Single Photon Emission Computed Tomography (SPECT)
Single-photon emission computerized tomography (SPECT) scans provide three-dimensional images of the interior of your organs using radioactive chemicals and a specialized gamma camera. Healthcare professionals can use this kind of imaging to non-invasively assess the condition of specific body parts, most frequently the heart, brain, and bones.
SPECT scans can display an organ's level of function, which distinguishes them from other imaging techniques. For instance, the SPECT scan images can be used to determine where epileptic patients experience their seizures and to determine whether the various parts of the brain are receiving enough blood flow.
Single-photon emission computed tomography scan (SPECT Scan) is a nuclear medicine tomographic imaging method that uses gamma rays. Using a gamma camera is very similar to traditional nuclear medicine planar imaging, yet it can produce accurate 3D data.
SPECT Scan Indications
The versatility of SPECT scans accounts for their widespread availability in hospitals, clinics, and imaging facilities. Your healthcare provider may decide to request this test for a variety of reasons such as a suspicion or the need for monitoring:
- Neurologic and brain conditions
- Cardiac disorders
- Bone abnormalities
Like other nuclear scans, SPECT uses radioactive tracers, carrier molecules bound to radioactive atoms, to assess, identify, and treat a variety of medical conditions. The healthcare professional chooses the proper tracer for you based on your symptoms or the disease that is being assessed because different tracers serve various tasks.
Neurological and Brain Conditions
The following alterations in brain function brought on by disease processes can be detected with SPECT scans:
- Traumatic brain injury (TBI)
- Alzheimer's disease
- Issues affecting the brain's blood supply
When radioactive tracers are employed during a SPECT scan, it is possible to detect potential cardiac disease processes as well as how well your heart is functioning. It can identify a variety of problems, including:
- Arterial stenosis
- Obstructed arteries
- Scarring from previous heart attacks
- Ineffective blood pumping
- Whether successful surgical interventions, such as bypass surgeries or other procedures.
Bone problems can benefit from SPECT scans since trouble spots frequently light up on the images. This technique can be used to investigate the following conditions:
- Stress fractures are less obvious bone fractures.
- Bone cancer or cancer that has spread to some bone regions.
- Infected bones
SPECT Scan Contraindications
Although there are no clear contraindications to SPECT imaging alone, patients may sometimes develop adverse responses to the tracer substance. Contraindications for SPECT imaging are most frequently associated with the underlying process rather than the real SPECT scan. For instance, a SPECT-enhanced cardiac stress test carries the same hazards and contraindications as a standard stress test. When sending pregnant patients for SPECT, clinicians should also carefully examine the dangers of radiation exposure, and radioactive iodine isotopes should be avoided in these patients due to fetal iodine uptake. Finally, some obese patients may weigh more than the scanner's weight capacity.
The majority of patients tolerate SPECT scans well, however, occasionally the test may not be necessary. For the following reasons, your healthcare provider can decide against conducting this test:
- You are nursing or pregnant. Low radiation levels used in the tests are not advised for pregnant mothers. You might need to wait a set length of time before nursing if you are breastfeeding so that your body has time to eliminate the radioactive tracer.
- You are allergic to the tracer. Although uncommon, this type of allergy is possible, and if you are known to be allergic to the tracer, you shouldn't undergo the scan. Know that the medical professionals nearby are prepared to help you if you experience an allergic reaction while having the scan.
SPECT Scan Preparation
Depending on why you are having the scan done, there may be different things you need to do to prepare. Your medical staff should provide you with detailed preparation instructions.
Inquire with your medical staff how much time you should give for the scan. Some SPECT scans take around 30 minutes, while others may take longer or shorter depending on the reason for the scan.
An imaging center, clinic, or hospital may all be used for testing. Usually, a nuclear medicine-trained medical staff will perform the scan.
For the process, you can dress however you choose, but before the scan, you will probably be asked to change into a gown. You could discover that wearing comfortable, loose-fitting clothing is a good idea for the test. Watches, jewelry, and earrings made of metal should be left at home.
If there are any foods or beverages you must avoid before the scan, your medical staff will let you know. For instance, you might need to abstain from coffee for many hours before the test if you are having a SPECT scan for cardiac concerns.
For your SPECT scan to be covered by your insurer, prior permission may be necessary. To find out what, if any, fees you will be responsible for paying, be sure to ask the company whether and how much the scan is covered. Without insurance, SPECT scans can cost more than $1,000. Bring a form of identification, your insurance card, and any papers you were asked to sign before the scan.
Make sure your doctor has a current list of all the prescriptions you are taking, including any over-the-counter drugs and dietary supplements. Before the procedure, your doctor might ask you to cease using a particular medication. Tell your healthcare practitioner if you are pregnant or nursing a child as well.
SPECT Scan Equipment
A rotating multi-headed gamma camera, a collimator, and a radio-labeled tracer particular to the target tissue are needed for SPECT imaging. The primary purpose of the camera is to detect photons that are emitted from the patient in all directions as a result of the gamma decay of the tracer molecule. These photons are filtered by the collimator, which only lets pass particles that are parallel to the detector. As a result, the collimator concentrates the radiation, and the choice of collimator affects the resulting image's sensitivity and resolution. The number of gamma camera heads reduces the scan time while increasing the resolution of the final image. However, trained medical physicists and nuclear radiologists can produce high-quality images with single-headed cameras.
