Parkinson's disease-related perfusion and glucose metabolic brain patterns identified with PCASL-MRI and FDG-PET imaging

AbstractIntroductionUnder normal conditions, the spatial distribution of resting cerebral blood flow and cerebral metabolic rate of glucose are closely related. A relatively new magnetic resonance (MR) technique, pseudo-continuous arterial spin labeling (PCASL), can be used to measure regional brain perfusion. We identified a Parkinson's disease (PD)-related perfusion and metabolic covariance pattern in the same patients using PCASL and FDG-PET imaging and assessed (dis)similarities in the disease-related pattern between perfusion and metabolism in PD patients.MethodsNineteen PD patients and seventeen healthy controls underwent [18F]-fluorodeoxyglucose positron emission tomography (FDG-PET) imaging. Of 14 PD patients and all healthy controls PCASL-MRI could be obtained. Data were analyzed using scaled subprofile model/principal component analysis (SSM/PCA).ResultsUnique Parkinson's disease-related perfusion and metabolic covariance patterns were identified using PCASL and FDG-PET in the same patients. The PD-related metabolic covariance brain pattern is in high accordance with previously reports. Also our disease-related perfusion pattern is comparable to the earlier described perfusion pattern. The most marked difference between our perfusion and metabolic patterns is the larger perfusion decrease in cortical regions including the insula.ConclusionWe identified PD-related perfusion and metabolic brain patterns using PCASL and FDG-PET in the same patients which were comparable with results of existing research. In this respect, PCASL appears to be a promising addition in the early diagnosis of individual parkinsonian patients

In vivo evaluation of [F-18]FEAnGA-Me:a PET tracer for imaging beta-glucuronidase (beta-GUS) activity in a tumor/inflammation rodent model

Introduction: The PET tracer, 1-O-(4-(2-fluoroethyl-carbamoyloxymethyl)-2-nitrophenyl)-O-beta-D-glucopyronuronate ([F-18]FEAnGA), was recently developed for PET imaging of extracellularl beta-glucuronidase (beta-GUS). However,[F-18]FEAnGA exhibited rapid renal clearance, which resulted in a relatively low tracer uptake in the tumor. To improve the pharmacokinetics of [F-18]FEAnGA, we developed its more lipophilic methyl ester analog, [F-18]FEAnGA-Me. Methods: [F-18]FEAnGA-Me was obtained by alkylation of the O-protected glucuronide methyl ester precursor with [F-18]-fluoroethylamine ([F-18]FEA), followed by removal of the acetate protecting groups with NaOMe/MeOH. The PET tracer was evaluated by in vitro and in vivo studies. Results: [F-18]FEAnGA-Me was obtained in 5%-10% overall radiochemical yield. It is 10-fold less hydrophilic than [F-18]FEAnGA and it is stable in PBS and in the presence of beta-GUS for 1 h. However, in the presence of esterase or plasma [F-18]FEAnGA-Me is converted to [F-18]FEAnGA, and subsequently converted to [F-18]FEA by beta-GUS. MicroPET studies in Wistar rats bearing a C6 glioma and a sterile inflammation showed similar uptake in tumors after injection of either [F-18]FEAnGA-Me or [F-18]FEAnGA. Both tracers had a rapid two-phase clearance of total plasma radioactivity with a half-life of 1 and 8 min. The [F-18]FEAnGA fraction generated from [F-18]FEAnGA-Me by in vivo hydrolysis had a circulation half-life of 1 and 11 min in plasma. Similar distribution volume in the viable part of the tumor was found after injection of either [F-18]FEAnGA-Me or [F-18]FEAnGA. Conclusion: The imaging properties of [F-18]FEAnGA-Me were not significantly better than those of [F-18]FEAnGA. Therefore, other strategies should be applied in order to improve the kinetics of these tracers. (C) 2012 Elsevier Inc. All rights reserved

