Pulmonary blood volume assessment from a standard cardiac rubidium-82 imaging protocol: impact of adenosine-induced hyperemia.

BACKGROUND: This study aimed to assess the feasibility of estimating the pulmonary blood volume noninvasively using standard Rubidium-82 myocardial perfusion imaging (MPI) and characterize the changes during adenosine-induced hyperemia. METHODS: This study comprised 33 healthy volunteers (15 female, median age = 23 years), of which 25 underwent serial rest/adenosine stress Rubidium-82 MPI sessions. Mean bolus transit times (MBTT) were obtained by calculating the time delay from the Rubidium-82 bolus arrival in the pulmonary trunk to the arrival in the left myocardial atrium. Using the MBTT, in combination with stroke volume (SV) and heart rate (HR), we estimated pulmonary blood volume (PBV = (SV × HR) × MBTT). We report the empirically measured MBTT, HR, SV, and PBV, all stratified by sex [male (M) vs female (F)] as mean (SD). In addition, we report grouped repeatability measures using the within-subject repeatability coefficient. RESULTS: Mean bolus transit times was shortened during adenosine stressing with sex-specific differences [(seconds); Rest: Female (F) = 12.4 (1.5), Male (M) = 14.8 (2.8); stress: F = 8.8 (1.7), M = 11.2 (3.0), all P ≤ 0.01]. HR and SV increased during stress MPI, with a concomitant increase in the PBV [mL]; Rest: F = 544 (98), M = 926 (105); Stress: F = 914 (182), M = 1458 (338), all P < 0.001. The following test-retest repeatability measures were observed for MBTT (Rest = 17.2%, Stress = 17.9%), HR (Rest = 9.1%, Stress = 7.5%), SV (Rest = 8.9%, Stress = 5.6%), and for PBV measures (Rest = 20.7%, Stress = 19.5%) CONCLUSION: Pulmonary blood volume can be extracted by cardiac rubidium-82 MPI with excellent test-retest reliability, both at rest and during adenosine-induced hyperemia.

uPAR PET/CT for Prognostication and Response Assessment in Patients with Metastatic Castration-Resistant Prostate Cancer Undergoing Radium-223 Therapy: A Prospective Phase II Study.

The aim of this Phase II study was to investigate the potential for response assessment and prognostication of positron emission tomography (PET) using the ligand 68Ga-NOTA-AE105 targeting the urokinase-type plasminogen activator receptor (uPAR) in patients receiving Radium-223-dichloride therapy (223RaCl2). A combined whole-body uPAR PET and computed tomography (CT) was performed before initiation of 223RaCl2 and after two cycles of therapy. Standardized uptake value (SUV) in selected bone metastases was measured and the lesion with the highest SUVmax was considered the index lesion. Clinical outcomes were overall survival (OS), radiographic progression free survival (rPFS) and occurrence of symptomatic skeletal event (SSE). A total of 17 patients were included and 14 patients completed both baseline and follow-up uPAR-PET/CT. Baseline SUVmax of the index lesion was associated with OS; hazard ratio 2.51 (95% CI: 1.01-6.28, p = 0.05) per unit increase in SUVmax. No association between changes in SUVmax from baseline to follow-up and OS, progression during therapy, or rPFS was found. Baseline SUVmax was a significant predictor of SSE with receiver operating characteristics (ROC) area under the curve (AUC) = 0.81 (95% CI: 0.58-1.00, p = 0.034). A cut-off for tumor SUVmax could be established with an odds ratio of 14.0 (95% CI: 1.14-172.6, p = 0.023) for occurrence of SSE within 12 months. Although based on a small number of patients, uPAR-PET SUVmax in bone metastases was predictive for OS and risk of SSE in mCRPC patients receiving 223RaCl2. However, a relatively low uptake of the uPAR ligand in bone metastases impedes visual evaluation and requires another modality for lesion delineation.

Non-invasive assessment of temporal changes in myocardial microvascular function in persons with type 2 diabetes and healthy controls.

