Development of a dual-head mobile DOI-TOF PET system having multi-modality compatibility

We previously proposed the concept of “FlexiblePET”, a dual-head mobile DOI-TOF PET system which scans the patient lying on a bed equipped by another imaging/therapy device. Following the development of a small prototype with dual-head SiPM-based detectors showing a proof-of-concept for MR compatibility, we are now developing a human prototype with DOI-TOF detectors and a scalable data acquisition system. Each detector module consists of a 2-D crystal array (2.9 mm × 2.9 mm × 20 mm LGSO in a 16 × 16 array), a light guide and a 4 × 4 4-ch SiPM array. The detector has a four-layer DOI capability by a special reflector arrangement and is expected to have < 500 ps coincidence timing resolution. The scanner has two arced detector heads (central angle: 135 degree, diameter: 778 mm), and each consists of 18 detector modules in transaxial direction and 3 rings in axial direction. This geometric configuration provides 715 mm transaxial FOV and 150 mm axial FOV. The detector head arrangement is changeable into four types: Top-Bottom, Left-Right, Side-C and Top-C, depending on imaging purpose. In addition, high-sensitivity imaging is possible by moving detector heads close to the patient. To compensate image quality degradation caused by the limited angle coincidence measurement, which is inherent in stable dualhead scanning, a new regularized TOF list-mode reconstruction algorithm that combines weighted maximum likelihood estimation and projection-space regularization was also developed. In this study, we will report initial results of physical performance evaluations of the prototype FlexiblePET system according to the NEMA NU 2-2007 standards. The experimental results support that the developed dual-head DOI-TOF PET protoptype system has the MR-compatibility and the acceptable image quality from the incomplete TOF projection measurement.