Design considerations for a partial-ring, multi-modal compatible whole-body TOF PET scanner: Flexible PET

Abstract

Along with the popularization and technological maturation of integrated PET-CT, the center of research interest has moved to integrated PET-MR. In this situation, we are developing a multi-modal compatible flexible PET scanner. In our concepts, the scanner consists of adjustable two detector units and their support apparatus, and then scans a patient lying on a bed equipped by other medical imaging/non-imaging device.Therefore, depending on the size and shape of the patient and the patient bed and other demands, the detector geometry can be changed flexibly. Although, due to the limited angular coverage, distortion-and artifact-free image reconstruction is not feasible without detector rotation, it is known that accurate time-of-flight (TOF) information helps to improve reconstruction quality in such a partial-ring scanner.In this study, we performed whole-body 2-D imaging simulations to investigate detector geometric and TOF requirements for the partial-ring scanner for obtaining comparable image quality to a conventional full-ring non-TOF scanner. In particular, required angular coverage by the detector units in relation with the timing resolution and the influence of the arrangement of the opposed detector units (i.e., missing direction is perpendicular to patient's front-to-back or left-to right direction) to the reconstruction image quality were investigated. The simulation results on the image appearance and contrast-noise performance showed that the partial-ring scanner consisting of the two detector arcs each having the central angle of 150 degree and 400-500 ps timing resolution could provide comparable image quality to the conventional scanner regardless of the arrangement of the opposed detectors. However, in the case of the 130 degree coverage with the 400-500 ps timingresolution, the contrast-noise performance of the partial-ring geometries could not reach partially that of the conventional scanner due to the missed spatial and/or statistical information.In this point, we showed that the use of the object support constraint in the iterative reconstruction could reduce the intensity bias and blurring and then improves the contrast-noise performance.

Comparison of PET/CT with Sequential PET/MRI Using an MR-Compatible Mobile PET System

“…As shown in Figure 1, the fxPET scanner is a partial-ring scanner rather than a conventional full-ring scanner, and its limited angular coverage results in missed line-of-responses in sinogram space. Degradation of image quality caused by data loss due to incomplete coincidence data was confirmed by a previous phantom study and was found to be reduced by using TOF information and more suitable list-mode reconstruction algorithms (8,9). Each crystal is 20 mm long, with a cross-sectional area of 2.9 • 2.9 mm and 4-layer depth-of-interaction capability.…”

“…The most likely cause of the lack of superior performance was degradation of image quality caused by incomplete coincidence data derived from the partial-ring detector. Two studies reported that accurate TOF information improved reconstruction image quality in a partial-ring PET scanner with no detector rotation (8,9). Therefore, the technology of TOF was added to the fxPET system to improve image quality, although the image quality of fxPET was not superior to that of commercial WB PET scanners that do not have TOF capability.…”

“…The fxPET scanner ( Fig. 1) consists of 2 detector units that enable the fitting of beds or other imaging modalities and patients of various body sizes (8). The dual arc-shaped detector heads can be arranged in various configurations, including top-bottom and left-right, depending on the purpose of imaging.…”

Application of a Flexible PET Scanner Combined with 3 T MRI Using Non-local Means Reconstruction: Qualitative and Quantitative Comparison with Whole-Body PET/CT

“…This system has two partial-ring (arc-shaped, 135°) detectors with depth-of-interaction (DOI) and time-of-flight (TOF) capability [2,5]. These detectors effectively compensate for the count loss caused by incomplete detector coverage [5,6].…”

Positron Emission Tomography of Not-Full-Ring Sensors Arrangement: Simulation and Verification for Internal Imaging of Hydraulic Cylinder

“…Therefore, depending on the size and shape of the patient and the patient bed and other demands, the detector geometry can be changed flexibly. [14]. Chih-Chieh Liu et al proposed a crystal arrays with curved surfaces to reduce the dead space between detector modules and hence improve the sensitivity of PET.…”