This article, the fourth in a five-part series on nuclear medicine imaging techniques, explains how radionuclide ventriculography works and what precautions are required when it is used
Nuclear medicine provides imaging modalities that can be used to observe physiological processes in the human body, particularly in the bones, heart, lungs, renal system and brain. This fourth article in a five-part series explains how radionuclide ventriculography – also called a multiple-gated acquisition (MUGA) scan – works and what precautions need to be taken with and around patients undergoing this investigation.
Citation: Purden J, Morton F (2019) Nuclear medicine 4: radionuclide ventriculography (MUGA scan). Nursing Times [online]; 115: 6, 63-64.
Authors: Joseph Purden and Faye Morton are lecturers in medical physics technology, College of Human and Health Sciences, Swansea University.
Radionuclide ventriculography uses images of the heart to determine the ejection fraction (Box 1). The ejection fraction is often used as a measure of the cardiotoxicity that can be caused by some chemotherapy agents (Metcalfe, 2005). As an example, radionuclide ventriculography can be used to monitor the ejection fraction of patients who are receiving the monoclonal antibody trastuzumab as part of a chemotherapy protocol for breast cancer (Chavez-MacGregor et al, 2015).
Radionuclide ventriculography is also called a multiple-gated acquisition (MUGA) scan because of the imaging technique used.
How does it work?
A radioisotope (see part 1) is injected into the patient intravenously, travels in the circulation and moves into the red blood cells. To ensure that it remains in the red blood cells, a stannous (tin) agent is injected into the patient 10-30 minutes before the procedure. This is taken up by the red blood cells and makes them ‘sticky’, so they are able to ‘trap’ the radioisotope when it is administered.
Imaging – during which the patient is in a supine position with their arms above their head – is undertaken approximately 20 minutes after the radioactive element has been injected. A three-lead electrocardiogram (ECG) triggers the acquisition of images timed to systole and diastole. Each image takes approximately 10-15 minutes to acquire (Hesse et al, 2008). Images are obtained from the left anterior oblique view (or projection) and additional projections are sometimes used (Fig 1).
Source: Peter Lamb
The ECG trace is split at each R wave into 24 segments. The imaging system assigns the counts detected during each of the 24 segments of the cardiac cycle to corresponding ‘bins’. Data from each bin is compiled to produce an image of the heart in each phase of the cardiac cycle.
Emissions from the radioisotope are detected by a gamma camera, which allows nuclear medicine professionals to see the outline of the left ventricle. Views of the heart are taken to work out the volume of blood it contains during diastole and systole. The difference between the two is the ejection fraction. A baseline ejection fraction is calculated and repeat investigations are performed.
Patients who are about to undergo a MUGA scan usually go to the nuclear medicine department. If they have reduced mobility, it is useful to inform the department beforehand, to ensure the correct protocols are adhered to during imaging. There is minimal preparation and patients should:
- Follow their normal diet;
- Take their normal medications.
A cannula is usually inserted before the procedure so the stannous agent and radioisotope can be administered using one injection site.
In cases of severe urinary incontinence, it is advised that patients have a catheter in situ for the duration of the procedure to avoid contamination of the camera by spills of radioactive urine. The catheter bag should be emptied regularly to prevent an accumulation of radioactive urine.
Patients should be encouraged to drink and urinate often after the scan (unless contraindicated), to help clear the radiopharmaceutical from their system.
If samples of blood, urine or faeces need to be collected from a patient in the 24 hours after a MUGA scan, nurses should take extra care by:
- Wearing gloves, an apron and shoe coverings;
- Using absorbent pads to clean up any spillages.
If possible, it is advisable to either perform sample collection before the investigation or more than 24 hours after it.
Patients should not have close contact with young children or pregnant women –the two groups most at risk from radiation – for 24 hours after administration of the radiopharmaceutical. Ideally, pregnant members of staff should not care for patients who have just had a MUGA scan, and all staff need to take extra care to reduce their own exposure to radiation. After 24 hours, normal staff rotas and standard care protocols can be resumed.
- Radionuclide ventriculography uses repeat images of the heart to monitor ejection fraction
- It is also called multiple-gated acquisition (MUGA) scan because of the imaging technique that is used
- The ejection fraction is often used as a measure of chemotherapy-induced cardiotoxicity
- Precautions to avoid radioactive contamination are needed for 24 hours after a MUGA scan
Chavez-MacGregor M et al (2015) Cardiac monitoring during adjuvant trastuzumab-based chemotherapy among older patients with breast cancer. Journal of Clinical Oncology; 33: 19, 2176-2183.
Foley TA et al (2012) Measuring left ventricular ejection fraction: techniques and potential pitfalls. European Cardiology Review; 8: 2, 108-114.
Hesse B et al (2008) EANM/ESC guidelines for radionuclide imaging of cardiac function. European Journal of Nuclear Medicine and Molecular Imaging; 35: 4, 851-885.
Metcalfe MJ (2005) The cardiovascular system. In: Sharp PF et al (eds) (2005) Practical Nuclear Medicine. London: Springer Verlag.
Mininni NC, Tasota FJ (2003) Measuring injection fraction with a MUGA scan. Nursing; 33: 7, 26.