Echo particle image velocity (EPIV) and echo particle tracking velocimetry (EPTV) system and method

• US 20080015440A1
• Filed: 07/13/2007
• Published: 01/17/2008
• Est. Priority Date: 07/13/2006
• Status: Abandoned Application

• Current Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Original Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Inventors: Zhang, Fuxing, Hertzberg, Jean, Liu, Lingli, Zheng, Hairong, Shandas, Robin
• Application Number:
  US11/777,412
• Publication Number:
  US 20080015440A1
• Time in Patent Office: Days
• US Class Current: 600/458
• 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 8/0883 for diagnosis of the heart
• CPC Class Codes: A61B 8/0891 for diagnosis of blood vessels
• CPC Class Codes: A61B 8/13 Tomography A61B8/10, A61B8/12 take precedence; tomography for radiation diagnosis A61B6/02
• CPC Class Codes: A61B 8/481 involving the use of contrast agent, e.g. microbubbles introduced into the bloodstream analysis of echo signal exploiting properties of a contrast enhancer in devices for short-range imaging with acoustic waves G01S7/52039
• CPC Class Codes: A61B 8/5238 for combining image data of patient, e.g. merging several images from different acquisition modes into one image for image registration algorithms G06T7/30
• CPC Class Codes: G01S 15/8984 Measuring the velocity vector
• CPC Class Codes: G01S 7/52071 Multicolour displays; using colour coding; Optimising colour or information content in displays, e.g. parametric imaging
• CPC Class Codes: G06T 7/20 Analysis of motion motion estimation for coding, decoding, compressing or decompressing digital video signals H04N19/43, H04N19/51

Abstract

A system and method for detecting fluid flow. An ultrasound system comprises a signal generator providing ultrasound firing sequences applied to a linear array transducer. The transducer generating ultrasound energy applied to the fluid flow. A pre-processor comprises a digital RF data acquisition component receiving an RF signal from the transducer of back-scattered ultrasound energy and a B-mode image generation component for reconstructing images form the RF data. A post-processor executes particle image velocity (PIV) algorithms for generating velocity vectors indicative of the fluid flow. The sequences may have triangular waveforms.

Claims

1. A method comprising:

seeding tracers within a flow field;

sweeping ultrasound beams through a desired flow field of view within the tracer-seeded flow;

receiving back-scattered ultrasound signals (RF data) from the tracers as the beams sweep the tracers;

obtaining brightness mode (B-mode) images from the RF data; and

analyzing the B-mode images to determine velocity vectors indicative of flow within the field.

2. The method of claim 1 wherein the tracers comprises ultrasound contrast microbubbles and wherein the beams comprise at least one of a focused, narrow band ultrasound beams or an unfocused broadband ultrasound beams.

3. The method of claim 1 wherein the obtaining comprises analyzing the RF data to extract a fundamental harmonic component used to create the B-mode images so that other harmonic components, including but not limited to the sub-harmonic, the ultra-harmonic, or the second harmonic, are eliminated or minimized from the RF data used to obtain the ultrasound B-mode images.

4. The method of claim 1 further comprising dividing the B-mode images into interrogation windows (sub-windows);

performing a rough velocity estimation by cross-correlation on the sub-window images to provide local displacement of the tracers;

extending the cross-correlation to all sub-windows over the entire frame to determine a velocity vector field indicative of flow within the field.

5. The method of claim 1 wherein sweeping includes sweeping with broad-beam (unfocused) ultrasound beams, and wherein the method further comprises analyzing two sequential images by dividing the images into interrogation windows;

applying cross-correlation to obtain average displacement of microbubbles within the sub-window;

and determining the velocity vectors based on the time interval between the two sequential images.

6. The method of claim 1 wherein the RF data is filtered by a template matching filter prior to obtaining the B-mode images from the RF data.

7. The method of claim 1 wherein the RF data is filtered by at least one of a wiener filter and a bandpass filter prior to obtaining the B-mode images from the RF data.

