NUCLEAR CARDIOLOGY CLINICAL RESEARCH ACTIVITIES
The Clinical Nuclear Cardiology Laboratory is located on the 2nd floor of the Milstein Hospital building. The laboratory has 3 state-of-the-art cameras, two dual-headed SPECT cameras (Siemens E.CAM) and a SPECT/CT (Phillips Precedence, 16-slice CT) camera. In addition, the Laboratory utilizes a PET camera (Siemens ECAT, LSO crystals) (located on the 3rd floor of the Milstein Hospital building) for Cardiac PET studies. PET myocardial perfusion imaging is routinely performed using Rb-82 generator as well as PET viability imaging using F-18 FDG. The staff primarily responsible for conducting the research projects listed below include Stella Hernandez, research assistant, Sabahat Bokhari MD, principal investigator, Kenji Fijita MD, cardiology fellow, Lynne Johnson MD, principal investigator.
Focus for clinical research includes imaging of sympathetic nervous system function in the heart using both a PET tracer and a SPECT tracer, investigating the value of FDG imaging of atherosclerotic plaque metabolic activity as a marker of plaque vulnerability, and participation in multi-center trials to assess the clinical and prognostic usefulness of imaging tests including coronary artery calcium scores and/or CT coronary angiography combined with or compared to SPECT myocardial perfusion scintigraphy. On-going clinical research protocols and brief descriptions are listed below.
Atherosclerotic Imaging Management Strategies (AIMS): A Randomized Trial Comparing Myocardial Perfusion SPECT vs. Myocardial Perfusion SPECT with Coronary Calcium Screening by CT
This multi-center, randomized clinical trial is designed to address the frequency of clinically significant coronary atherosclerosis in patients without known Coronary Artery Disease who are undergoing myocardial perfusion SPECT and whether the addition of coronary calcium score alters the short-term patient management. The assessment of the coronary calcium score (CCS) by EBCT scans or CT scans has been shown to be a sensitive and specific marker of coronary atherosclerosis and to be strongly related to overall coronary plaque burden. The CCS provides incremental information over coronary risk factors for prediction of cardiac events. Because of this characteristic, CCS has become a highly effective means of determining long-term risk of cardiac events. The CCS may provide complementary anatomical correlates for SPECT physiological perfusion and function data resulting in enhanced predictive accuracy and more precisely guide medical management decisions in diagnostic patient cohorts. Furthermore, the combination of SPECT-CT may soon provide an evaluation of coronary anatomy in the same setting as perfusion imaging and offer even more clinical efficacy. Dual-modality imaging presents an opportunity for using a single piece of equipment to be used for distinctly different purposes, such as the determination of perfusion, function, coronary calcification, and angiography. Combined CT with SPECT offers the promise that one device will address diverse manifestations of cardiovascular disease pathophysiology, including perfusion, function, and anatomy.
Funded by Phillips. Drs Sabahat Bokhari and Lynne Johnson PIs for CUMC
Study of myocardial perfusion and coronary anatomy imaging roles in CAD (SPARC)
SPARC including its pilot CT angiographic study, is a prospective, open-label, multicenter, sequentially sampled, observational registry to define the clinical value of stress perfusion (stress SPECT, stress PET), noninvasive angiography (CTA) and combined perfusion-anatomy (PET/CT) studies in patients with known or suspected CAD with respect to post-test resource utilization and prediction of cardiac death and non-fatal myocardial infarction.
Funded by Brigham and Women's Hospital, Dr Marcello DiCarli as overall PI, Drs Bokhari and Johnson site PIs.
