Test object for use in orthopaedic surgery, and associated evaluation and monitoring methods

Abstract

The present invention relates to a test object (100) for use in orthopaedic surgery, in particular for imaging a lumbar spine of a subject, the test object comprising a receiving volume (5) that accommodates: - a first vertebra element (10a) having properties similar to those of a first vertebra of a subject; - a second vertebra element (10b) having properties similar to those of a second vertebra of the subject, adjacent to the first vertebra of the subject; - at least one orthopaedic implant (20a, 20b, 21a, 21b, 25a, 25b) connecting the first vertebra element to the second vertebra element; and - a scattering medium (30) surrounding the first vertebra element, the second vertebra element and the orthopaedic implant, the scattering medium having scattering properties similar to those of a portion of a body of the subject located near the first vertebra and the second vertebra.

Description

TITLE: Test object for use in orthopaedic surgery and associated evaluation and monitoring methods TECHNICAL FIELD OF THE INVENTION [0001 ] The technical field of the invention is that of medical imaging.

[0002] The invention more particularly relates to test objects used in the medical field, in particular herein in orthopaedic surgery. The invention is particularly advantageous for medical applications relating to the lumbar spine.

[0003] The present invention relates to a test object for use in orthopaedic surgery, a method for evaluating quality of an image acquired by a medical imaging system, and a method for monitoring a setting parameter of a medical imaging system. TECHNICAL BACKGROUND OF THE INVENTION

[0004] Test objects (also referred to as ‘phantoms’) are objects that simulate specific clinical situations. They are commonly employed in the field of medical imaging to monitor quality of images provided by different pieces of equipment.

[0005] In orthopaedic surgery, orthopaedic implants, such as screws, plates or rods, are usually placed during surgical procedures.

[0006] In order to verify correct positioning of these orthopaedic implants, a monitoring image is acquired at the end of the procedure. This image is generally acquired by an X-ray imaging system. This image is essential for post-operative followup.

[0007] However, the quality of this image acquired is often highly heterogenous. Indeed, image quality is highly dependent on the acquisition parameters used for the imaging system, but also heavily influenced by the patient’s anatomy. It is therefore necessary to optimise acquisition parameters of the imaging system prior to acquiring the post-operative picture in order to ensure the quality thereof. SUMMARY OF THE INVENTION

[0008] The present invention therefore proposes improving optimisation of the acquisition parameters of an imaging system in order to improve quality of the monitoring images acquired after a surgical procedure (which must be interpreted by medical staff to ensure, for example, correct positioning of an orthopaedic implant).

[0009] More particularly, the invention relates to a test object for use in orthopaedic surgery,   the   test   object   comprising a reception   volume   housing: - a first vertebra element having properties similar to those of a first vertebra of a subject,   the   first   vertebra element comprising a   polymer   material, - a second vertebra element having properties similar to those of a second vertebra of the subject adjacent to the first vertebra of the subject, the second vertebra element comprising the polymer material, - at least one orthopaedic implant connecting the first vertebra element to the second vertebra element, the orthopaedic implant comprising a metal material, and - a diffusing medium surrounding the first vertebra element, the second vertebra element and the orthopaedic implant, the diffusing medium having diffusion properties similar to those of a portion of a body of the subject located in proximity to the first vertebra and the second vertebra.

[0010] Thus, advantageously according to the invention, the test object has the shape, dimensions, structure and anatomical details (with or without pathologies) of a portion of the subject’s spine and the adjacent medium so as to reproduce as closely as possible the clinical conditions encountered during the acquisition of post-operative pictures in orthopaedic surgery.

[0011] This test object is particularly adapted to evaluate quality of images acquired by a medical imaging system used in orthopaedic surgery (and in particular for imaging a subject’s lumbar spine).

[0012] It is also particularly adapted to verify the setting parameters of the medical imaging system to ensure that the medical imaging system is suitably set before it is actually used to acquire post-operative pictures of patients. This subsequently ensures better post-operative monitoring of patients who have undergone orthopaedic surgical procedure. In particular, this will enable effective monitoring of the positioning of orthopaedic implants following a surgical procedure.

[0013] Further to the characteristics just discussed in the preceding paragraph, the test object according to one aspect of the invention may have one or more of the following additional characteristics, either individually or according to any technically possible combination: - the polymer material comprises a polyepoxide; - the orthopaedic implant comprises a titanium alloy; - the orthopaedic implant takes the form of a screw with a length of 50 millimetres or less and a diameter of between 4 and 7 millimetres; - the orthopaedic implant takes the form of a rod with a diameter of 7 millimetres or less; - a plurality of orthopaedic implants connecting the first vertebra element to the second vertebra element are provided; - the plurality of orthopaedic implants comprises four screws and two rods connecting the first vertebra element to the second vertebra element, two screws being positioned in the first vertebra element, two other screws being positioned in the second vertebra element, each rod connecting a screw positioned in the first vertebra element and another screw positioned in the second vertebra element; - the diffusing medium comprises a polymer material; - the diffusing medium comprises a hydrogel; - the reception volume is surrounded by an outer wall comprising an elastomeric polymer material; - at least one positioning marker located on the outer wall of the reception volume is provided; - the reception volume has a parallelepiped shape; - the first vertebra element, the second vertebra element and the orthopaedic implant forming a vertebra set, said vertebra set is positioned at a predetermined distance from a first face of the parallelepiped shape of the reception volume and at another predetermined distance from a second face of the parallelepiped shape of the reception volume, the second face being orthogonal to the first face; - a disc element, positioned between the first vertebra element and the second vertebra element is provided, the disc element having properties similar to those of an intervertebral disc positioned between the subject’s first vertebra and second vertebra; - a plurality of vertebra elements having properties similar to those of a plurality of the subject’s vertebrae is provided, each vertebra element of the plurality of vertebra elements comprising a polymer material, two adjacent vertebra elements of the plurality of vertebra elements being connected by at least one orthopaedic implant; and - the plurality of vertebra elements is associated with a Cobb angle of less than 35 degrees.

