Alexandros Georgakopoulos

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.

Impact of 18F-FDG PET/CT on therapeutic decisions in patients with colorectal cancer and liver metastases.

OBJECTIVES Surgical resection and radio-frequency ablation (RFA) are standard therapeutic procedures for colorectal metastases confined to the liver. The presence of extrahepatic disease has a significant effect on the management of these patients. The goal of this study is to assess the value of positron emission tomography/computed tomography with 18F-fluorodeoxyglucose (18F-FDG PET/CT) in the decision making whether to perform RFA or surgical resection of liver metastases in patients with metastatic colorectal cancer. MATERIAL AND METHODS Thirty-five consecutive patients (23 men, 12 women; age range: 46-78 years) with colorectal carcinoma and liver metastases were prospectively enrolled. Nineteen of them were considered candidates for surgical resection and 16 for RFA. All underwent 18F-FDG PET/CT, helical computed tomography of the chest and abdomen and, some of them, magnetic resonance imaging of the abdomen. The 18F-FDG PET/CT studies were performed within 4 weeks from conventional imaging, and additional findings were later confirmed or not, either by histology or follow up. RESULTS In the surgical candidate group, 18F-FDG PET/CT detected extrahepatic disease, missed by conventional imaging, in 9/19 patients (47.3%). These findings directly altered the management in 7 patients (36.8%). In the group of RFA candidates, 18F-FDG PET/CT detected additional extrahepatic disease in 4/16 patients (25%) and directly altered management in all of them. Overall, in 11/35 patients (31.4%), 18F-FDG PET/CT detected extrahepatic metastatic disease. CONCLUSION In patients with colorectal cancer and liver metastases, 18F-FDG PET/CT provides relevant additional information that has significant impact on management.

Quantitative evaluation of the memory bias effect in ROC studies with PET/CT

PURPOSE. The purpose of the study was to evaluate the memory bias effect in ROC experiments with tomographic data and, specifically, in the evaluation of two different PET/CT protocols for the detection and diagnosis of recurrent thyroid cancer. MATERIALS AND METHODS. Two readers participated in an ROC experiment that evaluated tomographic images from 43 patients followed up for thyroid cancer recurrence. Readers evaluated first whole body PET/CT scans of the patients and then a combination of whole body and high-resolution head and neck scans of the same patients. The second set was read twice. Once within 48 hours of the first set and the second time at least a month later. The detection and diagnostic performances of the readers in the three reading sessions were assessed with the DBMMRMC and LABMRMC software using the area under the ROC curve as a performance index. Performances were also evaluated by comparing the number and the size of the detected abnormal foci among the three readings. RESULTS. There was no performance difference between first and second treatments. There were statistically significant differences between first and third, and second and third treatments showing that memory can seriously affect the outcome of ROC studies. CONCLUSION. Despite the fact that tomographic data involve numerous image slices per patient, the memory bias effect is present and substantial and should be carefully eliminated from analogous ROC experiments.

Inflamed human carotid plaques evaluated by PET/CT exhibit increased temperature: insights from an in vivo study

Aims To explore the relationship between temperature measurements derived by microwave radiometry (MWR) and carotid flurodeoxyglucose (FDG) uptake and assess their association with histological and immunohistochemistry findings in patients with high-grade carotid stenosis. Methods and results In 21 patients undergoing carotid endarterectomy, carotid inflammation was evaluated by both FDG positron emission/computed tomography (FDG-PET/CT) imaging and MWR measurements. Carotid inflammation was assessed by PET/CT as target-to-background ratio (TBR) by obtaining measurements in consecutive axial slices 2 cm below to 2 cm above the carotid bifurcation. Temperature difference (ΔT) by MWR was assigned as the maximum-minimum temperature measurements over the corresponding carotid segments. The extent of lipid core, calcification as well as CD68 and CD31 levels were also assessed. There was a significant correlation between ΔT values and FDG uptake (R = 0.40, P = 0.01), but no correlation between the degree of angiographic stenosis and ΔT values (R = -0.02, P = 0.91) or PET/CT measurements (R = -0.28, P = 0.86). Patients with plaques containing high lipid core extension or low calcification exhibited higher ΔT (P = 0.001 and P < 0.001, respectively) and FDG uptake values (P = 0.02 and P = 0.02, respectively). Patients with plaques containing increased CD68 expression exhibited higher ΔT and FDG uptake measurements. Conclusion Carotid plaque inflammation was evaluated by temperature measurements, which were correlated with FDG-PET/CT indices, confirmed by histopathology and immunohistochemistry findings. Structural changes did not predict inflammatory process. The implications of these findings in risk stratification and management of patients with carotid atherosclerosis and the precise algorithm for potential clinical utilization of MWR and PET/CT remain to be determined.

