High-resolution all-optical photoacoustic imaging system for remote interrogation of biological specimens

Ashwin Sampathkumar

doi:10.1117/12.2053412

22 May 2014 High-resolution all-optical photoacoustic imaging system for remote interrogation of biological specimens

Ashwin Sampathkumar

Proceedings Volume 9107, Smart Biomedical and Physiological Sensor Technology XI; 91071B (2014) https://doi.org/10.1117/12.2053412
Event: SPIE Sensing Technology + Applications, 2014, Baltimore, MD, United States

Abstract

Conventional photoacoustic imaging (PAI) employs light pulses to produce a photoacoustic (PA) effect and detects the resulting acoustic waves using an ultrasound transducer acoustically coupled to the target tissue. The resolution of conventional PAI is limited by the sensitivity and bandwidth of the ultrasound transducer. We have developed an all-optical versatile PAI system for characterizing ex vivo and in vivo biological specimens. The system employs noncontact interferometric detection of the acoustic signals that overcomes limitations of conventional PAI. A 532-nm pump laser with a pulse duration of 5 ns excited the PA effect in tissue. Resulting acoustic waves produced surface displacements that were sensed using a 532-nm continuous-wave (CW) probe laser in a Michelson interferometer with a GHz bandwidth. The pump and probe beams were coaxially focused using a 50X objective giving a diffraction-limited spot size of 0.48 μm. The phase-encoded probe beam was demodulated using a homodyne interferometer. The detected time-domain signal was time reversed using k-space wave-propagation methods to produce a spatial distribution of PA sources in the target tissue. Performance was assessed using PA images of ex vivo rabbit lymph node specimens and human tooth samples. A minimum peak surface displacement sensitivity of 0.19 pm was measured. The all-optical PAI (AOPAI) system is well suited for assessment of retinal diseases, caries lesion detection, skin burns, section less histology and pressure or friction ulcers.

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Ashwin Sampathkumar "High-resolution all-optical photoacoustic imaging system for remote interrogation of biological specimens", Proc. SPIE 9107, Smart Biomedical and Physiological Sensor Technology XI, 91071B (22 May 2014); https://doi.org/10.1117/12.2053412

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KEYWORDS

Tissue optics

Teeth

Signal detection

Acoustics

Laser beam diagnostics

Lymphatic system

Photoacoustic spectroscopy

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