Non-invasive kinetic modelling approaches for quantitative analysis of brain PET studies.

Pharmacokinetic modelling with arterial sampling is the gold standard for analysing dynamic PET data of the brain. However, the invasive character of arterial sampling prevents its widespread clinical application. Several methods have been developed to avoid arterial sampling, in particular reference region methods. Unfortunately, for some tracers or diseases, no suitable reference region can be defined. For these cases, other potentially non-invasive approaches have been proposed: (1) a population based input function (PBIF), (2) an image derived input function (IDIF), or (3) simultaneous estimation of the input function (SIME). This systematic review aims to assess the correspondence of these non-invasive methods with the gold standard. Studies comparing non-invasive pharmacokinetic modelling methods with the current gold standard methods using an input function derived from arterial blood samples were retrieved from PubMed/MEDLINE (until December 2021). Correlation measurements were extracted from the studies. The search yielded 30 studies that correlated outcome parameters (VT, DVR, or BPND for reversible tracers; Ki or CMRglu for irreversible tracers) from a potentially non-invasive method with those obtained from modelling using an arterial input function. Some studies provided similar results for PBIF, IDIF, and SIME-based methods as for modelling with an arterial input function (R2 = 0.59-1.00, R2 = 0.71-1.00, R2 = 0.56-0.96, respectively), if the non-invasive input curve was calibrated with arterial blood samples. Even when the non-invasive input curve was calibrated with venous blood samples or when no calibration was applied, moderate to good correlations were reported, especially for the IDIF and SIME (R2 = 0.71-1.00 and R2 = 0.36-0.96, respectively). Overall, this systematic review illustrates that non-invasive methods to generate an input function are still in their infancy. Yet, IDIF and SIME performed well, not only with arterial blood calibration, but also with venous or no blood calibration, especially for some tracers without plasma metabolites, which would potentially make these methods better suited for clinical application. However, these methods should still be properly validated for each individual tracer and application before implementation.

Quantification of P-glycoprotein function at the human blood-brain barrier using [18F]MC225 and PET.

INTRODUCTION: P-glycoprotein (P-gp) is one of the most studied efflux transporters at the blood-brain barrier. It plays an important role in brain homeostasis by protecting the brain from a variety of endogenous and exogeneous substances. Changes in P-gp function are associated both with the onset of neuropsychiatric diseases, including Alzheimer's disease and Parkinson's disease, and with drug-resistance, for example in treatment-resistant depression. The most widely used approach to measure P-gp function in vivo is (R)-[11C]verapamil PET. (R)-[11C]verapamil is, however, an avid P-gp substrate, which complicates the use of this tracer to measure an increase in P-gp function as its baseline uptake is already very low. [18F]MC225 was developed to measure both increases and decreases in P-gp function. AIM: The aim of this study was (1) to identify the pharmacokinetic model that best describes [18F]MC225 kinetics in the human brain and (2) to determine test-retest variability. METHODS: Five (2 male, 3 female) of fourteen healthy subjects (8 male, 6 female, age 67 ± 5 years) were scanned twice (injected dose 201 ± 47 MBq) with a minimum interval of 2 weeks between scans. Each scanning session consisted of a 60-min dynamic [18F]MC225 scan with continuous arterial sampling. Whole brain grey matter data were fitted to a single tissue compartment model, and to reversible and irreversible two tissue-compartment models to obtain various outcome parameters (in particular the volume of distribution (VT), Ki, and the rate constants K1 and k2). In addition, a reversible two-tissue compartment model with fixed k3/k4 was included. The preferred model was selected based on the weighted Akaike Information Criterion (AIC) score. Test-retest variability (TRTV) was determined to assess reproducibility. RESULTS: Sixty minutes post-injection, the parent fraction was 63.8 ± 4.0%. The reversible two tissue compartment model corrected for plasma metabolites with an estimated blood volume (VB) showed the highest AIC weight score of 34.3 ± 17.6%. The TRVT of the VT for [18F]MC225 PET scans was 28.3 ± 20.4% for the whole brain grey matter region using this preferred model. CONCLUSION: [18F]MC225 VT, derived using a reversible two-tissue compartment model, is the preferred parameter to describe P-gp function in the human BBB. This outcome parameter has an average test-retest variability of 28%. TRIAL REGISTRATION: EudraCT 2020-001564-28 . Registered 25 May 2020.

