Abstract
Due to multiple light scattering inside biological tissues, deep non-invasive optical medical imaging is very challenging. Acousto-optic imaging is a technique coupling ultrasound and light that allows recovering optical contrast at depths of few centimeters with a millimeter resolution. Recent advances in acousto-optic imaging are using short focused ultrasound pulses often averaged over several hundred or thousand pulses. As the pulsing rate of commercial probes is limited to about few ultrasound cycles every 100 μs, acquiring an acousto-optic image usually takes several tens of seconds due to the high number of acoustic pulses excitation. We propose here a new acousto-optic imaging technique based on the use of ultrasound plane waves instead of focused ones that allows increasing drastically the imaging rate.
Highlights
Biological tissues are very strong light scattering media, so deep optical imaging is impossible unless invasive techniques are used
We propose here a new acousto-optic imaging technique based on the use of ultrasound plane waves instead of focused ones that allows increasing drastically the imaging rate
We propose a new pattern based on transducers arrays and US plane waves that allows reducing the number of pulses necessary to create an image while maintaining the firing rate at the limit of the probe heat damage threshold
Summary
Biological tissues are very strong light scattering media, so deep optical imaging is impossible unless invasive techniques are used. Classical AO US sequences use focused US pulses and need about 100 lines, i.e. as many pulses, to get an image so that the theoretical framerate using standard US scanners is of the order 100 fps Though this theoretical limit is acceptable for video rate display and most of in vivo applications, it is dramatically reduced by the low amount of useful signal in AO imaging and the resulting high number of averaging. In [10] Lai et al used an optimized photorefrective-based detection thanks to, among others, a very high numerical aperture fiber bundle and long US pulses (from 10 to 100 cycles) in order to decrease the number of averaging down to 64 at the cost of the longitudinal resolution (along the US propagation direction) Though this method reaches unprecedented depths, its main drawbacks are that it uses a single element transducer at relatively low repetition rate (100 Hz). To ultrafast acousto-electric imaging technique [13], it will be shown below that high imaging framerates can be performed at the cost of an image distortion and a resulting loss of resolution in the lateral direction, the amplitude of which will be quantified
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