Prospects of molecular photoacoustic imaging at 1064 nm wavelength

Abstract

An analysis of the photoacoustic (PA) signal from murine tissue in vivo revealed several benefits of contrast-enhanced PA imaging at a wavelength of 1064nm. Of all the wavelengths tested in a range from 710 to 1064nm, the background PA signal from tissue in vivo was lowest and more homogeneous at 1064nm. For blood-laden tissue, the background PA signal was up to 70% less at 1064nm. Furthermore, when plasmonic nanoparticles, such as silver nanoplates, were introduced in vivo as contrast agents, the contrast in PA images at 1064nm increased 38% compared to 750nm. Therefore, contrast-enhanced PA imaging at 1064nm is advantageous because of the low and homogeneous signal from native tissue, enabling high contrast in PA imaging when exogenous, molecularly targeted agents are employed.

Fig. 1

(Color online) Photoacoustic and ultrasound imaging setup.

Fig. 2

(a) Background PA signal from murine tissue in vivo overlaid on absorption coefficient data for tissue components, and (b) the std divided by the mean for the PA signal from tissue in vivo.

Fig. 3

(a) Extinction spectra for the NPs and (b) a TEM image of NP₇₅₀ (scale bar, 100 nm). US images after direct injection of (c) NP₇₅₀ and (g) NP₁₀₆₄ (arrows indicate injection sites). PA images obtained using (d) and (h) 750 nm and (e) and (i) 1064 nm wavelengths. The injected NPs are even better visualized in combined PAUS images [(f) and (j)]. All images are 10 mm × 10:5 mm.

Fig. 4

(a) US image of a xenograft tumor grown subcutaneously in a mouse. PA images of the tumor taken at (b) 720, (c) 810, and (d) 1064 nm wavelengths. (e) A photograph of the tumor showing that the bright PA signal was due to a large blood vessels that were feeding the tumor (white arrows indicate the imaging plane, and the scale bar is 5 mm). PAUS images are 13 mm × 10:5 mm.