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

ABSTRACT 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.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper describes a non-contact optical technique for imaging and detection of early-stage dental caries. Tooth decay, at its earliest stages, manifests itself as small, white, subsurface lesions in the enamel. Current detection methods including visual and tactile investigations and bite-wing X-ray radiographs suffer from poor sensitivity and specificity at the earliest (and reversible) stages of the disease due to the small size (<100 microns) of the lesion. We have developed a fine-resolution (500-nm) ultra-broadband (GHz) all-optical photoacoustic imaging (AOPAI) system to image the early stages of tooth decay. Photoacoustic (PA) signals are generated using a Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser operating at 532 nm with a 5-ns pulse duration. The light-induced broadband ultra-sound wave is detected at the surface of the tooth with a path-stabilized Michelson interferometer. 2D images are generated from PA signals using k-wave reconstruction methods. Ex-vivo tooth samples exhibiting white-spot lesions were scanned and were found to generate a larger PA signal in the lesion regions compared to healthy enamel. This high contrast potentially allows lesions to be imaged and measured at a much earlier stage compared to current clinical techniques. PA images were cross referenced with histological and micro-CT images to validate our experimental results. Our AOPAI system provides a non-contact method for early detection of white-spot lesions with a high detection bandwidth that offers advantages over previously demonstrated ultrasound methods. The technique provides the ample sensing depth afforded by an ultrasound system combined with the fine spatial resolution of an optical system.
    IEEE Ultrasonics Symposium, Chicago; 09/2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents an acousto-optic (AO) sensor based on resonance grating waveguide structure. The sensor is fabricated using elastic polymer materials to achieve a good sensitivity to ultrasound pressure waves. Ultrasound pressure waves modify the structural parameters of the sensor and result in the optical resonance shift of the sensor. This converts into a light intensity modulation. A commercial ultrasound transducer at 20 MHz is used to characterize a fabricated sensor and detection sensitivity at different optical source wavelength within a resonance spectrum is investigated. Practical use of the sensor at a fixed optical source wavelength is presented. Ultimately, the geometry of the planar sensor structure is suitable for two-dimensional, optical pressure imaging applications such as pressure wave detection and mapping, and ultrasound imaging.
    Sensors and Actuators A Physical 09/2014; 216:364–369. DOI:10.1016/j.sna.2014.06.012 · 1.94 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a series of experiments on laser pulsed photoacoustic excitationin turbid polymer samples addressed to evaluate the sound speed in the samples and the presence of inhomogeneities in the bulk. We describe a system which allows the direct measurement of the speed of the detected waves by engraving the surface of the piece under study with a fiduciary pattern of black lines. We also describe how this pattern helps to enhance the sensitivity for the detection of an inhomogeneity in the bulk. These two facts are useful for studies in soft matter systems including, perhaps, biological samples. We have performed an experimental analysis on Grilon(R) samples in different situations and we show the limitations of the method.
    12/2013; 5. DOI:10.4279/PIP.050005


Available from