[0014] The invention also relates to a computer data medium comprising data executable by a three-dimensional printing system to generate printing of a test object as defined previously.

[0015] The invention also relates to a method for evaluating quality of an image acquired by a medical imaging system, the evaluation method comprising steps of: - providing a test object as defined previously, - acquiring, by the medical imaging system, an image of the test object, - determining, within the image acquired, a first region of interest associated with a first part of the test object and a second region of interest associated with a second part of the test object, and - determining an evaluation parameter for the quality of the image acquired by comparing the first region of interest and the second region of interest.

[0016] Further to the characteristics just discussed in the preceding paragraph, the evaluation method according to another aspect of the invention may include one or more of the following additional characteristics, considered individually or according to any technically possible combination: - the first part of the test object is the first vertebra element and the second part of the test object is the second vertebra element; - the first part of the test object is the first vertebra element or the second vertebra element and the second part of the test object is the orthopaedic implant; - the evaluation parameter is a signal-to-noise ratio; and - the evaluation parameter is a contrast-to-noise ratio.

[0017] The invention also relates to a method for monitoring a setting parameter of a medical imaging system, the monitoring method comprising steps of: - providing a test object as defined previously, - acquiring, by the medical imaging system, an image of the test object, - determining, on the image acquired, a piece of data associated with the test object, - comparing the piece of data determined with a corresponding piece of reference data by determining a difference between the piece of data determined and the corresponding piece of reference data, and - monitoring the setting parameter of the medical imaging system by comparing the difference determined with a predetermined threshold.

[0018] Further to the characteristics just discussed in the preceding paragraph, the monitoring method according to another aspect of the invention may comprise one or more of the following additional characteristics, considered individually or according to any technically possible combination: - the piece of data determined is a Cobb angle; and - the piece of data determined is an angle of implantation of the orthopaedic implant.

[0019] The invention and its different applications will be better understood upon reading the following description and upon examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0020] The figures are set forth by way of indicating and in no way limiting purposes of the invention.

[0021] Fig. 1 schematically represents a first example of a test object in accordance with the invention,

[0022] Figure 2a shows a schematic top view of a second example of a test object in accordance with the invention;

[0023] Figure 2b represents a schematic side view of the second example of a test object in accordance with the invention;

[0024] Figure 2c shows another schematic side view of the second example of a test object in accordance with the invention;

[0025] Figure 3 schematically represents a vertebra set included in the test object of Fig. 1;

[0026] Figure 4 represents, in the form of a flowchart, an example of an evaluation method in accordance with the present invention;

[0027] Figure 5 represents an image of a test object in accordance with the invention acquired by a medical imaging system;

[0028] Figure 6 represents an image of a test object as used in step E8 of the evaluation method of Figure 4; and

[0029] Figure 7 represents, in the form of a flowchart, an example of a monitoring method in accordance with the present invention.

[0030] For more clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION [0031 ] This invention is placed in the field of medical imaging. It is more particularly intended to improve quality of post-operative images acquired following a procedure, especially in orthopaedic surgery.

[0032] The invention finds a particular application in the case of a medical imaging system adapted for imaging a subject’s lumbar spine. This includes, for example, an imaging system using X-rays, such as radiography or scans. It also includes a medical imaging system using magnetic resonance or ultrasound.

[0033] For this, the present invention relates to a test object specifically designed to meet the quality requirements of post-operative pictures. These post-operative pictures are, for example, acquired following a surgical procedure in orthopaedic surgery.

[0034] In this description, a test object, also referred to as a ‘phantom’, relates to an object aimed at simulating clinical situations encountered in orthopaedic surgery. This test object is used to monitor quality of post-operative images acquired by imaging systems, in particular those adapted to imaging the subject’s lumbar spine.

[0035] More particularly, herein, the test object 1; 100 according to the invention is associated with a subject’s spine. In other words, the test object 1; 100 has an anthropomorphic shape, reproducing, in part, the subject’s spine and the medium surrounding the subject’s spine.

[0036] Figures 1 to 3 schematically represent a test object 1; 100 in accordance with the invention. This test object 1; 100 herein comprises a reception volume 5, at least a first vertebra element 10a, a second vertebra element 10b, at least one orthopaedic implant 20a, 20b, 21a, 21b, 25a, 25b and a diffusing medium 30.

[0037] The reception volume 5 comprises an outer wall 6 that delimits a reception housing 7. This reception housing 7 is adapted to accommodate the first vertebra element 10a, the second vertebra element 10b, the orthopaedic implant 20a, 20b, 21a, 21b, 25a, 25b and the diffusing medium 30.

[0038] Herein, the reception volume 5 has an overall parallelepiped shape delimited by the outer wall 6. The outer wall 6 therefore comprises six rectangular side walls (or faces of the parallelepiped shape) for defining the reception volume 5 (only three side walls 6A, 6B, 6C are visible in Fig. 1). The dimensions of each rectangular side wall are, for example, as follows: a width of between 20 and 40 centimetres (cm) and a length of between 10 and 30 cm. Preferably, each side wall has a width in the order of 30 cm and a length of 20 cm.

[0039] Alternatively, the reception volume may have any other shape capable of containing the other elements of the test object, simulating clinical situations encountered in orthopaedic surgery, and monitoring quality of the post-operative images acquired by imaging systems adapted for imaging the subject’s lumbar spine.

[0040] In order to replicate the subject’s human body tissues as well as possible, the outer wall 6 of the reception volume 5 comprises an elastomeric polymer material. [0041 ] As is visible in Fig. 1, the outer wall 6 of the reception volume 5 comprises at least one positioning marker M1, M2, M3. This positioning marker M1, M2, M3 allows for the precise and reproducible positioning of the test object 1; 100 when used for image acquisition (especially to monitor the setting parameters of an imaging system as described hereinafter).

