Nuclear cardiology in the era of cardiac CT and MRI

Full text: Current indications for classical nuclear cardiology are summarized (diagnosis, prognosis, myocardial viability, ventricular function). First, the use of nuclear cardiology is discussed within the clinical context (typical vs. atypical history of ischemia, findings on resting ECG etc.). An overview of different perfusion tracers is given both for SPECT (thallium, MIBI, microspheres) and PET (NH4, H2O, Rb). The advantages of gated imaging are mentioned, thus combining information regarding perfusion, ventricular function, regional wall motion and thickening. Then specificity and sensitivity data for detection of significant coronary artery disease are reviewed in both diabetic and non-diabetic patients: sensitivity values of 86% are reached for coronary artery stenosis of >50% in both populations. Sensitivity increases to around 90% for coronary artery stenosis of >70%. The issue of risk stratification and prognosis in both populations is raised: Negative predictive values as high as 0.97 for death and 0.94 for death or myocardial infarction are reached when patients have normal myocardial perfusion scans (follow-up 23+/-17 months). The current strengths and weaknesses of CT and MR imaging for detection of coronary artery disease are mentioned, including dobutamine stress MRI and perfusion imaging. With dobutamine stress MRI, sensitivity values between 83% and 91% are observed. When comparing dobutamine stress MRI with dobutamine echocardiography, image quality has a huge impact on sensitivity and specificity values with echo, but only minimal impact on MRI sensitivity/specificity values. In a second part of the talk, the advantages of positron emission tomography (PET) and its use in clinical cardiology (mainly detection of viability) are discussed. First, advantages of positron tomography are listed: short half life of the tracer, physiological labelling, absolute quantification, tomographic imaging. Different cardiac tracers are mentioned, such as carbohydrates, free fatty acids, receptor tracers of hypoxic sensitizers. The concepts of hibernation and stunning are reviewed as well as the different PET patterns (match, mismatch) typically seen when studying viability. PET imaging is compared with radiological (MR) techniques such as late enhancement or infarct imaging. Finally, differences in nuclear cardiology between US and Europe are highlighted as well as strengths and weaknesses. (author)