Abstract
.Significance: Collagen is a basic component of many tissues such as tendons, muscles, and skin, and its imaging helps diagnose and monitor treatments in a variety of fields, including orthopedics. However, due to the overlapping peaks of the absorption spectrum with water in the short-wave infrared region (SWIR), it is difficult to select an optimal wavelength and obtain the photoacoustic (PA) image for collagen-based tissues. Therefore, an additional approach to selecting the proper wavelength is needed.Aim: The aim of this study is to derive an effective PA absorption spectrum of collagen to select the optimal wavelength for high-sensitive PA imaging (PAI).Approach: We measure the absorption spectrum by acquiring the PA signal from various collagen-based samples. To derive an effective PA absorption spectrum in the SWIR band, the following two parameters should be considered: (1) the laser excitation for generating the PA signal and (2) the absorption spectrum for water in the SWIR band. This molecular intrinsic property suggests the optimal wavelength for high-sensitive PAI of collagen-based samples.Results: PA absorption spectral peaks of collagen were found at wavelengths of 1200, 1550, and 1700 nm. Thereby, the PA signal increased by up to five times compared with the wavelength commonly used in collagen PAI. We applied a pulsed fiber laser with a center wavelength of 1560 nm, and the three-dimensional PA image of a collagen patch was obtained.Conclusions: The effective PA absorption spectrum contributes to the improvement of the PA image sensitivity by presenting the optimal wavelength of the target samples.
Highlights
Photoacoustic imaging (PAI) is a promising hybrid imaging technique for biomedical applications, combining optical contrast and acoustic resolution.[1]
Thereby, the PA signal increased by up to five times compared with the wavelength commonly used in collagen PAI
The effective PA absorption spectrum contributes to the improvement of the PA image sensitivity by presenting the optimal wavelength of the target samples
Summary
Photoacoustic imaging (PAI) is a promising hybrid imaging technique for biomedical applications, combining optical contrast and acoustic resolution.[1] PAI provides anatomical and functional information based on strong optical absorption sensitivity.[1,2,3] The optimization of the wavelength according to the target molecule can enhance the selectivity of the visualization of target organs and allows for the extension into functional PAI such as multispectral imaging.[4,5] Typically, in the ultraviolet region (10 to 400 nm), the imaging of cell nuclei is performed utilizing the strong absorption by DNA and RNA at wavelengths of ∼260 nm.[6] In the visible (VIS) region (400 to 700 nm), vascular imaging is typically performed using wavelengths of around 532 nm.[7] In the first window of the near-infrared region (NIR-I, 700 to 1000 nm), Journal of Biomedical Optics
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