Myocardial perfusion imaging is an imaging test that can show if there is adequate blood flow to the heart and if the heart is pumping as it should be. It is important for the diagnosis and management of patients with known or suspected coronary artery disease (CAD).
Although nuclear cardiology is one of the most common approaches for myocardial perfusions, such as SPECT or PET scans, other techniques like MR have been explored and even recognised as favourable alternatives, due to their non-invasive method.
There are several different imaging modality techniques that are used for myocardial perfusion imaging. These include:
- SPECT scan (Single-photon emission computerized tomography)
- PET scan (Positron emission tomography)
- MR myocardial perfusion imaging (Magnetic resonance)
- CT scan (Computerised tomography)
Each method plays a pivotal role in the prevention, diagnosis, and treatment of cardiac-related conditions, but some are more commonly used than others.
In this article, we will be exploring the different techniques used, as well as exploring how alternative approaches work, how accurate they are, and leading market software that is compatible with the alternative techniques.
What is myocardial perfusion imaging?
Serious health problems including ischaemic heart disease, or coronary artery disease, can occur when the coronary arteries, which deliver blood to the heart, become too narrow and the supply of fresh blood and oxygen becomes inadequate, resulting in a sudden heart attack with no prior warning.
Cardiac imaging, such as myocardial perfusion imaging, can show doctors if your heart is getting enough blood, and how well it is pumping. It is used to identify signs of coronary artery disease, obstructed CAD, and to check for any damage caused by a heart attack.
SPECT (single-photon emission computerized tomography) is the most common test used for clinical myocardial perfusion imaging, due to its ability to demonstrate indispensable practicality and efficacy in the diagnosis and evaluation of patients with suspected or known cardiovascular disease. However, the success of each technique largely depends on the features and processes that are most suited to a specific condition or patient. For example, the SPECT method is more suited to patients with a high BMI.
Myocardial perfusion PET stress test, also known as a Rubidium PET, shares many similar qualities to a SPECT test as they both use radiopharmaceuticals to generate 3D images which provide metabolic and functional diagnostics of the heart. Like a SPECT test, a PET stress test is more adapted to diagnosing problems in the early stages of ischemia.
Cardiac MRI, or CMR, has been recognised as a practical alternative technique in the evaluation of myocardial perfusion. CMR is being used more and more to assess rest and stress perfusion and to recognise infarct and myocardial ischemia with a high level of accuracy. This non-ionizing method utilises contrast agents that are intravenously injected to measure the change of regional myocardial magnetic properties. Because of the spatial resolution and high contrast, an MRI allows differentiating sub-epicardial and sub-endocardial perfusion, which makes it a strong candidate for an alternative method to myocardial perfusion.
CT perfusion imaging offers accurate coronary angiography data, using an invasive catheter-based method that can measure coronary compulsion and circulation. Although this method is not frequently used, studies show CT scans can achieve the quantification of pathophysiological specifications of myocardial ischaemia.
How does myocardial perfusion imaging work?
Magnetic resonance myocardial perfusion imaging (stress CMR) is frequently used to assess patients with symptoms most associated with ischemia, such as breathlessness or chest pain. This technique is also used to evaluate the physiologic importance of coronary artery lesions to determine whether patients will need to be medically treated, or will need coronary artery stenting or bypass surgery. In addition, heart muscle damage caused by underlying CAD can also be discovered by using this technique.
It usually takes around 30-45 minutes to complete this test, depending on the patient’s heart rhythm and ability to follow the instructions. There are two scans for this approach. The first one is performed using an injection of a contrast medium that is transferred into a patient’s vein during the scan. The contrast formula accentuates parts of the heart muscle that are receiving an adequate supply of blood. Areas that are failing to receive a good supply of blood are not highlighted as well, which can indicate ischaemic heart disease.
