Single photon emission computed tomography

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Single-Photon Emission-Computed Tomography (SPECT) is a type of computed tomography that uses radionuclides which emit a single photon of a given energy. The camera is rotated 180 or 360 degrees around the patient to capture images at multiple positions along the arc. The computer is then used to reconstruct the transaxial, sagittal, and coronal images from the 3-dimensional distribution of radionuclides in the organ. The advantages of SPECT are that it can be used to observe biochemical and physiological processes as well as size and volume of the organ. The disadvantage is that, unlike positron-emission tomography where the positron-electron annihilation results in the emission of 2 photons at 180 degrees from each other, SPECT requires physical collimation to line up the photons, which results in the loss of many available photons and hence degrades the image".[1]


The patient slides into a imaging gantry, on which one or more SPECT cameras are mounted.

Clinical uses

Common uses in nuclear medicine include assessment of cardiac function before and after exercise, with 99Tc (Technetium) serving as an analogue to potassium in cardiac tissue. The scan differentiates between infarcted and ischemic cardiac muscle; revascularization will help the latter but not the former.


  1. National Library of Medicine. Tomography, Emission-Computed, Single-Photon 1. Retrieved on 2007-12-09.