Biomedical subjects

Naizhang Feng

Publications and source records attributed to Naizhang Feng.

4 recordsLinked to original sources

PubMed2006

An adaptive clutter rejection method based on AR model in color flow imaging.

The ultrasound Doppler signal scattered from blood is heavily corrupted by the clutter signal reflected from slowly moving muscular tissue. The Doppler frequency shift of blood flow and clutter in different parts of human body greatly changes. Therefore, if a fixed wall filter is selected, the optimal filtering effect can not be attained. An adaptive clutter rejection method is proposed in this paper, which consists of a weak clutter rejector and a 2-order AR estimator. The clutter and blood power thresholds were preliminary defined in the weak clutter rejector. The echo power is compared with the two pre-defined thresholds, and the result was used to select an appropriate wall filter. The output of the weak clutter rejector is estimated by a 2-order AR estimator and two poles are acquired. The low frequency pole denotes the clutter signal and the high frequency pole denotes the blood signal. Before the AR estimation, a static signal is added to avoid producing split spectral peaks. It is illustrated in the simulation that the proposed method can detect the slower blood flow with smaller variance compared with the traditional wall filtering method.

Algorithms↗

PubMed2006

A quadrature demodulation method based on tracking the ultrasound echo frequency.

The ultrasound echo attenuation depends on frequency, propagating depth and tissue characteristics. Thus, the attenuation dependent on frequency results in a larger attenuation of high frequencies than lower when the wave propagates through the tissue. As a result, the central frequency of the echo generates the increasing downshift with the increasing of depth. In the traditional I/Q demodulation method, it is assumed that the central frequency of the echo is the same as the transmitting frequency and unchanged all time. The assumption directly causes that the acquired I/Q signals are not perfect baseband ones but biased due to the echo attenuation. In addition, the unreasonable assumption will keep the echo from getting better signal-to-noise ratio. A quadrature demodulation method based on tracking the ultrasound echo frequency is proposed in this paper. The method consists of the traditional I/Q demodulator, the frequency tracking module, the phase compensation module and the dynamic filtering module. The outputs of I/Q demodulator are biased. Autocorrelation technique is utilized in the frequency tracking unit to estimate the frequency bias according to the outputs of I/Q demodulator. The estimated bias feeds to the phase compensation unit which can eliminate the frequency bias by simple trigonometric function transform. The compensated signals feed to the dynamic filter and are further processed. The bandwidth of the dynamic filter decreases with the increasing of the depth, which makes the echo acquire better SNR in different depth. The efficiency of the proposed method is testified by both simulations and experiments.

Algorithms↗

PubMed2006

[Study on the method of testing the wall filter performance].

In order to test the performance of wall filters, we propose a method for simulation of Hybrid Doppler testing signal, which adopts a rectangular power spectrum. In the method, the parameters of clutter, blood flow and system noise can be adjusted with flexibility. The problem about choosing model parameters is discussed as an emphasis. Several reasonable and typical parameter combination patterns are presented. Furthermore, an example is given to explain the process of choosing the parameters and testing the wall filter performance.

Blood Flow Velocity↗

PubMed2006

[A new MTI scheme in ultrasonic color flow mapping systems].

In color flow imaging systems, the ultrasound Doppler signal scattered from blood is heavily corrupted by the strong clutter signal reflected from the slow-moving muscular tissue. Moving target indicator (MTI) is a key technique of rejecting the clutter signal and detecting blood flow. To improve the performance of detecting blood flow, a new MTI scheme is proposed in this paper. It consists of a pre-filter, a clutter weak-rejector and a 2-order AR estimator. After the processing of pre-filtering and clutter weak-rejection, the strong clutter signal is effectively eliminated and its strength is comparable with blood flow. Under such condition, the optimal performance can be attained by the 2-order AR estimator. It is illustrated in the simulation that, compared with the data from traditional methods, the blood flow parameters are estimated with smaller deviation and the lower speed flow is detected.

Blood Flow Velocity↗