Figure 2.

(a) Photo of a pair of dual-wavelength LED bars that emits 690-nm and 850-nm light alternatively. (b) PA (pseudo color) and US (gray scale) combined image showing the microvessels in the cross-section of a human finger. (c) Correlation between the dual-wavelength PA measurements of the blood sO₂ in the finger and the SpO₂ readouts from a pulse oximeter. A fitting line (dashed line, y = a x + b, a = 1.251, b = −0.234) is presented, and R-square of 0.9838 is achieved. At each SpO₂ level, the asterisk on red line shows the mean, and the distance above or below it shows the standard deviation of the PA measurements.