The nuclear pharmacist's choice of a radio-labeled tracer substance is first administered to the patient. For brain tests, the patient will be advised to remain still and silent for at least 10 minutes before the injection of the tracer. If at all possible, sedation should be given after the tracer if the patient needs it for the procedure. There is a variable waiting period after injection to allow the tracer to circulate and be absorbed by the target tissues. For brain studies, this waiting period may last up to 90 minutes, while it may only last 15 minutes for cardiac stress testing. The choice of tracer and dose will also affect the wait times for a certain study.
The patient will subsequently be placed inside the detection device after the waiting period has passed. By established stress testing standards, the patient will be administered cardiac stimulants, such as atropine, if they are undergoing cardiac stress testing. Vasodilatory drugs may be used in cardiac and brain studies to evaluate tissue perfusion. The detector will circle the patient after administering the required drugs and obtaining planar scans every 3 to 6 degrees. These scans will be merged to create the final 3D image. Different imaging methods may call for a single scan, as in the case of brain imaging, or multiple scans conducted at predetermined intervals, as in the case of stress/rest imaging for cardiac SPECT. Even though SPECT has limits, it can nonetheless yield precise information about the tissues. Without accompanying anatomical imaging, small metabolic anomalies that may be seen on SPECT are frequently challenging to localize. A combined SPECT/computed tomography strategy has been designed to get around these problems by concurrently imaging functional and structural abnormalities found by the SPECT study on computed tomography as well.
How to Reduce Radiation Exposure During SPECT Scan
The following are some SPECT protocols that can be used to lessen radiation exposure and risks:
- Individuals' unnecessary radiation exposure will be reduced and there will be less chance of an error if the right patients are chosen for SPECT imaging based on a clear rationale.
- SPECT protocols based on technetium-99m (sestamibi and tetrofosmin) expose patients to less radiation than those based on thallium-201 (stress/redistribution and stress/reinjection). Technetium-99m-based procedures are safer and recommended for the evaluation of chest discomfort and the diagnosis of ischemia.
- To maximize the needed radioactivity dose, the radiotracer dose should be weight-based.
- The image camera's cadmium zinc telluride detectors offer better energy and spatial resolution and are more sensitive to incident ionizing radiation. Radiation procedures can be improved by using cadmium zinc telluride and Anger cameras.
- In comparison to standard rest/stress tests, SPECT stress-only procedures using technetium-99m tagged radiotracers may result in a 25% reduction in radiation dose. In patients who are good imaging candidates and who do not have a high pretest chance of an abnormal study, stress-first imaging is advised. Young patients, especially those with low to moderate pretest probabilities of coronary artery disease, are especially important and capable of achieving this.
- Radiation exposure can be reduced by optimizing the 2-day rest/stress technetium-99m (14 mSv) protocol to either stress only (7 mSv) or one-day rest/stress protocols (10 mSv).
- The methods used to get images can be improved to use less radioactivity. Lengthening acquisition times can lower the radiotracer dose in cooperative patients. To reduce the necessary radiation dose, it's essential to keep the camera as close to the patient as feasible throughout the acquisition.
- Despite lowering the radiotracer dose, newly created reconstruction techniques can preserve image quality from SPECT studies. A revolutionary wide-beam reconstruction approach allows for the acquisition of improved image quality while reducing radiation exposure by 50%.
- The acquisition protocol can be improved to use the lowest dose possible for attenuation correction if a scanner uses a CT scan for attenuation correction (rod-source).
- Software innovations like resolution-recovery methods can drastically lower radiation exposure.
SPECT Scan Risks
Mild reactions to the vasodilators and other drugs used during the test are the most frequent consequences of the procedure. Flushing, headaches, GI trouble, and lightheadedness are some of these side effects. There may also be more serious adverse effects including hypotension, arrhythmias, chest pain, or AV block. There is a small chance that the tracer molecule or research drugs will cause an allergic reaction. The patient's radiation exposure concerns should also be taken into account by the medical team, especially if the patient is pregnant or intends to become pregnant. The maximum effective radiation dosage for a Tc stress/rest heart scan is 11.8 mSv, while the effective dose for a Tc brain scan is 5.7 mSv. Except for cardiac stress/rest studies, the effective dose for the majority of SPECT scans is typically less than 10 mSv. Comparatively, head computed tomography, chest computed tomography, and computed tomography coronary angiography had effective radiation doses of 2.0, 7.0, and 16.0 mSv, respectively.
SPECT Scan Results
Where the radioactive tracer has been taken by your organs and tissues, your SPECT scan images will display bright or dark areas, either in color or in grayscale.
It is unlikely that your results will be ready right away. Your healthcare provider will need to be informed of the findings by a radiologist or nuclear medicine doctor.
You will be contacted by your healthcare physician or a member of their team to discuss the findings and determine whether further testing is necessary. You can obtain copies of your SPECT scan results and report for your records or if you would like to get a second opinion, which is something to keep in mind.
SPECT Scan Follow-Up
The kind of follow-up you might require after your SPECT scan will depend on what, if anything, was found by the test. Discuss with your doctor if the results will require any more diagnostic tests, monitoring, or appointments.
The field of molecular imaging clearly defines the function of SPECT imaging. High spatial and temporal resolution, as well as high detection efficiencies, are now possible with recent developments in specialized preclinical systems, and there is still room for improvement. Biological events could be characterized using hybrid SPECT imaging systems in a single imaging session. When used in conjunction with SPECT technology, reliable animal models that closely resemble human diseases will provide additional insights into the early diagnosis of diseases, the development of new tracers and therapies, and the design of effective treatment plans. Shortly, a great deal of fresh approaches is anticipated for SPECT imaging in molecular medicine.