Spect Imaging Has Significantly Changed The Way We Understand The Human Condition
SPECT (Single Photon Emission Computed Tomography) imaging is a nuclear medicine procedure where the NM “camera” rotates around the patient acquiring images at specific angles for a predefined amount of time. For cardiac you image for 180 degrees, for all other SPECT images (brain, bone, etc.) you image for 360 degrees. This data is then processed.
While 3D images are available for cardiac imaging, they aren’t the images that are relied upon for the primary diagnosis. Depending on the software used, 3D imaging for brain can be used more heavily for the diagnosis. What makes SPECT (nuclear medicine) imaging unique is that it shows the function of the organ being imaged. You inject a patient with a low-dose radioactive source tagged to go to a specific part of the body (brain, heart, bone, lungs, kidneys, liver, etc.). The patient is then imaged to show function – how much blood is, or is not, being pumped through the heart, activity in different parts of the brain, kidney function, etc.
As an example, you can image a deceased person on a CT or MRI system and still get an image – structural image of the body. You can’t image a deceased person with Nuclear Medicine. NM imaging relies on blood flowing through the body. It relies on the body functioning. If you tried to image a deceased person all you would see is a hot spot where you injected the radioactive source.
A Primer on Spect Imaging
A SPECT scan involves two steps. The first part of the procedure involves the intravenous injection of a low-dose radioactive tracer “tagged” to go to the specific part of the body being imaged. The dose that’s given to the patient is very small and shouldn’t have any negative effects. There have been a few rare cases in which the patient may have had an allergic reaction to the radioactive tracer; however, there are no long-term effects. The only time that it might pose a serious issue is if the patient is pregnant or breastfeeding. If this is the case, the radioactive tracer could be passed to the fetus or the baby. SPECT scans are considered unsafe for pregnant women or breastfeeding women for this reason.
Once injected, the patient will feel a cold sensation as the radioactive tracer is absorbed by the body. Usually, it will take around 20 minutes, although it can take several hours or, in rare cases, a couple of days, before the patient can go on to the second step. The delay between injection and imaging is to allow the radioactive source to flow through the body and “collect” in the area being imaged.
Once the body has absorbed the radioactive tracer, the patient will need to be placed into the SPECT machine in order to undergo a SPECT scan. The machine is a large circular device that encircles a table. The patient lies on the table while the machine rotates around them. The machine contains a special electronics that detect the radioactive tracer that was absorbed by the patient’s body. As the machine rotates, images will be taken of the patient’s inner organs and other structures.
The images that are acquired by the SPECT system are then sent to a computer to be processed for review and diagnosis. The imaging process varies depending on the reason behind the procedure. When analyzing the images, doctors will be able to see what parts of your body absorb more of the radioactive tracer and what parts absorb less. The amount absorbed depends on the activity of an area of the body. For example, if the patient has a seizure, the part of the brain that causes the seizure will retain more of the radioactive tracer. This, in turn, helps doctors to identify what part of the patient’s brain is causing the seizures.
As for the radioactive substance that was injected into the patient’s body, the majority of it will be flushed from their body through their urine within a few hours of the scan. What little remains will be broken down by the body within a few days.
Common Uses of SPECT Imaging
Although traditional 2-D images of the inside of a patient’s body can be very helpful in diagnosing certain conditions, it’s worth noting that the internal organs and structures function in three dimensions. As such, 2-D images will never tell the full story. In certain situations, getting a 3-D view can make it much easier to identify problem areas, especially how certain parts of the body are functioning. This is especially true in the case of the patient’s heart, brain, and bones.
For example, a doctor can use a SPECT scan to identify how the patient’s blood is flowing to their heart, thereby allowing them to see how effectively the heart chambers are emptying during contractions or whether the patient has any clogged coronary arteries.
The use of SPECT can help a doctor to get a better look at the blood flow to the heart of a patient, which allows them to identify a range of potential health issues that may be difficult to pinpoint otherwise. For example:
- Heart pumping efficiency – A SPECT scan can help a doctor determine how effectively the heart chambers of a patient are emptied during contractions. If one or more of the chambers aren’t emptying all the way during contractions, it could mean the patient has coronary artery disease, which might put the patient at risk of heart failure.
- Clogged coronary arteries – SPECT images make it easy for doctors to see whether the arteries connected to the heart are narrower than usual or whether they have become clogged. These issues can cause parts of the heart muscle that are served by these arteries to weaken or die.
- Heart scar tissue – Scar tissue is often left in areas that are dead as a result of a previous heart attack. Doctors can identify scar tissue due to a lack of the radioactive tracer in an area. Essentially, the presence of scar tissue confirms that the patient suffered a heart attack. Additionally, the presence of too much scar tissue can be problematic since it can lead to congestive heart failure or dilated cardiomyopathy.
Besides being able to identify potential issues with the heart, SPECT imaging also makes it possible for doctors to track how certain heart procedures are holding up. For example, they can use SPECT images to see how effective were certain cardiac procedures, such as bypass surgery.
SPECT imaging can be used as part of a stress test as well. Stress tests, also called nuclear stress tests, provide doctors with an idea of how well a patient’s heart performs under stress (such as during physical exertion). In some cases, SPECT imaging may reveal normal blood flow in a patient. However, if they undergo SPECT imaging as part of a stress test, it could show that their blood flow is abnormal. This usually means that not enough blood flows to a certain area of the heart when it’s under stress — which can occur due to blockages in the arteries.
