The word “SPECT” signifies Single Photon Emission Computed Tomography. SPECT is a technology used in Nuclear Medicine to evaluate the parenchyma of certain structures such as the heart, brain, skeleton, kidneys and tumors. It appears to be very similar to a normal CT Scanner, but consists of 2 large Gamma Cameras situated on the outside of the gantry at 90 degrees from each other. In most cases, SPECT is used to observe and monitor the progression of a known pathology.
In order to do a SPECT Scan, the patient is required to take a radioisotope, emitting gamma rays, by ingestion, inhalation or injection. There exists many different kinds of radioisotopes that can be used during this scan, each depending on certain factors such as the type of scan you are about to perform and what you are looking for. Also, depending on the scan, the patient may be required to wait a certain amount of time after the radioisotope has been taken before the scan can begin. This could be seconds, minutes, hours or days. At this time, the patient will be positioned on the table and the Gamma Cameras will rotate around the patient, taking an image at every 3 degrees.
For example, in a full rotation of 360 degrees, roughly 120 images will be captured. The system itself is very similar to the CT Scanner in the sense that your are able to produce 3D images in different planes. This type of reconstruction is done using the “Filtered back-projection”. SPECT scanners are often compared to the PET scanners. What differentiates these two is the type of radioisotope the gamma camera is able to detect. There is a large variety of radioisotopes that can be used for a SPECT Scan compared to a PET scan because they do not all have to be positron emitting radioisotopes. According to Computed Tomography, 4th Edition written by Euclid Steeram, PET and SPECT are indeed very similar.
Though PET is more expensive and much more sensitive to information than SPECT, only 1 in 10,000 gamma rays emitted by the patient will actually be detected by the gamma camera during a SPECT. Therefore, it requires a longer scanning time to have better quality images. In this case, it is important to remember that the closer the Gamma cameras are to the patient, the better the spatial resolution will be.