[0042] The positioning marker M1, M2, M3 takes the form, for example, of a ‘+’ cross (corresponding to the ‘plus’ sign commonly used). As an alternative, it may be another ‘x’ cross (corresponding to the ‘multiplication’ sign commonly used). Alternatively, the positioning marker may take any other form that can be adapted to form a landmark.

[0043] Herein, in the case of a parallelepiped-shaped reception volume 5, a positioning marker M1, M2, M3 is positioned at the centre of each side wall 6A, 6B, 6C of the outer wall 6 (since only three side walls 6A, 6B, 6C are visible in Fig. 1, only three positioning markers M1, M2, M3 are also visible in Fig. 1).

[0044] In practice, each positioning marker M1, M2, M3 is formed from a radiolucent material so as not to obstruct the path of rays (e.g. X-rays) involved in the imaging system concerned.

[0045] The other elements (first vertebra element 10a, second vertebra element 10b, orthopaedic implants 20a, 20b, 21a, 21b, 25a, 25b, diffusing medium 30) of the test object 1; 100 are housed within the reception volume 5. In other words, these other elements are positioned in the reception housing 7 defined inside the reception volume 5.

[0046] In the present description, a vertebra element corresponds to a manufactured element having properties similar to those of a subject’s vertebra. By ‘similar properties’, it is meant properties of shapes, dimensions and structures equivalent to those of a subject’s vertebra in order to simulate relevant clinical conditions (especially for the acquisition of monitoring images after a surgical procedure).

[0047] The vertebrae concerned in the present invention are, for example, the lumbar vertebrae L1, L2, L3, L4, L5 and the thoracic vertebrae such as the thoracic vertebra Th12. They may also be vertebrae of the sacrum such as the vertebra S1.

[0048] In other words, each vertebra element 10a, 10b, 10c, 10d, 10e, 10f has a shape modelled on the anatomy of a vertebra, as well as inclusions representing anatomical details present in a subject’s vertebrae. Each vertebra element allows representation of a healthy vertebra of a subject or a vertebra exhibiting a pathology. In particular, the vertebra elements 10a, 10b, 10c, 10d, 10e, 10f may include artifacts simulating the presence of pathologies on the vertebrae, such as lesions or collapses, for example. The vertebra elements 10a, 10b, 10c, 10d, 10e, 10f may also have a structure simulating the presence of osteoporosis, as might be observed in a subject’s vertebra.

[0049] In the example represented in Figures 2a to 2c, the test object 1 comprises the first vertebra element 10a and the second vertebra element 10b. This example therefore reproduces only two vertebrae of the subject’s spine. These are, for example, the lumbar vertebrae L4 and L5.

[0050] In the example represented in Figs. 1 and 3, the test object 100 comprises a plurality of vertebra elements 10a, 10b, 10c, 10d, 10e, 10f, 10g. This example therefore reproduces a larger portion of the subject’s spine. The vertebra elements 10a, 10b, 10c, 10d, 10e, 10f, 10g herein correspond, for example, to the five lumbar vertebrae L1, L2, L3, L4, L5, one thoracic vertebra Th12 and one sacral vertebra S1.

[0051] Thus, as is visible in Figs. 1 to 3, the vertebra elements 10a, 10b, 10c, 10d, 10e, 10f, 10g are arranged one after the other so as to reproduce as accurately as possible the portion concerned of the subject’s spine.

[0052] In particular, in the example represented in Figures 2a to 2c, the first vertebra element 10a and the second vertebra element 10b have properties similar to those of two adjacent vertebrae in the subject’s spine. For example, herein, the first vertebra element 10a and the second vertebra element 10b have properties similar to those of two vertebrae, L4 and L5.

[0053] In the example represented in Figs. 1 and 3, the plurality of vertebra elements 10a, 10b, 10c, 10d, 10e, 10f, 10g has properties similar to those of the plurality of adjacent vertebrae of the portion concerned of the subject’s spine. For example, herein, the plurality of vertebra elements 10a, 10b, 10c, 10d, 10e, 10f, 10g has properties similar to those of the lumbar vertebrae L1, L2, L3, L4, L5 and the thoracic vertebra Th12.

[0054] In particular, the plurality of vertebra elements 10a, 10b, 10c, 10d, 10e, 10f, 10g exhibits a curvature such as that observed in the subject’s spine. This curvature is characterised by a Cobb angle 3 (shown in Figure 3). Conventionally, this Cobb angle is defined based on the directions respectively associated with the vertebra elements exhibiting the greatest tilt (herein, vertebra elements 10b and 10f). The Cobb angle 3 is measured between a superior endplate of the proximal vertebra (i.e. the one closest to the centre of the spine) the most tilted in the coronal plane (i.e. the plane perpendicular to the median and transverse planes, which divides the body into a ventral and a dorsal portion), and the inferior endplate of the caudal vertebra (i.e. the one located in the posterior part of the spine) that is most tilted.

[0055] Preferably, the Cobb angle p is herein less than or equal to 35 degrees. This indicates mild scoliosis. Even more preferably, the Cobb angle 3 is herein in the order of 30 degrees.

[0056] Alternatively, if the test object is associated with a clinical situation involving more pronounced scoliosis, the Cobb angle may be greater than 35 degrees.

[0057] Each vertebra element 10a, 10b, 10c, 10d, 10e, 10f, 10g herein comprises a polymer material. Preferably, the polymer material comprises a polyepoxide. This is, for example, an epoxy resin to represent the bone portions of each vertebra. This is, for example, a polyurethane to represent the flexible portions (such as the spinal cord) of the subject’s spine.

[0058] Finally, the vertebra elements 10a, 10b, 10c, 10d, 10e, 10f, 10g reproduce the shape, texture and absorption characteristics of a subject’s vertebrae.

[0059] In order to replicate the result of orthopaedic surgery, the test object 1; 100 also comprises at least one orthopaedic implant 20a, 20b, 21a, 21b, 25a, 25b.