BACKGROUND: Cardiac Rubidium-82 (82 Rb) positron emission tomography/computed tomography (PET/CT) provides a measure of the myocardial blood flow and the myocardial flow reserve, which reflects the function of both large epicardial arteries and the myocardial microcirculation. Knowledge on changes in the myocardial microvascular function over time is lacking. METHODS: In this cohort study, we recruited 60 persons with type 2 diabetes and 30 non-diabetic controls, in 2013; all free of overt cardiovascular disease. All underwent a cardiac 82 Rb PET/CT scan. In 2019, all survivors (n = 82) were invited for a repeated cardiac 82 Rb PET/CT scan using the same protocol, and 29 with type 2 diabetes and 19 controls participated. RESULTS: Median duration between visits was 6.2 years (IQR: 6.1-6.3). In the total cohort, the mean age was 66.4 years (SD: 9.3) and 33% were females. The myocardial flow reserve was lower in persons with type 2 diabetes compared to controls (p = 0.002) but there was no temporal change in the myocardial flow reserve in participants with type 2 diabetes: mean change: -0.22 (95% CI: -0.47 to 0.02) nor in controls: -0.12 (-0.49 to 0.25) or when comparing type 2 diabetes to controls: mean difference: -0.10 (95% CI: -0.52 to 0.31). The temporal reduction in stress-induced myocardial blood flow did not differ within the groups but was more pronounced in type 2 diabetes compared to controls: mean difference: -0.30 (95% CI: -0.55 to -0.04). CONCLUSION: The myocardial microvascular function was impaired in persons with type 2 diabetes compared to controls but did not change significantly in either of the groups when evaluated over 6 years.

Pharmacokinetic analysis of [68Ga]Ga-DOTA-TOC PET in meningiomas for assessment of in vivo somatostatin receptor subtype 2.

PURPOSE: DOTA-D-Phe1-Tyr3-octreotide with gallium-68 ([68Ga]Ga-DOTA-TOC) is one of the PET tracers that forms the basis for peptide receptor radionuclide therapy based on somatostatin receptor subtype 2 (SSTR2) expression in meningiomas. Yet, the quantitative relationship between [68Ga]Ga-DOTA-TOC accumulation and SSTR2 is unknown. We conducted a correlative analysis of a range of [68Ga]Ga-DOTA-TOC PET metric(s) as imaging surrogate(s) of the receptor binding in meningiomas by correlating the PET results with SSTR2 expression from surgical specimens. We additionally investigated possible influences of secondary biological factors such as vascularization, inflammation and proliferation. METHODS: Fifteen patients with MRI-presumed or recurrent meningiomas underwent a 60-min dynamic [68Ga]Ga-DOTA-TOC PET/CT before surgery. The PET data comprised maximum and mean standardized uptake values (SUVmax, SUVmean) with and without normalization to reference regions, and quantitative measurements derived from kinetic modelling using a reversible two-tissue compartment model with the fractional blood volume (VB). Expressions of SSTR2 and proliferation (Ki-67, phosphohistone-H3, proliferating cell nuclear antigen) were determined by immunohistochemistry and/or quantitative polymerase chain reaction (qPCR), while biomarkers of vascularization (vascular endothelial growth factor A (VEGFA), endothelial marker CD34) and inflammation (cytokine interleukin-18, microglia/macrophage-specific marker CD68) by qPCR. RESULTS: Histopathology revealed 12 World Health Organization (WHO) grade I and three WHO grade II meningiomas showing no link to SSTR2. The majority of [68Ga]Ga-DOTA-TOC PET metrics showed significant associations with SSTR2 protein, while all PET metrics were positively correlated with SSTR2 mRNA with the best results for mean tumour-to-blood ratio (TBRmean) (r = 0.757, P = 0.001) and SUVmean (r = 0.714, P = 0.003). Significant positive correlations were also found between [68Ga]Ga-DOTA-TOC PET metrics, and VEGFA and VB. SSTR2 mRNA was moderately correlated with VEGFA (r = 0.539, P = 0.038). Neither [68Ga]Ga-DOTA-TOC PET metrics nor SSTR2 were correlated with proliferation or inflammation. CONCLUSION: [68Ga]Ga-DOTA-TOC accumulation in meningiomas is associated with SSTR2 binding and vascularization with TBRmean being the best PET metric for assessing SSTR2.

An Uncommon Case of Pediatric Esthesioneuroblastoma Presenting as SIADH: 18F-FDG PET/CT in Staging and Post-Therapeutic Assessment.

