ABSTRACT
Non simultaneous acquisition between CT and PET module can introduce misalignment artefact in cardiac PET/CT imaging due to patient motion. We assessed the clinical impact of patient motion and the resulting mismatch between CT and corresponding CT-based attenuation corrected [CTAC] PET images on apparent myocardial uptake values in cardiac PET/CT imaging. The evaluation of patient motion was performed using clinical and experimental phantom studies acquired on the Biograph TP 64 PET/CT scanner. In order to simulate patient motion, CT images were manually shifted from 0 to 20 mm in steps of 5-mm in six different directions. The reconstructed PET images using shifted CT were compared with the original PET images. The assessment of PET images was performed through qualitative interpretation by an experienced nuclear medicine physician and through quantitative analysis using volume of interest based analysis. Moreover, Box and Whisker plots were calculated and bull's eye view analysis performed. PET images were also reoriented along the short, horizontal and vertical long axis views for a better qualitative interpretation. A 20-mm shift in the right direction between attenuation and PET emission scans produced mean absolute percentage difference in uptake values in the lateroanterior [33.42 +/- 9.07] and lateroinferior [27.39 +/- 10.43] segments of the myocardium. Misalignment could introduce artifactual nonuniformities in apparent myocardial uptake value and the variations were more significant for the misalignment toward the right, feet and head directions, in such a way that even with a 5-mm shift in the CT image, errors in interpretation of PET images could occur. Furthermore, errors in PET uptake estimates were observed for movements as large as 10-mm in the left, posterior and anterior directions
ABSTRACT
Purpose: Positron Emission Tomography [PET] imaging offers the possibility of measuring brain metabolic activity in vivo. However, brain PET images remain difficult to interpret in clinical setting because of the limited spatial resolution of current generation clinical PET scanners. Therefore, the resulting partial volume effect [PVE] is a challenging issue for brain PET image interpretation and quantitative analysis. To overcome this limitation, several algorithms allowing the correction for PVE [PVC] have been developed and assessed mainly in research setting. In this work, we perform a comparative study of 5 different PVC methods using clinical studies. Methods: 17 clinical studies of patients suffering from neurodegenerative disease were included in our study protocol. 3D T1-weighted MRI and FDG-PET were acquired on dedicated MR and PET-CT systems, respectively. MR images were rigidly co-registered to corresponding PET images using the Hermes multimodality platform and segmented using statistical parametric mapping package [SPM8]. The resulting images were corrected for PVE using four voxel-based techniques proposed by different groups including Alfano, Muller-Gartner, Meltzer, and Shidahara, and one volume of interest [VOI]-based technique proposed by Rousset. Results: Our results demonstrate a significant increase of the activity concentration in the gray matter. Consequently, the activity in the white matter decreases considerably when using all PVC methods, except for Meltzer and Shidahara. The comparative analysis demonstrates that, among all considered techniques, Alfano's method appears to substantially increase the GM signal. When applying the different PVC methods to specific regions of interest linked to a specific pathology, the results highlight the bias when using uncorrected PET images, but still respecting specific modification patterns of the disease. Conclusion: Our results confirm the necessity of applying PVC to brain PET images in order to obtain more reliable and accurate quantification. This applies particularly to elderly patients with neurodegenerative disease where atrophy induces underestimation of the true PET signal
ABSTRACT
Due to the large number of PET systems available in the market, it is not very easy to decide about the scanner of choice. Conducting a research in order to compare all different PET scanners is very time consuming and expensive and practically impossible. However, such comparison may be conducted using PET simulators. In this study, the performance of 6 different PET scanners in cardiology is evaluated using a dedicated PET simulator. In this study only the design of the system were evaluated. Activity and attenuation phantoms were produced using 4D-NCAT phantom. EC AT EXACT HR+, EC AT 953B, ECAT 966, EC AT ART, GE Advance and 16HI-REZ scanners were simulated using Eidolon PET simulator and the output sinograms were reconstructed using STIR software. The reconstructed images were processed using Interview software installed on the Mediso cardiac imaging system. Counts of pixels determined by ROI were used to drawn curves and then the correlations of these curves calculated using SPSS. True coincidences 2D was 4651791 +/- 5900 for ECAT 966, 4651965 +/- 5660 for ECAT ART, 4742731 +/- 5328 for ECAT EXACT HR+, 6018435 +/- 5167 for ECAT 953B, 6566769 +/- 4734 for GE Advance and 6846339 +/- 51850 for 16HI-REZ. Resulted correlations calculated for these scanners were 0.806, 0.795, 0.718, 0.858, 0.726 and 0.896 respectively. There was a considerable different in scatter fractions of different scanners. Curves drawn using count of pixels determined by ROI and correlations of these curves showed differences in performances of scanners in cardiology. The results showed that the 16HI-REZ scanner is the best scanner of the six scanners for simulating of cardiac PET images