WO2015145011A1

WO2015145011A1 - Method for the acoustic detection of bubbles in the blood

Info

Publication number: WO2015145011A1
Application number: PCT/FR2015/050527
Authority: WO
Inventors: Olivier Couture; Mickaël TANTER; Mathias Fink
Original assignee: Centre National De La Recherche Scientifique - Cnrs -; INSERM (Institut National de la Santé et de la Recherche Médicale)
Priority date: 2014-03-28
Filing date: 2015-03-04
Publication date: 2015-10-01
Also published as: FR3019141A1; FR3019141B1

Abstract

The invention relates to a method for the acoustic detection of bubbles in a person's (P) blood, using an ultrasound probe (2) positioned against the sternum of the person. Ultrasounds of a frequency lower than 1 MHz are emitted by the ultrasound probe and then flow through the right ventricle (RV) of the heart of the person via the sternum (S), and reflected ultrasound signals are captured by the ultrasound probe and processed in order to obtain information about the presence of bubbles in the blood.

Description

ACOUSTIC DETECTION METHOD FOR BUBBLES IN BLOOD

FIELD OF THE INVENTION

The invention relates to methods and devices for detecting bubbles in the blood, intended in particular for applications related to the safety of divers.

BACKGROUND OF THE INVENTION

The EP2383179 discloses an example of an acoustic method for detecting bubbles in the blood by Doppler detection, using an ultrasound sensor operating at a frequency of between 2 and 8 MHz, disposed between the 2 ^nd and 3 ^rd coast left of the sternum of a user to perform measurements on the right ventricle of the heart. The detection of bubbles in the right ventricle is particularly advantageous, since this ventricle is the seat of a venous return from all the organs, which allows optimal detection of bubbles.

In such methods, the positioning of the ultrasonic sensor, on the side of the sternum, is made necessary by the fact that the sternum, which masks the right ventricle, is opaque to ultrasound at frequencies useful for Doppler. This positioning is however difficult to achieve and the imaging window is unstable. In practice, the implementation of such a method is reserved for an experienced professional or a doctor.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention is intended to overcome these disadvantages.

For this purpose, the invention proposes a method of acoustically detecting bubbles in the blood of a person with an ultrasound probe, this method comprising at least the following steps:

(a) a positioning step during which the ultrasound probe is positioned on the skin of the person, against the sternum of said person, (b) a measurement step during which said ultrasound probe emits ultrasounds of a frequency less than 1 MHz, which propagate in the right ventricle of said person's heart through the sternum, and is sensed by the ultrasonic probe, reflected ultrasonic signals,

(c) a processing step in which the reflected ultrasonic signals are processed to derive information about the presence of bubbles in the blood.

Thanks to the use of low ultrasonic frequencies, the ultrasonic wave passes easily through the sternum and therefore the ultrasound transducer can be placed directly on the sternum. The positioning of the ultrasonic transducer thus becomes very simple and accessible even to an inexperienced person, for example an amateur diver, since the sternum is easy to locate. The ultrasound transducer is also directly in front of the right ventricle, which improves the quality and stability of the detection.

It will be noted that the above-mentioned ultrasound probe may comprise one or more ultrasonic transducers, used either in transmission and reception, or certain (s) only in transmission and some (s) only in reception.

In various embodiments of the method according to the invention, one or more of the following provisions may also be used:

the ultrasound probe used comprises a single transmission transducer;

the emission transducer is unfocused;

the ultrasound transducer of emission is also used in reception to pick up the reflected ultrasonic signals; the ultrasonic probe comprises at least one reception transducer used to pick up the reflected ultrasonic signals;

the ultrasound probe comprises a plurality of reception transducers used to pick up the reflected ultrasonic signals;

during the treatment step, the bubbles are detected in the blood by a method chosen from: the subtraction between successive signals, the detection of harmonics, the inversion of pulses, the amplitude modulation, the radial modulation, chirps (these methods are known per se);

during the measuring step (a), the frequency of the ultrasound emitted is between 100 and 1000 kHz, advantageously of the order of 200 kHz;

during the measurement step (a), the ultrasound is transmitted in the form of pulse trains, each pulse having a duration of less than 50 is and the successive pulses of the pulse train being separated from each other by a duration less than 200 is;

during the positioning step (a), the correct positioning of the ultrasound probe is verified by sensing acoustic signals from the person's pulmonary valve with the aid of the ultrasound probe.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent from the following description of one of its embodiments, given by way of non-limiting example, with reference to the accompanying drawings.

On the drawings:

- Figures 1 and 2 are views respectively in perspective and cut away, showing a person carrying a bubble detection device implementing the method according to the invention; FIG. 3 is a block diagram of the bubble detection device of FIGS. 1 and 2;

and FIG. 4 is a block diagram of a variant of the ultrasonic probe of FIG. 3.

DESCRIPTION DETAILED

In the different figures, the same references designate identical or similar elements.

As shown diagrammatically in FIGS. 1 and 2, the object of the invention is to detect acoustically bubbles in the blood of a person P with a detection device 1 comprising an ultrasound probe 2. The person P may especially be a diver.

The ultrasound probe 2 can be held on the chest of the person P by any means, for example by an elastic strap 3 surrounding the chest of the person P.

The ultrasonic probe 2 can communicate with a digital processing device 4, either during the detection of bubbles on the person P, or after.

The digital processing device 4 may for example be a dive computer, which may in particular be attached to the wrist of the person P.

The communication between the ultrasound probe 2 and the digital processing device 4 can be carried out by radio waves according to any known communication protocol, or by wire.

The ultrasound probe 1 may comprise a single ultrasonic transducer 6 (T - FIG. 3) used both for transmission and reception. This ultrasound transducer 6 may advantageously be unfocused, so as to emit a wide ultrasound beam F which effectively scans the right ventricle of the heart of the person P, as will be explained hereinafter (see FIG. 2).

