WO2016131717A1

WO2016131717A1 - Corrected flow field estimation

Info

Publication number: WO2016131717A1
Application number: PCT/EP2016/053003
Authority: WO
Inventors: Romain LACROIX; Sherif Makram-Ebeid; Raoul Florent
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2015-02-16
Filing date: 2016-02-12
Publication date: 2016-08-25
Anticipated expiration: 2017-08-16

Abstract

The present invention relates to correcting flow estimation inside an anatomy. In order to provide a further improved flow estimation, a method (100) for correcting flow estimation of a fluid inside an anatomy is provided having the following steps: A temporal sequence of at least two images of the anatomy is provided (102) comprising data of an identifiable fluid. The anatomy comprises at least one lumen within enclosing walls and filled with a flowing fluid. Further, data of a border region inside the anatomy along the enclosing walls and data of a remaining main region inside the at least one lumen is provided (104). Next, a flow inside the lumen is estimated (106) based on the temporal sequence of at least two images. The estimation comprises estimating a constrained flow for the border region. In the constrained flow, flow vectors of the estimated flow are corrected by a correction. Further, the constrained flow and an estimated flow in the main region are combined (108) to form a corrected flow field. The corrected flow field is then displayed (110).

Description

Corrected Flow Field Estimation

FIELD OF THE INVENTION

The present invention relates to correcting flow estimation inside an anatomy, and relates in particular to a device for correcting flow estimation inside an anatomy, to a medical imaging system, and to a method for correcting flow estimation of a fluid inside an anatomy, and also to a computer program element and to a computer-readable medium.

BACKGROUND OF THE INVENTION

Flow estimation is used, as an example, in relation with different types of examinations of a patient. For example, flow estimation is used for vascular related examination procedures, such as in relation with an aneurysm. Further, flow field estimation is also used for cardiologic related aspects. The flow estimation may be based on image data acquired of an object, such as a region of interest of a patient. US 8 175 358 B2 describes the use of perfusion images to deliver information about the blood supply of a tissue. To visualize the current flow characteristic, flow estimation is performed based on data acquired by a medical imaging modality. The flow estimation gives an impression of the current flow and may support diagnostic or treatment procedures of a patient. Different types of algorithms are used to achieve respective flow estimation data for visualizing purposes. However, it has been shown that due to the nature of the estimation procedure and due to being based on the available image data, some deviations between the estimated flow and the actual, i.e. current flow that exists in the anatomy may occur.

SUMMARY OF THE INVENTION

There may thus be a need to provide further improved flow estimation with increased concordance with an existing flow.

The object of the present invention is solved by the subject-matter of the independent claims, wherein further embodiments are incorporated in the dependent claims. It should be noted that the following described aspects of the invention apply also for the device for correcting flow estimation inside an anatomy, and for the medical imaging system, as well as for the method for correcting flow estimation of a fluid inside an anatomy.

According to the present invention, a device for correcting flow estimation inside an anatomy is provided. The device comprises a data provision unit, a processor and a display. The data provision unit is configured to provide a temporal sequence of at least two images of the anatomy comprising data of an identifiable fluid. The anatomy comprises at least one lumen within enclosing walls and that is filled with a flowing fluid. The data provision is further configured to provide data of a border region inside the anatomy along the enclosing walls and data of a remaining main region inside the at least one lumen. The processor is configured to estimate a flow inside the lumen based on the temporal sequence of at least two images. The estimation comprises an estimation of a constrained flow for the border region. In the constrained flow, flow vectors of the estimated flow are corrected by a correction procedure. The processor is further configured to combine the constrained flow and an estimated flow in the main region to form a corrected flow field. The display is configured to display the corrected flow field.