Since the radioactive substance that’s injected into the patient is absorbed by areas with high activity, it makes SPECT imaging particularly effective for certain bone disorders, specifically bone fractures and cancer.
- Bone Fractures – Breaks or fractures in the bone aren’t always visible in regular X-ray scans, especially very minor fractures or breaks that are difficult to make out in a standard 2-D image. SPECT imaging makes it much easier to identify bone breaks and fractures. This is because the healing activity in the area of the break or fracture will “light up” as a result of the radioactive tracer, making it very visible on a SPECT-produced image.
- Cancer – SPECT imaging can actually be very beneficial in helping to identify cancer in its early stages, thereby increasing the chances of being able to treat it successfully. This is especially true for prostate cancer. The reason for this is that although the most common site of metastatic disease in the lymph nodes, the second most common site is the bone. Doctors can use SPECT imaging to identify the presence of metastatic disease in the bone, which can help them to diagnose cancer in a patient.
Brain activity is directly related to a patient’s blood flow, which is why SPECT imaging is particularly insightful for not only diagnosing brain disorders, but also learning more about what causes certain brain disorders and how the brain functions as a whole.
A normal SPECT scan of the brain will reveal a full, symmetrical perfusion (the passage of blood through the circulatory system to an organ — in this case, the brain). To identify issues with the brain, doctors will look for symmetry in addition to areas with increased or decreased perfusion.
Decreased perfusion is a sign of some sort of illness, injury, or toxicity to the brain. Patients with histories of drug and alcohol abuse often showcase decreased perfusion in their brain scans. It can also be caused by exposure to environmental toxins, such as carbon monoxide poisoning, as well as infectious diseases, from meningitis to hypothyroidism. SPECT imaging can also reveal traumatic injuries that occurred in the past, which can account for symptoms the patient may be suffering in the present.
What’s really incredible about SPECT imaging is that it can be used to help evaluate cognitive decline. For example, although autopsy reports are considered the most effective way to diagnose Alzheimer’s Disease, research suggests that SPECT imaging can be used in conjunction with other diagnostic tests as well as the patient’s clinical history to make a more accurate diagnosis.
Other types of cognitive disorders can be linked to decreased perfusion in specific parts of the brain. Frontal lobe dementia can be identified by decreased perfusion in the frontal and temporal lobes, while Lewy Body Dementia can be identified by a decreased perfusion in the occipital lobe.
The ability to identify and diagnose many cognitive disorders, illnesses, and traumatic injuries wouldn’t have been possible without being able to compare SPECT scans of various brains, thereby pinpointing what parts of the brain are affected when patients have certain disorders.
Some Amazing Insights Gained From SPECT Imaging
SPECT imaging has made it easier to diagnose many different conditions and disorders much more accurately than 2-D images have previously allowed. This has reduced the risk of missing potential problems that the patient might have, from minor fractures to major illnesses (such as cancer) since doctors have access to a much more complete picture of the patient’s organs and structures as a result of the 3-D images a SPECT scan produces.
Not only has SPECT imaging been incredibly beneficial to the ability to make accurate diagnoses that allow for earlier and more effective treatment, but they have also allowed researchers to discover how certain conditions or disorders affect different parts of the body, giving them more insight into previously misunderstood or little-understood conditions.
What Future Insights Might We Gain From SPECT Imaging
SPECT imaging has been around since the 1950’s; however, widespread use didn’t occur until the 1980s due to the limited availability and the high costs of the involved technology. Since then, use of SPECT imaging has increased significantly, which has led to great improvements throughout the healthcare industry on both the diagnosis and discovery fronts. SPECT imaging technology continues to advance as well. For instance, imaging times have recently been greatly reduced with the introduction of new gamma camera technology.
New camera designs have also allowed for better image reconstruction software. In fact, there have been many advances in SPECT software over the years, many of which have allowed doctors to reduce the doses of radioactive tracers while improving the quality of the image resolution.
As such advancements continue to be made in the technology of SPECT imaging, it shouldn’t be a reach to expect advances in medical research to be made as a result. There are still many mysteries concerning the brain. It was only recently that researchers found that SPECT could help distinguish between depression and other cognitive disorders — something that was often difficult to differentiate due to overlapping symptoms.
Additionally, there are still plenty of mysteries involving the brain that new SPECT imaging technology could help solve. For example, CTE (Chronic Traumatic Encephalopathy) has been all over the news lately due to the controversy surrounding concussions in the NFL. The problem is that CTE can only be identified through autopsy. It’s also quite difficult at the moment to differentiate CTE from other neurodegenerative diseases. However, there’s no reason not to believe that further advancements in SPECT imaging technology and further use of SPECT imaging in the research of CTE could result in a breakthrough in the near future.
More and more NM systems are being sold with a CT attached. The benefit is that the CT provides the anatomical (structural) images, SPECT provides the functional image. When one is overlaid on the other you can see exactly where in the body the activity is taking place. Think of it like a weather map. If they just showed you the colored weather (NM scan) it would be difficult for you to tell whether the storm was over WI or MI. Once you overlay the US map (CT image) with the states outlined you can tell exactly where the storm is.