Physical performance of a long axial field‐of‐view PET scanner prototype with sparse rings configuration: A Monte Carlo simulation study

Abstract

Purpose: There is a growing interest in extending the axial fields-of-view (AFOV) of PET scanners. One major limitation for the widespread clinical adoption of such systems is the multifold increase in the associated material costs. In this study, we propose a cost-effective solution to extend the PET AFOV using a sparse detector rings configuration. The corresponding physical performance was validated using Monte Carlo simulations. Methods: Monte Carlo model of the Siemens Biograph TM mCT PET/CT, with a 21.8 cm AFOV and a set of compact rings of LSO crystals was developed as a gold standard. The mCT configuration was then modified by interleaving the LSO crystals in the axial direction within each detector block with 4 mm physical gaps (equivalent to the LSO crystal axial dimension) thus extending the AFOV to 43.6 cm (Ex-mCT). The physical performances of the two MC models were assessed and then compared using NEMA NU 2-2007 standards. Results: Ex-mCT showed <0.2 mm difference in transaxial spatial resolution, and, 0.8 mm and 0.3 mm deterioration in axial spatial resolution, compared to the mCT, at 1 and 10 cm off-center of the transaxial field-of-view respectively. The system sensitivities for the mCT and Ex-mCT models were 9.4 AE 0.2 and 10.75 AE 0.2 cps/kBq respectively. The higher sensitivity of Ex-mCT was due to four additional detector rings required to double the mCT AFOV. PET images of the NEMA Image Quality (IQ) phantom showed no artifacts due to detector rings sparsity, and all spheres were visible in both configurations. Ex-mCT achieved percent contrast recoveries within 5.6% of those of the mCT for all spheres and a maximum of 36% higher background variability at the center of the AFOV. The Ex-mCT, however, showed a more uniform noise distribution over an axial range of almost twice the length of the mCT AFOV. Conclusions: Using the proposed sparse detector-ring configuration, the AFOV of current generation PET systems can be doubled while maintaining the original number and volume of detector crystal elements, and without jeopardizing the system's overall physical performance. Despite an increase in the noise level, the Ex-mCT exhibited an improved noise uniformity.

Performance Characteristics of the Biograph Vision Quadra PET/CT System with a Long Axial Field of View Using the NEMA NU 2-2018 Standard

“…Furthermore, in many clinical scenarios, time consuming multiple bed positions must be imaged to cover the relevant portion of the patient. Stretching the FOV by axially spacing out the detector rings increases coverage of the patient body but not the overall sensitivity (12). The viable solution is to increase the number of detector rings at the down side of increased costs (13).…”

Prospects and Clinical Perspectives of Total-Body PET Imaging Using Plastic Scintillators

“…Therefore, there is a need for new technical solution that would enable to substantially decrease the cost of the extended axial field-of-view (AFOV) PET, where approximately half of the cost is in scintillators, and the other half of the costs is in silicon photomultipliers (SiPM) and electronics. 16 The ongoing investigations aiming at cost reduction focuses on the possibilities of (1) scintillator thickness reduction 17 ; (2) sparse detector configurations 18,19 ; and (3) application of BGO crystals 20,21 with Cherenkov light readout for the improved timing properties. [22][23][24][25] The reduction of detector thickness decreases the sensitivity approximately as a square of the reduction thickness coefficient, whereas the cost of scintillators decreases only linearly without reducing the costs of electronics.…”

Monte Carlo Simulation of the Siemens Biograph Vision PET With Extended Axial Field of View Using Sparse Detector Module Rings Configuration

“…This method, which is validated on the Siemens Biograph Vision geometry, is expected to yield nearly double the AFOV for the same number of detectors. The sparse ring configuration involves interleaving with uniform axial gaps between modules and thus is fundamentally different from our previous approach where the uniform axial gaps were much narrower and interleaved between detector elements of the same module or block [18], [28]. In this study, the gaps are smaller in number, but each has a significantly larger width.…”