The effect of image translation table on diagnostic efficacy of myocardial perfusion SPECT studies

BACKGROUND: The aim of this study was to determine which of the most popular colour scales used in the Xeleris processing system (GE) should preferably be used during a clinical interpretation of myocardial perfusion images, and to find out whether a colour scale saturation level affects the diagnostic efficacy of the study. MATERIAL AND METHODS: From among 100 patients in whom a myocardial perfusion scintigraphy had been performed, a subgroup of people referred for coronary angiography, with neither prior history nor ECG signs of a myocardial infarction has been selected retrospectively. This group consisted of 41 patients (14 females) in the age group 46 to 76 years. All patients underwent two-day myocardial perfusion SPECT imaging using 99mTc-MIBI as a radiopharmaceutical. Reconstructed slices were interpreted in 3 colour scales: white-red-yellow-green-blue-black with computer-assigned thresholds (French 100%), the same French scale but without a white colour (image maximum set manually to a border value between red and white &#8212; French w.w.), and a white-yellow-violet- pink-blue-black scale (GEcolor), by consensus of two experienced nuclear medicine specialists. A semiquantitative method for evaluation of perfusion images was applied, based on myocardium segmentation. Perfusion in each segment was scored using a five-point system. Study interpretation (normal/ abnormal perfusion) was based on summed stress scores (SSS), being equal/above or below a given threshold value. The choice of optimal SSS threshold value was based on sensitivity and specificity of the study in detection of perfusion defects resulting from critical stenoses of main coronary arteries RESULTS: SSS values differed among colour scales (p < 0.00001). The lowest values were obtained for a French 100% scale (mean value = 5.0, SD = 8.0), the highest for French w.w. (mean values = 8.1, SD = 8.7), and for GE colour scale &#8212; mean value &#8212; 5.6, SD &#8212; 7.9. A French 100% scale gave high sensitivity (88%), as well as specificity (83%), but only when a low SSS threshold value of 2, hardly acceptable for study interpreters, was used. When higher threshold values were applied, they compromised the sensitivity of the study. A French w.w. scale with SSS threshold values lower than 3 provided a slightly higher sensitivity (94%), but with a significant reduction in specificity (to values below 50%). Only a threshold value of 4 provided acceptable, but still low specificity (63%) with preserved high sensitivity (88%). At the same time, the scale GE colour provided indices of diagnostic efficacy with the SSS threshold value of 3 as high as a scale French 100% with threshold value of 2. CONCLUSIONS: A French scale (Xeleris, GE) is not the scale of choice for the interpretation of myocardial perfusion SPECT images. It seems that a GE colour scale is better suited for this purpose. SSS threshold values accepted as diagnostic criteria for the detection of myocardial perfusion abnormalities should be suited separately for every translation table. The choice of optimal value should be verified by results of coronary angiography. Nuclear Med Rev 2010; 13, 2: 64&#8211;6

Evaluation of PET quantitation accuracy among multiple discovery IQ PET/CT systems via NEMA image quality test

Introduction: Quantitative imaging biomarkers are becoming usual in oncology for assessing therapy response. The harmonization of image quantitation reporting has become of utmost importance due to the multi-center trials increase. The NEMA image quality test is often considered for the evaluation of quantitation and is more accurate with a radioactive solid phantom that reduces variability. The goal of this project is to determine the level of variability among imaging centers if acquisition and imaging protocol parameters are left to the center's preference while all other parameters are fixed including the scanner type. Methods: A NEMA-IQ phantom filled with radioactive Ge-68 solid resin was imaged in five clinical sites throughout Europe. Sites reconstructed data with OSEM and BSREM algorithms applying the sites' clinical parameters. Images were analyzed according with the NEMA-NU2-2012 standard using the manufacturer-provided NEMA tools to calculate contrast recovery (CR) and background variability (BV) for each sphere and the lung error (LE) estimation. In addition, a F-18-filled NEMA-IQ phantom was also evaluated to obtain a gauge for variability among centers when the sites were provided with identical specific instructions for acquisition and reconstruction protocol (the aggregate of data from 12 additional sites is presented). Results: The data using the Ge-68 solid phantom showed no statistical differences among different sites, proving a very good reproducibility among the PET center models even if dispersion of data is higher with OSEM compared to BSREM. Furthermore, BSREM shows better CR and comparable BV, while LE is slightly reduced. Two centers exhibit significant differences in CR and BV values for the F-18 NEMA NU2-2012 experiments; these outlier results are explained. Conclusion: The same PET system type from the various sites produced similar quantitative results, despite allowing each site to choose their clinical protocols with no restriction on data acquisition and reconstruction parameters. BSREM leads to lower dispersion of quantitative data among different sites. A solid radioactive phantom may be recommended to qualify the sites to perform quantitative imaging