Esthesioneuroblastoma (ENB) is an uncommon neuroendocrine tumor originating from the olfactory neuroepithelium and accounts for 3-6% of all intranasal tumors [¹]. ENBs can be locally aggressive and cause invasion and destruction of surrounding structures. Histological grading and clinical stage at presentation are highly predictive of survival and especially presence of lymph node and distant metastases are determining prognostic factors [²,³,4,5]. Thus, reliable imaging is essential in these patients. Conventional imaging modalities for staging ENB are magnetic resonance imaging (MRI) and computed tomography (CT). However, fluorine-18 fluoro-2-deoxy-d-glucose positron emission tomography/CT (18F-FDG PET/CT) has been reported as a valuable adjunct and was found to upstage 36% of ENB patients compared to conventional imaging [6]. We present a case demonstrating the diagnostic work-up and follow-up with 18F-FDG PET/CT in a young patient with ENB with a highly atypical clinical presentation.

223Ra Therapy of Advanced Metastatic Castration-Resistant Prostate Cancer: Quantitative Assessment of Skeletal Tumor Burden for Prognostication of Clinical Outcome and Hematologic Toxicity.

The aim of this study was to investigate the prognostic value of the quantitative assessment of skeletal tumor burden on bone scintigraphy (Bone Scan Index [BSI]) in patients who have advanced metastatic castration-resistant prostate cancer (mCRPC) and are receiving 223RaCl2 We hypothesized that the BSI can serve as a prognostic biomarker of overall survival (OS) and hematologic toxicity and as a tool for response assessment in patients with mCRPC treated with 223RaCl2Methods: This study was a retrospective investigation of a Danish cohort of mCRPC patients who received 223RaCl2 therapy between March 2014 and October 2015 and for whom baseline bone scintigraphy was available. Bone scintigraphy studies were reviewed and graded according to the extent of disease. Furthermore, an automated BSI (EXINI BoneBSI) was obtained for baseline scintigraphy studies and follow-up scans after 3 cycles as well as at the end of therapy. Clinical outcomes were OS and occurrence of hematologic toxicity of grades 2-5. Associations between the BSI and clinical outcomes were investigated in multivariate regression models including the visual assessment of bone scintigraphy and other relevant covariates. Results: A total of 88 patients were included. The median number of completed 223RaCl2 cycles was 4, and 27 patients (31%) completed 6 cycles. The BSI was significantly associated with OS in the multivariate analysis; the median OS for patients with a BSI of greater than 5 was 8.2 mo, and the median OS for patients with a BSI of less than or equal to 5 was 15.0 mo (hazard ratio, 2.65 [95% confidence interval, 1.5-4.71]; P = 0.001). Likewise, the baseline BSI was prognostic for the occurrence of hematologic toxicity; patients with a BSI of greater than 5 had an odds ratio of 3.02 (95% confidence interval, 1.2-7.8; P = 0.02) for toxicity. The BSI declined during therapy in 44% of the patients who completed 3 cycles of 223RaCl2 (n = 52) and in 84% of the patients after the end of therapy (n = 32). There was no significant association between a change in the BSI during therapy and OS. Conclusion: The BSI is a promising biomarker for prognostication of OS and hematologic toxicity in late-stage mCRPC patients receiving 223RaCl2 Further prospective studies are needed to evaluate the potential of the BSI for response assessment in 223RaCl2 therapy.

Efficacy and safety assessment of a TRAF6-targeted nanoimmunotherapy in atherosclerotic mice and non-human primates.

Macrophage accumulation in atherosclerosis is directly linked to the destabilization and rupture of plaque, causing acute atherothrombotic events. Circulating monocytes enter the plaque and differentiate into macrophages, where they are activated by CD4+ T lymphocytes through CD40-CD40 ligand signalling. Here, we report the development and multiparametric evaluation of a nanoimmunotherapy that moderates CD40-CD40 ligand signalling in monocytes and macrophages by blocking the interaction between CD40 and tumour necrosis factor receptor-associated factor 6 (TRAF6). We evaluated the biodistribution characteristics of the nanoimmunotherapy in apolipoprotein E-deficient (Apoe-/-) mice and in non-human primates by in vivo positron-emission tomography imaging. In Apoe-/- mice, a 1-week nanoimmunotherapy treatment regimen achieved significant anti-inflammatory effects, which was due to the impaired migration capacity of monocytes, as established by a transcriptome analysis. The rapid reduction of plaque inflammation by the TRAF6-targeted nanoimmunotherapy and its favourable toxicity profiles in both mice and non-human primates highlights the translational potential of this strategy for the treatment of atherosclerosis.

Author Correction: Efficacy and safety assessment of a TRAF6-targeted nanoimmunotherapy in atherosclerotic mice and non-human primates.

