Photoacoustic imaging in the second near-infrared window: a review

Abstract

Photoacoustic (PA) imaging is an emerging medical imaging modality that combines optical excitation and ultrasound detection. Because ultrasound scatters much less than light in biological tissues, PA generates high-resolution images at centimeters depth. In recent years, wavelengths in the second near-infrared (NIR-II) window (1000 to 1700 nm) have been increasingly explored due to its potential for preclinical and clinical applications. In contrast to the conventional PA imaging in the visible (400 to 700 nm) and the first NIR-I (700 to 1000 nm) window, PA imaging in the NIR-II window offers numerous advantages, including high spatial resolution, deeper penetration depth, reduced optical absorption, and tissue scattering. Moreover, the second window allows a fivefold higher light excitation energy density compared to the visible window for enhancing the imaging depth significantly. We highlight the importance of the second window for PA imaging and discuss the various NIR-II PA imaging systems and contrast agents with strong absorption in the NIR-II spectral region. Numerous applications of NIR-II PA imaging, including whole-body animal imaging and human imaging, are also discussed.

An IR820 Dye–Protein Complex for Second Near‐Infrared Window and Photoacoustic Imaging

“…In this study, based on the fact that IR820 has structural similarity to ICG as well as two sulfonic acid groups, we hypothesize that it may bind to HSA, and the resulting IR820–HSA protein complex can be effectively used for NIR‐II imaging. Moreover photoacoustic imaging (PAI) offers numerous advantages, including high spatial resolution, deeper penetration depth, and reduced optical absorption, and tissue scattering . Corresponding tumor PA imaging of IR820–HSA was also investigated.…”

“…Moreover photoacoustic imaging (PAI) offers numerous advantages, including high spatial resolution, deeper penetration depth, and reduced optical absorption, and tissue scattering. [30,31] Corresponding tumor PA imaging of IR820-HSA was also investigated.…”

Photoacoustic imaging depth comparison at 532-, 800-, and 1064-nm wavelengths: Monte Carlo simulation and experimental validation

“…Recently, a second window of near-infrared region (NIR-II, 900 to 1200 nm) has been used for PAI. 15,[27][28][29][30][31][32] This increased interest in NIR-II imaging has been attributed to further decrease in scattering of light by tissue in this region, and to the increased maximum permissible exposure (MPE) of light illumination in accordance with the American National Standards Institute (ANSI) safety limit. 33 However, as compared to the NIR-I window, absorption of light by surrounding tissues is higher in NIR-II.…”

High resolution, label‐free photoacoustic imaging of live chicken embryo developing in bioengineered eggshell

“…These wavelengths were not chosen for this work as absorption coefficient of blood is low in these wavelengths. Use of contrast agent with 1064 nm excitation is another possibility for embryo imaging, which can be explored in the future . Different organs or structures of the developing embryo can be targeted using such external contrast agents .…”