阅读说明：本技术 用于自动选择用于计算粘弹性介质的性质的深度范围的方法 (Method for automatically selecting a depth range for calculating a property of a viscoelastic medium ) 是由 洛朗·桑德兰 米歇尔·克莱特 于 2019-10-01 设计创作，主要内容包括：一种用于在测量粘弹性介质的性质时自动选择计算深度范围的方法,所述深度范围选自P个可能范围,所述方法包括以下步骤：·根据使用用于弹性成像的探头采集的超声信号,计算(CALC)P个深度范围中的至少一个中的粘弹性介质的性质,以及探头与粘弹性介质的壁之间的距离(PCD)；·确定(TEST-PCD)P个计算深度范围中的至少一个的有效性；·确定(TEST-VAL)在一个或多个有效计算深度范围内粘弹性介质的性质的计算的有效性；·从其中粘弹性介质的性质的值的计算是有效的有效深度范围中选择(SEL)满足选择标准的深度范围。(A method for automatically selecting a calculated depth range when measuring a property of a viscoelastic medium, the depth range being selected from P possible ranges, the method comprising the steps of: calculating (CALC) properties of the viscoelastic medium in at least one of the P depth ranges and a distance (PCD) between the probe and a wall of the viscoelastic medium from the ultrasound signals acquired using the probe for elastography; determining the validity of at least one of the (TEST _ PCD) P calculated depth ranges; determining (TEST _ VAL) the validity of the calculation of the property of the viscoelastic medium in one or more valid calculation depth ranges; selecting (SEL) a depth range satisfying the selection criterion from among effective depth ranges in which the calculation of the value of the property of the viscoelastic medium is effective.)

1. A method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium, the depth range being selected from P possible ranges, P being an integer greater than or equal to 2, the method comprising the steps of:

calculating (CALC) the property of the viscoelastic medium in at least one of P possible depth ranges from ultrasound signals acquired using a probe for elastography, and a distance (PCD) between the probe and a wall defining a viscoelastic medium;

determining the validity of at least one of (TEST PCD) P calculated depth ranges, a calculated depth range being considered valid if it satisfies a validity criterion calculated from the distance (PCD) between the probe and the wall delimiting the viscoelastic medium;

determining (TEST _ VAL) the validity of the calculation of the value of the property of the viscoelastic medium within the one or more valid calculation depth ranges, the calculation being considered valid if it satisfies a validity criterion calculated from the quality of the elasticity map;

selecting (SEL) a depth range satisfying a predetermined selection criterion from the at least one efficiently calculated effective depth range comprising the property of the viscoelastic medium.

2. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to the preceding claim, characterized in that:

each depth range is bounded by a first depth and a second depth;

defining the depth range as valid if the distance (PCD) between the probe and the wall defining the viscoelastic medium is less than the first depth and the second depth.

3. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to one of the preceding claims, characterized in that: during the step of calculating (CALC), the property of the viscoelastic medium is calculated from M measurements made in at least one of the P possible depth ranges, M being an integer greater than or equal to 2.

4. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to the preceding claim, characterized in that: the selection criterion of the depth range calculated is based only on the last measurement made.

5. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to the preceding claim, characterized in that: the depth range selected during the step of Selecting (SEL) is the depth range in which the elasticity map has the highest signal-to-noise ratio.

6. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to claim 4, characterized in that: the depth range selected during the step of Selecting (SEL) is the depth range in which the elastic map has the best quality.

7. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to claim 4, characterized in that: the depth range selected during the step of Selecting (SEL) is a depth range that meets a criterion determined according to the homogeneity of the medium.

8. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to claim 3, characterized in that: the selection criterion is based on the complete set of measurements made.

9. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to the preceding claim, characterized in that: the depth range selected during the step of Selecting (SEL) is the depth range that minimizes the dispersion between the calculated values of the property.

10. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to claim 8, characterized in that: the depth range selected during the step of Selecting (SEL) is the depth range that maximizes the number of valid calculations of the property.

11. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to claim 8, characterized in that: the depth range selected during the step of Selecting (SEL) is the depth range in which the computed elasticity map has the highest signal-to-noise ratio.

12. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to claim 8, characterized in that: the depth range selected during the step of selecting is the depth range for which the elasticity map has the best quality.

13. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to claim 8, characterized in that: the selected depth range is a depth range that meets a quality criterion determined from homogeneity of the medium.

14. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to claim 1 or claim 2, characterized in that: if the depth range in which the calculation of the value of the property has been performed is not valid, the calculation is performed at a deeper range.

15. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to one of the preceding claims, characterized in that: selecting a shallower range if at least two depth ranges meet the selection criterion during the step of Selecting (SEL).

16. Method (PRO) for automatically selecting a depth range for calculating a property of a viscoelastic medium according to one of the preceding claims, characterized in that: selecting a deeper range if at least two depth ranges meet the selection criterion during the step of Selecting (SEL).

17. A method for global measurement of at least one property of a viscoelastic medium, comprising the steps of:

automatically selecting (a) the calculated depth range using the method (PRO) according to one of claims 1 to 16;

globally calculating (B) a property of the viscoelastic medium according to the values of said property calculated efficiently in said selected depth range, said calculation being performed using a mathematical function of the median or mean type.

18. Method for the global measurement of at least one property of a viscoelastic medium according to the previous claim, characterised in that: the property of the viscoelastic medium is selected from the group comprising: elasticity, Young's modulus, shear rate within the viscoelastic medium, ultrasonic attenuation parameters, or a combination thereof.