In the context of this application, the term "flow estimation" relates to an estimation of the flow velocity field of the flow. Hence, the term "flow estimation" has to be understood as "flow velocity field estimation", unless otherwise stated. The estimation of the flow velocity field of the flow is different to a flow rate (or volume flow rate) of a flow that can also be estimated, i.e. by flow (rate) estimation. Hence, in the following the term "flow estimation" is used as an easier reference, instead of the term "flow velocity field estimation".

According to an example, for the correction of the estimated flow, the processor is configured to at least partly correct an angle deviation between an estimated velocity vector and a wall tangent such that the angle deviation is reduced.

According to a further preferred example, the processor is configured to reduce the angle deviation to a deviation of 0° such that the corrected velocity vector is aligned with the wall tangent.

According to an example, the display is configured to visualize the border region to indicate in which region the estimated flow is corrected.

According to an example, the display is configured as a graphical user interface for user interaction to determine the degree of correction and/or to determine an extent of the border region.

The term "degree of correction" relates to the amount or intensity of the correction and hence to the correction's effect or result. Whereas the term "extent" relates to the geometrical aspect of how large (or small) the corrected zone is.

In an example, the extent of the border region relates to how far the border region reaches into the main region, i.e. the extent refers to a dimension in a direction transverse, or orthogonal, to the wall.

In another example, the graphical user interface is provided to determine the extent of the border region with respect to a direction transverse (orthogonal) to the walls' inner surface and a direction parallel to the walls. In other words, the extension along the anatomy can be determined by user interaction.

In an example, in 3D the component parallel to the wall lies in a plane (defined by two directions) and the orthogonal is a single direction.

In an example, the processor is configured to estimate a flow velocity field based on an optical-flow-based method.

According to the present invention, also a medical imaging system is provided. The system comprises an image acquisition device and a device for correcting flow estimation inside an anatomy according to one of the above-mentioned examples. The image acquisition device is configured to provide image data comprising at least a temporal sequence of at least two images. The device for correcting flow estimation inside an anatomy is configured to compute flow estimation based on the image data.

According to the present invention, also a method for correcting flow estimation of a fluid inside an anatomy is provided. The method comprises the following steps:

al) Providing a temporal sequence of at least two images of the anatomy comprising data of an identifiable fluid. The anatomy comprises at least one lumen within enclosing walls, and filled with a flowing fluid.

a2) Providing data of a border region inside the anatomy along the enclosing walls and data of a remaining main region inside the at least one lumen.

b) Estimating a flow inside the lumen based on the temporal sequence of the at least two images. The estimation comprises estimating a constrained flow for the border region. In the constrained flow, flow vectors of the estimated flow are corrected by a correction.

c) Combining the constrained flow and an estimated flow in the main region to form a corrected flow field.

d) Displaying the corrected flow field. The correction of the estimation, in order to achieve a constrained flow for the border region, provides corrected data for this region and thus provides corrected displayed information. The correction is provided in order to improve the accuracy of the displayed flow field, which is provided, for example, to a user, such as a surgeon or other medical staff. The correction takes into account that flow estimation, e.g. based on optical-flow-based methods, may show deviations in particular in regions close to vessel walls, for example. In these regions, vectors may occur that are pointing in a transverse way towards the vessel wall, and thus transverse to the actual flow direction. In order to further improve the flow estimation, such flow vectors are corrected in order to improve the displayed information.

According to an example, for the correction of the estimated flow, in step b) an angle deviation between an estimated velocity vector and a wall tangent is at least partly corrected such that the angle deviation is reduced.

According to an example, for the correction of the estimated flow, in step b) the angle deviation is reduced to a deviation of 0° such that the corrected velocity vector is aligned with the wall tangent.

In an example, it is provided that at any point within the border region, the angle deviation between the estimated velocity vector and the plane parallel to the closest wall and containing this point is partly corrected, or corrected such that an alignment of the vector and the wall tangent is achieved.

According to an example, before step a2), a segmentation of the anatomy is provided. As a further option, before step a2), the border region is determined. As a still further option, step b) also comprises a sub- step bl) of estimating a main flow for the remaining main region. In step c), the constrained flow is combined with the main flow to form the corrected flow field.

