Imaging using the human epidermal growth factor receptor 2 (HER2)-binding tracer ⁶⁸Ga-labeled Z_HER2:2891-Cys-MMA-DOTA ([⁶⁸Ga]Ga-ABY-025) was shown to reflect HER2 status determined by immunohistochemistry and in situ hybridization in metastatic breast cancer (MBC). This single-center open-label phase II study investigated how [⁶⁸Ga]Ga-ABY-025 uptake corresponds to biopsy results and early treatment response in both primary breast cancer (PBC) planned for neoadjuvant chemotherapy and MBC. Methods: Forty patients with known positive HER2 status were included: 19 with PBC and 21 with MBC (median, 3 previous treatments). [⁶⁸Ga]Ga-ABY-025 PET/CT, [¹⁸F]F-FDG PET/CT, and core-needle biopsies from targeted lesions were performed at baseline. [¹⁸F]F-FDG PET/CT was repeated after 2 cycles of therapy to calculate the directional change in tumor lesion glycolysis (Δ-TLG). The largest lesions (up to 5) were evaluated in all 3 scans per patient. SUVs from [⁶⁸Ga]Ga-ABY-025 PET/CT were compared with the biopsied HER2 status and Δ-TLG by receiver operating characteristic analyses. Results: Trial biopsies were HER2-positive in 31 patients, HER2-negative in 6 patients, and borderline HER2-positive in 3 patients. The [⁶⁸Ga]Ga-ABY-025 PET/CT cutoff SUV_max of 6.0 predicted a Δ-TLG lower than -25% with 86% sensitivity and 67% specificity in soft-tissue lesions (area under the curve, 0.74 [95% CI, 0.67-0.82]; P = 0.01). Compared with the HER2 status, this cutoff resulted in clinically relevant discordant findings in 12 of 40 patients. Metabolic response (Δ-TLG) was more pronounced in PBC (-71% [95% CI, -58% to -83%]; P < 0.0001) than in MBC (-27% [95% CI, -16% to -38%]; P < 0.0001), but [⁶⁸Ga]Ga-ABY-025 SUV_max was similar in both with a mean SUV_max of 9.8 (95% CI, 6.3-13.3) and 13.9 (95% CI, 10.5-17.2), respectively (P = 0.10). In multivariate analysis, global Δ-TLG was positively associated with the number of previous treatments (P = 0.0004) and negatively associated with [⁶⁸Ga]Ga-ABY-025 PET/CT SUV_max (P = 0.018) but not with HER2 status (P = 0.09). Conclusion: [⁶⁸Ga]Ga-ABY-025 PET/CT predicted early metabolic response to HER2-targeted therapy in HER2-positive breast cancer. Metabolic response was attenuated in recurrent disease. [⁶⁸Ga]Ga-ABY-025 PET/CT appears to provide an estimate of the HER2 expression required to induce tumor metabolic remission by targeted therapies and might be useful as an adjunct diagnostic tool.

Background: High expression of human epidermal growth factor receptor type 2 (HER2) represents an aggressive subtype of breast cancer. Anti-HER2 treatment requires a theragnostic approach wherein sufficiently high receptor expression in biopsy material is mandatory. Heterogeneity and discordance of HER2 expression between primary tumour and metastases, as well as within a lesion, present a complication for the treatment and require multiple biopsies. Molecular imaging using the HER2-targeting Affibody peptide ABY-025 radiolabelled with Ga-68-gallium for PET/CT is currently under investigation as a non-invasive tool for whole-body evaluation of metastatic HER2 expression. Initial studies demonstrated a high correlation between Ga-68-ABY-025 standardized uptake values (SUVs) and histopathology. However, detecting small liver lesions might be compromised by high background uptake. This study aimed to explore the applicability of kinetic modelling and parametric image analysis for absolute quantification of Ga-68-ABY-025 uptake and HER2-receptor expression and how that relates to static SUVs.

Methods: Dynamic Ga-68-ABY-025 PET of the upper abdomen was performed 0-45 min post-injection in 16 patients with metastatic breast cancer. Five patients underwent two examinations to test reproducibility. Parametric images of tracer delivery (K-1) and irreversible binding (K-i) were created with an irreversible two-tissue compartment model and Patlak graphical analysis using an image-derived input function from the descending aorta. A volume of interest (VOI)-based analysis was performed to validate parametric images. SUVs were calculated from 2 h and 4 h post-injection static whole-body images and compared to K-i.

Results: Characterization of HER2 expression in smaller liver metastases was improved using parametric images. K-i values from parametric images agreed very well with VOI-based gold standard (R-2 > 0.99, p < 0.001). SUVs of metastases at 2 h and 4 h post-injection were highly correlated with K-i values from both the two-tissue compartment model and Patlak method (R-2 = 0.87 and 0.95, both p < 0.001). Ga-68-ABY-025 PET yielded high test-retest reliability (relative repeatability coefficient for Patlak 30% and for the two-tissue compartment model 47%).

Conclusion: Ga-68-ABY-025 binding in HER2-positive metastases was well characterized by irreversible two-tissue compartment model wherein K-i highly correlated with SUVs at 2 and 4 h. Dynamic scanning with parametric image formation can be used to evaluate metastatic HER2 expression accurately.

While Roux-en-Y gastric bypass (RYGB) surgery in obese individuals typically improves glycemic control and prevents diabetes, it also frequently causes asymptomatic hypoglycemia. Previous work showed attenuated counterregulatory responses following RYGB. The underlying mechanisms as well as the clinical consequences are unclear. In this study, 11 subjects without diabetes with severe obesity were investigated pre- and post-RYGB during hyperinsulinemic normo-hypoglycemic clamps. Assessments were made of hormones, cognitive function, cerebral blood flow by arterial spin labeling, brain glucose metabolism by F-18-fluorodeoxyglucose (FDG) positron emission tomography, and activation of brain networks by functional MRI. Post- versus presurgery, we found a general increase of cerebral blood flow but a decrease of total brain FDG uptake during normoglycemia. During hypoglycemia, there was a marked increase in total brain FDG uptake, and this was similar for post- and presurgery, whereas hypothalamic FDG uptake was reduced during hypoglycemia. During hypoglycemia, attenuated responses of counterregulatory hormones and improvements in cognitive function were seen postsurgery. In early hypoglycemia, there was increased activation post- versus presurgery of neural networks in brain regions implicated in glucose regulation, such as the thalamus and hypothalamus. The results suggest adaptive responses of the brain that contribute to lowering of glycemia following RYGB, and the underlying mechanisms should be further elucidated.

Affibody molecules constitute a new class of probes for radionuclide tumor targeting. The small size of affibody molecules is favorable for rapid localization in tumors and clearance from circulation. However, high renal re-absorption of affibody molecules prevents the use of residualizing radiometals, including a number of promising low energy beta- and alpha-emitters, for radionuclide therapy. We tested a hypothesis that affibody-based pretargeting mediated by a bioorthogonal interaction between trans-cyclooctene (TCO) and tetrazine would provide higher accumulation of radiometals in tumor xenografts than in the kidneys.

Methods:

TCO was conjugated to the anti-HER2 affibody molecule Z2395. DOTA-tetrazine was labeled with indium-111 and lutetium-177. In vitro pretargeting was studied in HER2-expressing SKOV-3 and BT474 cell lines. In vivo studies were performed on BALB/C nu/nu mice bearing SKOV-3 xenografts.

