WO2016016581A1 - System and method for measuring blood flow - Google Patents

Abstract

The invention relates to a method and system (1) for determining a value indicating the position of an ultrasound probe (2) relative to a portion of the cardiovascular system (C) of a person (P) and for measuring blood flow in a portion of the cardiovascular system (C) of a person (P). The system comprises an ultrasound probe (2) positioned on the skin of the person such as to emit ultrasounds which propagate inside the person and to pick up reflected ultrasound signals indicating a blood flow in the portion of the cardiovascular system, as well as a control unit (3) comprising a processing circuit (4) for processing the reflected ultrasound signals in order to determine a value indicating the position of the ultrasound probe.

Description

 System and method for measuring blood flow.

FIELD OF THE INVENTION

 The present invention relates to systems and methods for measuring blood flow in a portion of a person's cardiovascular system, particularly for decompression bubble detection operations.

 These operations are commonly performed on divers as part of studies or surveillance aimed in general to better prevent decompression sickness.

 The field of application of the present invention, however, extends more generally to any type of hyperbaric / hypobaric environment, in particular tunnel boring machines, hyperbaric chambers, saturation diving systems where measurements are performed during decompression itself. , or the aerospace field, this list being obviously non-limiting.

 The present invention relates more particularly to the detection, by acoustic waves, of bubbles in the blood of a portion of the cardiovascular system of a person.

 The portion of the cardiovascular system may be one or more cardiac cavities, or a blood vessel, such as an axillary vein, a subclavian vein, or a femoral vein.

 In this respect, the cardiac cavities and the blood vessels each have relative advantages and disadvantages.

Thus, unlike the detection of bubbles at a vein, the detection of bubbles in the heart has the particular interest that the entire blood flow passes through the heart chambers. The heart is found at the confluence of all blood vessels and therefore the amount of decompression bubbles that is detected at this specific location can be considered representative of the body-wide bubble production of the diver.

 BACKGROUND OF THE INVENTION

 In order to carry out bubble measurements at the level of the heart or of a vein, a doppler acoustic detection apparatus, in particular an ultrasonic probe, is used in known manner.

 In this case, the operator, who may in particular be the diver himself, places an ultrasound probe on the diver's chest or in the subclavian position and targets the heart chamber (s) of interest or the vein of interest, for example the right heart cavities which correspond to the venous return.

 The operator guides the positioning of the probe by means of the audio signal delivered by the probe, seeking to recognize the Doppler signal associated with the blood flow of the target heart chamber (s) and, where appropriate, Doppler signals characteristic of the presence of bubbles.

 When the operator has identified, by ear, a signal that he associates with a correct positioning of the probe in front of the heart cavities, he usually proceeds to the quotation of the signal heard.

 By the term "quotation", it is meant in particular to count or estimate the number of characteristic signals of bubbles heard among the cardiac flow signals.

However, this operation is not easy and requires training. This method of positioning the probe and, where appropriate, the rating of the signal heard has several disadvantages. Thus, the operator must be trained to recognize the audio signals of the cavities to be able to guide "by ear" the positioning of the probe and must be able to recognize the signal characteristic of a good positioning of the probe.

 In particular, the operator may be mistaken if his ear is not exercised enough and the probe may be incorrectly positioned and detect the signal in the wrong place.

 The operator may not even know how to position the probe, if it is a non-expert. In the latter case the probability of achieving a good quality and reproducible measurement is low.

 Moreover, this method necessarily requires listening to an audio signal, an operation that is not convenient in a noisy environment.

 Finally, when the probe is well positioned and decompression bubbles are present, the passage of these bubbles whose signals are characteristic may be audible in the audio signal and, people with acoustic range of the audio signal - including the diver on whom the measurement is made - can hear these signals.

 For reasons of privacy, confidentiality but also to avoid causing anxiety or stress of the diver listening to these bubbles, it is interesting to achieve such an operation without having to listen to a signal audio during the on-site measurement operation.

 The importance of the latter disadvantage should not be underestimated because stress is a factor that favors the occurrence of a decompression sickness.

 OBJECTS OF THE INVENTION

The present invention is intended in particular to to overcome the disadvantages presented.

 Thus the present invention aims in particular to provide a method and system for measuring blood flow in a portion of a person's cardiovascular system in which the positioning of the ultrasound probe and the quotation of the signal can be performed without requiring listening. of audio signal.