After a short delay, the second scan is performed to highlight any parts of the heart muscle that may be scarred, which is usually the occurrence of a previous heart attack. The images from the MRI can indicate how thick and prominent the scarring is.
Overall, the CMR test is considered a very safe procedure, and far more accurate at detecting ischemic heart disease than the treadmill exercise test. Because the heart is being stressed pharmacologically, patients will not need to perform any exercise during a CMR, which makes it the perfect test for patients who cannot exercise due to their health conditions.
What can a myocardial perfusion scan show?
As mentioned above, the test can highlight a lack of blood flow to the heart, which is a big indicator of ischaemic heart disease. It can also determine if there is any scarring of the heart muscle caused by a heart attack. It is frequently used to assess patients who experience symptoms of ischemia in the heart, such as breathlessness and or chest pain.
Stress CMR is also used to show patients with current or exacerbating symptoms following a prior:
- Stress imaging test
- Exercise ECG test
- obstructive coronary artery disease test
- non-obstructive coronary artery disease test
Why do I need a myocardial perfusion imaging test?
There are several reasons why your doctor might order myocardial perfusion imaging. These include:
- For the diagnosis of CAD (the narrowing of the coronary arteries)
- If you experience frequent chest pain
- To assess blood flow to the heart following coronary artery bypass surgery, stent placement, or angioplasty
- To assess muscle damage after a heart attack
Myocardial perfusion imaging accuracy
While myocardial perfusion imaging can’t display the obstruction in a blood vessel, it is able to indicate the arteries that are affected. Myocardial perfusion imaging with SPECT cameras has been found to have an accuracy of between 44% to 70%, depending on which blood vessels are involved. Research has found that myocardial perfusion imaging performed on cadmium-zinc-telluride cameras, is significantly more accurate in detecting obstructive CAD than when traditional single-photon emission computed-tomography (SPECT) camerasare used.
However, Studies show the CMR test is proven to be more sensitive (sensitivity rating of 86.5%, whereas SPECT was 66.5%) and offers a higher specificity than a SPECT test when analysing CAD.
A SPECT test also has a significantly lower negative predictive value (79.1%) than a CMR test (90.5%) and a lower positive predictive value (71.4%) than CMR (77.2%). Furthermore, there is no concern about being subjected to radiation during a CMR test as it does not use ionising radiation, whereas a SPECT test does.
It’s evident CMR has higher diagnostic accuracy than SPECT in coronary heart disease, reflecting CMR's superiority over SPECT. Furthermore, CMR provides a non-invasive and radiation-free examination of myocardial perfusion, wall motion, left ventricular function, and myocardial viability, therefore it may be thought of as the favoured imaging modality to assess patients with suspected or known coronary artery disease. This concludes that CMR should be adopted more widely than its counterparts for the diagnosis, investigation, and measurement of CAD.
Quantitative myocardial perfusion software
Of the software packages on today’s market, quantitative perfusion software such as cvi42 from Circle CVI is considered to be the leading option. It offers more clinically cleared diagnosis tools and more accurately quantifying and qualifying research tools than any other type of myocardial perfusion software.
cvi42 is a fully comprehensive reading and reporting solution that doesn’t just cover quantitative perfusion but also encompasses cardiac MR and CT, myocardial strain, 4D flow, electrophysiology, and interventional planning.
As the global leader in cardiac imaging solutions, the cvi42 will outperform qualitative & semi-quantitative techniques, providing a high level of diagnostic accuracy and fast, automatic analysis. No manual segmentation is required with the fully automatic quantification of user-independent cvi42, which offers a more cost-effective and non-ionizing option than alternative myocardial perfusion imaging modalities. The intuitive post-processing analysis of cvi42 allows findings to be communicated with ease.
Discover why clinicians value robust and user-friendly cvi42 as an essential tool in their long-term development. Try cvi42 for 42 days and realize the benefits of a seamless post-processing solution. Download a trial of cvi42 today.
For more information, contact the Circle CVI team.