19. Apparatus for measuring properties of a viscoelastic medium with automatic selection of a calculation depth range using the method according to one of claims 17 or 18, the apparatus comprising:

a probe for elastography;

a computing device comprising at least a memory and a microprocessor; the apparatus is constructed and arranged to:

calculating a distance (PCD) between the probe and a wall bounding the viscoelastic medium from ultrasound signals acquired using the probe and the computing device for elastography;

calculating a value of the property of the viscoelastic medium in at least one of P possible calculation depth ranges from ultrasound signals acquired using the probe for elastography and the computing device;

determining the validity of at least one of the P calculated depth ranges, a calculated depth range being considered valid if it satisfies a validity criterion calculated from the distance (PCD) between the probe and the wall bounding the viscoelastic medium;

determining the validity of said calculation of said property of said viscoelastic medium in one or more valid said depth ranges, said calculation being considered valid if it meets a validity criterion determined from the quality of the elasticity map;

selecting a depth range satisfying a predetermined selection criterion among the available depth ranges including at least one available property calculation;

calculating a global value of the viscoelastic property from the effectively calculated values of the property within the selected depth range, the global value being calculated using a mathematical function of the median or mean type.

Technical Field

The present invention is in the field of elastography for measuring at least one property of a viscoelastic medium. One aspect of the invention relates to a method for automatically selecting a calculation depth range when measuring properties of a viscoelastic medium. The method according to the invention makes it possible to improve the speed, reliability and reproducibility of the measurement by selecting a depth range that meets predetermined selection criteria. A second aspect of the invention relates to a method for global measurement of at least one property of a viscoelastic medium, wherein one or more calculated depth ranges are automatically selected using the automatic selection method according to the invention. A third aspect of the invention relates to an apparatus for measuring a property of a viscoelastic medium with an automatically selected calculation depth range.

Background

Transient elastography (also known as pulse elastography) is one of the most well known and effective methods for determining the elasticity of a viscoelastic medium. For example, transient elastography is commonly used to determine the elasticity of a human or animal liver.

In transient elastography, a shear wave pulse is generated and its propagation velocity within the viscoelastic medium of interest is measured. Then, the propagation velocity of the shear wave is used to calculate the young's modulus of the medium, thereby measuring its elasticity.

Several techniques exist for achieving temporal elastography.

For example, applicants have developed and marketed Vibration Controlled Transient Elastography (VCTE) technology. Is called asThe device using this technique is capable of measuring the elasticity of a human liver in a fast, non-invasive and reproducible manner. In such a device for transient elastography, the shear waves are generated by a vibrator placed in contact with the medium to be characterized. The propagation of the shear wave is then tracked by a series of ultrasound acquisitions performed by an ultrasound transducer with a high repetition rate. Each ultrasound acquisition corresponds to at least one hyperAn acoustic beam. Each ultrasound beam may be associated with the instantaneous detection and recording of echoes generated by reflection of particles present in the medium under investigation for a defined depth range. The reflected ultrasound signals are processed by cross-correlation to infer tissue motion caused by the propagation of the shear wave as a function of time and position in the medium. Studies of these motions have been able to infer the speed of propagation of shear waves in viscoelastic media and hence tissue elasticity, as explained in "Transmission elastomer: a new nonlinear method for assessment of magnetic fibers" by L.Sandrin et al (published in ultrasounds in Medicine and Biology, Vol.29, p.1705-1713, 2003.)

In the case of measuring the viscoelastic properties of a medium, such as a human liver, it is necessary to select the portion of the reflected ultrasound wave that corresponds to the depth at which the medium is located.

This selection operation is complicated because the depth varies greatly depending on the morphology of the patient. For example, in the case of an obese patient, the viscoelastic medium to be analyzed is more likely to be at a greater depth than in the case of a patient with a normal morphology.

Therefore, in useIn the case of elasticity measurement of (2), a plurality of calculation depth ranges may be considered. Fig. 1 shows the distribution of ultrasound power in a patient for an S-sized probe as a function of the in-vivo depth Pr. For example, the calculated depth range may be selected from two possible ranges S1 and S2. S1 corresponds to a depth range between 15mm and 40 mm. S2 corresponds to a depth range of 20-50 mm.

Figure 2 shows the measurement of liver properties using a depth range between 35mm and 75 mm. In the example of fig. 2, the distance between the probe and the outer wall of the liver (or the probe to capsule distance PCD) is 38 mm. If the depth range in which the property is calculated is between 35mm and 75mm, this is not optimal as it is not fully included in the liver. In particular, the presence of the outer wall of the liver or liver capsule within the calculation range may distort the measurement.

In the solutions currently known to the person skilled in the art, the depth at which the viscoelasticity is to be calculated is fixed or left to the operator's choice. This may distort the measurement if the fixed depth range is not appropriate for the patient's morphology, or make it operator dependent, thereby reducing its reliability and reproducibility.

Furthermore, operator changes to the depth range cause all measurements to be deleted. As a result, the duration of the examination may increase significantly.

That is, when measuring properties of a viscoelastic medium, such as a human or animal liver, the prior art solutions do not allow for an optimal and automatic selection of a calculated depth range.

Disclosure of Invention

In order to at least partially solve the problems of the prior art, the object of the present invention is a method for automatically selecting a depth range for calculating a property of a viscoelastic medium, the depth range being selected from P possible ranges, P being an integer greater than or equal to 2, said method comprising the steps of:

-calculating, from the ultrasound signals acquired using the probe for elastography, values of properties of the viscoelastic medium in at least one of the P possible depth ranges, and distances between the probe and the walls delimiting the viscoelastic medium;

-determining the validity of at least one of the P calculated depth ranges, a calculated depth range being considered valid if it satisfies a validity criterion calculated from the distance between the probe and the wall delimiting the viscoelastic medium;

-determining the validity of the calculation of the property of the viscoelastic medium in one or more valid calculation depth ranges, the calculation of the value being considered valid if it satisfies a validity criterion calculated from the quality of the elasticity map;

-selecting a depth range satisfying a predetermined selection criterion from the effective depth ranges comprising at least one value of an effectively calculated property of the viscoelastic medium.

The property of the viscoelastic medium refers to the viscoelastic or ultrasonic properties of the viscoelastic medium. One example of viscoelasticity is the propagation velocity of a shear wave in a viscoelastic medium. Another example of the viscoelasticity of the medium is the elasticity of the viscoelastic medium. One example of an ultrasonic property of a viscoelastic medium is an ultrasonic attenuation parameter within the viscoelastic medium.

