Method for determining the position of a target element in an image of interest of an area of the body

Abstract

The present invention relates to a method for determining the position of a target element in an image of interest (IMI) of an area of the body, the area of the body comprising an intermediate element imaged in the image of interest (IMI), the image of interest (IMI) having been acquired by an imaging device (12), each image acquired by the imaging device (12) having a specific reference, referred to as the image reference (RI), in which the elements of the image are referenced, the position of the imaging device (12) on each image acquisition being referenced in a fixed reference frame, referred to as the tracking reference frame (RS), the area of the body being stationary in the tracking reference frame (RS) during the implementation of the method.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for determining the position of a target element on an image of interest of a body area

[0003] The present invention relates to a method for determining the position of at least one target element on at least one image of interest of a body area. The present invention also relates to an associated determination system.

[0004] Therapeutic management of endometrial cancer depends on estimating the theoretical risk of recurrence and lymph node metastasis. In practice, lymphadenectomy, resection of the lymph node chain, is only performed on patients at real risk of recurrence. In order to reduce its morbidity, the concept of the sentinel lymph node was developed to isolate the first lymph node(s) draining a solid tumor.

[0005] Sentinel lymph node detection is currently based on a combined technique combining a radioisotope injection before the operation and either an injection of blue dye just after anesthetic induction, or colorimetric detection alone with indocyanine green intraoperatively.

[0006] However, the failure rate for sentinel node detection, especially bilateral detection, is approximately 25%. In addition, current procedures have several limitations, including reliability, accuracy, and potential procedure-related complications.

[0007] Thus, during a coelioscopy (also called laparoscopy), it is difficult to locate the sentinel lymph node on the coelioscopic images.

[0008] There is therefore a need for a method and a system for facilitating the detection of at least one target element, such as the sentinel lymph node, on an image of a body area.

[0009] For this purpose, the present description relates to a method for determining the position of at least one target element on at least one image of interest of a body area, the body area comprising at least one intermediate element imaged on the image of interest, the image of interest having been acquired by an imaging device, each image acquired by the imaging device having its own reference frame, called image reference frame, in which the elements of the image are identified, the position of the imaging device at each image acquisition being identified in a fixed reference frame, called tracking reference frame, the body area being stationary in the tracking reference frame during the implementation of the method, the method being implemented by computer and comprising: a. a preparatory phase comprising the following steps: i.obtaining a geometric representation, called a local geometric representation, of the intermediate element, the local geometric representation being located in a fixed geometric reference frame, called a local reference frame, the target element having a relative position with respect to the intermediate element which is known in the local reference frame, 11. obtaining preparatory images of the body area, the preparatory images having been acquired by the imaging device for different positions of the imaging device, each position of the imaging device corresponding to a different viewing angle of the body area, 11. determining a transformation, called a local transformation, between the tracking reference frame and the local reference frame as a function of the local geometric representation, the preparatory images, and the positions of the imaging device during the acquisition of the preparatory images, 11. an exploitation phase comprising the following steps: 11.obtaining an image of interest of the body area, il. determining a transformation, called image transformation, between the local reference frame and the image reference frame of the image of interest, the image transformation being determined as a function of the determined local transformation and the position of the imaging device during the acquisition of the image of interest, and ill. determining the position of the target element on the image of interest as a function of the determined image transformation and the known relative position of the target element with respect to the intermediate element.

[0010] According to particular embodiments, the method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0011] - the steps of the exploitation phase are repeated over time for images of interest corresponding to different positions of the imaging device;

[0012] - the exploitation phase comprises a step of displaying the image of interest on a screen with a superimposed representation of the target element at the position determined on the image of interest;

[0013] - the local geometric representation is obtained as a function of cross-sectional images of the body area comprising the intermediate element and the target element, the cross-sectional images having been acquired by a medical imaging device;

[0014] - the step of determining the local transformation comprises: a. determining, for each preparatory image, a geometric representation, called an annotated representation, of the intermediate element, the annotated representations being located in the tracking frame as a function of the position of the imaging device during the acquisition of said images, b. placing the local geometric representation at an initial position in the tracking frame, c. determining, in the tracking frame, as a function of the annotated representations, a representation, called a preparatory geometric representation, and d. determining the local transformation by resetting the local geometric representation and the preparatory geometric representation in the tracking frame (R s ) ;

[0015] - the preparatory geometric representation is obtained by projection of the annotated representations and cross-referencing of said projections;

[0016] - the intermediate element has an invariant form in projective geometry; and

[0017] - the intermediate element is an arterial network, such as the iliac arterial network, and the target element is a lymph node, preferably a sentinel lymph node.