 To this end, the invention firstly relates to a method for determining an indicative value for positioning an ultrasound probe with respect to a portion of a person's cardiovascular system, the method comprising at least the following steps:

 an initial positioning step during which the ultrasonic probe is positioned on the skin of the person,

 a positioning control step during which said ultrasound probe causes ultrasound to be transmitted, which propagates within the person, and the ultrasound probe is sensed with reflected ultrasonic signals of control,

 a doppler processing step of the control signals during which the reflected control ultrasonic signals are processed to determine at least one indicative positioning value of the ultrasound probe, the doppler processing step comprising

 determining frequency offset data, said frequency offset data being a function of a doppler signal determined from the control ultrasound and the reflected ultrasonic control signals, and

the determination of a value indicative of positioning of the ultrasonic probe with respect to a portion of the person's cardiovascular system based on the frequency shift data.

 In preferred embodiments of the invention, one or more of the following may also be used:

 the frequency offset data comprising at least one of a maximum amplitude, a periodicity, a statistical distribution and / or a signal-to-noise ratio indicator, of the Doppler signal;

 determining an indicative value for positioning the ultrasound probe in accordance with the frequency offset data comprises selecting a value indicative of positioning the ultrasound probe in a database associating frequency offset data with values indicative positioning of the ultrasonic probe;

 at least one indicative value for positioning the ultrasound probe of said database is recorded in the database as being a value indicative of positioning of the ultrasonic probe corresponding to a correct positioning of the ultrasonic probe relative to the portion of cardiovascular system,

 in particular, a plurality of indicative positioning values of the ultrasound probe of said database are recorded in the database as values indicative of positioning of the ultrasonic probe corresponding to correct positioning of the ultrasonic probe with respect to the portion cardiovascular system;

the method further comprises a step of displaying a visual indicator according to said indicative positioning value;

 said display step is at least implemented when the value indicative of a positioning corresponds to a correct positioning of the ultrasound probe relative to the portion of the cardiovascular system, and the method furthermore comprises a measurement step during from which ultrasound probe, which propagates in the cardiovascular system portion of the person, is made to emit by said ultrasound probe, and ultrasonic probe, ultrasonic reflected signals of measurement indicative of a blood flow in the portion of the cardiovascular system;

 the process further comprises

 an adjusted positioning step during which the ultrasound probe is moved on the person's skin according to the visual indicator, and

 a measuring step in which the ultrasound probe emits ultrasound, which propagates in the cardiovascular system portion of the person, and the ultrasonic probe detects indicative ultrasonic reflected measurement signals; a blood flow in the portion of the cardiovascular system,

 preferably the display step is at least implemented when said value indicative of a positioning does not correspond to a correct positioning of the ultrasound probe relative to the portion of the cardiovascular system;

the reflected ultrasonic measurement signals are processed to derive information on the presence of bubbles in the blood of the cardiovascular system portion of the person; the control ultrasound emitted by the ultrasound probe is defocused or non-focused;

 during the processing step, at least one characteristic of the control ultrasonic signals selected from a list comprising an amplitude over a predefined frequency range, a frequency of an amplitude peak, a spectral density, is determined, standard deviation, saturation level and noise level of the reflected ultrasonic control signals;

 the characteristic of the reflected control ultrasonic signals is determined from the reflected ultrasonic control signals included in a predefined time window, in particular a sliding time window;

 during the treatment step, a heart rate of the person is determined and the predefined time window has a duration equal to a whole number of times an inverse of the heart rate;

 during the processing step, at least one index which is a function of the characteristic of the reflected control ultrasonic signals is determined and said index is compared with at least one threshold value recorded in a database of threshold value values;

 the portion of the cardiovascular system is selected from a heart chamber, an axillary vein, a subclavian vein and a femoral vein.

The invention also relates to a system for measuring blood flow in a portion of a person's cardiovascular system, the system comprising:

an ultrasound probe adapted to be positioned on the person's skin to emit ultrasound of control and measurement ultrasound propagating within the person, and for capturing reflected ultrasonic control signals and reflected ultrasound measurement signals indicative of a blood flow in the portion of the cardiovascular system, and

 a control unit comprising a processing circuit Doppler control signals for processing the reflected control ultrasonic signals to determine at least a value indicative of positioning of the ultrasound probe by determining

 frequency offset data, said frequency offset data being functions of a Doppler signal determined from the control ultrasound and the reflected ultrasonic control signals, and

 an indicative value of positioning the ultrasound probe with respect to a portion of the cardiovascular system of the person according to the frequency offset data.

