FR2696000A1 - Measuring blood flow using ultrasound probe - using ultrasound probe connected to processing module which uses ultrasound echo signals to calculate aorta diameter and blood flow average rate - Google Patents

Abstract

The method involves inserting an ultrasound probe through the oesophagus of a patient for measuring the blood flow in the aorta. The probe is connected to a control unit which processes the signals transmitted to calculate the aorta diameter assuming that its section is circular. The echo generated by ultrasound reflections in the aorta is used to evaluate the average flowing rate (Vm) of the blood crossing the aorta section. By measuring the backscattered energy in the blood flow the mass of the moving liquid can be inferred. A corrected average flow rate is then calculated. USE/ADVANTAGE - For measuring rate and flow of liquid. Enables accurate measurements during diastole and systole.

Description

PROCESS FOR PRECISION DETERMINING THE SPEED OF A
LIQUID MEDIUM AND, IN PARTICULAR, AORTIC FLOW WITH
AN INTRACORPOREAL SENSOR
The present invention relates to the technical field of speed and / or flow rate measurements using ultrasonic probes capable of ensuring, in particular, intracorporeal measurements, by being introduced into the human body through a natural orifice.

 The invention finds a particularly advantageous application for measuring the aortic flow rate by means of the probe introduced inside the esophagus.

 French patent 78-14 494 proposed an intracorporeal probe composed of a catheter forming a flexible sheath containing a flexible connected by one of its ends, to a support block on which is mounted at least one ultrasound transducer connected, externally to the catheter, to a control and treatment unit. The other end of the hose is mounted integral with a member for rotating the support block on itself.

 Such a probe makes it possible, by the Doppler effect, to determine the speed and, consequently, if the diameter is otherwise known, the flow of blood circulating inside a vessel. It is recalled that the flow rate is equal to the section of the vessel multiplied by the mean space velocity inside the vessel.

 If the probe described above has made it possible to make significant progress with regard to the measurement of aortic flow rates, it appears that the flow rate measurements carried out by such a probe lack precision.

 Indeed, during the cardiac cycle, and in particular, during the diastole, the spatial velocity profile reveals zones of velocities zero or sufficiently low so that they cannot be measured using the probe and the treatment device. used together. The average spatial velocity thus measured is erroneous, since only targets animated with a sufficiently rapid movement are taken into account. Under these conditions, the measurement of the flow rate leads to an extremely large error since the average speed measured is then multiplied by the total section of the vessel. This error is all the more important as the surface covered by the immobile liquid veins or sufficiently slow not to be detected by the probe, is itself significant compared to the section of the vessel.

 The present invention therefore aims to remedy the above drawbacks by proposing a method capable of significantly improving the accuracy of the measurement of the spatial speed of a moving target for an accurate measurement of the target flow and, in particular, of the flow aortic.

 Another object of the invention is to provide a method capable of carrying out precise measurements of speed and, consequently, of flow, both during diastole and systole, or of flows having low-speed liquid veins.

To achieve the above objective, the method according to the invention consists in
- measure the total backscattered energy of the moving target, when this
last occupies the entire middle section,
- measure the localized backscattered energy of the moving target, when
the latter occupies a partial section of the middle,
- and correct the speed or flow measurement during traffic
of the moving target through a partial section of the medium, by a
factor dependent on localized energy and total energy.

 Various other characteristics will emerge from the description given below with reference to the appended drawings which show, by way of nonlimiting examples, embodiments and implementation of the subject of the invention.

 Fig. 1 is a sectional elevation of a probe allowing the implementation of the invention.

 Fig. 2 is a diagram illustrating, over time, the energy backscattered by the moving target.

 Fig. 3 is an example of a curve of speed as a function of time, obtained from the probe.