An elastographic probe refers to a probe having at least one ultrasound transducer. The probe may be used to measure viscoelastic properties of a medium. An example of a probe for elastography is a probe configured to perform transient elastography measurements.

Measuring viscoelastic properties refers to the complete set of steps of the method for providing values of properties of a viscoelastic medium, from the step of calculating the properties to the step of automatically selecting an optimal depth range.

Global measurement of a property of a viscoelastic medium refers to repeating the measurement method previously defined in M measurements and enabling global calculation of the value of the property. The global computation may be performed using a median or mean type of mathematical function applied to the efficiently computed property values. Depth refers to the spatial direction extending within the viscoelastic medium of interest. For example, the depth is a direction corresponding to a propagation direction of ultrasound emitted during measurement of a property of the viscoelastic medium. When the medium is a human liver, the patient's skin corresponds to zero depth. Since the probe for elastography is in contact with the skin of the patient, the distance of the skin to the envelope of the liver corresponds to the distance of the probe to the envelope of the liver.

The calculated depth range refers to a depth interval in which the property is calculated. For example, if one or more ultrasound acquisitions are used to measure viscoelastic properties, the calculated depth range is the region in which the ultrasound signal detected and used to calculate the property is reflected.

The step of calculating a value of a property of the viscoelastic medium may comprise the step of measuring by transient elastography, the transient elastography comprising calculating an elastogram.

An elasticity map refers to the variation of a displacement parameter as a function of time and depth, which represents the propagation of a shear wave in a viscoelastic medium.

The calculating step may further comprise a series of ultrasound acquisitions comprising calculating a distance between the probe and a wall bounding the viscoelastic medium, each acquisition comprising transmitting an ultrasound pulse and detecting reflected ultrasound signals in real time. During the calculation step, the value of the viscoelasticity can be calculated in one depth range or in several possible depth ranges.

The validity criterion of the depth range refers to a criterion calculated from the distance between the ultrasonic probe and the wall of the viscoelastic medium. This distance is also referred to as the "probe-to-capsule distance" or PCD.

A depth range is defined as valid if it does not include a wall or surface of the viscoelastic medium. For example, if the viscoelastic medium to be characterized is a human or animal liver, it is defined as valid if the depth range does not include the liver envelope. That is, a depth range is defined as valid if it is completely within the medium to be characterized.

The validity criterion for the calculation of the properties of the viscoelastic medium refers to the criterion established on the basis of the elasticity map constructed by the ultrasound acquisition.

According to an embodiment, the validity criterion for the calculation of the property of the viscoelastic medium in a given depth range may take into account the quality of the shear wave propagation. It may correspond, for example, to a determined coefficient of a linear regression obtained from the propagation of the shear wave represented in the elastogram (see the article by Ultrasound in Medicine and Biology, volume 29, No. 12, 2003, page 3, or to the signal-to-noise ratio of the elastogram in these cases, the calculation of the property is considered valid within a given depth range only if the determined coefficient or signal-to-noise ratio is greater than a predetermined value.

If more than one depth range is valid, a selection criterion is applied to the values of the property calculated validly to automatically select the optimal depth range.

Advantageously, the method according to the invention enables to discard depth ranges that are not completely within the medium to be characterized. I.e. the calculation of the property is performed automatically within the organ or medium to be characterized.

Advantageously, the method according to the invention enables discarding values of the property of poor propagation quality of the shear wave on the elastogram. Therefore, the calculation of the propagation velocity of such shear waves is more reliable.

Advantageously, the method for automatically selecting the calculation depth range makes the measurement morphology adaptive. In fact, the depth range selected by the method according to the invention is automatically located within the organ, irrespective of the morphology of the patient.

Advantageously, the method for automatically selecting a depth range allows to avoid at least partially the dependency on the operator. I.e. the selection of the calculated depth range is no longer performed by the operator.

Advantageously, by means of the method according to the invention, the measurement will cover a larger area of the viscoelastic medium to be characterized.

Advantageously, when the viscoelastic medium is an organ, such as a human or animal liver, the examination is faster, especially for patients with large probe-to-organ wall distances or PCD.

If several depth ranges are valid, selection criteria are applied during the step of selecting in order to select a calculated depth range. There are several criteria for selecting a depth range.

The method according to the invention further comprises a step for determining the validity of the calculation of the property of the viscoelastic medium, the calculation being considered valid if it meets the validity criterion calculated from the mass of the elasticity map.

The depth range selection criterion is applied only to at least one valid depth range in which the calculation of the value of the property is valid.

The method is implemented each time M is newly measured. In carrying out the method, the property of the viscoelastic medium is calculated at least 1 times and at most P times.

During the step of determining the validity of the computed depth ranges, the validity of each of the P depth ranges is determined for each new measurement M.

During the step of determining the validity of the calculation of the property of the viscoelastic medium, the validity of each calculation of said property is determined for each new measurement M.

According to an embodiment, the selection criterion is based on the last measurement only. That is, the method according to the invention only considers the information available at the last measurement to select the depth range.

In this case, the depth range selected in the step of selecting may be a depth range in which the maximum signal-to-noise ratio is observed in the calculated elasticity map.

According to an embodiment, the depth range selected in the step of selecting is the depth range in which the elasticity map has the best quality.

According to an embodiment, the depth range selected in the selecting step is a depth range that meets a criterion calculated from homogeneity of the medium. Homogeneity of the medium may be measured from a series of acquisitions of the ultrasound signal.

Advantageously, these criteria enable the selection of a depth range in which the shear wave propagates appropriately.

According to an embodiment, if the calculation of the property of the viscoelastic medium in one depth range is not valid, the next depth range is selected until a valid property calculation is obtained. If no valid property calculation is characterized as valid in all valid depth ranges, a new measurement is performed, otherwise at least one of the previous selection criteria must be met. This allows viewing a larger portion of the organ and optimizes examination time.