In the version of this Article originally published, the surname of the author Edward A. Fisher was spelt incorrectly as 'Fischer'. This has now been corrected.

Assessment of muscle function using hybrid PET/MRI: comparison of 18F-FDG PET and T2-weighted MRI for quantifying muscle activation in human subjects.

PURPOSE: The aim of this study was to determine the relationship between relative glucose uptake and MRI T 2 changes in skeletal muscles following resistance exercise using simultaneous PET/MRI scans. METHODS: Ten young healthy recreationally active men (age 21 - 28 years) were injected with 18F-FDG while activating the quadriceps of one leg with repeated knee extension exercises followed by hand-grip exercises for one arm. Immediately following the exercises, the subjects were scanned simultaneously with 18F-FDG PET/MRI and muscle groups were evaluated for increases in 18F-FDG uptake and MRI T 2 values. RESULTS: A significant linear correlation between 18F-FDG uptake and changes in muscle T 2 (R 2 = 0.71) was found. for both small and large muscles and in voxel to voxel comparisons. Despite large intersubject differences in muscle recruitment, the linear correlation between 18F-FDG uptake and changes in muscle T 2 did not vary among subjects. CONCLUSION: This is the first assessment of skeletal muscle activation using hybrid PET/MRI and the first study to demonstrate a high correlation between 18F-FDG uptake and changes in muscle T 2 with physical exercise. Accordingly, it seems that changes in muscle T 2 may be used as a surrogate marker for glucose uptake and lead to an improved insight into the metabolic changes that occur with muscle activation. Such knowledge may lead to improved treatment strategies in patients with neuromuscular pathologies such as stroke, spinal cord injuries and muscular dystrophies.

Transthoracic Doppler echocardiography compared with positron emission tomography for assessment of coronary microvascular dysfunction: The iPOWER study.

BACKGROUND: Coronary microvascular function can be assessed by transthoracic Doppler echocardiography as a coronary flow velocity reserve (TTDE CFVR) and by positron emission tomography as a myocardial blood flow reserve (PET MBFR). PET MBFR is regarded the noninvasive reference standard for measuring coronary microvascular function but has limited availability. We compared TTDE CFVR with PET MBFR in women with angina pectoris and no obstructive coronary artery disease and assessed repeatability of TTDE CFVR. METHODS: From a cohort of women with angina and no obstructive coronary artery stenosis at invasive coronary angiography, TTDE CFVR by dipyridamole induced stress and MBFR by rubidium-82 PET with adenosine was successfully measured in 107 subjects. Repeatability of TTDE CFVR was assessed in 10 symptomatic women and in 10 healthy individuals. RESULTS: MBFR was systematically higher than CFVR. Median MBFR (interquartile range, IQR) was 2.68 (2.29-3.10) and CFVR (IQR) was 2.31 (1.89-2.72). Pearson's correlation coefficient was 0.36 (p<0.01). Limits of agreement (2·standard deviation) assessed by the Bland-Altman (confidence interval, CI) method was 1.49 (1.29;1.69) and unaffected by time-interval between examinations. Results were similar when adjusting for rate pressure product or focusing on perfusion of the left anterior descending artery region. Limits of agreement (CI) for repeated CFVR in 10 healthy individuals and in 10 women with angina was 0.44 (0.21;0.68) and 0.48 (0.22; 0.74), respectively. CONCLUSION: CFVR had a good repeatability, but the agreement between CFVR and MBFR was modest. Divergence could be due to methodology differences; TTDE estimates flow velocities whereas PET estimates myocardial blood flow.

Copenhagen comorbidity in HIV infection (COCOMO) study: a study protocol for a longitudinal, non-interventional assessment of non-AIDS comorbidity in HIV infection in Denmark.