 Fig. 1 shows an exemplary embodiment of a probe allowing the implementation of the method according to the invention, intended to ensure intracorporeal measurements of speed and / or flow rate. To this end, the intracorporeal probe comprises a catheter 1 forming a sheath or a flexible tube produced in a known manner by materials chosen for their characteristics of non-toxicity and good tolerance for the mucous membranes. The sheath 1 contains a hose 2 which is connected, by one of its ends, to at least one support block 3 on which ultrasonic transducers 4 and 5 are mounted. In a conventional manner, this end of the probe 1 , which is intended to be introduced into the body, is provided with a balloon 6 surrounding the support block 3. The transducers 4, 5 are connected to an electrical cable 7 placed in the sheath 1 and exiting outside the catheter to be connected to a unit 8 for controlling the transducers and for processing the signals delivered by the latter. The end of the hose 2, opposite that provided with the support block 3, is connected to an operating member 9, such as a knurled button ensuring rotation of the hose 2 on itself.

 The support block 3 is arranged to receive at least one ultrasonic transducer 4, having a so-called wide beam 4a, namely adapted to cover at least the entire section S of a medium 10, such as a vessel forming, preferably, the aorta and occupied by a moving target 11 formed, for example, by a blood flow.

 The probe described in the illustrated example is intended to be introduced through a natural orifice in a natural way, such as the esophagus 13 shown in phantom, then moved axially so that the transducers 4 and 5 are placed opposite a section S of the aorta 10. The support block 3 is then moved on itself by means of the operating button 9 transmitting its effect through the hose 2, so as to orient the transducers 4, 5 in azimuth properly.

 The control and processing unit 8 comprises means 14 connected to the transducer 5 by a link 71, and designed to determine the amplitude of the signals received echoed by the narrow beam transducer 5. The determination means 14 are connected to means 15 designed to detect the maximums of the amplitude of the reflected signals.

 The control and processing unit 8 also comprises means 16 connected to the means 15, in order to determine the interval d2-dl corresponding to the two extreme points of the aorta detected from the maximums of the amplitude of the echoes. relating to the signal from the transducer 5. Knowledge of the interval d2-dl makes it possible to calculate the section since it is known or considered that the vessel is of circular section.

 The means 16 then determine the interval P2-P1 from the interval d2-dl and from the angle of divergence 8 between the two beams, known in particular by construction. These determination means 16 control selection means 17 connected to the transducer 4 by a link 72. These means 17 make it possible to select only the echoes of the signals from the transducer 4 which are obtained in a response time range corresponding to the interval P2 -P1. The selection means 17 are connected to conventional processing means 19 ensuring the obtaining of a Doppler signal. These processing means 19 are connected to means 20 known per se, capable of determining the mean spatial speed Vm of the blood passing through the section S of the aorta 10.

 According to an advantageous characteristic, the probe is capable of implementing a method in accordance with the invention allowing precise measurements of spatial average speed which take account of the section of the liquid veins animated by a speed zero or sufficiently low to be considered as null by the means 19, 20 operating in a conventional manner. The method according to the invention is thus able to allow speed measurements which take account of the actual or actual section occupied by the red blood cells considered to be moving inside the aorta.

To this end, the unit 8 comprises means 21 capable of measuring the energy backscattered by the moving particles, namely the red cells in the case of blood. The backscattered energy E, which is proportional to the number of red blood cells in motion, is measured at each instant, in order to know the mass of liquid in motion (Fig. 2). Thus, the energy E of the received signal, is given by the following formula:
E = eclS

with c being the concentration of particles, namely red cells, e the energy backscattered by a particle and, the product 1.S being the measurement volume in which the moving particles are found.

The energy calculation means 21 which receive the Doppler signal from the processing means 19, determine at each instant the amplitude or the energy
E backscattered by moving targets. The Doppler signal amplitude is proportional to the square root of the backscattered energy. The output of the calculation means 21 is connected to means 22 designed to determine the value of the energy appearing at one or more defined times, in particular, during systole. The means 22 are thus connected to means 23 capable of determining the instants when the systole occurs. Typically, systole can be detected from maximum blood speed, backscattered energy, or an electrocardiogram.

 The means 22 therefore deliver the value of the backscattered energy Es during the systole. Preferably, the backscattered energy Es, during systole, is measured over several cardiac cycles, for example of the order of ten, then averaged, in order to take account of normal physiological variations.

