INFLUENCE OF OSEM, ELLIPTIC ORBITS AND BACKGROUND ACTIVITY ON SPECT 3D RESOLUTION RECOVERY

In maximum-likelihood expectation-maximization (MLEM) reconstruction o f SPECT images, if both attenuation correction (AC) and detector respo nse correction (DRC) are included, the reconstruction can be too time consuming to be clinically useful. With use of the ordered-subset expe ctation-maximization (OSEM) reconstruction, it has been reported that the reconstruction time can be substantially reduced. We investigated the reconstruction of point sources in a non-uniform attenuation mediu m in terms of the normalized FWHM of these sources. We compared MLEM v ersus OSEM reconstructions; circular versus elliptical orbits; and the presence versus the absence of background activity in the object. We found: (i) that OSEM does speed up the reconstruction by a factor of 1 0 over MLEM; (ii) that the resolution recovery does not depend on the type of orbit if both AC and DRC are included in the reconstruction; h owever, when there is background activity, a significant number of ite rations are required to alleviate the effect of orbit; (iii) that back ground activity significantly slows down the resolution recovery of th e point sources; and (iv) that if reconstruction only includes AC, and not DRC, changing orbit can change isotropy of recovered resolution, whereas introducing background activity may degrade the recovered reso lution and also changes the isotropy.