Design Features and Mutual Compatibility Studies of the Time-of-Flight PET Capable GE SIGNA PET/MR System

Abstract

A recent entry into the rapidly evolving field of integrated PET/MR scanners is presented in this paper: a whole body hybrid PET/MR system (SIGNA PET/MR, GE Healthcare) capable of simultaneous acquisition of both time-of-flight (TOF) PET and high resolution MR data. The PET ring was integrated into an existing 3T MR system resulting in a (patient) bore opening of 60 cm diameter, with a 25 cm axial FOV. PET performance was evaluated both on the standalone PET ring and on the same detector integrated into the MR system, to assess the level of mutual interference between both subsystems. In both configurations we obtained detector performance data. PET detector performance was not significantly affected by integration into the MR system. The global energy resolution was within 2% (10.3% versus 10.5%), and the system coincidence time resolution showed a maximum change of < 3% (385 ps versus 394 ps) when measured outside MR and during simultaneous PET/MRI acquisitions, respectively. To evaluate PET image quality and resolution, the NEMA IQ phantom was acquired with MR idle and with MR active. Impact of PET on MR IQ was assessed by comparing SNR with PET acquisition on and off. B0 and B1 homogeneities were acquired before and after the integration of the PET ring inside the magnet. In vivo brain and whole body head-to-thighs data were acquired to demonstrate clinical image quality.

PET/MRI: Where might it replace PET/CT?

“…Initial papers using PET/MRI in place of PET/CT have reported a greater than 50% decrease in dose as expected, from the removal of the CT component . In addition to the removal of dose from the CT component of the exam, new solid state detectors and improved geometry (longer z‐axis coverage and narrower ring diameter) results in sensitivities up to three times higher with new PET/MRI systems than comparable photomultiplier tube PET/CTs . Therefore, the injected dose of radiotracer can be lowered without sacrificing image quality.…”

Transmission imaging for integrated PET-MR systems

“…A similar methodology as used in this study; however, could be applied to develop the optimal source geometry for combined TX and emission scanning on TOF systems. This may be particularly applicable to the recently released TOF capable GE SIGNA PET-MR (Levin et al 2016), which also has a relatively small diameter bore and tight space confines. We only examined source geometries capable of fully tomographic acquisitions.…”

Principles of Simultaneous PET/MR Imaging

“…Chilled water is also used to control the temperature based on the feedback received from 280 thermistors positioned throughout the scanner. In terms of performance, the reported energy resolution is 10.3%, the timing resolution is less than 400 ps, the spatial resolution is 4.4 mm FWHM at 1 cm offset from the center of the field of view and the scanner sensitivity is 23.3 kcps/MBq (44). …”

“…When successful, this method was shown to reduce the error in the SUV estimation from 15–50% to less than 5% (51). A similar algorithm that uses the non-attenuation corrected TOF reconstructed PET image to estimate the patient outline is available on the Signa PET/MRI scanner (44, 52). …”