[0018] The present invention also relates to a system for determining the position of at least one target element on at least one image of interest of a body area, the body area comprising an intermediate element imaged on the image of interest, the image of interest having been acquired by an imaging device, each image acquired by the imaging device having its own reference frame, called image reference frame, in which the elements of the image are identified, the position of the imaging device at each image acquisition being identified in a fixed reference frame, called tracking reference frame, the system comprising a computer configured to implement the steps of a method according to the invention; and

[0019] - the system also comprises: a. the imaging device for acquiring the preparatory images and the images of interest, b. a support on which the imaging device is mounted, and c. a tracking device connected to the support for moving the imaging device and tracking the movements of the imaging device.

[0020] The present description also relates to a computer program product on which is stored a computer program comprising program instructions, the computer program being loaded onto a data processing unit and causing the implementation of a method as described above when the computer program is implemented on the data processing unit.

[0021] The present description also relates to a readable information medium on which is stored a computer program product comprising program instructions, the computer program being loaded onto a data processing unit and causing the implementation of a method as described previously when the computer program is implemented on the data processing unit.

[0022] The present description also relates to a surgical method comprising: the placement of an imaging device in the body of the (anesthetized) patient, the acquisition, by the imaging device, of preparatory images of a body area, the body area comprising an intermediate element (visible on the images) and a target element (visible or not on the images), the implementation of the preparatory phase of the determination method as described previously as a function of the acquired preparatory images, the acquisition, by the imaging device, of an image of interest of the body area, and the implementation of the operating phase of the determination method as described previously for the acquired image of interest.

[0023] Other features and advantages of the invention will become apparent upon reading the following description of embodiments of the invention, given by way of example only and with reference to the drawings which are:

[0024] [Fig 1], Figure 1, a schematic view of an example of a system for determining the position of a target element on images of interest of a body area, [Fig 2], Figure 2, a flowchart of an example of implementation of a method for determining the position of a target element on images of interest of a body area,

[0025] [Fig 3], Figure 3, a schematic view illustrating an example of obtaining a local geometric representation based on cross-sectional images (from a medical imaging device),

[0026] [Fig 4], Figure 4, a schematic representation of an example of an annotated representation of an intermediate element, the annotated representation having been obtained from a preparatory image, and

[0027] [Fig 5], Figure 5, a schematic representation of an example of registration of a local geometric representation and a preparatory geometric representation in the tracking frame.

[0028] An example of a system 10 for determining the position of a target element Ec on images of interest of a body area Z is illustrated in Figure 1. The target element Ec is illustrated in Figure 3.

[0029] In this example, the system 10 comprises an imaging device 12, a support 14, a tracking device 16, and a computer 18. In a variant, the system 10 comprises only the computer 18.

[0030] The imaging device 12 is capable of acquiring images of a body area Z. The imaging device 12 is, for example, a camera.

[0031] In a primary embodiment, the acquired images are two-dimensional (2D) images.

[0032] Alternatively, the acquired images are three-dimensional (3D) images, for example obtained directly from a 3D video stream or resulting from two 2D video streams combined to obtain the 3D images.

[0033] The support 14 supports the imaging device 12. The support 14 is capable of being moved, thus allowing the imaging device 12 to be moved.

[0034] The support 14 is, for example, a tube into which the imaging device 12 is inserted.

[0035] The tracking device 16 is connected to the support 14. The tracking device 16 is capable of moving the imaging device 12 and of tracking the movements of the support 14, and therefore of the imaging device 12.

[0036] In one example, the tracking device 16 is an instrumented arm.

[0037] The computer 18 is, for example, connected by wire or wireless means (Wifi, Bluetooth), on the one hand, to the imaging device 12 so as to receive the images acquired by the imaging device 12, and on the other hand, to the tracking device 16 to obtain the position of the imaging device 12.

