Constantinos D. Anagnostopoulos

Myocardial perfusion scintigraphy: the evidence.

This review summarises the evidence for the role of myocardial perfusion scintigraphy (MPS) in patients with known or suspected coronary artery disease. It is the product of a consensus conference organised by the British Cardiac Society, the British Nuclear Cardiology Society and the British Nuclear Medicine Society and is endorsed by the Royal College of Physicians of London and the Royal College of Radiologists. It was used to inform the UK National Institute of Clinical Excellence in their appraisal of MPS in patients with chest pain and myocardial infarction. MPS is a well-established, non-invasive imaging technique with a large body of evidence to support its effectiveness in the diagnosis and management of angina and myocardial infarction. It is more accurate than the exercise ECG in detecting myocardial ischaemia and it is the single most powerful technique for predicting future coronary events. The high diagnostic accuracy of MPS allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularisation. This in turn allows more appropriate utilisation of resources, with the potential for both improved clinical outcomes and greater cost-effectiveness. Evidence from modelling and observational studies supports the enhanced cost-effectiveness associated with MPS use. In patients presenting with stable or acute chest pain, strategies of investigation involving MPS are more cost-effective than those not using the technique. MPS also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly and those with diabetes, and its use will have a favourable impact on cost-effectiveness in these groups. MPS is already an integral part of many clinical guidelines for the investigation and management of angina and myocardial infarction. However, the technique is underutilised in the UK, as judged by the inappropriately long waiting times and by comparison with the numbers of revascularisations and coronary angiograms performed. Furthermore, MPS activity levels in this country fall far short of those in comparable European countries, with about half as many scans being undertaken per year. Currently, the number of MPS studies performed annually in the UK is 1,200/million population/year. We estimate the real need to be 4,000/million/year. The current average waiting time is 20 weeks and we recommend that clinically appropriate upper limits of waiting time are 6 weeks for routine studies and 1 week for urgent studies.

EANM/ESC guidelines for radionuclide imaging of cardiac function

Radionuclide imaging of cardiac function represents a number of well-validated techniques for accurate determination of right (RV) and left ventricular (LV) ejection fraction (EF) and LV volumes. These first European guidelines give recommendations for how and when to use first-pass and equilibrium radionuclide ventriculography, gated myocardial perfusion scintigraphy, gated PET, and studies with non-imaging devices for the evaluation of cardiac function. The items covered are presented in 11 sections: clinical indications, radiopharmaceuticals and dosimetry, study acquisition, RV EF, LV EF, LV volumes, LV regional function, LV diastolic function, reports and image display and reference values from the literature of RVEF, LVEF and LV volumes. If specific recommendations given cannot be based on evidence from original, scientific studies, referral is given to “prevailing or general consensus”. The guidelines are designed to assist in the practice of referral to, performance, interpretation and reporting of nuclear cardiology studies for the evaluation of cardiac performance.

EANM procedural guidelines for radionuclide myocardial perfusion imaging with SPECT and SPECT/CT : 2015 revision

Since the publication of the European Association of Nuclear Medicine (EANM) procedural guidelines for radionuclide myocardial perfusion imaging (MPI) in 2005, many small and some larger steps of progress have been made, improving MPI procedures. In this paper, the major changes from the updated 2015 procedural guidelines are highlighted, focusing on the important changes related to new instrumentation with improved image information and the possibility to reduce radiation exposure, which is further discussed in relation to the recent developments of new International Commission on Radiological Protection (ICRP) models. Introduction of the selective coronary vasodilator regadenoson and the use of coronary CT-contrast agents for hybrid imaging with SPECT/CT angiography are other important areas for nuclear cardiology that were not included in the previous guidelines. A large number of minor changes have been described in more detail in the fully revised version available at the EANM home page: http://eanm.org/publications/guidelines/2015_07_EANM_FINAL_myocardial_perfusion_guideline.pdf.

