A comprehensive method for optical-emission computed tomography

Abstract

Optical-computed tomography (CT) and optical-emission computed tomography (ECT) are recent techniques with potential for high-resolution multi-faceted 3D imaging of the structure and function in unsectioned tissue samples up to 1–4 cc. Quantitative imaging of 3D fluorophore distribution (e.g. GFP) using optical-ECT is challenging due to attenuation present within the sample. Uncorrected reconstructed images appear hotter near the edges than at the center. A similar effect is seen in SPECT/PET imaging, although an important difference is attenuation occurs for both emission and excitation photons. This work presents a way to implement not only the emission attenuation correction utilized in SPECT, but also excitation attenuation correction and source strength modeling which are unique to optical-ECT. The performance of the correction methods was investigated by the use of a cylindrical gelatin phantom whose central region was filled with a known distribution of attenuation and fluorophores. Uncorrected and corrected reconstructions were compared to a sectioned slice of the phantom imaged using a fluorescent dissecting microscope. Significant attenuation artifacts were observed in uncorrected images and appeared up to 80% less intense in the central regions due to attenuation and an assumed uniform light source. The corrected reconstruction showed agreement throughout the verification image with only slight variations (∼5%). Final experiments demonstrate the correction in tissue as applied to a tumor with constitutive RFP.