A multiplex “OpenPET” geometry to extend axial FOV without increasing the number of detectors

At the last MIC conference, we proposed an “OpenPET” geometry, which consists of two axially separated detector rings of axial length W. A long and continuous field-of-view (FOV) including a 360-degree open gap G between two detector rings can be imaged though iterative image reconstruction. In addition to providing stress-less PET scanning and simultaneous PET/CT, the OpenPET is expected to lead to realization of in-beam PET. The OpenPET also extends the axial FOV with a limited number of detectors. The range of G to obtain the axially continuous FOV is represented as aW (0≪a≪=1). The extension gain, which is defined as [extended axial FOV size] / [original axial FOV size], is limited to (2+a)/2. In order to increase the gap and the axial FOV, therefore, we have to extend W itself. However the extension of W results in cost enhancement of the scanner. In this paper, we propose a new “multiplex OpenPET” geometry, which can extend axial FOV without increasing the number of detectors. In the first step, two detector rings of axial length W are separated by the gap aW, and we have a pseudo scanner, unit[1], of axial length W[1] =(2+a)W. In the second step, two unit[1]s can be separated by the gap aW[1], and we have unit[2] of axial FOV W[2]=(2+a)²W. After repeating these steps N times, we finally have unit[N], which has a long axial FOV of W[N]=(2+a)^NW. Here the extension gain is represented as {(2+a)/2}^N. Theoretically it can be increased to an unlimited extent, although there is no gain in sensitivity. Simulation results show that fine reconstructed images are obtained by the multiplex OpenPET geometry. In addition to the extended gap, the proposed geometry is expected to help realize an affordable entire body PET scanner that enables whole body dynamic imaging.