BACKGROUND: Modern combination antiretroviral therapy (cART) has improved survival for people living with HIV (PLWHIV). Non-AIDS comorbidities have replaced opportunistic infections as leading causes of mortality and morbidity, and are becoming a key health concern as this population continues to age. The aim of this study is to estimate the prevalence and incidence of non-AIDS comorbidity among PLWHIV in Denmark in the cART era and to determine risk factors contributing to the pathogenesis. The study primarily targets cardiovascular, respiratory, and hepatic non-AIDS comorbidity. METHODS/DESIGN: The Copenhagen comorbidity in HIV-infection (COCOMO) study is an observational, longitudinal cohort study. The study was initiated in 2015 and recruitment is ongoing with the aim of including 1500 PLWHIV from the Copenhagen area. Follow-up examinations after 2 and 10 years are planned. Uninfected controls are derived from the Copenhagen General Population Study (CGPS), a cohort study including 100,000 uninfected participants from the same geographical region. Physiological and biological measures including blood pressure, ankle-brachial index, electrocardiogram, spirometry, exhaled nitric oxide, transient elastography of the liver, computed tomography (CT) angiography of the heart, unenhanced CT of the chest and upper abdomen, and a number of routine biochemical analysis are uniformly collected in participants from the COCOMO study and the CGPS. Plasma, serum, buffy coat, peripheral blood mononuclear cells (PBMC), urine, and stool samples are collected in a biobank for future studies. Data will be updated through periodical linking to national databases. DISCUSSION: As life expectancy for PLWHIV improves, it is essential to study long-term impact of HIV and cART. We anticipate that findings from this cohort study will increase knowledge on non-AIDS comorbidity in PLWHIV and identify targets for future interventional trials. Recognizing the demographic, clinical and pathophysiological characteristics of comorbidity in PLWHIV may help inform development of new guidelines and enable us to move forward to a more personalized HIV care. TRIAL REGISTRATION: ClinicalTrials.gov: NCT02382822 .

A Delphic consensus assessment: imaging and biomarkers in gastroenteropancreatic neuroendocrine tumor disease management.

The complexity of the clinical management of neuroendocrine neoplasia (NEN) is exacerbated by limitations in imaging modalities and a paucity of clinically useful biomarkers. Limitations in currently available imaging modalities reflect difficulties in measuring an intrinsically indolent disease, resolution inadequacies and inter-/intra-facility device variability and that RECIST (Response Evaluation Criteria in Solid Tumors) criteria are not optimal for NEN. Limitations of currently used biomarkers are that they are secretory biomarkers (chromogranin A, serotonin, neuron-specific enolase and pancreastatin); monoanalyte measurements; and lack sensitivity, specificity and predictive capacity. None of them meet the NIH metrics for clinical usage. A multinational, multidisciplinary Delphi consensus meeting of NEN experts (n = 33) assessed current imaging strategies and biomarkers in NEN management. Consensus (>75%) was achieved for 78% of the 142 questions. The panel concluded that morphological imaging has a diagnostic value. However, both imaging and current single-analyte biomarkers exhibit substantial limitations in measuring the disease status and predicting the therapeutic efficacy. RECIST remains suboptimal as a metric. A critical unmet need is the development of a clinico-biological tool to provide enhanced information regarding precise disease status and treatment response. The group considered that circulating RNA was better than current general NEN biomarkers and preliminary clinical data were considered promising. It was resolved that circulating multianalyte mRNA (NETest) had clinical utility in both diagnosis and monitoring disease status and therapeutic efficacy. Overall, it was concluded that a combination of tumor spatial and functional imaging with circulating transcripts (mRNA) would represent the future strategy for real-time monitoring of disease progress and therapeutic efficacy.

Comparison of (18)F-FET and (18)F-FLT small animal PET for the assessment of anti-VEGF treatment response in an orthotopic model of glioblastoma.

BACKGROUND: The radiolabeled amino acid O-(2-(18)F-fluoroethyl)-L-tyrosine (FET) and thymidine analogue 3'-deoxy-3'-(18)F-fluorothymidine (FLT) are widely used for positron emission tomography (PET) brain tumor imaging; however, comparative studies are scarce. The aim of this study therefore was to compare FLT and FET PET for the assessment of anti-VEGF response in glioblastoma xenografts. METHODS: Xenografts with confirmed intracranial glioblastoma were treated with anti-VEGF therapy (B20-4.1) or saline as control. Weekly bioluminescence imaging (BLI), FLT and FET PET/CT were used to follow treatment response. Tracer uptake of FLT and FET was quantified using maximum standardized uptake (SUVmax) values and tumor-to-background ratios (TBRs). Survival, the Ki67 proliferation index and micro-vessel density (MVD) were evaluated. RESULTS: In contrast to FLT TBRs, FET TBRs were significantly lower as early as one week after treatment initiation in the anti-VEGF group as compared to the control group. Following two weeks of treatment, both FLT and FET TBRs were significantly lower in the anti-VEGF group. In contrast, no significant difference between the treatment groups was detected using BLI. Furthermore, we found a significantly lower MVD in the anti-VEGF group as compared to the control group. However, we found no difference in the Ki67 proliferation index or mean survival time. CONCLUSION: FET appears to be a more sensitive tracer than FLT to measure early response to anti-VEGF therapy with PET. Advances in knowledge and implications for patient care FET PET appears to be an early predictor of anti-VEGF efficacy. Confirmation of these results in clinical studies is needed.