[0038] The calculator 18 is, for example, a computer interacting with a computer program product.

[0039] The computer 18 typically comprises a processor comprising a data processing unit, memories and an information medium reader. The computer 18 also typically comprises a human-machine interface (keyboard), a screen (touch or not) and a mouse.

[0040] The computer program product includes an information medium.

[0041] The information medium is a medium readable by the computer 18, usually by the data processing unit. The readable information medium is a medium suitable for storing electronic instructions and capable of being coupled to a bus of a computer system.

[0042] For example, the information medium is a USB key, a floppy disk, an optical disk, a CD-ROM, a magneto-optical disk, a ROM memory, a RAM memory, an EPROM memory, an EEPROM memory, a magnetic card, an optical card or a punched card. The computer program including program instructions is stored on the information medium.

[0043] The computer program is loadable onto the data processing unit of the computer 18 and is adapted to cause the implementation of a method for determining the position of a target element Ec on images of interest of a body area Z.

[0044] The operation of the device 10 will now be described with reference to the example of FIG. 2, which illustrates a flowchart of a method for determining the position of a target element Ec on images of interest of a body area Z and FIGS. 1 and 3 to 5, which illustrate examples of implementation of steps of the method.

[0045] The determination method described below aims to determine the position of a target element Ec on images of interest of a body area Z. The body area Z comprises at least one intermediate element Ei and at least one target element Ec. The intermediate element Ei is visible on the images of interest, the target element Ec is generally not visible on the images of interest (hidden by organs or tissues of the body area Z). It is understood that the intermediate element Ei and the target element Ec are in proximity.

[0046] Preferably, the intermediate element Ei has an invariant shape in projective geometry, that is to say that the shape of the intermediate element does not vary when the element is projected (in a plane for example). The intermediate element Ei has for example a tubular shape.

[0047] Preferably, the intermediate element Ei is an arterial network, such as the iliac arterial network, and the target element Ec is a lymph node, preferably a sentinel lymph node.

[0048] Figure 1 generally illustrates the geometric reference points and transformations considered when implementing this method.

[0049] In particular, three distinct geometric reference points are considered, namely:

[0050] - an image reference Ri (variable) specific to each image acquired by the imaging device 12 and in which the elements of the image are identified. The images considered in the remainder of the description are the preparatory images IM P and IMi images of interest.

[0051] - a tracking marker R s(fixed) in which the positions of the imaging device 12 are identified during the acquisition of the different images. Thus, the positions, in the tracking frame Rs, of the images acquired by the imaging device 12 are a function of the position of the imaging device 12. The tracking frame Rs is for example a frame relating to the tracking device (base of the articulated arm for example). - a local frame RL (fixed) in which a local geometric representation GL of the intermediate element Ei is identified (obtained from sectional images also identified in the local frame).

[0052] Figure 1 also illustrates the transformations allowing one to move from one reference point to another, namely:

[0053] - local transformation L T S allowing to move from the tracking marker R s to the local reference point RL. The local transformation L T Sis a constant transformation regardless of the position of the imaging device 12.

[0054] - the preparatory transformation s Ti' allowing you to move from the image reference point Ri to the tracking reference point R s . The preparatory transformation s Ti' is a transformation that varies depending on the position of the imaging device 12 during the acquisition of the image considered (the index “i” indicates that the transformation is variable, i being incremented over time).

[0055] - image transformation L Ti' allowing to move from the image reference frame Ri to the local reference frame RL. The image transformation L Ti' is a transformation that varies depending on the position of the imaging device 12 during the acquisition of the image considered (the index “i” indicates that the transformation is variable, i being incremented over time).

[0056] These transformations are linked together by the following formula:

[0057] LT = L T S . s Ti'

[0058] The aim of this method is to determine the image transformation L Ti' allowing the recalibration of position information (position of the target element) located in the image frame Ri of the image considered to the local frame RL. To do this, it is necessary to know the preparatory transformation s Ti' for the image considered and the local transformation L T S . The preparatory transformation s Ti' is suitable to be obtained via the tracking device 16. Thus, it remains to determine the local transformation L Ts.

[0059] The determination method comprises a preparatory phase 100 and an operating phase 200.

