Recent advances in nuclear cardiology in the study of coronary artery disease

Abstract

A variety of new radiopharmaceutical agents have been introduced to probe myocardial function in vivo. This review will introduce these new techniques which have recently been available in Japan. Tc-99m perfusion imaging agents provide excellent myocardial perfusion images which may enhance diagnostic accuracy in the study of coronary artery disease. In addition, greater photon flux from the tracer permits simultaneous assessment of regional perfusion and function with use of first-pass angiography or ECG-gated acquisition. Positron emission tomography enables metabolic assessment in vivo. Preserved FDG uptake indicates ischemic but viable myocardium which is likely to improve regional dysfunction after revascularization. In addition, FDG-PET seems to be valuable for selecting a high risk subgroup. Recently I-123 BMIPP, a branched fatty acid analog, has been clinically available in Japan. Less uptake of BMIPP than thallium is often observed in the ischemic myocardium. Such perfusion metabolic mismatch which seems to be similarly observed in FDG-PET is identified in the stunned or hibernating myocardium with regional dysfunction. Both of them are likely to recover afterwards. Severe ischemia is identified as reduced BMIPP uptake at rest, suggesting its role as an ischemic memory imaging. I-123 MIBG uptake in the myocardium reflects adrenergic neuronal function in vivo. In the study of coronary artery disease, neuronal denervation is often observed around the infarcted myocardium and post ischemic region as well. More importantly, reduced MIBG uptake in these patients can identify high risk for ventricular arrhythmias and assess severity of congestive heart failure. These new techniques will provide insights into new pathological states in the ischemic heart disease and enable to select optimal treatment in these patients.

Characterization of Japanese standards for myocardial sympathetic and metabolic imaging in comparison with perfusion imaging

“…BMIPP distribution is homogeneous. The result of the relatively homogeneous distribution of BMIPP in this study is in accordance with a previous study [23]. The BMIPP compound is designed for SPECT imaging, which requires long myocardial retention of the tracer for good image quality.…”

“…In an ischemic condition, discordant 123 I-BMIPP uptake less than that of perfusion tracer may reflect decreased pO 2 levels and tissue ATP concentrations, leading to a switch from fatty acid to glycolytic oxidation [26]. 123 I-BMIPP provides valuable information on myocardial metabolism reflecting mitochondrial function [23]. Therefore, reading BMIPP images using an appropriate standard database in comparison with perfusion imaging is vitally important [12,26].…”

Metabolic imaging using SPECT

“…BMIPP defect size in subacute phase of myocardial infarction correlated well with the risk area revealed by contrast ventriculography or echocardiography [56,61], and the area with BMIPP reduction 1 week after the onset of myocardial infarction corresponded well to the area with perfusion defect which was demonstrated before revascularization therapy at admission [62]. These observations suggested that BMIPP imaging obtained in subacute phase of myocardial infarction can be called "ischemic memory imaging" because it reflects prior ischemic damage or metabolically stunned myocardium even after the restoration of perfusion abnormality [56,63,64]. In chronic phase of myocardial infarction, mismatched uptake of BMIPP less than thallium is not an uncommon finding.…”

Endogenous compounds labeled with radionuclides of short half‐life—some perspectives

“…As an example, fatty acids have been used for following the kinetics of biological processes, such as membrane transport, blood flow, and cardiac fatty acid metabolism . [ω‐ 11 C]Palmitate is a well‐established PET tracer to probe myocardial fatty acid metabolism . Synthesis of [ω‐ 11 C]palmitate involves incorporation of 11 C‐alkyl iodide employing Grignard reaction, Suzuki cross coupling, organocopper chemistry, or functionalized copper–zinc reagent (Scheme ) …”