SPECT (Single Photon Emission Computed Tomography) is a nuclear medicine tomographic imaging technique using gamma rays. The technique results in a set of image slices through a patient, showing the distribution of a radiopharmaceutical. There are several steps involved in producing the final set of slices.

Firstly a patient is injected with a gamma-emitting radiopharmaceutical. Then a series of projection images are acquired using a gamma camera. The acquisition involves the gamma camera rotating around the patient acquiring images at various positions. The number of images and the rotation angle covered varies depending on the type of investigation required, but a typical example involves the gamma camera rotating 360 degrees around the patient, acquiring 64 equally spaced images.

The projection images are stored digitally and a sophisticated computer program is used to process them and produce the slices (this is called reconstruction). There are a number of different methods for performing the reconstruction. At the time of writing (2004), by far the most commonly used method is 'filtered back projection'.

Other tomographic imaging modalities include:

• X-ray computerised tomography
• Magnetic resonance imaging
• Positron emission tomography.

SPECT tracers

Several other agents are also used, see Cardiac stress testing.

See also

• gamma camera
• brain imaging
• functional neuroimaging
• magnetic resonance imaging
• positron emission tomography