Investigation of image-derived input functions for non-invasive quantification of myelin density using [11C]MeDAS PET.

Multiple sclerosis (MS) is an inflammatory demyelinating disease. Current treatments are focussed on immune suppression to modulate pathogenic activity that causes myelin damage. New treatment strategies are needed to prevent demyelination and promote remyelination. Development of such myelin repair therapies require a sensitive and specific biomarker for efficacy evaluation. Recently, it has been shown that quantification of myelin density is possible using [11C]MeDAS PET. This method, however, requires arterial blood sampling to generate an arterial input function (AIF). As the invasive nature of arterial sampling will reduce clinical applicability, the purpose of this study was to assess whether an image-derived input function (IDIF) can be used as an alternative way to facilitate its routine clinical use. Six healthy controls and 11 MS patients underwent MRI and [11C]MeDAS PET with arterial blood sampling. The application of both population-based whole blood-to-plasma conversion and metabolite corrections were assessed for the AIF. Next, summed images of the early time frames (0-70 s) and the frame with the highest blood-brain contrast were used to generate IDIFs. IDIFs were created using either the hottest 2, 4, 6 or 12 voxels, or an isocontour of the hottest 10% voxels of the carotid artery. This was followed by blood-to-plasma conversion and metabolite correction of the IDIF. The application of a population-based metabolite correction of the AIF resulted in high correlations of tracer binding (Ki) within subjects, but variable bias across subjects. All IDIFs had a sharper and higher peak in the blood curves than the AIF, most likely due to dispersion during blood sampling. All IDIF methods resulted in similar high correlations within subjects (r = 0.95-0.98), but highly variable bias across subjects (mean slope=0.90-1.09). Therefore, both the use of population based blood-plasma and metabolite corrections and the generation of the image-derived whole-blood curve resulted in substantial bias in [11C]MeDAS PET quantification, due to high inter-subject variability. Consequently, when unbiased quantification of [11C]MeDAS PET data is required, individual AIF needs to be used.

Quantitative assessment of myelin density using [11C]MeDAS PET in patients with multiple sclerosis: a first-in-human study.

PURPOSE: Multiple sclerosis (MS) is a disease characterized by inflammatory demyelinated lesions. New treatment strategies are being developed to stimulate myelin repair. Quantitative myelin imaging could facilitate these developments. This first-in-man study aimed to evaluate [11C]MeDAS as a PET tracer for myelin imaging in humans. METHODS: Six healthy controls and 11 MS patients underwent MRI and dynamic [11C]MeDAS PET scanning with arterial sampling. Lesion detection and classification were performed on MRI. [11C]MeDAS time-activity curves of brain regions and MS lesions were fitted with various compartment models for the identification of the best model to describe [11C]MeDAS kinetics. Several simplified methods were compared to the optimal compartment model. RESULTS: Visual analysis of the fits of [11C]MeDAS time-activity curves showed no preference for irreversible (2T3k) or reversible (2T4k) two-tissue compartment model. Both volume of distribution and binding potential estimates showed a high degree of variability. As this was not the case for 2T3k-derived net influx rate (Ki), the 2T3k model was selected as the model of choice. Simplified methods, such as SUV and MLAIR2 correlated well with 2T3k-derived Ki, but SUV showed subject-dependent bias when compared to 2T3k. Both the 2T3k model and the simplified methods were able to differentiate not only between gray and white matter, but also between lesions with different myelin densities. CONCLUSION: [11C]MeDAS PET can be used for quantification of myelin density in MS patients and is able to distinguish differences in myelin density within MS lesions. The 2T3k model is the optimal compartment model and MLAIR2 is the best simplified method for quantification. TRIAL REGISTRATION: NL7262. Registered 18 September 2018.

Impact of an Adenosine A2A Receptor Agonist and Antagonist on Binding of the Dopamine D2 Receptor Ligand [11C]raclopride in the Rodent Striatum.

