How to obtain length from an image representing a cross-section of tissue volume

Abstract

In a method for obtaining a first length from a first two-dimensional image (71) representing a cross-section of a three-dimensional tissue volume at a first time, and a second length from a second two-dimensional image (81) representing a cross-section of a three-dimensional tissue volume at a second time, a first point (61.1) and a second point (61.2) are marked in the first two-dimensional image (71). Next, a third piece of data relating to the first two-dimensional image (71) is obtained. A fourth point (61.4) and a fifth point (61.5) are marked in the second two-dimensional image (81), and a sixth piece of data relating to the second two-dimensional image (81) is obtained. The marked first, second, fourth, and fifth points (61.1, 61.2, 61.4, 61.5), along with the third and sixth data, are used to check whether the positions and orientations of the first two-dimensional image (71) and the second two-dimensional image (72) match sufficiently. If they match, the first length is determined from the marked first and second points (61.1, 61.2) and the third data, and the second length is determined from the marked fourth and fifth points (61.4, 61.5) and the sixth data. In particular, the third and sixth data are obtained by marking the third point (61.3) and the sixth point (61.6), respectively. The third point (61.3) and the sixth point (61.6) may correspond to physiological landmarks visible in the first image (71) and the second image (81), respectively.

Description

Technical Field

[0001] The present invention relates to a method of obtaining a first length from a first two-dimensional image representing a cross-section of a three-dimensional tissue volume at a first time and obtaining a second length from a second two-dimensional image representing a cross-section of the three-dimensional tissue volume at a second time.

Background Art

[0002] There are various applications in which the characteristics or progression of a physiological state are examined or monitored based on data obtained from medical imaging. The images may be obtained, for example, by ultrasound, magnetic resonance, X-ray or OCT imaging. In many cases, the size of a recognizable structure in the image is determined and forms an important basis for further evaluation of the physiological state. Usually, the size is characterized by one or several lengths.

[0003] A method including the measurement of a first length at a first time point and the measurement of a second length at a second time point is described in Patent Document 1 of the same applicant, which is concurrently filed. It is used for examining the temporal progression of the elasticity of tissue structures.

[0004] In many cases, corresponding results obtained from two or more images taken at different times and / or under different external or internal influences such as different applied external pressures, different phases of the blood circulation or respiratory cycle are compared. Usually, such a comparison is meaningful only if the tissue volumes represented by the first image and the second image and the measurement modality (for example, the orientation of the axis along which the length value is determined) are sufficiently consistent.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The object of the present invention is to create a method relating to the art described above that enables reliable comparison of length values ​​obtained from two or more two-dimensional images representing cross-sections of three-dimensional tissue volumes. [Means for solving the problem]

[0007] The solution of the present invention is defined by the features of claim 1. According to the present invention, the method is a) A step of marking a first point in the first two-dimensional image, b) A step of marking a second point in the first two-dimensional image, c) A step of acquiring third data relating to the first two-dimensional image, d) A step of marking a fourth point in the second two-dimensional image, e) A step of marking a fifth point in the second two-dimensional image, f) A step of acquiring sixth data relating to the second two-dimensional image, g) A checking step of checking whether the positions and orientations of the first two-dimensional image and the second two-dimensional image match sufficiently using the marked first point, second point, fourth point and fifth point and the third data and sixth data, If they matched, (h) A step of determining the first length from the marked first and second points and the third data, i) a step of determining the second length from the marked fourth and fifth points and the sixth data.

[0008] The first, second, fourth, and fifth points may be manually marked by the user using an appropriate user interface. Marking the points may be done by directly marking the point-like locations (such as pixels in the image data) in the first or second two-dimensional image, respectively. The marking process may be done by providing a cursor, crosshairs, or similar visual aids. All or some of the points may be indirectly marked by marking extended one-dimensional and / or two-dimensional structures such as: - A line or arrow, wherein a single point is mapped to a designated location on the line or arrow, e.g., a center point or a designated endpoint, or two points are mapped to two designated locations, in particular two endpoints, on the line or arrow. - An arc in which a single point is mapped to a specified location on the arc, for example, the center point of the arc, the center of rotation of the arc, or a specified endpoint, or two points are mapped to two specified locations, in particular to two endpoints of the arc. - A shape such as a circle, triangle, or rectangle, where a single point maps to a specified location, e.g., the center point of a circle, triangle, or rectangle or a specified corner of a polygon; two points map to the center and a further specified location or two specified locations on the perimeter; or three points map to the center and / or further specified locations, particularly locations on the perimeter.

[0009] Points marked on the first two-dimensional image and / or the second two-dimensional image may be obtained from calculations based on the marked structure, or on two or more marked structures (of the same or different kinds). These calculations may include determining the center or symmetry point of a line or area, forming an average, and so on.