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

Optimized dose regimen for whole-body FDG-PET imaging

BACKGROUND: The European Association of Nuclear Medicine procedure guidelines for whole-body fluorodeoxyglucose positron-emission tomography (FDG-PET) scanning prescribe a dose proportional to the patient’s body mass. However, clinical practice shows degraded image quality in obese patients indicating that using an FDG dose proportional to body mass does not overcome size-related degradation of the image quality. The aim of this study was to optimize the administered FDG dose as a function of the patient’s body mass or a different patient-dependent parameter, providing whole-body FDG-PET images of a more constant quality. METHODS: Using a linear relation between administered dose and body mass, FDG-PET imaging was performed on two PET/computed tomography scanners (Biograph TruePoint and Biograph mCT, Siemens). Image quality was assessed by the signal-to-noise ratio (SNR) in the liver in 102 patients with a body mass of 46 to 130 kg. Moreover, the best correlating patient-dependent parameter was derived, and an optimized FDG dose regimen was determined. This optimized dose regimen was validated on the Biograph TruePoint system in 42 new patients. Furthermore, this relation was verified by a simulation study, in which patients with different body masses were simulated with cylindrical phantoms. RESULTS: As expected, both PET systems showed a significant decrease in SNR with increasing patient’s body mass when using a linear dosage. When image quality was fitted to the patient-dependent parameters, the fit with the patient’s body mass had the highest R(2). The optimized dose regimen was found to be A(new)= c/t × m(2), where m is the body mass, t is the acquisition time per bed position and c is a constant (depending on scanner type). Using this relation, SNR no longer varied with the patient’s body mass. This quadratic relation between dose and body mass was confirmed by the simulation study. CONCLUSION: A quadratic relation between FDG dose and the patient’s body mass is recommended. Both simulations and clinical observations confirm that image quality remains constant across patients when this quadratic dose regimen is used

Modeling of [F-18]FEOBV Pharmacokinetics in Rat Brain

Purpose: [18F]Fluoroethoxybenzovesamicol ([18F]FEOBV) is a radioligand for the vesicular acetylcholine transporter (VAChT), a marker of the cholinergic system. We evaluated the quantification of [18F]FEOBV in rats in control conditions and after partial saturation of VAChT using plasma and reference tissue input models and test-retest reliability. Procedure: Ninety-minute dynamic [18F]FEOBV PET scans with arterial blood sampling were performed in control rats and rats pretreated with 10 μg/kg FEOBV. Kinetic analyses were performed using one- (1TCM) and two-tissue compartmental models (2TCM), Logan and Patlak graphical analyses with metabolite-corrected plasma input, reference tissue Patlak with cerebellum as reference tissue, standard uptake value (SUV) and SUV ratio (SUVR) using 60- or 90-min acquisition. To assess test-retest reliability, two dynamic [18F]FEOBV scans were performed 1 week apart. Results: The 1TCM did not fit the data. Time-activity curves were more reliably estimated by the irreversible than the reversible 2TCM for 60 and 90 min as the influx rate Ki showed a lower coefficient of variation (COV, 14–24 %) than the volume of distribution VT (16–108 %). Patlak graphical analysis showed a good fit to the data for both acquisition times with a COV (12–27 %) comparable to the irreversible 2TCM. For 60 min, Logan analysis performed comparably to both irreversible models (COV 14–32 %) but showed lower sensitivity to VAChT saturation. Partial saturation of VAChT did not affect model selection when using plasma input. However, poor correlations were found between irreversible 2TCM and SUV and SUVR in partially saturated VAChT states. Test-retest reliability and intraclass correlation for SUV were good. Conclusion: [18F]FEOBV is best modeled using the irreversible 2TCM or Patlak graphical analysis. SUV should only be used if blood sampling is not possible

Relationships between Serotonin Transporter Binding in the Raphe Nuclei, Basal Ganglia, and Hippocampus with Clinical Symptoms in Cervical Dystonia:A [C]DASB Positron Emission Tomography Study