Adenosine A2A and dopamine D2 receptors in the basal ganglia form heterotetrameric structures that are involved in the regulation of motor activity and neuropsychiatric functions. The present study examines the A2A receptor-mediated modulation of D2 receptor binding in vivo using positron emission tomography (PET) with the D2 antagonist tracer [11C]raclopride. Healthy male Wistar rats (n = 8) were scanned (60 min dynamic scan) with [11C]raclopride at baseline and 7 days later following an acute administration of the A2A agonist CGS21680 (1 mg/kg), using a MicroPET Focus-220 camera. Nondisplaceable binding potential (BPND) values were calculated using a simplified reference tissue model (SRTM), with cerebellum as the reference tissue. SRTM analysis did not show any significant changes in [11C]raclopride BPND (p = 0.102) in striatum after CGS21680 administration compared to the baseline. As CGS21680 strongly affects hemodynamics, we also used arterial blood sampling and a metabolite-corrected plasma input function for compartment modeling using the reversible two-tissue compartment model (2TCM) to obtain the BPND from the k3/k4 ratio and from the striatum/cerebellum volume of distribution ratio (DVR) in a second group of animals. These rats underwent dynamic [11C]raclopride scans after pretreatment with a vehicle (n = 5), a single dose of CGS21680 (1 mg/kg, n = 5), or a single dose of the A2A antagonist KW6002 (1 mg/kg, n = 5). The parent fraction in plasma was significantly higher in the CGS21680-treated group (p = 0.0001) compared to the vehicle-treated group. GCS21680 administration significantly reduced the striatal k3/k4 ratio (p < 0.01), but k3 and k4 estimates may be less reliable. The BPND (DVR-1) decreased from 1.963 ± 0.27 in the vehicle-treated group to 1.53 ± 0.55 (p = 0.080) or 1.961 ± 0.11 (p = 0.993) after the administration of CGS21680 or KW6002, respectively. Our study suggests that the A2A agonist CGS21680, but not the antagonist KW6002, may reduce the D2 receptor availability in the striatum.

Pharmacokinetic Modeling of [11C]GSK-189254, PET Tracer Targeting H3 Receptors, in Rat Brain.

The histamine H3 receptor has been considered as a target for the treatment of various central nervous system diseases. Positron emission tomography (PET) studies with the radiolabeled potent and selective histamine H3 receptor antagonist [11C]GSK-189254 in rodents could be used to examine the mechanisms of action of novel therapeutic drugs or to assess changes of regional H3 receptor density in animal models of neurodegenerative disease. [11C]GSK-189254 was intravenously administered to healthy Wistar rats (n = 10), and a 60 min dynamic PET scan was carried out. Arterial blood samples were obtained during the scan to generate a metabolite-corrected plasma input function. PET data were analyzed using a one-tissue compartment model (1T2k), irreversible (2T3k) or reversible two-tissue compartment models (2T4k), graphical analysis (Logan and Patlak), reference tissue models (SRTM and SRTM2), and standard uptake values (SUVs). The Akaike information criterion and the standard error of the estimated parameters were used to select the most optimal quantification method. This study demonstrated that the 2T4k model with a fixed blood volume fraction and Logan graphical analysis can best describe the kinetics of [11C]GSK-189254 in the rat brain. SUV40-60 and the reference tissue-based measurements DVR(2T4k), BPND(SRTM), and SUV ratio could also be used as a simplified method to estimate H3 receptor availability in case blood sampling is not feasible.

Binding of the Dual-Action Anti-Parkinsonian Drug AG-0029 to Dopamine D2 and Histamine H3 Receptors: A PET Study in Healthy Rats.

Introduction: Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor dysfunction and a diverse range of nonmotor symptoms. Functional relationships between the dopaminergic and histaminergic systems suggest that dual-action pharmaceuticals like AG-0029 (D2/D3 agonist/H3 antagonist) could ameliorate both the motor and cognitive symptoms of PD. The current study aimed to demonstrate the interaction of AG-0029 with its intended targets in the mammalian brain using positron emission tomography (PET). Methods: Healthy male Wistar rats were scanned with a small-animal PET camera, using either the dopamine D2/D3 receptor ligand [11C]raclopride or the histamine H3 receptor ligand [11C]GSK-189254, before and after treatment with an intravenous, acute, single dose of AG-0029. Dynamic [11C]raclopride PET data (60 min duration) were analyzed using the simplified reference tissue model 2 (SRTM2) with cerebellum as reference tissue and the nondisplaceable binding potential as the outcome parameter. Data from dynamic [11C]GSK-189254 scans (60 min duration) with arterial blood sampling were analyzed using Logan graphical analysis with the volume of distribution (VT) as the outcome parameter. Receptor occupancy was estimated using a Lassen plot. Results: Dopamine D2/3 receptor occupancies in the striatum were 22.6 ± 18.0 and 84.0 ± 3.5% (mean ± SD) after administration of 0.1 and 1 mg/kg AG-0029, respectively. In several brain regions, the VT values of [11C]GSK-189254 were significantly reduced after pretreatment of rats with 1 or 10 mg/kg AG-0029. The H3 receptor occupancies were 11.9 ± 8.5 and 40.3 ± 11.3% for the 1 and 10 mg/kg doses of AG-0029, respectively. Conclusions: Target engagement of AG-0029 as an agonist at dopamine D2/D3 receptors and an antagonist at histamine H3 receptors could be demonstrated in the rat brain with [11C]raclopride and [11C]GSK-189254 PET, respectively. The measured occupancy values reflect the previously reported high (subnanomolar) affinity of AG-0029 to D2/D3 and moderate (submicromolar) affinity to H3 receptors.

