Siemens Inveon PET Research Articles

Comparison of scandium-44\u2009g with other PET radionuclides in pre-clinical PET phantom imaging

PurposeThe decay characteristics of radionuclides in PET studies can impact image reconstruction. 44gSc has been the topic of recent research due to potential theranostic applications and is a promising radiometal for PET imaging. In this study, the reconstructed images from phantom measurements with scandium in a small-animal PET scanner are compared with 18F and two prominent radiometals: 64Cu and 68GaMethodsThree phantoms filled with 18F, 64C, 68Ga, and 44gSc were imaged in the Siemens Inveon PET scanner. The NEMA image quality phantom was used to determine the recovery coefficients (RCs), spill-over ratios (SORs), and noise (%SD) under typical pre-clinical imaging conditions. Image contrast was determined using a Derenzo phantom, while the coincidence characteristics were investigated using an NEC phantom. Three reconstruction algorithms were used, namely filtered back projection (FBP), ordered subset expectation maximization (OSEM), and maximum a-posteriori (MAP).ResultsImage quality parameters were measured for 18F, 64Cu, 68Ga, and 44gSc respectively; using FBP, the %SD are 5.65, 5.88, 7.28, and 7.70; the RCs for the 5-mm rod are 0.849, 1.01, 0.615, and 0.825; the SORs in water are 0.0473, 0.0595, 0.141, 0.0923; and the SORs in air are 0.0589, 0.0484, 0.0525, and 0.0509. The contrast measured in the 2.5-mm rods are 0.674, 0.637, 0.196, and 0.347. The NEC rate with 44gSc increased at a slower rate than 18F and 68Ga as a function of activity in the field of view.Conclusion44gSc demonstrates intermediate behavior relative to 18F and 68Ga with regard to RC and contrast measurements. It is a promising radionuclide for preclinical imaging.

Comparison of Reconstruction Algorithms for F-18 FP CIT PET Images

Fludeoxyglucose-18-(3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane positron emission tomography (F-18 FP CIT PET) was used for the diagnosis of Parkinson’s disease in nuclear medicine. However, no study of the effect of reconstruction parameters on the quality images obtained using F-18 FP CIT PET has been done. For that reason, this study compares the quality of F-18 FP CIT PET images reconstructed with different algorithms in terms of the recovery coefficient (RC), maximum PET counts, and binding potential (BP). The RCs of images were measured according to the National Electrical Manufacturers Association (NEMA) standard NU 4-2008 (NEMA NU4-2008). The PET images of the phantoms were reconstructed using various reconstruction algorithms (OSEM2D, FBP, 3DRP and OSEM3D/MAP) and filters. For the FBP reconstruction, the ramp, Butterworth (order: 1), Hamming, Hanning, Parzen, and SheppLogan filters were used. The cutoff frequency was 0.5 (even though the, ramp filter needed no cut-off frequency). For the OSEM3D/MAP reconstruction, various smoothing factors (β = 0.05, 0.5 and 1.5) were used with 18 iterations number. The β value was provided as a penalty function for constraint on neighboring voxels during the MAP algorithm. The β values of 0.05, 0.5 and 1.5 corresponded to predicted target resolutions of 1.5 mm, 2 mm, and 2.3 mm for the OSEM3D/MAP reconstruction algorithm, respectively. For the 3DRP reconstruction, Hanning filters were used. We used OSEM2D with 4 iterations and 16 subsets (default number in Siemens Inveon PET scanner) in this study for OSEM2D method. To compare the chosen parameters between the F-18 FP CIT PET images and phantoms, we used BALB nude mice (20 g body weight) were used to obtain mouse images. For evaluating the reconstruction methods, the maximum PET counts (counts/s/voxel) and BP (for image contrast ratio with striatum and cerebellum) of each reconstruction algorithm the striatal diameter of mice was observed to be 3 mm. Therefore, the RC values of the phantoms with a diameter of 3 mm were chosen. For phantoms with Φ = 3 mm, the OSEM2D provided the most appropriate 0.95 of RC value. Moreover, the maximum PET counts and the BP of the striatum with the OSEM2D reconstruction were observed to be high compared to the value for the other reconstruction methods. OSEM3D/MAP also showed high values for the maximum PET counts and the BP; however, the RC of OSEM3D/MAP (β = 0.05) exceeded 1 at Φ = 3 mm, and other OSEM3D/MAPs (β = 1.5 and 0.5) were lower than those of OSEM2D. Therefore, OSEM3D/MAP was not considered for decisions regarding the optimal reconstruction method. Through actual PET images we verified that the images with OSEM2D were identified more clearly and with higher image contrast. The OSEM2D reconstruction algorithm provided the best values (0.95) on reconstructed PET data; thus, OSE2D would be suitable for quantification of F-18 FP CIT PET images of mice obtained with a Siemens Inveon PET.

Comparison of Imaging Characteristics of (124)I PET for Determination of Optimal Energy Window on the Siemens Inveon PET.

