V.A. Simonova

Point spread function of array transducers in 2D optoacoustic tomography

In this work the spatial resolution provided by the array transducers in 2D optoacoustic (OA) imaging is considered numerically. The resolution is determined from the point spread function (PSF) of an array, that is a 2D OA image of a point source of the spherical acoustic wave. Numerical simulations consisted of the following steps. First, the OA signals excited by the point source and detected by each element of the array calculated using the Rayleigh integral. Radial backprojection algorithm was then employed to obtain the image of the point source in the imaging plane. The influence of the geometrical parameters of array elements, number of the detectors and a single detector bandwidth on the PSF was studied in detail. It was shown that the spatial resolution provided by the array transducer in the imaging plane can be unambiguously determined from the detector frequency band, array aperture angle and the width of a single array detector, and does not depend on the number of the detectors.

Wideband focused transducer array for optoacoustic tomography

The calculation procedure of the parameters of a multielement transducer array for the optoacoustic tomography of biological objects with high spatial resolution values is proposed. A multielement transducer with given spatial resolution values in three dimensions has been developed based on the proposed procedure for the early detection of breast cancer. The transducer array consists of a set of 8 linear PVDF piezoelectric films located on a plane and a focusing cylindrical acoustic lens. A map of the transducer’s focal area and point spread function have been measured using the constructed transducer array. Spatial resolutions of the transducer array obtained experimentally are in agreement with their calculated values.

Laser-induced ultrasonic imaging for measurements of solid surfaces in optically opaque liquids [Invited]

The paper describes a novel laser ultrasonic profilometry method which uses pulsed laser radiation for imaging of the surface profile of solid objects in optically opaque liquids by scattering of ultrasonic waves. Algorithms for the construction of laser ultrasonic images and for profile segmentation are presented. An experimental setup for profile measurements is described. It allows reconstructing of laser ultrasonic images with a frame rate of 10 Hz and performing an automated 3D scanning of samples. The results of the experimental testing of laser ultrasonic profilometry on duralumin samples are presented. The approximation error of duralumin cylinder surface profile measurements in water is 15 μm. The results are compared to those obtained by x-ray tomography.

On the use of an optoacoustic and laser ultrasonic imaging system for assessing peripheral intravenous access

We describe a universal system for research in combined real-time optoacoustic (OA) and laser-ultrasonic (LU) imaging. The results of its testing on the task of needle insertion into the blood vessel model diagnostics are presented. In OA mode, where laser light is absorbed directly in the sample, the contents of blood vessel model is clearly visible. In LU mode, where the short ultrasonic probe pulse scattered on the sample is detected, the needle is clearly visible. The developed solution combining OA and LU imaging modalities due to the common detection system allowed real-time diagnostics of the position of medical needles (0.63 mm and 0.7 mm in diameter) inside blood vessel models (1.6 mm and 2.4 mm in diameter). Frame rate was 10 Hz. High longitudinal spatial resolution of the system − 0.1 mm − allows distinguishing the two walls of the vessel model and the position of the needle inside.

Lateral spatial resolution of widened focused transducer array for optoacoustic tomography

Numerical investigation of a point spread function for a optoacoustic transducer array is described. Analysis of the minimal reconstructed dimension for an optoacoustic image of a point source of spherical waves is performed within the proposed approach. The influence of the array geometrical parameters, number of array transducers, and the frequency band of a single transducer on the lateral resolution in the image plane is investigated in detail. It is demonstrated that the lateral resolution obtained with the help of a transducer array in the image plane is determined unambiguously by the frequency band of a transducer, the flare angle of the array, and the transducer width and does not depend on the number of transducers.

A refraction-corrected tomographic algorithm for immersion laser-ultrasonic imaging of solids with piecewise linear surface profile

In this paper, a technique for reflection mode immersion 2D laser-ultrasound tomography of solid objects with piecewise linear 2D surface profiles is presented. Pulsed laser radiation was used for generation of short ultrasonic probe pulses, providing high spatial resolution. A piezofilm sensor array was used for detection of the waves reflected by the surface and internal inhomogeneities of the object. The original ultrasonic image reconstruction algorithm accounting for refraction of acoustic waves at the liquid-solid interface provided longitudinal resolution better than 100 μm in the polymethyl methacrylate sample object.In this paper, a technique for reflection mode immersion 2D laser-ultrasound tomography of solid objects with piecewise linear 2D surface profiles is presented. Pulsed laser radiation was used for generation of short ultrasonic probe pulses, providing high spatial resolution. A piezofilm sensor array was used for detection of the waves reflected by the surface and internal inhomogeneities of the object. The original ultrasonic image reconstruction algorithm accounting for refraction of acoustic waves at the liquid-solid interface provided longitudinal resolution better than 100 μm in the polymethyl methacrylate sample object.

Point spread function of the limited‐view array transducers in optoacoustic tomography: numerical and experimental studies

Optoacoustic (OA) tomography utilizes pulsed laser radiation for thermoelastic excitation of wideband ultrasonic pulses. The distribution of laser‐induced heat release can be reconstructed if the ultrasonic pulses are detected by an array of transducers. The resolution provided by an array depends on various aspects of its design ‐ the number of elements, element size, spacing and arrangement ‐ and is determined by the point spread function (PSF) of the array. In present work PSFs of arrays with different characteristics are calculated using the Rayleigh integral for simulating the direct problem, and backprojection algorithm for solving the inverse problem of OA tomography. Universal dependencies of the resolution provided by an array on the dimensions and arrangement of its elements are found. Numerical studies are validated by experimental measurements of PSFs of different arrays.