Assessment of myocardial perfusion and viability by Positron Emission Tomography

An important evolution has taken place recently in the field of cardiovascular Positron Emission Tomography (PET) imaging. Being originally a highly versatile research tool that has contributed significantly to advance our understanding of cardiovascular physiology and pathophysiology, PET has gradually been incorporated into the clinical cardiac imaging portfolio contributing to diagnosis and management of patients investigated for coronary artery disease (CAD). PET myocardial perfusion imaging (MPI) has an average sensitivity and specificity around 90% for the detection of angiographically significant CAD and it is also a very accurate technique for prognostication of patients with suspected or known CAD. In clinical practice, Rubidium-82 ((82)Rb) is the most widely used radiopharmaceutical for MPI that affords also accurate and reproducible quantification in absolute terms (ml/min/g) comparable to that obtained by cyclotron produced tracers such as Nitrogen-13 ammonia ((13)N-ammonia) and Oxygen-15 labeled water ((15)O-water). Quantification increases sensitivity for detection of multivessel CAD and it may also be helpful for detection of early stages of atherosclerosis or microvascular dysfunction. PET imaging combining perfusion with myocardial metabolism using (18)F-Fluorodeoxyglucose ((18)F FDG), a glucose analog, is an accurate standard for assessment of myocardial hibernation and risk stratification of patients with left ventricular dysfunction of ischemic etiology. It is helpful for guiding management decisions regarding revascularization or medical treatment and predicting improvement of symptoms, exercise capacity and quality of life post-revascularization. The strengths of PET can be increased further with the introduction of hybrid scanners, which combine PET with computed tomography (PET/CT) or with magnetic resonance imaging (PET/MRI) offering integrated morphological, biological and physiological information and hence, comprehensive evaluation of the consequences of atherosclerosis in the coronary arteries and the myocardium.

High-Dose Adenosine Overcomes the Attenuation of Myocardial Perfusion Reserve Caused by Caffeine

OBJECTIVES We studied whether an increase in adenosine dose overcomes caffeine antagonism on adenosine-mediated coronary vasodilation. BACKGROUND Caffeine is a competitive antagonist at the adenosine receptors, but it is unclear whether caffeine in coffee alters the actions of exogenous adenosine, and whether the antagonism can be surmounted by increasing the adenosine dose. METHODS Myocardial perfusion scintigraphy (MPS) was used to assess adenosine-induced hyperemia in 30 patients before (baseline) and after coffee ingestion (caffeine). At baseline, patients received 140 microg/kg/min of adenosine combined with low-level exercise. For the caffeine study, 12 patients received 140 microg/kg/min of adenosine (standard) and 18 patients received 210 microg/kg/min (high dose) after caffeine intake (200 mg). Myocardial perfusion was assessed semiquantitatively and quantitatively, and perfusion defect was characterized according to the presence of reversibility. RESULTS Caffeine reduced the magnitude of perfusion abnormality induced by standard adenosine as measured by the summed difference score (SDS) (12.0 +/- 4.4 at baseline vs. 4.1 +/- 2.1 after caffeine, p < 0.001) as well as defect size (18% [3% to 38%] vs. 8% [0% to 22%], p < 0.01), whereas it had no effect on the abnormalities caused by high-dose adenosine (SDS, 7.7 +/- 4.0 at baseline vs. 7.8 +/- 4.2 after caffeine, p = 0.7). There was good agreement between baseline and caffeine studies for segmental defect category (kappa = 0.72, 95% confidence interval: 0.65 to 0.79) in the high-dose group. An increase in adenosine after caffeine intake was well tolerated. CONCLUSIONS Caffeine in coffee attenuates adenosine-induced coronary hyperemia and, consequently, the detection of perfusion abnormality by adenosine MPS. This can be overcome by increasing the adenosine dose without compromising test tolerability.

Therapeutic Effects of an Anti-Myc Drug on Mouse Pancreatic Cancer

BACKGROUND Pancreatic ductal adenocarcinoma (PDA) is frequently driven by oncogenic KRAS(KRAS*) mutations. We developed a mouse model of KRAS*-induced PDA and, based on genetic results demonstrating that KRAS* tumorigenicity depends on Myc activity, we evaluated the therapeutic potential of an orally administered anti-Myc drug. METHODS We tested the efficacy of Mycro3, a small-molecule inhibitor of Myc-Max dimerization, in the treatment of mouse PDA (n = 9) and also of xenografts of human pancreatic cancer cell lines (NOD/SCID mice, n = 3-12). Tumor responses to the drug were evaluated by PET/CT imaging, and histological, immunohistochemical, molecular and microarray analyses. The Students t test was used for differences between groups. All statistical tests were two-sided. RESULTS Transgenic overexpression of KRAS* in the pancreas resulted in pancreatic intraepithelial neoplasia in two-week old mice, which developed invasive PDA a week later and became moribund at one month. However, this aggressive form of pancreatic tumorigenesis was effectively prevented by genetic ablation of Myc specifically in the pancreas. We then treated moribund, PDA-bearing mice daily with the Mycro3 Myc-inhibitor. The mice survived until killed at two months. PET/CT image analysis (n = 5) demonstrated marked shrinkage of PDA, while immunohistochemical analyses showed an increase in cancer cell apoptosis and reduction in cell proliferation (treated/untreated proliferation index ratio: 0.29, P < .001, n = 3, each group). Tumor growth was also drastically attenuated in Mycro3-treated NOD/SCID mice (n = 12) carrying orthotopic or heterotopic xenografts of human pancreatic cancer cells (eg, mean tumor weight ± SD of treated heterotopic xenografts vs vehicle-treated controls: 15.2±5.8 mg vs 230.2±43.9 mg, P < .001). CONCLUSION These results provide strong justification for eventual clinical evaluation of anti-Myc drugs as potential chemotherapeutic agents for the treatment of PDA.

