ABSTRACT
Background: Harmonization methods reduce variability between different make and models of positron emission tomography (PET) scanners. The study aims to explore harmonization strategies that lead to comparable and robust quantitative metrics in a multicenter setting. Methods: NEMA IEC Phantom data acquisition was performed for low and high spheres-to-background ratios (SBR4:1 and 10:1) on six PET/CT (computed tomography) scanners. Different reconstruction sets, including the number of sub-iterations, number of subsets, and full width at half maximum (FWHM) for each scanner, were evaluated towards optimized and harmonized reconstruction settings. Recovery coefficients (RCs) of four quantitative metrics, including standardized uptake value (SUV)max, SUVISO-50 (SUVmean in 50% isocontour), SUVpeak, and mean uptake of 10 highest concentration voxels were evaluated as RCmax, RCISO-50, RCpeak, and RC10V, representing percent difference relative to the static ground truth case as functions of sphere sizes. A set of image reconstruction parameters was proposed for harmonized reconstruction to minimize variability between scanners. The root mean square error (RMSE), curvature, and reproducibility were examined. The proposed reconstruction protocols for harmonization and standard clinical reconstruction settings were compared to each other across all scanners. Results: A significant difference (P value <0.0001) was observed in the aforementioned quantitative metrics between SBR10 and SBR4. Reconstruction parameter sets with the smallest RMSE and RC values within 10% bias were identified as the best candidate for harmonization. The coefficient of variation of the mean value of RCs (CVMRC) shows a remarkable reduction of about 28%, 26%, 32%, and 19% in harmonized reconstruction settings for MRCmax, MRCISO-50, MRCpeak, and MRC10V, respectively. CVMRC for MRC10V in the harmonized reconstruction setting was 5.9% in SBR4, while the smallest value in SBR10 belongs to MRCpeak, with a value of 5.8%. The reproducibility of RC is improved by deriving the value from ten hottest voxels and is equally reproducible with RCpeak. Compared to RCmax and RCISO-50, the variability is reduced by 18% and 22% if ten voxels are pooled. Conclusions: Harmonizing PET/CT systems with and without point spread function/time of flight (PSF/TOF) using various vendor-developed image reconstruction algorithms improves the quantification reproducibility. RC10V, likewise RCpeak, is superior to the rest of the quantitative indices in terms of accuracy and reproducibility and helpful in quantifying lesion volume below 1 mL.
ABSTRACT
The data presented here provide information about the role of reconstruction parameters on Positron Emission Tomography (PET) image quantification. Multiple phantom measurements in four different Spheres to Background Ratio (SBR) were performed on Biograph 6 TruePoint TrueV PET/CT scanner. PET raw data were reconstructed with/without resolution recovery algorithm using six various iteration x subsets with five different Full-Width Half-Maximum (FWHM) values of Gaussian post-smoothing filter. The Recovery Coefficient (RC) of six spheres using three common Volume of Interest (VOI) methods (max, 3D-50% Isocontour, and peak) were calculated. Moreover, SUVmax, SUVmean, and SUVpeak and volumetric indices, such as metabolic tumor volume (MTV), volume recovery coefficient (VRC), and total lesion glycolysis (TLG) were measured. RCmax, RC50%, and RCpeak as a function of sphere size were plotted in all reconstruction methods considering different SBRs. The data could be noticeable for standardization and optimization of quantitative metrics in PET imaging.
ABSTRACT
UNLABELLED: Patient motion during myocardial perfusion SPECT is a common source of errors. The extent and severity of motion artifacts have been described for filtered backprojection (FBP) reconstruction. In recent years, iterative reconstruction has been used increasingly in reconstruction of myocardial perfusion SPECT images and has been shown to be more accurate than FBP even in cases of incomplete datasets. This study evaluated the effect of iterative reconstruction on the extent and severity of motion artifacts. METHODS: Six normal, motion-free, and nongated (99m)Tc myocardial perfusion SPECT scans were selected, and simulated motion of 3 pixels was applied to the early, middle, and late phases of acquisition in 2 types of movement, returning and nonreturning. The images were acquired by a single-head gamma-camera in 32 steps at 30 s per step and in a 180 degrees arc from right anterior oblique to left posterior oblique. All original and shifted images were reconstructed using FBP and ordered-subset expectation maximization (OSEM) techniques and interpreted by 2 nuclear medicine specialists qualitatively and semiquantitatively (using 17 segments and a 5-point scoring system). RESULTS: Overall, 68.1% and 70.8% of shifted images were categorized as definitely abnormal in the FBP and OSEM reconstructions, respectively (P > 0.5). The mean summed score was 11.9 (+/-5.7) and 11.3 (+/-5.2) for nonreturning shifted images (P = 0.13) and 5.2 (+/-2.4) and 3.9 (+/-2.0) for returning shifted images (P < 0.001) in the OSEM and FBP reconstructions, respectively. The incidence of defects in different myocardial segments was similar with the 2 reconstruction methods. The summed score was higher with shifting in the middle phase of acquisition than in the late or early phase. CONCLUSION: Our study showed that the incidence of abnormal findings and the location of defects were not different between the 2 reconstruction types; however, with semiquantitative assessment, the severity of defects increased with OSEM reconstruction. Although OSEM reconstruction has been reported to be more tolerant to missing data than is FBP reconstruction, our study showed that OSEM reconstruction may be less tolerant to motion artifacts than is FBP reconstruction.
