# US 7,611,467 B2 · Method and apparatus for extracting an envelope curve of a spectrogram > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,611,467 B2 - Document ID: US7611467B2 - Status: Granted - Kind: B2 - Application number: 11/316,048 - Filed: 2005-12-21 - Published: 2007-01-18 - Granted: 2009-11-03 - Earliest claimed: 2005-06-10 - Assignees: Shenzhen Mindray Bio-Medical Electronics Co., Ltd. - Inventors: Yu Zhang - Web page: https://patentgrep.com/patent/US7611467B2 ## CPC - A61B 8/06: Measuring blood flow - A61B 8/488: {involving Doppler signals} - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract A method and apparatus for extracting an envelope curve of a spectrogram, for use in measurement of blood flow velocity by using spectral Doppler techniques, the method comprising steps of: processing RF ultrasound echo signals to obtain Doppler signals; performing spectral analysis on the Doppler signals, to obtain a corresponding power spectrum P(f); estimating a forward maximum frequency fmax+ and a backward maximum frequency fmax− for the Doppler signals at a predetermined moment, according to the power spectrum P(f) of the Doppler signals at the predetermined moment; determining a noise frequency range according to the two maximum frequencies, so as to estimate an average noise power E; and correcting the forward maximum frequency and the backward maximum frequency by using the average noise power E. With the method of the invention, influence from the SNR and bandwidth on the envelope curve may be reduced, so as to be useful for accurate computation of blood flow parameters. ## Claims ### Claim 1 A method for extracting an envelope curve of a spectrogram, for use in measurement of blood flow velocity by using spectral Doppler techniques, comprising steps of: A. processing RF ultrasound echo signals to obtain Doppler signals; B. performing spectral analysis on the Doppler signals, to obtain a power spectrum P(f) of the Doppler signals which varies over time; C. estimating a forward maximum frequency fmax+ and a backward maximum frequency fmax− for the Doppler signals at a predetermined moment, according to the power spectrum P(f) of the Doppler signals at the predetermined moment; D. determining a noise frequency range based on the estimated forward maximum frequency and the estimated backward maximum frequency, and estimating an average noise power E within the determined noise frequency range; and E. correcting the forward maximum frequency and the backward maximum frequency by using the average noise power E to obtain the corrected forward maximum frequency Fmax+ and the corrected backward maximum frequency Fmax−. ### Claim 2 (depends on 1) The method according to claim 1, wherein: the noise frequency range is a function of the forward maximum frequency and the backward maximum frequency, represented as [f0, F(fmax)]+[F(fmax+), f1], where F(fmax−) is a function of variable fmax−, F(fmax+) is a function of variable fmax+and [f0, f1] is the frequency range of the power spectrum P(f). ### Claim 3 (depends on 1) The method according to claim 1, wherein the step E further comprises steps of: a. setting a threshold Th(E) according to the average noise power E and previous average noise powers E at previous moments; b. subtracting the threshold from the power spectrum P(f) of the Doppler signals at the predetermined moment to get a difference function P(f)−Th(E); and c. integrating the difference function to get a function Ø″(f) and obtaining a maximum value and a minimum value of the function Ø″(f) , wherein positions of the maximum value and the minimum value corresponding to the corrected forward maximum frequency Fmax+ and backward maximum frequency Fmax−, respectively. ### Claim 4 (depends on 3) The method according to claim 3, wherein: the threshold Th(E) is represented as a function of the average noise power and the previous average noise powers at previous moments, that is, Th(E)=F(Et, Et−1, Et−2, . . . ), wherein Et is the average noise power and Et−i(i=1, 2, . . . ) is the previous average noise power at a previous moment t−i. ### Claim 5 (depends on 1) The method according to claim 1, wherein the step E is followed by the step of: F. determining one of the corrected forward maximum frequency Fmax+ and the corrected backward maximum frequency Fmax− as the maximum frequency according to the direction of the blood flow velocity. ### Claim 6 (depends on 5) The method according to claim 5, wherein the step F further comprises: estimating an