Results:

¹²⁵I-Z2395-TCO bound specifically to HER2-expressing cells in vitro with an affinity of 45±16 pM. ¹¹¹In-tetrazine bound specifically and selectively to Z2395-TCO pre-treated cells. In vivo studies demonstrated HER2-specific ¹²⁵I-Z2395-TCO accumulation in xenografts. TCO-mediated ¹¹¹In-tetrazine localization was shown in tumors, when the radiolabeled tracer was injected 4 h after an injection of Z2395-TCO. At 1 h post injection, the tumor uptake of ¹¹¹In-tetrazine and ¹⁷⁷Lu-tetrazine was ca. 2-fold higher than the renal uptake. Pretargeting provided more than a 56-fold reduction of renal uptake of ¹¹¹In in comparison with direct targeting.

Conclusion:

The feasibility of affibody-based bioorthogonal chemistry-mediated pretargeting was demonstrated. The use of pretargeting provides a substantial reduction of radiometal accumulation in kidneys, creating preconditions for palliative radionuclide therapy.

Affibody molecules are small (7 kDa) nonimmunoglobulin scaffold proteins with favorable tumor-targeting properties. Studies concerning the influence of chelators on biodistribution of ^99mTc-labeled Affibody molecules demonstrated that the variant with a C-terminal glycyl-glycyl-glycyl-cysteine peptide–based chelator (designated Z_HER2:V2) has the best biodistribution profile in vivo and the lowest renal retention of radioactivity. The aim of this study was to evaluate ¹⁸⁸Re-Z_HER2:V2 as a potential candidate for radionuclide therapy of human epidermal growth factor receptor type 2 (HER2)–expressing tumors.

Methods:

Z_HER2:V2 was labeled with ¹⁸⁸Re using a gluconate-containing kit. Targeting of HER2-overexpressing SKOV-3 ovarian carcinoma xenografts in nude mice was studied for a dosimetry assessment.

Results:

Binding of ¹⁸⁸Re-Z_HER2:V2 to living SKOV-3 cells was demonstrated to be specific, with an affinity of 6.4 ± 0.4 pM. The biodistribution study showed a rapid blood clearance (1.4 ± 0.1 percentage injected activity per gram [%ID/g] at 1 h after injection). The tumor uptake was 14 ± 2, 12 ± 2, 5 ± 2, and 1.8 ± 0.5 %IA/g at 1, 4, 24, and 48 h after injection, respectively. The in vivo targeting of HER2-expressing xenografts was specific. Already at 4 h after injection, tumor uptake exceeded kidney uptake (2.1 ± 0.2 %IA/g). Scintillation-camera imaging showed that tumor xenografts were the only sites with prominent accumulation of radioactivity at 4 h after injection. Based on the biokinetics, a dosimetry evaluation for humans suggests that ¹⁸⁸Re-Z_HER2:V2 would provide an absorbed dose to tumor of 79 Gy without exceeding absorbed doses of 23 Gy to kidneys and 2 Gy to bone marrow. This indicates that future human radiotherapy studies may be feasible.

Conclusion:

¹⁸⁸Re-Z_HER2:V2 can deliver high absorbed doses to tumors without exceeding kidney and bone marrow toxicity limits.

Brown adipose tissue (BAT) expends chemical energy to produce heat, which makes it a potential therapeutic target for combating metabolic dysfunction and overweight/obesity by increasing its metabolic activity. The most well-established method for measuring BAT metabolic activity is glucose uptake rate (GUR) measured using ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET). However, this is expensive and exposes the subjects to potentially harmful radiation. Cheaper and safer methods are warranted for large-scale or longitudinal studies. Potential alternatives include infrared thermography (IRT) and magnetic resonance imaging (MRI). The aim of this study was to evaluate and further develop these techniques. Twelve healthy adult subjects were studied. The BAT GUR was measured using ¹⁸F-FDG PET during individualized cooling. The temperatures of the supraclavicular fossae and a control region were measured using IRT during a simple cooling protocol. The fat fraction and effective transverse relaxation rate of BAT were measured using MRI without any cooling intervention. Simple and multiple linear regressions were employed to evaluate how well the MRI and IRT measurements could estimate the GUR. Results showed that both IRT and MRI measurements correlated with the GUR. This suggest that these measurements may be suitable for estimating the cold-induced BAT GUR in future studies.

Cardiac amyloidosis is a differential diagnosis in heart failure and is associated with high mortality. There is currently no noninvasive imaging test available for specific diagnosis. N-[methyl-¹¹C]2-(4′-methylamino-phenyl)-6-hydroxybenzothiazole (¹¹C-PIB) PET is used in the evaluation of brain amyloidosis. We evaluated the potential use of ¹¹C-PIB PET in systemic amyloidosis affecting the heart.

Methods:

Patients (n = 10) diagnosed with systemic amyloidosis—including heart involvement of either monoclonal immunoglobulin light-chain (AL) or transthyretin (ATTR) type—and healthy volunteers (n = 5) were investigated with PET/CT using ¹¹C-PIB to study cardiac amyloid deposits and with ¹¹C-acetate to measure myocardial blood flow to study the impact of global and regional perfusion on PIB retention.

Results:

Myocardial ¹¹C-PIB uptake was visually evident in all patients 15–25 min after injection and was not seen in any volunteer. A significant difference in ¹¹C-PIB retention in the heart between patients and healthy controls was found. The data indicate that myocardial amyloid deposits in patients diagnosed with systemic amyloidosis could be visualized with ¹¹C-PIB. No correlation between ¹¹C-PIB retention index and myocardial blood flow as measured with ¹¹C-acetate was found on the global level, whereas a positive correlation on the segmental level was seen in a single patient.

Conclusion:

¹¹C-PIB and PET could be a method to study systemic amyloidosis of type AL and ATTR affecting the heart and should be investigated further both as a diagnostic tool and as a noninvasive method for treatment follow-up.

COVID-19 can cause life-threatening lung-inflammation that is suggested to be mediated by neutrophils, whose effector mechanisms in COVID-19 is inexplicit. The aim of the present work is to evaluate a novel PET tracer for neutrophil elastase in COVID-19 patients and healthy controls.

METHODS: In this open-label, First-In-Man study, four patients with hypoxia due to COVID-19 and two healthy controls were investigated with positron emission tomography (PET) using the new selective and specific neutrophil elastase PET-tracer [¹¹C]GW457427 and [¹⁵O]water for the visualization and quantification of NE and perfusion in the lungs, respectively.

RESULTS: [¹¹C]GW457427 accumulated selectively in lung areas with ground-glass opacities on computed tomography characteristic of COVID-19 suggesting high levels on NE in these areas. In the same areas perfusion was severely reduced in comparison to healthy lung tissue as measured with [¹⁵O]water.

CONCLUSION: The data suggests that NE may be responsible for the severe lung inflammation in COVID-19 patients and that inhibition of NE could potentially reduce the acute inflammatory process and improve the condition.

In idiopathic Parkinson disease and atypical parkinsonian disorders, central dopaminergic and overall brain functional activity are altered to different degrees, causing difficulties in achieving an unambiguous clinical diagnosis. A dual examination using I-123-FP-CIT (I-123-N-omega-fluoropropyl- 2 beta-carbomethoxy-3 beta-(4-iodophenyl) nortropane, or I-123-ioflupane) SPECT and F-18-FDG PET provides complementary information on dopamine transporter (DAT) availability and overall brain functional activity, respectively. Parametric images based on a single, dynamic C-11-PE2I (N-(3-iodoprop-2E-enyl)-2 beta-carbomethoxy-3 beta-(4-methyl-phenyl) nortropane) scan potentially supply both DAT availability (nondisplaceable binding potential [BPND]) and relative cerebral blood flow (relative delivery [R-1]) at voxel level. This study aimed to evaluate the validity of C-11-PE2I PET against the dual-modality approach using I-123-FP-CIT SPECT and F-18-FDG PET.

