Optimization of iterative reconstruction parameters with 3-dimensional resolution recovery, scatter and attenuation correction in ¹²³I-FP-CIT SPECT

The aim of this study was to determine the optimal reconstruction parameters on ordered-subset expectation maximization iterative reconstruction with resolution recovery, scatter and attenuation correction (OSEM_RRSCAC) on ¹²³I-FP-CIT SPECT in terms of the image quality, quantification and diagnostic ability.

We evaluated the quality and quantification in ¹²³I-FP-CIT SPECT images obtained by different reconstruction parameters using the anthropomorphic striatal phantom. The phantom images were acquired using a SPECT/CT system equipped with a low- and medium-energy general-purpose collimator and then were reconstructed using OSEM_RRSCAC with various update numbers and the full width at half maximum (FWHM) of the Gaussian filter. The count ratio of the striatum, the coefficient of variation (CV) on the background and the specific binding ratio (SBR) were calculated to determine the optimal reconstruction parameters. Then, 42 consecutive patients who underwent ¹²³I-FP-CIT SPECT were selected for clinical study. The patients were grouped into potentially decreasing group (20 with Parkinson’s disease, 5 with parkinsonian syndrome and 5 with dementia with Lewy bodies) and potentially normal binding group (4 with Alzheimer disease and 8 with essential tremor). Clinical images were reconstructed using OSEM_RRSCAC and FBP with Chang’s AC (FBP_AC). The performance of OSEM_RRSCAC with the optimal reconstruction parameters was evaluated according to the receiver operating characteristic analysis and visual assessment.

The count ratio increased with an increasing update number and converged uniformly with an update number over 90. The CV continuously increased with the update number. The SBR also increased with an increasing update number and converged uniformly with an update number of 90 or larger. The FWHM of the Gaussian filter influenced the image quality and quantification. In the clinical study, the area under curve (AUC) for the OSEM_RRSCAC and FBP_AC were 0.9812 and 0.9759, respectively. The quality of the SPECT images of OSEM_RRSCAC (3.8 ± 0.8) was significantly superior to that of FBP_AC (2.2 ± 0.7).

We determined that the optimal reconstruction parameter for OSEM_RRSCAC was 90 update numbers with 6.6 mm FWHM of the Gaussian filter. Our results suggested that the optimal reconstruction parameters have a potential to improve the performance and the image quality of ¹²³I-FP-CIT SPECT in comparison with the FBP reconstruction.