360° free space Fluorescence Molecular Tomography using silhouette surface reconstruction

Complete projection (360°) free-space fluorescence tomography of opaque media is poised to enable highly performing three-dimensional imaging through entire small animals in-vivo. This approach can lead to a new generation of Fluorescence Molecular Tomography (FMT) systems since it allows high spatial sampling of photon fields propagating through tissue at any projection, employing non-constricted animal surfaces. Key features of this development is the implementation of non-contact illumination, for example by using beam scanning techniques for light delivery on the tissue surface and direct non-contact imaging with CCD cameras. Similarly, the development of free-space geometries, i.e. implementations that do not utilize immersion of the animal in matching fluids are essential for obtaining appropriate experimental simplicity and avoid unnecessary diffusion through scattering matching media. To facilitate these developments it is important to retrieve the three-dimensional surface and a common coordinate system for the illumination system, the detection system and the animal. Herein, we employ a volume carving method to capture three-dimensional surfaces of diffusive objects from its silhouettes and register the captured surface in the geometry of an FMT 360°-projection acquisition system to obtain three-dimensional fluorescence image reconstructions. Using experimental measurements we evaluate the accuracy of the surface capture procedure by reconstructing the surfaces of phantoms of known dimensions and demonstrate how this surface extraction method can be utilized in an FMT inversion scheme. We then employ this methodology to characterize the animal movement of anaesthetized animals and study the effects of animal movement on the FMT reconstructed image quality.