Methods: Sixteen patients with parkinsonian disorders had a dual examination with F-18-FDG PET and I-123-FP-CIT SPECT following clinical routines and additionally an experimental C-11-PE2I PET scan. Parametric BPND and R-1 images were generated using receptor parametric mapping with the cerebellum as a reference. T1-weighted MR imaging was used for automated definition of volumes of interest (VOI). The DAT VOIs included the basal ganglia, whereas the overall brain functional activity was examined using VOIs across the brain. BPND and R-1 values were compared with normalized I-123-FP-CIT and F-18-FDG uptake values, respectively, using Pearson correlations and regression analyses. In addition, 2 masked interpreters evaluated the images visually, in both the routine and the experimental datasets, for comparison of patient diagnoses.

Results: Parametric C-11-PE2I BPND and R-1 images showed high consistency with I-123-FP-CIT SPECT and F-18-FDG PET images. Correlations between C-11-PE2I BPND and I-123-FP-CIT uptake ratios were 0.97 and 0.76 in the putamen and caudate nucleus, respectively. Regional C-11-PE2I R-1 values were moderately to highly correlated with normalized F-18-FDG values (range, 0.61-0.94). Visual assessment of DAT availability showed a high consistency between C-11-PE2I BPND and I-123-FP-CIT images, whereas the consistency was somewhat lower for appraisal of overall brain functional activity using I-123-FP-CIT and F-18-FDG images. Substantial differences were found between clinical diagnosis and both neuro-imaging diagnoses.

Conclusion: A single, dynamic C-11-PE2I PET investigation is a powerful alternative to a dual examination with I-123-FP-CIT SPECT and F-18-FDG PET for differential diagnosis of parkinsonian disorders. A large-scale patient study is, however, needed to further investigate distinct pathologic patterns in overall brain functional activity for various parkinsonian disorders.

PURPOSE: To evaluate whether, in patients with non-small cell lung carcinoma (NSCLC), tumor uptake of [(11)C]erlotinib can be quantified and imaged using positron emission tomography and to assess whether the level of tracer uptake corresponds with the presence of activating tumor EGF receptor (EGFR) mutations.EXPERIMENTAL DESIGN: Ten patients with NSCLCs, five with an EGFR exon 19 deletion, and five without were scanned twice (test retest) on the same day with an interval of at least 4 hours. Each scanning procedure included a low-dose computed tomographic scan, a 10-minute dynamic [(15)O]H(2)O scan, and a 1-hour dynamic [(11)C]erlotinib scan. Data were analyzed using full tracer kinetic modeling. EGFR expression was evaluated using immunohistochemistry.RESULTS: The quantitative measure of [(11)C]erlotinib uptake, that is, volume of distribution (V(T)), was significantly higher in tumors with activating mutations, that is, all with exon 19 deletions (median V(T), 1.76; range, 1.25-2.93), than in those without activating mutations (median V(T), 1.06; range, 0.67-1.22) for both test and retest data (P = 0.014 and P = 0.009, respectively). Good reproducibility of [(11)C]erlotinib V(T) was seen (intraclass correlation coefficient = 0.88). Intergroup differences in [(11)C]erlotinib uptake were not correlated with EGFR expression levels, nor tumor blood flow.CONCLUSION: [(11)C]erlotinib V(T) was significantly higher in NSCLCs tumors with EGFR exon 19 deletions.

Parenteral iron-polysaccharide complexes are increasingly applied. The pharmacokinetics of iron sucrose have been assessed by our group using positron emission tomography (PET). A single intravenous injection of 100 mg iron as iron (III) hydroxide-polymaltose complex, labelled with a tracer in the form of 52Fe/59Fe, was similarly assessed in six patients using PET for about 8 h. Red cell utilization was followed for 4 weeks. Iron polymaltose was similarly distributed to the liver, spleen and bone marrow. However, a larger proportion of this complex was rapidly distributed to the bone marrow. The shorter equilibration phase for the liver, about 25 min, indicates the minimal role of the liver for direct distribution. Splenic uptake also reflected the reticuloendothelial handling of this complex. Red cell utilization ranged from 61% to 99%. Despite the relatively higher uptake by the bone marrow, there was no saturation of marrow transport systems at this dose level. In conclusion, high red cell utilization of iron polymaltose occurred in anaemic patients. The major portion of the injected dose was rapidly distributed to the bone marrow. In addition, the reticuloendothelial uptake of this complex may reflect the safety of polysaccharide complexes. Non-saturation of transport systems to the bone marrow indicated the presence of a large interstitial transport pool, which might possibly be transferrin.

Parenteral iron-polysaccharide complexes are increasingly applied. The pharmacokinetics of iron sucrose have been assessed by our group using positron emission tomography (PET). A single intravenous injection of 100 mg iron as iron (III) hydroxide-polymaltose complex, labelled with a tracer in the form of ⁵²Fe/⁵⁹Fe, was similarly assessed in six patients using PET for about 8 h. Red cell utilization was followed for 4 weeks. Iron polymaltose was similarly distributed to the liver, spleen and bone marrow. However, a larger proportion of this complex was rapidly distributed to the bone marrow. The shorter equilibration phase for the liver, about 25 min, indicates the minimal role of the liver for direct distribution. Splenic uptake also reflected the reticuloendothelial handling of this complex. Red cell utilization ranged from 61% to 99%. Despite the relatively higher uptake by the bone marrow, there was no saturation of marrow transport systems at this dose level. In conclusion, high red cell utilization of iron polymaltose occurred in anaemic patients. The major portion of the injected dose was rapidly distributed to the bone marrow. In addition, the reticuloendothelial uptake of this complex may reflect the safety of polysaccharide complexes. Non-saturation of transport systems to the bone marrow indicated the presence of a large interstitial transport pool, which might possibly be transferrin.

The enzyme phosphodiesterase 10A (PDE10A) is abundant in striatal medium spiny neurons and has been implicated in the pathophysiology of schizophrenia in animal models and is investigated as a possible new pharmacological treatment target. A reduction of prefrontal cortical thickness is common in schizophrenia, but how this relates to PDE10A expression is unknown. Our study aim was to compare, we believe for the first time, the striatal non-displaceable binding potential (BPND) of the new validated PDE10A ligand [(11)C]Lu AE92686 between patients with schizophrenia and healthy controls. Furthermore, we aimed to assess the correlation of PDE10A BPND to cortical thickness. Sixteen healthy male controls and 10 male patients with schizophrenia treated with clozapine, olanzapine or quetiapine were investigated with positron emission tomography (PET) and magnetic resonance imaging (MRI). Striatal binding potential (BPND) of [(11)C]Lu AE92686 was acquired through dynamic PET scans and cortical thickness by structural MRI. Clinical assessments of symptoms and cognitive function were performed and the antipsychotic dosage was recorded. Patients with schizophrenia had a significantly lower BPND of [(11)C]Lu AE92686 in striatum (P=0.003) than healthy controls. The striatal BPND significantly correlated to cortical thickness in the medial prefrontal cortex and superior frontal gyrus across patients with schizophrenia and healthy controls. No significant correlation was observed between the BPND for [(11)C]Lu AE92686 in striatum and age, schizophrenia symptoms, antipsychotic dosage, coffee consumption, smoking, duration of illness or cognitive function in the patients. In conclusion, PDE10A may be important for functioning in the striato-cortical interaction and in the pathophysiology of schizophrenia.