[0060] Preparatory phase 100 aims to determine local transformation L T Sallowing to move from the tracking marker R s to the local reference point RL. During the exploitation phase 200, the local transformation L T S determined is used to determine the image transformation L Ti' allowing to determine the position of the target element on the image of interest IMi considered.

[0061] The determination method is implemented for a stationary body area Z in the tracking frame R s. Thus, if the body area Z moves or is in motion, the different phases of the method must be repeated. The determination method is implemented by the computer 18 of the determination device 10, i.e. is implemented by computer. In particular, it is emphasized that the phases and steps described for the determination method relate to image processing on previously acquired images of a body area Z. In particular, it is emphasized that the present method does not relate to the acquisition of the images, these images being only obtained, in the sense of a data loading, by the computer 18.

[0062] The steps of the method are therefore entirely implemented outside the human body, without contact with the human body. None of these steps are therefore of a surgical or therapeutic nature. The determination method therefore concerns a non-surgical method for determining the position of a target element Ec on images of interest of a body area Z.

[0063] The preparatory phase 100 will now be described in more detail. In particular, as previously indicated, the preparatory phase 100 aims to identify the local transformation L T S (constant) allowing to move from the tracking reference point R s to the local reference point RL.

[0064] The preparatory phase 100 comprises a step 110 of obtaining a geometric representation, called local geometric representation GL, of the intermediate element Ei. As indicated previously, by the term “obtaining”, it is understood loading of the images by the computer 18, these images having been for example previously stored in a memory of the computer 18, or coming from a digital data stream to which the computer 18 is connected.

[0065] The local geometric representation GL is a three-dimensional representation. The local geometric representation GL is located in the local reference frame RL. The target element Ec has a relative position with respect to the intermediate element Ei which is known in the local reference frame RL (for example obtained via the sectional images located in the local reference frame RL and used to obtain the local geometric representation GL).

[0066] In an exemplary embodiment, the local geometric representation GL is obtained as a function of cross-sectional images of the body area Z comprising the intermediate element Ei and the target element Ec. The cross-sectional images were obtained by a medical imaging device. The medical imaging device is, for example, an MRI device, a CBCT device, an optical imaging device, a scanner, or an ultrasound device.

[0067] Cross-sectional images are for example IM scanner images S . A CT image is a slice image of a body area Z obtained by positron emission tomography (SPECT) coupled with computed tomography (CT), thus making it possible to image both the intermediate element Ei and the target element Ec. In particular, as illustrated in Figure 3, CT images IM S2D are used to reconstruct a 3D representation of the intermediate element Ei (iliac arterial network). The image processing software used (3D slicer® for example, see for example the following article: Fedorov A, Beichel R, Kalpathy-Cramer J, Finet J, Fillion-Robin JC, Pujol S, et al. 3D Slicer as an image computing platform for the Quantitative Imaging Network. Magn Reson Imaging. Nov 2012;30(9):1323-41 ) allows to generate a skeletonization of the arterial network. This skeleton forms the local geometric representation GL.

[0068] In the case where the intermediate element Ei is the iliac arterial network, this skeleton is, for example, formed of 2D curves immersed in 3D (represented by points or mathematical functions (splines, Bézier curves, etc.)). In particular, the skeleton materializes the points of the intermediate element Ei respecting a property of projective invariance (axis of revolution of the tubes for example).

[0069] The preparatory phase 100 comprises a step 120 of obtaining preparatory images IM P of the body area Z. The preparatory IM images P were acquired by the imaging device 12 for different positions of the imaging device 12. Each position of the imaging device 12 corresponds to a different viewing angle of the body area Z.

[0070] IM preparatory images P each have a known position in the tracking frame R s . This known position has for example been obtained as a function of the position of the imaging device 12 obtained via the tracking device 16, to which the preparatory transformation is applied. s Ti' allowing you to move from the image reference point Ri to the tracking reference point R s . The preparatory transformation s Ti' is considered known when the position of the imaging device 12 is known. For example, the preparatory transformations Ti' as a function of the position of the imaging device 12 is obtained upstream, for example from supplier data or via prior calibration.