Long axial field of view PET scanners: a road map to implementation and new possibilities.

In this contribution, several opportunities and challenges for long axial field of view (LAFOV) PET are described. It is an anthology in which the main issues have been highlighted. A consolidated overview of the camera system implementation, business and financial plan, opportunities and challenges is provided. What the nuclear medicine and molecular imaging community can expect from these new PET/CT scanners is the delivery of more comprehensive information to the clinicians for advancing diagnosis, therapy evaluation and clinical research.

Effect of Dopamine D2 Receptor Antagonists on [18F]-FEOBV Binding.

The interaction of dopaminergic and cholinergic neurotransmission in, e.g., Parkinson's disease has been well established. Here, D2 receptor antagonists were used to assess changes in [18F]-FEOBV binding to the vesicular acetylcholine transporter (VAChT) in rodents using positron emission tomography (PET). After pretreatment with either 10 mg/kg haloperidol, 1 mg/kg raclopride, or vehicle, 90 min dynamic PET scans were performed with arterial blood sampling. The net influx rate (Ki) was obtained from Patlak graphical analysis, using a metabolite-corrected plasma input function and dynamic PET data. [18F]-FEOBV concentration in whole-blood or plasma and the metabolite-corrected plasma input function were not significantly changed by the pretreatments (adjusted p > 0.07, Cohen's d 0.28-1.89) while the area-under-the-curve (AUC) of the parent fraction of [18F]-FEOBV was significantly higher after haloperidol treatment (adjusted p = 0.022, Cohen's d = 2.51) than in controls. Compared to controls, the AUC of [18F]-FEOBV, normalized for injected dose and body weight, was nonsignificantly increased in the striatum after haloperidol (adjusted p = 0.4, Cohen's d = 1.77) and raclopride (adjusted p = 0.052, Cohen's d = 1.49) treatment, respectively. No changes in the AUC of [18F]-FEOBV were found in the cerebellum (Cohen's d 0.63-0.74). Raclopride treatment nonsignificantly increased Ki in the striatum 1.3-fold compared to control rats (adjusted p = 0.1, Cohen's d = 1.1) while it reduced Ki in the cerebellum by 28% (adjusted p = 0.0004, Cohen's d = 2.2) compared to control rats. Pretreatment with haloperidol led to a nonsignificant reduction in Ki in the striatum (10%, adjusted p = 1, Cohen's d = 0.44) and a 40-50% lower Ki than controls in all other brain regions (adjusted p < 0.0005, Cohen's d = 3.3-4.7). The changes in Ki induced by the selective D2 receptor antagonist raclopride can in part be quantified using [18F]-FEOBV PET imaging. Haloperidol, a nonselective D2/σ receptor antagonist, either paradoxically decreased cholinergic activity or blocked off-target [18F]-FEOBV binding to σ receptors. Hence, further studies evaluating the binding of [18F]-FEOBV to σ receptors using selective σ receptor ligands are necessary.

Hemodialysis Induces an Acute Decline in Cerebral Blood Flow in Elderly Patients.