We assessed glucose uptake in different tissues in type 2 diabetes (T2D), prediabetes, and control subjects to elucidate its impact in the development of whole-body insulin resistance and T2D. Thirteen T2D, 12 prediabetes, and 10 control subjects, matched for age and BMI, underwent OGTT and abdominal subcutaneous adipose tissue (SAT) biopsies. Integrated whole-body ¹⁸F-FDG PET and MRI were performed during a hyperinsulinemic euglycemic clamp to asses glucose uptake rate (MRglu) in several tissues. MRglu in skeletal muscle, SAT, visceral adipose tissue (VAT), and liver was significantly reduced in T2D subjects and correlated positively with M-values (r=0.884, r=0.574, r=0.707 and r=0.403, respectively). Brain MRglu was significantly higher in T2D and prediabetes subjects and had a significant inverse correlation with M-values (r=-0.616). Myocardial MRglu did not differ between groups and did not correlate with the M-values. A multivariate model including skeletal muscle, brain and VAT MRglu best predicted the M-values (adjusted r²=0.85). In addition, SAT MRglu correlated with SAT glucose uptake ex vivo (r=0.491). In different stages of the development of T2D, glucose uptake during hyperinsulinemia is elevated in the brain in parallel with an impairment in peripheral organs. Impaired glucose uptake in skeletal muscle and VAT together with elevated glucose uptake in brain were independently associated with whole-body insulin resistance, and these tissue-specific alterations may contribute to T2D development.

AIMS/HYPOTHESIS: The aim of this study was to investigate pancreatic perfusion and its response to a glucose load in patients with type 1 diabetes mellitus compared with non-diabetic ('healthy') individuals.

METHODS: Eight individuals with longstanding type 1 diabetes and ten sex-, age- and BMI-matched healthy controls underwent dynamic positron emission tomography scanning with (15)O-labelled water before and after intravenous administration of glucose. Perfusion in the pancreas was measured. Portal and arterial hepatic perfusion were recorded as references.

RESULTS: Under fasting conditions, total pancreatic perfusion was on average 23% lower in the individuals with diabetes compared with healthy individuals. Glucose increased total pancreatic and portal hepatic blood perfusion in healthy individuals by 48% and 38%, respectively. In individuals with diabetes there was no significant increase in either total pancreatic or portal hepatic perfusion.

CONCLUSIONS/INTERPRETATION: Individuals with type 1 diabetes have reduced basal pancreatic perfusion and a severely impaired pancreatic and splanchnic perfusion response to intravenous glucose stimulation.

[(11)C]5-hydroxy-tryptophan ([(11)C]5-HTP) PET of the pancreas has been shown to be a surrogate imaging biomarker of pancreatic islet mass. The change in islet mass in different stages of type 2 diabetes (T2D) as measured by non-invasive imaging is currently unknown. Here, we describe a cross-sectional study where subjects at different stages of T2D development with expected stratification of pancreatic islet mass were examined in relation to non-diabetic individuals. The primary outcome was the [(11)C]5-HTP uptake and retention in pancreas, as a surrogate marker for the endogenous islet mass.We found that metabolic testing indicated a progressive loss of beta cell function, but that this was not mirrored by a decrease in [(11)C]5-HTP tracer accumulation in the pancreas. This provides evidence of retained islet mass despite decreased beta cell function. The results herein indicates that beta cell dedifferentiation, and not necessarily endocrine cell loss, constitute a major cause of beta cell failure in T2D.

Mental disorders represent an increasing source of disability and high costs for societies globally. Molecular imaging techniques such as positron emission tomography (PET) represent powerful tools with the potential to advance knowledge regarding disease mechanisms, allowing the development of new treatment approaches. Thus far, most PET research on pathophysiology in psychiatric disorders has focused on the monoaminergic neurotransmission systems, and although a series of discoveries have been made, the results have not led to any material changes in clinical practice. We outline areas of methodological development that can address some of the important obstacles to fruitful progress. First, we point towards new radioligands and targets that can lead to the identification of processes upstream, or parallel to disturbances in monoaminergic systems. Second, we describe the development of new methods of PET data quantification and PET systems that may facilitate research in psychiatric populations. Third, we review the application of multimodal imaging that can link molecular imaging data to other aspects of brain function, thus deepening our understanding of disease processes. Fourth, we highlight the need to develop imaging study protocols to include longitudinal and interventional paradigms, as well as frameworks to assess dimensional symptoms such that the field can move beyond cross-sectional studies within current diagnostic boundaries. Particular effort should be paid to include also the most severely ill patients. Finally, we discuss the importance of harmonizing data collection and promoting data sharing to reach the desired sample sizes needed to fully capture the phenotype of psychiatric conditions.

BACKGROUND:

Osteoprotegerin (OPG), a soluble member of the tumor necrosis factor receptor superfamily, is linked to cardiovascular disease. Negative associations exist between circulating OPG and cardiac function. The adipocytokine adiponectin (ADPN) is downregulated in type 2 diabetes mellitus (T2DM) and coronary artery disease and shows an inverse correlation with insulin sensitivity and cardiovascular disease risk. We assessed the relationship of plasma OPG and ADPN and arterial function, cardiac function and myocardial glucose metabolism in T2DM.

METHODS:

We included 78 asymptomatic men with uncomplicated, well-controlled T2DM, without inducible ischemia, assessed by dobutamine-stress echocardiography, and 14 age-matched controls. Cardiac function was measured by magnetic resonance imaging, myocardial glucose metabolism (MMRglu) by 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography. OPG and ADPN levels were measured in plasma.

RESULTS:

T2DM patients vs. controls showed lower aortic distensibility, left ventricular (LV) volumes, impaired LV diastolic function and MMRglu (all P < 0.05). In T2DM men vs. controls, OPG levels were higher (P = 0.02), whereas ADPN concentrations were decreased (P = 0.04). OPG correlated inversely with aortic distensibility, LV volumes and E/A ratio (diastolic function), and positively with LV mass/volume ratio (all P < 0.05). Regression analyses showed the associations with aortic distensibility and LV mass/volume ratio to be independent of age-, blood pressure- and glycated hemoglobin (HbA1c). However, the associations with LV volumes and E/A ratio were dependent of these parameters. ADPN correlated positively with MMRglu (P < 0.05), which, in multiple regression analysis, was dependent of whole-body insulin sensitivity, HbA1c and waist.

CONCLUSIONS:

OPG was inversely associated with aortic distensibility, LV volumes and LV diastolic function, while ADPN was positively associated with MMRglu. These findings indicate that in asymptomatic men with uncomplicated T2DM, OPG and ADPN may be markers of underlying mechanisms linking the diabetic state to cardiac abnormalities.

TRIAL REGISTRATION:

Current Controlled Trials ISRCTN53177482.

The development of tau-specific positron emission tomography (PET) tracers allows imaging in vivo the regional load of tau pathology in Alzheimer's disease (AD) and other tauopathies. Eighteen patients with baseline investigations enroled in a 17-month follow-up study, including 16 with AD (10 had mild cognitive impairment and a positive amyloid PET scan, that is, prodromal AD, and six had AD dementia) and two with corticobasal syndrome. All patients underwent PET scans with [(18)F]THK5317 (tau deposition) and [(18)F]FDG (glucose metabolism) at baseline and follow-up, neuropsychological assessment at baseline and follow-up and a scan with [(11)C]PIB (amyloid-β deposition) at baseline only. At a group level, patients with AD (prodromal or dementia) showed unchanged [(18)F]THK5317 retention over time, in contrast to significant decreases in [(18)F]FDG uptake in temporoparietal areas. The pattern of changes in [(18)F]THK5317 retention was heterogeneous across all patients, with qualitative differences both between the two AD groups (prodromal and dementia) and among individual patients. High [(18)F]THK5317 retention was significantly associated over time with low episodic memory encoding scores, while low [(18)F]FDG uptake was significantly associated over time with both low global cognition and episodic memory encoding scores. Both patients with corticobasal syndrome had a negative [(11)C]PIB scan, high [(18)F]THK5317 retention with a different regional distribution from that in AD, and a homogeneous pattern of increased [(18)F]THK5317 retention in the basal ganglia over time. These findings highlight the heterogeneous propagation of tau pathology among patients with symptomatic AD, in contrast to the homogeneous changes seen in glucose metabolism, which better tracked clinical progression.Molecular Psychiatry advance online publication, 16 May 2017; doi:10.1038/mp.2017.108.