[0071] In one example, the preparatory transformation s Ti' is composed of two elements. A first transformation between the imaging device 12 and the support 14 (at the end of the tracking device 16, for example an instrumented arm). This transformation is fixed and is obtained by a calibration (for example with a target). Then, there is a second transformation between the support 14 (at the end of the tracking device 16, for example an instrumented arm) and the base of the tracking device 16 (in this case, the base of the instrumented arm) which is variable due to the movements of the arm. This second transformation is obtained via the tracking device 16.

[0072] The preparatory phase 100 includes a step 130 of determining the local transformation L T S allowing to move from the tracking marker R s to the local reference point RL. The local transformation L T S is determined based on the local geometric representation GL, the preparatory images IMP, and the positions of the imaging device 12 during the acquisition of the preparatory images IM P .

[0073] In the following, a particular example of determining the local transformation is described. L Ts. Nevertheless, the invention applies to any other embodiment making it possible to determine the local transformation L T S .

[0074] In this example, the determination step 130 comprises a sub-step 130A according to which, for each preparatory image IM P, a geometric representation of the intermediate element Ei is determined, called annotated representation GA. In this example, at least three preparatory images IM P are considered.

[0075] In this example, each annotated representation GA is a two-dimensional representation. The annotated representations GA are located in the tracking frame Rs according to the position of the imaging device 12 during the acquisition of said images.

[0076] In this example, the annotated representation GA of each preparatory image IM P is obtained by the action of an operator annotating / highlighting / pointing at a portion of the intermediate element Ei on the image (for example via a touch screen).

[0077] Alternatively, the annotated GA representation of each preparatory IM image Pis obtained semi-automatically, that is to say by an annotation carried out by the computer followed by validation / rectification by an operator. The annotation carried out by the computer is for example carried out by a detection algorithm.

[0078] Figure 4 illustrates an example of a preparatory IM image P on which a part of the intermediate element Ei has been identified by annotation, highlighting or pointing (automatically, manually or semi-automatically), the annotations / highlights / pointings thus forming the annotated representation GA.

[0079] The determination step 130 comprises a sub-step 130B of placing the local geometric representation GL at a starting position in the tracking frame R s The initial position is known (but can be chosen in any way).

[0080] Determination step 130 includes a determination sub-step 130C, in the tracking reference frame Rs , based on the annotated representations GA, of a representation, called preparatory geometric representation G P .

[0081] In particular, in the example illustrated by Figure 5, the preparatory geometric representation G P is obtained by projection of the annotated representations GA and intersection of said projections. Indeed, the intersection of the projective surfaces corresponds to the annotated / highlighted / pointed invariant portion of the intermediate element Ei (typically the center C of the artery). The preparatory geometric representation G P is then a “skeleton” of the network at the intersection of the projected surfaces as illustrated in Figure 5.

[0082] Step 130 of determination includes a sub-step 130D of determination of the local transformation L T S depending on the local geometric representation GL and the preparatory geometric representation Gp.

[0083] In particular, local transformation L T S is obtained by recalibrating (preferably by superimposing) the local geometric representation GL and the preparatory geometric representation Gp in the tracking frame R s (and knowing the initial position of the local geometric representation GL in the tracking frame R s ).

[0084] Local transformation L T s is, for example, obtained by minimizing the distances between the local geometric representation GL and the preparatory geometric representation Gp. For example, the minimization consists of minimizing the root mean square (RMS) of the distances between the curves forming the local geometric representation GL and the preparatory geometric representation Gp. In another example, the minimization is carried out by a method called gradient descent or by any other corresponding method of minimizing distances.

[0085] In particular, Figure 5 illustrates an example of iterations to minimize the distances between the local geometric representation GL and the preparatory geometric representation Gp.

[0086] Preferably, if the degree of similarity is below a predetermined threshold (threshold set by default in the software but adaptable by the operator), new GA annotated representations are required and the previous steps are repeated with these new GA annotated representations.

[0087] Preferably, conditions have been set for the algorithm to stop the computation iterations. These conditions include at least one of the following:

[0088] - the error is sufficiently small (less than a predetermined threshold),

[0089] - the maximum number of iterations is reached, or

[0090] - the error no longer varies.