Intratumoral accumulation of podoplanin-expressing lymph node stromal cells promote tumor growth through elimination of CD4+ tumor-infiltrating lymphocytes

ABSTRACT The beneficial effects of checkpoint blockade in tumor immunotherapy are limited to patients with increased tumor-infiltrating lymphocytes (TILs). Delineation of the regulatory networks that orchestrate the presence of TILs holds great promise for the design of effective immunotherapies. Podoplanin/gp38 (PDPN)-expressing lymph node stromal cells (LNSCs) are present in tumor stroma; however, their effect in the regulation of TILs remains elusive. Herein we demonstrate that intratumor injection of ex-vivo-isolated PDPN+ LNSCs into melanoma-bearing mice induces elimination of TILs and promotes tumor growth. In support, PDPN+ LNSCs exert their function through direct inhibition of CD4+ T cell proliferation in a cell-to-cell contact independent fashion. Mechanistically, we demonstrate that PDPN+ LNSCs mediate T cell growth arrest and induction of apoptosis to activated CD69+CD4+ T cells. Importantly, LTbR-Ig-mediated blockade of PDPN+ LNSCs expansion and function significantly attenuates melanoma tumor growth and enhances the infiltration and proliferation of CD4+ TILs. Overall, our findings decipher a novel role of PDPN-expressing LNSCs in the elimination of CD4+ TILs and propose a new target for tumor immunotherapy.

Initial in vitro and in vivo assessment of Au@DTDTPA-RGD nanoparticles for Gd-MRI and 68Ga-PET dual modality imaging

Gadolinium chelate coated gold nanoparticles (Au@DTDTPA) can be applied as contrast agents for both in vivo X-ray and magnetic resonance imaging. In this work, our aim was to radiolabel and evaluate this gold nanoparticle with Ga-68, in order to produce a dual modality PET/MRI imaging probe. For a typical preparation of 68Ga-labeled nanoparticles, the Au@DTDTPA nanoparticles (Au@DTDTPA/Au@DTDTPA-RGD) were mixed with ammonium acetate buffer, pH 5 and 40 MBq of 68Ga eluate. The mixture was then incubated for 45 min at 65 AaC. Radiochemical purity was determined by ITLC. In vitro stability of both radiolabeled species was assessed in saline and serum. In vitro cell binding experiments were performed on integrin ανβ3 receptor-positive U87MG cancer cells. Non-specific Au@DTDTPA was used for comparison. Ex vivo biodistribution studies and in vivo PET and MRI imaging studies in U87MG tumor-bearing SCID mice followed. The Au@DTDTPA nanoparticles were labeled with Gallium-68 at high radiochemical yield (>95%) and were stable at RT, and in the presence of serum, for up to 3 h. The cell binding assay on U87MG glioma cells proved that 68Ga-cRGD-Au@DTDTPA had specific recognition for these cells. Biodistribution studies in U87MG tumor-bearing SCID mice showed that the tumor to muscle ratio increased from 1 to 2 h p.i. (3,71 ± 0.22 and 4,69 ± 0.09 respectively), showing a clear differentiation between the affected and the non-affected tissue. The acquired PET and MRI images were in accordance to the ex vivo biodistribution results. The preliminary results of this study warrant the need for further development of Au@DTDTPA nanoparticles radiolabeled with Ga-68, as possible dual-modality PET/MRI imaging agents.