Purpose. 124I has a half-life of 4.2 days, which makes it suitable for imaging over several days over its uptake and washout phases. However, it has a low positron branching ratio (23%), because of prompt gamma coincidence due to high-energy γ-photons (602 to 1,691 keV), which are emitted in cascade with positrons. Methods. In this study, we investigated the optimal PET energy window for 124I PET based on image characteristics of reconstructed PET. Image characteristics such as nonuniformities, recovery coefficients (RCs), and the spillover ratios (SORs) of 124I were measured as described in NEMA NU 4-2008 standards. Results. The maximum and minimum prompt gamma coincidence fraction (PGF) were 33% and 2% in 350~800 and 400~590 keV, respectively. The difference between best and worst uniformity in the various energy windows was less than 1%. The lowest SORs of 124I were obtained at 350~750 keV in nonradioactive water compartment. Conclusion. Optimal energy window should be determined based on image characteristics. Our developed correction method would be useful for the correction of high-energy prompt gamma photon in 124I PET. In terms of the image quality of 124I PET, our findings indicate that an energy window of 350~750 keV would be optimal.

Effect of filters and reconstruction algorithms on I-124 PET in Siemens Inveon PET scanner

Purpose: To assess the effects of filtering and reconstruction on Siemens I-124 PET data.Methods: A Siemens Inveon PET was used. Spatial resolution of I-124 was measured to a transverse offset of 50 mm from the center FBP, 2D ordered subset expectation maximization (OSEM2D), 3D re-projection algorithm (3DRP), and maximum a posteriori (MAP) methods were tested. Non-uniformity (NU), recovery coefficient (RC), and spillover ratio (SOR) parameterized image quality. Mini deluxe phantom data of I-124 was also assessed. Results: Volumetric resolution was 7.3 mm3 from the transverse FOV center when FBP reconstruction algorithms with ramp filter was used. MAP yielded minimal NU with β =1.5. OSEM2D yielded maximal RC. SOR was below 4% for FBP with ramp, Hamming, Hanning, or Shepp-Logan filters. Based on the mini deluxe phantom results, an FBP with Hanning or Parzen filters, or a 3DRP with Hanning filter yielded feasible I-124 PET data.Conclusions: Reconstruction algorithms and filters were compared. FBP with Hanning or Parzen filters, or 3DRP with Hanning filter yielded feasible data for quantifying I-124 PET.

Technical Note: Characterization of custom 3D printed multimodality imaging phantoms.

Imaging phantoms are important tools for researchers and technicians, but they can be costly and difficult to customize. Three dimensional (3D) printing is a widely available rapid prototyping technique that enables the fabrication of objects with 3D computer generated geometries. It is ideal for quickly producing customized, low cost, multimodal, reusable imaging phantoms. This work validates the use of 3D printed phantoms by comparing CT and PET scans of a 3D printed phantom and a commercial "Micro Deluxe" phantom. This report also presents results from a customized 3D printed PET/MRI phantom, and a customized high resolution imaging phantom with sub-mm features. CT and PET scans of a 3D printed phantom and a commercial Micro Deluxe (Data Spectrum Corporation, USA) phantom with 1.2, 1.6, 2.4, 3.2, 4.0, and 4.8 mm diameter hot rods were acquired. The measured PET and CT rod sizes, activities, and attenuation coefficients were compared. A PET/MRI scan of a custom 3D printed phantom with hot and cold rods was performed, with photon attenuation and normalization measurements performed with a separate 3D printed normalization phantom. X-ray transmission scans of a customized two level high resolution 3D printed phantom with sub-mm features were also performed. Results show very good agreement between commercial and 3D printed micro deluxe phantoms with less than 3% difference in CT measured rod diameter, less than 5% difference in PET measured rod diameter, and a maximum of 6.2% difference in average rod activity from a 10 min, 333 kBq/ml (9 μCi/ml) Siemens Inveon (Siemens Healthcare, Germany) PET scan. In all cases, these differences were within the measurement uncertainties of our setups. PET/MRI scans successfully identified 3D printed hot and cold rods on PET and MRI modalities. X-ray projection images of a 3D printed high resolution phantom identified features as small as 350 μm wide. This work shows that 3D printed phantoms can be functionally equivalent to commercially available phantoms. They are a viable option for quickly distributing and fabricating low cost, customized phantoms.

Comparison of reconstruction methods and quantitative accuracy in Siemens Inveon PET scanner

