Abstract
The detection of ultrasound in photoacoustic tomography (PAT) and ultrasonography (US) usually relies on ultrasonic transducers in contact with the biological tissue. This is a major drawback for important potential applications such as surgery and small animal imaging. Here we report the use of remote optical detection, as used in industrial laser-ultrasonics, to detect ultrasound in biological tissues. This strategy enables non-contact implementation of PAT and US without exceeding laser exposure safety limits. The method uses suitably shaped laser pulses and a confocal Fabry-Perot interferometer in differential configuration to reach quantum-limited sensitivity. Endogenous and exogenous inclusions exhibiting optical and acoustic contrasts were detected ex vivo in chicken breast and calf brain specimens. Inclusions down to 0.5 mm in size were detected at depths well exceeding 1 cm. The method could significantly expand the scope of applications of PAT and US in biomedical imaging.
Highlights
Biomedical imaging techniques are presently intensively developed [1]
The only difference is the temporal delay used for the image reconstruction: the one-way propagation delay is used for NCPAT and the two-way propagation delay is used for NCUS
Blood vessel phantoms (20 mm long) were prepared to mimic the optical blood absorption coefficient at the generation laser wavelength while minimizing the acoustic impedance mismatch with the surrounding tissue
Summary
Photoacoustic tomography (PAT), which provides images of the optical absorption contrast, holds promise for many biomedical applications [2,3]. Ultrasonography (US) is a well established imaging modality providing acoustic properties of tissues. Both PAT and US usually rely on ultrasonic transducers in contact with the tissue using a coupling fluid (water or gel). Non-contact optical detection of ultrasound in biological tissues is of great interest. Generation and detection of ultrasound by remote optical means would facilitate endoscopic implementations of PAT and US as well as compatibility with other imaging modalities such as optical coherence tomography (OCT) [2,5,7]. Attempts have been made to replace piezoelectric transducers by optical means but most of these attempts require a contact with the tissue [9,10,11]
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