According to an embodiment, the selection criterion is based on the complete set of measurements made. That is, the method according to the invention takes into account the available information from the first measurement to the last measurement to select the depth range.

According to an embodiment, the depth range selected in the step of selecting is the depth range that results in the most number of valid property calculations out of the M measurements taken.

According to an embodiment, the depth range selected in the step of selecting is a depth range that minimizes the dispersion of the M calculated values in each range. For example, the dispersion of the calculated values may be given by the interquartile range or by the standard deviation of the calculated values.

According to an embodiment, the depth range selected in the step of selecting is the depth range that results in the best signal-to-noise ratio over the computed M elasticity maps.

According to an embodiment, the depth range selected in the step of selecting is a range in which the calculated M elasticity maps have the best quality.

Advantageously, the quality of the elasticity map reflects good propagation of the shear wave over the depth range of the viscoelastic medium.

According to an embodiment, the depth range selected during the step of selecting is a depth range that meets a criterion calculated from homogeneity of the medium.

Homogeneity of the medium can be measured from a series of ultrasound signal acquisitions.

The method according to the invention for automatically selecting a depth range when measuring properties of a viscoelastic medium may also have one or more of the following features, considered individually or in any technically possible combination:

-each depth range is bounded by a first depth and a second depth and is defined as valid if the distance between the probe and the wall bounding the viscoelastic medium is smaller than the first depth and the second depth;

-defining the calculation of the property of the viscoelastic medium as valid within the considered depth range if the calculation of the property of the viscoelastic medium meets the validity criterion calculated from the masses of the elasticity map;

-calculating, during the step of calculating, a property of the viscoelastic medium in at least one of the P possible depth ranges;

-in the step of calculating, calculating a property of the viscoelastic medium from M measurements carried out in at least one of the P possible depth ranges, M being an integer greater than or equal to 2;

the criteria for selecting the calculation depth range are based only on the last measurement made;

-the depth range selected in the step of selecting is the depth range in which the computed elasticity map has the highest signal-to-noise ratio;

-the depth range selected in the step of selecting is the depth range in which the elasticity map has the best quality;

-the depth range selected in the step of selecting is a depth range that meets a criterion determined according to homogeneity of the medium;

-the selection criterion is based on the complete set of measurements made;

-the depth range selected in the selecting step is the depth range that minimizes the dispersion between the values calculated for the property during the calculating step;

-the selected depth range is the depth range that maximizes the number of valid calculations of the property;

-the depth range selected in the step of selecting is the depth range in which the computed elasticity map has the highest signal-to-noise ratio;

-the depth range selected in the step of selecting is the depth range in which the elasticity map has the best quality;

-the selected depth range is a depth range that meets a quality criterion determined from homogeneity of the medium;

-if the value of the viscoelasticity already calculated in the depth range is not valid, performing the calculation of the property for the deeper range;

-selecting a shallower range if at least two depth ranges meet the selection criterion during the step of selecting;

-selecting a deeper range if at least two depth ranges meet the selection criterion during the step of selecting;

the validity criterion of the depth range is binary and can take a value corresponding to a valid depth range or a value corresponding to an invalid depth range;

the validity criterion of the property calculation is binary and can take a value corresponding to a valid calculation or a value corresponding to an invalid calculation;

-the property of the viscoelastic medium is selected from the group comprising: elasticity of the viscoelastic medium, young's modulus of the viscoelastic medium, propagation velocity of shear waves within the viscoelastic medium, shear modulus, ultrasonic attenuation parameter, or a combination of the above properties;

-the validity criterion of a depth range is a binary indicator, which is equal to 1 if the depth range is valid and equal to 0 if the depth range is not valid;

the validity criterion of the property calculation is a binary indicator, which is equal to 1 if the calculation is valid and equal to 0 if the calculation is not valid.

A second object of the invention is a method for global measurement of at least one property of a viscoelastic medium. The global measurement method comprises a first step of automatically selecting a calculated depth range using the automatic selection method according to the invention. The values of the property of the viscoelastic medium calculated in the step of selecting the depth range are stored, for example, in a memory.

The global measurement method further comprises a second step of globally calculating a property value of the viscoelastic medium from the property values effectively calculated within the selected depth range, the global calculation being performed using a mathematical function of the median or mean type.

The global computation may be performed using a median or mean type mathematical function. According to an embodiment, the first step of automatically selecting a depth range is repeated for each new measurement, for a valid depth range and for a valid calculated property value.

In the case where the depth range selection is based only on the last measurement, the median or mean of all the property values that are effectively calculated within the previously selected and potentially different depth range is calculated as the global property value of the viscoelastic medium. In each new measurement, the selected depth range is independent of the previous depth range.

In the case where a depth range is selected based on all measurements made, the median or mean of all property values that are effectively calculated within the same depth range will be calculated as the global value of the viscoelastic medium property. The property of the viscoelastic medium is selected from the group comprising: elasticity, Young's modulus, shear rate within a viscoelastic medium, ultrasonic attenuation parameters, or a combination of the foregoing.

A third object of the present invention is an apparatus for measuring the viscoelastic properties of a viscoelastic medium with automatic selection of a calculation depth range, said apparatus comprising:

a probe for elastography;

a computing device comprising at least a memory and a microprocessor; the apparatus is constructed and arranged to:

calculating the distance between the probe and the wall delimiting the viscoelastic medium from the ultrasound signals acquired using the probe and the calculation means for elastography;

calculating the property of the viscoelastic medium in at least one of the P possible calculation depth ranges from the ultrasound signals acquired using the probe and the calculation means for elastography;

determining the validity of at least one of the P calculated depth ranges, a calculated depth range being considered valid if it satisfies a validity criterion calculated from the distance between the probe and the wall delimiting the viscoelastic medium;

determining the validity of a calculation of the value of the property of the viscoelastic medium within one or more valid depth ranges, the calculation being considered valid if it satisfies a validity criterion determined from the quality of the elasticity map;

selecting a depth range satisfying a predetermined selection criterion among the valid depth ranges comprising values of the at least one valid calculated property;

calculating a global value of the viscoelastic property from the values of the property effectively calculated within the selected depth range, said global value being calculated using a mathematical function of the median or mean type.

