Development and initial results of a tomographic dual-modality positron/optical small animal imager

Herein, we present a novel concept for fully integrated dual-modality in vivo tomographic imaging yielding simultaneous detection of positron and optically labeled probes in small animals. The imager consists of an allocation of optical detector modules and, in radial extension, the allocation of positron emission detector modules. Laser scanning and large-field light sources are integrated to facilitate fluorescence imaging in addition to bioluminescence imaging. Each optical detector unit consists of a large-area photon sensor for light detection, a microlens array for field-of-view definition, a septum mask for cross-talk suppression, and a transferable filter for wavelength selection. To prove the working principle of the dual-modality detector system a pair of optical detectors along with a large-field excitation source was placed inside the bore of a Siemens EXACT HR+ scanner, performing simultaneous imaging. The imaging characteristics of the optical detector were evaluated experimentally using a prototypical setup with geometrical phantoms. The sensitivity of the optical detector prototype was found less than that of a reference CCD camera. We propose several ways of increasing optical detector sensitivity.