Radionuclide angiography (RNA) is also known by other synonyms such as radionuclide ventriclography or multi gated acquisition (MUGA). RNA refers to a nuclear medicine imaging technique where a radioactive chemical, often Technetium 99m (metastable), is attached to a patient's previously drawn blood and then reinjected into the patient.
Technetium 99m then decays into technetium 99 and emits a gamma ray in the process. A gamma ray is a single photon as opposed to alpha decay (essentially a helium nucleus) or beta decay (electron or positron)
As the radiolabeled blood circulates through the body, a gamma camera will be positioned over the region of interest on the patient's body. As this radiolabeled blood emits gamma rays, the gamma camera will collect these rays and convert them into an image.
Radionuclide angiography is named as such as the technique involves the use of radioactive tracers, and by imaging the blood pool, a "gram" or picture of perfusion is obtained.
SPECT stands for single photon emission computed tomography. A "T"omogram refers to the practice of acquiring several slices of a certain image from different angles. A SPECT technique will then use a "C"omputer to assemble the slices together to generate a 3 dimensional model of the region of interest.
The "S"ingle "P"hoton "E"mission portion refers to the type of radiation being used to generate the image, which is gamma radiation. This is in contrast to positron emission tomography (PET scanning), which uses positrons for imaging purposes.
Finally, gating refers to the practice of correlating a specific slice to a specific time point, taking several images from different time points, and then stitching them together so that a moving image is constructed.
A non-gated image creates an image without respect to the time point it was captured.
The most common application of radionuclide angiography is for the calculation of left ventricular ejection fraction. The formula for calculating ejection fraction is
(End diastolic volume) - (End systolic volume) / End diastolic volume
In this case radionuclide angiography needs to be gated so that one can determine the end diastolic and end systolic frames.
Planar RNA can be used to calculate EF, where the measured radioactivity at diastole and systole can be used directly to calculate the EF. SPECT RNA can also be used, where the radioactivity is measured from 360 deg to construct a 3d cast during diastole and systole.
Hope this helps!