The initiation of hemodialysis is associated with an accelerated decline of cognitive function and an increased incidence of cerebrovascular accidents and white matter lesions. Investigators have hypothesized that the repetitive circulatory stress of hemodialysis induces ischemic cerebral injury, but the mechanism is unclear. We studied the acute effect of conventional hemodialysis on cerebral blood flow (CBF), measured by [15O]H2O positron emission tomography-computed tomography (PET-CT). During a single hemodialysis session, three [15O]H2O PET-CT scans were performed: before, early after the start of, and at the end of hemodialysis. We used linear mixed models to study global and regional CBF change during hemodialysis. Twelve patients aged ≥65 years (five women, seven men), with a median dialysis vintage of 46 months, completed the study. Mean (±SD) arterial BP declined from 101±11 mm Hg before hemodialysis to 93±17 mm Hg at the end of hemodialysis. From before the start to the end of hemodialysis, global CBF declined significantly by 10%±15%, from a mean of 34.5 to 30.5 ml/100g per minute (difference, -4.1 ml/100 g per minute; 95% confidence interval, -7.3 to -0.9 ml/100 g per minute; P=0.03). CBF decline (20%) was symptomatic in one patient. Regional CBF declined in all volumes of interest, including the frontal, parietal, temporal, and occipital lobes; cerebellum; and thalamus. Higher tympanic temperature, ultrafiltration volume, ultrafiltration rate, and pH significantly associated with lower CBF. Thus, conventional hemodialysis induces a significant reduction in global and regional CBF in elderly patients. Repetitive intradialytic decreases in CBF may be one mechanism by which hemodialysis induces cerebral ischemic injury.

Quantification, improvement, and harmonization of small lesion detection with state-of-the-art PET.

In recent years, there have been multiple advances in positron emission tomography/computed tomography (PET/CT) that improve cancer imaging. The present generation of PET/CT scanners introduces new hardware, software, and acquisition methods. This review describes these new developments, which include time-of-flight (TOF), point-spread-function (PSF), maximum-a-posteriori (MAP) based reconstruction, smaller voxels, respiratory gating, metal artefact reduction, and administration of quadratic weight-dependent 18F-fluorodeoxyglucose (FDG) activity. Also, hardware developments such as continuous bed motion (CBM), (digital) solid-state photodetectors and combined PET and magnetic resonance (MR) systems are explained. These novel techniques have a significant impact on cancer imaging, as they result in better image quality, improved small lesion detectability, and more accurate quantification of radiopharmaceutical uptake. This influences cancer diagnosis and staging, as well as therapy response monitoring and radiotherapy planning. Finally, the possible impact of these developments on the European Association of Nuclear Medicine (EANM) guidelines and EANM Research Ltd. (EARL) accreditation for FDG-PET/CT tumor imaging is discussed.

The Psychobiology of Authentic and Simulated Dissociative Personality States: The Full Monty.

The etiology of dissociative identity disorder (DID) remains a topic of debate. Proponents of the fantasy model and the trauma model of DID have both called for more empirical research. To this end, the current study presents new and extended data analyses of a previously published H2O positron emission tomography imaging study. This study included 29 subjects: 11 patients with DID and 10 high- and 8 low-fantasy-prone DID-simulating mentally healthy control subjects. All subjects underwent an autobiographical memory script-driven (neutral and trauma related) imagery paradigm in 2 (simulated) dissociative personality states (neutral and trauma related). Psychobiological and psychophysiological data were obtained. Results of the new post-hoc tests on the psychophysiological responses support the trauma model. New results of the brain imaging data did not support the fantasy model. This study extends previously published results by offering important new supporting data for the trauma model of DID.

PET imaging of focal demyelination and remyelination in a rat model of multiple sclerosis: comparison of [11C]MeDAS, [11C]CIC and [11C]PIB.

PURPOSE: In this study, we compared the ability of [(11)C]CIC, [(11)C]MeDAS and [(11)C]PIB to reveal temporal changes in myelin content in focal lesions in the lysolecithin rat model of multiple sclerosis. Pharmacokinetic modelling was performed to determine the best method to quantify tracer uptake. METHODS: Sprague-Dawley rats were stereotactically injected with either 1 % lysolecithin or saline into the corpus callosum and striatum of the right brain hemisphere. Dynamic PET imaging with simultaneous arterial blood sampling was performed 7 days after saline injection (control group), 7 days after lysolecithin injection (demyelination group) and 4 weeks after lysolecithin injection (remyelination group). RESULTS: The kinetics of [(11)C]CIC, [(11)C]MeDAS and [(11)C]PIB was best fitted by Logan graphical analysis, suggesting that tracer binding is reversible. Compartment modelling revealed that all tracers were fitted best with the reversible two-tissue compartment model. Tracer uptake and distribution volume in lesions were in agreement with myelin status. However, the slow kinetics and homogeneous brain uptake of [(11)C]CIC make this tracer less suitable for in vivo PET imaging. [(11)C]PIB showed good uptake in the white matter in the cerebrum, but [(11)C]PIB uptake in the cerebellum was low, despite high myelin density in this region. [(11)C]MeDAS distribution correlated well with myelin density in different brain regions. CONCLUSION: This study showed that PET imaging of demyelination and remyelination processes in focal lesions is feasible. Our comparison of three myelin tracers showed that [(11)C]MeDAS has more favourable properties for quantitative PET imaging of demyelinated and remyelinated lesions throughout the CNS than [(11)C]CIC and [(11)C]PIB.