PURPOSE: The aim of this study was to explore the cerebral distribution of the tau-specific PET tracer [(18)F]THK5317 (also known as (S)-[(18)F]THK5117) retention in different stages of Alzheimer's disease; and study any associations with markers of hypometabolism and amyloid-beta deposition.

METHODS: Thirty-three individuals were enrolled, including nine patients with Alzheimer's disease dementia, thirteen with mild cognitive impairment (MCI), two with non-Alzheimer's disease dementia, and nine healthy controls (five young and four elderly). In a multi-tracer PET design [(18)F]THK5317, [(11)C] Pittsburgh compound B ([(11)C]PIB), and [(18)F]FDG were used to assess tau pathology, amyloid-beta deposition and cerebral glucose metabolism, respectively. The MCI patients were further divided into MCI [(11)C]PIB-positive (n = 11) and MCI [(11)C]PIB-negative (n = 2) groups.

RESULTS: Test-retest variability for [(18)F]THK5317-PET was very low (1.17-3.81 %), as shown by retesting five patients. The patients with prodromal (MCI [(11)C]PIB-positive) and dementia-stage Alzheimer's disease had significantly higher [(18)F]THK5317 retention than healthy controls (p = 0.002 and p = 0.001, respectively) in areas exceeding limbic regions, and their discrimination from this control group (using the area under the curve) was >98 %. Focal negative correlations between [(18)F]THK5317 retention and [(18)F]FDG uptake were observed mainly in the frontal cortex, and focal positive correlations were found between [(18)F]THK5317 and [(11)C]PIB retentions isocortically. One patient with corticobasal degeneration syndrome and one with progressive supranuclear palsy showed no [(11)C]PIB but high [(18)F]THK5317 retentions with a different regional distribution from that in Alzheimer's disease patients.

CONCLUSIONS: The tau-specific PET tracer [(18)F]THK5317 images in vivo the expected regional distribution of tau pathology. This distribution contrasts with the different patterns of hypometabolism and amyloid-beta deposition.

BACKGROUND: Patient motion constitutes a limitation to ¹⁵O-water cardiac PET imaging. We examined the ability of image readers to detect and correct patient motion using simulated motion data and clinical patient scans.

METHODS: Simulated data consisting of 16 motions applied to 10 motion-free scans were motion corrected using two approaches, pre-analysis and post-analysis for motion identification. Both approaches employed a manual frame-by-frame correction method. In addition, a clinical cohort was analyzed for assessment of prevalence and effect of motion and motion correction.

RESULTS: Motion correction was performed on 94% (pre-analysis) and 64% (post-analysis) of the scans. Large motion artifacts were corrected in 91% (pre-analysis) and 74% (post-analysis) of scans. Artifacts in MBF were reduced in 56% (pre-analysis) and 58% (post-analysis) of the scans. The prevalence of motion in the clinical patient cohort (n = 762) was 10%. Motion correction altered exam interpretation in only 10 (1.3%) clinical patient exams.

CONCLUSION: Frame-by-frame motion correction after visual inspection is useful in reducing motion artifacts in cardiac ¹⁵O-water PET. Reviewing the initial results (parametric images and polar maps) as part of the motion correction process, reduced erroneous corrections in motion-free scans. In a large clinical cohort, the impact of motion correction was limited to few patients.

Hybrid imaging using PET in conjunction with CT-based coronary angiography (PET/CTCA) enables near-simultaneous quantification of myocardial blood flow (MBF) and anatomical evaluation of coronary arteries. CTCA is an excellent imaging modality to rule out obstructive coronary artery disease (CAD), but functional assessment is warranted in the presence of a CTCA-observed stenosis because the specificity of CTCA is relatively low. Quantitative H 2 15O PET/CTCA may yield complementary information and enhance diagnostic accuracy. The purpose of this study was to evaluate the diagnostic accuracy of quantitative H2 15O PET/CTCA in a clinical cohort of patients with suspected CAD who underwent both cardiac H 2 15O PET/CTCA and invasive coronary angiography (ICA). In addition, this study aimed to evaluate and compare the accuracy of hyperemic MBF versus coronary flow reserve (CFR). Methods: Patients (n = 120; mean age ± SD, 61 ± 10 y; 77 men and 43 women) with a predominantly intermediate pretest likelihood for CAD underwent both quantitative H 2 15O PET/CTCA and ICA. A ≥50% stenosis at ICA or a fractional flow reserve ≤ 0.80 was considered significant. Results: Obstructive CAD was diagnosed in 49 of 120 patients (41%). The diagnostic accuracy of hyperemic MBF was significantly higher than CFR (80% vs. 68%, respectively, P = 0.02), with optimal cutoff values of 1.86 mL/min/g and 2.30, respectively. On a per-patient basis, the sensitivity, specificity, negative predictive value, and positive predictive value of CTCA were 100%, 34%, 100%, and 51%, respectively, as compared with 76%, 83%, 83%, and 76%, respectively, for quantitative hyperemic MBF PET. Quantitative H2 15O PET/CTCA reduced the number of false-positive CTCA studies from 47 to 6, although 12 of 49 true-positive CTCAs were incorrectly reclassified as false-negative hybrid scans on the basis of (presumably) sufficient hyperemic MBF. Compared with CTCA (61%) or H2 15O PET (80%) alone (both P &lt; 0.05), the hybrid approach significantly improved diagnostic accuracy (85%). Conclusion: The diagnostic accuracy of quantitative H 2 15O PET/CTCA is superior to either H2 15O PET or CTCA alone for the detection of clinically significant CAD. Hyperemic MBF was more accurate than CFR, implying that a single measurement of MBF in diagnostic protocols may suffice.

Background

There has been increasing interest in quantitative myocardial blood flow (MBF) imaging over the last years and it is expected to become a routinely used technique in clinical practice. Positron emission tomography (PET) using [¹⁵O]H₂O is the established gold standard for quantification of MBF in vivo. A fundamental issue when performing quantitative MBF imaging is to define the limits of MBF in a clinically suitable population. The aims of the present study were to determine the limits of MBF and to determine the relationship among coronary artery disease (CAD) risk factors, gender and MBF in a predominantly symptomatic patient cohort without significant CAD.

Methods

A total of 128 patients (mean age 54 ± 10 years, 50 men) with a low to intermediate pretest likelihood of CAD were referred for noninvasive evaluation of CAD using a hybrid PET/computed tomography (PET/CT) scanner. MBF was quantified with [¹⁵O]H₂O at rest and during adenosine-induced hyperaemia. Obstructive CAD was excluded in these patients by means of invasive or CT-based coronary angiography.

Results

Global average baseline MBF values were 0.91 ± 0.34 and 1.09 ± 0.30  ml·min⁻¹·g⁻¹ (range 0.54–2.35  and 0.59–2.75 ml·min⁻¹·g⁻¹) in men and women, respectively (p < 0.01). However, no gender-dependent difference in baseline MBF was seen following correction for rate–pressure product (0.98 ± 0.45 and 1.09 ± 0.30 ml·min⁻¹·g⁻¹ in men and women, respectively; p = 0.08). Global average hyperaemic MBF values were 3.44 ± 1.20 ml·min⁻¹·g⁻¹ in the whole study population, and 2.90 ± 0.85 and 3.78 ± 1.27 ml·min⁻¹·g⁻¹ (range 1.52–5.22 and 1.72–8.15 ml·min⁻¹·g⁻¹) in men and women, respectively (p < 0.001). Multivariate analysis identified male gender, age and body mass index as having an independently negative impact on hyperaemic MBF.

