布 樹輝¹, 近藤 健悟¹, 山川 誠³, 椎名 毅¹, 福谷 和彦², 染田 恭宏², 浅尾 恭史^{1, 2}

Shuhui BU¹, Kengo KONDO¹, Makoto YAMAKAWA³, Tsuyoshi SHIINA¹, Kazuhiko FUKUTANI², Yasuhiro SOMEDA², Yasufumi ASAO^{1, 2}

¹京都大学大学院医学研究科, ²キヤノン株式会社総合R＆D本部, ³京都大学先端医工学研究ユニット

¹Graduate School of Medicine, Kyoto University, ²Medical Imaging Project, Corporate R&D Headquarters, Canon Inc., ³Advanced Biomedical Engineering Research Unit, Kyoto University

キーワード :

【目的】
Photoacoustic （PA） tomography is a rapidly developing imaging modality which can provide high contrast and spatial-resolution images of light absorption distribution in tissue. One major problem in PAT is that the reconstructed information is not quantitative. Since tissue absorbs and scatters light, the optical fluence is decreased along light penetration depth. The pixels or voxels in reconstructed PAT images represent the level of absorbed optical energy, which is the product of the absorption coefficient and the optical fluence. Therefore, the CNR in the deep region of reconstructed image is low. In this study, we propose an adaptive and quantitative reconstruction algorithm for reducing amplification of noises and artifacts in deep position due to light fluence compensation. Since this method uses a global optimized compensation, better CNR can be obtained. The results of simulation and phantom experiment indicate that the proposed method provide better CNR at deep region. We expect that the capability of increasing imaging depth will broaden clinical applications.
【方法】
In this paper, we introduce an adaptive fluence compensation algorithm for 3-D planar PAT which can partly resolve the problem that amplification of noises and artifacts in deep region. In this method, the quantitative processing is integrated into the model-based（iterative） reconstruction, and absorption coefficient distribution is iteratively updated. At each iteration step, the residual is calculated from detected PA signals and the signals calculated from a forward model by using the initial pressure which is calculated from the production of voxel value and the light fluence. By minimizing the residual, the reconstructed values are converged to the true absorption coefficient distribution. Because the light fluence compensation is combined in the reconstruction and a feedback is performed at each iteration, the amplification of noises and artifacts is less. The advantage of the proposed method is that reconstruction can be done under arbitrary illumination condition, less assumption is needed, and noises or artifacts at deep region of the reconstructed images are less. The results of simulation and phantom experiments indicate that the proposed method performs better than conventional methods.
【結論】
In this paper, we presented an adaptive and quantitative reconstruction method for 3-D planar PAT. The light fluence compensation is performed at each iteration, which can make the noise and amplification of artifacts minimized. In addition, matrix compress techniques make the proposed method applicable for 3-D planar scanning conditions, and the calculation speed is also accelerated. The simulation and phantom experiment results indicate that the proposed method reconstructs better quality images. We expect that the capability of increasing imaging depth will broaden clinical applications of PAT.