What Is the Difference Between SPECT and PET Imaging for Cardiology?Posted on: 02.07.20 by Digirad
Cardiac imaging is a critical technology, particularly as cardiovascular disease is the leading cause of mortality for most developed nations.
While SPECT remains the leading modality for cardiac imaging, PET has continued to see growing interest. Naturally, patients and physicians want to know if one is better than the other and what the benefits and limitations are. In this article, we’re examining PET vs. SPECT in terms of utility for cardiology. Here is our comparison:
Both PET and SPECT imaging use cameras that detect injected radiotracers. However, each type of imaging works differently:
Single-Photon Emission Computed Tomography (SPECT) imaging provides metabolic and functional information about the heart. It is a non-invasive technique that involves injecting radioactive tracers into the bloodstream to get pictures which indicate whether or not a patient has cardiovascular disease.
The SPECT gamma camera picks up signals from the radioactive tracers as they move around the patient’s chest, then these signals are transformed into computer images. SPECT can be used to examine the heart while the patient is at rest, or during a nuclear stress test.
Perfusion imaging is generally performed twice – once at rest, then again after cardiac stress. It measures the blood flow to the heart.
The half-life of technetium-99m, the radiotracer used for SPECT is around six hours, which means technologists have plenty of time to perform the imaging that is required. This is how they are able to perform nuclear stress tests.
If we look at the decay of the radiotracer, it is quite straightforward. Each decay provides one gamma ray which is detected by the camera. Combining thousands of these gamma ray detections assist in the image creation that the physician uses for diagnosis.
Positron Emission Tomography (PET) is also non-invasive and uses injections of radiopharmaceuticals to assist a camera to create images of the heart. PET can be used to examine blood flow to the heart and will also show any damage, such as scar tissue from a heart attack.
A PET image can help physicians to identify areas of the heart that are damaged, but can be saved if blood flow is restored. They can identify whether a percutaneous coronary intervention (PCI) or coronary artery bypass is appropriate.
PET imaging mainly uses rubidium-82 as the radiotracer, which has a relatively short half-life of just 75 seconds. This means that technicians need to work very quickly to get the images required.
Looking at the decay of the PET radiotracer, it is slightly more complex than SPECT in that a positron emission occurs with each decay. Each positron decay site produces two gamma rays that are detected by the camera.
SPECT vs PET: Pros and cons
How do the two types of technology compare in terms of costs and benefits for cardiac imaging? Each modality has its own pros and cons:
SPECT is much more widely available than PET. It’s also much more affordable, with the average camera costing between $400,000 and $600,000. Due to its widespread use, there are more trained technologists available too.
The longer half-life of the SPECT radiotracer makes it more widely available and is ideal for cardiac stress testing. Improvements in radiotracer and camera technology are expected to boost image quality, helping to overcome a common SPECT complaint.
Image quality is the most common comparison point between SPECT and PET cardiac imaging. It is reported that SPECT resolution is at 12mm to 15mm and images can be prone to attenuation on older cameras. SPECT also does not provide a quantifiable estimate of the blood flow.
PET is less widely available and much more costly to implement, with cameras running into the millions of dollars. Cardiac stress testing can be performed with existing radiopharmaceuticals but can be challenging due to their short half-life, although this is potentially going to be solved in the future as new radiotracers are being developed.
One of the biggest pluses for PET scanning is the superiority of its image quality. For example, it tends to have fewer artifacts in images than SPECT. PET provides high spatial resolution and the capability to provide quantitative estimates of blood flow.
SPECT and PET are both used for cardiac imaging, although SPECT is more broadly available. Each has its own strengths and challenges, but each can provide quality images that allow for accurate diagnosis.
Is one better than the other? That very much depends on the technology involved. New developments are being made for both SPECT and PET, improving image quality, attenuation and other issues associated with imaging.
While there are studies that lean toward PET as a more accurate option for cardiology, there’s no denying that SPECT is still the go-to choice for most cardiologists .