TU‐FF‐A4‐03: Improving the Accuracy of Optical‐Emission‐CT Imaging Through Application of a Non‐Uniform Attenuation Correction
Purpose: Optical computed tomography (optical‐CT) and emission tomography (optical‐ECT) are new techniques with demonstrated potential for imaging structure and function (including gene expression) in unsectioned tissue samples. This work presents the first attempts to improve the accuracy of optical‐ECT by incorporating an attenuation correction analogous to that applied in SPECT. Method and Materials: Optical‐ECT can be described as a linear system Ax=b, where x is the fluorescing distribution, b is the expected value of measured projections, and A describes the mapping from x to b. An in‐house code (Spect‐Map) originally developed for SPECT reconstruction was adapted for application to optical‐ECT. Verification of the method was performed by imaging a phantom containing a known distribution of fluorescing wires. Optical‐CT/ECT projections were taken consecutively to ensure accurate co‐registration. Attenuation‐uncorrected and ‐corrected optical‐ECT images were reconstructed by calculating A assuming zero attenuation and the optical‐CT‐measured non‐uniform attenuation, respectively. Successful preliminary verification led to the application of attenuation correction to optical‐ECT images of unsectioned human breast xenograft tumors which had transcribed fluorescing proteins labeling viable tumor burden (RFP) and HIF1 distribution (GFP). Results: Significant attenuation artifacts were observed in the uncorrected optical‐ECT image of the phantom. The middle wire appeared artificially less intense due to greater attenuation from the surrounding ink‐doped gel. This artifact was successfully removed in the attenuation‐corrected image, demonstrating basic performance of the method. Fluorescence intensities of the wires varied by as much as 29% in the uncorrected image versus 3% in the corrected image. Application of the attenuation correction to xenograft tumor images shows significant changes in apparent expression of fluorescing proteins. Interpretation and results will be presented. Conclusion: These results suggest that Spect‐Map has been successfully adapted to perform attenuation correction for optical‐ECT imaging. Preliminary xenograft tumor reconstructions indicate that attenuation correction is vital for accurate optical‐ECT imaging. © 2008, American Association of Physicists in Medicine. All rights reserved.
Kim, E; Bowsher, J; Sakhalkar, H; Dewhirst, M; Oldham, M
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