PET reconstruction is key to the quantification of PET data. To our knowledge, no comparative study of reconstruction methods has been performed to date. In this study, we compared reconstruction methods with various filters in terms of their spatial resolution, non-uniformities (NU), recovery coefficients (RCs), and spillover ratios (SORs). In addition, the linearity of reconstructed radioactivity between linearity of measured and true concentrations were also assessed.A Siemens Inveon PET scanner was used in this study. Spatial resolution was measured with NEMA standard by using a 1 mm3 sized 18F point source. Image quality was assessed in terms of NU, RC and SOR. To measure the effect of reconstruction algorithms and filters, data was reconstructed using FBP, 3D reprojection algorithm (3DRP), ordered subset expectation maximization 2D (OSEM 2D), and maximum a posteriori (MAP) with various filters or smoothing factors (β). To assess the linearity of reconstructed radioactivity, image quality phantom filled with 18F was used using FBP, OSEM and MAP (β =1.5 & 5 × 10−5).The highest achievable volumetric resolution was 2.31 mm3 and the highest RCs were obtained when OSEM 2D was used. SOR was 4.87% for air and 3.97% for water, obtained OSEM 2D reconstruction was used. The measured radioactivity of reconstruction image was proportional to the injected one for radioactivity below 16 MBq/ml when FBP or OSEM 2D reconstruction methods were used. By contrast, when the MAP reconstruction method was used, activity of reconstruction image increased proportionally, regardless of the amount of injected radioactivity. When OSEM 2D or FBP were used, the measured radioactivity concentration was reduced by 53% compared with true injected radioactivity for radioactivity <16 MBq/ml.The OSEM 2D reconstruction method provides the highest achievable volumetric resolution and highest RC among all the tested methods and yields a linear relation between the measured and true concentrations for radioactivity Our data collectively showed that OSEM 2D reconstruction method provides quantitatively accurate reconstructed PET data results.

Comparison of Normalization Methods for ${^{124}}{\rm I}$ PET on Siemens Inveon PET Scanner

<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68</sup> Ge has conventionally been used for the normalization of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> F PET. However, because <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> I PET has different characteristics such as a low positron branching ratio (23%), the presence of higher gamma energy (602 keV and 723 keV), and a larger positron range, the use of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68</sup> Ge should be validated for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> I PET. To the best of our knowledge, there has been no previous report on the effect of normalization between conventional <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68</sup> Ge and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> I. In this study, we examined image quality to assess the effect of normalization. For this purpose, we measured the non-uniformities (NUs) and recovery coefficients (RCs) using a NEMA NU4 image quality phantom (NU4 phantom) and compared the values for the conventionally used <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68</sup> Ge and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> I. A Siemens Inveon PET scanner was used throughout. Emission data were obtained using the NU4 phantom filled with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> I solution (3.7 MBq) for 20 min within 250-750 keV. The normalization data were acquired for 40 h using a cylindrical phantom (diameter: 6 cm, length: 13.5 cm) filled with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> I in a water solution (9.25 MBq). To match the energy window of an emission scan, the energy window setting for the normalization was 250-750 keV. The obtained list mode data were sorted into 3D sinograms. For comparison, normalization data were acquired using a cylindrical <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68</sup> Ge normalization phantom (diameter: 6 cm, length: 15 cm). The data with no normalization correction were also acquired. The list mode emission PET data were reconstructed using FBP with a ramp filter and normalization, and attenuation and scatter correction were applied. The image quality of the reconstructed images was assessed in terms of the radial, axial, and volume NUs and RCs as a standard using the NEMA NU4 protocol. There were no significant differences in the NUs and RCs between <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68</sup> Ge and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> I. These results indicate that conventional <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68</sup> Ge can be used for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">124</sup> I PET.

Quantification accuracy and partial volume effect in dependence of the attenuation correction of a state-of-the-art small animal PET scanner

Quantification accuracy and partial volume effect (PVE) of the Siemens Inveon PET scanner were evaluated. The influence of transmission source activities (40 and 160 MBq) on the quantification accuracy and the PVE were determined. Dynamic range, object size and PVE for different sphere sizes, contrast ratios and positions in the field of view (FOV) were evaluated. The acquired data were reconstructed using different algorithms and correction methods. The activity level of the transmission source and the total emission activity in the FOV strongly influenced the attenuation maps. Reconstruction algorithms, correction methods, object size and location within the FOV had a strong influence on the PVE in all configurations. All evaluated parameters potentially influence the quantification accuracy. Hence, all protocols should be kept constant during a study to allow a comparison between different scans.

Study of Highly Pixelated CdZnTe Detector for PET Applications

We are investigating the feasibility of a high-resolution PET insert device based on a Cadmium Zinc Telluride (CdZnTe) detector with 350 μm anode pixel pitch to be integrated into a conventional animal PET scanner to improve its image resolution to sub-500 micrometer range. In this work, we have used a simplified version of the future 2048-pixel CdZnTe planar detector with 250 μm anode pixel size and 100 μm gap. This simplified 9 anode pixel structure makes it possible to conduct experiments without a complete ASIC readout system (with 2048 channels) that is still under development. We characterized this CdZnTe detector by investigating it charge sharing, spatial resolution, and energy resolution. We imaged a Na-22 point source using the coincidence events between this 350 μm pixelated CdZnTe detector and a lutetium oxyorthosilicate (LSO) based Siemens Inveon PET detector. The reconstructed PET image shows a resolution of 590 μm full width at half maximum (FWHM) by using single-pixel events. When we included double-pixel charge sharing events in the image reconstruction, the image resolution was degraded to 655 μm, but the sensitivity of the coincidence system increased 2.5 to 3 times.