NEMA NU2-2012 performance measurements of the United Imaging uPMR790: an integrated PET/MR system

PURPOSE

In this paper, we aimed to evaluate the positron emission tomography (PET) performance of, to the best of our knowledge, the third commercially available whole-body integrated PET/magnetic resonance (MR) system.

METHODS

The PET system performance was measured following the NEMA standards with and without simultaneous MR operation. PET spatial resolution, sensitivity, scatter fraction, count-rate performance, accuracy of count losses and random corrections, image quality, and time-of-flight (TOF) resolution were quantitatively evaluated. Clinical scans were acquired at the PET/MR system and compared with images acquired at a PET/CT with the same digital detector technology.

RESULTS

Measurement results of essential PET performance were reported in the form of MR idle (MR pulsing). The axial, radial, and tangential spatial resolutions were measured as 2.72 mm (2.73 mm), 2.86 mm (2.85 mm), and 2.81 mm (2.82 mm) FWHM, respectively, at 1 cm radial offset. The NECR peak was measured as 129.2 kcps (129.5 kcps) at 14.7 kBq mL^-1 (14.2 kBq mL^-1). The scatter fraction at NECR peak was 37.9% (36.5%), and the maximum slice error below NECR was 4.1% (4.5%). Contrast recovery coefficients ranged from 51.8% (52.3%) for 10 mm hot sphere to 87.3% (87.2%) for 37 mm cold sphere. TOF resolution at 5.3 kBq mL^-1 was measured at 535 ps (540 ps). With point source, TOF was measured to be 474 ps (485 ps). Clinical scans revealed similar image quality from the PET/MR and the comparative PET/CT system.

CONCLUSION

The PET performance of the newly introduced integrated PET/MR system is not significantly affected by the simultaneous operation of an MR sequence (2-point DIXON sequence). Measurement results demonstrate comparable performance with other state-of-the-art PET/MR systems. The clinical benefits of high spatial resolution and long axial coverage remain to be further evaluated in specific clinical imaging applications.

Performance Evaluation of the Vereos PET/CT System According to the NEMA NU2-2012 Standard

The aim of this study was to evaluate the physical performance of the Vereos whole-body PET/CT system according to the National Electrical Manufacturers Association (NEMA) NU2-2012 standard and to compare it with other state-of-the-art PET/CT systems. Methods: Spatial resolution, sensitivity, count-rate performance, count rate accuracy, and image quality were assessed. Specifically, spatial resolution was measured using an ¹⁸F point-source. System sensitivity was calculated from acquisitions of an ¹⁸F line source inside aluminum tubes of varying thickness. Assessment of count rate performance and count rate accuracy was based on measurements of an ¹⁸F line source inside a 20-cm-diameter polyethylene cylinder. PET image quality was assessed using a NEMA IQ phantom. All measurements were performed according to the predefined and implemented NEMA NU2-2012 acquisition protocols at a clinical installation of a Vereos PET/CT system. Evaluation was performed using the software provided by the vendor. Results: The average (radial and tangential) transverse spatial resolution was 4.2, 4.5, and 5.5 mm in full width at half maximum for a 1-, 10-, and 20-cm radial offset, respectively, from the center of the field of view. Axial spatial resolution varied between 4.2 and 4.6 mm in full width at half maximum, depending on the radial source position. The average sensitivity was 5.2 cps/kBq. A peak noise-equivalent count (NEC) rate of 153.4 kcps was measured at an activity concentration of 54.9 kBq/mL. The scatter fraction at peak NEC rate was 33.9%, and the maximum count rate error at and below peak NEC rate was 6.8%. Contrast recovery coefficients varied from 54.3% (10-mm sphere) to 83.9% (22-mm sphere) for the hot spheres, and between 81.4% (28-mm sphere) and 87% (37-mm sphere) for the cold spheres for a given sphere-to-background ratio of 4:1. Conclusion: The overall performance characteristics of the Vereos PET/CT system are comparable to state-of-the-art whole-body PET/CT systems with the exception that the peak NEC rate occurs at a higher activity concentration, thus indicating the ability of the Vereos PET/CT system to cover a wider range of activities.