Method and apparatus for processing signal data to form an envelope on line

• US 5,271,404 A
• Filed: 06/25/1992
• Issued: 12/21/1993
• Est. Priority Date: 06/25/1992
• Status: Expired due to Term

• Current Assignee: Volcano Corporation (Koninklijke Philips N.V.)
• Original Assignee: Cardiometrics, Inc. (JOMED NV)
• Inventors: Kaiser, David, Lifshitz, Ilan, Corl, Paul D.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): MANUEL, GEORGE C
• Application Number:
  US07/904,195
• Time in Patent Office: 544 Days
• Field of Search: 128/661.08, 128/661.09, 128/662.06, 128/660.07, 128/660.05, 73/861.25
• US Class Current: 600/454
• CPC Class Codes: A61B 8/06 Measuring blood flow measuring volume flow in general G01F, e.g. G01F1/66, G01F1/72; measuring speed of fluids in general G01P5/00
• CPC Class Codes: A61B 8/12 in body cavities or body tracts, e.g. by using catheters catheters per se A61M25/00
• CPC Class Codes: G01P 5/244 involving pulsed waves
• CPC Class Codes: G01S 15/8977 using special techniques for image reconstruction, e.g. FFT, geometrical transformations, spatial deconvolution, time deconvolution
• CPC Class Codes: G01S 15/8979 Combined Doppler and pulse-echo imaging systems

Abstract

An apparatus for generating a velocity spectrogram is described. The apparatus includes a transducer which is positionable within a vessel. The transducer receives a time-varying Doppler signal which contains information related to fluid velocity values within the vessel. A Fourier transformation device processes the time-varying Doppler signal to generate a sequence of spectra. Each spectrum corresponds to a segment of the time-varying Doppler signal and defines a set of velocities and their corresponding spectral values. A device is used to identify the instantaneous spectral peak velocity within each spectra. The peak velocity corresponds to the highest velocity within a spectra which has a spectral value above a defined threshold value which is related to the background noise level. The sequence of spectral peak velocities is plotted on a visual interface device to form an instantaneous spectral peak velocity waveform.

Claims

1. A method for forming a real-time representation of an instantaneous spectral peak frequency envelope of a frequency spectrogram of a measured parameter displayed on an output device, said method comprising the steps of:

generating an electrical signal in the time domain with respect to a measured parameter, dividing the signal into a succession of segments and converting the segments into a corresponding succession of frequency spectra, displaying the frequency spectra as a gray scale spectrogram on an output device, finding a sequence of highest bin numbers corresponding to said succession of frequency spectra, each highest bin number corresponding to a frequency bin containing a value above a calculated threshold to substantially eliminate noise from the measured parameter data, filtering the sequence of highest bin numbers to substantially eliminate strong transient disturbances, said filtering step including the steps of removing spikes from the sequence of highest bin numbers and thereafter smoothing the sequence of highest bin numbers, highlighting the resultant sequence of highest bin numbers which represents the instantaneous spectral peak frequency envelope to distinguish the instantaneous spectral peak frequency envelope from the gray scale picture elements which form the frequency spectrogram.

2. A method as in claim 1 wherein said finding step includes filtering of narrow spectrum noise, calculating the average noise strength, calculating the signal to noise ratio, identifying said signal strength threshold, performing a wide band search to ascertain the highest frequency region with a signal strength which is greater than said signal strength threshold, conducting a narrow band search to ascertain the highest frequency region with signal strength which is greater than the narrow band signal strength threshold.

3. A method as in claim 1 wherein said highlighting step consists of interconnecting sequential highest bins to form an envelope as a function of time which is superimposed on the spectrogram.

4. A method for providing an on line envelope of a frequency spectrogram from a Doppler signal which varies with time, said method comprising the steps of receiving a Doppler signal by utilizing a Doppler ultrasound transducer with a divergent beam having a 3 dB one-way beam width of 20 to 90 degrees, generating spectra corresponding to segments of said Doppler signal, identifying a peak frequency within each of said spectra and plotting a sequence of peak frequencies to form an instantaneous spectral peak frequency envelope corresponding to an instantaneous spatial peak velocity waveform signal.

5. The method of claim 4 wherein said reading step includes the step of positioning a transducer within a vessel.

6. The method of claim 4 wherein said generating step includes the step of performing a series of Fourier transformations on said Doppler signal to produce said spectra.