Clinical Performance Comparison of a Long Versus a Short Axial Field-of-View PET/CT Using EARL-Compliant Reconstructions.

PURPOSE: To ensure comparable PET/CT image quality between or within centres, clinical inter-system performance comparisons following European Association of Nuclear Medicine Research Ltd. (EARL) guidelines is required. In this work the performance of the long axial field-of-view Biograph Vision Quadra is compared to its predecessor, the short axial field-of-view Biograph Vision. PROCEDURES: To this aim, patients with suspected tumour lesions received a single weight-based (3 MBq/kg) 2-deoxy-2-[18F]fluoro-D-glucose injection and underwent routine clinical ( ∼ 15 min) scans on the Vision and 3-min scans on the Quadra in listmode in balanced order. Image quality (IQ), image noise (IN), and tumour demarcation (TD) were assessed visually by four nuclear medicine physicians using a 5-point Likert scale and semiquantitative analysis was performed using standardised uptake values (SUVs). Inter-reader agreement was tested using Wilcoxon's signed rank test and the SUVs were statistically compared using a paired t-test. RESULTS: Twenty patients (mean age, 60 years ± 8.8 [standard deviation], 16 male) were enrolled. Inter-reader agreement ranged from good to very good for IQ and IN (0.62 ≤ W ≤ 0.81), and fair for TD (0.29 ≤ W ≤ 0.39). Furthermore, a significant difference was found for TD (p = 0.015) between the systems, showing improved TD for the Quadra. CONCLUSION: This study demonstrates that the Quadra can be used in routine clinical practice with multiple PET/CT systems or in multicentre studies. This system provides comparable diagnostic image quality and semiquantitative accuracy, improved TD, and has the advantage of shorter scan durations.

Pharmacokinetic Analysis of [18F]FES PET in the Human Brain and Pituitary Gland.

PURPOSE: Estrogen receptors (ER) are implicated in psychiatric disorders. We assessed if ER availability in the human brain could be quantified using 16α-[18F]-fluoro-17ß-estradiol ([18F]FES) positron emission tomography (PET). PROCEDURES: Seven post­menopausal women underwent a dynamic [18F]FES PET scan with arterial blood sampling. A T1-weighted MRI was acquired for anatomical information. After one week, four subjects received a selective ER degrader (SERD), four hours before the PET scan. Pharmacokinetic analysis was performed using a metabolite-corrected plasma curve as the input function. The optimal kinetic model was selected based on the Akaike information criterion and standard error of estimated parameters. Accuracy of Logan graphical analysis and standardized uptake value (SUV) was determined via correlational analyses. RESULTS: The reversible two-tissue compartment model (2T4k) model with fixed K1/k2 was preferred. The total volume of distribution (VT) could be more reliably estimated than the binding potential (BPND). A high correlation of VT with Logan graphical analysis was observed, but only a moderate correlation with SUV. SERD administration resulted in a reduced VT in the pituitary gland, but not in other regions. CONCLUSIONS: The optimal quantification method for [18F]FES was the 2T4k with fixed K1/k2 or Logan graphical analysis, but specific binding was only observed in the pituitary gland.

Female orgasm but not male ejaculation activates the pituitary. A PET-neuro-imaging study.