[0060] In this description, an ‘orthopaedic implant’ corresponds to a device used in orthopaedic surgery to hold bone portions in order to prevent the risk of rotation or displacement of these bone portions. This thereby ensures greater stability of the joint concerned. [0061 ] As is visible in Figures 2a to 2c and 3, the orthopaedic implant 20, 25 serves herein to connect two adjacent vertebra elements 10a, 10b. More particularly, the orthopaedic implant 20a, 20b, 21a, 21b, 25a, 25b herein serves to secure the first vertebra element 10a to the second vertebra element 10b. The orthopaedic implant 20a, 20b, 21a, 21b, 25a, 25b thus enables positioning of orthopaedic equipment, as made for example during a vertebral arthrodesis, so as to secure several vertebrae together so that they can no longer move relative to one another.

[0062] The orthopaedic implant 20a, 20b, 21a, 21b, 25a, 25b comprises a metal material. This metal material comprises, for example, titanium, chromium or cobalt. Preferably, the orthopaedic implant 20, 25 comprises a titanium alloy. This is, for example, the titanium alloy said to be ‘Ti6Al4V’ (defined according to ISO standard 5832-3). The orthopaedic implant may also comprise a chromium-cobalt alloy.

[0063] In practice, the orthopaedic implant 20a, 20b, 21a, 21b takes the form of a screw. This screw has, for example, a length of 50 millimetres (mm) or less and a diameter of between 4 and 7 mm. Preferably, this screw has a length in the order of 40 mm and a diameter in the order of 5.5 mm or 6.5 mm.

[0064] The orthopaedic implant 25a, 25b may also take the form of a rod with a diameter of 7 mm or less. Preferably, this rod has a diameter in the order of 5.5 mm. The length of the rod is herein greater than 25 mm. For example, it is between 35 and 40 mm when the vertebrae concerned are the vertebrae L4-L5. For other vertebrae, the length of the rod may be greater than one hundred millimetres.

[0065] Preferably, according to the invention, the test object 1; 100 comprises a plurality of orthopaedic implants 20a, 20b, 21a, 21b, 25a, 25b connecting two adjacent vertebra elements. More particularly, as is represented in Figures 2a to 2c and 3, several orthopaedic implants 20a, 20b, 21a, 21b, 25a, 25b are used to secure the first vertebra element 10a and the second vertebra element 10b. This allows the first vertebra element 10a and the second vertebra element 10b to be fixed so as to ensure better locking of each vertebra element in a predefined position.

[0066] In a preferred embodiment of the present invention (represented in Figures 2a to 2c and 3), the test object 1; 100 comprises four screws 20a, 20b, 21a, 21b and two rods 25a, 25b (as a plurality of orthopaedic implants). Two screws 20a, 20b are implanted in the first vertebra element 10a. Two screws 21a, 21b are implanted in the second vertebra element 10b.

[0067] In practice, the screws 20a, 20b positioned in the first vertebra element 10a are positioned so as to observe a predetermined implantation angle a (Figure 2a). More particularly, by defining a first implantation direction Z1 associated with a first screw 20a implanted in the first vertebra element 10a and a second implantation direction Z2 associated with a second screw 20b implanted in the first vertebra element 10a, the implantation angle a is the angle formed between the first implantation direction Z1 and the second implantation direction Z2.

[0068] Likewise, the screws 21a, 21b positioned in the second vertebra element 10a are positioned so as to observe the predetermined implantation angle a (the same angle as the implantation angle between the screws 20a, 20b in the first vertebra element 10a).

[0069] The first screw 20a implanted in the first vertebra element 10a is positioned facing another first screw 21a implanted in the second vertebra element 10b. Similarly, the second screw 20b implanted in the first vertebra element 10a is positioned facing another second screw 21b implanted in the second vertebra element 10b.

[0070] Additionally, herein, the first screw 20a and the second screw 20b are implanted, in the first vertebra element 10a, in a first plane P1 (Figure 2c). Similarly, the other first screw 21a and the other second screw 21b are implanted, in the second vertebra element 10b in a second plane P2 (Figure 2c). In a preferred embodiment, the first plane P1 and the second plane P2 are substantially parallel to one another. [0071 ] In order to block movement of the first vertebra element 10a and the second vertebra element 10b, the screws 20a, 20b, 21a, 21b implanted are connected two by two by a rod 25a, 25b. More particularly, as is visible in Figures 2c and 3, a first rod 25a connects the first screw 20a implanted in the first vertebra element 10a to the other first screw 21a implanted in the second vertebra element 10b. Similarly, a second rod 25b connects the second screw 20b implanted in the first vertebra element 10a to the other second screw 21b implanted in the second vertebra element 10b. In practice, the test object further comprises four blocking screws (not represented in the figures) for fixing the rods 25a, 25b to the relevant screws 20a, 20b, 21a, 21b in order to ensure blocking of the entire structure.

[0072] Positioning the orthopaedic implants in the present invention is implemented using the spinal fixation, so-called Magerl technique. Further details relating to this fixation technique can be found in the article by Magerl, F. P., ‘Stabilization of the lower thoracic and lumbar spine with external skeletal fixation’, Clin. Orthop. 189, 125-130 (1984).

[0073] Alternatively, other spinal fixation techniques may be used, such as the Krag or Roy-Camille techniques. Further details on these other fixation techniques can be found in the following articles: - Roy-Camille, R., Saillant, G. & Mazel, C, “Internal fixation of the lumbar spine with pedicle screw plating”, Clin. Orthop. Relat. Res, 203, 7-17 (1986) and - Krag, M. H., Van Hal, M. E. & Beynnon, B. D., “Placement of transpedicular vertebral screws close to anterior vertebral cortex: Description of methods”, Spine (Phila Pa 1976), 14, 879-883 (1989).