In preferred embodiments of the invention, one or more of the following may also be used:

 the ultrasound probe used comprises a single transmission transducer;

 the transmission transducer is unfocused;

 the ultrasound transducer of emission is also used in reception to pick up the reflected ultrasonic signals of control and the reflected ultrasonic signals of measurement;

the ultrasound probe used comprises a single transmission transducer and a single reception transducer; the control unit further comprises a display for displaying a visual indicator according to said indicative value of the positioning;

 the control unit further comprises a communication unit for transmitting the measured ultrasonic measurement signals to a remote server comprising a rating module able to process reflected ultrasonic signals for measurement in order to obtain information on the presence of bubbles in the cardiovascular system portion blood of the person;

 the control unit comprises a scoring module adapted to process reflected ultrasonic signals of measurement to derive information about the presence of bubbles in the blood of the portion of the cardiovascular system of the person;

 - The control unit further comprises a parameter input unit for entering a plunger identity and / or acoustic parameters specific to a plunger and / or additional parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

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

 On the drawings:

FIG. 1 is a schematic view of a system for measuring blood flow in a portion of a person's cardiovascular system according to an embodiment of the invention in which said portion is a cardiac cavity, FIG. 2 is a detailed schematic view of the system of FIG. 1, and

 Fig. 3 is a flow chart of a method of measuring blood flow in a portion of a person's cardiovascular system according to one embodiment of the invention.

 DESCRIPTION DETAILED

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

 In Figure 1 is illustrated a person P with a portion of the cardiovascular system C.

 In FIG. 1, the portion of the cardiovascular system is a cardiac cavity C of the person P and more particularly the right ventricle of the heart of the person P.

 Alternatively, the portion of the cardiovascular system may be an axillary vein, a subclavian vein or a femoral vein.

 A system 1 for measuring blood flow in the portion of the cardiovascular system C according to one embodiment of the invention is also illustrated and comprises an ultrasonic probe 2 and a control unit 3.

 In this example, the ultrasound probe 2 is positioned on the skin of the person P, against the chest of the person, and emits ultrasound that propagates within the person P.

The ultrasound probe 2 is also able to capture reflected ultrasonic control signals and reflected ultrasound measurement signals indicative of a blood flow in the person P and in particular in the portion C of the cardiovascular system that is sought to observe.

 In one embodiment of the invention, the ultrasonic probe 2 used comprises a single emission transducer 2a emitting ultrasound in an insonification zone.

 The emission transducer 2a may advantageously be unfocused. In this way the ultrasound emitted by the probe 2 are defocused. The zone of insonification can thus be of important dimensions.

 The ultrasonic emission transducer 2a can also be used in reception to capture the reflected ultrasonic control and measurement signals. Alternatively, the ultrasonic probe 2 used may include receiving transducers specifically for sensing the reflected ultrasonic signals.

 In one embodiment, the ultrasonic probe 2 used comprises a single transmitting transducer 2a and a single receiving transducer. In this embodiment, the ultrasonic probe thus comprises only two transducers which makes it possible to obtain a particularly simple and inexpensive system to manufacture.

 The control unit 3 further comprises a processing circuit 4 and may further comprise a display 5.

 The control unit 3 may in particular comprise a single housing 3a integrating the processing circuit 4 and the display 5. Said housing 3a may advantageously be waterproof. The case 3a can still be designed for use in a hyperbaric environment. The ultrasonic probe 2 may in particular be connected to said housing 3a by an electrical connection cable 3b.

The housing 3a may for example comprise a battery for supplying electrical power to the processing circuit 4 and the display 5.

 In this way, the measuring system 1 can be used in a field of operation, for example on a diving boat or in a hyperbaric chamber.

 The processing circuit 4 is more particularly designed and / or programmed to process the ultrasonic signals reflected so as to determine at least one indicative positioning value of the ultrasonic probe 2. The display 5 is able to display a visual indicator 5a depending on said indicative positioning value.

 According to one embodiment of the invention, the system 1 is more specifically intended to implement a method for determining an indicative positioning value of an ultrasound probe (2) with respect to a portion of the cardiovascular system C d a person P, and a method of measuring blood flow in a portion of the cardiovascular system C of a person P as will now be presented.

 According to the steps included in the method, it will be understood that the method may be called a method for determining a value indicative of the positioning of an ultrasound probe with respect to a portion of the cardiovascular system C of a person P, or measurement method blood flow in a portion of the cardiovascular system C of a person P.

 Such a method firstly comprises an initial positioning step (a) during which the ultrasound probe 2 is positioned on the skin of the person P.

