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What is a Thallium Scan?

A thallium scan is a type of imaging technique that helps measure the amount of blood flowing through the heart, both at rest and during vigorous activity. It is mainly done to assess the functioning of the heart after a heart attack and to find the cause of unexplained angina (chest pain).

In this test, a radioactive tracer, thallium chloride is injected into the bloodstream. This tracer has an affinity for certain body parts such as heart, brain, muscles, parathyroid glands and thyroid. As it starts collecting in these organs, thallium chloride releases radioactive energies, which are then picked up by a specific camera to reveal any pathological changes in these organs. 

Two sets of pictures are taken during this test. One set of pictures is taken at rest and the other is taken during vigorous activity, after an exercise or after giving a medicine. Both the sets are compared to provide interpretation.

Thallium scan is also known as myocardial perfusion scintigraphy, sestamibi stress test, MIBI stress test, dobutamine stress test, Persantine stress test, thallium stress test, adenosine stress test, regadenoson stress test, stress test-nuclear, coronary artery disease-nuclear stress, angina-nuclear stress and chest pain-nuclear stress.

  1. Why is a Thallium Scan performed?
  2. How do you prepare for a Thallium Scan?
  3. How is a Thallium Scan performed?
  4. What do Thallium Scan results indicate?

A thallium scan is performed in the following scenarios:

  • To diagnose and identify a coronary artery disease (CAD)
  • To determine the treatment for CAD 
  • To determine the cause of chest pain or pressure (which generally occurs after exercise)
  • To know the location and extent of damage caused after a heart attack
  • To check the amount of blood flowing through the heart after heart surgery or angioplasty
  • To identify a congenital heart defect and determine its severity (can also be done after a surgery to correct a congenital heart defect)
  • To determine the pumping capacity of heart
  • To check heart size

Before undergoing this test, inform your doctor about your current medications or any allergies (if you have any) to medicines and anaesthetics.

You may be advised not to drink or eat anything three hours prior to the test. Only a small amount of water is permitted to take medicines. Do not consume alcohol, tobacco or any nonprescribed medicines 24 hours prior to the test. Avoid all types of caffeinated beverages, including tea, coffee, sodas, and chocolates and pain relievers with caffeine.

Make sure to wear comfortable clothes and shoes, and remove all jewellery before the test.

Tell your healthcare provider if you are pregnant or breastfeeding, as the radioactive material could reach your breast milk and harm your baby. Do not breastfeed your baby for at least two days after the test.

This test is performed in stages.

Firstly, radioactive thallium will be introduced into your bloodstream with the help of an intravenous (IV) line. After about 15-45 minutes, a special camera will be used to scan your heart and capture images to assess the movement of the radioactive material in your body and heart. 

Then, you will be asked to walk on a treadmill and gradually increase your pace. Your blood pressure and electrocardiogram (ECG) will be monitored throughout the test. 

As your heart starts to pick up with the pace of the exercise, you’ll be given another injection of the radioactive substance. After 15-45 minutes, the camera will again scan your heart and capture images. Both sets of pictures will be compared to assess the condition of your heart.

Your healthcare provider will give you the results of your thallium scan in 1-3 days.

Normal results: Result would be considered normal if there is an even distribution of radioactive tracer throughout your heart muscles

Abnormal results: Results would be considered abnormal if there is an uneven distribution of the radioactive tracer in your heart muscles. It can be due to

  • Insufficient blood flow in the heart 
  • Any damage to the heart
  • Presence of CAD
  • Scarring of heart muscles because of a previous heart attack

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. Health Link. Cardiac Perfusion Scan. British Columbia. [internet].
  2. UFhealth. Nuclear stress test. University of Florida health. [internet].
  3. Penn State Health. Nuclear stress test. Milton S. Hershey Medical Center; Pennsylvania
  4. MedlinePlus Medical: US National Library of Medicine; Nuclear stress test
  5. NPS MedicineWise. Thallium scanning. Australia. [internet].