[0074] Still alternatively, the first plane (containing screws 20a, 20b) and the second plane (containing screws 21a, 21b) may form a non-zero angle between them.

[0075] Still alternatively, the first implantation direction and the second implantation direction may be substantially parallel.

[0076] Still alternatively, the test object may comprise orthopaedic implants for which implantation has not been suitably performed. Implantation problems include, for example, an orthopaedic implant that is not strictly within the vertebra element (corresponding to a situation where the orthopaedic is not strictly intraosseous) or incorrect positioning or alignment of the orthopaedic implants within the vertebra elements.

[0077] The first vertebra element 10a, the second vertebra element 10b and the orthopaedic implants 20a, 20b, 21a, 21b, 25a, 25b form a vertebra set 2. Similarly, the plurality of vertebra elements 10a, 10b, 10c, 10d, 10e, 10f and the orthopaedic implants 20a, 20b, 21a, 21b, 25a, 25b form a vertebra set 200.

[0078] This vertebra set 2; 200 is housed within the reception housing 7 defined within the reception volume 5. In practice, the vertebra set 2; 200 is positioned at a predetermined distance from the outer wall 6 of the reception volume 5.

[0079] More particularly, in the case of a parallelepiped-shaped reception volume 5, the vertebra set 2; 200 is positioned at a predetermined distance from a side wall 6C of the outer wall 6 and at another predetermined distance from another side wall 6A of the outer wall 6.

[0080] The predetermined distance and the other predetermined distance are, for example, in the order of a few centimetres. Preferably, the predetermined distance is of the order of one centimetre.

[0081] As is visible in Fig. 1, the test object 1; 100 also comprises the diffusing medium 30 surrounding the vertebra set 2; 200. More particularly, the diffusing medium 30 surrounds the first vertebra element 10a, the second vertebra element 10b and the orthopaedic implants 20a, 20b, 21a, 21b, 25a, 25b. In other words, the diffusing medium 30 fills the reception housing 7 around the vertebra set 2; 200. The reception volume 5 is therefore full.

[0082] The diffusing medium 30 is adapted to replicate the surrounding medium of the subject’s spine. The diffusing medium 30 thus replicates the anatomical structures adjacent to the vertebrae. This enables the reproduction of a clinical contrast gradient so as to ensure clinical image quality.

[0083] To this end, the diffusing medium 30 exhibits diffusing properties similar to those of a portion of the subject’s body located in proximity to the vertebrae concerned. In other words, the diffusing medium 30 exhibits diffusing properties similar to those of the anatomical structures adjacent to the vertebrae concerned.

[0084] In practice, the diffusing medium 30 comprises a polymer material. This material has a specific gravity, for example, of between 1 and 2. The diffusing medium 30 is, for example, formed of a hydrogel.

[0085] Optionally, the test object may also comprise a disc element 15 positioned between two adjacent vertebra elements.

[0086] In the present description, a disc element corresponds to a manufactured element having properties similar to those of an intervertebral disc positioned between two adjacent vertebrae. By ‘similar properties’, it is meant properties of shapes, dimensions and structures equivalent to those of a subject’s intervertebral disc in order to simulate relevant clinical conditions (especially for the acquisition of monitoring images after a surgical procedure).

[0087] In other words, the disc element 15 has a shape modelling anatomy of an intervertebral disc, as well as inclusions representing the anatomical details present in a subject’s intervertebral discs. The disc element allows for the representation of a subject’s healthy intervertebral disc or an intervertebral disc exhibiting a pathology. In particular, the disc element 15 may comprise artifacts simulating presence of pathologies in intervertebral discs, such as the presence of osteoarthritis or pronounced wear, for example.

[0088] In Figure 3, a disc element 15 is visible between the first vertebra element 10a and another vertebra element 10g. The test object 1; 100 according to the invention may comprise a plurality of disc elements.

[0089] In practice, the disc element 15 herein comprises a polymer material. Preferably, the polymer material comprises a polyurethane.

[0090] The present invention also relates to a three-dimensional printing system configured to generate printing of a test object 1; 100 as described previously.

[0091] For this, a control unit (not represented) is provided, equipped with a processor and a memory. A data medium then comprises executable data describing the test object 1; 100 and enabling it to be generated (by three-dimensional printing). The executable data are, for example, stored in the memory.

[0092] The processor is configured to control the three-dimensional printing system (for example, based on a stereolithography method) so as to generate the test object 1; 100. More particularly, when the three-dimensional printing system receives the control instruction from the processor, it executes the data for generating print of the test object 1; 100.

[0093] It is to be noted that the test object may herein be generated digitally (i.e. as a virtual three-dimensional representation) using computer-aided design software. The processor then executes instructions corresponding to the data executable by the three-dimensional printing system so as to obtain a digital representation of the test object.

[0094] In other words, according to the invention, the test object 1; 100 obtained may be a physical object (obtained by a three-dimensional printing system) or a virtual object (produced by virtue of computer-aided design software). This is particularly advantageous, as the evaluation and monitoring methods described hereinafter can be implemented entirely by computer (with all steps then being carried out by the processor based on the digitally generated test object) or using customary ‘physical’ medical imaging systems (and the test object manufactured in a factory or produced by 3D printing).

[0095] Finally, test object 1:100, in accordance with the invention, has the shape, dimensions, structure and anatomical details (with or without pathologies) of a section of the subject’s spine and the adjacent environment, so as to reproduce as closely as possible the clinical conditions encountered when acquiring post-operative pictures in orthopaedic surgery. In other words, the test object according to the invention exhibits a degree of biomimicry such that it reproduces, more particularly, the heterogeneities encountered herein within and in proximity to the subject’s spine.

[0096] The test object 1; 100 in accordance with the invention is particularly adapted to enabling evaluation of quality of the images acquired by a medical imaging system used in orthopaedic surgery (and in particular for imaging the lumbar spine of a subject).