In an example, in step d), the border region is visualized to indicate in which region the estimated flow is corrected.

According to an example, for step b), it is provided to determine the correction by a user interaction, e.g. to determine the degree of correction.

According to an example, for step a2), it is provided to determine an extent of the border region and the remaining main region by user interaction.

In an example, the border region is determined with respect to its extent in the direction transverse to the walls' inner surface, i.e. the width of the border region is determined. In another example, the border region is determined with respect to its extent in a direction oriented in length direction of the vessel, i.e. the length of the border region along the lumen is determined.

According to an aspect, a flow estimation is used based on optical flow estimation methods, and this flow estimation is then adjusted or adapted with respect to identified or determined regions along the inner side of, for example, vessels' wall segments or inner border areas. In these areas along the vessel walls, the estimated velocity of the fluid flow, or the flow vectors, are aligned in order to indicate the existing laminar flow along the inner walls, to be more in accordance with the remaining flow in the main part of the vessel. This alignment of the vectors results in an improved visualization of the existing flow, although being based on flow estimation.

These and other aspects of the present invention will become apparent from and be elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will be described in the following with reference to the following drawings:

Fig. 1 schematically illustrates an example of a device for correcting flow estimation inside an anatomy.

Fig. 2 shows an example of a medical imaging system.

Fig. 3 illustrates basic steps of an example of a method for correcting flow estimation of a fluid inside an anatomy.

Fig. 4 shows further options of an example of the method of Fig. 3.

Fig. 5 schematically illustrates a border region inside an anatomy and a correction approach for flow vectors.

Fig. 6 shows a further example of a method for correcting flow estimation.

Fig. 7 shows a still further example of another method.

Fig. 8 shows a further example of a method for correcting flow estimation. DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a device 10 for correcting flow estimation inside an anatomy. The device comprises a data provision unit 12, a processor 14 and a display 16.

The data provision unit 12 is configured to provide a temporal sequence of at least two images of an anatomy comprising data of an identifiable fluid. The anatomy comprises at least one lumen with enclosing walls and that is filled with a flowing fluid. The data provision unit 12 is further configured to provide data of a border region inside the anatomy along the enclosing walls and data of remaining main region inside the at least one lumen. The data provision unit 12 is also referred to as input unit or data provision means. The data provision unit 12 provides the above described data to the processor 14.

The processor 14 is configured to estimate a flow inside the lumen based on the temporal sequence of the at least two images. The estimation comprises an estimation of a constrained flow for the border region. In the constrained flow, flow vectors of the estimated flow are corrected by a correction. The processor 14 is further configured to combine the constrained flow and an estimated flow in the main region to form a corrected flow field. The processor 14 is configured to estimate a flow field, for example based on an optical-flow- based method. The processor 14 is also referred to as processing unit. The processor 14 provides the data of the corrected flow field to the display 16.

The display 16 is configured to display the corrected flow field.

For example, for the correction of the estimated flow, the processor 14 is configured to at least partly correct an angle deviation between an estimated velocity vector and a wall tangent such that the angle deviation is reduced (see also below). In an example, the processor 14 is configured to reduce the angle deviation to a deviation of 0° such that the corrected velocity vector is aligned with the wall tangent.

In an example (not further shown), as an option, the display 16 is configured to visualize the border region to indicate in which region the estimated flow is corrected. In a further example, as a further option, the display 16 is configured as a graphical user interface 18 (shown as an option in Fig. 1) for user interaction to determine the degree of correction. Alternatively or additionally, the graphical user interface is provided for user interaction to determine an extent of the border region.

According to another option, the graphical user interface is provided for user interaction to determine the extent of the border region with respect to a direction oriented in length direction of the vessel.