[0010] To improve the accuracy of the marking process, an enlarged view of the image may be displayed. The present invention includes variations of a method in which three or more (or four or more) points are marked on each of an image, as well as variations in which three or more images acquired at different points in time are marked. In principle, the number of points to be marked does not need to be the same for all processed images.

[0011] Depending on the characteristics being examined, two (or more) images may be acquired at intervals of several minutes, hours, days, weeks, or months. Point marking and acquisition of third and / or sixth data may be performed approximately simultaneously with or at a later stage of each image capture, before or after the capture of further images. Nevertheless, to enable immediate user feedback, it is preferable that the marking of fourth and fifth points and the acquisition of sixth data be performed approximately simultaneously with the capture of the second two-dimensional image. Immediate user feedback allows for the capture of further image data until a second image that meets the criteria for matching with the first image becomes available.

[0012] The method of the present invention ensures that two or more images representing the same tissue volume used to examine a condition meet certain concordance criteria. The two or more images may be taken sequentially in a single measurement session and / or in independent sessions with time intervals ranging from minutes to months. In the first case, the two or more images may represent conditions under different external or internal influences, such as different applied external pressures or different phases of the blood circulation or respiratory cycle. In the second case, the images may be used to monitor the temporal progression of a condition affecting tissue volume.

[0013] In particular, the matching criteria are selected to ensure that relevant characteristics and their changes from image to image are reliably captured from the image and / or sensor data. This is especially relevant to captured images in independent sessions, involving independent placements of imaging devices and potentially different operators.

[0014] The concordance criteria or associated thresholds may differ between comparing two images acquired in the same measurement session and comparing two images acquired in separate measurement sessions. For example, if relative characteristics (such as the ratio of distance values) are acquired in each of the individual measurement sessions, then strict agreement of the site and imaging conditions is far more important for two or more images from individual sessions used to acquire relative characteristics by comparing them with images from different sessions.

[0015] The method of the present invention is particularly useful for processing B-mode ultrasound images, but is applicable to a variety of other imaging modalities, including X-ray, OCT, and MRI. In embodiments of the method of the present invention, one or more of the first, second, fourth, and fifth points are automatically marked based on the structure captured in each of the images. The automatic marking may be based on known digital image processing techniques, including machine learning-based methods. The structure may be an easily identifiable landmark, such as an interlayer interface of captured tissue, blood vessels, bone, etc.

[0016] All points mentioned may be automatically marked, especially if they all relate to structures that can be automatically identified within the image data. In a modified example, only some of the points may be automatically marked; for example, a second point may be automatically marked based on the manual marking of a first point, and a fourth point may be automatically marked based on the manual marking of a third point. After one or more points have been automatically marked, operator verification may be required. The operator may be given the opportunity to either verify the automatic markings or to manually modify the markings or some of them.

[0017] In a preferred embodiment of this method, the third data is obtained by marking a third point in the first two-dimensional image, and the sixth data is obtained by marking a sixth point in the second two-dimensional image.

[0018] Again, the third and sixth points may be manually marked, and the same options as described above in relation to the first, second, fourth, and fifth points are available. The third and sixth points may be obtained in a single marking step, for example, from the marking of an extended one-dimensional or two-dimensional structure, together with the first and / or second or fourth and / or fifth points respectively.

[0019] Similarly, the third and sixth points may be automatically marked using the techniques described above in relation to the first, second, fourth, and fifth points. In a preferred embodiment, the third point and the sixth point are automatically marked, and the first point, the second point, the fourth point, and the fifth point are manually marked. In this case, the marked first and second points may be considered to automatically define and / or mark the third point, and the marked fourth and fifth points may be considered to automatically define and / or mark the sixth point. In this case, it is not essential to display the third point or the sixth point on the respective images, and they may be used for internal purposes only. Nevertheless, in many cases, it is also useful to display the points marked by a fully automatic process to enable the user to monitor the process.

[0020] Nevertheless, even in this case, the manual marking process of the first, second, fourth, and fifth points may be assisted based on image processing or segmentation. This may include, for example, providing suggestions about the locations of the first, second, fourth, and fifth points that are confirmed (or optionally changed) by the operator.

[0021] To check whether the positions and orientations of the first and second two-dimensional images match sufficiently, several criteria can be adopted. One criterion relates to intensity or grayscale value, i.e., for the checking process, the intensity or grayscale value in the region of the third marked point is compared with the intensity or grayscale value in the region of the sixth marked point. If the difference exceeds a certain threshold, the images are considered not to match. The region may be as small as a single pixel at the location of the marked point, or, preferably, may include an area surrounding the marked point. The intensity or grayscale value of the points in the area may be appropriately averaged, for example, using a weighted average, and the weighting of the pixels decreases as the distance from each marked point increases.

