PORTABLE ULTRASONIC MEASURING DEVICE SUITABLE FOR MEASURING PELVIC TILT

Abstract

An ultrasound measuring device includes: a support bearing two ultrasound probes movable relative to each other by slide link, each of the two probes being movable relative to the support by ball-joint link, wherein the probes are capable of simultaneously acquiring two ultrasound images. The device includes a first set of measuring elements to measure a relative positioning of the probes, including one travel sensor and at least two orientation sensors. The device includes a second set of measuring elements to measure a positioning of the device relative to a reference plane, including at least one orientation sensor. The device localizes at least one point of interest on each of the two ultrasound images, and processes data coming from the first and second measuring elements, delivering a relative spatial position of the points of interest located in the images.

Claims

1. An ultrasound measuring device comprising: a support bearing first and second ultrasound probes movable relative to each other by slide link, each of the first and second probes being movable relative to the support by ball-joint link, said probes being capable of simultaneously acquiring first and second ultrasound images; a first set of measuring elements for measuring a relative positioning of said probes, comprising a travel sensor and at least two orientation sensors; a second set of measuring elements for measuring a positioning of said device relative to a reference plane, comprising at least one orientation sensor; a localizer, which is configured to localize at least one point of interest on each of said first and second ultrasound images; and a processing device, which is configured to process data coming from said first and second sets of measuring elements and deliver a relative spatial position of said at least one point of interest located in said first and second ultrasound images.

2. The ultrasound device according to claim 1, wherein said first and second ultrasound images comprise a first ultrasound image of an upper right-hand or left-hand zone of an individual's iliac bone and a second ultrasound image of a lower zone of said iliac bone, respectively, and said at least one point of interest comprises an anterior-superior iliac spine and a public symphysis of said individual, and said device comprises means to determine a pelvic tilt of said individual on the basis of said relative spatial position of said at least one point of interest.

3. The ultrasound device according to claim 1, wherein said localizer for localizing said at least one point of interest comprises means for processing said ultrasound images by segmentation capable of detecting said at least one point of interest in said ultrasound images.

4. The ultrasound device according to claim 3, wherein said means for processing said first ultrasound image comprise means for identifying a longer segment in said first ultrasound image, means for adjusting a parabola on said segment and means for detecting said at least one point of interest as a vertex of said parabola.

5. The ultrasound device according to claim 3, wherein said means for processing said second ultrasound image comprise means for identifying a segment in said second ultrasound image, means for determining an axis of symmetry in said second ultrasound image, means for adjusting a straight line on said segment and means for detecting said point of interest as an intersection of said axis of symmetry and of said straight line.

6. The ultrasound device according to claim 3, further comprising comprises means of validation, by a user of said device, of said at least one point of interest detected by said localizer.

7. The ultrasound device according to claim 1, wherein said ultrasound device comprises a screen enabling said ultrasound images to be viewed.

8. The ultrasound device according to claim 7, wherein said screen is fixed to said support by an adjusting ball joint.

9. The ultrasound device according to claim 1, wherein the localizer comprises means for selecting said at least one point of interest on the screen by a user of said device.

10. The ultrasound device according to claim 1, wherein at least one of said probes is connected to said support by a spherical link.

11. The ultrasonic device of claim 1, wherein: the support bears two ultrasonic probes, comprising the first and second ultrasound probes; and the first set of measuring elements comprises one travel sensor, recited in claim 1.

Description

4. LIST OF FIGURES

[0045] Other goals, features and advantages of the invention shall appear more clearly from the following description of a preferred embodiment given by way of a simple illustratory and non-exhaustive example, made with reference to the appended drawings, of which:

[0046] FIG. 1 is an overall view of the portable ultrasound measuring device in one embodiment of the invention;

[0047] FIG. 2 is a schematic illustration of the kinematics of the measuring apparatus of FIG. 1;

[0048] FIGS. 3A to 3C show the position of the pelvic plane relative to a reference plane, respectively in a standing position (FIG. 3A), a supine position (FIG. 3B) and seated position (FIG. 3C);

[0049] FIG. 4 illustrates the three anatomical landmarks necessary to determine the anterior pelvic plane of FIGS. 3A to 3C;

