Frequently Asked Questions for patients

Who should be referred for Myocardial Perfusion Scintigraphy (MPS)?

The most common reason for referral for MPS is the evaluation of chest pain and the diagnosis of coronary artery disease given the poor sensitivity and specificity of ECG exercise testing. Other common categories of patient referral are: the assessment of myocardial damage following infarction, targeting of revascularisation procedures and non cardiac pre-operative risk assessment.

Are there any long term radiation risks due to the procedure?

Typical doses from this imaging procedures is in the range of 7 -12 mSv. Studies on radiation risk estimate that the probability of a fatal cancer developing from an exposure to 1 mSv of ionising radiation is approximately 50 in a million. People are exposed to natural background ionising radiation every day and the average dose across the UK from this is approximately 2.6 mSv per year.

What patient preparation does it involve?

Patients would be asked to refrain from consuming caffeine containing beverages (including some decaffeinated drinks) for at least 24 hours before the stress test. Medication withdrawal may be considered depending on the modality of stress testing.

Why are patients told to be caffeine-free prior to MPS?

The stress procedure is often undertaken using the vasodilators regadenoson, adenosine or dipyridamole to induce coronary vasodilation by targeting the coronary adenosine receptors. Caffeine is a competitive antagonist of the adenosine receptors and interferes with this effect. Other compounds (xanthines) that have a similar effect on the adenosine receptors are theobromine (in chocolate) and aminophylline.

What medications need to be stopped prior to MPS?

Where it is safe to stop, patients are advised to omit betablockers, ivabradine, diltiazem and verapamil (heart rate limiting drugs) as these medications will blunt haemodynamic response to exercise and ionotropic pharmacological stress. Patients are advised to stop these medication 48 hours prior to stress imaging. Medications can be restarted after the stress test. Depending on the test indication, some anti-anginal medication may be withdrawn.

How long does the procedure take?

When both stress and rest imaging are performed on the same day (one day protocol) the procedure can take up to 6 hours as it is recommended that there is at least 2 hours between tracer injections and 1 hour between injection and imaging. When the procedure is performed over 2 days each visit should take about 3 hours each visit, assuming the picture quality is diagnostic on the first scan.

Are there any absolute contra-indications to MPS?

No. A relative contraindication to the injected radiopharmaceutical is pregnancy and breast feeding. If there is an urgent clinical need to perform the test under these circumstances, a risk/benefit assessment will be made.

How long will I remain radioactive after the test?

The “half life” of technetium (the most commonly used agent) is 6 hours. Therefore at 12 hours only 1/8 (12%) and at 24 hours only 1/16 (6%) of the activity remains which is considered negligible.

Are there any precautions to take following MPS?

There are no special precautions to be taken after a myocardial perfusion SPECT or a PET study. However, some centres advise patients to avoid prolonged close contact with pregnant women and children 11 years old and under for 24 hours following the test.