The graphical user interface 18 provides an interactive tool for the user to enforce to which degree the directions of the estimated velocity vectors shall stay aligned with, or at least less deviating from, the anatomy border (see also below). The graphical user interface 18 also provides an interactive tool for the user to determine the geometrical factor. The graphical user interface provides the possibility to control the extent of the area where the enforcement occurs and, additionally or alternatively, the stringency of this enforcement.

In an example, the graphical user interface comprises one or two dedicated sliders (not further shown) as a function of a touch sensitive surface for intuitive controlling by the user (see also Fig. 5).

An immediate or direct recalculating can be foreseen in order to provide the user with a result of the interaction displayed in the display area next to the graphical user interface. For example, the updated corrected flow field is shown on the display in addition to displaying the graphical user interface.

In an example, the data provision unit 12 is configured to provide a segmentation of the anatomy. In another example, the processor is configured to compute the segmentation based on the sequence of images, or based on further image data. In an example, the processor is configured to determine the border region. In another example, an interface is provided that is configured for determination of the border region by a user interaction. For example, as indicated above, the user interface is a graphical user interface or a manual or acoustic input device.

In an example, the processor 14 is configured to estimate a main flow for the remaining main region, and to combine the constrained flow with the main flow to form the corrected flow field.

Fig. 2 shows a medical imaging system 50 comprising an image acquisition device 52 and a device 54 for correcting flow estimation inside an anatomy, which is provided as one of the above-mentioned examples of the device 10 for correcting flow estimation inside the anatomy. The image acquisition device 52 is configured to provide image data comprising at least the temporal sequence of the at least two images. The device for correcting flow estimation 54, i.e. the device 10, is configured to compute flow estimation based on the image data.

In the example shown, the image acquisition device is an X-ray image acquisition device. However, as further example, not further shown, the image acquisition device is provided as a magnetic particle imaging device. In an example, the processor 14 is configured to provide the flow estimation, for example as an optical flow estimation using an optical-flow-based method based on X-ray image data or image data from magnetic particle imaging.

As indicated, the image acquisition device 52 is shown as an X-ray imaging system, for example a C-arm system, comprising a C-arm 56 having an X-ray source 58 and an X-ray detector 60 attached at opposing ends. The C-arm 56 can be moved around several axes around an object of interest 62, for example a patient. For supporting the patient, a patient table or patient support 64 is provided that may be adjustable in height and also in the length direction. Further, lighting equipment 66 is indicated, together with further display or monitors 68. The device 54 for correcting flow estimation is shown with a number of monitors 70 for providing the display 16.

In Fig. 3, a method 100 for correcting flow estimation of a fluid inside an anatomy is shown. The method 100 comprises the following steps:

- In a first provision step 102, a temporal sequence of at least two images of the anatomy comprising data of an identifiable fluid is provided. The anatomy comprises at least one lumen with enclosing walls and is filled with a flowing fluid.

In a second provision step 104, data of a border region inside the anatomy along the enclosing walls is provided. Further, also data of a remaining main region inside the at least one lumen is provided (at least implicitly).

In an estimation step 106, a flow inside the lumen is estimated based on the temporal sequence of the at least two images. The estimation comprises estimating a constrained flow for the border region. In the constrained flow, flow vectors of the estimated flow are corrected by a correction.

- In a combination step 108, the constrained flow and an estimated flow in the main region are combined to form a corrected flow field.

In a display step 110, the corrected flow field is displayed.

The first provision step 102 is also referred to as step al), the second provision step 104 as step a2), the estimation step 106 as step b), the combination step 108 as step c), and the display step 110 as step d).

The first and the second provision steps 102, 104 are provided before performing the estimation step 106. However, they can be arranged simultaneously or can be arranged in the above-mentioned order or in a reverse order.

As an example, the images, i.e. the temporal sequence of at least two images of the anatomy, comprises X-ray image data.