[0050] FIGS. 5A and 5B illustrate the ultrasound capturing of an anterior-superior iliac spine (FIG. 5A) and a pubic symphysis (FIG. 5B) by means of the measuring apparatus of FIG. 1;

[0051] FIG. 6 presents a geometrical diagram of the device for measuring the pelvic tilt in one embodiment of the invention;

[0052] FIG. 7 presents a flow chart, in the form of a block diagram, of the implementing of the measuring device of FIG. 1;

[0053] FIG. 8 presents an example of a positioning of the inertial measurement units on the measuring apparatus of FIG. 1;

[0054] FIG. 9 illustrates an example of a positioning of a travel sensor on the support of the measuring apparatus of FIG. 1;

[0055] FIGS. 10A and 1013 present the details of the attachment of the ultrasound probes to the support of the measuring apparatus of FIG. 1;

[0056] FIG. 11 presents the portable measuring apparatus of FIG. 1 in its carrying case;

[0057] FIG. 12 is a view, in the form of a block diagram, of the electronic architecture of the measuring apparatus of FIG. 1.

5. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0058] The general principle of the invention relies on the designing of a portable ultrasound measuring apparatus comprising two ultrasound probes and an integrated system for measuring the position of the probes. The localizing of the anatomical points of interest in the ultrasound images, combined with knowledge of the position of the probes, makes it possible to determine the relative spatial position of the anatomical points of interest. When such a measuring apparatus is used to measure an individual's pelvic tilt, it therefore makes it possible to obtain a direct, precise and reproducible measurement of the pelvic tilt by using a single, non-irradiating, compact apparatus that can be easily and speedily used by the clinician.

[0059] Here below in this document, we shall strive to describe an embodiment of the invention in the context of the operation of total hip replacement surgery. The portable ultrasound measuring device of the invention can however be advantageously used for other medical applications.

[0060] To begin with, FIGS. 3A to 3C and 4 serve to present a reminder of the definition of an individual's pelvic tilt. FIG. 4 presents the pelvic plane (XY) defined by the points corresponding to the two anterior-superior iliac spines 41 and 42 and to the pubic symphysis 43 on the iliac bone 44.

[0061] As can be seen in FIGS. 3A, 3B and 3C, the pelvic plane 31A, 31B, 31C can vary relative to a vertical or horizontal reference plane 32A, 32B and 32C. This dynamic behavior of the pelvis introduces modifications related to the functional orientation of the hip prosthesis and more particularly that of the acetabulum. It is therefore important to measure the pelvic tilt, i.e. the inclination of the patient's pelvic plane relative to the reference plane in different positions.

[0062] To this end, it is enough to locate three known points of the pelvis (namely the two iliac spines 41 and 42 and the pubic symphysis 43) defining the APP or anterior pelvic plan (XY).

[0063] Referring now to FIG. 1, an overall view is presented of the portable, ultrasound measurement device of the invention.

[0064] Such a measuring apparatus enables the easy and speedy measurement of the pelvic tilt in different positions of daily life, in order to integrate it into the scheduling of a total hip replacement operation. The use of such an apparatus must make it possible to reduce the number of operations of revision surgery and thus improve the quality of life of patients.

[0065] Such a measurement is done by means of the ultrasound probes during pre-operative consultation in at least three positions (for example the standing, seated and supine positions). When it is done by means of the portable ultrasound device in one embodiment of the invention, its main characteristics are that it is: [0066] Reliable [0067] Autonomous [0068] Fast [0069] Precise [0070] Simple to use.

[0071] As illustrated in FIG. 1, the ultrasound apparatus consists of a support 10, which takes the form of an arm, and two ultrasound probes 11.sub.1 and 11.sub.2 mounted on the support 10. A screen 12 is also integrated into the ultrasound apparatus for the purpose of viewing the images of the anatomical sites acquired by the probes. This screen also serves as an interface between the apparatus and the practitioner. For this screen 12 to be speedily pivotable, and so that the user can have it permanently in his field of vision, it is mounted on the support 10 by means of an adjusting ball joint, comparable for example to that of a camera tripod.

