Development of a small prototype of a novel transformable single-ring OpenPET

Objectives:We are developing a world-first, open-type 3D PET scanner "OpenPET" for PET-image guided particle therapy such as in situ dose verification and/or direct tumor tracking. Our initial idea was a dual-ring Open PET (DROP) geometry to visualize a physically opened space between two detector rings. In the last year, we also proposed a second-generation geometry, single-ring OpenPET (SROP), which is more efficient than the DROP in terms of a cost and sensitivity. The detector ring of the SROP geometry was the cylinder both ends of which were cut by parallel aslant planes. For realization of this geometry, however, we have to pay attention to the arrangement of rectangular block detectors. One method, with which we developed a small SROP geometry in the last year, is a slanted ellipse geometry where oval detector rings are slanted and stacked. In this paper, we develop another SROP prototype based on a new detector arrangement.\nMethods:The new SROP prototype was based on an axial shift geometry, in which block detectors originally forming a conventional PET scanner were axially shifted little by little. Sixteen detector units each of which consisted of two depth-of-interaction detectors were arranged to form a perfect circle of 25cm in diameter. Each detector unit had a mechanism for axially shifting to be transformed into the SROP. Transformation between a normal PET and the OpenPET, which was controlled by a single rotation handle, was completed within 10 seconds.\nResults:We measured the micro-Derenzo phantom, and we confirmed that 2.2 mm rods were clearly separated for both modes. Absolute sensitivity at the center was 8.3% in the normal mode and 6.0% in the open mode.\nConclusions:We developed a small prototype of a new transformable SROP geometry. The open mode obtained almost the same quality of image as the normal mode did at the cost of 25% loss of sensitivity. This supports the importance of the transformable geometry; we can limit the use of the open mode to the case where the OpenPET is essentially required.SNMMI 2013 Annual Meetin