The term "identifiable fluid" relates to a fluid that can be identified in the image data with respect to its movement that occurs between the at least two images of the sequence. The fluid can be identified in the image depending on the fluid type, e.g. blood or urine, and the imaging modality. In an example, the fluid comprises contrast agent for achieving visibility of its movement (i.e. the flow) in X-ray imaging. In another example, the fluid comprises particles or markers for achieving visibility in magnetic particle imaging.

In an example of the method, the flow estimation is provided as an optical flow estimation using an optical-flow-based method, based on X-ray image data.

The correction relates to applying a constraint to the flow in the border region. The correction is provided as enforcement applied to the flow vectors.

The border region can also be referred to as constraining zone.

For example, for the correction of the estimated flow, in step b) an angle deviation between an estimated velocity vector and a wall tangent is at least partly corrected such that the angle deviation is reduced.

In another example, for the correction of the estimated flow, in step b) the angle deviation is reduced to a deviation of 0° such that the corrected velocity vector is aligned with the wall tangent.

Fig. 4 shows a further example of the method, in which several options are shown.

As a first option, before step a2), i.e. before the second provision step 104, a segmentation of the anatomy is provided in a further provision step 112. The hashed line indicates that this is shown as an option.

In a further option, before step a2), i.e. before the second provision step 104, the border region is determined in a determination step 114.

As a further option, step b), i.e. the estimation step 106, indicated with a hashed frame, comprises an estimation sub-step 116, in which a main flow for the remaining main region is estimated. A second, separate frame 118 indicates the estimation of the constrained flow. In the combination step 108, i.e. in step c), the constrained flow is combined with the main flow to form the corrected flow field, which is then displayed in the further step (not further shown).

It is noted that the above-mentioned options can be provided separately or in a combination of the first and the second option or in a combination of the first and the third option or as a combination of all three options, or as a combination of the second and the third option.

The term "segmentation" relates to identifying a vessel structure in image data and hence to providing an understanding of the vessel structure. The term "anatomy" relates to a vasculature, or a chamber, e.g. a heart chamber, or an organ or any natural or pathologic cavity containing or crossed by a flowing fluid, such as an aneurysm. The term "anatomy" relates in particular to a lumen, in which a flow of fluid is present. The anatomy thus relates to a region of interest, for example of a patient.

The correction of the flow field, i.e. the combination of the constrained flow and the estimated flow in the main region thus form and provides a corrected flow field of the of the vessel's region of interest.

The term "lumen" relates to the volume provided by the vasculature, or the chamber, e.g. the heart chamber (or cardiac chamber), or the organ or any natural or pathologic cavity containing or crossed by a flowing fluid, such as the aneurysm.

The term "vasculature" relates to vessels or vascular organs or parts.

The term "vessel" relates to a lumen in an anatomy. For example, a blood vessel, such as an artery used for blood flow (blood stream) is referred to.

In another example, the vessel also relates to different types of lumen used for flow of other types of fluid or liquids inside an anatomy.

The term "vessel segment" or "anatomy segment" relates to a part or portion of a vessel or anatomy. The vessel or anatomy comprises the lumen enclosed by a wall structure, or walls.

The term "flow" relates to the motion of the fluid, e.g. liquid, inside the lumen of the vessel, such as blood flow or blood streaming.

The term "border region" relates to a part of the vessel's lumen assigned or allocated to the outer wall, which outer wall so-to-speak forms the outer border of the lumen.

The term "border" relates to the part of the flow that is in contact with the wall, and where, due to friction, the flow is influenced. For example, an otherwise laminar flow is having turbulences and distractions in the border region. However, the border region may be determined independent whether turbulences are actually present or not.

The term "main region" relates to the region of the lumen, or volume of the vessel, where the (blood or other fluid) flow occurs with no or minimal influence from the outer wall's effect (which is present in the border region). The main region may relate to the center portion of the vessel. However, it is possible to define the border region (for the purpose of correcting flow velocities) such that the main region no more, or only to a very small amount, exists. The term "main flow" relates to the flow velocity field in the area with no or only minimal effect from the enclosing side walls, e.g. the flow in the main region.

