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Proceedings Paper

Effect of reference spectra in spectral fitting to discriminate enzyme-activatable photoacoustic probe from intrinsic optical absorbers
Author(s): Takeshi Hirasawa; Shinpei Okawa; Ryu J. Iwatate; Mako Kamiya; Yasuteru Urano; Miya Ishihara
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Paper Abstract

Multispectral photoacoustic (MS-PA) imaging has been researched to image molecular probes in the presence of strong background signals produced from intrinsic optical absorbers. Spectral fitting method (SFM) discriminates probe signals from background signals by fitting the PA spectra that are calculated from MS-PA images to reference spectra of the probe and background, respectively. Because hemoglobin is a dominant optical absorber in visible to near-infrared wavelength range, absorption spectra of hemoglobin have been widely used as reference background spectra. However, the spectra of background signals produced from heterogeneous biological tissue differ from the reference background spectra due to presence of other intrinsic optical absorbers and effect of optical scattering. Due to the difference, the background signals partly remain in the probe images. To image the probe injected in subcutaneous tumors of mice clearly, we added the melanosome absorption spectrum to the reference background spectra because skin contains nonnegligible concentration of melanosome and the spectrum is very similar to the scattering spectrum of biological tissue. The probe injected in the subcutaneous tumor of mice was an enzyme-activatable probe which show their original colors only in the presence of γ-glutamyltranspeptidase, an enzyme associated with cancer. The probes have been successfully used for rapid fluorescence imaging of cancer. As a result of MS-PA imaging, by considering the melanosome absorption spectrum, the background signals were successfully suppressed and then clearer probe image was obtained. Our MS-PA imaging method afforded successful imaging of tumors in mice injected with activatable PA probes.

Paper Details

Date Published: 15 March 2016
PDF: 6 pages
Proc. SPIE 9708, Photons Plus Ultrasound: Imaging and Sensing 2016, 970834 (15 March 2016); doi: 10.1117/12.2213778
Show Author Affiliations
Takeshi Hirasawa, National Defense Medical College (Japan)
Shinpei Okawa, National Defense Medical College (Japan)
Ryu J. Iwatate, The Univ. of Tokyo (Japan)
Mako Kamiya, The Univ. of Tokyo (Japan)
Yasuteru Urano, The Univ. of Tokyo (Japan)
Miya Ishihara, National Defense Medical College (Japan)

Published in SPIE Proceedings Vol. 9708:
Photons Plus Ultrasound: Imaging and Sensing 2016
Alexander A. Oraevsky; Lihong V. Wang, Editor(s)

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