We describe an optoacoustic imaging technique based on time-resolved measurements of laser-induced thermoelastic expansion. Tomographic images of tissue phantoms are formed using such measurements made at several locations following irradiation with a Q-switched Nd:YAG (λ=1064nm) laser pulse. Our system is based on a modified Mach–Zehnder interferometer that measures surface displacement with a temporal resolution of 4ns and a displacement sensitivity of 0.3nm. Images formed from data sets acquired from several highly scattering tissue phantoms provide better than 200μm resolution and show great promise for high-resolution noninvasive imaging of heterogeneous tissues at depths approaching 1cm.
POISe is a spectroscopic imaging technique based on the measurement of surface motion resulting from thermoelastic stress waves produced by short pulse laser irradiation of optically heterogeneous turbid samples. Here we show the capability of POISe to form tomographic images of tissue phantoms using surface displacement measurements taken at several locations following irradiation of a sample with a Q-switched Nd:YAG laser λ=1064 nm. The principal component of POISe is a modified Mach-Zehnder interferometer that provides surface displacement measurements with a temporal resolution of 4 ns and a displacement sensitivity of 0.2 nm. By performing simple image reconstructions on data sets acquired from several tissue-like phantoms, we demonstrate the ability of POISe to provide better than 250 µm spatial resolution at depths of 6 to 8 mm in a strongly scattering medium (µ s =1/mm). This technique shows great promise for high-resolution non-invasive imaging of superficial (< 1 cm) tissue structures.
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