average frequency according to the frequency components between the corrected forward maximum frequency Fmax+ and the corrected backward maximum frequency Fmax−; determining the direction of the blood flow velocity corresponding to the average frequency; and determining one of the corrected forward maximum frequency Fmax+ and the corrected backward maximum frequency Fmax− as the maximum frequency according to the determined direction of the blood flow velocity. ### Claim 7 (depends on 5) The method according to claim 5, wherein the step F further comprises: determining one of the corrected forward maximum frequency Fmax+ and the corrected backward maximum frequency Fmax− as the maximum frequency according to the integration values of the power spectrums for the forward and backward blood flow in the power spectrum of the Doppler signals at the predetermined moment. ### Claim 8 (depends on 5) The method according to claim 5, wherein: errors for the maximum frequency are reduced further through linear or nonlinear smooth filtering. ### Claim 9 (depends on 6) The method according to claim 6, wherein: errors for the maximum frequency are reduced further through linear or nonlinear smooth filtering. ### Claim 10 (depends on 7) The method according to claim 7, wherein: errors for the maximum frequency are reduced further through linear or nonlinear smooth filtering. ### Claim 11 (depends on 5) The method according to claim 5, wherein the step F further comprises: fitting the maximum frequencies at different moments to get an envelope curve; and displaying the envelope curve on the spectrogram. ### Claim 12 (depends on 6) The method according to claim 6, wherein the step F further comprises: fitting the maximum frequencies at different moments to get an envelope curve; and displaying the envelope curve on the spectrogram. ### Claim 13 (depends on 7) The method according to claim 7, wherein the step F further comprises: fitting the maximum frequencies at different moments to get an envelope curve; and displaying the envelope curve on the spectrogram. ### Claim 14 An apparatus for extracting an envelope curve of a spectrogram, for use in measurement of blood flow velocity by using spectral Doppler techniques, the apparatus comprising: a processing unit configured to process RF ultrasound echo signals to obtain Doppler signals; an analyzing unit configured to perform spectral analysis on the Doppler signals to obtain power spectrum P(f) of the Doppler signals which varies over time; a frequency estimation unit configured to estimate a forward maximum frequency fmax+ and a backward maximum frequency fmax− for the Doppler signals at a predetermined moment according to the power spectrum P(f) of the Doppler signals at the predetermined moment; a noise estimation unit configured to determine a noise frequency range based on the estimated forward maximum frequency and the estimated backward maximum frequency, and to estimate an average noise power E within the determined noise frequency range; and a correcting unit configured to correct the forward maximum frequency and the backward maximum frequency by using the average noise power E to obtain the corrected forward maximum frequency Fmax+ and the corrected backward maximum frequency Fmax−. ### Claim 15 (depends on 14) The apparatus according to claim 14, wherein the noise estimation unit is further configured to estimate the noise frequency range as a function of the forward maximum frequency and the backward maximum frequency, represented as [f0, F(fmax−)]+[F(fmax+), f1], wherein F(fmax−) is a function of variable fmax−, F(fmax+) is a function of variable fmax+ and [f0, f1] is the frequency range of the power spectrum P(f). ### Claim 16 (depends on 14) The apparatus according to claim 14, wherein the correcting unit further comprises: a threshold setting subunit configured to set a threshold Th(E) according to the average noise power E and previous average noise powers E at previous moments; a difference computation subunit configured to subtract the threshold from the power spectrum P(f) of the Doppler signals at the predetermined moment to get a difference function P(t)−Th(E); and a frequency correction subunit configured to integrate the difference function to get a function Ø″(f) and to obtain a maximum value and a minimum value of the function Ø″(f), wherein positions of the maximum value and the minimum value correspond to the corrected forward maximum frequency Fmax+ and backward maximum frequency Fmax−, respectively.