8. The method of claim 1 wherein the analyzing comprises at least one of hybrid processing of the B-mode images and adaptive processing of the B-mode images.

9. The method of claim 8 wherein the hybrid processing of the B-mode images comprises:

selecting a region of interest (ROI);

detecting particles in the ROI and detecting position of the particles to create a first image;

cross-correlating between two images of the ROI to obtain a vector map;

with the vector map from cross-correlation, estimating each particle image velocity (PIV) displacement and comparing results to the first image; and

calculating particle displacements by using a probability match method to obtain a particle tracking velocimetry (PTV) vector map.

10. The method of claim 8 wherein the adaptive processing comprises:

Setting the cross-correlation parameters including window size, overlap, options for window offset, and sub-pixel interpolation;

Choosing the ROI;

Implementing Fast Fourier transform cross correlation;

Applying the final cross-correlation with sub-pixel interpolation to improve the dynamic range of velocity measurement;

Improving the vector field by applying vector filters, including at least one of a local filter, a global filter and a SNR filter;

Outputting a vector field quality report.

11. The method of claim 10 further comprising selecting or marking of an area by:

Selecting the ROI;

masking areas that are needed within the ROI; and

Saving a boundary file of the masked areas.

12. The method of claim 10 further comprising setting a filter threshold, filtering and interpolating after filtering.

13. The method of claim 10 wherein the vector field quality report is generated as follows:

Computing a correlation SNR from a correlation map;

Computing a standard deviation of the vector field;

Estimating an outlier number and percentage in the vector field; and

Outputting the quality report.

14. The method of claim 1 wherein the RF signal is processed as follows:

cross-correlating between a template signal and a target signal wherein the target signal is a particle echoed (RF) signal and the template signal is a standard Gaussian weighted pulse to obtain a correlation index; and

peak detecting the correlation index by assigning a threshold or range such that indexes over the threshold or within the range are indicative of signals corresponding to tracers.

15. The method of claim 14 wherein the template signal comprises at least one of:

A Gaussian-weighted pulse which is a linear representation of bubble scatter;

A simulated bubble-scattered pulse using a Rayleigh-Plesset (RP) equation, which allows consideration of bubble non-linearity; and

A measured bubble-scattered pulse from measured bubble scatter.

16. The method of claim 14 wherein template matching by cross-correlation comprises:

Applying the normalized cross-correlation between the target signal and the template signal, and obtaining a correlation index;

Peak detecting the correlation index by thresholding, and finding the bubble positions from the peaks; and

Adding the template signal to the found bubble positions.

17. The method of claim 1 wherein a max-min filter processes the RF data to minimize non-uniform intensity distribution of particle images in the B-mode image.

18. The method of claim 1 wherein the velocity vectors are smoothed by at least one of global filters, local filters, and interpolation.

19. The method of claim 1 further comprising employing an adaptive window size to maximize velocity field resolution and applying a maximum measurable velocity range and a minimum resolvable velocity measurement.

20. The method of claim 1 wherein the sweeping comprises providing ultrasound firing sequences having triangular waveforms applied to a linear or curvilinear array transducer, said transducer generating ultrasound energy applied to the flow field.

21. The method of claim 1 wherein the sweeping comprises providing ultrasound firing sequences having Guassian or rectangular/square waveforms applied to a linear or curvilinear array transducer, said transducer generating ultrasound energy applied to the flow field.

22. The method of claim 1 wherein several groups of transducer elements are fired simultaneously to create several focused ultrasound beams generated at the same time to scan through flow field, thereby improving the frame rate.

23. The method of claim 1 further comprising at least one of the following:

noninvasive measuring of multi-component blood velocity vectors and mapping as a prognostic aid and/or for cardiovascular disease and treatment progression;

using an imaging system to facilitate clinical imaging on and off-site; and

/or

providing quantitative hemodynamics parameters such as shear stress, vorticity and flow pattern streamlines in following disease progression to (1) evaluate vulnerable plaques in carotid arteries, (2) evaluate anastamotic hyperplasic in vascular grafts, (3) predict risk of rupture for vascular aneurysms;

(4) evaluate changes in hemodynamics as a consequence of atherosclerosis;

(5) examine variations in wall shear stress at regions of vascular stenosis;

(6) evaluate changes in hemodynamics including shear stress during flow-mediated dilation studies of the peripheral vasculature;

(7) evaluate changes in coronary flow hemodynamics during exercise and/or stress testing; and

/or (8) follow changes in hemodynamics including wall shear stress in pediatric patients with congenital heart disease before, during and after surgical treatment.

24. The method of claim 1 wherein the flow field comprises at least one of:

flow of fluids in a conduit, flow of complex fluids, flow of multi-phase fluids, flow of polymers, flow near free and bounded surfaces, flow within micro-fabricated devices, and flow within MEMS.

25. The method of claim 1 further comprising peripheral vascular imaging and/or blood velocity measuring in at least one of the carotid vessels, brachial vessels, femoral vessels, popliteal vessels 1, iliac vessels, aortic vessels, renal arteries, cerebrovascular vessels, central veins and peripheral veins.

26. The method of claim 1 further comprising coronary and/or cardiac blood velocity measuring in the coronary arteries and veins, and least one of the various chambers of the heart.

27. A method comprising:

Acquiring RF data corresponding to positions of tracers in a flow;

Filtering the RF data;

Constructing B-mode images from the filtered RF data;

Improving the constructed image;

Cross-correlating the improved images;

Generating a velocity field based on the cross-correlated images; and

Improving the velocity field by filtering or interpolation.

28. A system for detecting fluid flow comprising:

an ultrasound system comprising a signal generator providing ultrasound firing sequences applied to a linear array transducer, said transducer generating ultrasound energy applied to the fluid flow;

a pre-processor component comprising a digital RF data acquisition component receiving an RF signal from the transducer of back-scattered ultrasound energy and a B-mode image generation component for constructing images from the RF data; and

a post-processor component generating velocity vectors indicative of the fluid flow from the constructed images.

29. The system of claim 28 wherein:

the ultrasound system scans bubbles in a flow field;

the transducer receives back-scattered ultrasound signals representing images the flow fluid;

the pre-processor generates brightness-mode (B-mode) ultrasound contrast images by sweeping a focused ultrasonic beam through the desired field of view of the fluid, resulting in a digital RF contrast-based image of bubble positions;

the pre-processor reconstructs a series of B-mode images from the recorded RF data after filtering processing, which sequentially represents the motion of the microbubbles motion within the fluid;

the post-processor conditions the B-mode images and cross-correlates two consecutive images to produce a velocity vector map of flow field; and

the post processor processes the vector data to improve vector quality and accuracy.

30. The system of claim 28 wherein said preprocessor component comprises:

An RF data filtering component filtering the RF data;

A B-mode image construction component constructing B-mode images from the filtered RF data; and

An image component for processing the B-mode images.

31. The system of claim 28 wherein said postprocessor component comprises:

a cross correlation component providing estimated velocities from the B-mode images;

a velocity field component for generating a velocity field from the estimated velocities;

a vector component for generating a vector field from the estimated velocities.

32. A process comprising:

constructing B-mode particle images from RF data; and

implementing at least one of;

A hybrid echo particle tracking velocimetry (EPTV) with echo particle image velocity (EPIV) analysis of the constructed images; and

An adaptive EPIV analysis of the constructed images.

33. A system for detecting fluid flow comprising:

an ultrasound system comprising a signal generator providing ultrasound firing sequences having triangular or Gaussian or square/rectangular waveforms applied to a linear or curvilinear array transducer, said transducer generating ultrasound energy applied to the fluid flow; and

a processor comprising a digital RF data acquisition component receiving an RF signal from the transducer of back-scattered ultrasound energy and a B-mode image generation component for reconstructing images form the RF data, said processor generating velocity vectors indicative of the fluid flow.