[0091] The operating phase 200 comprises a step 210 of obtaining an image of interest IMi of the body area Z. The image of interest IMi was acquired by the imaging device 12 for a position of the imaging device 12 known via the tracking device 16.

[0092] As indicated previously, by the term “obtaining”, it is understood loading of the images by the computer 18, these images having been for example previously stored in a memory of the computer 18, or coming from a digital data stream to which the computer 18 is connected. The exploitation phase 200 comprises a step 220 of determining an image transformation L Ti' for the image of interest IMi as a function of the local transformation L Ts determined previously and the position of the imaging device 12 during the acquisition of the image of interest IMi.

[0093] In particular, the position of the imaging device 12 makes it possible to obtain the preparatory transformation s Ti' for the image of interest IMi considered (for example in the same way as in the examples described previously for the preparatory phase). The image transformation L Ti' for the image of interest IMi is then obtained with the following formula: L Ti' = L T s . s Ti'.

[0094] The exploitation phase 200 comprises a step 230 of determining the position Pi of the target element Ec on the image of interest IMi as a function of the image transformation L Ti' determined and the known relative position of the target element Ec with respect to the intermediate element Ei.

[0095] Preferably, the operating phase 200 comprises a step 240 of displaying the image of interest IMi on a screen (of the computer 18) with superimposed (i.e. augmented reality) a representation of the target element Ec at the position Pi determined on the image of interest IMi.

[0096] Preferably, the steps of the operating phase 200 are repeated over time for images of interest I Mi corresponding to different positions of the imaging device 12. The repetition is preferably carried out in real time and continuously, that is to say as the images of interest IMi are received by the computer 18.

[0097] Thus, the present method and the present system 10 make it possible to determine the position of a target element Ec on images of a body area Z acquired from different points of view. For this, an intermediate element Ei is used to recalibrate a representation of the target element Ec on the image of interest I Mi considered.

[0098] One of the advantages of the present method is that once the local transformation L Ts obtained, and provided that the body area Z remains stationary, the registration can be carried out on images of interest IMi of the body area Z acquired regardless of the position of the imaging device 12. In other words, the imaging device 12 can be freely moved to acquire different images of interest I Mi of the body area Z without having to re-perform a preparatory calibration phase.

[0099] The method can therefore be used to locate sentinel nodes (i.e. target element Ec ) invisible by the imaging device 12 (e.g. endoscopic camera, laparoscope). Indeed, the intermediate element Ei (iliac arterial network) makes it possible to recalibrate information obtained previously (preferably from SPECT images coupled with a preoperative CT (computed tomography) on which the lymph nodes will have been previously identified) on the images acquired by the imaging device 12. It is thus possible to generate a visible overlay in augmented reality.

[0100] Those skilled in the art will understand that the previously described embodiments and variations may be combined to form new embodiments provided that they are technically compatible.

[0101] For example, although the present description has given an example with a single intermediate element and a single target element, those skilled in the art will understand that the invention also applies to the case where several intermediate elements and / or several target elements are considered.

[0102] In addition, it should be noted that in the examples of the present description, the transformations between the different reference points have been described in the direction of the arrows in figure 1. Nevertheless, those skilled in the art will understand that the present description also applies in the case where:

[0103] - the local transformation considered allows to move from the local reference frame RL to the tracking reference frame R s (transformation S T ), and

[0104] - the preparatory transformation considered allows to pass from the tracking reference R s to the image reference Ri (transformation 'T s '), And

[0105] - the image transformation considered allows to move from the local reference frame RL to the image reference frame Ri (transformation 'TJ).

[0106] These transformations are in this case linked together by the following formula: 'TL 1 = S^TL