[0097] The present invention therefore relates to a method for evaluating quality of an image acquired by a medical imaging system used in orthopaedic surgery (this method is also referred to as the ‘evaluation method’ in the remainder of this description). Figure 4 is a flowchart illustrating an example of an evaluation method in accordance with the present invention.

[0098] As shown in this figure, the evaluation method starts with a step E2 of providing a test object 1; 100 as described previously. The test object 1; 100 therefore has all the appropriate characteristics to reproduce as closely as possible the clinical conditions encountered following orthopaedic surgery.

[0099] The evaluation method then comprises a step E4 of acquiring an image Im1 of the test object 1; 100. This image Im1 is acquired herein by a medical imaging system used in orthopaedic surgery. This may, for example, be an imaging system using X-rays, such as radiography, or scans, for instance. It may also be a medical imaging system using magnetic resonance or ultrasound. An example of an image Im1 acquired is represented in Figure 5. In this figure, an orthopaedic implant 20, as well as a vertebra element 10, are visible.

[00100] As shown in Figure 4, the evaluation method continues with step E6, of processing the image Im1 acquired in step E4. This step E6 enables, for example, the identification of the different parts of the test object 1; 100. In particular, this step E6 is, for example, a segmentation step enabling identification of the pixels in the image Im1 acquired corresponding to the orthopaedic implant, on the one hand, and to the vertebra element, on the other hand.

[00101] This step E6 is, for example, implemented by a computer (more particularly by a control unit, not represented, conventionally equipped with a processor and memory), via a segmentation algorithm. Alternatively, it may be carried out by implementing an artificial neural network which receives, as an input, the image Im1 acquired and provides, as an output, segmentation of the pixels of this image Im1 acquired to identify the pixels corresponding to the orthopaedic implant, on the one hand, and to the vertebra element, on the other hand.

[00102] In step E8, the processor determines a first region of interest RO1 associated with a first part of the test object 1; 100 and a second region of interest RO2 associated with a second part of the test object 1; 100.

[00103] In a first example, the first part of the test object 1; 100 is the first vertebra element 10a or the second vertebra element 10b. In other words, the first region of interest RO1 is associated with the first vertebra element 10a or the second vertebra element 10b of the test object 1; 100.

[00104] In this first example, the second part of test object 1; 100 is the orthopaedic implant 20a, 20b, 21a, 21b. In other words, the second region of interest RO2 is associated with the orthopaedic implant 20a, 20b, 21a, 21b implanted in the first vertebra element 10a or in the second vertebra element 10b.

[00105] Figure 6 shows an example of an image acquired on which a first region of interest RO1 and a second region of interest RO2 corresponding to this first example have been identified.

[00106] In a second example, the first part of the test object 1; 100 is the first vertebra element 10a. The first region of interest RO1 is therefore associated with the first vertebra element 10a.

[00107] In this second example, the second part of the test object 1; 100 is the second vertebra element 10b. The second region of interest RO2 is therefore associated with the second vertebra element 10b. In this second example, both regions of interest are therefore associated with the vertebra elements.

[00108] For each of the first region of interest RO1 and the second region of interest RO2, the processor then stores values of the pixels respectively associated therewith.

[00109] As shown in Figure 4, the evaluation method continues with step E10 of determining a parameter for evaluating quality of the image Im1 acquired by comparing the first region of interest RO1 and the second region of interest RO2.

[00110] This evaluation parameter is, for example, the signal-to-noise ratio SNR determined between the first region of interest RO1 and the second region of interest RO2. More particularly, the signal-to-noise ratio SNR is determined, based on the pixel values of the first region of interest RO1 or the second region of interest RO2, according to the following formula:

[00111] SNR Mean (Pixel values RO1) Standard deviation (Pixel values 101) and / or          SNR = Mean (Pixel values 202) Standard deviation (Pixel values 202)

[00112] Determining the signal-to-noise ratio SNR is therefore based on determining the mean of the pixel values associated with the first region of interest RO1 and determining the standard deviation of the pixel values associated with the first region of interest RO1. It may also be based on determining the mean of the pixel values associated with the second region of interest RO2 and on determining the standard deviation of the pixel values associated with the second region of interest RO2.

[00113] Another example of an evaluation parameter is the contrast-to-noise ratio CNR, determined between the first region of interest RO1 and the second region of interest RO2. More particularly, the contrast-to-noise ratio CNR is determined from the pixel values of the first region of interest RO1 and the second region of interest RO2 according to the following formula: mn-i-i / n run _ Mean (Pixelva lues RO 1)-Me an(Pixel values RO 2) UUT14 Civ —------------------------------------ Standard deviation (Pixel values RO 1)

[00115] Determining the contrast-to-noise ratio CNR is therefore based on determining the mean of the pixel values associated with the first region of interest RO1, determining the mean of the pixel values associated with the second region of interest RO2, and determining the standard deviation of the pixel values associated with the first region of interest RO1.

[00116] In practice, the contrast-to-noise ratio CNR evaluates the contrast between the signal (for example, associated with the orthopaedic implant) and a background signal (associated, for example, with the vertebra element in which the orthopaedic implant is positioned).

[00117] Preferably, several evaluation parameters are determined in step E10 to enable a more precise evaluation of the image quality. Herein, for example, both the signal-to-noise ratio SNR and the contrast-to-noise ratio CNR are determined.

[00118] The evaluation method ends in step E12, during which the evaluation parameter determined is interpreted in order to derive a quality evaluation of the image Im1 acquired.

[00119] If the evaluation parameter is based on the signal-to-noise ratio SNR, a high value thereof is indicative of good image quality. The higher the value of the signal-to-noise ratio SNR, the better the image quality.

[00120] Similarly, if the evaluation parameter is based on the contrast-to-noise ratio CNR, a high value is indicative of good image quality. The higher the CNR value, the better the image quality.

