Biomedical subjects

Xiufen Gong

Publications and source records attributed to Xiufen Gong.

8 recordsLinked to original sources

PubMed2006

Evaluation of ultrasonic scattering in human cancellous bone by using a binary mixture model.

A weak scattering model based on small perturbations in a binary mixture is developed to estimate the ultrasonic scattering from human cancellous bone, which is modelled as a random isotropic continuum containing identical scatters. Ultrasonic scattering is determined by both velocity fluctuation and density fluctuation, when k(2)a(2) << 1 is satisfied. Two kinds of trabeculae thickness distributions, i.e. even distribution and Gauss distribution, are applied in the calculation of attenuation and backscattering. Frequency dependence of the backscatter coefficient is found to be Af(3.13) and Af(2.84) with the Gauss distribution and an even distribution, respectively. Both backscattering and attenuation change significantly against porosity for the case of high porosity. The predicted results are close to the measured ones from the literature. The errors of this theoretical model are also discussed in this paper.

Anisotropy↗

PubMed2006

Nonlinear absorption in biological tissue for high intensity focused ultrasound.

In recent years the propagation of the high intensity focused ultrasound (HIFU) in biological tissue is an interesting area due to its potential applications in non-invasive treatment of disease. The base principle of these applications is the heat effect generated by ultrasound absorption. In order to control therapeutic efficiency, it is important to evaluate the heat generation in biological tissue irradiated by ultrasound. In his paper, based on the Khokhlov-Zabolotkaya-Kuznetsov (KZK) equation in frequency-domain, the numerical simulations of nonlinear absorption in biological tissues for high intensity focused ultrasound are performed. We find that ultrasound thermal transfer effect will be enhanced with the increasing of initial acoustic intensity due to the high harmonic generation. The concept of extra absorption factor is introduced to describe nonlinear absorption in biological tissue for HIFU. The theoretical results show that the heat deposition induced by the nonlinear theory can be nearly two times as large as that predicated by linear theory. Then, the influence of the diffraction effect on the position of the focus in HIFU is investigated. It is shown that the sound focus moves toward the transducer compared with the geometry focus because of the diffraction of the sound wave. The position of the maximum heat deposition is shifted to the geometry focus with the increase of initial acoustic intensity because the high harmonics are less diffraction. Finally, the temperature in the porcine fat tissue changing with the time is predicated by Pennes' equation and the experimental results verify the nonlinear theoretical prediction.

Adipose Tissue↗

PubMed2006

Third order harmonic imaging for biological tissues using three phase-coded pulses.

Compared to the fundamental and the second harmonic imaging, the third harmonic imaging shows significant improvements in image quality due to the better resolution, but it is degraded by the lower sound pressure and signal-to-noise ratio (SNR). In this study, a phase-coded pulse technique is proposed to selectively enhance the sound pressure of the third harmonic by 9.5 dB whereas the fundamental and the second harmonic components are efficiently suppressed and SNR is also increased by 4.7 dB. Based on the solution of the KZK nonlinear equation, the axial and lateral beam profiles of harmonics radiated from a planar piston transducer were theoretically simulated and experimentally examined. Finally, the third harmonic images using this technique were performed for several biological tissues and compared with the images obtained by the fundamental and the second harmonic imaging. Results demonstrate that the phase-coded pulse technique yields a dramatically cleaner and sharper contrast image.

Algorithms↗

PubMed2006

Performance evaluation of eigendecomposition-based adaptive clutter filter for color flow imaging.

In this paper, a newly developed eigendecomposition-based adaptive filter is applied in flow velocity estimation and its performance is evaluated and compared with the static polynomial regression filter. Results demonstrate that the eigendecomposition-based filter is the fully-adaptive and can not only suppress the clutter signals with minimal loss of low-flow signal, but also give less influence on the flow velocity estimation especially under the circumstance of high clutter velocity.

Algorithms↗

PubMed2006

A novel approach for description of nonlinear field radiated from a concave source with wide aperture angle.

A new approach is proposed to study the nonlinear sound field radiated from a concave spherical source with a wide aperture angle. The nonlinear sound field is theoretically described by a set of equations deduced reversely from the second-order Westervelt nonlinear wave equation. To examine the validity of the theoretical model, numerical calculations are performed on a concave spherical radiator with the aperture angle wide up to 40 degrees. Numerical calculation is implemented by the finite difference time domain algorithm in the oblate spheroidal coordinate system. Numerical results are in agreement with those obtained by Kamakura's solutions.

Journal Article↗

PubMed2006

Investigation of superharmonic sound propagation and imaging in biological tissues in vitro.

This article presents both theoretical and experimental studies on the superharmonic generation and its imaging in biological tissues. A superharmonic component is defined as a summation of the third-, fourth-, and fifth-order harmonics. A superharmonic signal is produced using an 8-mm-diam, 2.5-MHz planar piston source that is excited by eight-cycle, 2.5-MHz tone bursts. Axial and lateral field distributions of the superharmonic component and the second harmonic are first calculated based on the nonlinear KZK model and then compared with those experimentally determined at two different source pressures of 0.5 and 1 MPa. Results indicate that the amplitude of the superharmonic component can exceed that of the second harmonic, depending on the axial distance and the fundamental pressure amplitude. Also, the 3-dB beamwidth of the superharmonic component is about 23% narrower than that of the second harmonic. Additional experiments are performed in vitro using liver and fatty tissues in transmission mode and produced two-dimensional images using the fundamental, the second harmonic, and the superharmonic signals. Although the clinical applicability of this work still needs to be assessed, these results indicate that the superharmonic image quality is better than that of the other two images.

Acoustics↗

PubMed2005

Improvement of tissue harmonic imaging using the pulse-inversion technique.

Harmonic imaging has brought about significant improvements in image quality by taking advantage of the second harmonic component, but it still has one shortcoming, namely, a low signal-to-noise ratio. In this paper, a pulse-inversion technique is used in second harmonic imaging for biologic tissues to increase the signal-to-noise ratio. Enhancement of the second harmonic component is theoretically analyzed based on the theory of the finite amplitude sound wave and confirmed by the measurement. Second harmonic imaging for biologic tissues is constructed with the pulse-inversion technique and compared with the traditional fundamental frequency and also with second harmonic imaging before the use of this technique. Results demonstrate that this technique yields a dramatically cleaner and sharper contrast between the different structures of biologic tissues in ultrasonic images.

Acoustics↗

PubMed2004

Study of acoustic nonlinearity parameter imaging methods in reflection mode for biological tissues.

Three novel methods for acoustic nonlinearity parameter B/A imaging in reflection mode are developed in this paper. They are: (1) the acoustic nonlinearity parameter B/A tomography by detecting reflective second harmonic wave, (2) the B/A tomography in reflection mode via the measurement of the difference frequency wave generated by a parametric array, and (3) the C-scan imaging of B/A via the measurement of the echo second-harmonic signal. A theoretical analysis and the experimental imaging of normal and pathological biological tissues by using these methods are also present and discussed. Results show that using the acoustic nonlinearity parameter imaging we can more easily distinguish the diseased tissue from the normal one than using the linear acoustic parameters.

Adipose Tissue↗