Thus, in the example of FIG. 1, an operator, who may in particular be the person P, by example a plunger P, places the ultrasonic probe 2 on the chest of the person P.

 The operator can, as far as possible, aim at one or more cardiac cavities of interest, for example, right heart cavities.

 Then, the method comprises a positioning control step (b) in which the ultrasound probe 2 is made to transmit control ultrasound, which propagates within the person P.

 The control ultrasounds that propagate within the person P are reflected in particular by the interfaces separating the various organs present in the body of the person P as well as by the diffusers present in the tissues and in the blood of the person P to form reflected ultrasonic signals of control.

 Thus, during the positioning control step (b), the ultrasound probe 2 also receives the reflected ultrasonic control signals.

 The temporal evolution of the ultrasonic reflected signals of control is in particular a function of the movements of the observed organs as well as the speed of movement of the blood. Thus in the example in which the portion of the cardiovascular system C is a cardiac chamber C, the movements of the heart chamber and the movements of the blood in the heart under the effect of the contraction of the heart give the reflected ultrasonic control signals a particular acoustic signature and detectable in the way that will now be detailed.

Advantageously, in this embodiment, the emission transducer 2a may be unfocused or large, in particular of large diameter, so that the ultrasound emitted by the probe 2 are defocused, or non-focused, and the insonification zone of sufficiently large dimensions to encompass a target artery and / or vein.

 The method then comprises a step of processing (c) doppler control signals during which the reflected ultrasonic control signals are processed to determine at least one indicative positioning value of the ultrasound probe.

 A first embodiment of such a treatment step (c) is described below.

 Such a treatment step is called a "treatment step" or a "doppler processing step" in the rest of the description.

 In this embodiment, the processing step (c) comprises different operations to obtain a value indicating the positioning of the probe.

 In a first operation, the worst-case reflected control ultrasonic signals, in particular noisy or saturated signals above a predefined threshold, are eliminated.

 For this purpose, it is possible in particular to determine at least one characteristic of the reflected ultrasonic control signals. This characteristic is for example calculated from the absolute value of the demodulated Doppler signal. Examples of such a characteristic are the standard deviation of the signal, the signal saturation rate (also called TSA) or the signal noise rate (also known as TBR).

The saturated signals thus usually have a TSA higher than the signals that one seeks to preserve while the noisy signals have a smaller standard deviation and a TBR more important than a signal that one seeks to preserve. Conversely, a too large standard deviation will mean bad placement.

 It is thus possible to define TSA or TBR thresholds beyond or below which signals are retained or eliminated.

 In the case where the reflected ultrasonic control signals are preserved following this first operation, a second operation makes it possible to determine at least one indication indicative value differentiating on the one hand the signals corresponding to an ultrasonic probe well positioned relative to the portion of the cardiovascular system to be observed, and secondly the signals corresponding to an ultrasound probe less well positioned.

 For this purpose, one can start by calculating the heart rate of the person P.

 If the frequency is aberrant, the positioning indicative value is defined as corresponding to a poorly positioned ultrasound probe.

 Otherwise, a characteristic of the reflected ultrasonic control signals is again determined. Advantageously, this characteristic of the ultrasonic signals is a function of a time-frequency diagram of the ultrasonic reflected control signals, obtained in particular by a Fourier transformation operation.

 For example, one can choose several frequencies of the reflected ultrasonic control signals to be analyzed, for example four acoustic frequencies, for example 400, 700, 1200 and 2000Hz and respectively extract several time series of amplitudes of the signal at each of said frequencies.

In one embodiment, it is possible in particular for determining each of said time series associated with each frequency of the reflected control ultrasonic signals selected, averaging said frequency time diagram of the signal on a frequency window around said frequency.

 Then, in a subsequent operation, the standard deviations of these time series are determined and the maximums are recorded for each time series.

 Several normalized indices are then calculated with respect to the length of each time series and the heart rate associated with each selected frequency.

 To avoid having indices that are too high because of a maximum detection carried out on noise, it is advantageous to set one or more minimum detection thresholds. If the maximum amplitude of a time series is less than the threshold, it is possible for example to define the corresponding index equal to 0.

 In the opposite case, it is possible to define an index by frequency for example by the following equation:

 Ifi = 60 * 44100 * nb_max_fi / (puls * length (sig))

In which Ifi is the index associated with the frequency i with i between 1 and n where n is the number of frequencies of the chosen control reflected ultrasonic signals, for example four. And where nb_max_fi is the number of maximums for each time series, then the heart rate and length (sig) the time length of the time series associated with the frequency i.

