Speaker
Description
Backgrounds and Aims
Total-body (TB) PET systems have significantly increased system sensitivity compared with conventional whole-body PET scanners. However, currently available clinical TB-PET systems are based on pixelated crystals without depth-of-interaction (DOI) capability, which may limit spatial resolution homogeneity at large radial offsets due to parallax errors. We present the initial performance evaluation and pilot clinical results of IMAS, a 71-cm axial FOV TB-PET prototype that combines simultaneous time-of-flight (TOF) and DOI capabilities using semi-monolithic LYSO detectors. The aim of this work is to describe the system design, calibration strategy, performance characterization inspired by NEMA NU 2-2018, and preliminary clinical validation.
Materials and Methods
The IMAS system consists of five 10-cm detector rings separated by 5-cm gaps, providing 71 cm axial coverage and an 82 cm bore diameter. Detector blocks are based on 3 × 25 × 20 mm³ LYSO semi-monolithic slabs arranged in 1×8 arrays and coupled to 8×8 SiPM matrices. A proprietary 64-to-16 multiplexed readout preserves 3D positioning and timing information. Data acquisition is performed with PETsys electronics, incorporating dual DAQ boards and an FPGA-based energy filter to improve count-rate capability.
Spatial positioning in the monolithic (y) and DOI (z) directions is estimated using multilayer perceptron (MLP) neural networks trained on reference super-modules and extended to all detector blocks. Timing skew correction is performed iteratively using a rotating FDG-filled bar and validated with a ²²Na point source.
Image reconstruction is performed using OSEM (5 iterations, 5 subsets), including DOI correction, TOF, attenuation correction and scatter correction. System performance was evaluated using NEMA NU 2-2018-inspired procedures, including spatial resolution, sensitivity, count-rate performance (NECR), energy resolution, coincidence time resolution (CTR), and image quality using a torso phantom. Preliminary clinical comparison was performed against a Philips Gemini TF-64 PET/CT scanner in a patient with multiple lesions.
Results
Detector-level measurements showed a detector time resolution of 196 ± 13 ps and an energy resolution of 11 ± 1%. After skew correction, system CTR improved from 2863 ps (uncorrected) to 565 ± 5 ps FWHM for a ²²Na point source. At the NECR peak (3.26 kBq/mL), CTR was 690 ps with an energy resolution of 12.8%.
The system achieved homogeneous spatial resolution across the full FOV. At the axial center, radial FWHM was 3.34 mm at 1 cm offset and 3.53 mm at 30 cm. DOI correction prevented radial mispositioning errors up to 6 mm at 30 cm off-center. The average spatial resolution was 3.3 ± 0.5 mm.
Measured sensitivity was 56.54 cps/kBq, corresponding to a peak sensitivity of 7.6% at the scanner center. The peak NECR was 79 kcps at 3.26 kBq/mL, lower than other LAFOV systems, likely due to data-transfer limitations. CTR degraded moderately with activity concentration, ranging from 550 to 725 ps over the tested range.
Preliminary clinical imaging demonstrated improved lesion delineation and higher apparent signal-to-noise ratio compared with the conventional PET/CT system. DOI capability improved lesion localization at radial distances up to 16 cm from the scanner center.
| Track | TBPET |
|---|---|
| Presentation type | Oral |