[00121] Thus, advantageously, the test object 1; 100 according to the invention enables quality of the images obtained by the medical imaging system in question to be evaluated. This then ensures good picture quality prior to acquiring images of patients (following a surgical procedure). This subsequently guarantees better postoperative follow-up of patients who have undergone a surgical procedure in orthopaedic surgery. In particular, this will enable effective monitoring of the positioning of orthopaedic implants following an operation.

[00122] Test object 1; 100, in accordance with the invention, is also particularly adapted to monitoring the setting parameters of the medical imaging system used in orthopaedic surgery (and in particular for imaging the lumbar spine of a subject). This then ensures high quality of the images acquired by this medical imaging system.

[00123] In practice, it herein relates to, for example, setting the product of the tube current by the X-ray exposure time, or setting the kilovoltage for imaging systems using X-rays. The setting may also relate to modifying the parameters of the reconstruction algorithm in CT scan or MRI. The setting may also concern a modification in the operating parameters of a probe used in ultrasound imaging.

[00124] The present invention therefore relates to a method for monitoring a setting parameter of a medical imaging system used in orthopaedic surgery (this method is also referred to as the ‘monitoring method’ in the remainder of this description). Figure 7 is a flowchart illustrating an example of a monitoring method in accordance with the present invention.

[00125] As shown in this figure, the monitoring method starts with a step E20 of providing a test object 1; 100 as described previously. The test object 1; 100 therefore has all the appropriate characteristics to reproduce as closely as possible the clinical conditions encountered following orthopaedic surgery.

[00126] The monitoring method then comprises a step E22 of acquiring an image Im1 of the test object 1; 100. This image Im1 is herein acquired by a medical imaging system used in orthopaedic surgery. This may, for example, be an imaging system using X-rays, such as radiography or scans for example. It may also be a medical imaging system using magnetic resonance or ultrasound. An example of an image Im1 acquired is represented in Figure 5.

[00127] As shown in Figure 7, the monitoring method continues with step E24 of processing the image Im1 acquired in step E22. This step E24 enables, for example, the identification of the different parts of the test object 1; 100. In particular, this step E24 is, for example, a segmentation step enabling identification of the pixels in the image Im1 acquired corresponding to the orthopaedic implant, on the one hand, and to the vertebra elements, on the other hand.

[00128] Like step E6 described previously, this step E24 is, for example, implemented by a computer (more particularly by a processor) via a segmentation algorithm. Alternatively, it may be carried out by implementing an artificial neural network which receives, as an input, the image Im1 acquired and provides, as an output, segmentation of the pixels of this image Im1 acquired to identify the pixels corresponding to the orthopaedic implant, on the one hand, and to the vertebra element, on the other hand.

[00129] This step E24 is optional in the monitoring method. However, it helps to speed up implementation and improve efficiency of this monitoring method.

[00130] As shown in Figure 7, the monitoring method then comprises a step E26 of determining, on the image acquired, a piece of data that characterises the test object 1; 100. A piece of data characterising the test object 1; 100 is, for example, a dimension of this test object 1; 100, the Cobb angle p, the implantation angle a of the orthopaedic implants, the pathology grade of a disc element 15 (if the disc element 15 exhibits a pathology), etc.

[00131] In practice, this step E26 is implemented via an analysis of the image Im1 acquired. This analysis of the image Im1 acquired is, for example, implemented by the processor using a dedicated image analysis algorithm. Alternatively, step E26 may be carried out by implementing an artificial neural network which receives, as an input, the image Im1 acquired and provides, as an output, a piece of data that characterises the test object 1; 100.

[00132] And then, in step E28, the processor compares the piece of data determined in step E26 with a corresponding piece of reference data. This piece of reference data corresponds, for example, to the actual value of the Cobb angle used to manufacture test object 1; 100 or the actual value of the implantation angle a used when positioning orthopaedic implants in the vertebra elements. All manufacturing data relating to the test object are, for example, stored in a memory associated with the processor.

[00133] In practice, the comparison between the piece of data determined in step E26 and the corresponding piece of reference data is carried out by determining the difference between this piece of data determined in step E26 and the corresponding piece of reference data.

[00134] If this difference is less (in absolute value) than a predetermined threshold, the monitoring method continues to step E30, during which a message is issued to indicate that the setting parameters of the medical imaging system are suitable. The predetermined threshold is, for example, 10%, and preferably 5%. The medical imaging system can therefore be used to acquire post-operative pictures of patients who have undergone a surgical procedure in orthopaedic surgery.

[00135] If, in step E28, the processor determines that the difference (in absolute value) between the piece of data determined in step E26 and the corresponding piece of reference data is greater than the predetermined threshold, the monitoring method proceeds to step E32. In this step E32, the processor controls adjustment of the setting parameters of the medical imaging system.

[00136] As previously indicated, this herein involves, for example, setting the product of the tube current by the X-ray exposure time, or setting the kilovoltage for X-ray imaging systems. It may also involve modifying the parameters of the reconstruction algorithm in CT scan or MRI. The setting may also concern a modification in the operating parameters of a probe used in ultrasound imaging

[00137] The adjustment of the setting parameters of the medical imaging system is then carried out in step E34. The monitoring method then resumes in step E22 in order to acquire a new image of the test object 1; 100 using the new setting parameters of the medical imaging system.

[00138] Thus, advantageously, the test object 1; 100 according to the invention makes it possible to monitor that the medical imaging system is suitably set before it is actually used to acquire post-operative pictures of patients. In other words, the test object 1; 100 allows verification that the medical imaging system is suitably calibrated before being used to acquire post-operative pictures of patients. This subsequently ensures better post-operative monitoring of patients who have undergone a surgical procedure in orthopaedic surgery. In particular, this will enable effective monitoring of positioning of the orthopaedic implants following a surgical procedure.