An Open-Label, Multicenter, Phase 3 study Evaluating the Prognostic Usefulness of I-123 MIBG Scintigraphy for Identifying Subjects with Heart Failure who will Experience an Adverse Cardiac Event
Radiolabelled meta-iodobenzylguanidine (MIBG) was originally developed in the 1970s as an agent for imaging the adrenal medulla. As an analogue of the false neurotransmitter guanethidine, increased MIBG uptake occurs in numerous other tissues besides the adrenal glands, specifically those in which norepinephrine (NE) and to a lesser extent certain other neurotransmitters are concentrated and its uptake signals SNS function. The mechanism of MIBG uptake involves re-uptake of NE into pre-synaptic vesicles (uptake 1 pathway). This compound, labeled with radioiodine tags has been extensively used in research and clinical imaging of the sympathetic nervous system of myocardium for more than 20 years. Published studies have shown that reductions in regional myocardial sympathetic function in CAD following myocardial infarction is associated with an increased incidence of adverse outcomes and ventricular arrhythmias. In heart failure from different etiologies (ischemic and non-ischemic cardiomyopathies) there is down-regulation of sympathetic NS function that can be detected as reduction in myocardial uptake of MIBG.
This phase-three open-label multicenter trial was designed to access the prognostic usefulness of I-123 MIBG imaging to identify those subjects with NYHA Class II and III HF who will experience an adverse cardiac event. Patients undergo both SPECT perfusion imaging with a Tc-99m labeled myocardial perfusion imaging agent and planar and SPECT MIBG imaging. The H/M ratio (heart to mediastinum ratio) from planar scans and distribution and washout of regional and global MIBG will be measured from SPECT scans in order to identify HF subjects at higher risk of experiencing an adverse cardiac event, (HF progression, potentially fatal ventricular arrhythmias, or cardiac death). Multivariant regression analysis will be performed using MIBG scan parameters as well as other clinical and laboratory variables to see if the scan offers incremental prognostic information.
Funded by GE Healthcare. Dr Sabahat Bokhari is PI for CUMC.
Fluorodeoxyglucose Uptake on PET is a Marker for Internal Carotid and Aortic Plaque Instability
This study will test the hypothesis that F-18 FDG uptake is a marker of plaque instability in patients with documented plaque in the internal carotid arteries and/or in the aorta. Vascular disease is a major cause of morbidity and mortality in the aging population. Patients with vascular disease are at greater risk for atherothrombotic events. Inflammation has been identified as a marker of plaque instability and is related to the risk of future vascular, cerebrovascular, and cardiovascular events. Major sources of embolic stroke are atherothrombotic lesions at the bifurcation of the common carotid. Large, multicenter studies have shown that patients with severe carotid artery stenosis benefit from endarterectomy, but management of patents with moderate stenosis is not clear. In addition, aortic plaque thickness or ulceration is identified as a potential, but not confirmatory source for emboli. There is a need to identify patients with vascular disease who are at risk for future vascular events. By determining areas of plaque instability through markers for inflammation, patients at risk can be treated to prevent future events. Serum markers do not localize inflammation to specific vascular sites. A noninvasive imaging study that could localize unstable plaques would be clinically very useful. F-18 fluorodeoxyglucose (FDG) is a glucose analog that is taken up in metabolically active cells including myocytes and tumor cells. It is also taken up in regions of inflammation. Uptake into myocytes depends on substrate, insulin levels, and glut 4 transporter. Uptake by tumor and by regions of inflammation presumably uses glut 1, a non insulin dependent transporter. Observational studies have documented vascular F-18 FDG uptake on positron emission tomography scans. Others have shown that uptake in carotid arteries localized to macrophages. These data suggest that FDG imaging has the potential to localize sites of plaque instability and to aid in preventive approaches. Hybrid scanners (PET/CT) are now widely available for oncology. The combined and registered images allows for localization of focal radiotracer to blood vessel walls as well as providing information on both anatomy and biology simultaneously.