Conclusion

Gender, age and body mass index substantially influence reference values and should be corrected for when interpreting hyperaemic MBF values.

Background Myocardial ischaemia occurs principally in the subendocardial layer, whereas conventional myocardial perfusion imaging provides no information on the transmural myocardial blood flow (MBF) distribution. Subendocardial perfusion measurements and quantification of the transmural perfusion gradient (TPG) could be more sensitive and specific for the detection of coronary artery disease (CAD). The current study aimed to determine the impact of lesion severity as assessed by the fractional flow reserve (FFR) on subendocardial perfusion and the TPG using [O-15]H2O positron emission tomography (PET) imaging in patients evaluated for CAD. Methods and results Sixty-six patients with anginal chest pain were prospectively enrolled and underwent [O-15] H2O myocardial perfusion PET imaging. Subsequently, invasive coronary angiography was performed and FFR obtained in all coronary arteries irrespective of the PET imaging results. Thirty (45%) patients were diagnosed with significant CAD(i.e. FFR <= 0.80), whereas on a per vessel analysis (n = 198), 53 (27%) displayed a positive FFR. Transmural hyperaemic MBF decreased significantly from 3.09 +/- 1.16 to 1.67 +/- 0.57 mL min(-1) g(-1) (P < 0.001) in non-ischaemic and ischaemic myocardium, respectively. The TPG decreased during hyperaemia when compared with baseline (1.20 +/- 0.14 vs. 0.94 +/- 0.17, P < 0.001), and was lower in arteries with a positive FFR (0.97 +/- 0.16 vs. 0.88 +/- 0.18, P < 0.01). ATPG threshold of 0.94 yielded an accuracy to detect CAD of 59%, which was inferior to transmural MBF with an optimal cutoff of 2.20 mL min(-1) g(-1) and an accuracy of 85% (P < 0.001). Diagnostic accuracy of subendocardial perfusion measurements was comparable with transmural MBF (83 vs. 85%, respectively, P = NS). Conclusion Cardiac [O-15]H2O PET imaging is able to distinguish subendocardial from subepicardial perfusion in the myocardium of normal dimensions. Hyperaemic TPG is significantly lower in ischaemic myocardium. This technique can potentially be employed to study subendocardial perfusion impairment in more detail. However, the diagnostic accuracy of subendocardial hyperaemic perfusion and TPG appears to be limited compared with quantitative transmural MBF, warranting further study.

This study evaluates the impact of hybrid imaging on referral for invasive coronary angiography (ICA) and revascularization rates. A total of 375 patients underwent hybrid O-15-water positron emission tomography (PET)/computed tomography (CT)-based coronary angiography (CTCA) imaging for the evaluation of coronary artery disease (CAD). Downstream treatment strategy within a 60-day period after hybrid PET/CTCA imaging for ICA referral and revascularization was assessed. CTCA examinations were classified as showing no (obstructive) CAD, equivocal (borderline test result), or obstructive CAD, while the PET perfusion images were classified into normal or abnormal. On the basis of CTCA imaging, 182 (49) patients displayed no (obstructive) CAD. Only 10 (5) patients who showed no (obstructive) CAD on CTCA were referred for ICA, which were all negative. An equivocal CT study was observed in 80 (21) patients, among whom 56 (70) showed normal myocardial perfusion imaging (MPI), resulting in referral rates for ICA of 18 for normal MPI and 71 for abnormal MPI, respectively. No revascularizations were performed in the presence of normal MPI, while 59 of those with abnormal MPI were revascularized. CTCA indentified obstructive CAD in 113 (30) patients accompanied in 59 (52) patients with abnormal MPI. Referral rate for ICA was 57 for normal MPI and 88 for those with abnormal MPI, resulting in revascularization rates of 26 and 72, respectively. Hybrid O-15-water PET/CTCA imaging impacts clinical decision-making with regard to referral for ICA and revascularization procedures. Particularly, in the presence of an equivocal or abnormal CTCA, MPI could guide in the decision to refer for ICA and revascularization.

Aims There is growing evidence that coronary artery disease (CAD) affects not only the conduit epicardial coronary arteries, but also the microvascular coronary bed. Moreover, coronary microvascular dysfunction (CMVD) often precedes the stage of clinically overt epicardial CAD. Coronary artery calcium (CAC) and carotid intima-media thickness (C-IMT) measured with computed tomography (CT) and ultrasound, respectively, are among the available techniques to non-invasively assess atherosclerotic burden. An increased CAC score and C-IMT have also been associated with CMVD. It is therefore of interest to explore and compare the potential of CAC against C-IMT to predict minimal coronary vascular resistance (CVR). Methods and results We evaluated 120 patients (mean age 56 +/- 9 years, 58 men) without a documented history of CAD in whom and results obstructive CAD was excluded. All patients underwent C-IMT measurements, CAC scoring, and vasodilator stress O-15-water positron emission tomography (PET)/CT, during which the coronary flow reserve (CFR) and minimal CVR were analysed. Minimal CVR increased significantly with increasing tertiles of C-IMT (22 +/- 6, 27 +/- 11, and 28 +/- 9 mmHg mL(-1) min(-1) g(-1), P < 0.01), whereas the CFR was comparable across all C-IMT groups (P = 0.50). Minimal CVR increased significantly with an increase in CAC score (23 +/- 9, 27 +/- 8, 32 +/- 10, and 32 +/- 7 mmHg mL(-1) min(-1) g(-1). P < 0.01), whereas the CFR did not show a significant decrease with higher CAC scores (P = 0.18). Multivariable regression analysis revealed that C-IMT (P = 0.03), but not CAC, was independently associated with minimal CVR. Conclusion C-IMT, but not CAC score, independently predicts minimal CVR in patients with multiple cardiovascular risk factors and suspected of CAD.

Purpose

The perfusable tissue index (PTI) is a marker of myocardial viability. Recent technological advances have made it possible to generate parametric PTI images from a single [¹⁵O]H₂O PET/CT scan. The purpose of this study was to validate these parametric PTI images.

Methods

The study population comprised 46 patients with documented or suspected coronary artery disease who were studied with [¹⁵O]H₂O PET and late gadolinium-enhanced (LGE) cardiac magnetic resonance imaging (CMR).

Results

Of the 736 myocardial segments included, 364 showed some degree of LGE. PTI and perfusable tissue fraction (PTF) diminished with increasing LGE. The areas under the curve of the PTI and PTF, used to predict (near) transmural LGE on CMR, were 0.86 and 0.87, respectively. Optimal sensitivity and specificity were 91 % and 73 % for PTI and 69 % and 87 % for PTF, respectively.

Conclusion

PTI and PTF assessed with a single [¹⁵O]H₂O scan can be utilized as markers of myocardial viability in patients with coronary artery disease.

With antiangiogenic agents, tumor shrinkage may be absent, despite survival benefit. The present study assessed the predictive value of molecular imaging for the identification of survival benefit during antiangiogenic treatment with bevacizumab and erlotinib in patients with advanced non–small cell lung cancer.

Methods:

Patients were evaluated using an imaging protocol including CT, ¹⁸F-FDG PET, H₂¹⁵O PET, and dynamic contrast-enhanced MRI to derive measurements on tumor size, glucose metabolism, perfusion, and microvascular permeability. The percentage change in imaging parameters after 3 wk of treatment as compared with baseline was calculated and correlated with progression-free survival (PFS).

