SPECT stands for “Single Photon Emission Computed Tomography.”
A SPECT scanner is a machine that detects the distribution of radiopharmaceutical concentrations in different parts of the body and reconstructs it in three dimensions using a computer.
A radiopharmaceutical is a drug to which radioactive atoms are attached so the location where the drug is concentrating in the body can be easily detected. There are different radiopharmaceuticals designed by manufacturers to concentrate in different patient organs and tissues that are of interest to their doctor in diagnosing disease.
SPECT scanners use the same technology as gamma cameras. While a gamma camera is limited to only 2D images, a SPECT scanner rotates a gamma camera around the patient to create 3D patient images. The high-energy gamma photons from the radiopharmaceutical meet a detector called a scintillation crystal that converts them into light. This light is then amplified and processed by the camera to reveal the distribution of the radiopharmaceutical.
Just as slices of a three-dimensional loaf of bread can be taken in any direction, so too can slices of the three-dimensional concentration of a radiopharmaceutical which may then be displayed for the doctor’s interpretation. One example is the uptake of a radiopharmaceutical in cardiac muscle, which helps the doctor to assess how well a patient’s heart is functioning.
An increasing number of SPECT scanners are combined with CT. This is useful for two purposes: improved image quality and quantitative accuracy and improved localization and diagnosis of SPECT radiopharmaceutical uptake by reading combined (layered) SPECT/CT images. The use of CT data also allows for the correction of minor errors that occur naturally in the SPECT data, giving doctors more accurate images to read.