In one embodiment, in order to prevent the indices Ifi having outliers, in particular following a maximum detection over a time series whose signal-to-noise ratio is too low, the Ifi indices which have a value which are too high are passed. different from the indices adjacent, for example Ifi + 1 and Ifi + 1, to 0.

 Finally, each of the indices Ifi is respectively compared with a respective index threshold value recorded in a database of threshold values of indices.

 Finally, each of the standard deviations of the time series can be compared respectively with a respective standard deviation threshold value recorded in a standard deviation threshold value database.

 These comparisons make it possible to determine a value indicative of positioning of the ultrasound probe according to the position of the probe relative to the portion of the cardiovascular system C, in particular as a function of the position of the probe relative to the cardiac cavity in the example of Figure 1.

 For example, depending on the number of indices greater than or less than each index threshold value and the number of standard deviations greater or less than each standard deviation threshold value, it is possible, for example, to define a positioning indicative value. of the ultrasonic probe. In one embodiment of the method, it is thus possible to define a value indicative of positioning of the ultrasound probe with a value associated with three categories: for example 0 for a misplaced probe, 1 for a well placed probe or 2 for an intermediate zone if it is not possible to conclude as to the good or bad position of the ultrasound probe.

 The value 0 can thus correspond to a non-correct positioning of the probe and the value 1 to a correct positioning of the probe.

In another embodiment of the treatment step (c) according to the invention, possibly combined with the previous embodiment, the step of Doppler treatment can understand

 determining frequency offset data, said frequency offset data being a function of a doppler signal determined from the control ultrasound and the reflected ultrasonic control signals, and

 determining a value indicative of positioning the ultrasound probe with respect to a portion of the cardiovascular system C of the person P as a function of the frequency offset data.

 Doppler signal means that the frequencies of the reflected ultrasonic control signals are offset with respect to the frequencies of the control ultrasound under the effect of movement of fluids in the cardiovascular system portion C of the person P, in particular under the effect of the movement of blood.

 The Doppler signal can directly correspond to the reflected ultrasonic control signals.

 The doppler signal can also be determined by demodulating the reflected ultrasonic control signals, for example by centering the frequency of the signals to zero, removing a frequency of the control ultrasound.

 The doppler signal can also be determined by filtering, for example by high pass filtering to eliminate frequency shifts due to tissue movements.

 It is also possible to eliminate the worst reflected control ultrasonic signals, in particular the noisy or saturated signals beyond a predefined threshold as indicated above.

The frequency offset data comprises at least one of a maximum amplitude, a periodicity, a statistical distribution and / or a ratio indicator signal on noise, Doppler signal

 The determination of the indicative positioning value of the ultrasound probe may then comprise the selection of a value indicating the positioning of the ultrasound probe in a database associating frequency offset data with values indicative of positioning of the ultrasound probe. .

 The indicative positioning values of the ultrasound probe may be representative of different portions of the cardiovascular system C of the person P. For example, an indicative value of positioning of the ultrasound probe may be an alphanumeric "heart" indicator or a "femoral vein" indicator ".

 Moreover, at least one indicative positioning value of the ultrasound probe of said database can be recorded in the database as being a value indicative of positioning of the ultrasonic probe corresponding to a correct positioning of the ultrasound probe with respect to the portion of the cardiovascular system C.

 In a variant, a plurality of indicative positioning values of the ultrasound probe of said database are recorded in the database as being values indicative of positioning of the ultrasonic probe corresponding to correct positioning of the ultrasound probe with respect to the portion of the cardiovascular system C.

 In this way, several positions of the ultrasonic probe 2 may be considered correct.

In another embodiment of the step of treatment (c) according to the invention, possibly combined with one or more of the previously described embodiments, it is possible to determine a characteristic of the ultrasonic reflected control signals which is a function of the amplitude of the reflected ultrasonic signals of control over a time window predefined.

 In such an embodiment, the indicative positioning value may then be a quasi-continuous value that is a function of said amplitude of the reflected ultrasonic control signals, for example a linear or logarithmic function of said amplitude.

 In all these embodiments, the indicative positioning value of the ultrasound probe may take a plurality of discrete values or a continuous value.

 The indicative positioning value of the ultrasonic probe may also be a multi-dimensional value, in particular a pair or triplet of values. Thus, for example, the indicative positioning value of the ultrasound probe may be a value indicative of a two-dimensional or three-dimensional angle of the ultrasound probe with respect to the portion of the cardiovascular system C and / or indicative of a two-dimensional or three-dimensional position. the position of the ultrasound probe 2 with respect to the portion of the cardiovascular system C.