Patients with atherosclerosis, including those with type II diabetes and vascular disease, are referred for PET scanning from the vascular and cardiac (TEE) ultrasound laboratories. All patients have laboratory evaluation of C reactive protein at the time of enrollment. PET/CT is performed on all patients from the base of the skull to the proximal thighs after injection of F-18 fluorodeoxyglucose. Uptake of tracer is localized and scored by extent and intensity. All patients are followed for events including CNS events (stroke, TIA) as well as myocardial infarction since vascular inflammation may be a widespread process. Levels of CRP will also be correlated with events as well as with scan findings.
This study is funded by internal source and PI is Dr Bokhari
Detection and Assessment of Free Fatty Acid Utilization by Cardiac Muscle in Patients with Lipoprotein Lipase Deficiency using Positron Emission Tomography
Fatty Acids provide over than 70% of the energy needs for cardiac functions. Fatty acids are generated by lipoprotein lipases through their action on triglycerides stored in adipose tissues or circulate in the blood with albumin. The purpose of this investigation is to determine how the hearts of patients with LPL deficiency obtain fatty acids as a source for energy and whether they use glucose as the main source of energy. The study design includes measurements of myocardial blood flow, oxygen consumption and substrate metabolism of free fatty acids and glucose using PET tracers in patients with LPL deficiency. These results are compared to those of normal subjects.
The funding source is internal. The two PI's are Dr Ira Goldberg and Dr Bokhari.
Effect of Diabetes Control on Cardiac Autonomic Nerves
Autonomic dysfunction in diabetes has been associated with increased morbidity and mortality. PET imaging allows quantitative assessment of cardiac nerve function. The objective of this study is to quantitatively assess cardiac carbon (C-11) hydroxyephedrine uptake as a marker for the imaging of SNS function assessed by parameter Bmax and correlate the regional Bmax with conventional markers of sympathetic and parasympathetic dysfunction in patients with autonomic neuropathy. A second objective is to determine whether observed scintigraphic findings are due to irreversible or potentially reversible functional disturbances of sympathetic neurons. Final enrollment will include 15 diabetic patients and 7 normal control subjects. Diabetic patients will be studied twice with the standard 3-test American Diabetic Association (ADA) battery for the diagnosis of cardiac autonomic neuropathy and quantitative C-11 hydroxyephedrine imaging as evaluated by PET: first shortly after initial diagnosis and then again after 3-6 months of glycemic control. We expect to find a correlation between autonomic dysfunction, as assessed by ADA testing criteria, and regional variation in Bmax and that the degree of blood glucose control in diabetics is a determinant of autonomic nervous system function and that improvement in glycemic control will correlate with improved autonomic function and improvement in Bmax.
This study is funded by a research award from ASNC to Dr Bokhari
MOLECULAR IMAGING LABORATORY RESEARCH ACTIVITIES
The molecular imaging research laboratory is located on the eighth floor of the Black building. Equipment includes a high-resolution planar imaging device for small animal imaging and a micro-SPECT camera (HiSPECT, Bioscan) for small animal SPECT imaging. Additional equipment includes Image-pro plus software Media cyberntics LP on Hewlett Packard pavilion 8700 computer, spectrophotometer, ELISA reader with printer, standard and fluorescent microscope with digital camera, computer, and monitor, column chromatography, electrophoresis (SDS-PAGE), HPLC (Shimatzu), gamma counter, centrifuge, protein purification system, isotemp refrigerators, small and large animal anesthesia delivery system.
