Characterization of a Commercial Bioluminescence Tomography System for Pre-Clinical Radiation Research

Abstract

<h3>Purpose/Objective(s)</h3> To advance image-guided irradiation for soft tissue targeting and treatment assessment, we collaborated with our industrial partner and developed a bioluminescence tomography system (BLT, MuriGlo) for pre-clinical radiation research. We characterize the system performance and demonstrate its capability in target localization for radiation guidance. <h3>Materials/Methods</h3> MuriGlo consists of four-mirror system, filters, lens and CCD camera, enabling a compact imaging platform and multi-projection and multi-spectral BLT. The imaging mouse bed includes a base, and a detachable and transportable bed, allowing animal imaged in MuriGlo and transferred to small animal radiation research platform (SARRP) for CBCT imaging and BLT-guided irradiation. A transparent polycarbonate plate covering the middle of the mouse bed is used to support and image animal at 180⁰ projection under the bed. We investigated its effects on optical signal acquisition, 3D BLT reconstruction accuracy and dosimetric impact. Imaging phantoms are designed to evaluate 2D imaging resolution, focal plane, depth of field, signal acquisition linearity, imaging uniformity and distortion. An optimization routine with pinhole camera model was developed to map 2D bioluminescence images (BLIs) to the surface of the numerical mesh of imaged object generated from the CBCT image. The mapped BLIs are used as input data for BLT reconstruction. Spectral derivative method with compressed sensing conjugate gradient algorithm was implemented for BLT volumetric reconstruction. To minimize the ambient temperature in affecting in vivo bioluminescence signal intensity and spectrum, a temperature control module was also developed to maintain consistent temperature in the MuriGlo imaging chamber. Phantom and glioblastoma (GBM) mouse model will be used to validate the localization accuracy of the BLT system for guidance. <h3>Results</h3> The depth of field of MuriGlo was measured at 24mm, and the focal plane is set at 16mm above the mouse bed to have clear surface BLIs of mouse at all projections. The linearity between signal and exposure time from 0.1 to 180s is within 0.6% deviation. Our initial test shows within a given region of interest, the image uniformity is within 5% variation and image shift due to distortion is within 0.25mm. The data mapping from the 2D BLIs to 3D CBCT image is within 0.6mm. With temperature control turned on, the imaging chamber could be warmed up to 37°C from room temperature in 13 mins. Our phantom test shows MuriGlo can localize 3D bioluminescent target at 1mm accuracy and only 0.2mm deviation was observed for the case with and without transparent plate. <h3>Conclusion</h3> This work is the first systematic study in characterizing the commercial BLT-guided system for pre-clinical radiation research. We expect the information and methods developed in this study will support MuriGlo users, cross different institutes, in performing accurate image-guided radiation research and facilitating study reproducibility.