis was slightly smaller than that by NLS, there was strong correlation among the K(1) values obtained by these 3 methods. In the simulation study, for graphical analysis, the differences between the true and mean of K(1) estimates became larger and the coefficient of variation (COV) of K(1) estimates became smaller as the end time of linear regression became later. The COV of graphical analysis was almost equal to that of NLS with the 1-input compartment model.The transfer of (11)C-verapamil from plasma to the brain was able to be quantitatively estimated by graphical analysis because this method can provide K(1) from the data of the initial few minutes without considering the effect of the metabolites in plasma.

P-glycoprotein (P-gp) is a membrane protein that functions as an adenosine triphosphate-dependent efflux pump for xenobiotics at the blood-brain barrier (BBB). Polymorphisms of MDR1 gene have been reported to be associated with the expression level of P-gp. (11)C-Verapamil is considered to be one of the suitable radioligands for evaluating P-gp functions. However, the metabolites of verapamil might complicate the quantitative analysis because of their possible brain penetration. In the present study, we investigated the P-gp functional differences at the BBB between the haplotypes (1236TT, 2677TT, 3435TT vs. 1236CC, 2677GG, 3435CC) of the MDR1 gene with different quantitative analyses of (11)C-verapamil.Thirty-three healthy male volunteers were enrolled in this study after identification of the haplotypes of the MDR1 gene. Brain PET scans with (11)C-verapamil were performed for 16 min. Integration plot analysis, which yields brain uptake clearance, was performed with the first 3-min data. Integration plot analysis was then compared with several other quantitative analyses with 16-min data (1-input, 1-tissue compartment model, and the area under the curve ratio (AUC(ratio)) between brain and plasma).In the integration plot, there was no difference in the absolute values of brain uptake clearance (CL(uptake)) between the haplotypes; CL(uptake) of (11)C-verapamil for the haplotypes (1236TT, 2677TT, 3435TT vs. 1236CC, 2677GG, 3435CC) were 0.053 +/- 0.011 and 0.051 +/- 0.011 mL/g/min, respectively. CL(uptake) of (11)C-verapamil in the integration plot was significantly correlated with K1 and DV(K1/k2) (DV is distribution volume; K1 and k2 are plasma and tissue rate constants) in the 1-input, 1-tissue compartment model and the AUC(ratio).On the basis of the several quantitative analyses of (11)C-verapamil, the assumption that the function of P-gp at the BBB is different between the haplotypes (3 single nucleotide polymorphisms: C1236T, G2677T, and C3435T) of MDR1 gene was not supported.

Background and objectives To estimate the presynaptic function of the central dopaminergic system, the rate of endogenous dopamine synthesis has been measured by using L-[β- 11 C]DOPA or 6-[ 18 F]fluoro-L-DOPA with positron emission tomography. However, the regional kinetics of L-[β- 11 C]DOPA in human brain have not been investigated in detail. In the present study, the regional kinetics of L-[β- 11 C]DOPA in normal human brain and the accuracy of the method for quantifying L-[β- 11 C]DOPA kinetics, employing reference regions, were investigated. Methods After intravenous injection of L-[β- 11 C]DOPA, dynamic scanning was performed on ten healthy subjects for 89 min. The overall uptake rate constant K was calculated by the kinetic and graphical approaches, in which the occipital cortex was used as a reference brain region. Results Regional distribution of K was similar to those of dopamine D 2 receptor. A significant negative correlation was observed between the neutral amino acid concentration in plasma and the influx rate constant through the blood-brain barrier (K 1 ). The K values calculated by graphical approach were in good agreement with the values calculated by kinetic approach for both experimental and simulated data. Conclusions The regional distribution of K corresponds to that of the nigrostriatal and mesolimbic dopaminergic system. Negative correlation between neutral amino acid concentration and K 1 supports the suggestion that L-DOPA is transported in a competitive fashion via the same carrier system as neutral amino acids at the blood-brain barrier. Because the graphical approach can obviate the need for an arterial input function, it is useful for investigating the rate of regional dopamine synthesis in neuropsychiatric and neurodegenerative diseases.