18 F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Infected Polycystic Kidney Disease

A positron emission tomography/computed tomography (PET/CT) study using 18 F-fluorodeoxyglucose ( 18 F-FDG) was performed in a 54-year-old female with polycystic kidney disease, fever, and abdominal discomfort. Cyst′s infection was suspected, but CT and U/S findings were not specific to accurately depict pyocysts and guide surgical treatment. In PET/CT, both kidneys are enlarged with multiple cysts and little remaining parenchyma. There is intense focal or ring-shaped FDG uptake in cysts in the upper and lower poles of the left kidney indicative of active infection. There is also increased FDG uptake in para-aortic lymph nodes bilaterally. Hepatic and right renal cysts do not present increased FDG uptake. As this case illustrates, FDG PET/CT can be helpful for the precise localization of cyst infections in patients with polycystic kidney disease considered for surgical treatment.

Positron Emission Tomography for Risk Assessment of Women Investigated for Coronary Artery Disease

celerates atheroma formation leading to endothelial dysfunction, impaired vasoreactivity, and clinical instability. Focal epicardial disease can therefore be a later manifestation of atherosclerosis that follows the aforementioned pathophysiological alterations [8] . Unmasking them is challenging for the conventional noninvasive cardiac imaging tests and this is manifested by the often negative results for myocardial ischemia in women presenting with chest pain. Taken together these data suggest that accurate assessment of the atherosclerosis burden, endothelial function, and health of the microcirculation is very important for timely risk stratification and this has implications for the noninvasive approaches used to investigate women with chest pain. The goal of such stratification is to identify patients at risk for specific adverse events (cardiac death or nonfatal MI) and to develop posttest management strategies which might reduce patients’ risk of these outcomes. A variety of tests have been employed and these include exercise ECG, functional imaging with SPECT myocardial perfusion imaging (MPI) or stress echocardiography; more recently, CT coronary angiography and even cardiac magnetic resonance (CMR) imaging and positron emission tomography (PET) have been utilized for risk stratification. Hybrid imaging in the form of SPECT/CT or PET/CT has also been proposed as a comprehensive tool for assessing prognosis because it has the ability to provide concurrent quantitative information on myocardial perfusion, coronary anatomy, and plaque morphology [9] . Coronary heart disease remains the leading cause of death of women in the USA and is responsible for more deaths in women than all forms of cancer combined [1] . Moreover, recent data from the National Health and Nutrition Examination Survey (NHANES) looking at trends in midlife coronary heart disease risk show that over the past 2 decades the prevalence of myocardial infarction (MI) has increased in women aged 35–54 years while declining in men of the same age [2] . For Europe, data from the World Health Organization (WHO) demonstrate that cardiovascular disease accounts for 55% of deaths in women compared to just 43% of deaths in men [3] . In addition, there is evidence that symptomatic women with angiographically normal or nonobstructive coronary lesions have increased rates of MI, stroke, hospitalization for congestive heart failure, and cardiac mortality compared with a similarly matched cohort of asymptomatic community-based women [4] . Along with the knowledge on sex differences regarding clinical outcomes, results from the Women’s Ischemia Syndrome Evaluation (WISE) study and related studies implicate abnormal coronary reactivity [5] , microvascular dysfunction [6] , and plaque erosion/distal microembolization as important pathophysiological determinants of adverse outcomes [7] . Dysfunction of microcirculation is more common in women than men, presumably as a consequence of hormonal variations that result in vascular inflammation and subsequent remodeling. In the presence of risk factors for coronary artery disease (CAD), this process acReceived and accepted: March 25, 2011 Published online: June 1, 2011