Prediction of left ventricular remodelling by radionuclide imaging

Left ventricular remodelling is a complex process by which mechanical, neurohormonal and genetic factors alter ventricular structure and function leading to reduced mechanical performance, electrical instability and sudden death [1]. It is an important aspect of heart failure progression, characterized by dilatation and change of shape of the left ventricle (LV) as well as alterations in the ventricular wall which include hypertrophy, loss of myocytes and increased interstitial fibrosis [2]. At the molecular level, it is characterized by a regression to the fetal pattern, i.e. increase of β-myosin heavy chain, α-actin, atrial natriuretic peptide overexpression, sarco/endoplasmic reticulum CaATPase activity decrease and a shift of myocardial metabolism towards glucose utilization [3, 4]. Acute myocardial infarction (MI) is a common cause of LV remodelling. It is estimated that despite primary percutaneous coronary intervention (PCI) and standard current therapy, around 30% of anterior MIs will develop remodelling. The three major biomechanical mechanisms contributing to the increase of LV volumes over time after MI are: (1) expansion of the infarct in the subacute phase [5], (2) subsequent non-ischaemic infarct extension into the adjacent non-infarcted region [6, 7] and (3) hypertrophy and dilatation of non-infarcted myocardium in the chronic phase [8–10]. The main factors associated with remodelling are size of infarction, anterior location and late or unsuccessful (or absence of) reperfusion therapy both at the epicardial vessel level and at the microvasculature level. LV remodelling, however, is a potentially reversible or even possibly preventable process. Regression is manifested as a return to a more normal ventricular size and shape and appears to be a good predictor of a reduction in morbidity and mortality [2, 11]. Several trials on post acute MI patients have demonstrated that this can be achieved by a combination of treatment regimes [12]. This is understandable considering that the three aforementioned mechanisms operate in different regions of the LV and during different time frames after MI, thus making it unlikely for any single drug to be completely effective in addressing all three mechanisms [12]. A major determinant to the selection of the appropriate treatment is the propensity of the underlying MI to result in LV remodelling. Therefore, accurate monitoring of post acute MI patients to identify those who are likely to develop LV remodelling is of great importance. Based on the mechanistic rationale described above, monitoring is performed with non-invasive imaging and usually includes assessment of heart size, shape and mass, ejection fraction (EF), end-diastolic and end-systolic volumes and regional contractility. Cardiac magnetic resonance (CMR) is the gold standard to assess these parameters as well microvascular obstruction and infarct size. A consistent finding from the CMR literature in the post acute MI setting is that scar size is a key determinant of long-term LV remodelling. Moreover, there are distinct time-dependent patterns of infarct healing and LV remodelling which suggest that the timing of CMR performance is important for assessment of infarct size and prediction of C. D. Anagnostopoulos (*) Nuclear Medicine Division, PET/CT Department, Clinical Research Center, Biomedical Research Foundation Academy of Athens, 4 Soranou Ephessiou St., 115 27 Athens, Greece e-mail: cdanagnostopoulos@bioacademy.gr

3D reconstruction of coronary arteries and atherosclerotic plaques based on computed tomography angiography images

Abstract The purpose of this study is to present a new semi-automated methodology for three-dimensional (3D) reconstruction of coronary arteries and their plaque morphology using Computed Tomography Angiography (CTA) images. The methodology is summarized in seven stages: pre-processing of the acquired CTA images, extraction of the vessel tree centerline, estimation of a weight function for lumen, outer wall and calcified plaque, lumen segmentation, outer wall segmentation, plaque detection, and finally 3D surfaces construction. The methodology was evaluated using both expert’s manual annotations and estimations of a recently presented Intravascular Ultrasound (IVUS) reconstruction method. As far as the manual annotation validation process is concerned, the mean value of the comparison metrics for the 3D segmentation were 0.749 and 1.746 for the Dice coefficient and Hausdorff distance, respectively. On the other hand, the correlation coefficients for the degree of stenosis 1, the degree of stenosis 2, the plaque burden, the minimal lumen area and the minimal lumen diameter, when comparing the derived from the proposed methodology 3D models with the IVUS reconstructed models, were 0.79, 0.77, 0.75, 0.85, 0.81, respectively. The proposed methodology is an innovative approach for reconstruction of coronary arteries, since it provides 3D models of the lumen, the outer wall and the CP plaques, using the minimal user interaction. Its first implementation demonstrated that it provides an accurate reconstruction of coronary arteries and thus, it may have a wide clinical applicability.