Advantageously, the characteristics of the ultrasonic reflected control signals, the indices according to said characteristics and / or the positioning indicative values can be stored in a memory 12 of the measurement system 1, so as to allow a subsequent transmission or rating to be reused. In a subsequent step, the method may comprise a step of displaying (d) a visual indicator according to said indicative positioning value.

 The visual indicator may be a one-dimensional indicator, for example an encrypted, colored indicator, or a cursor movable in rotation or in position relative to a display background. The visual indicator may further be a one-dimensional indicator, for example an indicator of current position or distance or position relative to an optimal position.

 In general, any type of visual indicator capable of visually transmitting the indicative value of positioning to the operator or a characteristic of the indicative positioning value may be used, for example a visual indicator indicating in a binary manner whether the indicative value of positioning corresponds to a correct positioning of the ultrasound probe with respect to the portion of the cardiovascular system (C).

 The visual indicator can be displayed on a display such as a screen, especially a digital screen, can advantageously be used to allow compactness and increased reading efficiency.

 In one embodiment, the display step (d) is implemented when said value indicative of a positioning does not correspond to a correct positioning of the ultrasound probe relative to the portion of the cardiovascular system C.

 In this embodiment, the method also comprises an adjusted positioning step during which the ultrasound probe 2 is moved on the skin of the person P according to the visual indicator.

The operator, as indicated by the visual indicator can then position the ultrasound probe in an optimal position, or at least better, relative to the targeted portion of the cardiovascular system.

 By "moving the ultrasound probe on the skin of the person", it is intended in particular to modify the orientation and / or the position of the ultrasound probe 2 with respect to the person P.

 Of course, in the case where, by chance or by the usual practice of the operator, the ultrasound probe 2 has been correctly placed relative to the person P from the initial positioning step (a), this adjusted positioning step (e) can be "zero", that is to say that the ultrasound probe 2 can maintain the same orientation and / or position relative to the person P, the movement of the probe by the operator then being zero.

 Finally, the method may comprise a measurement step (f) during which ultrasonic probe 2 emits ultrasound.

 The measurement ultrasound may differ from the control ultrasound but may also be substantially similar.

 When the ultrasound probe 2 is correctly positioned relative to the cardiovascular system portion C, the measurement ultrasound propagates in the cardiovascular system portion C of the person P.

As detailed above for the control ultrasounds, the measurement ultrasounds propagating within the person P are reflected by the interfaces separating the different organs as well as by the diffusers present in the tissues and blood of the person P. to form reflected ultrasonic signals of measurement. The ultrasonic reflected measurement signals are thus advantageously indicative of a blood flow in the portion of the cardiovascular system C.

 During the measuring step, the ultrasound probe 2 then receives the reflected ultrasonic signals of measurement.

 In an alternative embodiment, the display step (d) is implemented when the indicative value of a positioning corresponds to a correct positioning of the ultrasound probe relative to the portion of the cardiovascular system C.

 The use can thus move the ultrasound probe by repeating the steps (a), (b) and (c) indicated above until display of the visual indicator.

 The measurement step (f) can then be implemented in a manner similar to that described above.

 In variants, the display step (d) can be implemented when the indicative value of a positioning corresponds to a correct positioning of the ultrasonic probe and when the value indicative of a positioning does not correspond to a correct positioning. of the ultrasonic probe.

 In a subsequent step of processing the measurement signals (g), the reflected ultrasonic signals of measurement can then be processed to derive information on the presence of bubbles in the blood of the cardiovascular system portion C of the person P.

For this purpose, the control unit 3 may for example also comprise a communication unit 6 for transmitting the measured ultrasonic measurement signals to a remote server 8. The communication unit 6 may be able to communicate directly with the server 8 or to communicate with the server 8 via a computer, for example a laptop computer to which the blood flow measurement system 1 can be connected. .

 The communication unit 6 may thus comprise a wired or wireless internet communication module, a communication module on a cellular network, for example a GSM network, a communication module on a telephone network, for example a modem, or a satellite communication module.

 In an embodiment where the communication unit 6 communicates with the server 8 via a computer, the communication unit 6 comprises a communication module with said wired computer, for example a USB module, or without -file, for example a Bluetooth module or wifi. The communication unit 6 further comprises said computer and a communication module connecting said computer to the server 8, for example a wired or wireless internet communication module, a communication module on a cellular network, for example a network GSM, a communication module on a telephone network, for example a modem, or a satellite communication module.

