Position Emission Tomography (PET) – Myocardial Perfusion Scan
PET stands for Positron Emission Tomography and is an imaging technique which uses small amount of a radioactive tracer to help in the diagnosis of heart disease.
The commonest tracer used in Rubidium-82(Rb-82 or 82Rb). 82Rb is a potassium analogue that is a generator product with a physical half-life of 76 seconds. Owing to the distinct advantage of not requiring an on-site cyclotron, 82Rb is the most widely used radioactive tracer for assessment of myocardial perfusion with PET.
The 82Rb tracer is introduced into the body by intravenous (I/V) injection directly from a small portable generator and a PET Scanner is used to produce an image showing the distribution of the tracer in the heart muscles.
Following the intravenous administration, 82Rb is carried in the blood stream and in the blood vessels supplying the heart muscles. 82Rb is then rapidly taken up by the heart muscles. 82Rb activity is noted in the heart within the first minute after injection. As the uptake of 82Rb by the heart muscle is related to the blood flow, therefore, areas of the heart with adequate blood flow would have more 82Rb activity in comparison to those areas with compromised blood flow.
A PET scanning camera takes 3D images of the 82Rb uptake of the heart muscles and is visualised/coded as an orange/yellow colouration of the muscles. Further analysis of these images help to identify the location, severity and extent of reduced blood flow to the heart muscles.
PET is the most accurate test to reveal coronary artery disease or rule out its presence. It has a high sensitivity of 95% (i.e. accuracy of predicting a positive result and correctly identifying the percentage of significant reduction in blood flow to the heart muscles) and a specificity of 95% (i.e. accuracy of predicting a negative result and correctly identifying the percentage of healthy individuals who do not have significant blood vessel blockages supplying the heart muscles).
How is PET Myocardial Perfusion Scan with 82Rb performed?
There are 3 steps to this procedure :
Rest Scan Imaging after I/V 82Rb administered at rest
Pharmacological stress test using I/V Persantin or Adenosine to stress the heart with increased heart rate and blood pressure
Stress Scan Imaging after pharmacological heart stress
The entire procedure including the rest/stress scans will take about 1 hours (60 minutes)
Normal PET 82Rb myocardial perfusion scan. Note yellow/orange coded tracer filling the muscles of the heart completely in cross-section in upper segment and longitudinal section in the lower segment
Abnormal PET 82Rb myocardial perfusion scan. Note yellow/orange coded tracer filling defects in the muscles of the heart (see green arrows) in cross-section in upper segment and longitudinal section in the lower segment