[0072] In addition, the probes 11.sub.1 and 11.sub.2 are movable relative to each other along a slide link, to enable the practitioner to adjust the distance between them. Moreover, they are mounted relative to the support 10 with a ball-joint link for the probe 11.sub.1, and with a ball-joint link and slide link for the probe 11.sub.2.

[0073] It is indeed necessary that the two probes should be easily adaptable to the patient's morphology in all three positions, standing, seated and supine, whatever the patient's body mass. Preferably, the spacing between the probes 11.sub.1 and 11.sub.2 is chosen so that it can vary between about 10 cm and 25 cm.

[0074] The apparatus is handled by taking the probes 11.sub.1 and 11.sub.2 directly by hand. Thus, the mechanism of the apparatus (support 10, screen 12 and hinges) are situated above the practitioner's hands and therefore do not hamper the handling of the apparatus.

[0075] FIG. 2 gives a schematic view of the kinematics of the apparatus of FIG. 1. The kinematic capacities of the ball-joint socket links between the probes 11.sub.1 and 11.sub.2 and the support 10 are created by means of links 21.sub.1 and 21.sub.2 with concave and convex spherical surfaces. It is indeed desirable that the probes should have six degrees of freedom relative to each other.

[0076] FIGS. 10A and 1013 provide a more detailed illustration of an embodiment of this kinematics. Thus, the mobility of the probe 11.sub.1 relative to the support 10 is ensured by means of the ball-joint link 21.sub.1 while the mobility of the probe 11.sub.2 relative to the support 10 is ensured by means of the ball-joint link 21.sub.2 and a slide link 22. This slide link referenced 22 ensures the translation between the right-hand and left-hand parts of the apparatus.

[0077] This architecture enables the practitioner to easily adjust the probes to the anatomical sites of interest for the measurement of pelvic tilt, namely the pubic symphysis and the iliac spines. This architecture is moreover compact, robust and stable.

[0078] In addition, in order to localize the two probes 11.sub.1 and 11.sub.2 relative to each other, the orientation and the distance between the two probes must be measured. It is indeed necessary to know the position of the two probes relative to each other when the practitioner is capturing the ultrasound images.

[0079] The embodiment of FIG. 1 thus provides for three orientation sensors, also called inertial measurement units, fixedly attached to the probes 11.sub.1 and 11.sub.2 and to the support 10. Such sensors are, for example, inertial measurement units by OMNI Instruments (registered mark) of the LPMS-B motion sensor type. These instruments are compact and robust.

[0080] One solution for the position of the inertial measurement units 80.sub.2 and 80.sub.3 fixedly attached to the ultrasound probes 11.sub.1 and 11.sub.2 is illustrated in FIG. 8.

[0081] The translation between the two probes 11.sub.1 and 11.sub.2 is measured by means of a travel sensor 90, illustrated in FIG. 9. Such a travel sensor is for example the HC-SR04 (registered mark) ultrasonic sensor module which comprises an ultrasonic transmitter and receiver and deduces distance from the time of travel of the ultrasound. In the embodiment of FIG. 9, the transmitter and the receiver are fixedly attached to the element supporting the ball element of one of the probes. This element slides (slide link 22) in a chamber. The wall of this chamber, opposite that of the sensor reflects the ultrasounds. When the operator adapts the apparatus to the patient, he applies forces to each part of the apparatus, thus causing a translation of the two parts of the ultrasound measuring apparatus relative to each other, and enabling the sensor to detect the travel.

[0082] Finally, in order to know the position of the ultrasound measurement apparatus of the invention relative to the vertical, this apparatus also comprises an inertial measurement unit 80.sub.1, illustrated in FIG. 8. Such an inertial measurement unit is for example of the LPMS-B (registered mark) motion sensor type by OMNI Instruments. This instrument has very high 3D precision and is very compact. Such an inertial measurement unit 80.sub.1 can be placed at any point whatsoever of the structure of the apparatus 10. FIG. 8 illustrates an example of positioning of this inertial measurement unit 80.sub.1, which does not get in the way during handling and provides load-balancing for the apparatus.