[11C]DAA1106 is a potent and selective ligand for the peripheral benzodiazepine receptor (PBR) with high affinity. It has been reported that the density of PBR is related to brain damage, so a reliable tracer method for the evaluation of PBR would be of use. We evaluated a quantification method of [11C]DAA1106 binding in simulated data and human brain data. In the simulation study, the reliability of parameters estimated from the nonlinear least-squares (NLS) method, graphical analysis (GA), and multilinear analysis (MA) was evaluated. In GA, variation of the estimated distribution volume (DV) was small. However, DV was underestimated as noise increased. In MA, bias was smaller, and variation of the estimated DV was larger than in GA. In NLS, although variation was larger than in GA, it was small enough in regions of interest analysis, and not only DV but also binding potential (BP), determined from the k3 /k4 without any constraint, could be estimated. The variation of BP estimated with NLS became larger as k3 or k4 became smaller. In human studies with normal volunteers, regions of interest were drawn on several brain regions, BP was calculated by NLS, and DV was also estimated by NLS, GA, and MA. As a result, DVs estimated with each method were well correlated. However, there was no correlation between BP with NLS and DV with NLS, GA, and MA, because of the variation of K1 /k2 between individuals. In conclusion, BP is estimated most reliably by NLS with the two-tissue compartment model.

N-(5-Fluoro-2-phenoxyphenyl)-N-(2-(18)F-fluoroethyl-5-methoxybenzyl)acetamide ((18)F-FEDAA1106) is a potential PET ligand with highly selective and specific binding to peripheral benzodiazepine receptor (PBR). It has been reported that the regional density of PBR in the brain is increased in several neurodegenerative and psychiatric disorders. Thus, a reliable tracer method for evaluating PBR would be of use clinically and for research. To our knowledge, this is the first study to investigate the (18)F-FEDAA1106 binding to PBR in living human brain by PET. We also aimed to evaluate various analytic methods to quantify the density of PBR.PET studies with (18)F-FEDAA1106 were performed on 7 healthy men. Volumes of interest (VOIs) were drawn on PET images. In each VOI, binding potential (BP) was calculated by nonlinear least-squares (NLS) fitting based on the 2-tissue compartment model, and the distribution volume (DV) was also estimated by NLS, Logan plot, and multilinear analysis (MA) methods. To estimate errors in calculation of BP and DV, simulation studies were also performed.The DVs estimated with each of the methods were significantly correlated. There was also significant correlation between BP with NLS and DV with NLS, Logan plot, or MA. But the interindividual differences in the distribution volume of the free and nonspecific binding compartment (K(1)/k(2)) were relatively large. In a simulation study, variation of the DV estimated by Logan plot was relatively small, but it was underestimated as the noise increased. By MA, the bias of DV was smaller, but the variation of DV was larger than by Logan plot. Within a 3% noise level, there was almost no difference between Logan plot and MA in both bias and variation. DVs estimated by both Logan plot and MA were underestimated by 10%-20%. Although the variation of DV was larger by NLS than by Logan plot, it was small enough in the noise level of VOI analysis, and the bias of DV was 0%-2%.The simulation studies indicated that NLS is a suitable method for the estimation of (18)F-FEDAA1106 binding to PBRs.

Schizophrenia is believed to involve altered activation of dopamine receptors, and support for this hypothesis comes from the antipsychotic effect of antagonists of the dopamine D2 receptor (D2R). D2R is expressed most highly in the striatum, but most of the recent positron emission tomography (PET) studies have failed to show any change in D2R densities in the striatum of schizophrenics, raising the possibility that other receptors may also be involved. In particular, the dopamine D1 receptor (D1R), which is highly expressed in the prefrontal cortex, has been implicated in the control of working memory, and working memory dysfunction is a prominent feature of schizophrenia. We have therefore used PET to examine the distribution of D1R and D2R in brains of drug-naive or drug-free schizophrenic patients. Although no differences were observed in the striatum relative to control subjects, binding of radioligand to D1R was reduced in the prefrontal cortex of schizophrenics. This reduction was related to the severity of the negative symptoms (for instance, emotional withdrawal) and to poor performance in the Wisconsin Card Sorting Test. We propose that dysfunction of D1R signalling in the prefrontal cortex may contribute to the negative symptoms and cognitive deficits seen in schizophrenia.