7. The method of claim 4 wherein said identifying step includes the steps of defining a threshold signal value, locating a peak frequency band within each of said spectra, said peak frequency band including a set of frequency components with corresponding spectral values above said threshold, selecting a peak frequency from each of said peak frequency bands, said peak frequency representing the highest frequency component which has a spectral value above said threshold, and filtering the sequence of said peak frequency values.

8. The method of claim 4 wherein said plotting step includes presenting said peak frequency values on a presentation device and connecting said peak frequency values to adjacent peak frequency values.

9. An apparatus for generating an instantaneous spatial peak velocity waveform, said apparatus comprising a transducer positionable within a vessel containing a moving fluid, said transducer generating a transmission signal and receiving a Doppler signal corresponding to said transmission signal, said Doppler signal corresponding to velocity values of said moving fluid within said vessel, a Fourier transformation device coupled to said transducer, said Fourier transformation device executing Fourier transformations on said Doppler signal to generate velocity spectra, each of said spectra corresponding to a segment of said Doppler signal, means, coupled to said Fourier transformation device, for identifying selected velocity bins within said spectra, said selected velocity bins corresponding to the highest velocity bin within each spectrum of said spectra which contains a value which is above a defined threshold value, said identifying means including means for defining a threshold value, means for locating velocity bands with corresponding spectral values above said threshold, means for selecting said highest velocity bins containing spectral values above said threshold, and means for filtering the sequence of said highest velocity bin numbers, and means, coupled to said identifying means, for plotting said sequence of highest velocity bin numbers on a visual interface device to form an instantaneous spatial peak velocity waveform.

10. The apparatus of claim 9 wherein said Fourier transformation device is a digital signal processor.

11. The apparatus of claim 9 wherein said visual interface device is a cathode ray tube.

12. The apparatus of claim 9 wherein said plotting means includes means for presenting said spectra on said visual interface device, said sequence of highest velocity bin numbers being represented in conjunction with said spectra.

13. The apparatus of claim 9 wherein said transducer is a Doppler ultrasound transducer with a divergent beam having a 3 dB one-way beam width of 20 to 90 degrees.

14. The apparatus of claim 9 wherein said visual interface device forms said instantaneous spatial peak velocity waveform and simultaneously forms a spectrogram corresponding to said velocity values of said moving fluid so that the relationship between said spatial peak velocity waveform and said spectrogram may be assessed.

15. A method of establishing a spectral peak frequency envelope from a time-varying signal, said method comprising the steps of receiving a signal, generating a succession of frequency spectra corresponding to said signal, identifying a peak frequency bin within each spectrum of said succession of spectra to create a sequence of peak frequency bin numbers, said identifying step including the steps of defining a threshold value, locating frequency bands within said spectrum, said frequency bands including a set of frequency bins containing values above said threshold, selecting said peak frequency bin from said frequency bands, said peak frequency bin corresponding to the highest frequency which contains a value above said threshold, and plotting said sequence of said peak frequency bin numbers to form said spectral peak frequency envelope.

16. The method of claim 15 wherein said locating step includes the steps of calculating a signal-to-noise ratio for each spectrum of said succession of spectra, determining an interference threshold value based on said signal-to-noise ratio, locating, within said frequency spectrum, target bands of frequency bins at least one of which contains a value which is above said interference threshold value, and filtering said values of said target bands.

17. The method of claim 15 wherein said receiving step is performed by utilizing a Doppler ultrasound transducer with a divergent beam having a 3 dB one-way beam width of 20 to 90 degrees.

18. The method of claim 15 further comprising the step of filtering said sequence of peak frequency bin numbers.

19. An apparatus for establishing a spectral peak frequency envelope from a time-varying signal, said apparatus comprising means for receiving a signal, means for generating a succession of frequency spectra corresponding to said signal, means for identifying a peak frequency bin within each spectrum of said succession of spectra to create a sequence of peak frequency bin numbers, said identifying means including the means for defining a threshold value, means for locating frequency bands within said spectrum, said frequency bands including a set of frequency bins containing values above said threshold, means for selecting said peak frequency bin from said frequency bands, said peak frequency bin corresponding to the highest frequency which contains a value above said threshold, and means for plotting said sequence of said peak frequency bin numbers to form said spectral peak frequency envelope.