The major research focus is imaging atherosclerosis with emphasis on targeting the biology of the vulnerable plaque in both small and large animal models. Our interest in vascular imaging extends to projects to document the onset and progression of the vascular lesions in primary pulmonary hypertension using radionuclide imaging. We have developed collaboration with Dr Stan Majewsky from the Jefferson Laboratories (Dept of Energy), with Dr Ann Marie Schmidt MD from the Department of Surgery at CUMC, Drs Frank Kolodgie and Renu Virmani at CVPath, Ban An Khaw PhD at Northeastern University (targeted antibody imaging), and Dr Jagat Narula at University of California at Irvine (imaging atherosclerosis). For 2006-2007 there are two post-doc researchers in the lab: Eileen Rattigan MD, and Yared Tekabe PhD. Dr Rattigan's projects include documenting the time course of the vascular lesions and the clinical manifestations in monocrotalin induced rat model of pulmonary artery hypertension, and documenting the pathology of accelerated atherosclerosis in diabetic hyperlipidemic pigs (Gerrity model). Dr Tekabe's background is in developing radiolabeled antibody fragments that amplify the imaging signal. He is applying these radiopharmaceutical approaches to novel targets in atherosclerosis including proliferating smooth muscle cell antigen and Receptor for Advanced Glycated Endproducts (RAGE). His projects also include using radiotracers that target different aspects of the pathobiology of atherosclerosis (apoptosis and MMP expression) to document non-invasively lesion stage.
On-going research projects in the Molecular Imaging laboratory are listed below.
RAGE-directed imaging for monitoring the progression and complexity of established atherosclerosis in diabetic apolipoprotein E null mice
This study was designed to explore novel RAGE-directed imaging as an effective, non-invasive means of monitoring the progression and complexity of developing atherosclerosis in diabetic, apolipoprotein E deficient mice. We hypothesize that we can image the sites and time course of expression of RAGE, the Receptor for Advanced Glycosylated End Products, in the vasculature that reflects the progression and complexity of atherosclerosis in diabetic subjects. This work is conducted in collaboration with Dr. Ann Marie Schmidt. Her group has identified a unique peptide sequence in the V-type Ig extracellular domain of RAGE and generated an antibody to this epitope. Our goal is to determine if anti-RAGE (Fab')2, when labeled with Tc-99m, can detect and monitor RAGE expression in diabetic, hyperlipidemic mice when non-invasively imaged with a gamma camera. Using this radiolabeled antibody, we hope correlate the degree of vascular inflammation and identify atherosclerotic plaque vulnerability when compared to standard histopathology. These exploratory studies will be performed in a validated mouse model, the diabetic, ApoE null mouse.
Funding is internal for pilot data; submitted to NIH as RO1. Yared Tekabe PhD as investigator, Lynne Johnson MD as PI
Molecular imaging for monitoring the progression of atherosclerosis in apoE null mice
This study was designed to document the time course for targeting vascular apoptosis and connective tissue matrix degradation in the atherosclerotic lesions in apoE null mice on hyperlipidemic diet. We hypothesized that we can image the sites and document the time course of apoptosis and matrix degradation in the vasculature that reflects atherosclerotic plaque destabilization. Our goal was to determine if annexin V or broad-based inhibitor of matrix metalloproteinases (MPI), when labeled with radioisotopes, can be used to identify the biology of atherosclerotic lesions prone to rupture in hyperlipidemic, apolipoprotein E null mice when non-invasively imaged with a gamma camera. Tc99m-labeled annexin V probe binds with high affinity to exposed phosphatidylserine on the cell membranes of apoptotic cells. Apoptosis of both macrophages and vascular smooth muscle cells is seen in atherosclerotic blood vessels. There is emerging evidence that apoptosis contributes to the instability of the atherosclerotic lesion. The Tc99m-labeled MPI localizes to areas of matrix metalloproteinase (MMP) expression and activity for MMP 1-3, 7, 9, and 13, enzymes involved in the proteolytic degradation of extracellular matrix. MMPs are expressed in macrophages and vascular cells, and are implicated in atherosclerotic plaque vulnerability and rupture.
