Cardiac Nuclear Medicine: Techniques, Applications, and Imaging Findings
Abstract
The full digital presentation is available online.
TEACHING POINTS
■ Nuclear imaging uses dedicated detectors to image photons emitted by injected radiotracers that target specific in vivo receptors or molecular pathways.
■ Nuclear imaging is valuable for the evaluation of cardiovascular diseases, allowing noninvasive evaluation of cardiac physiology and function and providing complementary information to that provided by anatomic techniques.
■ Common cardiovascular applications of nuclear imaging techniques include ischemic heart disease, inflammation, infiltrative disorders, masses, infection, and quantification of ejection fraction.
Nuclear imaging uses dedicated detectors to image photons emitted by injected radiotracers that target specific in vivo receptors or molecular pathways. SPECT cameras detect γ emitters, while PET detectors detect high-energy photons produced by the annihilation of positrons. These techniques are combined with CT or less commonly MRI for attenuation correction and anatomic colocalization. Nuclear imaging plays a valuable role in the evaluation of cardiovascular diseases, allowing noninvasive evaluation of cardiac physiology and function that provides complementary information to that obtained by using anatomic imaging techniques. Common cardiovascular applications of nuclear medicine techniques include evaluating ischemic heart disease, inflammation, infiltrative disorders, masses, and infection and quantification of ejection fraction. Technetium 99m (99mTc) is the workhorse for cardiac SPECT. Fluorine 18 (18F) fluorodeoxyglucose (FDG), gallium 68 (68Ga), nitrogen 13 ammonia (13N-NH3), and rubidium 82 (82Rb) are PET tracers.
Myocardial perfusion imaging (MPI) helps assess myocardial blood flow in response to either exercise or pharmacologic stress. Two sets of rest and stress images, each obtained after injection of a radiotracer, are compared to detect ischemia (reversible perfusion defect) and infarct (fixed perfusion defect). Additionally, MPI with PET allows myocardial blood flow quantification, which is useful in the assessment of multivessel disease (balanced ischemia) and microvascular disease. PET MPI can also be combined with 18F-FDG PET after glucose loading for assessing myocardial viability. A perfusion-metabolism mismatch of reduced perfusion and preserved 18F-FDG metabolism indicates hibernating myocardium, which can then be salvaged with coronary revascularization procedures.
In cardiac sarcoidosis, dual-tracer PET with both 18F-FDG and a perfusion agent (13N-NH3 or 82Rb) after the patient follows a “sarcoid diet” (high fat, low carbohydrate) is useful for detecting early disease, distinguishing active from chronic disease, and assessing response to therapy. A focal area of 18F-FDG uptake with or without associated perfusion defect indicates active sarcoidosis (Fig 1), whereas a perfusion defect without 18F-FDG uptake indicates “burnt-out” sarcoidosis. In cardiac amyloidosis, it is critical to noninvasively distinguish transthyretin amyloidosis (ATTR) from light-chain amyloidosis as the treatment strategies for each differ. A positive 99mTc-pyrophosphate examination in the absence of serum monoclonal proteins confirms ATTR with high specificity without the need for endomyocardial biopsy. Both visual interpretation (cardiac uptake equal to or greater than that of bone) and semiquantitative ratios are described.

Figure 1. Biopsy-proven diffuse large B-cell lymphoma in a 65-year-old woman. Axial fused FDG PET/CT image obtained as part of disease staging shows circumferential nodular pericardial uptake (straight arrows) and adjacent paracardiac lymph nodes (curved arrows), consistent with a neoplasm.
For cardiac masses, 18F-FDG PET is useful for delineating local extent and staging primary and secondary cardiac tumors (Fig 1). 18F-FDG PET is also useful to differentiate benign from malignant cardiac masses found at echocardiography, CT, or MRI and from normal variants. Pathologic 18F-FDG uptake can be intramural, intracavitary, pericardial, or vascular. Somatostatin receptor imaging (68Ga–tetraazacyclododecane tetraaceticacid–octreotate [DOTATATE] PET) is useful for primary cardiac paragangliomas (Fig 2) and cardiac metastases from neuroendocrine tumors.

Figure 2. Incidentally detected hypervascular mass at invasive coronary angiography in a 55-year-old-woman. Axial fused 68Ga-DOTATATE PET/CT image shows intense uptake in the mass (arrow) posterior to the right atrium. This was confirmed to be a primary cardiac paraganglioma at surgery.
Cardiovascular infections include prosthetic valve endocarditis and infections of cardiovascular implantable electronic devices, left ventricular assist devices, and vascular grafts. While radiolabeled–white blood cell scintigraphy is specific, 18F-FDG PET is increasingly used owing to higher spatial resolution and the superior capability for detecting multifocal infections. Non–attenuation-corrected and attenuation-corrected PET images are evaluated to exclude metallic artifacts and diagnose pathologic uptake. Physiologic myocardial uptake is eliminated by using a sarcoid diet preparation.
18F-FDG PET is useful in large vessel vasculitis, such as Takayasu arteritis and giant cell arteritis, to evaluate disease activity, disease extent, and assessment of response to therapy. Vasculitis and atherosclerosis can also be evaluated with novel non–18F-FDG radiotracers. Ejection fraction can be reliably quantified by MUltiGated Acquisition (MUGA) imaging after injecting 99mTc–labeled red blood cells. Gated SPECT after injection of 99mTc-sestamibi is an alternative examination. A decline in ejection fraction greater than 10% after cardiotoxic chemotherapy compared with that at baseline is indicative of cardiotoxicity.
In this slide presentation, we review the common nuclear medicine techniques used in cardiovascular disease, illustrate the applications of these techniques, and discuss the nuclear medicine imaging findings of cardiovascular diseases.
Presented as an education exhibit at the 2021 RSNA Annual Meeting.
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Article History
Received: Feb 7 2022Revision requested: Mar 7 2022
Revision received: Mar 15 2022
Accepted: Mar 17 2022
Published online: Dec 09 2022