As shown in FIG. 3, the ultrasonic probe 2 may optionally comprise, in addition to the transducer ultrasound 6:

an electronic central unit 5 (UC1) such as a microprocessor or the like, which controls the transducer 6 and receives the signals picked up by the ultrasonic transducer 6,

a communication interface 7 (COM1), for example a radio interface or the like, communicating with the electronic central unit 5.

The processing device 4 may comprise, for example:

an electronic central unit 8 (UC2) such as a microprocessor or the like,

a communication interface 9 (COM2) compatible with the communication interface 7 of the ultrasonic probe 2 and communicating with the electronic central unit 8,

a display 10 controlled by the electronic central unit 8,

a user interface 11, comprising for example a few control buttons 12, communicating with the electronic central unit 8.

In use, a positioning step (a) is first carried out during which the ultrasonic probe 2 is placed against the skin of the person P, against the sternum S of said person, and held in place by example by the strap 3 (Figures 1 and 2).

The heart C of the person comprises in particular the aorta AO, the left ventricle VG and the right ventricle VD, which receives the venous blood flow and is behind the sternum S. The ultrasound probe 2 is therefore in front of the right ventricle VD.

During this positioning step (a), the correct positioning of the ultrasonic probe 2 can be verified by sensing with the aid of said ultrasonic probe acoustic signals coming from the valve pulmonary of the person. The ultrasonic probe can then communicate to the processing device 4, the result of this verification, and said processing device 4 can thus indicate to the person P, for example by the display 10, if the positioning is correct.

Once the ultrasound probe 2 is correctly positioned, a measurement step (b) is performed during which an ultrasound beam F of ultrasound of frequency lower than 1 MHz, which propagates in the ventricle, is emitted by said ultrasound probe 2. right of the heart of said person through the sternum S, and is sensed by the ultrasonic probe 2, ultrasonic signals reflected by the right ventricle VD and the blood contained therein. The frequency of the ultrasound emitted may be between 100 and 1000 kHz, for example of the order of 200 kHz.

This measurement step is prolonged during the entire use of the ultrasonic probe 2, for example during the duration of a dive or during the duration of a control after diving. Advantageously, the ultrasound is transmitted in the form of pulse trains, each pulse having a duration of less than 50 is and the successive pulses of the pulse train being separated from each other by a duration less than 200 is used to receive the signals. reflected ultrasound.

The detection method also includes a processing step (c) in which the reflected ultrasound signals are processed to derive information about the presence of bubbles in the blood.

This processing step can be performed for example by the electronic central unit 8 of the processing device 4, which receives via the communication interfaces 7, 9, the reflected signals picked up by the ultrasonic probe 2.

The processing step can be performed almost in real time or in deferred time. During the treatment step (c), bubbles can be detected in the blood by various known methods.

For example, subtraction can be carried out between successive signals, which makes it possible to highlight the bubbles moving with the blood flow.

It is also possible to proceed by other known methods such as harmonic detection, inversion of pulses, emission of amplitude modulated signals, emission of low frequency modulated signals (for example with a modulation of the order of 50 kHz) for to generate a modulation of the radius of the bubbles allowing their better detection, emission of chirps (signals modulated in frequency), etc. These different methods will not be detailed here, we can refer for example to Qin et al. (2009) "Ultrasound contrast microbubbles in imaging and therapy: physical principles and engineering" Physics in Medicine and Biology

Alternatively, as shown in FIG. 4, the ultrasound probe 2 may comprise a transmission transducer 6 (T) as defined above and at least one reception transducer 6a (T1, T2, ...) used for to pick up the reflected ultrasonic signals, possibly at a frequency different from the emission frequency. Advantageously, it is possible to use a plurality of reception transducers 6a, possibly capturing at different frequencies.

Claims

CLAIMS:

A method of acoustically detecting bubbles in the blood of a person (P) with an ultrasound probe (2), said method comprising at least the following steps:

(a) a positioning step during which the ultrasound probe (2) is positioned on the skin of the person, against the sternum of said person, (b) a measurement step during which the probe is made to emit ultrasound (2), ultrasounds with a frequency less than 1 MHz, which propagate in the right ventricle of the heart of the person through the sternum, and the ultrasonic probe (2) is sensed, reflected ultrasonic signals,

2. The method of claim 1, wherein the ultrasonic probe used comprises a single transmitting transducer (6).

The method of claim 2, wherein the transmitting transducer (6) is unfocused.

4. The method of claim 2 or claim 3, wherein the ultrasonic transducer transmitter (6) is also used in reception to capture the reflected ultrasonic signals.

5. Method according to any one of the preceding claims, wherein the ultrasound probe comprises at least one receiving transducer (6a) used to capture the reflected ultrasonic signals.

The method of claim 5, wherein the ultrasonic probe comprises a plurality of receiving transducers (6a) used to pick up the reflected ultrasound signals.

7. Method according to any one of the preceding claims, wherein during the treatment step, the bubbles are detected in the blood by a method selected from: the subtraction between successive signals, the detection of harmonics, the inversion of pulses, amplitude modulation, radial modulation, chirps.

8. Method according to any one of the preceding claims, wherein during the measuring step (a), the frequency of the emitted ultrasound is between 100 and 1000 kHz.

9. Method according to any one of the preceding claims, wherein during the measuring step (a), the ultrasound is emitted in the form of pulse trains, each pulse having a duration less than 50 is and the pulses successive pulse train being separated from each other by a duration less than 200 is.

The method according to any one of the preceding claims, wherein during positioning step (a), correct positioning of the ultrasonic probe (2) is verified by sensing with said ultrasonic probe, acoustic signals from the person's pulmonary valve.