This study is almost completed. Comparing uptake of the two radiotracers that target different biological processes in the atherosclerotic plaque we have found the following. In the 9 week apoE null high fat fed mice neither tracer is taken up and the plaque burden is very low. By 15 week some of the animals show aortic uptake of Tc-99 annexin V corresponding to AHA class II lesions. None have shown uptake of the MPI. Histopathology of these lesions showed apoptosis of smooth muscle cells and no staining for MMPs corresponding to little plaque matrix. By 20 weeks more mice have aortic uptake of the annexin V and some show uptake of the MPI. The more advanced lesions show uptake of both MPI and annexin. This corresponded to histopathology showing apoptosis of mostly macrophages and MMP staining localized to macrophages in matrix rich lesions. These data were presented at 2 scientific meetings.
Funding through NIH via RO1, PI is Jagat Narula MD, sub-contract to Lynne Johnson MD. Investigator is Yared Tekabe PhD.
Imaging Atherosclerosis in Diabetic Swine
Vulnerable plaque is complex biological milieu of dysfunctional endothelium, LDL cholesterol deposition, macrophage migration, smooth muscle cell proliferation and neovascularization. Metabolically active macrophages secrete proatherogenic cytokines and growth factors as well as matrix metalloproteinases (MMP) that lead to the instability of the plaque. MMP are a large class of enzymes that degrade supportive extracellular matrix. MMPs are expressed in atherosclerotic plaques. These molecules are implicated in converting the thick, protective fibrous cap covering a plaque to a thin one, leaving plaque vulnerable to rupture. Therefore, MMP production and activity are important markers in the pathophysiology of progressive atherosclerosis that can be targeted by nuclear imaging techniques for the non-invasive detection vulnerable atheroslerotic plaque. Metabolically active macrophages also take up F-18 FDG. This uptake has been documented in atherosclerotic plaques in experimental animal models and in humans.
We are using an established swine model of advanced human atherosclerosis, the diabetic and hyperlipidemic pig, developed by Gerrity and colleagues. The animals are made diabetic by the administration of drug streptozotocin (STZ). STZ destroys enough of the pancreatic beta cells to produce hyperglycemia without diabetic ketoacidosis. The animals are fed a high cholesterol, high fat diet. Typically, the pigs develop widespread atherosclerosis by twenty weeks post-STZ treatment.
According to the work of Gerrity, by 26 wk the animals have established and widespread atherosclerosis. Our experience to date with 5 animals show within each animal at 26 wk there is a spectrum of lesions from fatty streaks in the proximal aorta and innominate artery to complex and calcified plaque in the distal aorta and iliac bifurcation. We inject the animals with Tc-99m labeled MPI and perform SPECT imaging and then with F-18 and perform PET imaging. Once the imaging is complete, the animals are euthanized. The hearts and aortae are harvested and sent to CVPath laboratory for histopathological analysis. The pathology is correlated with the imaging data.
Funding through NIH via RO1, PI is Jagat Narula MD, sub-contract to Lynne Johnson MD. Investigator is Eileen Rattigan MD.
Early Changes in PAH detected by Molecular Imaging
Histological studies of pulmonary hypertension in relevant animal models have identified both proliferation of smooth muscle cells in the small arteries as well as apoptosis of vascular endothelial cells. Recent experimental evidence suggests that endothelial cell apoptosis may be the first and instigating lesion. The goal of our imaging studies is to detect pulmonary arterial changes early, before the onset of irreversible vascular changes and right ventricular failure. We first undertook a time course experiment in the monocrotalin rat model to map significant molecular events in the development of pulmonary arterial hypertension, namely pulmonary arterial endothelial cell apoptosis and pulmonary arterial smooth muscle cell proliferation, and correlate this data with clinical observations, non-invasive hemodynamics as measured by echocardiography, gross anatomic pathology and histology. From the histological time course study we were able to identify the time window for apoptosis. We then proceeded to injection of the animals with Tc-99m annexin V that targets apoptosis with SPECT imaging at various time points. These data show correspondence between the predicted onset and peak of apoptotic activity in the lungs and scan positivity and quantitative measurements of pulmonary radiotracer activity.
Funding through ASNC as research grant to Eileen Rattigan MD. Dr Rattigan is PI on this project.