Cardiac (82)Rb PET/CT for fast and non-invasive assessment of microvascular function and structure in asymptomatic patients with type 2 diabetes.

AIMS/HYPOTHESIS: Coronary flow reserve (CFR) and coronary artery calcium (CAC) represent functional and structural aspects of atherosclerosis. We examined the prevalence of reduced CFR and high CAC scores in three predefined groups of participants without known cardiovascular disease: (1) patients with type 2 diabetes and albuminuria; (2) patients with type 2 diabetes and normoalbuminuria; and (3) non-diabetic controls. METHODS: In a cross-sectional design, cardiac (82)Rb positron emission tomography/computed tomography was conducted in 60 patients with type 2 diabetes who were free of overt cardiovascular disease and who were stratified by normoalbuminuria (<30 mg/24 h) (n = 30; age [mean ± SD] 60.9 ± 10.1 years) and albuminuria (≥ 30 mg/24 h) (n = 30; age 65.6 ± 4.8 years), and in 30 healthy, non-diabetic controls (age 59.8 ± 9.9 years). RESULTS: In controls, normoalbuminuric and albuminuric patients, CFR was 3.0 ± 0.8, 2.6 ± 0.8 and 2.0 ± 0.5, respectively. Reduced CFR (<2.5) was observed in 16.7%, 40.0% and 83.3% of participants, respectively, and median (interquartile range) CAC scores were 0 (0-81), 36 (1-325) and 370 (152-1,025), respectively (p for trend <0.01). After adjustment, the difference in CFR and CAC between albuminuric patients and controls remained significant (p ≤ 0.001). There were trends towards lower CFR and higher CAC scores in normoalbuminuric patients vs controls (p ≤ 0.023) and towards higher CAC scores in albuminuric vs normoalbuminuric patients (p = 0.026). In multivariate regression analysis, a higher urinary albumin excretion rate (UAER) tended to predict reduced CFR in the total population (p = 0.045). When the CAC score was added, there was also a trend (p = 0.032) towards an inverse association with reduced CFR. CONCLUSIONS/INTERPRETATION: Type 2 diabetic patients who were free of overt cardiovascular disease had a high prevalence of coronary microvascular dysfunction, especially with concomitant albuminuria, suggesting a common microvascular impairment occurring in multiple microvascular beds. Prospective studies are needed to show the prognostic significance of this finding.

64Cu-DOTATATE for Noninvasive Assessment of Atherosclerosis in Large Arteries and Its Correlation with Risk Factors: Head-to-Head Comparison with 68Ga-DOTATOC in 60 Patients.

UNLABELLED: The somatostatin receptor subtype 2 is expressed on macrophages, an abundant cell type in the atherosclerotic plaque. Visualization of somatostatin receptor subtype 2, for oncologic purposes, is frequently made using the DOTA-derived somatostatin analogs DOTATOC or DOTATATE for PET. We aimed to compare the uptake of the PET tracers (68)Ga-DOTATOC and (64)Cu-DOTATATE in large arteries, in the assessment of atherosclerosis by noninvasive imaging technique, combining PET and CT. Further, the correlation of uptake and cardiovascular risk factors was investigated. METHODS: Sixty consecutive patients with neuroendocrine tumors underwent both (68)Ga-DOTATOC and (64)Cu-DOTATATE PET/CT scans, in random order. For each scan, the maximum and mean standardized uptake values (SUVs) were calculated in 5 arterial segments. In addition, the blood-pool-corrected target-to-background ratio was calculated. Uptake of the tracers was correlated with cardiovascular risk factors collected from medical records. RESULTS: We found detectable uptake of both tracers in all arterial segments studied. Uptake of (64)Cu-DOTATATE was significantly higher than (68)Ga-DOTATOC in the vascular regions both when calculated as maximum and mean uptake. There was a significant association between Framingham risk score and the overall maximum uptake of (64)Cu-DOTATATE using SUV (r = 0.4; P = 0.004) as well as target-to-background ratio (r = 0.3; P = 0.04), whereas no association was found with (68)Ga-DOTATOC. The association of risk factors and maximum SUV of (64)Cu-DOTATATE was found driven by body mass index, smoking, diabetes, and coronary calcium score (P < 0.001, P = 0.01, P = 0.005, and P = 0.03, respectively). CONCLUSION: In a series of oncologic patients, vascular uptake of (68)Ga-DOTATOC and (64)Cu-DOTATATE was found, with highest uptake of the latter. Uptake of (64)Cu-DOTATATE, but not of (68)Ga-DOTATOC, was correlated with cardiovascular risk factors, suggesting a potential role for (64)Cu-DOTATATE in the assessment of atherosclerosis.

