Backward-mode multiwavelength photoacoustic scanner using a planar Fabry-Perot polymer film ultrasound sensor for high-resolution three-dimensional imaging of biological tissues

Department of Medical Physics and Bioengineering, University College London, Gower Street, London WC1E 6BT, UK.
Applied Optics (Impact Factor: 1.78). 03/2008; 47(4):561-77. DOI: 10.1364/AO.47.000561
Source: PubMed


A multiwavelength backward-mode planar photoacoustic scanner for 3D imaging of soft tissues to depths of several millimeters with a spatial resolution in the tens to hundreds of micrometers range is described. The system comprises a tunable optical parametric oscillator laser system that provides nanosecond laser pulses between 600 and 1200 nm for generating the photoacoustic signals and an optical ultrasound mapping system based upon a Fabry-Perot polymer film sensor for detecting them. The system enables photoacoustic signals to be mapped in 2D over a 50 mm diameter aperture in steps of 10 microm with an optically defined element size of 64 microm. Two sensors were used, one with a 22 microm thick polymer film spacer and the other with a 38 mum thick spacer providing -3 dB acoustic bandwidths of 39 and 22 MHz, respectively. The measured noise equivalent pressure of the 38 microm sensor was 0.21 kPa over a 20 MHz measurement bandwidth. The instrument line-spread function (LSF) was measured as a function of position and the minimum lateral and vertical LSFs found to be 38 and 15 microm, respectively. To demonstrate the ability of the system to provide high-resolution 3D images, a range of absorbing objects were imaged. Among these was a blood vessel phantom that comprised a network of blood filled tubes of diameters ranging from 62 to 300 microm immersed in an optically scattering liquid. In addition, to demonstrate the applicability of the system to spectroscopic imaging, a phantom comprising tubes filled with dyes of different spectral characteristics was imaged at a range of wavelengths. It is considered that this type of instrument may provide a practicable alternative to piezoelectric-based photoacoustic systems for high-resolution structural and functional imaging of the skin microvasculature and other superficial structures.

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Available from: Jan Laufer, Nov 03, 2015
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    • "Illumination of the coating through the fibre core was performed with pulsed laser light (2 ns pulse duration, 1064 nm, 35 µJ pulse energy, SPOT-10- 500-1064, Elforlight, UK), and through the photoacoustic effect a broad-band acoustic field was transmitted. This field propagated through the acoustic lens and was subsequently detected optically using a custom planar Fabry-Pérot etalon with a thickness of 10 µm exhibiting a broadband sensitivity of 0 − 110 MHz [10]. Using a custom 3D-printed holder, the source fibre was centered with respect to the acoustic lens, with its distal end located at a distance of 4.5 mm from the acoustic lens; the etalon was located on the other side of the lens at a distance of 7 mm from the lens centre with its surface perpendicular to the axial direction. "
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    ABSTRACT: As recently demonstrated, all-optical B-mode ultra-sound imaging can be performed with a pair of coated optical fibres for transmission and reception that is translated to create a virtual array of elements. However, with translation in the in-plane dimension, the small lateral dimensions of the fibres results in out-of-plane acoustic divergence, which leads to image clutter and loss of sensitivity. This study is focussed on the fabrication of acylindrical acoustic lenses to provide an acoustic focus in the out-of-plane dimension. Two fabrication methods were considered: laser-cutting of acrylic (PMMA), and 3D-printing of VeroWhite Plus (VWP). Using acoustic transmission measurements, the acoustic properties of PMMA (speed of sound: 2750 m/s, differential attenuation coefficient: 0.5 dB/cm/MHz at 5 MHz) and VWP (2539 m/s, 4.0 dB/cm/MHz at 5 MHz) were determined and subsequently used to optimise the lens shapes for both materials by means of a genetic algorithm. With both methods, lenses that accurately reproduced the designed shape were manufactured. However, the out-of-plane focus achieved with the 3D-printed VWP lens was closer to the modelled field focus than that generated by the laser-cut PMMA lens. In addition, while the acoustic attenuation coefficient of the former was eight times greater than that of the latter, the acoustic field propagated through both lenses had very similar fractional bandwidths of around 160%, centered around 15 MHz. This study highlights the potential benefits of 3D-printed VWP lenses over laser-cut PMMA lenses for diagnostic ultrasound applications.
    IEEE IUS 2015, Taipei, Taiwan; 10/2015
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    • "Different spacer thicknesses have been employed, chosen to optimise the sensitivity and bandwidth for the given application. For example, as part of the photoacoustic scanner described in [9] "

    IEEE International Ultrasonics Symposium, Taipei, Taiwan; 10/2015
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    • "Zhang et al., reported a planar Fabry–Perot polymer film ultrasound sensor for high-resolution 3D imaging of a blood vessel phantom [70] "
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    ABSTRACT: Development of both fundamental research and clinical applications of photo acoustic imaging call for ultrasound detectors of high sensitivity, flat frequency response and compact size, which are not easily satisfied by traditional ultrasound detectors. Therefore, many alternative ultrasound detectors have been investigated in recent years and are presentative one is the imprinted polymer microring resonator based detector. This review covers its principle, device fabrication, characterization and application, with an emphasis on how the microring’sunique properties make it actas a high performance ultrasound detector in photo acoustic imaging systems. The imprinted polymer microring has high detection sensitivity, broadband frequency response, compact size and good operation robustness. Application of microrings in photo acoustic tomography generates truthful reconstructed images; use of microring in photo acoustic microscopy leads to improved image resolution; the detector’scompact sizemakes it promising for photo acoustic endoscopic applications. When integrated with other electromagnetic wave absorbers, novel applications such as real-time terahertz pulse detection can be realized.
    Journal of Lightwave Technology 08/2015; DOI:10.1109/JLT.2015.2466661 · 2.97 Impact Factor
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