Advantageously, the device according to the invention allows measuring the viscoelastic properties of a viscoelastic medium by automatically selecting an optimal calculation depth range. The automatic selection of the depth range is performed using the depth range selection process according to the present invention. This makes the measurement of viscoelastic properties reliable, reproducible and independent of the operator.

The device according to the invention may also have one or more of the following features, considered alone or in any technically feasible combination:

the probe for elastography is a probe for transient elastography;

the device according to the invention and the computing means are comprised in the probe for elastography;

the device according to the invention further comprises means for displaying the measurement results. For example, the display device is configured to display the measured elasticity map, the selected depth range for the measurement, and the measured value of the viscoelastic property.

Drawings

Other characteristics and advantages of the invention will become clear from the following description thereof, given by way of illustration and not of limitation with reference to the accompanying drawings, in which:

fig. 1 shows the distribution of the acoustic power of an ultrasound wave propagating within the viscoelastic medium of interest during a measurement of the instantaneous elastography type, the operator being able to select between two depth ranges S1 and S2;

fig. 2 shows the measurement of the properties of a viscoelastic medium, such as a liver, according to the prior art: calculating the depth range may include walls of the medium;

figure 3 schematically shows the steps of the method according to the invention;

figure 4 shows an optimal choice of calculating a depth range when measuring properties of a viscoelastic medium according to the invention;

figures 5a to 5d show examples of validation for different probe-to-capsule distance PCD depth ranges;

figures 6a and 6b show examples of verification of the calculation of the value of the property of the viscoelastic medium in the range of P-3 depths;

figures 7a and 7b show an example of the calculation of the value of a property and the verification of the automatic selection of a calculated depth range, with P-3 possible depth ranges for implementing the method according to the invention, in which the validity criterion can be based on only the last measurement or on all measurements made;

figure 8 schematically shows the steps of a method for globally measuring a property of a viscoelastic medium by automatically selecting a calculation depth range and a value of a globally calculated property;

fig. 9 summarizes the method PRO of automatically selecting a calculation depth range according to different selection criteria.

Detailed Description

Fig. 3 schematically shows the steps of the method PRO according to the invention.

The method PRO according to the invention comprises the following steps:

a CALC step of calculating viscoelastic properties in at least one of the P possible depth ranges from the ultrasound signals acquired using the probe for elasticity imaging. In this step, the property may be calculated in a single depth range or in several depth ranges; during this step, the ultrasound signals acquired by the probe for elastography are used to calculate the distance PCD between the probe for elastography and the wall of the viscoelastic medium;

-a step TEST PCD, verifying a calculated depth range in which the viscoelastic properties have been calculated. Defining a depth range as valid if it meets a criterion calculated from the distance between the probe and the wall of the medium or the "probe-to-envelope distance" PCD;

-a step TEST _ VAL, verifying the calculation of the values of the viscoelastic medium property values within one or more valid calculation depth ranges. During this step, a validation criterion is applied to each calculation of viscoelastic properties to determine its effectiveness. The calculation is considered valid if it meets the validity criterion calculated from the quality of the elastic map. For example, a calculation is considered valid if the quality of the elastic map measured in the calculated depth range is sufficiently high. That is, if the signal-to-noise ratio of the measured elastogram is sufficiently high, the calculation is considered valid;

-a step SEL of selecting a depth range from the valid depth ranges comprising at least one valid calculation according to a selection criterion. The selection criterion may be based only on the last measurement made or all measurements made. That is, if the calculation step CALC comprises performing a single measurement, the selection criterion is based only on the last or current measurement. If the calculation step CALC comprises taking a plurality of measurements, the selection criterion may take into account the different measurements taken, i.e. the history of the measurements taken.

These steps may be performed in the order shown in fig. 3 or in a different order. All or some of the steps may be performed in parallel.

According to an embodiment, the selection criterion for calculating the depth range is based only on the current measurement. In this case, the selection of the optimal depth range takes into account only the information provided by the last measurement performed.

The depth range selected in the selection step SEL may be:

-observing a depth range of optimal signal-to-noise ratio in the measured elastogram;

-observing the best propagation of the shear wave on the elastogram, i.e. the depth range of the best-quality elastogram;

-depth range where maximum homogeneity of the medium is observed.

Advantageously, these depth range selection criteria make it possible to select among the depth ranges within the medium, a depth range in which the shear wave propagates correctly or a depth range corresponding to greater homogeneity of the organ.

According to another embodiment, the depth range selection criterion is based on a history of measurements made. In this case, the selection of the optimal depth range takes into account the information provided by all measurements made.

The selected depth range may be:

-a depth range with the highest number of valid measurements out of the M measurements made;

-observing a minimum discrete depth range between the calculated property values in the M measurements made;

-a depth range satisfying criteria calculated from homogeneity of the environment;

-observing the depth range of the best average or median signal-to-noise ratio in the elastogram in the M measurements performed;

the depth range at which the best shear wave propagation (which is the best average or median quality criterion among the M measurements performed) on the elastogram is observed;

the depth range in which the maximum average or median homogeneity of the medium is observed in the M measurements performed.

The first CALC step comprises calculating a property of the medium in at least one of the P possible depth ranges, the calculation being performed on the basis of the ultrasound signals acquired by the ultrasound probe during the measurement. According to an embodiment, the calculation is repeated M times in at least one of the P ranges.

The property measured may be a viscoelastic property, such as the propagation velocity of a pulsed shear wave or the elasticity of the medium. In this case, the measurement is a transient elastography measurement.

The measured property may be an ultrasound property, such as a Controlled Attenuation Parameter (CAP). In this case, the measuring comprises generating a series of ultrasound acquisitions.

During step TEST _ PCD, the validity of each calculated depth range is determined. Each calculated depth range is considered valid only if the validity criterion satisfies a predetermined condition.