[0083] The portable ultrasound apparatus of FIG. 1 must furthermore comprise an information-processing system that integrates the data coming from the position and orientation sensors described here above, and the position of the anatomical sites located in the ultrasound images, as described in greater detail here below. Such a processing system comprises especially one or more analyzers cooperating with the ultrasound probes 11.sub.1 and 11.sub.2 and an electronic calculator or computer.

[0084] The assembly is easy to transport for use in medical consultation, as illustrated in FIGS. 11 and 12. A case 110 serves on the one hand as a fixed stand to be placed beside the patient and on the other hand as a carrying case. It contains the fixed part 121 of the ultrasound measuring apparatus, namely the analyzers 121.sub.1 and 121.sub.2, as well as a battery 121.sub.3 (or electrical transformer), the electronic computer 121.sub.3, and a screen 121.sub.4. It is connected to the movable part 122 illustrated in FIG. 1 by a cord. A large touch screen 121.sub.4 fixed to the lid of the case 110 is used to enter the anatomical points with high precision as described in greater detail here below. The movable part 122 of FIG. 1 is light (weighing about one kilogram or less), making its handling easy and precise. As already described with reference to FIG. 1, this mobile part comprises the viewing screen 12, the ultrasound probes 11.sub.1 and 11.sub.2 and the position sensors 122.sub.1 (namely the inertial measurement units 80.sub.1, 80.sub.2 and 80.sub.3 as well as the travel sensor 90).

[0085] Referring now to FIG. 7 we describe a flowchart of operation of the ultrasound measurement apparatus described here above.

[0086] During a medical consultation preparatory to a total hip replacement operation, the practitioner applies the ultrasound probes 11.sub.1, 11.sub.2 to the patient in order to simultaneously locate the pubic symphysis 43 and one of the anterior-superior iliac spines 41 or 42. Once these anatomical sites have been located, the practitioner launches the processing sequence which will integrate all the information coming from the different sensors 122.sub.1 integrated with the ultrasound measurement device enabling the computation of the pelvic tilt.

[0087] Thus, when a new measurement 70 is started, the practitioner first of all adjusts the ultrasound probes 11.sub.1, 11.sub.2 mounted on ball-joint links and mutually hinged by means of a slide link, in order to place them so that they face the anatomical sites of interest 41, 42, 43. He then views 71 the images obtained by means of the control screen 12, and adjusts 72 the position of the probes more finely if necessary. He validates these acquisitions when they enable him to distinguish the pubic symphysis 43 (FIG. 5B) and an anterior-superior iliac spine 41 or 42 (FIG. 5A).

[0088] The following step referenced 73 is that of the automatic treatment of the image, which makes it possible to achieve the automatic location of the anatomical sites of interest constituted by the pubic symphysis 43 and the iliac spines 41, 42.

[0089] A common processing base is first of all applied to the two images (of the pubic symphysis 43 and of one of the spines 41, 42); it is followed by processing operation specific to each of the anatomical sites taking account of their special geometrical features.

[0090] The basic processing of the ultrasound images can, for example, be broken down as follows: [0091] Anisotropic filtering [0092] Otsu thresholding [0093] Transformation of intensity [0094] <<South Shadow>> Filtering [0095] Canny filtering [0096] Preservation of the last segmented line on each column of the image [0097] Operations of mathematical morphology

[0098] The specific final processing operations are the following: [0099] for the iliac spine 41, 42 (FIG. 5A), the longest segment is kept and a parabola is adjusted to it. Its vertex will localize the anatomical point of interest. [0100] for the pubic symphysis 43 (FIG. 5B), an axis of symmetry is determined by using, for example, a method based on the Hough transform, a straight line is then adjusted to the previously obtained contour of the symphysis. The position of the anatomical point of interest consists of the intersection of this straight line with the axis of symmetry.

[0101] In the course of a step referenced 75, the user 74 validates or does not validate the automatic detection of the anatomical reference markers of interest operated by the apparatus during the step referenced 73.

[0102] If this automatic detection is validated, the user 74 views the results on the screen, during a step referenced 76.

[0103] If not, the user 74 can make a manual selection 77 of the symphysis 43 and/or of the iliac spine 41, 42 on the touch screen 121.sub.4.