Results:

Forty-four patients were included, and 40 underwent CT and ¹⁸F-FDG PET at both time points. Complete datasets, containing all imaging modalities, were available for 14 patients. Bevacizumab and erlotinib treatment resulted in decreased metabolism, perfusion, and tumor size. A decrease in standardized uptake value or tumor perfusion of more than 20% at week 3 was associated with longer PFS (9.7 vs. 2.8 mo, P = 0.01, and 12.5 vs. 2.9 mo, P = 0.009, respectively). Whole-tumor K^trans (the endothelial transfer constant) was not associated with PFS, but patients with an increase of more than 15% in the SD of tumor K^trans values—that is, an increase in regions with low or high K^trans values—after 3 wk had shorter PFS (2.3 vs. 7.0 mo, P = 0.008). A partial response, according to the response evaluation criteria in solid tumors (RECIST), at week 3 was also associated with prolonged PFS (4.6 vs. 2.9 mo, P = 0.017). However, 40% of patients with a partial response as their best RECIST response still had stable disease at week 3. In these cases tumor perfusion was already decreased and K^trans heterogeneity showed no increase, indicating that the latter parameters seem to be more discriminative than RECIST at the 3-wk time point.

Conclusion:

PET and dynamic contrast-enhanced MRI were able to identify patients who benefit from bevacizumab and erlotinib treatment. Molecular imaging seems to allow earlier response evaluation than CT.

Cardiac imaging has a pivotal role in the prevention, diagnosis and treatment of ischaemic heart disease. SPECT is most commonly used for clinical myocardial perfusion imaging, whereas PET is the clinical reference standard for the quantification of myocardial perfusion. MRI does not involve exposure to ionizing radiation, similar to echocardiography, which can be performed at the bedside. CT perfusion imaging is not frequently used but CT offers coronary angiography data, and invasive catheter-based methods can measure coronary flow and pressure. Technical improvements to the quantification of pathophysiological parameters of myocardial ischaemia can be achieved. Clinical consensus recommendations on the appropriateness of each technique were derived following a European quantitative cardiac imaging meeting and using a real-time Delphi process. SPECT using new detectors allows the quantification of myocardial blood flow and is now also suited to patients with a high BMI. PET is well suited to patients with multivessel disease to confirm or exclude balanced ischaemia. MRI allows the evaluation of patients with complex disease who would benefit from imaging of function and fibrosis in addition to perfusion. Echocardiography remains the preferred technique for assessing ischaemia in bedside situations, whereas CT has the greatest value for combined quantification of stenosis and characterization of atherosclerosis in relation to myocardial ischaemia. In patients with a high probability of needing invasive treatment, invasive coronary flow and pressure measurement is well suited to guide treatment decisions. In this Consensus Statement, we summarize the strengths and weaknesses as well as the future technological potential of each imaging modality.

Background: Of interest to women's mental health, a wealth of studies suggests sex differences in nicotine addiction and treatment response, but their psychoneuroendocrine underpinnings remain largely unknown. A pathway involving sex steroids could indeed be involved in the behavioural effects of nicotine, as it was found to inhibit aromatase in vitro and in vivo in rodents and non-human primates, respectively. Aromatase regulates the synthesis of oestrogens and, of relevance to addiction, is highly expressed in the limbic brain.

Methods: The present study sought to investigate in vivo aromatase availability in relation to exposure to nicotine in healthy women. Structural magnetic resonance imaging and two [11C]cetrozole positron emission tomography (PET) scans were performed to assess the availability of aromatase before and after administration of nicotine. Gonadal hormones and cotinine levels were measured. Given the region-specific expression of aromatase, a ROI -based approach was employed to assess changes in [11C]cetrozole non-displaceable binding potential.

Results: The highest availability of aromatase was found in the right and left thalamus. Upon nicotine exposure, [11C]cetrozole binding in the thalamus was acutely decreased bilaterally (Cohen's d =-0.99). In line, cotinine levels were negatively associated with aromatase availability in the thalamus, although as non-significant trend.

Conclusions: These findings indicate acute blocking of aromatase availability by nicotine in the thalamic area. This suggests a new putative mechanism mediating the effects of nicotine on human behaviour, particularly relevant to sex differences in nicotine addiction.

Objective: To obtain direct quantifications of glucose turnover, volumes and fat content of several tissues in the development of type 2 diabetes (T2D) using a novel integrated approach for whole-body imaging.

Design and methods: Hyperinsulinemic-euglycemic clamps and simultaneous whole-body integrated [18F]FDG-PET/MRI with automated analyses were performed in control (n = 12), prediabetes (n = 16) and T2D (n = 13) subjects matched for age, sex and BMI.

Results: Whole-body glucose uptake (Rd) was reduced by approximately 25% in T2D vs control subjects, and partitioning to brain was increased from 3.8% of total Rd in controls to 7.1% in T2D. In liver, subcutaneous AT, thigh muscle, total tissue glucose metabolic rates (MRglu) and their % of total Rd were reduced in T2D compared to control subjects. The prediabetes group had intermediate findings. Total MRglu in heart, visceral AT, gluteus and calf muscle was similar across groups. Whole-body insulin sensitivity assessed as glucose infusion rate correlated with liver MRglu but inversely with brain MRglu. Liver fat content correlated with MRglu in brain but inversely with MRglu in other tissues. Calf muscle fat was inversely associated with MRglu only in the same muscle group.

Conclusions: This integrated imaging approach provides detailed quantification of tissue-specific glucose metabolism. During T2D development, insulin-stimulated glucose disposal is impaired and increasingly shifted away from muscle, liver and fat toward the brain. Altered glucose handling in the brain and liver fat accumulation may aggravate insulin resistance in several organs.

In humans a well-developed serotonin system is localized to the pancreatic islets while being absent in exocrine pancreas. Assessment of pancreatic serotonin biosynthesis could therefore be used to estimate the human endocrine pancreas. Proof of concept was tested in a prospective clinical trial by comparisons of type 1 diabetic (T1D) patients, with extensive reduction of beta cells, with healthy volunteers (HV).C-peptide negative (i.e. insulin-deficient) T1D subjects (n=10) and HV (n=9) underwent dynamic Positron Emission Tomography with the radiolabeled serotonin precursor [(11)C]5-Hydroxy-Tryptophan ([(11)C]5-HTP).A significant accumulation of [(11)C]5-HTP was obtained in the pancreas of the HV, with large inter-individual variation. A substantial and highly significant reduction (66%) in the pancreatic uptake of [(11)C]5-HTP in T1D subjects was observed, and this was most evident in the corpus and caudal regions of the pancreas where beta-cells normally are the major constituent of the islets.[(11)C]5-HTP retention in the pancreas was reduced in T1D compared to non-diabetic subjects. Accumulation of [(11)C]5-HTP in the pancreas of both HV and subjects with T1D were in agreement with previously reported morphological observations on the beta cell volume implying that [(11)C]5-HTP retention is a useful non-invasive surrogate marker for the human endocrine pancreas.

Introduction: Development of a selective and specific high affinity PET tracer, [C-11]UCB-A, for the in vivo study of SV2A expression in humans. Radiochemistry and preclinical studies in rats and pigs including development of a tracer kinetic model to determine V-T. A method for the measurement of percent intact tracer in plasma was developed and the radiation dosimetry was determined in rats. Results: 3-5 GBq of [C-11]UCB-A could be produced with radiochemical purity exceeding 98% with a specific radioactivity of around 65 GBq/mu mol. In vitro binding showed high selective binding towards SV2A. [C-11]UCB-A displayed a dose-dependent and reversible binding to SV2A as measured with PET in rats and pigs and the V-T could be determined by Logan analysis. The dosimetry was favorable and low enough to allow multiple administrations of [C-11]UCB-A to healthy volunteers, and the metabolite analysis showed no sign of labeled metabolites in brain. Conclusions: We have developed the novel PET tracer, [C-11]UCB-A, that can be used to measure SV2A expression in vivo. The dosimetry allows up to 5 administrations of 400 MBq of [C-11]UCB-A in humans. Apart from measuring drug occupancy, as we have shown, the tracer can potentially be used to compare SV2A expression between individuals because of the rather narrow range of baseline V-T values. This will have to be further validated in human studies.