Claims

1. A test object (1; 100) for use in orthopaedic surgery, the test object (1; 100) comprising a reception volume (5) housing:- a first vertebra element (10a) having properties similar to those of a first vertebra of a subject, the first vertebra element (10a) comprising a polymer material,- a second vertebra element (10b) having properties similar to those of a second vertebra of the subject adjacent to the first vertebra of the subject, the second vertebra element (10b) comprising the polymer material,- at least one orthopaedic implant (20a, 20b, 21a, 21b, 25a, 25b) connecting the first vertebra element (10a) to the second vertebra element (10b), the orthopaedic implant (20a, 20b, 21a, 21b, 25a, 25b) comprising a metal material, and - a diffusing medium (30) surrounding the first vertebra element (10a), the second vertebra element (10b) and the orthopaedic implant (20a, 20b, 21a, 21b, 25a, 25b), the diffusing medium (30) having diffusion properties similar to those of a portion of the subject’s body located in proximity to the first vertebra and the second vertebra.

2. The test object (1; 100) according to claim 1, wherein the polymer material comprises a polyepoxide.

3. The test object (1; 100) according to claim 1 or 2, wherein the orthopaedic implant (20a, 20b, 21a, 21b, 25a, 25b) comprises a titanium alloy.

4. The test object (1; 100) according to any of claims 1 to 3, further comprising a plurality of orthopaedic implants (20a, 20b, 21a, 21b, 25a, 25b) connecting the first vertebra element (10a) to the second vertebra element (10b).

5. The test object (1; 100) according to claim 4, wherein the plurality of orthopaedic implants (20a, 20b, 21a, 21b, 25a, 25b) comprises four screws and two rods connecting the first vertebra element (10a) to the second vertebra element (10b), two screws being positioned in the first vertebra element (10a), two other screws being positioned in the second vertebra element (10b), each rod connecting a screw positioned in the first vertebra element (10a) and another screw positioned in the second vertebra element (10b).

6. The test object (1; 100) according to any of claims 1 to 5, wherein the diffusing medium (30) comprises a polymer material.

7. The test object (1; 100) according to any of claims 1 to 6, wherein the diffusing medium (30) comprises a hydrogel.

8. The test object (1; 100) according to any of claims 1 to 7, wherein the reception volume (5) is surrounded by an outer wall (6) comprising an elastomeric polymer material.

9. The test object (1; 100) according to claim 8, further comprising at least one positioning marker (M1, M2, M3) located on the outer wall (6) of the reception volume (5).

10. The test object (1; 100) according to any of claims 1 to 9, wherein the reception volume (5) has a parallelepiped shape.

11. The test object (1; 100) according to claim 10, wherein the first vertebra element (10a), the second vertebra element (10b) and the orthopaedic implant (20a, 20b, 21a, 21b, 25a, 25b) forming a vertebra set (2; 200), said vertebra set (2; 200) is positioned at a predetermined distance from a first face of the parallelepiped shape of the reception volume (5) and at another predetermined distance from a second face of the parallelepiped shape of the reception volume (5), the second face being orthogonal to the first face.

12. The test object (1; 100) according to any of claims 1 to 11, further comprising a disc element (15) positioned between the first vertebra element (20a, 20b, 21a, 21b, 25a, 25b) and the second vertebra element (20a, 20b, 21a, 21b, 25a, 25b), the disc element (15) having properties similar to those of an intervertebral disc positioned between the subject’s first vertebra and second vertebra.

13. The test object (1; 100) according to any of claims 1 to 12, further comprising a plurality of vertebra elements (10a, 10b, 10c, 10d, 10e, 10f, 10g) having properties similar to those of a plurality of the subject’s vertebrae, each vertebra element (10a, 10b, 10c, 10d, 10e, 10f, 10g) of the plurality of vertebra elements comprising a polymer material,two adjacent vertebra elements (10a, 10b) of the plurality of vertebra elements being connected by at least one orthopaedic implant (20a, 20b, 21a, 21b, 25a, 25b).

14. The test object (1; 100) according to claim 13, wherein the plurality of vertebra elements (10a, 10b, 10c, 10d, 10e, 10f, 10g) is associated with a Cobb angle (3) of less than 35 degrees.

15. A computer data medium comprising data executable by a threedimensional printing system to generate printing of a test object (1; 100) according to any of claims 1 to 14.

16. A method for evaluating quality of an image acquired by a medical imaging system, the evaluation method comprising the steps of: - providing a test object (1; 100) according to any of claims 1 to 14, - acquiring, by the medical imaging system, an image (Im1) of the test object (1; 100), - determining, in the image (Im1) acquired, a first region of interest (RO1) associated with a first part of the test object (1; 100) and a second region of interest (RO2) associated with a second part of the test object (1; 100), and- determining a parameter for evaluating quality of the image (Im1) acquired by comparing the first region of interest (RO1) and the second region of interest (RO2).

17. The evaluation method according to claim 16, wherein the first part of the test object (1; 100) is the first vertebra element (10a) and the second part of the test object (1; 100) is the second vertebra element (10b).

18. The evaluation method according to claim 16, wherein the first part of the test object (1; 100) is the first vertebra element (10a) or the second vertebra element (10b) and the second part of the test object (1; 100) is the orthopaedic implant (20a, 20b, 21a, 21b, 25a, 25b).

19. The evaluation method according to any of claims 16 to 18, wherein the evaluation parameter is a signal-to-noise ratio.

20. The evaluation method according to any of claims 16 to 19, wherein the evaluation parameter is a contrast-to-noise ratio.

21. A method for monitoring a setting parameter of a medical imaging system, the monitoring method comprising the steps of:- providing a test object (1; 100) according to any of claims 1 to 14, - acquiring, by the medical imaging system, an image (Im1) of the test object (1; 100), - determining, on the image (Im1) acquired, a piece of data associated with the test object (1; 100),- comparing the piece of data determined with a corresponding piece of reference data by determining a difference between the piece of data determined and the corresponding piece of reference data, and- monitoring the setting parameter of the medical imaging system by comparing the difference determined with a predetermined threshold.

Images