Ultrasound-modulated optical imaging using a confocal Fabry-Perot interferometer and a powerful long pulse laser
; Rousseau, Guy
; Blouin, Alain
NRC Industrial Materials Institute (IMI-IMI); National Research Council Canada
Photons Plus Ultrasound: Imaging and Sensing 2009. Session: Ultrasound Modulated (Acousto-Optical) Imaging I, San Jose, Californie, États-Unis, January 25, 2009
Proceedings of the SPIE
biomedical imaging; ultrasound-modulated optical tomography; acousto-optical imaging; ultrasound-tagged photons; scattering media; confocal Fabry-Perot interferometer; pulsed single-frequency laser
Ultrasound-modulated optical imaging combines the good spatial resolution of ultrasonic waves (mm scale) and the spectroscopic properties of light to detect optically absorbing objects inside thick (cm scale) highly scattering media. Light propagating in a scattering medium can interact with an ultrasonic wave thereby being tagged by a frequency shift equal to the ultrasound frequency or its harmonics. In this paper, a confocal Fabry-Perot interferometer(CFPI) is used as a tunable spectral filter to detect selectively the ultrasound-tagged photons. The CFPI allows obtaining high spectral resolution (MHz scale) while maintaining a high light gathering power when compared to other spectroscopic devices of comparable resolution. The contrast between the tagged photons and the untagged photons can be further enhanced by cascading CFPI. Moreover, the fast response of the CFPI allows performing measurements within the speckle decorrelation time typically encountered in biomedical applications. In this paper, the use of a single-frequency laser emitting powerful optical pulses allows illuminating the scattering medium only during the transit time of the probing ultrasonic pulses. Consequently, the acoustic and the optical power are both concentrated in time to enhance the signal-to-noise ratio of the tehcnique while remaining below the biomedical safety limits. The detection of optically absorbing objects (mm size) inside 30- and 60-mm thick scattering media is presented.