[0022] Another criterion is based on the data of a position sensor, especially a position sensor incorporated in an imaging device, especially a handheld imaging probe. In this case, the third data is obtained from a position sensor that measures the first position of the image sensor when capturing the first two-dimensional image, and the sixth data is obtained from a position sensor that measures the second position of the image sensor when capturing the second two-dimensional image. It is important to note that the second image may be obtained using the same imaging device as that used to capture the first image or from a different imaging device (thus, the sixth data is obtained by a different position sensor).

[0023] In particular, the first position is the first inclination, the second position is the second inclination, and the inclination is preferably a two-dimensional or three-dimensional inclination that can be represented by two or three Euler angles respectively.

[0024] Instead of or in addition to the inclination, the first position may be the first location with respect to the tissue, especially with respect to the patient's body surface. Preferably, the location is measured along two directions, for example, in an XY Cartesian coordinate system.

[0025] In a preferred embodiment, the location of a handheld device, i.e., an ultrasound probe, guided on the patient's body surface, is tracked using an optical sensor. This sensor may include a light source, e.g., an infrared laser diode, and an image sensor, e.g., a CCD sensor, similar to an optical computer mouse device. Such position sensors are small, reliable, and provide precise results, in particular, regarding the relative movement of the handheld device to the body surface, as long as there is contact between the device (and therefore the sensor) and the body surface. The computational load is dramatically reduced compared to tracking based on image data. In addition, even if the image data represents a single slice along an extending portion of the imaging array, the optical sensor allows tracking the position not only along this extending portion but also in a direction parallel to it.

[0026] Based on positional data, it may be possible to avoid processing (and comparing) views related to substantially different imaging planes. In other variations of the method of the present invention, location data, particularly location data, may be used to generate three-dimensional data. This data may include volumetric data that images the tissue in three dimensions. Alternatively, or in addition to this, the extent of tissue structures (e.g., compartments) may be tracked along a path advanced by the imaging probe. Based on this detection, the maximum extent along a given direction may be automatically determined, for example.

[0027] Within a single measurement session, sensors can be used to track the movement of the imaging device and detect movements associated with image quality degradation and / or the matching of images taken consecutively within the session. For example, if a measurement session anticipates the capture of two or more images at different values ​​of external pressure applied to a body part being examined by the imaging device, movement along the longitudinal axis of the device is required and acceptable, while other movements such as sliding movements that shift the measurement site, tilting movements that change the measurement axis, and rotational movements that change the imaged plane are minimized. Therefore, if unacceptable movement is detected from the position data, a warning may be issued to the operator. The warning may be accompanied by instructions to assist the operator in correcting the position and / or orientation of the imaging device, for example, an arrow indicating the direction (and possibly the degree) of correction, particularly aimed at minimizing errors resulting from suboptimal positioning during increasing external pressure. Warnings and / or instructions may be provided by visual, auditory, and / or tactile information directly on the probe and / or user interface used to display and mark the images. In the latter case, the information may be shown in and / or alongside the real-time image. Generally, visual representations may include light signals, changing colors, graphic symbols (such as arrows or lines), and numerical values.

[0028] Position data recorded throughout one or more measurement sessions may be used to provide the operator with a (summary) report, in particular to improve the accuracy of operator handling in future measurement sessions, and accuracy may relate in particular to probe positioning and / or movement to increase external pressure.

[0029] Alternatively, or in addition to this, relative torsion of the imaging plane may be detected based on the image data itself, for example, using speckle tracking techniques. If a vector representing the torsion can be obtained from the position data and / or image data, it may be possible to modify one or both images to enable a meaningful comparison. In these cases, the two images are classified as inconsistent only if modification is impossible or if the modification results in an unacceptable increase in the margin of error.

[0030] Another criterion concerns the geometric relationship between the marked points and the third and sixth data points, respectively. In this case, the checking step determines at least a first reference angle from the marked first and second points and the third data point, and at least a second reference angle from the marked fourth and fifth points and the sixth data point, after which the first and second reference angles are compared. Again, the reference angles indicate the orientation of the imaging plane. Similarly, a substantial discrepancy in these angles may indicate other problems regarding the comparability of the two images.

[0031] Another geometric criterion relates to length. In this case, the checking step determines at least a first reference length from the marked first and second points and the third data, and at least a second reference length from the marked fourth and fifth points and the sixth data, after which the first reference length and the second reference length are compared. When the locations of the marked points, the nature of the third and sixth data and the reference lengths are appropriately selected, these reference lengths relate to geometric relationships that are essentially constant in a given volume of tissue. In this case, if the reference length obtained from the first image differs significantly from the reference length obtained from the second image, this indicates a discrepancy between the images.

[0032] In some embodiments, the first length represents the distance between the first point and the second point, the second length represents the distance between the fourth point and the fifth point, the first length is normalized based on the third data, and the fourth length is normalized based on the sixth data.