18F-FET microPET and microMRI for anti-VEGF and anti-PlGF response assessment in an orthotopic murine model of human glioblastoma.

BACKGROUND: Conflicting data exist for anti-cancer effects of anti-placental growth factor (anti-PlGF) in combination with anti-VEGF. Still, this treatment combination has not been evaluated in intracranial glioblastoma (GBM) xenografts. In clinical studies, position emission tomography (PET) using the radiolabeled amino acid O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET) and magnetic resonance imaging (MRI) add complementary but distinct information about glioma growth; however, the value of 18F-FET MicroPET combined with MicroMRI has not been investigated preclinically. Here we examined the use of 18F-FET MicroPET and MicroMRI for evaluation of anti-VEGF and anti-PlGF treatment response in GBM xenografts. METHODS: Mice with intracranial GBM were treated with anti-VEGF, anti-PlGF + anti-VEGF or saline. Bioluminescence imaging (BLI), 18F-FET MicroPET and T2-weighted (T2w)-MRI were used to follow tumour development. Primary end-point was survival, and tumours were subsequently analysed for Ki67 proliferation index and micro-vessel density (MVD). Further, PlGF and VEGFR-1 expression were examined in a subset of the xenograft tumours and in 13 GBM patient tumours. RESULTS: Anti-VEGF monotherapy increased survival and decreased 18F-FET uptake, BLI and MVD, while no additive effect of anti-PlGF was observed. 18F-FET SUV max tumour-to-brain (T/B) ratio was significantly lower after one week (114 ± 6%, n = 11 vs. 143 ± 8%, n = 13; p = 0.02) and two weeks of treatment (116 ± 12%, n = 8 vs. 190 ± 24%, n = 5; p = 0.02) in the anti-VEGF group as compared with the control group. In contrast, T2w-MRI volume was unaffected by anti-VEGF. Gene expression of PlGF and VEGFR-1 in xenografts was significantly lower than in patient tumours. CONCLUSION: 18F-FET PET was feasible for anti-angiogenic response evaluation and superior to T2w-MRI; however, no additive anti-cancer effect of anti-PlGF and anti-VEGF was observed. Thus, this study supports use of 18F-FET PET for response evaluation in future studies.

[18F]FLT PET for non-invasive assessment of tumor sensitivity to chemotherapy: studies with experimental chemotherapy TP202377 in human cancer xenografts in mice.

AIM: 3'-deoxy-3'-[¹8F]fluorothymidine ([18F]FLT) is a tracer used to assess cell proliferation in vivo. The aim of the study was to use [18F]FLT positron emission tomography (PET) to study non-invasively early anti-proliferative effects of the experimental chemotherapeutic agent TP202377 in both sensitive and resistant tumors. METHODS: Xenografts in mice from 3 human cancer cell lines were used: the TP202377 sensitive A2780 ovary cancer cell line (n = 8-16 tumors/group), the induced resistant A2780/Top216 cell line (n = 8-12 tumors/group) and the natural resistant SW620 colon cancer cell line (n = 10 tumors/group). In vivo uptake of [18F]FLT was studied at baseline and repeated 6 hours, Day 1, and Day 6 after TP202377 treatment (40 mg/kg i.v.) was initiated. Tracer uptake was quantified using small animal PET/CT. RESULTS: TP202377 (40 mg/kg at 0 hours) caused growth inhibition at Day 6 in the sensitive A2780 tumor model compared to the control group (P<0.001). In the A2780 tumor model TP202377 treatment caused significant decrease in uptake of [18F]FLT at 6 hours (-46%; P<0.001) and Day 1 (-44%; P<0.001) after treatment start compared to baseline uptake. At Day 6 uptake was comparable to baseline. Treatment with TP202377 did not influence tumor growth or [18F]FLT uptake in the resistant A2780/Top216 and SW620 tumor models. In all control groups uptake of [18F]FLT did not change. Ki67 gene expression paralleled [18F]FLT uptake. CONCLUSION: Treatment of A2780 xenografts in mice with TP202377 (single dose i.v.) caused a significant decrease in cell proliferation assessed by [18F]FLT PET after 6 hours. Inhibition persisted at Day 1; however, cell proliferation had returned to baseline at Day 6. In the resistant A2780/Top216 and SW620 tumor models uptake of [18F]FLT did not change after treatment. With [18F]FLT PET it was possible to distinguish non-invasively between sensitive and resistant tumors already 6 hours after treatment initiation.