The term "constrained flow" relates to the flow estimation provided by a flow estimation algorithm, but corrected as described. The "constrained" relates to constraining, or limiting, or enforcing, the estimated flow to a certain range or degree of (estimated) flow direction.

The "border flow" relates to the flow in the border region.

The term "flow vector" relates to the direction and speed, i.e. the velocity, of a particular particle in the flow according to the flow estimation. The flow vector may be shown as an arrow to visualize this. A large plurality of vectors shown as arrows may indicate the flow field. Another example is to indicate the flow field with color-coding.

With reference to Fig. 4, in an example, the data of the border region is provided based on the segmentation. For example, the segmentation provides the definition of the wall structures and the border region is defined based on the wall structures.

In another example, the border region is determined directly without separate segmentation. For example, images are provided showing the anatomy, however without a segmentation indicating walls of the vessels or the like. However, the vessel walls are visible and the identification of the walls and the definition of the border region are provided in a single procedure, resulting in the definition of the border region, but without providing a full segmentation. The definition of the border region can thus also be referred to as a sort of segmentation. For example, the border regions are defined directly in the image.

In an alternative example, the border region is provided as predetermined border region. For example, the border region has been defined during another procedure before the correction of the flow field is provided. In an example, the border region has been defined for the purpose of being used in a flow field correction. In another example, the border region has been defined in form of defining the wall extension and a value is added to broaden the line representing the wall, e.g. of a vessel or organ enclosing the lumen where the flow appears that is to be corrected, such that the "broadened" line defines an area that is then used as the border region.

In an alternative example, an estimated flow is provided for the combination in step 108, or step c), e.g. estimated beforehand. In another example, a flow is estimated for the lumen segment, i.e. also including at least a part of the border region, e.g. the complete lumen, and the corrected or constrained flow is overlaid covering or masking the border region, but maintaining the flow field for the area of the main flow.

The term "correction" relates to a modification or adjustment of the flow field in order to correct the flow field to a predetermined approach. The correction can also be referred to as a correction procedure or correction factor. However, it is noted that the factor is not a single value for multiplication or the like. Rather, the correction is a geometrical alignment of flow field vectors.

In an example, the correction is an a posteriori correction, in which case flow is estimated everywhere in the lumen, and only those velocity vectors in the border region are post corrected to be better aligned to that border.

In another example, the correction procedure is an integral part of the estimation procedure, in which case there is no a priori estimation, but a single estimation procedure in which a border correction term is included. The term is such that it does not influence the estimation in the main part. For instance, the term vanishes when away from the border.

In an example, not further shown, in step d), the border region is visualized to indicate in which region the estimated flow is corrected.

The term "visualized" relates to show or display the border region, or an indicator of the border region, on the display. In an example, the border region is indicated with a border line, or by visually marking the border region.

In an example, in step a), a segmentation is calculated based on X-ray image data of the vasculature comprising contrast injected image data.

In an example, in step a), the segmentation is provided by a segmentation procedure.

According to a further example, not further shown, for step b) it is provided to determine the correction by user interaction. In an alternative example, the correction is predetermined.

In another example, for step a2), it is provided to determine an extent of the border region and the remaining main region by user interaction.

For example, the determination is provided with respect to at least one of the following: a direction transverse, e.g. orthogonal, to the wall's inner surface, and a direction oriented in length direction of the vessel, i.e. a direction parallel to the wall.

The term "transverse" relates to a direction non-parallel to the wall's inner surface. For example, the direction is a normal to the wall's inner surface, i.e. perpendicular to the surface. In case of a curved surface, this relates to the surface point closest to the particle or flow point under consideration.

The term "length direction" relates to direction of the main extension of the elongate vessel, i.e. in flow direction along the walls.