 Furthermore, the measurement system 1 can also make it possible to associate the reflected measurement ultrasonic signals with a user identity.

 For example, a user identity is an identifier associated with the person P, for example a name or a number.

The user identity may in particular be a unique identifier associated with the person P. Alternatively, the user identity may identify a group of people, for example a team of professional divers.

 The user identity can thus be a unique identifier associated with a group of persons P.

 The system 1 may thus comprise a parameter input unit 7 enabling an operator to provide the system 1 with such a user identity or to select such a user identity from a list of identities proposed by the system 1. Such a parameter input unit 7 may for example comprise a keyboard, if necessary tactile and possibly a pointer such as a mouse or a touchpad.

 In an advantageous variant embodiment, acoustic parameters specific to such a user identity can be stored in the system 1 or provided by the operator by means of the parameter input unit 7.

 Other additional parameters may also be stored in the system 1 or provided by the operator through the parameter input unit 7 and in particular the parameters specific to a dive performed, such as the depths and dive times, or parameters specific to an activity carried out, such as the type of work and its arduousness, or in a general way parameters of any kind likely to be useful for the treatment of ultrasound and the subsequent processing of these data, for example a temperature, weather conditions, underwater visibility, ...

During the implementation of the method, the operator can transfer the ultrasound signals reflected to the server 8 which advantageously centralizes other signals of the same nature.

 The server 8 thus comprises in particular a communication module 10 able to receive the reflected ultrasonic signals for measuring the system 1 and, if appropriate, a user's identity of the person P and / or acoustic parameters associated with the person P.

 The server 8 communicates with a database 11 (if the server 8 is a physical server, the database can be managed or not on the said physical server) to record the reflected ultrasonic signals and if necessary the identity of the person P and / or the acoustic parameters associated with the person P and / or the additional parameters detailed above.

 The server 8 also comprises a rating module 9 able to process the reflected measurement ultrasonic signals received to draw information on the presence of bubbles in the blood of the cardiovascular system portion C of the person P.

 The rating module 9 can in particular provide quotation values representative of the quantity of bubble signals contained in the reflected measurement ultrasonic signals transmitted to the server 8.

 In one embodiment, the dimension values can be returned to the measurement system 1, in particular to be displayed to the operator.

In another embodiment not illustrated in the figure, the dimensioning module 9 can be directly integrated in the measurement system 1 and not remote on the remote server 8. CLAIMS

A method for determining an indicative positioning value of an ultrasound probe (2) relative to a portion of a cardiovascular system (C) of a person (P), the method comprising at least the following steps:

 (a) an initial positioning step during which the ultrasound probe (2) is positioned on the skin of the person,

 (b) a positioning control step in which said ultrasonic probe (2) emits control ultrasound which propagates within the person and is sensed by the ultrasound probe (2), reflected ultrasonic signals of control,

 (c) a doppler processing step of the control signals in which the reflected control ultrasonic signals are processed to determine at least one indicative positioning value of the ultrasound probe, the doppler processing step comprising

 the determination of frequency offset data, said frequency offset data being a function of a Doppler signal determined from the control ultrasound and the reflected ultrasonic control signals,

 determining a value indicative of positioning the ultrasound probe with respect to a portion of the cardiovascular system (C) of the person (P) as a function of the frequency offset data.