 It must be considered that during systole all the red cells are in motion, so that the total energy backscattered Es at this instant corresponds to the movement of the targets occupying the total section S of the vessel. Outside the systole and, in particular, during the diastole, the area SD covered by the particles actually in motion is likely to be reduced compared to the complete section S.

 Taking into account the backscattered energy, during the systole Es and during the diastole ED, makes it possible to determine the theoretical actual or effective area SD participating in the flow rate. Such a surface is such that: SD = S. (E # / E5) = S.K.

 The correction factor K is determined by correction means 24 connected to the means 21, 22. In an advantageous manner, the correction means 24 weight the factor K by a practical correction coefficient which takes account of the technical characteristics of the transducer 4 used and means 19, in particular of the minimum value of the detected speeds and of the bandwidth of the Doppler signal. These correction means 24 are connected to means 25 which are connected to the means 20 for determining the spatial average speed. These means 25 make it possible to calculate, from the values of the average spatial speed and of the correction factor K, the corrected average speed Vc, and consequently, the flow of the moving blood on the localized surface SD, from knowledge of the section of the ship.

 Fig. 3 illustrates an example of a curve giving the corrected speed Vc as a function of time. This curve makes it possible to appreciate the correction carried out from the raw measurement speeds which are shown diagrammatically in broken lines during the diastole D. The method according to the invention makes it possible to obtain a high precision on the speed measurements and, consequently , of blood flow rates, since these measured values take account of the effective section participating in the blood flow rate.

 As shown more precisely in FIG. 2, the correction factor determined by the means 24 is applied only when the backscattered energy is less than a given threshold N, of fixed or adjustable nature, to take account of both physiological variations and normal statistical variations of the Doppler signal known elsewhere. Advantageously, the threshold N is between 10 and 50% of the maximum backscattered energy backscattered Es during systole and, preferably, of the order of 25%. Such a comparison carried out by means 26 interposed between means 21-22 and 24 makes it possible to correct at each instant of the cardiac cycle, the values of speed and flow, particularly during diastole D, as appears more precisely in FIG. . 3.

 Of course, the various constituent means of the unit 8 can be produced in a programmed or wired manner. In addition, it should be noted that the various circuits necessary for the operation of the transducers 4, 5 have not been described more precisely, since they are not part of the invention and are known per se. Furthermore, it should be considered that the foregoing description relates to a measurement method carried out using an intracorporeal probe. Of course, it is clear that the object of the invention can be applied to an extracorporeal probe.

In this case, the probe does not include the catheter 1 and the hose 2. For example, it may be envisaged to measure the flow rate of the ascending aorta by the susternal route.

 The invention is not limited to the examples described and shown, since various modifications can be made thereto without departing from its scope.

Claims (4)

CLAIMS:  1 - Method for measuring the flow rate of a moving target (11) inside a medium (10) of which at least one section (S) is explored by at least one ultrasonic transducer (4, 5), characterized in what it is  - to measure the total backscattered energy (Es) of the moving target,  when the latter occupies a total section (S # in the middle,  - to measure the localized backscattered energy (ED) of the moving target,  when the latter occupies a partial (southern) section of the middle,  - and to correct the measurement of speed or flow during traffic  of the moving target through a partial section of the medium, by a  factor dependent on localized energy (ED) and total energy  (Es).  2 - Method according to claim 1, characterized in that it consists in correcting the flow rate only when the energy measured is less than a given threshold (N) between 10 and 50% and, preferably, of the order 25%, maximum backscattered energy.  3 - Method according to claim 1, characterized in that it consists in measuring the total backscattered energy (Es) over several cycles during which the moving target occupies the total section of the medium.  4 - Method according to claim 1, characterized in that it consists in correcting the speed or flow measurement, by a correction factor (K) corresponding to the ratio of localized energy (ED) to total energy ( Es), the correction factor (K) being weighted by a correction coefficient depending on the characteristics of the transducer (4, 5).