The depth range validity criterion may be binary and have a first value corresponding to a valid range and a second value corresponding to an invalid range.

According to an embodiment, a depth range validity criterion is determined from the reflected ultrasound signal, from which a distance between the ultrasound probe and a wall of the viscoelastic medium is calculated. This distance is also referred to as the "probe-to-capsule distance" or PCD.

A depth range is defined as valid if it does not include a wall or surface of the viscoelastic medium. For example, if the viscoelastic medium to be characterized is a human or animal liver, it is defined as valid if the depth range does not include the liver envelope.

Advantageously, such validity criterion makes it possible to retain only the measurements that are completely comprised within the medium to be characterized.

During a step TEST _ VAL, the validity of the calculation of the value of the property of the viscoelastic medium within one or more valid calculation depth ranges is determined. That is, the validity of each calculated value is determined each time M is newly measured. Each calculation is considered valid only if the validity criterion satisfies a predetermined condition. The computational validity criterion may be binary and have a first value corresponding to a valid measurement and a second value corresponding to an invalid measurement.

According to an embodiment, the measurement validity criterion is defined in terms of a pulse elasticity map.

Elastograms are images used to visualize the propagation of shear waves during a pulse elastography measurement. The elastogram is defined by a two-dimensional matrix and provides a spatio-temporal representation of the displacements generated by the propagation of shear waves in the medium.

For example, a validity criterion may be established based on the quality of the measured pulse elastogram. The estimate of the quality of the pulse elastogram may be provided by the signal-to-noise ratio of the pulse elastogram. Its effectively calculated property value is then a measurement using a pulse elastogram having a signal-to-noise ratio above a predetermined threshold.

The calculation of the property of the medium in the range of the invalidation depth is automatically considered invalid.

Advantageously, such validity criterion makes it possible to discard measurements corresponding to low-mass pulse elastograms, for example due to poor positioning of the probe or poor propagation of transient shear waves within the viscoelastic medium.

During step SEL, an optimal depth range is selected from the one or more property values that are actively calculated. The depth range is defined as optimal if it meets the applied best selection criteria.

Advantageously, this step allows to automatically select an optimal depth range for measuring the properties of the medium.

Fig. 4 shows the choice of a calculated depth range according to the invention when the viscoelastic medium is the liver F and the validity criterion for the depth range (i.e. the probe-to-capsule distance PCD between the patient' S skin S and the liver wall) is determined from the ultrasound measurements. The horizontal axis in the figure represents the depth Pr measured from the patient' S skin S.

In the case shown in fig. 4, the probe-to-capsule distance PCD measured by one or more ultrasound acquisitions is 38 mm.

The calculated depth range P has a lower limit Pi and an upper limit Ps. In the case of fig. 4, Pi is 45mm, and Ps is 85 mm.

To obtain an effective depth range, the calculated depth range P is chosen such that its lower limit Pi is strictly greater than the probe-to-capsule distance PCD, Pi > PCD.

That is, if Pi > PCD, the validity criterion takes a value corresponding to the valid depth range. Otherwise, the validity criterion takes a value corresponding to the invalid depth range.

In order to improve the reliability of the validity criterion of the depth range, a transition region Tr may be introduced. The validity condition of the depth range in the depth range P then becomes: pi > PCD + Tr.

In the example of fig. 4, the transition zone has a thickness of 5mm, Tr-5 mm.

Advantageously, the use of validity criteria according to the depth range defined by the capsule-to-probe distance PCD ensures that the calculated depth range is fully included within the medium to be characterized.

That is, the use of validity criteria according to the depth range defined by the PCD probe-capsule distance enables measurement errors caused by the walls of the viscoelastic medium within the measurement zone to be avoided.

Fig. 5a, 5b, 5c and 5d show the validation of the measured depth range of the elastic properties of the liver F when there are three possible depth ranges. The three depth ranges represented have the following depths:

-between 35mm and 75mm P [35-75 ];

-between 40mm and 80mm P [40-80 ];

-P [45-85] between 45mm and 85 mm.

Fig. 5a corresponds to a probe-to-capsule distance PCD-26 mm. Using the quality criteria for the depth range shown with reference to FIG. 4, the result was 35mm > PCD + Tr, with 35mm being the lower limit of the shallower range. In this case, all three depth ranges correspond to the effective depth range VA.

Fig. 5b corresponds to a probe-to-capsule distance PCD of 32 mm. Using the quality criteria shown with reference to FIG. 4, the result was 35mm < PCD + Tr < 40 mm. The depth range P [35-75] has a lower limit equal to 35mm and thus corresponds to the ineffective depth range NVA. This is because the depth corresponding to PCD + TR 37mm falls within the range of P [35-75 ]. That is, the measurement of the properties of the liver corresponding to the range P [35-75] will change due to the presence of the liver wall and the transition region Tr. On the other hand, the depth ranges P [40-80] and P [45-85] correspond to valid depth ranges, since they are completely included in the environment F to be characterized.

Fig. 5c shows the case where the probe-envelope distance PCD is 38 mm. The depth PCD + Tr 43 is greater than the lower limits of the ranges P [35-75] and P [40-80 ]. Thus, these two depth ranges correspond to the invalid depth range NVA. In the case shown in FIG. 5c, only range P [45-85] corresponds to the effective depth range VA.

Figure 5d shows the case where the probe-to-capsule distance PCD is 60 mm. In this case, none of the depth ranges corresponds to the effective depth range VA.

Fig. 6a shows a step TEST _ VAL of determining the validity of the calculation of the value of the property of the viscoelastic medium in one or more valid calculation depth ranges. For each measurement M, a calculation quality criterion is calculated in one or more valid depth ranges.

The validity criterion for the property calculation is established from the quality criterion of the pulse elastogram E.

Fig. 6b shows an example of verification of the calculation of the value of the property of the viscoelastic medium in the form of a table constructed from an elasticity map such as that represented in fig. 6 a. The construction of a table such as that shown in fig. 6b is an embodiment of the step TEST _ VAL of determining the validity of each calculation of a property as a function of the valid depth range.