20. The apparatus of claim 19 wherein said locating means includes the means for calculating a signal-to-noise ratio for each spectrum of said succession of spectra, means for determining an interference threshold value based on said signal-to-noise ratio, means for locating, within said frequency spectrum, target bands of frequency bins at least one of which contains a value which is above said interference threshold value, and means for filtering said values of said target bands.

21. The apparatus of claim 19 wherein said receiving means is a Doppler ultrasound transducer with a divergent beam having a 3 dB one-way beam width of 20 to 90 degrees.

22. The apparatus of claim 19 further comprising the means for filtering said sequence of peak frequency bin numbers.

23. An apparatus for establishing a spectral peak frequency envelope from a time-varying signal, said apparatus comprising a Doppler ultrasound transducer, positionable within an elongated vessel, for receiving a signal, means for generating frequency spectra corresponding to said signal, means for identifying actual peak frequency bins within said spectra, said identifying means including means for defining a threshold value, means for locating, within said spectra, peak frequency bins containing values above said threshold, and means for plotting said peak frequency bins to form said spectral peak frequency envelope.

24. The apparatus of claim 23 wherein said locating means further includes means for establishing frequency bands within said frequency spectra, said frequency bands including a set of frequency bins with corresponding values above said threshold.

25. The apparatus of claim 24 wherein said locating means further includes means for selecting a peak frequency bin number from said frequency bands, each of said peak frequency bin numbers representing the highest frequency which includes a value above said threshold.

26. The apparatus of claim 23 wherein said locating means further includes means for calculating a signal-to-noise ratio for said frequency spectra, and means for determining a threshold value based on said signal-to-noise ratio.

27. The apparatus of claim 23 further comprising means for filtering said peak frequency bins.

28. Apparatus for displaying on a display device a peak frequency envelope which represents the spatial peak velocity of the blood flow in a blood vessel as a function of time at a location, comprising a guidewire having a distal extremity and having a forward looking Doppler ultrasound transducer thereon, said guidewire being adapted to be introduced into the blood vessel having blood flowing therein, first electrical means connected to the guidewire and to the transducer for causing the transducer to propagate an ultrasonic diverging beam in a forward direction into the blood flowing in the blood vessel forward of the transducer, second electrical means connected to the guidewire and to the transducer for receiving ultrasound signals reflected by the blood flowing in the blood vessel and producing a frequency spectrum which varies as a function of time as the blood flow velocity varies, means for establishing a threshold level substantially representing noise for the frequency spectrum, means for ascertaining when the values of the frequency spectrum go above and below the threshold level and generating therefrom a spectral peak velocity waveform with respect to time and means for visually displaying the spectral peak velocity waveform.

29. Apparatus as in claim 28 wherein said displaying means includes means for superimposing a grayscale spectrogram on said spectral peak velocity waveform.

30. In a method for displaying on a display device a peak frequency envelope which represents the spatial peak velocity of the blood flow in a blood vessel as a function of time at a location, by the use of a guidewire having a distal extremity and having an ultrasonic transducer mounted thereon and having first electrical means connected to the guidewire for causing the transducer to propagate an ultrasonic diverging beam in a forward direction into the blood flowing in the blood vessel and forward of the transducer and second electrical means connected to the guidewire and to the transducer for receiving ultrasonic signals reflected by the blood flowing in the blood vessel and producing a frequency spectrum which varies as a function of time as the blood flow velocity varies, comprising positioning the guidewire in the blood vessel so that the transducer is aimed in a direction substantially parallel to the blood flow, establishing a threshold level for the frequency spectrum, ascertaining when the value of the frequency spectrum goes above and below the threshold level and generating therefrom a spectral peak velocity waveform with respect to time, eliminating spurious signals from the spectral peak velocity waveform, displaying the spectral peak velocity waveform on the display device to form a peak frequency envelope in real time and observing the peak frequency envelope to ascertain the blood flow velocity in the vessel and thereafter shifting the guidewire and the transducer thereon to measure the blood flow velocity in another region of the vessel.

31. A method as in claim 30 wherein said displaying step includes superimposing a grayscale spectrogram on said spatial peak velocity waveform.