MUGA Scan

Excerpt

Multigated acquisition (MUGA) scanning is a nuclear medicine imaging modality that aids providers evaluate the heart's structural and dynamic properties. They are imaging modalities with many names, including radionucleotide ventriculography (RVG) and gated equilibrium radionucleotide angiography (ERNA). However, all of these have the same goal of imaging the heart non-invasively. The idea behind MUGA scans is to take multiple pictures of the heart at various time points to create a composite film of multiple cardiac cycles and present it in two dimensions on the computer. This aids the provider in evaluating certain heart parameters at rest and/or while under stress. An awareness of these parameters is extremely beneficial, especially in cancer and cardiac patient populations, as cardiotoxic chemotherapy and heart disease carry a high mortality. With an enhanced view of cardiac structure and dynamics, the MUGA scan allows for a better understanding of patients' cardiac function, increased diagnostic and prognostic accuracy, and cardiac function tracking before, during, and after chemotherapy.

Several techniques are employed in MUGA imaging. These include first pass, equilibrium radionucleotide angiography (ERNA), and single-photon emission computed tomography (SPECT). The first pass technique involves delivering a radioactive isotope bolus and imaging the tagged blood path as it completes initial transit through the heart. This technique is ideal for determining right ventricular ejection fraction (RVEF) and examining intracardiac shunts. In ERNA, the isotope is tagged to red blood cells (RBCs) and is given approximately 30 minutes to reach equilibrium in the patient, after which the patient is imaged with a camera. SPECT is a technology that builds upon ERNA as it eliminates the need for manual background signal noise reduction. ERNA and SPECT are preferred modalities when evaluating left ventricular ejection fraction (LVEF), size, and wall motion.

As with many nuclear medicine tests, MUGA scans rely on radioactive isotopes administered and tagged to RBCs. The goal behind tagging RBCs with radioisotopes or tracers is to capture photons emitted by these isotopes using a gamma camera. These cameras are equipped with a sodium iodide crystal coupled to photomultipliers, which help convert the captured photon's energy into an image. Technetium-99m (Tc-99m) is the preferred radioisotope used in MUGA scans because it has a half-life of six hours , and the heart receives adequate radiation to be picked up by the gamma camera. The radioisotope is also cleared by the kidneys and excreted in the urine. The camera illuminates the tagged blood, and in the process, the provider can evaluate the filling and pumping properties of the heart and can evaluate physical structures by comparing the illuminated blood pool to the darkened walls on the image.