The table in fig. 6b shows that three possible depth ranges are included: p35-75, P40-80 and P45-85, respectively, in the case of measuring the sequence of #1, #2, # 3.

The solid line represents the depth of the probe to capsule distance PCD + Tr at measurement # i.

The rows in the table show the binary significance results of the calculations for the properties of each depth range P. The lower line of each line corresponds to the boundary depth at which the depth range becomes invalid. When the depth range is invalid, determination of the property calculation validity criterion is not made, and it is defined as invalid.

This table shows the valid conditions for the calculation of the value of the viscoelastic property according to the change in the PCD value.

The validity criterion for the property calculation in fig. 6b is binary and may take two values "o" and "x". The value "o" corresponds to valid calculations within a given depth range and the value "x" corresponds to invalid calculations. Invalidity of the depth range is indicated by the abbreviation "NVA", meaning that the PCD capsule probe distance does not satisfy the previously defined condition: pi > PCD + Tr.

The property values of the calculated validity criterion show that measurement #1 is valid in the depth range P [40-80] and not valid in the other two depth ranges P [35-75] and P [45-85] indicating poor quality of the elasticity map.

The value of the depth range criterion indicates that measurement #2 is not valid in all depth ranges. The position of the black solid line shows the presence of liver capsule within the possible depth range when the measurement is performed.

The values of the validity criteria for the depth range show that measurement #3 is not valid in the depth range P [35-75] (shallower depth range). The computational ineffectiveness of property #3 corresponding to the depth range P [35-75] is caused by the presence of the liver envelope within this depth range.

The steps of determining the depth range validity TEST _ PCD and measuring TEST _ VAL are typically performed using computing means, such as a memory and a microprocessor present in the apparatus for making the measurements.

The step SEL of automatically selecting the depth range that meets the best selection criteria when the selection of the best range is based only on the current measurements is shown in fig. 7 a.

Fig. 7a shows the case where M is measured 6 times repeatedly over 3 possible ranges. Two tables represent the measurement history of the validity criterion at the time of measurement #3 and #6 in three depth ranges.

Each column represents the values of the valid criteria for the calculation of the value of the property of the viscoelastic medium calculated for a given measurement # i, each row corresponding to one of the three possible depth ranges.

Within a given depth range, the property computation may be invalidated by an invalid depth range or by an elasticity map quality criterion below a predetermined threshold.

For each measurement, the automatic selection of the depth range is independent of previous measurements, and the selected depth range appears as a bright background in the table. The history of selecting the optimal depth range is constant from one measurement to the next.

The mean or median value of the property of the viscoelastic medium is calculated from all the effective values of the property of the viscoelastic medium over the possible different depth ranges.

The step SEL of automatically selecting the depth range that meets the best selection criteria when selecting the best range based on history or all measurements is shown in fig. 7 b.

Fig. 7b again considers the example of fig. 7a, representing the case where the measurement M is repeated 6 times within 3 possible ranges. Two tables represent the history of the measurement validity criteria at measurements #3 and #6 in three depth ranges.

Each column represents the value of the valid criterion for the calculation of the property value calculated for a given measurement # i, each row corresponding to one of the three possible depth ranges.

Within a given depth range, the property computation may be invalidated by an invalid depth range or by an elasticity map quality criterion below a predetermined threshold.

For each measurement, a depth range is automatically selected and the selected depth range appears on a light background in the table. The history of depth range selections is updated from one measurement to the next. The depth range selected from all previous measurements is replaced by the optimal depth range of the last measurement.

For example, in measurement #3, a deeper depth range P [45-85] is selected for all measurements #1 to # 3. At measurement #6, the range P [40-80] satisfies the best selection criteria, and all previous range selections are updated and replaced with the same depth range P [40-80 ].

The mean or median value of the viscoelastic medium properties is calculated from all the effective property values within the same depth range.

According to an embodiment, if two or more depth ranges provide the same best selection criteria in the SEL selection step, a shallower depth range is selected.

Advantageously, this allows to select the depth range closest to the ultrasound transducer and thus the depth range with the highest signal-to-noise ratio.

Alternatively, according to another embodiment, a deeper depth range is selected.

Advantageously, this allows the depth range furthest from the liver envelope to be selected.

The selection step SEL is typically performed using computing means, such as a memory and a microprocessor present in the device for taking measurements.

Fig. 9 graphically summarizes the step TEST _ PCD of verifying the depth range, the step TEST _ VAL of verifying the calculation of the value of the property of the viscoelastic medium and the step SEL of selecting the optimal depth range.

According to an embodiment, the selection SEL of the optimal depth range is based only on the current measurement.

In another embodiment, the selection of the optimal depth range SEL is based on a history of measurements made.

Fig. 8 schematically shows method steps for globally measuring a property of a viscoelastic medium with an automatic selection of a calculated depth range, which is performed using a method PRO according to the invention.

The measuring method comprises a first step a of automatically selecting a calculation depth range using the method PRO according to the invention. In step a, the measured values of the viscoelastic properties are stored in a memory.

The global measurement method further comprises a second step B of global calculation of the viscoelastic properties according to the values calculated in step a. The global computation may be performed using a mean or median type function.

According to an embodiment, in step B, the property of the viscoelastic medium is calculated from the values of the property effectively calculated and already calculated in step a.

If the method PRO comprises performing M measurements, a global calculation of the property of the viscoelastic medium is performed on the basis of the values of the property calculated efficiently and performed in the previously selected depth range or ranges. For example, the property value of the viscoelastic medium is an average or median of the property values that are effectively calculated and obtained over the selected depth range or ranges.

In fact, in the case of depth range selection based only on the current measurement, once the depth range of the last measurement is selected, the global value of the measured property is determined using M measurements corresponding to the independent depth ranges. For example, the global measure may be an average of the values calculated corresponding to the selected range.