Use of cis-[18F]fluoro-proline for assessment of exercise-related collagen synthesis in musculoskeletal connective tissue.

Protein turnover in collagen rich tissue is influenced by exercise, but can only with difficulty be studied in vivo due to use of invasive procedure. The present study was done to investigate the possibility of applying the PET-tracer, cis-[(18)F]fluoro-proline (cis-Fpro), for non-invasive assessment of collagen synthesis in rat musculoskeletal tissues at rest and following short-term (3 days) treadmill running. Musculoskeletal collagen synthesis was studied in rats at rest and 24 h post-exercise. At each session, rats were PET scanned at two time points following injection of cis-FPro: (60 and 240 min p.i). SUV were calculated for Achilles tendon, calf muscle and tibial bone. The PET-derived results were compared to mRNA expression of collagen type I and III. Tibial bone had the highest SUV that increased significantly (p<0.001) from the early (60 min) to the late (240 min) PET scan, while SUV in tendon and muscle decreased (p<0.001). Exercise had no influence on SUV, which was contradicted by an increased gene expression of collagen type I and III in muscle and tendon. The clearly, visible uptake of cis-Fpro in the collagen-rich musculoskeletal tissues is promising for multi-tissue studies in vivo. The tissue-specific differences with the highest basal uptake in bone are in accordance with earlier studies relying on tissue incorporation of isotopic-labelled proline. A possible explanation of the failure to demonstrate enhanced collagen synthesis following exercise, despite augmented collagen type I and III transcription, is that SUV calculations are not sensitive enough to detect minor changes in collagen synthesis. Further studies including kinetic compartment modeling must be performed to establish whether cis-Fpro can be used for non-invasive in-vivo assessment of exercise-induced changes in musculoskeletal collagen synthesis.

Noninvasive 64Cu-ATSM and PET/CT assessment of hypoxia in rat skeletal muscles and tendons during muscle contractions.

UNLABELLED: The purpose of the present study was to investigate exercise-related changes in oxygenation in rat skeletal muscles and tendons noninvasively with PET/CT and the hypoxia-selective tracer (64)Cu-diacetyl bis(N(4)-methylthiosemicarbazone) (ATSM) and to quantitatively study concomitant changes in gene expression of 2 hypoxia-related genes, hypoxia-inducible factor 1alpha (HIF1alpha) and carbonic anhydrase III (CAIII). METHODS: Two groups of Wistar rats performed 1-leg contractions of the calf muscle by electrostimulation of the sciatic nerve. After 10 min of muscle contractions, (64)Cu-ATSM was injected and contractions were continued for 20 min. PET/CT of both hind limbs was performed immediately and 1 h after the contractions. The exercise group (n = 8) performed only muscle contractions as described, whereas the other group, exercise plus cuff (n = 8), in addition underwent cuff-induced hypoxia during the first PET/CT scan. Standardized uptake values (SUVs) were calculated for the Achilles tendons and triceps surae muscles and were correlated to gene expression of HIF1alpha and CAIII using real-time polymerase chain reaction. RESULTS: Immediately after the contractions, uptake of (64)Cu-ATSM was significantly increased, by approximately 1.5-fold in muscles and 1.3-fold in tendons, compared with resting conditions. The significant increase was maintained in late PET scans in stimulated muscles and tendons independently of cuff application. In muscles, SUV correlated significantly with gene expression of HIF1alpha and CAIII, whereas this coherence was not found in tendons. CONCLUSION: We found enhanced uptake of (64)Cu-ATSM in both early and late PET scans, thereby supporting the possibility that (64)Cu-ATSM registers exercise-induced transient hypoxia in both skeletal muscles and force-transmitting tendons. The fact that skeletal muscles but not tendons showed upregulation of HIF1alpha and CAIII could indicate that healthy tendons are less responsive than skeletal muscles to low levels of oxygen.