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Background We investigated the image quality of 11C, 68Ga, 18F and 89Zr, which have different positron fractions, physical half-lifes and positron ranges. Three small animal positron emission tomography/computed tomography (PET/CT) systems were used in the evaluation, including the Siemens Inveon, RAYCAN X5 and Molecubes β-cube. The evaluation was performed on a single scanner level using the national electrical manufacturers association (NEMA) image quality phantom and analysis protocol. Acquisitions were performed with the standard NEMA protocol for 18F and using a radionuclide-specific acquisition time for 11C, 68Ga and 89Zr. Images were assessed using percent recovery coefficient (%RC), percentage standard deviation (%STD), image uniformity (%SD), spill-over ratio (SOR) and evaluation of image quantification. Results 68Ga had the lowest %RC (18F had the highest maximum %RC (> 85%) and lowest %STD for the 5 mm rod across all systems. For 11C and 89Zr, the maximum %RC was close (> 76%) to the %RC with 18F. A larger SOR were measured in water with 11C and 68Ga compared to 18F on all systems. SOR in air reflected image reconstruction and data correction performance. Large variation in image quantification was observed, with maximal errors of 22.73% (89Zr, Inveon), 17.54% (89Zr, RAYCAN) and − 14.87% (68Ga, Molecubes). Conclusions The systems performed most optimal in terms of NEMA image quality parameters when using 18F, where 11C and 89Zr performed slightly worse than 18F. The performance was least optimal when using 68Ga, due to large positron range. The large quantification differences prompt optimization not only by terms of image quality but also quantification. Further investigation should be performed to find an appropriate calibration and harmonization protocol and the evaluation should be conducted on a multi-scanner and multi-center level.

In Positron Emission Tomography (PET), the data recorded in narrow energy window (EW) has the benefits of low scatter fraction (SF), which leads to a high contrast image, but it is rarely used in reconstruction because many trues are rejected. The data recorded in wide EW contains almost all trues, which leads to a noiseless image and a lot of scatters as well. To combine the characteristics of high contrast and low noise in one image, we propose a new approach to reconstruct image with both the data recorded in a narrow EW and a wide EW, which the digital PET has the ability to do. The wide EW generates a high-count, high-noise (HCHN) data and the narrow EW generates a low-count, low-noise (LCLN) data. The HCHN data is reconstructed by OSEM algorithm to obtain a prior image used in the LCLN data reconstruction. The LCLN data is reconstructed by the kernel expectation maximization (KEM) algorithm to obtain the final image. We performed a 2 step investigation on 3D brain phantom with simulated data: 1) we compare the effect of different iterations of prior image when the HCHN and LCLN data are both generated by a wide EW of 450 to 700 keV (87M trues, 41% SF); 2) we evaluate the effect of turning up the low-threshold of EW from 450 to 520 keV (17m trues, 22% SF) of LCLN data. The results show that a low iteration of prior image obtains a best final image (2 iterations 11 subsets in this work). The final image has a similar noise level but a higher contrast in the same iterations when the low-threshold of EW of LCLN data is turned up. In conclusion, the proposed method has the ability to combine the benefits of narrow EW and wide EW in one reconstructed Image

Additional file 1: Fig. S1. Construction scheme of the NEMA phantom with a photograph of the phantom. Data S1. Effect of using the standard 20 minute acquisition time for 11C and 68Ga. Data S1, Table S1. Recovery coefficients of the phantom rods with different radionuclides and acquisition times. Data S1, Table S2. Percentage standard deviation of recovery coefficients of the phantom rods with different radionuclides and acquisition times. Data S1, Table S3. The mean activity and the percentage standard deviation measured from the uniform compartment of the phantom with different acquisition times. Data S1, Fig. S2. Image quality comparison for 11C and 68Ga using the 20 minute acquisition time. Data S1, Fig. S3. Recovery coefficients with 11C and 68Ga only. Data S2. Effect of different reconstruction algorithms and parameters. Data S2, Table S4. Image reconstruction parameters and data corrections used for the reconstruction evaluation. Data S2, Fig. S4. Dependency of image quality parameters on the amount of iterations. Data S2, Table S5. Recovery coefficients of the phantom rods with different radionuclides and reconstruction options. Data S2, Table S6. Percentage standard deviation of recovery of the phantom rods with different radionuclides and reconstruction options. Data S2, Table S7. The mean radioactivity with percentage standard deviation and relative difference in the uniform compartment with the spill-over-ratios and their percentage standard deviations with different reconstruction schemes..

Considering the complexity of system structure and fault mechanism of complex system, a fault diagnosis method based on extended color fuzzy fault Petri net model is proposed (CFFPN) for civil aircraft. In o rder to increase the fault diagnosis efficiency, the CFFPN is modeled based on fuzzy mathematics and fault Petri net method through adding token, library and staining rules to describe the fault propagation. Fuzzy generated rules combined with matrix theory are utilized for fault diagnosis reasoning. CFFPN based reasoning algorithm is given. The validity of the proposed method is verified in one type aircraft pneumatic system.