SPECT scan

SPECT scan or Single Photon Emission Computed Tomography Scan uses advanced imaging technique. It is a type of nuclear imaging where radioactive substances are injected into the body and viewed with the help of a special camera. It is a part of diagnostic medicine that analyzes the perfusion capacity of body organs and their functionality. It gives a 3-dimensional picture of the organs and bones inside the body. 

Technique:

SPECT works on the principle of producing a 3-dimensional image of the tissues by the distribution of a radioactive tracer or probe. These tracers contain a detectable radioactive isotope coupled with a biologically active ligand specific to the tissue or organ that is imaged. The most common radioactive probes are technetium-99m (Tc), iodine-123, and thallium-201.

• Tecnetium-99m isotope: This tracer is most preferable as it loses half of its radioactivity in 6 hours, has lower scan times, and has lesser radiation exposure to the target organ. Hence, higher doses can be easily administered without increasing radiotoxicity to the patient. This tracer is attached to a compound that can easily cross into the brain to visualize brain disorders like dementia. If this tracer is attached to another compound that can cross the membranes of the blood vessels in the heart, it can be used to visualize heart disorders.
• Iodine-123: This tracer takes about 13 hours to lose its radioactivity and results in a greater concentration of iodine in the target tissue. Due to its longer half-life and greater concentration of iodine-123 increases the radiation exposure to the organ and is used for scanning thyroids.  

This radioactive tracer is injected into the blood vessel which is ultimately taken up by the tissues to be viewed. Once taken up by the tissues, specialized cameras are used to view them. SPECT machine is a huge round device with a camera. This gives information about the physiological status of the organ like its functioning capacity and perfusion status. 

Indications:

SPECT scanning is of immense use in tracking the functionality of various organs like the brain, heart, and bones. It is indicated for diagnosing, evaluating, and assessing the prognosis of various diseases and conditions. Hence it is indicated in:

• Brain disorders like dementia, Parkinsons, and clogged blood vessels, 
• To identify the focus of seizures before any surgery
• Flu-like brain inflammation called encephalitis
• Blood accumulation in brain conditions like subarachnoid hemorrhage and trauma
• Localizing brain perfusions in surgical interventions
• Diagnosing and evaluating various cerebrovascular conditions and predicting the prognosis in cerebrovascular accidents
• Brain death 
• Heart diseases like coronary artery disease and heart failure and also in presurgical evaluations. 
• It is also useful in identifying clogged arteries and knows the pumping action of the heart
• Apart from cardiac and neurological conditions, it is also used in bone infections called osteomyelitis, lung conditions like pulmonary embolism, and any abscesses. 

Contraindications:

Pregnancy and allergy to the tracers are contraindications for SPECT scans. 

Before the procedure:

An individual undergoing a SPECT scan procedure can have their regular diet and medications. It is advisable to inform the HCP of the medical history, previous surgeries, allergies to radioactive tracers, and medications. One should also inform the HCP of pregnancy and breastfeeding. Metal things like jewelry, watches, hairpins, spectacles, dentures, wigs, hearing aids, wired bras, and cosmetics with metal particles should be removed.  Information regarding the presence of any metal prostheses should be given to the healthcare provider. 

One should not do strenuous exercise as it can alter the uptake of tracer from the tissues. It is advisable to take a low-carbohydrate, no-sugar diet before the scan. Medications like dipyridamole and other phosphodiesterase-3 inhibitors should be avoided at least 2 days before the scan as they may cause a sudden drop in blood pressure. It is advisable to avoid caffeine, alcohol, or tobacco before the scan. One has to empty the bladder before taking the scan.

During the procedure:

While undergoing a SPECT scan, the patient is made to relax, and a tracer is injected into the blood vessel. Sedation is given to calm the patient. The amount of tracer to be given depends on the weight of the individual. After injecting the tracer, the patient is made to wait till the tracer is taken up by the body. The waiting time varies between the type of tracer and the area that is being scanned. Brain scans can take a waiting period of 90 minutes while heart scan studies can take about 15 minutes. 

After the waiting period, the patient is taken to the scanner room where the gamma detector is present. Perfusion capacity of the organs is measured by giving stimulant medications for perfusion assessment. The patient lies on a table and the detector or the camera rotates around the patient to capture images every 3-6 degrees. The camera should be placed as close as possible to the patient to obtain better images. Based on the protocols single scan or multiple scans are taken. All the images are combined to produce a 3D image. The images are sent to the computer which reconstructs the 3D images. Sometimes SPECT can be combined with anatomical scans like CT scans. 

After the procedure 

One can resume activities of daily living after a PET scan. The results will be interpreted by the HCP. The tracer will be removed through the urine. Individuals are advised to drink a lot of fluids to remove the tracer from the body. 

Interpretation

The results will be interpreted by the healthcare provider based on the abnormality they detect. Less uptake of the tracer shows a lighter color and more uptake of the tracer shows a darker color in the scans. 

Risks and Complications:

The main risks and complications are due to the allergies from the radioactive tracers, and reactions to the vasodilator medications that are given. These medications cause redness, flushing, headache, GI distress, and lightheadedness. Further complications like hypotension, arrhythmias, chest discomfort, or heart blockade can also occur. 

Conclusion:

SPECT is an advanced imaging technique used to visualize the physiological status of the body. It studies the perfusion and function of various internal organs. By taking the tracer, and obtaining 3D images of the tissue a lot of information can be obtained about it.