NEMA NU 2–2007 performance characteristics of GE Signa integrated PET/MR for different PET isotopes

Abstract

Background Fully integrated PET/MR systems are being used frequently in clinical research and routine. National Electrical Manufacturers Association (NEMA) characterization of these systems is generally done with 18 F which is clinically the most relevant PET isotope. However, other PET isotopes, such as 68 Ga and 90 Y, are gaining clinical importance as they are of specific interest for oncological applications and for follow-up of 90 Y-based radionuclide therapy. These isotopes have a complex decay scheme with a variety of prompt gammas in coincidence. 68 Ga and 90 Y have higher positron energy and, because of the larger positron range, there may be interference with the magnetic field of the MR compared to 18 F. Therefore, it is relevant to determine the performance of PET/MR for these clinically relevant and commercially available isotopes. Methods NEMA NU 2–2007 performance measurements were performed for characterizing the spatial resolution, sensitivity, image quality, and the accuracy of attenuation and scatter corrections for 18 F, 68 Ga, and 90 Y. Scatter fraction and noise equivalent count rate (NECR) tests were performed using 18 F and 68 Ga. All phantom data were acquired on the GE Signa integrated PET/MR system, installed in UZ Leuven, Belgium. Results 18 F, 68 Ga, and 90 Y NEMA performance tests resulted in substantially different system characteristics. In comparison with 18 F, the spatial resolution is about 1 mm larger in the axial direction for 68 Ga and no significative effect was found for 90 Y. The impact of this lower resolution is also visible in the recovery coefficients of the smallest spheres of 68 Ga in image quality measurements, where clearly lower values are obtained. For 90 Y, the low number of counts leads to a large variability in the image quality measurements. The primary factor for the sensitivity change is the scale factor related to the positron emission fraction. There is also an impact on the peak NECR, which is lower for 68 Ga than for 18 F and appears at higher activities. Conclusions The system performance of GE Signa integrated PET/MR was substantially different, in terms of NEMA spatial resolution, image quality, and NECR for 68 Ga and 90 Y compared to 18 F. But these differences are compensated by the PET/MR scann...

Monte Carlo Simulations of the GE Signa PET/MR for Different Radioisotopes

“…This dependency is clearly demonstrated at the interface between different tissues as shown in Figure 6. These findings are in agreement with previous studies on the positron range (Rickey et al, 1992;Cal-González et al, 2009;Shah et al, 2014;Alva-Sánchez et al, 2016;Huang et al, 2016;Caribé et al, 2017), and confirm a reduced positron range in the perpendicular direction of a magnetic field. Moreover, studies have also indicated (Iida et al, 1986;Wirrwar et al, 1997;Soultanidis et al, 2011;Kraus et al, 2012) that a higher magnetic field will also induce a greater reduction of the positron range.…”

“…In this work we have developed and evaluated a model for the GE Signa PET/MR to run realistic Monte Carlo simulations using GATE. The model was validated by comparing simulated sensitivity and NECR data 18 F and 68 Ga with corresponding measurements performed on a GE Signa PET/MR system (Caribé et al, 2019). Once validated, these simulations allowed us to evaluate the system characteristics in terms of sensitivity and NECR for different, less conventional PET isotopes such as 15 O, 13 N, 11 C, and 82 Rb.…”

“…As output, the spatial coordinates of the location of the annihilation end point were saved to a file for each recorded positron. These results are compared to the measured 18 F and 68 Ga-values (Caribé et al, 2019).…”

“…The GATE-model for the GE Signa PET/MR was used to simulate the sensitivity and NECR of the PET/MR system for isotopes other than 18 F and 68 Ga including 11 C, 15 O, 13 N, and 82 Rb. In terms of sensitivity, the simulated values were compared with the theoretical sensitivities based the branching ratio of each isotope and the average sensitivity of 21.5 cps/kBq measured for 18 F (Caribé et al, 2019).…”

Low-dose 18F-FDG TOF-PET/MR for accurate quantification of brown adipose tissue in healthy volunteers

“…At higher activities, detector saturation effects can start to paralyze the system and reduce performance such that the count rate is no longer linear with increasing activity. At low activities and in the normal clinical range, the true and scatter coincidences scale roughly linear with the activity (within limits), while the randoms scale more like a quadratic function (actual curves can be found in [31]). In a real low-dose PET scan, the amount of randoms is therefore likely lower than in our simulated low-dose PET.…”