PurposeAlterations of the central serotonergic system have been implicated in the pathophysiology of dystonia. In this molecular imaging study, we assessed whether altered presynaptic serotonin transporter (SERT) binding contributes to the pathophysiology of cervical dystonia (CD), concerning both motor and non-motor symptoms (NMS).MethodsWe assessed the non-displaceable binding potential (BPND) using the selective SERT tracer [11C]DASB and positron emission tomography (PET) in 14 CD patients and 12 age- and gender-matched controls. Severity of motor symptoms was scored using the Toronto Western Spasmodic Torticollis Rating Scale and Clinical Global Impression jerks/tremor scale. NMS for depressive symptoms, anxiety, fatigue, and sleep disturbances were assessed with quantitative rating scales. The relationship between SERT binding and clinical patient characteristics was analyzed with the Spearman’s rho test and multiple regression.ResultsWhen comparing the CD patients with controls, no significant differences in BPND were found. Higher BPND in the dorsal raphe nucleus was statistically significantly correlated (p < 0.001) with motor symptom severity (rs = 0.65), pain (rs = 0.73), and sleep disturbances (rs = 0.73), with motor symptom severity being the most important predictor of SERT binding. Furthermore, fatigue was negatively associated with the BPND in the medial raphe nucleus (rs = −0.61, p = 0.045), and sleep disorders were positively associated with the BPND in the caudate nucleus (rs = 0.58, p = 0.03) and the hippocampus (rs = 0.56, p = 0.02).ConclusionMotor symptoms, as well as pain, sleep disturbances, and fatigue in CD showed a significant relationship with SERT binding in the raphe nuclei. Moreover, fatigue showed a significant relationship with the medial raphe nucleus and sleep disorders with the caudate nucleus and hippocampus. These findings suggest that an altered serotonergic signaling in different brain areas in CD is related to different motor as well as NMS, which will further stimulate research on the role of serotonin in the pathogenesis of dystonia

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

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

Feasibility Study to Assess Canagliflozin Distribution and Sodium-Glucose Co-Transporter 2 Occupancy Using [18F]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 inter-individual 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-min dynamic PET scans with diagnostic intravenous [ 18 F]Canagliflozin administration and a full kinetic analysis in seven patients with type 2 diabetes. Patients received 50, 100 or 300mg 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 (AUC P0-24h ) varied largely (range 1715-25747 μg/L*h, mean 10580 μg/L*h) and increased dose dependently with mean values of 4543, 6525 and 20012 μg/L*h for 50, 100 and 300mg 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. </p

Analyzing the Estrogen Receptor Status of Liver Metastases with [F-18]-FES-PET in Patients with Breast Cancer

Background: Positron emission tomography (PET) with 16α-[18F]-fluoro-17β-estradiol ([18F]-FES) can visualize estrogen receptor (ER) expression, but it is challenging to determine the ER status of liver metastases, due to high physiological [18F]-FES uptake. We evaluated whether [18F]-FES-PET can be used to determine the ER status of liver metastases, using corresponding liver biopsies as the gold standard. Methods: Patients with metastatic breast cancer (n = 23) were included if they had undergone a [18F]-FES-PET, liver metastasis biopsy, CT-scan, and [18F]-FDG-PET. [18F]-FES-PET scans were assessed by visual and quantitative analysis, tracer uptake was correlated with ER expression measured by immunohistochemical staining and the effects of region-of-interest size and background correction were determined. Results: Visual analysis allowed ER assessment of liver metastases with 100% specificity and 18% sensitivity. Quantitative analysis improved the sensitivity. Reduction of the region-of-interest size did not further improve the results, but background correction improved ER assessment, resulting in 83% specificity and 77% sensitivity. Using separate thresholds for ER+ and ER− metastases, positive and negative predictive values of 100% and 75%, respectively, could be obtained, although 30% of metastases remained inconclusive. Conclusion: In the majority of liver metastases, ER status can be determined with [18F]-FES-PET if background correction and separate thresholds are applied