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 68Ge 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 18F-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 68Ge 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 18F 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.

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 - 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 - mean value - 5.6, SD - 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.

Impact of CT based attenuation correction on quantitative assessment of DaTSCAN ((123)I-Ioflupane) imaging in diagnosis of extrapyramidal diseases.

The quality of visually and semi-quantitatively assessed DaTSCAN images is crucial for differential diagnostics of extrapyramidal diseases. Neuroimaging with the use of presynaptic tracers of the dopaminergic system provides evidence of nigrostriatal degeneration and may support the clinical diagnosis of Parkinsonism. During the last two years (2007-2008) we tried to elaborate the optimal methodology of SPECT/CT examination with the use of DaTSCAN ((123)I-Ioflupane), and we sought to evaluate the effect of the reconstruction and attenuation correction method on semi-quantitative measures of relative uptake in the striatum. In a present study, we retrospectively studied DaTSCAN scans of 44 consecutive patients with clinical indications of Parkinson's disease or uncertain Parkinsonian syndromes. The quality of DaTSCAN images reconstructed with the use of ordered-subset expectation maximization reconstruction technique (OSEM) with attenuation correction based on CT maps was found to be superior to that provided by the commonly applied filtered backprojection method (FBP) with Chang attenuation correction. OSEM reconstructed transverse slices were more legible for clinical interpretation because of increased contrast and improved delineation between striatum structures. Semi-quantitative assessments of relative striatum uptake for OSEM reconstructed slices secured better intra-operator reproducibility than that obtained by FBP method.

Effect of attenuation correction on normal (99)mTc-MIBI myocardial perfusion scintigrams acquired with a hybrid SPECT/CT camera.

The aim of this study was to evaluate the effect of the CT-derived attenuation correction on (99m)Tc-MIBI normal myocardial perfusion scintigrams. Rest perfusion scintigrams of patients in whom coronary artery disease was suspected, without a history or any signs in ECG of a myocardial infarction, were analysed. Patients were included in the material if their rest perfusion scintigrams were normal. This criterion was fulfilled by 61 patients (29 men and 32 women) aged between 40 and 74 (mean value 57) years, with body mass between 50 and 120 (mean value 70) kg. Tomographic reconstruction of a radionuclide study was performed with an iterative OSEM method (10 subsets, 2 iterations) sequentially without and with attenuation and scatter corrections on a dedicated Xeleris workstation, applying an ACQC tool to enable manual realignment of SPECT and CT images. SPECT studies were evaluated visually and semiquantitatively. Visual analysis of tomograms was performed with the aim of finding sites of significantly lower counts in comparison with the maximal level (in the lateral wall). Semiquantitative analysis was based on counts in 20 segments of a polar map. Attenuation correction caused a complete (in 32 of 40 - 80% of patients) or partial (in 8 of 40 - 20% of patients) filling out of all areas of lower counts in the inferior wall. However, although in the anterior wall attenuation correction caused a complete (in 11 of 35 - 31% of cases) or partial (10 of 35 - 29% of cases) filling of areas of lower counts, in 14 cases (40%) those areas remained unchanged or increased, and in 8 cases (13% of all patients) new areas of decreased counts appeared. The same was true for the apical region, in which areas of decreased counts were detected in 14 of 61 (23%) cases without attenuation correction, but after application of the correction number of apical defects, this figure grew to 22 (36%) patients. Altogether, attenuation correction reduced the total number of lower count areas from 104 to 66. Semi-quantitative analysis revealed that attenuation correction reduced nonuniformity in counts in the whole myocardium - the mean difference between segment with maximum counts and values in all segments was reduced from 17.5 +/- +/- 12% to 11.0 +/- 10.3% (p < 0.0001) in male patients, and in female patients, from 11.5 +/- 9% to 10.5 +/- 8.6%, thus equalling non-uniformities in myocardial scintigrams of both sexes. Misalignment of CT and SPECT studies was observed in 17 (28%) patients but only in 2 (3% of all patients) patients did CT realignment evidently change the attenuation corrected scintigrams. Although attenuation correction can cause artefacts, its use is justified by the reduction of the total number of areas of lower counts and the improvement of uniformity of images of normally perfused myocardium.