Impact of different reconstruction algorithms and OSEM reconstruction parameters on quantitative results in SPECT/CT

Purpose: Impact of different reconstruction algorithms and OSEM reconstruction parameters on quantitative results in SPECT/CT [Abstract Objectives]:To evaluate the effects of 3-dimensional ordered subset expectation maximization(3D-OSEM), 2-dimensional ordered subset expectation maximization(2D-OSEM), filtered-back projection (FBP),and the number of OSEM iterations and subsets on quantitative results in SPECT/CT.

Methods: A Jaszczak cylindrical phantom and IEC body phantom were performed with routine SPECT/CT imaging using CT attenuation correction, scatter correction and 3D-OSEM reconstruct image. The system volume sensitivity(cpm/kBq) were acquired from the reconstructed image of Jaszczak phantom study, we calculated the absolute activity concentration (kBq /ml)of the hot sphere from IEC phantom study, then checking computations the quantitative accuracy of all. Change the reconstruction algorithm (2D-OSEM, FBP) and OSEM reconstruction parameters (number of iterations and subsets) to reconstruct the IEC phantom, Compared the difference of quantitative results from different reconstruction algorithms and OSEM iterations and subsets.

Results: When reconstructing images with 3D-OSEM, 2D-OSEM and FBP, the average quantitative error of each sphere increases with the decrease of the spherical volume(r= 0.831,0.831,0.826, p all<0.05). The average difference between the quantitative values and the true values of the different volume spheres among the three reconstruction algorithms was statistically significant (F = 8.850, p <0.05), among them that 3D -OSEM was less than 2D-OSEM (352 ± 198 and 423 ± 164 kBq / ml, p <0.05), 2D-OSEM was less than FBP (423 ± 164 and 695 ± 36 kBq / ml, p <0.05).The quantitative error of the seven different volume spheres (26.25 ~0.52ml) decreased with the increase of the number of iterations (r = 0.721, 0.681, 0.691, 0.711,0.845,0.893, p all<0.05), and decreased with the increase of the number of subsets (r = 0.670, 0.694, 0.717, 0.852, 0.956, 0.998, p all<0.05), But there was a significant difference in the variation between different volumetric spheres, the variation of the quantitative error tends to be stable when the number of iterations is greater than 8 and the number of subsets is greater than 6 in the larger sphere (26.25 ~ 5.57ml), and it was stable when the number of iterations is greater than 16,but it was continue to decreasd as the number of subsets increases in the smaller sphere (2.57 ~0.52ml).

Conclusions: The quantitative accuracy of 3D- OSEM reconstruction based on CT attenuation correction and scattering correction is significantly better than 2D-OSEM and FBP. Choosing the appropriate OSEM reconstruction parameters is helpful to improve the quantification accuracy in SPECT/CT.