impact of novel incorporation of ctbased segment mapping into a conjugated gradient algorithm on bone spect imaging: fundamental characteristics of a contextspecific reconstruction method

Objective(s): the latest single-photon emission computed tomography (spect)/computed tomography (ct) reconstruction system, referred to as xspect bone™, is a contextspecific reconstruction system utilizing tissue segmentation information from ct data, which is called a zone map. the aim of this study was to evaluate theeffects of zonemap enhancement incorporated into the orderedsubset conjugated gradient minimization (oscgm) reconstruction method on spect images.methods: image quality with zonemap enhanced oscgm (oscgmz) and nonenhanced oscgm methods was compared using various reconstruction parameters. the compartment phantom had 3 radioactive sections with ct values of about 1000, 250, and 0 hu. spect data were acquired using a lowenergy highresolution (lehr) collimator, with a 256×256 matrix and 2.4mm pixel size. the performances of the 2 reconstruction methods (oscgm vs.oscgmz) were evaluated on the basis of %error, coefficient of variation (%cv), and normalized mean squared error (nmse), and adequate iterative update numbers were determined. the relative cv representing the ratio of smoothed images to nonsmoothed images was calculated to evaluate the effects of the gaussian filter on each section set with different ct values.results: on comparing the oscgm and oscgmz methods, it was found that the %error of the oscgmz method tended to show convergence with fewer updates, especially in the high ct value section mimicking bone absorption. in the watersection, the %cv of the oscgmz method was lower than that of the oscgm method. the nmse minimum values for the oscgm and oscgmz methods were obtained at 30 and 20 updates, respectively. the relative cv for the oscgmzmethod in the water section decreased remarkably according to the size of the full width at half maximum (fwhm) of the gaussian filter.conclusion: the zonemap enhancement contributed to spect reconstruction for the reproduction of radioactive concentrations in bone tissues, using a low number of oscgm updates. our findings indicated that the incorporation of zone maps into spect reconstruction might improve image quality.