Imaging the Heart
Nuclear cardiology is changing to become an important application of molecular imaging.
Traditionally, cardiac PET and SPECT imaging has been used to a.) detect coronary artery disease (CAD); b.) determine the hemodynamic significance of coronary artery stenoses; c.) risk-stratify patients prior to cardiac and non-cardiac surgery; and d.) provide important prognostic assessments of patients with CAD. In addition, and in combination with 18F-FDG, radionuclide imaging of the heart has been used successfully to determine whether hypoperfused myocardium is viable or not. The latter approach has had a substantial impact on the management and outcome of patients with heart failure to ischemic heart disease.
Over the last couple decades, it has become evident that myocardial infarctions frequently occur in coronary arteries without hemodynamically significant stenoses. The concept of "soft plaque" implies that atherosclerotic lesions that exhibit little calcification, but that are subject to rupture with subsequent arterial occlusion, account for the majority of cardiac events including infarctions and sudden cardiac death. Current nuclear medicine procedures do not adequately address this aspect of CAD.
With the advent of hybrid PET/CT imaging, a more comprehensive assessment of coronary morphology and function has become available. Non-invasive CT coronary angiography, PET perfusion and wall motion studies scans can be performed near simultaneously. Moreover, the morphology of the coronary artery wall can be inspected, which may provide insights into plaque composition. Calcified coronary lesions can be distinguished from non-calcified lesions that might denote vulnerable plaques. Such lesions with low calcium content may identify patients who are at risk for subsequent cardiac events. Hybrid PET/MRI systems might provide even deeper insights into coronary morphology and function.
Further, novel molecular PET, MRI and optical imaging probes for improved assessments of coronary function and the innervations of the myocardium are emerging. There is, however, still an unmet clinical need to reliably detect vulnerable coronary plaques. A variety of probes for imaging inflammation (18F-FDG), apoptosis, or platelet binding have been tested. However, none of these approaches have been introduced for routine clinical use. This is, in part, due to limited detectability of frequently small soft plaques as well as limited target to background tracer activities.
Nevertheless, progress is being made that will result in non-invasive diagnostic strategies to identify those patients at highest risk for cardiac events. We hope this issue of Molecular Imaging Insight sheds some light on these recent developments.
Traditionally, cardiac PET and SPECT imaging has been used to a.) detect coronary artery disease (CAD); b.) determine the hemodynamic significance of coronary artery stenoses; c.) risk-stratify patients prior to cardiac and non-cardiac surgery; and d.) provide important prognostic assessments of patients with CAD. In addition, and in combination with 18F-FDG, radionuclide imaging of the heart has been used successfully to determine whether hypoperfused myocardium is viable or not. The latter approach has had a substantial impact on the management and outcome of patients with heart failure to ischemic heart disease.
Over the last couple decades, it has become evident that myocardial infarctions frequently occur in coronary arteries without hemodynamically significant stenoses. The concept of "soft plaque" implies that atherosclerotic lesions that exhibit little calcification, but that are subject to rupture with subsequent arterial occlusion, account for the majority of cardiac events including infarctions and sudden cardiac death. Current nuclear medicine procedures do not adequately address this aspect of CAD.
With the advent of hybrid PET/CT imaging, a more comprehensive assessment of coronary morphology and function has become available. Non-invasive CT coronary angiography, PET perfusion and wall motion studies scans can be performed near simultaneously. Moreover, the morphology of the coronary artery wall can be inspected, which may provide insights into plaque composition. Calcified coronary lesions can be distinguished from non-calcified lesions that might denote vulnerable plaques. Such lesions with low calcium content may identify patients who are at risk for subsequent cardiac events. Hybrid PET/MRI systems might provide even deeper insights into coronary morphology and function.
Further, novel molecular PET, MRI and optical imaging probes for improved assessments of coronary function and the innervations of the myocardium are emerging. There is, however, still an unmet clinical need to reliably detect vulnerable coronary plaques. A variety of probes for imaging inflammation (18F-FDG), apoptosis, or platelet binding have been tested. However, none of these approaches have been introduced for routine clinical use. This is, in part, due to limited detectability of frequently small soft plaques as well as limited target to background tracer activities.
Nevertheless, progress is being made that will result in non-invasive diagnostic strategies to identify those patients at highest risk for cardiac events. We hope this issue of Molecular Imaging Insight sheds some light on these recent developments.