The method of claim 1, wherein

Claims

the frequency offset data comprising at least one of a maximum amplitude, a periodicity, a statistical distribution and / or a signal-to-noise ratio indicator, of the Doppler signal. 3. Method according to one of claims 1 and 2, wherein the determination of a value indicative of positioning of the ultrasound probe according to the frequency offset data comprises the selection of a value indicative of positioning of the ultrasonic probe. in a database associating frequency offset data with values indicative of positioning of the ultrasound probe. 4. Method according to claim 3, wherein at least one indicative positioning value of the ultrasound probe of said database is recorded in the database as a value indicative of positioning of the ultrasonic probe corresponding to a correct positioning of the ultrasound probe. the ultrasound probe relative to the portion of the cardiovascular system (C),  in particular in which a plurality of values indicative of positioning of the ultrasound probe of said database are recorded in the database as values indicative of positioning of the ultrasonic probe corresponding to correct positioning of the ultrasound probe with respect to the portion of the cardiovascular system (C). The method of any one of claims 1 to 4, further comprising (d) a step of displaying a visual indicator according to said indicative positioning value. 6. Method according to claim 5, wherein said display step is at least implemented when the value indicative of a positioning corresponds to a correct positioning of the ultrasound probe relative to the portion of the cardiovascular system (C),  the method further comprising  (f) a measurement step in which said ultrasound probe (2) emits measurement ultrasound which propagates in the cardiovascular system portion (C) of the person (P) and is sensed by the ultrasonic probe (2), reflected ultrasonic signals of measurement indicative of a blood flow in the portion of the cardiovascular system (C). 7. The method of claim 5, the method further comprising  (e) an adjusted positioning step in which the ultrasound probe (2) is moved on the skin of the person according to the visual indicator, and (f) a measurement step in which said ultrasound probe (2) emits measurement ultrasound which propagates in the cardiovascular system portion (C) of the person (P) and is sensed by the ultrasonic probe (2), reflected ultrasonic signals of measurement indicative of a blood flow in the portion of the cardiovascular system (C), preferably wherein said display step is at least implemented when said indicative value of a positioning does not correspond to a correct positioning of the ultrasonic probe with respect to the portion of cardiovascular system (C). A method according to any one of claims 6 and 7, wherein the reflected ultrasonic measurement signals are processed to derive information about the presence of blood bubbles in the cardiovascular system portion (C) of the person (P). ). 9. Method according to any one of claims 1 to 8, wherein the control ultrasound emitted by the ultrasound probe (2) are defocused or non-focused. The method according to any one of claims 1 to 9, wherein during the processing step, at least one characteristic of the reflected control ultrasonic signals selected from a list comprising an amplitude over a predefined frequency range is determined. , a frequency of an amplitude peak, a spectral density, a standard deviation, a saturation level and a noise level of the reflected ultrasonic control signals. The method of claim 10, wherein the characteristic of the reflected control ultrasonic signals is determined from the reflected ultrasonic control signals included in a predefined time window, including a sliding time window. The method of claim 11, wherein, during the treatment step, determining a heart rate of the person (P) and wherein the predefined time window has a duration equal to a whole number of times an inverse of the heart rate. The method according to any one of claims 10 to 12, wherein, during the processing step, at least one index is determined that is a function of the characteristic of the reflected ultrasonic control signals and said index is compared with at least one a threshold value stored in a database of threshold values of indices. The method of any one of claims 1 to 13, wherein the portion of the cardiovascular system (C) is selected from a heart chamber, an axillary vein, a subclavian vein and a femoral vein. 15. System (1) for measuring blood flow in a portion of a person's cardiovascular system (C) (P), the system comprising:  an ultrasound probe (2) adapted to be positioned on the person's skin to emit control ultrasound and measurement ultrasound which propagate within the person, and to capture reflected ultrasonic control signals and reflected ultrasound signals measuring a blood flow in the portion of the cardiovascular system, and a control unit (3) comprising a processing circuit (4) doping control signals for processing the reflected control ultrasonic signals to determine at least one indicative positioning value of the ultrasound probe by determining frequency offset data, said frequency offset data being functions of a Doppler signal determined from the control ultrasound and the reflected ultrasonic control signals, and  an indicative value of positioning the ultrasound probe with respect to a portion of the cardiovascular system (C) of the person (P) according to the frequency offset data. 16. The system of claim 15, wherein the ultrasonic probe used comprises a single transmitting transducer (2a). The system of claim 16, wherein the transmit transducer (2a) is unfocused. The system of claim 15 or claim 16, wherein the ultrasonic transmit transducer (2a) is also used in reception to sense reflected ultrasonic control signals and reflected ultrasonic measurement signals. The system of claim 15 or claim 16, wherein the ultrasonic probe used comprises a single transmit transducer (2a) and a single receive transducer. 20. System according to any one of claims 15 to 19, wherein the control unit (3) further comprises a display (5) for displaying a visual indicator according to said indicative value of the positioning. System according to any one of claims 15 to 20, wherein the control unit (3) further comprises a communication unit (6) for transmitting the reflected measurement ultrasonic signals to a remote server (8) comprising a scoring module (9) adapted to process reflected ultrasonic measurement signals to derive information on the presence of bubbles in the blood portion of the cardiovascular system (C) of the person (P). 22. System according to any one of claims 15 to 21, wherein the control unit (3) comprises a dimensioning module (9) capable of processing reflected ultrasonic signals measurement to draw information on the presence of bubbles in the blood of the cardiovascular system portion (C) of the person (P). 23. System according to any one of claims 15 to 22, wherein the control unit (3) further comprises a parameter input unit (7) to enter a diver identity and / or acoustic parameters own to a diver and / or additional parameters.