Acoustic field of a medical ultrasound probe operated in continuous-wave mode investigated by TV holography

Abstract

Time-averaged TV holography has been shown to be a useful technique for investigating acoustic fields in transparent media. The theory of time-averaged TV-holography measurements of ultrasonic fields in water is described. Projections of the phase and the amplitude of a 3.25-MHz ultrasonic field from an annular ultrasound probe operated in cw mode are presented. Quantitative measurements with a spatial resolution of better than 100 mum have been obtained. A set of such projections may be processed into a three-dimensional mapping of the phase and the amplitude of the acoustic field by tomographic techniques. This process is described, and an example of a tomographic reconstruction of the same ultrasonic field is presented.

Full-field mapping of ultrasonic field by light-source-synchronized projection

“…In the projection measurement, the measured amplitude corresponds to an effective pressure along the optic projection line in the ultrasonic field. More accurate results can be obtained by reconstruction 5 as in the traditional tomographic measurements. Figure 3(a) shows the 1D amplitude profiles along the horizontal direction (Y axis in Fig.…”

“…where I i is the incident laser intensity, C is a constant, J n is the nth order Bessel function of the first kind, υ x,y and Φ x,y are respectively the effective Raman-Nath parameter and the effective phase of the ultrasonic field along the projection path, 5 ϕ is the initial phase of the ultrasonic wave, and Z is a normalized parameter defined as:…”

“…TV holography has been successfully applied to the investigation of ultrasonic fields in clear media and water. 5 In this letter, we demonstrate a simple method for mapping the projection of an ultrasonic field by using a source-synchronized parallel lock-in detection scheme. 6 The illuminating light is modulated at the frequency of the ultrasonic field.…”

Characterization of Transducer Performance and Narrowband Transient Ultrasonic Fields in Metals by Rayleigh-Sommerfeld Backpropagation of Compression Acoustic Waves Measured with Double-Pulsed Tv Holography

“…[8] When combined with tomographic techniques, this configuration provides data in three dimensions and thus yields quantitative mappings of acoustic beams. [9][10][11] When the measurements yield both the amplitude and phase of the acoustic wave, it can be numerically propagated forwards and backwards from the measurement surface. [12] The backpropagation of a 2-D set of experimental data, measured at some distance in front of the emitter, is an indirect approach to obtain the acoustic pressure or normal velocity distributions at the transducer surface, which give information about the actual vibration pattern of the device and are valuable for the subsequent modeling of its radiated field.…”

Nonperturbing measurements of spatially distributed underwater acoustic fields using a scanning laser Doppler vibrometer

“…Having extensively studied refractive index changes induced by airborne acoustic fields emanating from vibrating objects such as loudspeakers using ESPI, 20,21 the Applied Optics Group at the Norwegian University of Science and Technology successfully implemented the observation of underwater acoustic fields using the same technology. 22 In a more specific study, Rustad demonstrated the suitability of ESPI for studying the acoustic field generated by a 3.25 MHz continuous wave medical ultrasound probe, with a spatial resolution of better than 100 m. 23 This technique is, however, limited by the spatial resolution and fixed aspect ratio of the TV camera used to acquire the images and the fact that the sensitivity of the ESPI system is a complex function of the spherical spreading of the optical wave front and target shape and position.…”