[0104] The system of the invention then records the set of data and computes the pelvic tilt during a step referenced 78.

[0105] To this end, when the anatomical sites of interest have been located in the ultrasound images acquired by the probes, the system determines their relative spatial positions from the data delivered by the inertial measurement units, fixedly attached to the probes and the support, and by the translation sensor integrated into the slide link.

[0106] The geometrical principle of the computation of the pelvic tilt is illustrated in FIG. 6. The pelvic tilt could be computed for example by using the following formula:

[00001]$\mathrm{Pelvic}.Math..Math.\mathrm{tilt}=\mathrm{acos}\left(\frac{{\left(\stackrel{.fwdarw.}{v_{\mathrm{SP}-\mathrm{EI}}}\right)}_z}{\sqrt{{\left(\stackrel{.fwdarw.}{v_{\mathrm{SP}-\mathrm{EI}}}\right)}_x^2+{\left(\stackrel{.fwdarw.}{v_{\mathrm{SP}-\mathrm{EI}}}\right)}_y^2+{\left(\stackrel{.fwdarw.}{v_{\mathrm{SP}-\mathrm{EI}}}\right)}_z^2}}\right)$

With: {right arrow over (v.sub.SP-EI)}=[0 L 0].Math.R.sub.M+[L.sub.S+D.sub.x.sup.EI D.sub.y.sup.EI 0].Math.R.sub.S.sup.EI−[L.sub.S+D.sub.x.sup.SP D.sub.y.sup.SP 0].Math.R.sub.S.sup.SP,
where the different variables, measured at the time of the validation of the ultrasound images by the user are: [0107] L: the distance between the two ultrasound probes 11.sub.1 and 11.sub.2, measured by the distance sensor 90. [0108] L.sub.S: the length of the ultrasound probe (distance between the center of the ball-joint link and the extremity of the probe 11.sub.1, 11.sub.2). [0109] R.sub.M: a matrix containing the roll, pitch and yaw motions given by the inertial measurement unit 80.sub.1 mounted on the structure 10. [0110] R.sub.S.sup.EI: a matrix containing the roll, pitch and yaw motions given by the inertial measurement unit 80.sub.3 mounted on the probe 11.sub.2 locating the iliac spine EI 41 or EI 42. [0111] R.sub.S.sup.SP: a matrix containing the roll, pitch and yaw motions given by the inertial measurement unit 80.sub.2 mounted on the probe 11.sub.1 locating the pubic symphysis SP 43. [0112] D.sub.x.sup.EI: the abscissa value of the point representing the iliac spine EI 41 or EI 42, detected on the image by segmentation. [0113] D.sub.y.sup.EI: the ordinate value of the point representing the iliac spine EI 41 or EI 42, detected on the image by segmentation. [0114] D.sub.x.sup.SP: the abscissa value of the point representing the pubic symphysis SP 43, detected on the image by segmentation. [0115] D.sub.y.sup.SP: the ordinate value of the point representing the pubic symphysis SP 43, detected on the image by segmentation. [0116] {right arrow over (v.sub.SP-EI)}: the vector connecting the iliac spine EI 41 or EI 42 with the pubic symphysis SP 43 in space.

[0117] The portable ultrasound measuring apparatus resolves the problems of low precision or those linked to the invasive methods of measurement of the pelvic tilt as well as the autonomy, portability and ease of use of the equipment needed for this measurement. It enables especially: [0118] the acquisition and the viewing of the two simultaneous ultrasound images (the term <<simultaneous>> is herein understood to mean two images acquired at the same instant or at instants close enough to each other for the patient not to have moved between the acquisitions of the two shots); [0119] the automatic segmentation of the ultrasound images and the automatic detection of the anatomical sites of interest; [0120] the spatial locating of areas of interest through a system of measurement of positioning of the probes; [0121] the integrated computation of the pelvic tilt.

[0122] The method of measurement proposed by the present invention is non-irradiating and the precision of the measurement, estimated by simulation, shows a mean standard deviation of about 1.9°, which is comparable to that obtained by Dardenne et al.