Cerebral blood flow (CBF) measurements are of high clinical value and can be acquired non-invasively with no radiation exposure using pseudo-continuous arterial spin labeling (ASL). The aim of this study was to evaluate accordance in resting state CBF between ASL (CBF_ASL) and ¹⁵O-water positron emission tomography (PET) (CBF_PET) acquired simultaneously on an integrated 3T PET/MR system. The data comprised ASL and dynamic ¹⁵O-water PET data with arterial blood sampling of eighteen subjects (eight patients with focal epilepsy and ten healthy controls, age 21 to 61 years). ¹⁵O-water PET parametric CBF images were generated using a basis function implementation of the single tissue compartment model. Cortical and subcortical regions were automatically segmented using Freesurfer. Average CBF_ASL and CBF_PET in grey matter were 60 ± 20 and 75 ± 22 mL/100 g/min respectively, with a relatively high correlation (r = 0.78, p < 0.001). Bland-Altman analysis revealed poor agreement (bias = −15 mL/100 g/min, lower and upper limits of agreements = −16 and 45 mL/100 g/min, respectively) with a negative relationship. Accounting for the negative relationship, the width of the limits of agreement could be narrowed from 61 mL/100 g/min to 35 mL/100 g/min using regression-based limits of agreements. Although a high correlation between CBF_ASL and CBF_PET was found, the agreement in absolute CBF values was not sufficient for ASL to be used interchangeably with ¹⁵O-water PET.

Objectives: Arterial spin labelling (ASL) MRI promises clinical value in several common neurological disorders. Its quantitative accuracy and reproducibility, however, need to be further validated, ideally using simultaneously acquired measurements with ¹⁵O-water-PET on an integrated PET-MR scanner. However, so far, few studies have attempted this and the inclusion of bone in MR-based attenuation correction for PET has thus far been a challenge, compromising the quantitative accuracy of PET-MR based ¹⁵O-water PET data. The aim of the present work was to assess the correlation of ASL- and ¹⁵O-water-PET based regional cerebral blood flow (rCBF) values based on simultaneously acquired data, using zero-echo-time (ZTE)-based attenuation correction, as well as to assess the reproducibility of ASL-based rCBF.

Methods: Six subjects underwent 10 min PET scans after automated bolus injection of 400 MBq ¹⁵O-water (1 mL/s during 5 s followed by 35 mL saline at 2 mL/s) on a time-of-flight integrated PET-MR scanner (Signa PET-MR, GE Healthcare). Arterial blood radioactivity concentrations were monitored using continuous sampling from the radial artery (Swisstrace Twilite Two). Simultaneously, a 3D FSE pseudo-continuous ASL (3D pCASL) with a spiral read-out as supplied by the scanner manufacturer in the commercial software were acquired using an 8 channel head coil (Invivo Hi-Res Head Coil). In addition, 3D T1-w, ZTE and Dixon fat-water MRI were acquired. The ASL procedure was repeated after 2 h (patients remained in the scanner). Quantifiable ASL-based CBF maps were generated. PET images were reconstructed into 26 frames of increasing durations using time-of-flight OSEM (2 iterations, 28 subsets) and a 5 mm post-filter, with ZTE-based attenuation correction. Blood sampler data were corrected for delay and dispersion and ¹⁵O-water-based CBF maps were calculated using a basis function implementation of the single tissue compartment model including a fitted blood volume parameter. CBF maps were co-registered to each patient's T1-w image. 3D T1-w images were segmented and normalised to MNI space using SPM12, and anterior, middle and posterior flow territory volumes of interest (VOIs) were created from a standard template in MNI space and inversely transformed for each patient. In addition, a 45-VOI probabilistic template was applied using PVElab software. Correlations between PET- and ASL-based rCBF values were assessed using regression analysis, and reproducibility of ASL using a paired t-test.

Results: Mean (CI) total brain grey matter CBF values were 67.2 (48.0-86.5) mL/min/100 g for ¹⁵O-water-PET and 65.5 (55.7-75.5) mL/min/100 g for ASL. Although correlation and agreement between ¹⁵O-water and ASL-based rCBF for individual VOIs in the 45-VOI template were generally poor, significant correlations were found on a grey matter flow territory basis, with R² ranging from 0.70 in the anterior flow territory to 0.86 in the middle flow territory. rCBF values were significantly reduced between second and first ASL for all flow territories (p<0.01), with a mean decrease of 10%.

Conclusion: A good correlation between regional flow territory CBF values based on ASL and ¹⁵O-water-PET was found, using ZTE-based attenuation correction for PET data which takes bone tissue into account. ASL values for regional flow territories may have potential applications in patients with dementia or cerebrovascular diseases affecting blood flow such as moya moya. The decrease of ASL-based rCBF values in the reproducibility study needs to be investigated further to assess whether this is a methodological issue or reflects a true decrease in rCBF. Research Support: Uppsala County Council

OBJECTIVE: LMNB1-related autosomal dominant leukodystrophy is caused by an overexpression of the protein lamin B1, usually due to a duplication of the LMNB1 gene. Symptoms start in 5^th to 6^th decade. This slowly progressive disease terminates with death. We studied brain glucose metabolism in this disease using ¹⁸ F-fluorodeoxyglucose positron emission tomography (PET).

METHODS: We examined 8 patients, aged 48-64 years, in varying stages of clinical symptomatology. Two patients were investigated with quantitative PET on clinical indications after which six more patients were recruited. Absolute glucose metabolism was analyzed with the PVElab software in 6 patients and 18 healthy controls. A semiquantitative analysis using the CortexID software was performed in seven investigations, relating local metabolism levels to global glucose metabolism.

RESULTS: The clinical quantitative PET revealed low global glucose metabolism, with the most marked reduction in the cerebellum. In the PVElab analysis, patients presented low mean glucose metabolism in the cerebellum, brainstem and global grey matter. In the semiquantitative analysis, 2 patients showed a decreased metabolism in the cerebellum and 4 patients a relatively higher metabolism in parts of the temporal lobes. Since none of the patients showed an increased metabolism in the quantitative analysis, we interpret these increases as "pseudo-increases" related to a globally reduced metabolism.

CONCLUSIONS: Global reduction of grey matter glucose metabolism in this white matter disease most likely depends on a combination of cortical afferent dysfunction and, in later stages, neuronal loss. The lowest metabolism in the cerebellum is consistent with histopathological findings and prominent cerebellar symptoms.

Learning which environmental cues that predict danger is crucial for survival and accomplished through Pavlovian fear conditioning. In humans and rodents alike, fear conditioning is amygdala-dependent and rests on similar neurocircuitry. Rodent studies have implicated a causative role for dopamine in the amygdala during fear memory formation, but the role of dopamine in aversive learning in humans is unclear. Here, we show dopamine release in the amygdala and striatum during fear learning in humans. Using simultaneous positron emission tomography and functional magnetic resonance imaging, we demonstrate that the amount of dopamine release is linked to strength of conditioned fear responses and linearly coupled to learning-induced activity in the amygdala. Thus, like in rodents, formation of amygdala-dependent fear memories in humans seems to be facilitated by endogenous dopamine release, supporting an evolutionary conserved neurochemical mechanism for aversive memory formation.