In Fig. 5, a schematic illustration of an anatomy 120; for example, a vessel is shown. The anatomy 120 comprises a vessel portion 122 with a schematically shown aneurysm 124. A line 126 indicates an extent of a border region 128 defined by the line 126, and another line 130 indicates the vessel's outer wall. An extent e of the border region is indicated with a double arrow 132. The double arrow 132 indicates that the extent of the border region can be adjusted or manipulated by user interaction. Further, an angle 134 is indicated between an estimated velocity vector 136 and a line 138 indicating a surface parallel to the closest wall at the particular instance. The angle 134 is also referred to as ΔΘ.

Further, in Fig. 5, a possibility for a user for interaction, i.e. for determination, is shown with a first slider 140 for adjusting the extent of the border region's extension e, and a second slider 142 indicates the degree of correction that can also be adjusted for the angle referred to as ΔΘ. The sliders can be provided as graphical user interface.

As an example, for the correction of the estimated flow, in step b), an angle deviation, for example the angle 134, between an estimated velocity vector and surface parallel to the closet wall is at least partly corrected, such that the angle deviation is reduced. As an example, an alignment of the corrected velocity vector with the wall tangent is provided by the correction.

The term "angle deviation" relates to the angle between the estimated velocity vector and the wall tangent. In an example, for the correction of the estimated flow, in step b) a direction of a velocity vector is modified such that the angle formed between the direction and an axis of the vessel tangent to the vessel wall, i.e. the surface parallel to the closest wall at that point, is decreased. In other words, the velocity vector is adjusted in the direction along the wall, i.e. the velocity vector is tilted towards or projected in the plane parallel to the closest wall at that point.

In an example, in step b), the flow vectors of the estimated flow are corrected by the correction dependent on a distance to the enclosing walls. Weighting of the correction is applied in relation to the distance (see also below).

According to the invention, in an example, a velocity field is provided that even in the area close to the anatomy border is not pointing outwards, but is more or less, or at least to a certain degree, aligned to this border. Hence, inaccuracy nearby the borders is reduced or prevented for the velocity estimation. Thus, in case of contrast profiles provided by contrast agent imaging, in the boundary layer of the lumen, where the viscosity is dominant and slow travelling lamina adjacent to the wall and fast travelling lamina co-exists, the contrast density that would follow a parabolic profile more or less elongated according to the fluid viscosity is considered and so-to-speak compensated by the present invention. The direction of the estimated velocity in an area comparable to the boundary layer is corrected.

In an example, such as by providing the interactive tool to enforce the directions of the estimated velocity vectors staying aligned with the anatomy border, an adjustment is provided that follows a visually assessed compromise between reliability to physics of the estimated velocities, and their local spatial resolution.

In an example, for the visualization of the segmented anatomy, the anatomy is segmented either by the interactive tool itself or the segmentation is imported.

The visualization of the currently estimated velocity field within the anatomy is provided and the field is estimated by the tool itself in an example, for instance with the optical-flow-based method. The field can be rendered in different ways with vectors whose magnitude could be color-coded or represented by their length or width. This might correspond to a 2D projection, to a slice, or to a full 3D volume.

The extent of the area where velocity constraining occurs is also visualized. For example, a simple outline as shown in Fig. 5 can be positioned on the area extremity. It may be typically parallel to the anatomy border, but it could also be arranged differently. Of course, other visualization means are also provided, such as a different color.

The dedicated slider 140 controls the extent of the area where velocity enforcement occurs. This may displace the area boundary in a range from a very thin band to a limit close to the anatomy center.

The dedicated slider 142 controls the stringency (or degree) of the velocity enforcement. Typically, a maximum or a mean angle deviation between the estimated vectors and the vector's tangent to the boundary is provided. In another option, the enforcement is less quantitative, and the enforcement is controlled through a qualitative parameter, for example ranging from weak to strong.

