Editing Single-photon emission computed tomography (section)

==Reconstruction==
{{Unreferenced section|date=January 2014}}
[[File:SPECT Sinogram 360.jpg|alt=|thumb|SPECT [[Radon transform|Sinogram]]]]
Reconstructed images typically have resolutions of 64×64 or 128×128 pixels, with the pixel sizes ranging from 3–6&nbsp;mm. The number of projections acquired is chosen to be approximately equal to the width of the resulting images. In general, the resulting reconstructed images will be of lower resolution, have increased noise than planar images, and be susceptible to [[Artifact (observational)|artifacts]].

Scanning is time-consuming, and it is essential that there is no patient movement during the scan time. Movement can cause significant degradation of the reconstructed images, although movement compensation reconstruction techniques can help with this. A highly uneven distribution of radiopharmaceutical also has the potential to cause artifacts. A very intense area of activity (e.g., the bladder) can cause extensive streaking of the images and obscure neighboring areas of activity. This is a limitation of the [[filtered back projection]] reconstruction algorithm. [[Iterative reconstruction]] is an alternative algorithm that is growing in importance, as it is less sensitive to artifacts and can also correct for attenuation and depth dependent blurring. Furthermore, iterative algorithms can be made more efficacious using the [[Superiorization]] methodology.<ref>{{cite journal | doi=10.3934/ipi.2014.8.223 | year=2014| volume=8 | vauthors = Luo,S, Zhou,T| s2cid=119657086|title=Superiorization of EM algorithm and its application in single-photon emission computed tomography (SPECT) | journal=Inverse Problems and Imaging | pages=88–97| arxiv=1209.6116}}</ref>

Attenuation of the gamma rays within the patient can lead to significant underestimation of activity in deep tissues, compared to superficial tissues. Approximate correction is possible, based on relative position of the activity, and optimal correction is obtained with measured attenuation values. Modern SPECT equipment is available with an integrated X-ray CT scanner. As X-ray CT images are an attenuation map of the tissues, this data can be incorporated into the SPECT reconstruction to correct for attenuation. It also provides a precisely [[Image registration|registered]] CT image, which can provide additional anatomical information.

Scatter of the gamma rays as well as the random nature of gamma rays can also lead to the degradation of quality of SPECT images and cause loss of resolution. Scatter correction and resolution recovery are also applied to improve resolution of SPECT images.<ref>{{cite web|url=https://www.researchgate.net/publication/3134425|title= D. Boulfelfel, R.M. Rangayyan, L.J. Hahn, R. Kloiber, Restoration of Single Photon Emission Computed Tomography Images|access-date=10 January 2016}}</ref>