In recent years, computerized tomography (CT) has emerged as a rapid and accurate non-invasive cardiac imaging modality. Access to this type of imaging has changed the landscape of how providers can get a closer look at the heart and has become a valuable diagnostic tool in their toolkit. Unfortunately, it has also led to confusion on which CT is the right test for the patient. When a provider looks at the different exams in the electronic health record (EHR), the options can muddy the water. For cardiac alone, one can see single photon emission computed tomography with computed tomography (SPECT/CT), positron emission tomography with computed tomography (PET/CT), cardiac calcium scoring, cardiac perfusion CT, cardiac CT for structural heart, coronary CT angiography (CCTA) and CCTA with fractional flow reserve (FFR). In this blog, we will explore the different types of CT in the cardiac space.
How Is CT Used in SPECT and PET?
Due to the similarities in the imaging modalities, SPECT/CT and PET/CT will be grouped together for the CT discussion.
A SPECT/CT or PET/CT can be found in the nuclear medicine/PET department, where the patient is injected with a radiopharmaceutical before images of the heart are taken. A cardiac SPECT/CT or PET/CT scan starts with acquiring a low-dose, non-contrast CT scan immediately before the SPECT or PET imaging. Then, the CT images are fused (or superimposed) with the SPECT/PET images to provide an anatomical localization of the radiopharmaceutical uptake. The CT also provides attenuation correction from potential artifacts from the emitted gamma rays through the patient's body tissues. It is important to note that the CT scan taken during this procedure is considered a non-diagnostic CT. While a low dose CT can detect significant structural abnormalities, it may not be adequate to detect subtle disease.
Can a SPECT/CT or PET/CT camera be used for stand-alone diagnostic CT? The short answer is yes, but it depends on the camera specifications and imaging protocols used. Traditionally, a SPECT/CT or PET/CT camera uses the CT portion for fused images only and does not provide a stand-alone CT scan.
It is also important to note the requirements of "who can press the button" on these fused camera systems. Each state has different requirements on who is eligible to perform the nuclear medicine/PET component vs. the CT portion. For most states, fused or hybrid imaging can be performed by a credentialed nuclear medicine technologist (CNMT or ARRT(N)). Facilities should review state requirements to ensure appropriate personnel perform these procedures.
What Is Cardiac Calcium Scoring?
Calcium scoring CT is a non-invasive test that measures the amount of calcium (or plaque) buildup in the coronary arteries. The test involves a low-dose CT scan that produces images of the heart. The images are then analyzed to identify calcium deposits in the coronary arteries.
Calcium scoring CT is used to determine a patient's risk of developing coronary artery disease (CAD). A higher calcium score indicates a greater risk of CAD. This test benefits patients at moderate risk of developing CAD but with no symptoms. In addition, it allows doctors to identify patients who may benefit from lifestyle changes or medication before the onset of symptoms. However, this exam is seen as a screening tool for many insurance carriers and will be an out-of-pocket expense to the patient.
A calcium scoring CT does not require the injection of contrast and can be performed as a stand-alone exam or in conjunction with a SPECT/CT or PET/CT. As this is a stand-alone CT exam, the eligibility of who can perform the exam will need to be reviewed. It is a common requirement for the technologist to be board certified in CT (NMTCB(CT) or ARRT(CT)). Once again facilities should review state requirements to ensure the appropriate personnel are performing these procedures.
What is a Cardiac CT?
The term "cardiac CT" can be a broad category for any CT that images the heart. However, there is a distinction between a cardiac perfusion CT and cardiac CT for structural anatomy.
Cardiac CT for structural anatomy is a non-invasive test that uses X-rays to create detailed images of the heart anatomy and surrounding structures. The test can be performed with or without IV contrast. The CT scanner captures multiple images of the heart from different angles, later reconstructed by a computer to create a 3D image of the heart and its structures.
Cardiac CT for structural heart disease is used to diagnose and evaluate conditions such as heart valve disease, congenital heart disease, and aortic aneurysm. It can also be used to assess the effectiveness of treatment after surgery or other interventions.
This exam is often confused with a coronary CT angiogram (CCTA) as both review the heart. However, a Cardiac CT will evaluate the anatomy and structure, while a CCTA evaluates the blood flow to the heart muscle (myocardium).
What Is a Cardiac Perfusion CT?
Cardiac perfusion CT, also known as CCTA, is a non-invasive test that evaluates myocardial blood flow (or blood flow to the heart muscle). The CT scanner captures multiple images from different angles before and after the administration of IV contrast. Images are then analyzed to evaluate blood flow in different segments of the myocardium.
A CT technologist performs a stand-alone diagnostic CT. State requirements designate the criteria for who can perform this test. The most common pathway is to be CT board certified (ARRT(CT) or NMTCB(CT)). As previously stated, facilities should review state requirements to ensure the appropriate personnel are performing these procedures.
What Is CCTA With FFR?
CCTA with FFR is a type of CT exam that combines the non-invasive imaging capabilities of CCTA with a measurement of blood flow through the coronary arteries using a technique called fractional flow reserve (FFR).
During a CCTA with FFR, the patient undergoes a regular CCTA scan to produce detailed images of the coronary arteries. Then, special computer software analyzes the CCTA images to create a 3D model of the arteries and simulates the blood flow through them.
The FFR measurement helps to determine whether a narrowing in the artery is causing a reduction in blood flow and whether it requires revascularization with a stent or coronary bypass surgery. Combining CCTA with FFR can provide more detailed and accurate information about the extent and severity of CAD, allowing doctors to better plan and personalize treatment for their patients.
Conclusion
In summary, cardiac CT scans are a valuable tool for diagnosing and evaluating heart-related conditions. The different types of cardiac CT scans have unique purposes and advantages, making them useful in different scenarios. MedAxiom’s listservs are a great place to ask your peers and industry experts about equipment and staffing questions. Additionally, MedAxiom’s Care Transformation Services team is always happy to provide guidance and resources.