Claims

CLAIMS 1. Method for determining the position (Pi) of at least one target element (Ec) on at least one image of interest (IMi) of a body area (Z), the body area (Z) comprising at least one intermediate element (Ei) imaged on the image of interest (IMi), the image of interest (I Mi) having been acquired by an imaging device (12), each image acquired by the imaging device (12) having its own reference frame, called image reference frame (Ri), in which the elements of the image are identified, the position of the imaging device (12) at each image acquisition being identified in a fixed reference frame, called tracking reference frame (R s), the body area (Z) being stationary in the tracking frame (Rs) during the implementation of the method, the method being implemented by computer and comprising: a. a preparatory phase comprising the following steps: i. obtaining a geometric representation, called local geometric representation (GL), of the intermediate element (Ei), the local geometric representation (GL) being located in a fixed geometric frame, called local frame (R L ), the target element (Ec) having a relative position with respect to the intermediate element (Ei) which is known in the local reference frame (R L ), it. obtaining preparatory images (IMP) of the body area (Z), the preparatory images (IM P) having been acquired by the imaging device (12) for different positions of the imaging device (12), each position of the imaging device (12) corresponding to a different viewing angle of the body area (Z), ill. the determination of a transformation, called local transformation ( L Ts), between the tracking mark (R s ) and the local reference (R L ) depending on the local geometric representation (GL), preparatory images (IM P ), and positions of the imaging device (12) during the acquisition of the preparatory images (IMP), b. an exploitation phase comprising the following steps: i. obtaining an image of interest (IMi) of the body area (Z), ii. determining a transformation, called image transformation ( L Ti'), between the local reference frame (RL) and the image reference frame (Ri) of the image of interest (IMi), the image transformation ( L Ti') being determined as a function of the local transformation (L T S ) determined and the position of the imaging device (12) during the acquisition of the image of interest (IMi), and ill. the determination of the position (Pi) of the target element (Ec) on the image of interest (I Mi) as a function of the image transformation ( L Ti') determined and the known relative position of the target element (Ec) with respect to the intermediate element (Ei).

2. Method according to claim 1, in which the steps of the exploitation phase are repeated over time for images of interest (IMi) corresponding to different positions of the imaging device (12).

3. Method according to claim 1 or 2, in which the operating phase comprises a step of displaying the image of interest (IMi) on a screen with a superimposed representation of the target element (Ec) at the position (Pi) determined on the image of interest (IMi).

4. Method according to any one of claims 1 to 3, in which the local geometric representation (GL) is obtained as a function of sectional images (IMs) of the body area (Z) comprising the intermediate element (Ei) and the target element (Ec), the sectional images (IMs) having been acquired by a medical imaging device.

5. Method according to any one of claims 1 to 4, in which the step of determining the local transformation ( L T S ) includes: a. the determination, for each preparatory image (IMP), of a geometric representation, called annotated representation (GA), of the intermediate element (Ei), the annotated representations (GA) being located in the tracking frame (R s ) depending on the position of the imaging device (12) during the acquisition of said images, b. the placement of the local geometric representation (GL) at an initial position in the tracking frame (R s), c. the determination, in the tracking reference (R s ), based on the annotated representations (GA), of a representation, called preparatory geometric representation (Gp), and d. the determination of the local transformation ( L T S ) by recalibration of the local geometric representation (GL) and the preparatory geometric representation (Gp) in the tracking frame (R s ).

6. Method according to claim 5, in which the preparatory geometric representation (Gp) is obtained by projection of the annotated representations (GA) and cross-referencing of said projections.

7. Method according to any one of claims 1 to 6, in which the intermediate element (Ei) has an invariant shape in projective geometry.

8. Method according to any one of claims 1 to 7, in which the intermediate element (Ei) is an arterial network, such as the iliac arterial network, and the target element (Ec ) is a lymph node, preferably a sentinel lymph node.

9. System (10) for determining the position (Pi) of at least one target element (Ec) on at least one image of interest (IMi) of a body area (Z), the body area (Z) comprising an intermediate element (Ei) imaged on the image of interest (I Mi), the image of interest (IMi) having been acquired by an imaging device (12), each image acquired by the imaging device (12) having its own reference frame, called image reference frame (Ri), in which the elements of the image are identified, the position of the imaging device (12) at each image acquisition being identified in a fixed reference frame, called tracking reference frame (R s ), the system comprising a computer (18) configured to implement the steps of a method according to any one of claims 1 to 8.

10. The system (10) of claim 9, wherein the system (10) also comprises: a. the imaging device (12) for acquiring the preparatory images (IMP) and the images of interest (IMi), b. a support (14) on which the imaging device (12) is mounted, and c. a tracking device (16) connected to the support (14) for moving the imaging device (12) and tracking the movements of the imaging device (12).

Images