In the case of depth range selection based on the history of measurements made, once the depth range of the last measurement is selected, the global value of the property is determined using the property values of the M measurements corresponding to the last selected range. For example, the global value may be an average of the values calculated corresponding to the selected range. Advantageously, the global measurement method according to the invention makes it possible to improve the reproducibility and reliability of the measurement of viscoelastic properties by selecting efficiently calculated property values within one or more optimal depth ranges for the measurement.

According to the invention, the measurements necessary for the implementation of the method for automatically selecting a depth range and measuring properties of a viscoelastic medium can advantageously be used in the context of transient elastography measurements, for example To the apparatus of (1).

In this case, the property of the viscoelastic medium is selected from the group comprising: elasticity, young's modulus, shear modulus, speed of propagation of shear waves in a viscoelastic medium.

The P possible ranges are set within the range of ultrasound acquisition depths in which the medium is observed. The field of view depends on the nature of the probe used in the examination. As shown in fig. 1, there are several options for measuring the range P of depths.

Each measurement M implementing the method PRO according to the invention comprises monitoring the propagation of a transient shear wave within the viscoelastic medium to be characterized. To this end, during measurement # i, a transient elastogram E is created from the ultrasound signals acquired during the transient pulse elastography measurement. The elasticity map E makes it possible to measure one of the above-mentioned elastic properties and to determine the validity criterion for the calculation of the property within a defined depth range.

During propagation of the instantaneous shear wave, ultrasound acquisitions are generated at a high repetition rate to monitor the propagation of the instantaneous shear wave. The reflected signal may also be used to determine the probe-to-capsule distance. The value of the probe-to-capsule distance allows the validity criterion for the depth range to be calculated.

The step of automatically selecting a depth range is performed using a computing means comprised in the apparatus for performing transient elastography measurements. The computing device includes, for example, a memory and a microprocessor. The memory is configured to store the results of the M measurements made and the values of the various validity criteria calculated by the microprocessor.

The apparatus for performing transient elastography measurements further comprises means for displaying the results of the method such as the selected calculated depth range or the property value of the viscoelastic medium.

Alternatively, the property of the medium may be an ultrasound attenuation parameter, such as a Controlled Attenuation Parameter (CAP).

A third object of the invention is an apparatus for measuring a property of a viscoelastic medium by automatically selecting a calculation depth range using the method according to the invention, said apparatus comprising:

a probe for elastography;

a computing device comprising at least a memory and a microprocessor; the apparatus is constructed and arranged to:

calculating the distance (PCD) between the probe and the wall delimiting the viscoelastic medium from the ultrasound signals acquired using the probe and the calculation means for elastography;

calculating the property of the viscoelastic medium in at least one of the P possible calculation depth ranges from the ultrasound signals acquired using the probe and the calculation means for elastography;

determining the validity of at least one of the P calculated depth ranges, a calculated depth range being considered valid if it satisfies a validity criterion calculated from the distance between the probe and the wall delimiting the viscoelastic medium (PCD);

determining the validity of a calculation of the value of the property of the viscoelastic medium within one or more valid depth ranges, the calculation being considered valid if it satisfies a validity criterion determined from the quality of the elasticity map;

selecting a depth range satisfying a predetermined selection criterion among valid depth ranges comprised of at least one valid calculation;

calculating a global value of the viscoelastic property from the values of the property effectively calculated within the selected depth range, said global value being calculated using a mathematical function of the median or mean type.

A probe for elastography refers to a probe having at least one ultrasound transducer. An example of a probe for elastography is a probe for performing a transient elastography method.

The device is configured to implement a method according to the invention for automatically selecting a calculation depth range and calculating a global value of a property of a medium within the selected depth range.

According to an embodiment of the apparatus of the present invention, the computing device is comprised in a probe for elastography.

According to an embodiment, the device according to the invention further comprises means for displaying the measurement results. For example, the display device is configured to display the measured elasticity map, the depth range selected for the measurement, and the measured viscoelastic properties.

Fig. 9 summarizes the method PRO for automatically selecting a calculation depth range according to the invention.

During step CALC, the properties of the viscoelastic medium and the distance PCD between the probe and the wall of the viscoelastic medium are calculated using an ultrasound probe or probes for elastography. Properties of the viscoelastic medium and the PCD are calculated from the ultrasonic emissions emitted by the probe and the ultrasonic waves reflected by the medium and detected by the probe.

During step TEST _ PCD, the validity of the calculated depth range of the viscoelastic property is checked. A range is considered valid if it is fully included in the viscoelastic medium, i.e. if the distance from the probe to the wall of the medium is less than the limits of the depth range, PCD < Pmin.

According to an embodiment, if no depth range is valid, the calculation of the property value of the viscoelastic medium is performed at the next depth range. Alternatively, the PRO method is stopped.

During step TEST _ VAL, the validity of the calculation of the value of the property of the viscoelastic medium corresponding to the range of valid depths is checked. The calculation is defined as valid based on the quality of the elasticity map associated with the measurement.

In step SEL, a depth range is selected from the valid depth ranges having at least one valid property calculation. The selection of the depth range is made according to predetermined criteria.

Fig. 9 shows two embodiments of the selection step SEL.

According to a first embodiment, the choice of calculating the depth range is based only on the current or last measurement performed. In this case, if several depth ranges include values of a property that are effectively calculated, one of the following selection criteria is applied to select a depth range:

the best signal-to-noise ratio of the elasticity map in all depth ranges;

optimal shear wave propagation (quality criterion) on the elastogram in all depth ranges;

the best homogeneity criterion (LTT) in all depth ranges.

This embodiment is also shown in fig. 7 a.

In a second embodiment, the choice of calculating the depth range is based on history or all measurements made. In this case, the selected depth range meets one of the following criteria:

the number of values of the property that are effectively calculated is maximum;

the minimum dispersion of the mean or median of the properties;

the best average or median signal-to-noise ratio of the elasticity map in all depth ranges;

the best shear wave propagation (mean or median quality criterion) on the mesoelastic plots for all depth ranges;

the best average or median homogeneity criterion (LTT) in all depth ranges.

This embodiment is also shown in fig. 7 b.