Positron emission tomography (PET) has been utilized for determining the dosage of antipsychotic drugs. To evaluate the dosage of antidepressants such as selective serotonin reuptake inhibitors, serotonin transporter occupancy (5-HTT) is also a useful index. We investigated the degree of 5-HTT occupancy with different doses of the antidepressant duloxetine and the time-course of 5-HTT occupancy using PET. PET scans with [11C]DASB were performed before and after a single administration of duloxetine (5–60 mg), and three consecutive scans were performed after a single dose or repeated doses of 60 mg of duloxetine. 5-HTT occupancies by duloxetine were increased by 35.3 to 86.5% with dose and plasma concentration increments. The ED50 value of 5-HTT occupancy was 7.9 mg for dose and 3.7 ng/ml for plasma concentration. In the time-course of 5-HTT occupancy, mean occupancies were 81.8% at 6 h, 71.9% at 25 h, and 44.9% at 53 h after a single administration, and 84.3% at 6 h, 71.9% at 49 h, and 47.1% at 78 h after repeated administrations. Based on 5-HTT occupancy, 40 mg and more of duloxetine was needed to attain 80% occupancy, and 60 mg of duloxetine could maintain a high level of 5-HTT occupancy with a once-a-day administration schedule.

The reduction of acetylcholinesterase (AChE) activity in the brain has been measured in dementia disorders such as Alzheimer's disease and dementia with Lewy bodies using (11)C-labeled acetylcholine analogues, N-[(11)C]methylpiperidin-4-yl acetate and propionate, and positron emission tomography (PET). Our aim was to develop an (18)F-labeled acetylcholine analogue useful for brain AChE mapping with PET, since (18)F, with a longer half-life, has advantages over (11)C. In a preliminary study, a series of N-[(14)C]ethylpiperidin-3-yl or -4-ylmethanol esters (acetyl and propionyl esters) were newly designed and evaluated in vitro regarding the reactivity with and specificity to AChE using purified human enzymes, leading to a novel (18)F-labeled acetylcholine analogue, N-[(18)F]fluoroethylpiperidin-4-ylmethyl acetate. In rat experiments, the (18)F-labeled candidate showed desirable properties for PET AChE measurement: high brain uptake of the authentic ester, high AChE specificity, a moderate hydrolysis rate, and low membrane permeability (metabolic trapping) of the metabolite.

Purpose: The development of the novel carbon ion radiotherapy (CIRT) in the treatment of refractory cancers has resulted in the need for a way to accurately evaluate patient prognosis. We evaluated whether l-[methyl-11C]-methionine (MET) uptake and its change after CIRT were the early survival predictors in patients with unresectable bone and soft tissue sarcomas. Experimental Design: MET positron emission tomography was prospectively performed in 62 patients with unresectable bone and soft tissue sarcomas before and within 1 month after CIRT. Tumor MET uptake was measured with the semiquantitative tumor:nontumor ratio (T/N ratio). The MET uptake in the tumor and relevant clinical parameters were entered into univariate and multivariate survival analysis. Results: The overall median survival time was 20 months. Patients with a baseline T/N ratio of ≤6 had a significant better survival than patients with a baseline T/N ratio >6 (2-year survival rate: 69.4% versus 32.3%; P = 0.01). Patients with a post-CIRT ratio of ≤4.4 had a better survival than that with a post-CIRT ratio >4.4 (2-year survival rate: 63.7% versus 41.3%; P = 0.01). A significant higher survival rate was observed in patients with post-therapeutic MET uptake change of >30% than patients in lower change group (2-year survival rate: 74.6% versus 41.6%; P = 0.049). The multivariate analysis showed that both baseline and post-CIRT T/N ratio were statistically significant independent predictors of patient survival. Tumors with larger T/N ratio had a significantly poorer prognosis. Conclusions: MET uptake as measured by either baseline or post-CIRT T/N ratio was an independent predictor of survival in patients with bone and soft tissue sarcomas treated by carbon ion radiotherapy, whereas post-therapeutic MET uptake change might have potential value for the same purpose.

In Alzheimer's disease, cerebral cortical butyrylcholinesterase (BChE) activity is reported to be elevated. Our aim was to develop a novel (18)F-labeled tracer for quantifying cerebral BChE activity by positron emission tomography. With in vitro screening of N-[(14)C]ethylpiperidin-3- and 4-ylmethyl esters, N-[(14)C]ethylpiperidin-4-ylmethyl butyrate was selected as a lead for (18)F-labeling, affording N-[(18)F]fluoroethylpiperidin-4-ylmethyl butyrate. The (18)F-labeled butyrate showed the required properties for in vivo BChE measurement, that is, the lipophilic nature of the authentic ester, high specificity to BChE, a moderate hydrolysis rate, and the hydrophilic nature of the metabolite.

