Method and apparatus for adaptive wall filtering in spectral Doppler ultrasound imaging

A method for displaying a Doppler velocity-time waveform envelope, comprising the steps of:

• transmitting a multiplicity of pulses of ultrasound into a sample volume of ultrasound scatterers, said multiplicity of pulses forming a packet;
• acquiring a multiplicity of successive samples of Doppler signals backscattered from said sample volume of ultrasound scatterers;
• and
• processing said Doppler signals to produce spectral line data representing velocity for continuous display of a succession of spectral lines during Doppler signal acquisition, the data for each spectral line comprising a multiplicity of frequency bins for different frequency intervals, each bin containing spectral power data for a respective frequency interval, the spectral power data in each bin for each spectral line being displayed as a scale in a respective pixel of a corresponding column of pixels on a display monitor, said processing step comprising the steps of:
• demodulating said Doppler signal samples into in-phase and quadrature components;
• integrating the in-phase and quadrature components over a specific time interval;
• wall filtering the integrated in-phase and quadrature components to substantially reject clutter corresponding to stationary or very slow-moving tissue;
• selecting cutoff frequencies to be used in said wall filtering step as a function of the clutter power of said integrated in-phase and quadrature components;
• and
• producing spectral power data by Fast Fourier transformation of the wall-filtered in-phase and quadrature components,
• wherein said cutoff frequency selecting step comprises the steps of:
• low pass filtering said integrated in-phase and quadrature components to substantially reject flow frequency components which are above a clutter frequency range;
• computing the total power of the output of said low pass filtering step;
• providing an estimate of the mean system noise power in said low pass filtering output;
• comparing the total power of said low pass filtering output to the mean system noise power in said low pass filtering output;
• and
• selecting wall filter coefficients which are a function of the results of comparing the total power to the mean system noise power.

A system comprising:

• a transducer array comprising a multiplicity of transducer elements for transmitting wave energy in response to electrical activation and transducing returned wave energy into electrical signals;
• a display monitor for displaying spectral Doppler data;
• and
• a computer programmed to perform the following steps:
• activating transducer elements of said array to transmit a multiplicity of pulses of ultrasound into a sample volume of ultrasound scatterers, said multiplicity of pulses forming a packet;
• acquiring a multiplicity of successive samples of Doppler signals backscattered from said sample volume of ultrasound scatterers and detected by said array;
• and
• processing said Doppler signals to produce spectral line data representing velocity for continuous display of a succession of spectral lines during Doppler signal acquisition, the data for each spectral line comprising a multiplicity of frequency bins for different frequency intervals, each bin containing spectral power data for a respective frequency interval, the spectral power data in each bin for each spectral line being displayed as a scale in a respective pixel of a corresponding column of pixels on said display monitor, said processing step comprising the steps of:
• demodulating said Doppler signal samples into in-phase and quadrature components;
• integrating the in-phase and quadrature components over a specific time interval;
• wall filtering the integrated in-phase and quadrature components to substantially reject clutter corresponding to stationary or very slow-moving tissue;
• selecting cutoff frequencies to be used in said wall filtering step as a function of the clutter power of said integrated in-phase and quadrature components;
• and
• producing spectral power data by Fast Fourier transformation of the wall-filtered in-phase and quadrature components,
• wherein said cutoff frequency selecting step comprises the steps of:
• low pass filtering said integrated in-phase and quadrature components to substantially reject flow frequency components which are above a clutter frequency range;
• computing the total power of the output of said low pass filtering step;
• providing an estimate of the mean system noise power in said low pass filtering output;
• comparing the total power of said low pass filtering output to the mean system noise power in said low pass filtering output;
• and
• selecting wall filter coefficients which are a function of the results of comparing the total power to the mean system noise power.

A method for displaying Doppler blood flow information, comprising the steps of:

• transmitting a multiplicity of pulses of ultrasound into a sample volume of ultrasound scatterers, said multiplicity of pulses forming a packet;
• acquiring Doppler signals backscattered from said sample volume of ultrasound scatterers;
• low pass filtering the acquired Doppler signals to substantially reject flow frequency components which are above a clutter frequency range;
• computing the total power of the output of said low pass filtering step;
• comparing the total power of said low pass filtering output to an estimated mean system noise power in said low pass filtering output;
• selecting wall filter coefficients which are a function of the results of comparing the total power to the mean system noise power;
• wall filtering the Doppler signals to substantially reject clutter corresponding to stationary or very slow-moving tissue;
• and
• processing the wall-filtered Doppler signals to produce blood flow data for display.

An ultrasound imaging system comprising:

• a transmitter for transmitting a multiplicity of pulses of ultrasound into a sample volume of ultrasound scatterers, said multiplicity of pulses forming a packet;
• a receiver for acquiring Doppler signals backscattered from said sample volume of ultrasound scatterers;
• a low pass filter for low pass filtering the acquired Doppler signals to substantially reject flow frequency components which are above a clutter frequency range;
• a wall filter for wall filtering the acquired Doppler signals to substantially reject clutter corresponding to stationary or very slow-moving tissue;
• a display monitor for displaying blood flow data;
• and
• a computer programmed to perform the following steps:
• computing the total power of the output of said low pass filter;
• comparing the total power of said low pass filter output to an estimated mean system noise power in said low pass filter output;
• selecting filter coefficients for said wall filter which are a function of the results of comparing the total power to the mean system noise power;
• setting said wall filter in accordance with said selected wall filter coefficients;
• and
• processing the wall-filtered Doppler signals to produce blood flow data for display.