Fig. 6.

Multispectral photoacoustic images of the blood and fat samples. Photoacoustic images of the two tubes filled with oxygenated blood and fat at wavelengths of 800 and 1210 nm are shown in (a) and (b). Coregistered ultrasound image of the tubes are shown in (c). The colorbars in (a) and (b), and (c) correspond to photoacoustic and ultrasound image amplitudes, respectively. Photoacoustic images corresponded well to the ultrasound images. Photoacoustic images generated with excitation wavelengths ranging from 750 to 900 nm are shown in Video 1, and from 1150 to 1300 nm are shown in Video 2. Fluence-compensated average photoacoustic amplitudes for regions of interest (blood: ROI_b; fat: ROI_f; background noise: ROI_n) indicated in (a) to (c) are compared with the absorption spectra of oxygenated blood and fat in (d) and (e) for excitation light wavelengths from 750 to 900 nm and from 1150 to 1300 nm, respectively. The oxygenated blood and fat spectra are normalized to the measured average photoacoustic amplitudes at 750 and 1210 nm, respectively, for comparison. The photoacoustic signal amplitudes are averaged over 15 image frames; the error bars represent standard deviations. Good agreement between the measured spectra of oxygenated blood and fat and previous estimates were observed.³⁴ N, needle; W, water; CB, chicken breast; SN, second needle; B, blood; F, fat. (Video 1, mov, 374 KB [URL: http://dx.doi.org/10.1117/1.JBO.XX.XX.XXXXXX.1] and Video 2, mov, 471 KB) [URL: http://dx.doi.org/10.1117/1.JBO.XX.XX.XXXXXX.2].