We performed in vitro and in vivo assays of the metabolism of [ 11 C]Ro15-4513 over time in the plasma of mice, rats, monkeys and humans, using a radio-HPLC equipped with a sensitive positron detector, in order to compare the metabolic rates of the radiopharmaceutical agent among the different animal species and to establish a highly sensitive analytical method for the radiotracer agent. We also examined the metabolism of [ 11 C]Ro15-4513 in the brain tissue of mice and rats. The analytical method used in this study permitted detection of even extremely low levels of radioactivity (approximately 5,000 dpm). In vitro experiments revealed that [ 11 C]Ro15-4513 in the blood was metabolized to hydrolysate [ 11 C]A. The species were classified in descending order of the metabolic rate of the radiotracer in vitro as follows; mice, rats, and monkeys/humans. In the in vitro experiment, the percentage of the unchanged drug in the plasma at 60 minutes postdose was 9% in mice, 70% in rats, 97% in monkeys, and 98% in humans. In vivo metabolite analysis in the blood showed the presence of two radioactive metabolites, consisting of one hydrolysate [ 11 C]A and another unidentified substance. The species were classified in descending order of the metabolic rate of the radiotracer in vivo as follows; mice, rats/humans, and monkeys. The percentage of the unchanged drug in the plasma was 6% in mice, 21% in rats, 26% in humans, and 40% in monkeys. Furthermore, the in vitro and in vivo experiments conducted to analyze the metabolism of [ 11 C]Ro15-4513 in the brain tissue of mice and rats revealed that the radiotracer was metabolized to some extent in the brain tissue of these animals. In the in vivo experiment, the percentage of the unchanged drug at 60 min postdose was 86% in the brain tissue of mice and 88% in the brain tissue of rats, while in the in vitro experiment, the corresponding percentage was 93% in mice, and 91% in rats.

Serotonin (5-HT) is considered to be an important transmitter underlying mood and behaviour. Abnormalities of the 5-HT transporter have been suggested in mood disorders, since it is one of the major binding sites of antidepressants. A number of ligands have been developed to visualise the 5-HT transporter in vivo, but only a few have successfully visualised specific binding in vivo. In this study, we comparatively evaluated two ligands for 5-HT transporter, [(11)C](+)McN5652 and [(11)C]cyanoimipramine, in the human brain. Brain uptake of [(11)C](+)McN5652 and [(11)C]cyanoimipramine was measured with PET in 15 healthy volunteers. Second PET scans were performed after pretreatment with the potent 5-HT reuptake inhibitor clomipramine. Data were analysed as regional brain uptake as well as whole brain uptake. In six healthy volunteers uptake of the two ligands was also measured in the lung since it is one of the high-uptake organs in the body. In the brain, high accumulation was observed in the thalamus and striatum, the regions known to contain high densities of 5-HT transporter, for both [(11)C](+)McN5652 and [(11)C]cyanoimipramine. The average ratio of thalamus to cerebellum uptake at 90 min after the tracer injection was approximately 1.6 for [(11)C](+)McN5652 and 1.7 for [(11)C]cyanoimipramine, while the ratios obtained after pretreatment with clomipramine were approximately 1.2. However, the whole brain uptake of [(11)C](+)McN5652 was approximately twice that of [(11)C]cyanoimipramine, while the lung uptake of [(11)C](+)McN5652 was approximately half that of [(11)C]cyanoimipramine. Both [(11)C](+)McN5652 and [(11)C]cyanoimipramine showed sufficient specific binding for performance of a quantitative analysis in the brain. [(11)C](+)McN5652 could be superior because of its higher distribution to the brain.

[11C](+)McN5652 is a selective serotonin reuptake inhibitor with subnanomolar potency for the serotonin transporter, and is currently being used for positron emission tomography studies. However, quantification of the regional [11C](+)McN5652 binding potential in vivo is a controversial issue because of its complex characteristics. The authors examined the regional differences in nonspecific binding and proposed simple methods for estimating the binding potential of [11C](+)McN5652. The regional difference in nonspecific binding was evaluated by the activity ratio of the thalamus compared with the cerebellum for inactive-isomer [11C](−)McN5652 and [11C](+)McN5652 saturation studies. The distribution volume of the thalamus was approximately 1.16 times larger than that of the cerebellum. The thalamus-to-cerebellum distribution volume ratio was estimated by nonlinear least square and graphical methods, with and without arterial input function. The graphical method with k2′ without blood sampling was practical and most applicable for estimation of the distribution volume ratio because this method is more stable than the nonlinear least square method in the simulation study. Binding potential estimated with the distribution volume ratio of [11C](+)McN5652 and the correction with distribution volume ratio of [11C](−)McN5652 represent the most reliable parameters for the assessment of serotonin transporter binding.