FAMILIAL COMBINED HYPERLIPIDEMIA IS CHARACTERIZED BY HIGHER HEPATIC FDG UPTAKE AND VISCERAL ADIPOSE TISSUE VOLUME COMPARED TO HETEROZYGOUS FAMILIAL HYPERCHOLESTEROLAEMIA

Familial combined hyperlipidaemia (FCH) phenotype is associated with increased prevalence of non-alcoholic fatty liver disease and obesity. No data exists regarding the impact of heterozygous familial hypercholesterolaemia (heFH), another type of familial dyslipidaemia, on liver function and

18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomographic Imaging Detects Aortic Wall Inflammation in Patients With Repaired Coarctation of Aorta

Patients with surgically repaired coarctation of aorta (RCoA) are at increased cardiovascular mortality risk. Inflammation is an important element in RCoA.1,2 Positron emission tomography/computed tomography (PET/CT) with 18F-fluorodeoxyglucose (18F-FDG) is the gold-standard imaging modality to noninvasively assess vascular inflammation in vivo. In this pilot study, we explore the value of 18F-FDG PET/CT imaging in assessing aortic wall inflammation in RCoA subjects. A total of 15 patients with successful RCoA and 15 age- and sex-matched control subjects who have undergone treatment for lymphoma—a potentially high cardiovascular risk group—but were disease-free at the time of enrollment underwent 18F-FDG PET/CT to evaluate aortic wall inflammation. RCoA patients also underwent measurement of arterial elastic properties (augmentation index and carotid–femoral pulse wave velocity) by SphygmoCor (AtCor Medical, Sydney, Australia). The central arterial blood pressure was derived from the use of a generalized transfer function. Plasma levels of IL-6 (interleukin-6), TGF-β (transforming growth factor-β), and macrophage colony-stimulating factor were determined as markers of systemic inflammation and aortic wall remodeling. Patients with hypercholesterolemia or diabetes mellitus were excluded. To test the hypothesis that aortic coarctation is associated with increased aortic wall inflammation even in the absence of adverse hemodynamic burden to the aorta, patients with recoarctation were also …

PET/CT and CMR imaging in a patient with chest pain and unobstructed coronary vessels

a Center for Clinical Research, Experimental Surgery and Translational Research, Biomedical Research Foundation of the Academy of Athens, Athens, Greece b Second Department of Cardiology, Medical School, National and Kapodistrian University of Athens, General University Hospital ‘‘ATTIKON’’, Athens, Greece c Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar der Technischen Universitaet München, Munich, Germany d Cardiac MR Center, Hygeia Hospital, Athens, Greece e Tufts University School of Medicine, Boston, MA

SPNsim: A database of simulated solitary pulmonary nodule PET/CT images facilitating computer aided diagnosis

The aim of the present work was to design and develop a database of simulated solitary pulmonary nodules (SPN) in pairs of computed tomography (CT) and positron emission tomography (PET) images, using Monte Carlo (MC) simulation methods. We have developed an SPN image modeling pipeline to feed the database entitled SPNsim. The database is web-accessible and it is contains two subsets of simulated PET/CT SPN images. The first subset is currently composed of 1000 cases containing pairs of the transaxial CT and the corresponding PET slice with various types of simulated SPNs, presented as individual records. The second subset contains pairs of the transaxial CT and the corresponding PET slice of simulated SPNs, presenting cases of graded difficulty in diagnosis. The users of the database will have the ability to set queries in order to retrieve cases with certain characteristics, as well as characterized image sets. All images are freely available and may be downloaded from the website. SPNsim provides a useful reference data set for training and evaluation of computer aided detection (CAD) and diagnosis (CADx) systems focusing on SPN.