[0033] This can ensure a consistent imaging ratio, particularly relevant when the absolute value is determined from two images. Normalization may be based on lengths obtained from two points and additional data (e.g., additional marked points), and / or angles obtained from additional data that may indicate twist between the points and the imaging plane, as described above.

[0034] Preferably, in the second two-dimensional image capture process, the first two-dimensional image is displayed to the operator along with a candidate for the second two-dimensional image to assist in capturing the second two-dimensional image. In detail, the candidate for the second two-dimensional image represents the most recently captured image data ("live view"). This enables an immediate left-right comparison between the second image and the first image, and thus capture of a matching image.

[0035] It is particularly preferable that geometric objects representing the marked first and second points and the third data are displayed together with the first two-dimensional image. In particular, if the third data is a point, the geometric object may be a direct representation of this point. If the fourth and fifth points (and potentially the sixth point) are manually marked in the second image, displaying the markings in the first picture is useful to the operator and reduces the risk of incorrect marking.

[0036] In a preferred embodiment, geometric objects representing the fourth and fifth points and the sixth data are marked in the candidate of the second two-dimensional image, and the results and / or intermediate results of the verification based on the marked first, second, fourth, and fifth points and the third and sixth data are displayed together with the first two-dimensional image. If the sixth data is a point, the geometric object may be a direct representation of this point.

[0037] This allows for an iterative discovery process when capturing a second picture, for example, to correctly position the imaging probe. Positioning may be assisted by displaying appropriate information based on points and / or intermediate results of further data and validation. Appropriate information may be visualized by arrows, gauges, or other elements.

[0038] In some embodiments, in addition to the marked first, second, fourth, and fifth points, as well as the third and sixth data, seventh data is obtained from a position sensor that measures the first position of the image sensor when capturing the first two-dimensional image, and eighth data is obtained from a position sensor that measures the second position of the image sensor when capturing the second two-dimensional image. The seventh and eighth data are used to check whether the positions and orientations of the first and second two-dimensional images match well, and / or to determine a first length, and / or a second length.

[0039] In particular, the first position is the first inclination, the second position is the second inclination, and the inclinations are preferably two-dimensional or three-dimensional inclinations that can be represented by two or three Euler angles, respectively.

[0040] Instead of, or in addition to, the inclination, the first position may be a first location relative to the tissue, particularly to the patient's body surface. Preferably, the location is measured along two directions, for example, in an XY Cartesian coordinate system.

[0041] In a preferred embodiment, the location of a handheld device, i.e., an ultrasound probe, guided on the patient's body surface, is tracked using an optical sensor. This sensor may include a light source, e.g., an infrared laser diode, and an image sensor, e.g., a CCD sensor, similar to an optical computer mouse device. Such position sensors are small, reliable, and provide precise results, in particular, regarding the relative movement of the handheld device to the body surface, as long as there is contact between the device (and therefore the sensor) and the body surface. The computational load is dramatically reduced compared to tracking based on image data. In addition, even if the image data represents a single slice along an extending portion of the imaging array, the optical sensor allows tracking the position not only along this extending portion but also in a direction parallel to it.

[0042] The use of additional marked points and data acquired from position sensors allows for additional verification and / or modification. This embodiment of the method of the present invention may be combined with any of the optional characteristics described above with respect to embodiments that include marking of third and sixth points in first and second two-dimensional images, respectively.

[0043] Other advantageous embodiments and combinations of features will become apparent from the detailed description below and the entirety of the claims. [Brief explanation of the drawing]

[0044] [Figure 1] A flowchart of a method for processing a two-dimensional image representing a cross-section of a three-dimensional tissue according to the present invention. [Figure 2a] A schematic diagram of an embodiment of an imaging device having a position sensor, suitable for use in the context of this method. [Figure 2b] A schematic diagram of an embodiment of an imaging device having a position sensor, suitable for use in the context of this method. [Figure 3] A schematic diagram of a measurement session using an imaging device. [Figure 4a] Images representing cross-sections of three-dimensional tissue volume under different external pressures, with marked points corresponding to determined lengths and anatomical landmarks. [Figure 4b] Images representing cross-sections of three-dimensional tissue volume under different external pressures, with marked points corresponding to determined lengths and anatomical landmarks. [Figure 4c] Images representing cross-sections of three-dimensional tissue volume under different external pressures, with marked points corresponding to determined lengths and anatomical landmarks. [Figure 5a] Images representing cross-sections of three-dimensional tissue volume under different external pressures, with marked points associated with determined lengths and anatomical landmarks, including a reference angle. [Figure 5b] Images representing cross-sections of three-dimensional tissue volume under different external pressures, with marked points associated with determined lengths and anatomical landmarks, including a reference angle. [Figure 5c] Images representing cross-sections of three-dimensional tissue volume under different external pressures, with marked points associated with determined lengths and anatomical landmarks, including a reference angle. [Figure 6a] A diagram showing a portion of the graphical user interface of an imaging device, displaying the results of previous and current measurements, including a quality assessment of the current measurement. [Figure 6b] A diagram showing a portion of the graphical user interface of an imaging device, displaying the results of previous and current measurements, including a quality assessment of the current measurement. [Modes for carrying out the invention]

[0045] In drawings, identical components are assigned the same reference numeral. Figure 1 is a flowchart of a method for processing a two-dimensional image representing a cross-section of a three-dimensional tissue according to the present invention. The example described relates to a sequence for acquiring two images of the same tissue volume at different external pressures. In this example, the images are acquired from an ultrasound imaging device that provides B-mode ultrasound images schematically shown in Figures 2a and 2b. In the first embodiment shown in Figure 2a, the probe 1 comprises an ultrasound array 2 for transmitting and receiving ultrasound 8 by a method known in itself. The probe 1 comprises a flexible membrane 3 that defines a fluid chamber 4 on a contact surface with the skin surface 9 of a subject. A pressure sensor 5 is provided to measure the pressure in the fluid chamber 4. The corresponding device is described in the concurrently pending PCT / EP2022 / 079972 of the same applicant.

[0046] Furthermore, the probe 1 is provided with a position sensor, namely an accelerometer 6. The accelerometer 6 enables the determination of the orientation of the probe 1 in space with respect to three Euler angles α, β, and γ.

[0047] In the second embodiment shown in Figure 2b, the probe 101 comprises an ultrasonic array 102 for transmitting and receiving ultrasonic waves 108 by a method known in itself. The probe 101 comprises a flexible membrane 103 defining a fluid chamber 104 on the contact surface with the skin surface 9 of the subject. A pressure sensor 105 is provided to measure the pressure in the fluid chamber 104. The corresponding device is described in the concurrently pending PCT / EP2022 / 079972 of the same applicant.

[0048] Furthermore, the probe 101 is provided with an optical sensor 106 comprising a position sensor, i.e., an infrared laser source for illuminating a region of the skin surface 9 beneath the probe 101, and a CCD sensor for imaging this region. Based on the CCD image, the movement of the probe 101 relative to the skin surface 9 in two directions X and Y can be identified.

[0049] Further embodiments of the probe include an accelerometer and an optical sensor, the optical sensor enabling the determination of both the location and orientation of the probe. Therefore, a first image is acquired using probes 1 and 101 (step 10.1). The first image is pre-processed on a processing and display device connected to probe 1 and / or probes 1 and 101 (step 11.1). The pre-processed image is then displayed on a display (step 12.1). Steps 10.1 to 12.1 are repeated in a circular process to continuously update the displayed image. As soon as the operator chooses to mark a first point (step 13.1), the most recent image is used for subsequent steps, and no new image is acquired and / or displayed.

[0050] The marking of the first point (step 13.1) is performed manually by the operator using an appropriate input device (e.g., touchscreen, touchpad, cursor keys, etc.) to move a cursor over the image and confirm a cursor position by corresponding actions such as pressing a designated location on the touchscreen or pressing a confirmation button. The confirmed first marked point is displayed on the image, for example, using a crosshair (see Figure 4a and the description below).

[0051] As soon as the first point is manually marked by the operator, the proposed positions for the second and third points are automatically determined and displayed (steps 14.1, 15.1). The proposed positions are determined by processing the image data representing the first image, based on the location of the first point and the anatomical structures identified in the image data. This processing is described in more detail below in relation to Figure 4.

[0052] The proposed positions are displayed on the image along with the first marked point. The operator is then asked to confirm the proposal or to adapt the placement of the proposed positions (step 16.1). This is also done using an appropriate input device. As soon as all positions are deemed correct by the operator, the selection is confirmed. Here, the positions of the first, second, and third points are stored along with image data representing the first image and potential further data such as a timestamp and the pressure reading of the pressure sensor 5 at the time the first image was acquired.

[0053] Here, the operator is required to increase the external pressure applied to the skin surface 9 in particular to adapt the modality of image acquisition (step 20). As soon as the modality is successfully fitted, a second image is acquired using probes 1 and 101 (step 10.2), and the processing is identical to that for acquiring the first image, i.e., the second image is pre-processed (step 11.2) and displayed on the display (step 12.2). Steps 10.2 to 12.2 are repeated in a circular process to continuously update the displayed image.

[0054] As soon as the operator chooses to mark the fourth point (step 13.2), the most recent image is used for the subsequent step, and no new image is acquired and / or displayed. Based on the position of the first point in the first image, and potentially also based on the positions of the second and third points in the first image, the proposed position of the fourth point is determined from the image data representing the second image and displayed on the second image. The operator now has the option to confirm the proposed position or move the fourth point before confirmation.

[0055] As soon as the position of the fourth point is confirmed, the proposed positions for the fifth and sixth points are automatically determined and displayed (steps 14.2, 15.2). The proposed positions are determined by processing the image data representing the second image based on the potential locations of the fourth point for the first, second, and / or third points and the anatomical structures identified in the image data. The proposed positions are displayed on the image along with the fourth marked point. The operator is then asked to confirm the proposal or to adapt the placement of the proposed positions for the fifth and sixth points (step 16.2). As soon as all positions are deemed correct by the operator, the selection is confirmed.

[0056] Next, reference data is generated from the positions of the first to third points, and comparison data is generated from the positions of the fourth to sixth points (step 30). The reference data is compared with the comparison data (step 31). If the comparison indicates that the first and second images and / or the markings in the first and second images match well, the positions of the fourth, fifth, and sixth points are stored along with the image data representing the second image, as well as any further data such as the timestamp at the time of acquisition of the second image and the pressure reading of the pressure sensor 5. If the comparison indicates that the first and second images do not match well, the acquisition and marking of the second image are repeated (see steps 10.2 and below).

[0057] As soon as data for the two matching images becomes available, the lengths are determined from the positions of the first and second marked points, as well as the positions of the fourth and fifth marked points. This is described in more detail below in relation to Figure 4. The determined lengths are stored along with other data for the first and second images.

[0058] Figure 3 is a schematic diagram of a measurement session using an imaging device. Figure 3(a) shows the positioning of probe 1,101 relative to the subject's skin surface 9 when acquiring the first image. In the probe 1 of the first embodiment, the orientation in space is determined by the accelerometer 6 and stored along with the image data (and further data as described above) representing the first image. As shown in Figure 3(b), when acquiring the second image by the same measurement sequence, the orientation of probe 1 is continuously tracked by the accelerometer 6. As long as the difference between the current orientation and the stored orientation exceeds a certain threshold, a warning is displayed on the display, and marking of the fourth point and subsequent points is not possible until a sufficiently matching orientation of probe 1 is achieved. In addition to the warning, further information may be displayed to assist the operator in finding the previous orientation (e.g., arrows indicating the required change in orientation in a certain direction).

[0059] In the probe 101 of the second embodiment, the position of the probe 101 relative to the skin surface 9 is continuously determined by the optical sensor 106 and tracked during the measurement sequence. If the displacement of the probe 101 during the sequence exceeds a certain limit, a warning is displayed, and further measurements are only possible when the probe 101 has returned to its previous position that it had during the first measurement (or several previous measurements). In addition to the warning, further information may be displayed to assist the operator in finding the previous position (such as an arrow indicating the required change in position in a certain direction).

[0060] Based on the position data, further checks may be performed during the measurement session. For example, the acceleration and / or velocity of probe 1 may be monitored during the session, and a warning may be issued if they exceed certain limits.

[0061] Figures 4a–4c are images representing cross-sections of three-dimensional tissue volume under different external pressures, with marked points indicating determined lengths and anatomical landmarks. Figure 4a represents a first image taken at a certain first point in time. In the embodiments described, Figure 4 represents the tissue including the anterior tibial compartment 51 covered by the superficial fascia 52. Behind the anterior tibial compartment 51, the tibia 53 and interosseous membrane 54 are visible. For simplicity, only the skin surface 9, the interfaces between the mentioned structures, namely the interface 56 between the superficial fascia 52 and the anterior tibial compartment 51 and the interface 57 between the anterior tibial compartment 51 and the interosseous membrane 54, as well as the edge 58 of the tibia 53, are shown in Figures 4–6. In practice, pre-processed B-mode ultrasound images are displayed, and interfaces or edges may be identified by image processing depending on the brightness value of the pixels, as needed.

[0062] The first image shown in Figure 4a has three points marked on the skin surface 9, including a first point 61.1, which are represented by a cross shape. The second point 61.2 is marked where the axis running through the first point 61.1 intersects the edge 58 of the tibia 53, and the marking of the second point 61.2 is also represented by a cross shape. The third point 61.3 is marked where the edge 58 of the tibia 53 intersects the interface 57 between the anterior tibial compartment 51 and the interosseous membrane 54. This is an anatomical landmark that allows for easy and reproducible marking. The marking of the third point 61.3 is represented by a box shape. The markings were acquired by the procedure described above in relation to Figure 1 and are stored along with the image data.

[0063] Figure 4b shows a second image taken at a second point in time. The volume of tissue shown is approximately the same as that shown in the first image, but the external pressure applied to the subject's skin surface 9 has increased, and therefore the compressible structures in the volume, namely the anterior tibial compartment 51, superficial fascia 52, and interosseous membrane 54, are compressed. Again, three points are marked. These include a fourth point 61.4 on the skin surface 9, a fifth point 61.5 where the axis passing through the fourth point 61.4 intersects the edge 58 of the tibia 53, and a sixth point 61.6 representing the location where the edge 58 of the tibia 53 intersects the interface 57 between the anterior tibial compartment 51 and the interosseous membrane 54. Again, these markings are obtained by the procedure described above in relation to Figure 1 and are stored along with the image data.

[0064] Figure 4c shows another second image taken at a second time point under increased external pressure on the skin surface 9. Compared to the image shown in Figure 4b, the orientation, scale, and cropping are different. Again, three points are marked. These include a fourth point 62.4 on the skin surface 9, a fifth point 62.5 where the axis passing through the fourth point 62.4 intersects the edge 58 of the tibia 53, and a sixth point 62.6 representing the location where the edge 58 of the tibia 53 intersects the interface 57 between the anterior tibial compartment 51 and the interosseous membrane 54. Again, these markings are acquired by the procedure described above in relation to Figure 1 and stored along with the image data.

[0065] In Figure 4c, the axis between the fourth point 61.4 and the fifth point 61.5, as defined in Figure 4b, is shown by a dashed line. It is clear that this axis runs in a different direction compared to Figure 4b and also compared to the markings in the first image shown in Figure 4a. Clearly, if the length between the fourth point 61.4 and the fifth point 61.5 is determined to compare this length to, for example, the length between the first point 61.1 and the second point 61.2 in the first image, the measurement taken from the marked position in Figure 4c will yield a worse result compared to the measurement taken from the marked position in Figure 4b. Therefore, the marking in Figure 4c is declared invalid, and a different marking and / or acquisition cycle is initiated.

[0066] Possible methods for evaluating the quality of the second image are described with respect to Figures 5a and 5c. These figures basically correspond to Figures 4a and 4c, but with the addition of a reference angle. The reference angle 63.1 in the first image shown in Figure 5a is the angle between the axis passing through the first point 61.1 and the second point 61.2 and the line connecting the second point 61.2 to the third point 61.3. The value of the reference angle 63.1 is determined to be 114.8°. In parallel, the distance l1 between the second point 61.2 and the third point 61.3 is determined to be 43.3% of the image width in units of image dimensions.

[0067] In the second image represented by Figure 5b, the corresponding comparison angle 63.2 is determined to be 114.0°, and the distance l2 between the fifth point 61.5 and the sixth point 61.6 is determined to be 46.5% of the image width.

[0068] In the second image shown in Figure 5c, the corresponding comparison angle 64.2 is determined to be 120.3°, and the distance l3 between the fifth point 62.5 and the sixth point 62.6 is determined to be 39.6% of the image width.

[0069] When comparing the second image, represented by Figure 5b or Figure 5c, to the first image, the comparison angle is compared to the reference angle in the first step. A substantial deviation between the angles indicates that the lengths to be determined do not relate to the same axis and / or the same location in the tissue. If the difference exceeds a certain threshold, e.g., 1.5%, the quality of the second image is considered insufficient, and acquisition is repeated.

[0070] In the second step, if the angle comparison yielded a positive result, a comparison between the comparison length and the reference length may be used to normalize the length measurements in the second image. In this example, the comparison length is 7.4% larger than the reference length. Therefore, assuming isotropic scaling of the image, the distance measurement between the fourth point 61.4 and the fifth point 61.5 is scaled by a factor of 0.931 to compensate for the scaling difference. A further threshold may exist for the comparison between the reference length and the comparison length to discard images where the scaling difference exceeds a certain limit. In this case, even if the comparison between angles passes, it may be necessary to repeat the acquisition due to the excessive difference in scale.

[0071] Figures 6a and 6b show a portion of the imaging device's graphical user interface, which displays the results of previous and current measurements, including a quality assessment of the current measurement. The graphical user interface includes a first display area 70 that displays a first B-mode ultrasound image taken at a first time point, the first B-mode ultrasound image representing tissue volume at a first value of external pressure, which in the shown example is 10 mmHg. The graphical user interface further includes a second display area 80 that displays a second ultrasound image taken at a second time point after the first time point, the second ultrasound image representing essentially the same tissue volume at a second value of external pressure, which in the shown example is 80 mmHg. In both images, points 61.1...5 are manually and / or automatically marked as described above in relation to Figure 4.

[0072] Figure 6a shows an example where the second image 81 satisfies a predetermined matching criterion with the first image 71. Thus, the second image 81 is accepted, which is indicated by a checkmark symbol 86 above the second display area 80, and the distance between the fourth point 61.4 and the fifth point 61.5 is determined and displayed.

[0073] Figure 6b shows an example where the second image 82 does not meet the predetermined matching criteria with the first image 71. Clearly, the axis with the marked points 64.4, 64.5 is in a different location from the axis connecting the marked points 61.1, 61.2 in the first image. In the shown case, it was also not possible to mark the sixth point because the corresponding anatomical landmark was not present in the captured image. Therefore, the second image 82 is rejected, as indicated by the cross symbol 87 above the second display area 80. In this way, the acquisition of the second image is repeated.

[0074] The present invention is not limited to the embodiments described above. In particular, the effectiveness of the second image may be evaluated based on a combination of several criteria, including, in particular, the result of a comparison between reference geometric characteristics and comparison geometric characteristics (such as angles, lengths, or length ratios), as well as measurements taken by sensors such as position sensors and further characteristics obtained from processing the image data.

[0075] The marking process may differ from that described above. In some embodiments, all points are marked manually, while in other embodiments, the marking process may be fully automated without requiring user confirmation.

[0076] In summary, it should be noted that the present invention aims to create a method that enables reliable comparison of length values ​​obtained from two or more two-dimensional images representing cross-sections of three-dimensional tissue volumes.

Claims

1. A method for obtaining a first length from a first two-dimensional image representing a cross-section of a three-dimensional tissue volume at a first time, and a second length from a second two-dimensional image representing a cross-section of a three-dimensional tissue volume at a second time, a) A step of marking a first point in the first two-dimensional image, b) A step of marking a second point in the first two-dimensional image, c) A step of acquiring third data relating to the first two-dimensional image, d) A step of marking a fourth point in the second two-dimensional image, e) A step of marking a fifth point in the second two-dimensional image, f) A step of acquiring sixth data relating to the second two-dimensional image, g) A checking step of checking whether the positions and orientations of the first two-dimensional image and the second two-dimensional image are sufficiently consistent using the marked first point, second point, fourth point and fifth point, as well as the third data and sixth data, If they matched, (h) A step of determining the first length from the marked first point and second point and the third data, i) A method comprising the step of determining the second length from the marked fourth and fifth points and the sixth data.

2. The method according to claim 1, wherein one or more of the first point, the second point, the fourth point, and the fifth point are automatically marked based on the structure captured in each of the images.

3. The method according to claim 1 or 2, wherein the third data is obtained by marking a third point in the first two-dimensional image, and the sixth data is obtained by marking a sixth point in the second two-dimensional image.

4. The method according to claim 3, wherein at least one of the third point and the sixth point is automatically marked based on the respective images of the captured structure.

5. The method according to claim 4, wherein the third and sixth points are marked automatically, and the first, second, fourth and fifth points are marked manually.

6. The method according to any one of claims 3 to 5, wherein in the checking step, the intensity or grayscale value in the area of ​​the marked third point is compared with the intensity or grayscale value in the area of ​​the marked sixth point.

7. The method according to claim 1 or 2, wherein the third data is obtained from a position sensor that measures one or both of the first tilt and location of the image sensor when the first two-dimensional image is captured, and the sixth data is obtained from a position sensor that measures the second tilt or location of the image sensor when the second two-dimensional image is captured.

8. The method according to any one of claims 1 to 7, wherein in the checking step, at least a first reference angle is determined from the marked first and second points and the third data, at least a second reference angle is determined from the marked fourth and fifth points and the sixth data, and then the first reference angle and the second reference angle are compared.

9. The method according to any one of claims 1 to 8, wherein in the checking step, at least a first reference length is determined from the marked first and second points and the third data, at least a second reference length is determined from the marked fourth and fifth points and the sixth data, and thereafter the first reference length and the second reference length are compared.

10. The method according to any one of claims 1 to 9, wherein the first length represents the distance between the first point and the second point, the second length represents the distance between the fourth point and the fifth point, the first length is normalized based on the third data, and the fourth length is normalized based on the sixth data.

11. The method according to any one of claims 1 to 10, wherein, in the capture process of the second two-dimensional image, the first two-dimensional image is displayed to the operator together with a candidate for the second two-dimensional image in order to assist in the capture of the second two-dimensional image.

12. The method according to claim 11, wherein the marked first point, the second point, and the geometric objects representing the third data are displayed together with the first two-dimensional image.

13. The method according to claim 11 or 12, wherein geometric objects representing the fourth point, the fifth point, and the sixth data are marked in the candidate of the second two-dimensional image, and either or both of the results and / or intermediate results of the verification based on the marked first point, second point, fourth point, and fifth point, as well as the third data and the sixth data, are displayed together with the first two-dimensional image.

14. The method according to any one of claims 3 to 6, wherein seventh data is obtained from a position sensor that measures a first position of the image sensor, in particular one or both of a first tilt and location, when capturing the first two-dimensional image, and eighth data is obtained from a position sensor that measures a second position of the image sensor, in particular one or both of a second tilt and location, when capturing the second two-dimensional image, and the seventh data and the eighth data are used for one or more of the following: checking whether the position and orientation of the first two-dimensional image and the second two-dimensional image match sufficiently, determining the first length, determining the second length.

Images