Performance Characteristics of a New Generation 148-cm Axial Field-of-View uMI Panorama GS PET/CT System with Extended NEMA NU 2-2018 and EARL Standards

Abstract

The uMI Panorama GS PET/CT system is a new long-axial-field-of-view scanner featuring high sensitivity, time-of-flight (TOF) resolution, spatial resolution, and count rate performance. The aim of this study is to assess the PET system on the basis of the National Electrical Manufacturers Association (NEMA) NU 2-2018 and European Association of Nuclear Medicine Research Limited (EARL) standards. Methods: Spatial resolution, count rate performance, sensitivity, accuracy, image quality, TOF resolution, and coregistration accuracy were evaluated following the NEMA NU 2-2018 standard. Additional experiments included energy resolution, 200-cm-long line sources for sensitivity, a 175-cm-long scatter phantom for count rate and TOF resolution, as well as the compliance with the EARL guideline. Moreover, an ¹⁸F-FDG PET patient study was reconstructed with various frame durations. Results: The PET system achieved sub-3-mm transaxial and axial spatial resolutions at a 1-cm radial offset. The sensitivities with the 70-cm-long and 200-cm-long line sources were observed to be 176.3 and 90.8 kcps/MBq, respectively, at the center of the field of view. The noise-equivalent count rates (NECRs) of the 70-cm-long and 175-cm-long scatter phantoms were measured to be 3.35 Mcps at 57.57 kBq/mL and 2.24 Mcps at 33.27 kBq/mL, respectively. The TOF resolutions for both phantoms were approximately 189 ps at 5.3 kBq/mL and lower than 200 ps below the NECR peaks. The absolute count rate errors of all 34 acquisitions were less than 3% below the NECR peak for the 70-cm-long scatter phantom. With the standard NEMA image quality phantom experiment, the contrast recovery coefficient varied from 68.17% to 94.20% and the background variabilities were all below 2%. The maximum PET/CT coregistration error was 1.33 mm. Regarding EARL compliance, the gaussian filter of 5-mm full width at half maximum could produce acceptable images. The patient data demonstrate visually satisfactory image quality with short frames (less than 1 min). Conclusion: The uMI Panorama GS exhibits spatial resolution and TOF resolution similar to those of the uMI Panorama system (35-cm axial field of view), despite the extended axial field of view. The 148-cm axial coverage, sub-200-ps TOF resolution, high sensitivity, and count rate performances are expected to yield superior image quality and offer new opportunities for various clinical applications.

Keywords: EARL; LAFOV; NEMA; time of flight; uMI Panorama GS PET/CT.

Graphical abstract

FIGURE 1.

(A) Axial sensitivity profile of NEMA standard 70-cm-long line source positioned at transaxial center and 10 cm off-center. (B) Axial sensitivity profile of 200-cm-long line source positioned at transaxial center and 10 cm off-center. Nr. = number.

FIGURE 2.

(A) Results for true, scatter, random, prompt, and NECR as functions of activity concentration for NEMA standard 70-cm scatter phantom. Dashed line corresponds to NECR peak. (B) Results for true, scatter, random, prompt, and NECR as function of activity concentration for 175-cm scatter phantom. Dashed line corresponds to NECR peak. (C) NECR as function of activity concentration for both 70-cm-long and 175-cm-long scatter phantoms. Dashed lines correspond to NECR peaks for both phantoms. (D) Scatter fraction as function of activity concentration for both 70-cm-long and 175-cm-long scatter phantoms. Scatter fractions at 5.3 kBq/mL for 70-cm-long and 175-cm-long phantoms are 34.13% and 35.09%, respectively, and scatter fractions at peak NECR are 29.94% and 30.85%. (E) TOF resolution as functions of activity concentration for both 70-cm-long and 175-cm-long scatter phantoms. Dashed line corresponds to 5.3 kBq/mL. TOF at 5.3 kBq/mL is 188.8 and 189.7 ps for 70-cm-long and 175-cm-long phantoms, respectively, and TOF at peak NECR is 196.8 and 195.2 ps. FWHM = full width at half maximum.

FIGURE 3.

Accuracy of NEMA standard 70-cm-long scatter phantom. Dashed line corresponds to NECR peak. Turning points at high activity correspond to scenarios when measurement reached system bandwidth limit.

FIGURE 4.

Reconstructed images at different delay times with various time frames.

FIGURE 5.

(A) BV of 37-mm sphere. (B) CRC of 37-mm sphere. (C) BV of 10-mm sphere. (D) Lung residual results.

FIGURE 6.

Recovery coefficients based on EARL guideline. Left to right: maximum recovery coefficient (RCmax) of all 6 spheres, mean recovery coefficient (RCmean) of all 6 spheres, and peak recovery coefficient (RCpeak) of all 6 spheres.

FIGURE 7.

(A) Topogram, (B) maximum-intensity projection, and (C) transaxial images of patient data. Clear demarcations of reported lesions (indicated by arrows), including pulmonary nodule, retrocrural node, and subcutaneous nodule, are visible in each time frame.