Development of Multi-Spectral Frequency-Domain Photoacoustic imaging

Our PAR imager operating with linear frequency modulation (LFM chirp) of a CW laser beam [37] exhibits superior signal-to-noise ratio and at least similar depth resolution to conventional pulsed-laser tissue photoacoustics [2]. Very recently, we introduced a novel bi-spectral PAR tissue imaging methodology through the use of mismatched (weakly correlated) linear frequency swept signals (chirps). The feasibility of the method was tested on oxygen saturated HbO2 and deoxy Hb in-vitro in a blood circulating rig. The method was also employed for in-vivo imaging of a neck carcinoma tumor grown in mouse thigh [1]. Introducing and using the concept of “waveform engineering” in  the  form  of  two  laser  intensity  chirp  modulations  with  mismatched  coded  excitations,  we  could distinguish the PA response at each wavelength separately with minimum or no interference from the other laser. The time for image acquisition in PAR bi-spectral imaging is only hundreds of ms due to the simultaneous character of the image formation. This translates into < 1 min small-animal full-body scan. Furthermore, image artifact forming mechanisms like the breathing of the animal are avoided with simultaneous multi-spectral imaging, as all images are obtained at the same time. The images can be quantified in terms of total Hb and HbO2 concentrations [2].

References I.5

[1] B. Lashkari, S. S. Choi, M. E. Khosroshahi, E. Dovlo and A. Mandelis, Simultaneous Dual-wavelength Photoacoustic Radar Image Generation Using Waveform Engineering with Mismatched Frequency Modulated Excitation, Opt. Lett. 40 (7), 1145 – 1148 (April 1, 2015).

[2]  Sung soo (Sean) Choi, Andreas Mandelis, Xinxin Guo, Bahman Lashkari, Stephan Kellnberger, and Vasilis Ntziachristos, “Wavelength-Modulated Differential Photoacoustic Spectroscopy (WM-DPAS) for noninvasive early cancer detection and tissue hypoxia monitoring”, J. Biophotonics, 9, No. 4, 388–395 (2016) / DOI 10.1002/jbio.201500131. (WM-DPAS cover picture selected for Vol. 9, issue 4 of the journal: