A SYSTEM AND A METHOD FOR MEASURING ARTERIAL PARAMETERS

Abstract

The present invention relates to a system for measuring the arterial parameters. The system of the invention comprises a signal unit for providing radio frequency (RF) ultrasound signal and demodulated RF ultrasound signal and of the data relating thereto from the signal acquired therefrom; a detection unit for detecting the presence of blood flow in an artery; an identification unit for identifying the said artery; a processing unit for processing the said data and for providing the distension waveform of the said artery; and an estimating unit for estimating at least one of a plurality of localized arterial parameters of the said artery. The invention also relate to a method for measuring the arterial parameters by the system of the invention. The invention has the advantage of measuring localized blood pressure continuously and also other localized arterial parameters such as Peak Systolic Velocity, Pulse Wave Value and arterial compliance measures, in a non-imaging, non-invasive and cuff-less manner.

Claims

1. A system for measuring arterial parameters using ultrasound, the system comprising: a signal unit for providing a radio frequency (RF) ultrasound signal, a demodulated radio frequency ultrasound signal, and data obtained from the demodulated radio frequency ultrasound signal; a detection unit for detecting the presence of blood flow in an artery; an identification unit for identifying the artery; a processing unit for processing the data obtained from the demodulated radio frequency ultrasound signal and for providing a distension waveform of the artery; and an estimating unit for estimating at least one of a plurality of localized arterial parameters of the artery.

2. The system as claimed in claim 1, wherein the said signal unit comprises a plurality of transducer elements organized in a grid configuration.

3. The system as claimed in claim 2, wherein the said plurality of transducer elements are operated individually or collectively to provide RF ultrasound signal pertaining to an artery.

4. The system as claimed in claim 1, wherein the processing unit is provided for determining the motion of the vessel wall of the artery and the change in diameter of the artery.

5. The system as claimed in claim 1, wherein the identification unit comprises one or more models purporting to one or more arteries.

6. The system as claimed in claim 1, wherein the processing unit is provided for obtaining a pressure waveform from the distension waveform of the artery.

7. The system as claimed in claim 1, wherein the processing unit is provided for mapping the distension waveform of the artery, with the pressure waveform of the artery identified, using the model of the artery.

8. The system as claimed in claim 1, wherein the estimation unit is provided for estimating at least one of the localized arterial parameters such as localized blood pressure, Peak Systolic Velocity (PSV), Pulse Wave Value (PWV), arterial compliance measures.

9. The system as claimed in claim 8, wherein the arterial compliance measures include elastic modulus, arterial distensibility, arterial compliance, stiffness index.

10. The system as claimed in claim 1, wherein the system is a non-imaging and non-invasive based system for measuring arterial parameters.

11. A method for measuring arterial parameters using ultrasound, the method comprising: providing, by a signal unit, a radio frequency (RF) ultrasound signal, a demodulated radio frequency ultrasound signal, and data obtained from the demodulated radio frequency ultrasound signal; detecting the presence of blood flow in an artery by a detection unit; identifying the artery by an identification unit; processing, by a processing unit, the data obtained from the demodulated radio frequency ultrasound signal and providing a distension waveform of the artery; and estimating, by an estimating unit, at least one of a plurality of localized arterial parameters of the artery.

12. The method as claimed in claim 11, wherein the processing comprises determining the motion of the vessel wall of the artery and the change in diameter of the artery.

13. The method as claimed in claim 11, wherein the processing comprises obtaining a pressure waveform from the distension waveform of the artery.

14. The method as claimed in claim 11, wherein the processing comprises mapping the distension waveform of the artery, with the pressure waveform of the artery identified, using the model of the artery.

15. The method as claimed in claim 11, wherein the method is a non-imaging and non-invasive and continuous method for estimating localized arterial parameters such as localized blood pressure, Peak Systolic Velocity (PSV), Pulse Wave Value (PWV) and arterial compliance measures including elastic modulus, arterial distensibility, arterial compliance, stiffness index.

16. A computer program product comprising code means for performing the method as claimed in claim 11 when executed on a computer processor.

17. A computer readable medium comprising the computer program product as claimed in claim 16.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0021] With reference to the accompanying drawings in which:

[0022] FIG. 1 shows the system for measuring the arterial parameters, in accordance with the invention;

[0023] FIG. 2 illustrates acquisition of RF data from an artery of interest;

[0024] FIG. 3 depicts the echo pattern obtained at different part of an artery of interest; and

[0025] FIG. 4 shows a sample distension waveform.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The invention is further described hereinafter with reference to FIGS. 1 to 4 through non-exhaustive exemplary embodiments.

[0027] In FIG. 1, a system (100) for measuring the arterial parameters is shown. The system (100) comprises a Signal Unit (101) having a plurality of transducer elements organized in grid configuration. The transducer elements are operated either individually or collectively to provide raw RF ultrasound signals pertaining to the artery of interest subjected to measurement. The measurement in accordance with the invention includes utilizing the RF ultrasound signals both in raw form and demodulated form. The RF demodulation unit (102) demodulates the raw RF ultrasound signal. The detection unit (103) is provided to detect the presence of blood flow in the artery of interest using the Doppler Spectra data obtained from the demodulated RF ultrasound signal. Upon detecting the presence of blood flow, the artery of interest is specifically identified by the identification unit (104). A feedback signal is presented for continuous acquisition of data for few data cycle for further processing. The identification unit has one or more models pertaining to each of the corresponding arteries.

[0028] A processing unit (105) is provided to process the data purporting to the artery of interest, and explained herein after in the description.

[0029] The signal obtained from the transducer elements is affected with noise and transient behaviour. The raw RF echo signals are pre-processed to improve SNR, and the transients are removed by using matched filter followed by band pass filter. A non-linear gain is applied to suppress high amplitude reflections from skin gel interface.

[0030] The signal frames are obtained over a particular interval of time as shown in FIG. 2, in respect of the artery of interest. The transducer (201) placed on the surface of the body sends ultrasound pulses into the body passing through the soft tissues (202) to reach the artery (203) like carotid artery. The ultrasound sound pulses (204) from the transducer is shown reaching the farther wall of the artery (203) and the same been reflected. The reflected ultrasound pulse is shown as (205). Apparently, the ultrasound pulses are transmitted and the same gets reflected from the near, as well as far walls of the artery whose diameter is D. The echoes are received by the same transducer. The data frame (F1, F2 and F3) containing amplitude information A (a, u) formed over time interval T(ms), of the reflected echoes are shown

[0031] The artery of interest, so identified is mapped to RF data for computation of artery specific distension waveform.

[0032] FIG. 3. shows the echo patterns (1, 2, 3, 4) after the ultrasound waves gets reflected from the different anatomical site such as adventitia (301), media (302) and intima (303) of the artery (300) of interest. The transition from the inner layer of the wall (303), intima, to the cavity inside the artery, lumen (304) produces a distinct echo, visible both at the near wall and the far wall. A stronger echo represents the outermost layer, the adventitia (301). The middle layer, media (302), is hypo-echoic.

[0033] Echo pattern obtained is used to compute the distension waveform as it could be observed that the echo's obtained from an artery over the different regions as shown in FIG. 3 is not uniform.

[0034] The far wall and the near wall of an artery can be separated by performing the echo gate tracking. The echoes are identified to find the region of interest in acquired signals where the anatomical structure of an artery could be located. To identify the region of interest from an echo pattern, a probabilistic approach such as Maximum Likelihood approach is used. Firstly, the energy plot for the given signal is obtained using sliding window approach and regions of maximum energy are identified and various features are extracted from these regions of interest for different patients across frames. The feature data is trained using a Gaussian mixture model by obtaining mean and covariance. On providing a test frame, features are extracted and tested against the model built to provide the likelihood of region of interests. The data are classified based on a single class approach such as wall class approach. The method uses a cut-off value of likelihood to assign points to wall class.

[00001]$P\left(\frac{x}{c}\right)=\frac{1}{2.Math.{{\pi }^{\frac{d}{2}}\left(\det \left(c\right)\right)}^{0.5}}.Math.e^{-{\left(x-\mu \right)}^T.Math.C^{-1}\left(x-\mu \right)}$

where, [0035] d—dimension of feature vector [0036] c—covariance matrix [0037] μ—mean of Gaussian [0038] x—feature vector for test point

[0039] Further, the variation of the blood flow during systolic and diastolic causes the change in the elastic property of an artery. This change in elastic property is manifested in diameter change of the artery. Based on the echoes obtained due to wall motion, successive signal frames are analyzed, and the distension waveform of the artery is computed as the difference between the near and far wall movements.

[0040] Considering the echoes obtained in two successive acquisitions, NW.sub.i(t) be the near wall echo and FW.sub.i(t) be the far wall echo in the i.sup.th acquisition. Now, the near and far wall echoes obtained in the next iteration may be expressed as

NW.sub.i+1(t)=NW.sub.i(t±Γ.sub.nw)

FW.sub.i±1(t)=FW.sub.i(t±Γ.sub.fw)

[0041] where Γ.sub.fw and Γ.sub.nw are the shifts in the near and far wall echoes, respectively. Echo tracking involves estimating these shifts and following the movement of the echoes accordingly. To estimate the time shift of the echoes in between successive acquisitions, a shift and search approach is employed, and is ideal to compute the maximum cross correlation between the signals NW.sub.i(t) and NW.sub.i+1(t) and estimating the shift Γ.sub.fw and Γ.sub.nw as the time corresponding to maximum of the cross correlation.

[0042] Once the delay is identified, the wall movements are computed based on the sound velocity (v)

d.sub.nw(i)=0.5*v*[Γ.sub.nw(i)+Γ.sub.nw(i−1)]

d.sub.fw(i)=0.5*v*[Γ.sub.fw(i)+Γ.sub.fw(i−1)]

[0043] The artery distension waveform is computed as the difference between the near wall and far wall movements and is given by

Δd(i)=d.sub.fw(i)−d.sub.nw(i)

[0044] Substituting t=(i/fprf), the distension waveform Δd(t) can be determined as follows

Δd(t)=d.sub.fw(t)−d.sub.nw(t)

[0045] From the above mentioned distension waveform, peak to peak distension can be computed, which can be used to measure other arterial compliance measure.

[0046] FIG. 4 shows the sample distension waveform representing the change in wall diameter D(mm) through successive frames over the Sample S(#).

[0047] The pressure change in an artery is manifested better, by the change in cross section of an artery. Arterial wall cross-section as function of time is further computed based on distension waveform by the following equation.

[00002]$\begin{array}{cc}A\left(t\right)=\frac{\pi .Math..Math.{d\left(t\right)}^2}{4}& \mathrm{eq}.Math..Math.\left(1\right)\end{array}$

[0048] The functional relationship between the blood pressure waveform p(t) and arterial wall cross section A(t) is established as follows

p(t)=p.sub.oe.sup.γA(t)  eq (2)

[0049] Where p.sub.o is constant and γ varies between arteries of a patient and across patients. A look up table and arterial model is required to measure respective γ for the artery of interest. Identification Unit (104) as shown in FIG. 1 provides this input to estimate artery and artery specific γ value for better accuracy of pressure waveform estimation.

[0050] From eq (2), the pressure wave form can be computed and systolic, diastolic and mean arterial pressure could be estimated. It is hereby possible to continuously monitor the blood pressure for an artery of interest in non-invasive and non-imaging based approach.

[0051] As the change in diameter and the pressure associated with artery of interest are available, other arterial compliance measures such as Elastic modulus, Arterial distensibility, Arterial compliance and Stiffness index can be computed as below, where P.sub.s is systolic and P.sub.d is diastolic pressure.

[00003]$\mathrm{Elastic}.Math..Math.\mathrm{modulus},.Math.E=\frac{\Delta .Math..Math.P\times D}{\Delta .Math..Math.D}$$\mathrm{Arterial}.Math..Math.\mathrm{Distensibility},.Math.D=\frac{\Delta .Math..Math.D}{\Delta .Math..Math.P\times D_d}$$\mathrm{Arterial}.Math..Math.\mathrm{Compliance},.Math.C=\frac{\Delta .Math..Math.D}{\Delta .Math..Math.P}$$\mathrm{Stiffness}.Math..Math.\mathrm{index},.Math.\varphi =\frac{\ln \left(P_s/P_d\right)}{\left(\frac{D_s-D_d}{D_d}\right)}$

[0052] The invention therefore provides continuous measurement of localized blood pressure of the artery of interest along with other arterial parameters and arterial compliance measures.

[0053] Only certain features of the invention have been specifically illustrated and described herein, and many modifications and changes will occur to those skilled in the art. The invention is not restricted by the preferred embodiment described herein in the description. It is to be noted that the invention is explained by way of exemplary embodiment and is neither exhaustive nor limiting. Certain aspects of the invention that not been elaborated herein in the description are well understood by one skilled in the art. Also, the terms relating to singular form used herein in the description also include its plurality and vice versa, wherever applicable. Any relevant modification or variation, which is not described specifically in the specification are in fact to be construed of being well within the scope of the invention. The appended claims are intended to cover all such modifications and changes which fall within the spirit of the invention.

[0054] Thus, it will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.