The pituitary gland plays an important role in basic survival mechanisms by releasing fluctuating amounts of hormones into the bloodstream, depending on the circumstances the individual finds itself. However, despite these changes in pituitary hormonal production, neuroimaging studies have never been able to demonstrate changes in the activation level of the pituitary. The most apparent reason is the much higher blood flow rate in the pituitary than in the brain. However, the present PET-scanning study demonstrates for the first time that neuroimaging techniques can identify increased pituitary activity. In a study with 11 healthy women sexual orgasm compared to rest caused an increased blood supply to the pituitary. We assume that this increase signifies elevated pituitary activation in order to produce higher plasma concentrations of oxytocin and prolactin. These hormones induce vaginal and uterus movements, ovulation and enhancement of sperm and egg transport. No increased blood supply was observed comparing clitoral stimulation, orgasm attempt, and faked orgasm with rest. In a study with 11 healthy men comparing ejaculation with rest did not reveal increased pituitary activation, probably because ejaculation causes a much lower increase of oxytocin and prolactin plasma concentration than female orgasm.

Pontine control of ejaculation and female orgasm.

INTRODUCTION: The physiological component of ejaculation shows parallels with that of micturition, as both are essentially voiding activities. Both depend on supraspinal influences to orchestrate the characteristic pattern of activity in the pelvic organs. Unlike micturition, little is known about the supraspinal pathways involved in ejaculation and female orgasm. AIM: To identify brainstem regions activated during ejaculation and female orgasm and to compare them with those activated during micturition. METHODS: Ejaculation in men and orgasm in women were induced by manual stimulation of the penis or clitoris by the participants' partners. Positron emission tomography (PET) with correction for head movements was used to capture the pattern of brain activation at the time of sexual climax. MAIN OUTCOME MEASURES: PET scans showing areas of activation during sexual climax. RESULTS: Ejaculation in men and orgasm in women resulted in activation in a localized region within the dorsolateral pontine tegmentum on the left side and in another region in the ventrolateral pontine tegmentum on the right side. The dorsolateral pontine area was also active in women who attempted but failed to have an orgasm and in women who imitated orgasm. The ventrolateral pontine area was only activated during ejaculation and physical orgasm in women. CONCLUSION: Activation of a localized region on the left side in the dorsolateral pontine tegmentum, which we termed the pelvic organ-stimulating center, occurs during ejaculation in men and physical orgasm in women. This same region has previously been shown to be activated during micturition, but on the right side. The pelvic organ-stimulating center, via projections to the sacral parasympathetic motoneurons, controls pelvic organs involved in voiding functions. In contrast, the ventrolateral pontine area, which we term the pelvic floor-stimulating center, produces the pelvic floor contractions during ejaculation in men and physical orgasm in women via direct projections to pelvic floor motoneurons.

Feasibility Study to Assess Canagliflozin Distribution and Sodium-Glucose Co-Transporter 2 Occupancy Using [18 F]Canagliflozin in Patients with Type 2 Diabetes.

Sodium-glucose co-transporter 2 (SGLT2) inhibitors, including canagliflozin, reduce the risk of cardiovascular and kidney outcomes in patients with and without type 2 diabetes, albeit with a large interindividual variation. The underlying mechanisms for this variation in response might be attributed to differences in SGLT2 occupancy, resulting from individual variation in plasma and tissue drug exposure and receptor availability. We performed a feasibility study for the use of [18 F]canagliflozin positron emission tomography (PET) imaging to determine the association between clinical canagliflozin doses and SGLT2 occupancy in patients with type 2 diabetes. We obtained two 90-minute dynamic PET scans with diagnostic intravenous [18 F]canagliflozin administration and a full kinetic analysis in 7 patients with type 2 diabetes. Patients received 50, 100, or 300 mg oral canagliflozin (n = 2:4:1) 2.5 hours before the second scan. Canagliflozin pharmacokinetics and urinary glucose excretion were measured. The apparent SGLT2 occupancy was derived from the difference between the apparent volume of distribution of [18 F]canagliflozin in the baseline and post-drug PET scans. Individual canagliflozin area under the curve from oral dosing until 24-hours (AUCP0-24h ) varied largely (range 1,715-25,747 µg/L*hour, mean 10,580 µg/L*hour) and increased dose dependently with mean values of 4,543, 6,525, and 20,012 µg/L*hour for 50, 100, and 300 mg, respectively (P = 0.046). SGLT2 occupancy ranged between 65% and 87%, but did not correlate with canagliflozin dose, plasma exposure, or urinary glucose excretion. We report the feasibility of [18 F]canagliflozin PET imaging to determine canagliflozin kidney disposition and SGLT2 occupancy. This suggests the potential of [18 F]canagliflozin as a tool to visualize and quantify clinically SGLT2 tissue binding.