Fig. 2: Frequency wavelength multiplexed optoacoustic tomography (FWMOT) advantages at multiple wavelengths.
From: Frequency wavelength multiplexed optoacoustic tomography
a A pulse train of one wavelength with period T and repetition rate frep = 1/T, with Np pulses and acquisition time tacq in time domain (TD, left) and Fourier domain (right), with k frep the harmonics of frep with k an integer. b–d Multiple wavelength excitation in TD Optoacoustic (OA). b The excitation pattern of 4 wavelengths emitting at the same repetition rate frep with a time shift T/4, Np pulses for all wavelengths and tacq acquisition time. c The excitation pattern of 4 wavelengths with frep/4 repetition rate, Np/4 pulses for each wavelength and tacq acquisition time. d The excitation pattern of four wavelengths with frep/4 repetition rate, Np pulses per wavelength but with 4tacq acquisition time. e FWMOT excitation where all four wavelengths have different repetition rates frep,1, frep,2, frep,3, frep,4, Np pulses for each wavelength and tacq acquisition time. f–j The OA signal recorded by a black varnish layer on a petri dish from the excitation patterns in (a–e) respectively. The signal-to-noise ratio (SNR) and noise level are inset for all cases. f α, the electromagnetic interference from the laser diode circuitry when triggered, β the OA signal from the black varnish, γ the reflection of the OA signal in the petri dish or in the acoustic lens of the Ultrasound Transducer. g The OA signal from the excitation pattern b for all wavelengths (top line) is the sum of the OA signal from each wavelength (bottom line), with drastically reduced Depth-of-View (DoV) for each wavelength. The laser interference, OA signal and its reflections (α, β, γ) for each wavelength are indicated. h The OA signal at each wavelength has reduced SNR. i The OA signal has the same SNR but with increased acquisition time. j Signal from all four wavelengths has been recovered without any cross-talk between the lasers and correctly co-registered in time without compromising DoV, SNR or acquisition time. Blue, red, orange, purple, and green are used to indicate laser 1, laser 2, laser 3, and laser 4, respectively.