In an example, the invention proposes to solve the above described optical- flow aspect by minimizing a global energy comprising the tangency constrained. This can be expressed by the following equation (1): Term_opti_caifl_ow + a . (n.vf . Mask(e)

Playing on the factor a penalizes the dot product n.v between velocity vector v and wall normal n in the area defined by the thickness e. The higher a, the more v is parallel to the boundary. This also amounts to minimize the angle deviation ΔΘ by rewriting the constrained term as an equation (2):

This scheme corrects for the angle deviation ΔΘ between estimated velocity and wall tangent. The terms "wall tangent" or "wall tangent plane" relate to a virtual plane that is parallel to the closest wall, but does not have to be in contact with the wall. The term "tangent plane" usually relates to a surface or plane that is in contact with that reference surface (to which it is tangent). However, in the present application, the "wall tangent" is used differently and is meaning also parallel planes to the tangent plane, which is in contact with the closest point on the wall. The "wall tangent" is used as a reference for the angle between the velocity (vector) at a point and the tangent plane to the closest point on the wall. It is thus the same for any parallel plane to the tangent plane (and in particular to the plane containing the point at which the estimation is performed).

However, a more quantitative assessment of the wall tangency can be reached by re-estimating the velocity field until a maximum angle tolerance A6_max (or mean angle tolerance A0_mean) is reached. In such a procedure, a post-regularization is performed on the velocity field such that the tolerance threshold is rapidly reached.

In a further example, the full optical-flow-method is repeated over iterations.

This may ensure a better reliability to contrast information but at the cost of the

computational time.

In another example, the deviation penalty vanishes smoothly when moving away from the wall. A smooth weighting function W that decreases with the depth should weight the constraint spatially as follows with equation (3): . W(depth) . (n.vf with W(0)=1, and W(e)=0, as an example.

In an example, whenever one of the sliders is operated, new velocity estimation is carried out and the results are updated on the interface for further adjustment. Concerning the enforcement method, some further examples are shown in the following diagrams.

In another example, in step b), the flow vectors of the estimated flow are corrected by the correction dependent on a distance to the enclosing wall. A weighting of the correction is applied in relation to the distance.

For example, the full correction is applied for the part of the border region, which is closer to the wall, and only a reduced degree of correction is applied for the part of the border region, which is more oriented towards the center of the vessel. For example, the weighting can be applied stepwise or continuously along the direction transverse to the walls orientation or center line of the lumen. In an example, the full or normal correction is applied throughout the border region, and a weighting is then applied for a transition region between the center line and the border line of the border region.

Fig. 6 indicates a first option 200 of a flow-chart. A first frame 202 indicates the user interaction on a "weak-strong" slider. A second frame 204 indicates that the optical- flow estimation is performed. A third frame 206 indicates that the velocity field is displayed.

Fig. 7 indicates a second option 208 of a flow-chart. A first frame 210 indicates the user interaction on an "angle deviation" slider. A second frame 212 indicates the performance of optical-flow estimation. A third frame 214 indicates the feedback of the user on the Δθηιαχ. A fourth frame 216 below indicates the assessment of whether the value is inferior to a tolerance value. If yes, indicated by Y, the display of the velocity field is performed, as indicated by a further frame 218. If no, indicated by N, a post-regularization, indicated by a still further frame 220, is performed and the result is provided back to the frame 214.

Fig. 8 indicates a third option 222 of a flow-chart, according to which in a first frame 224, user action on an "angle deviation" slider is performed. Next, optical-flow estimation is performed, as indicated by a second frame 226. This is provided to a still further frame 228, in which a feedback on A0_max is provided and the result is provided to an assessment step 230, in which it is checked whether the value is inferior to tolerance value. If yes (Y), a display 232 of the velocity field is provided. If no (N), the result is provided back to the optical-flow estimation in step 226. In an example, it is provided that before step b), uncorrected flow estimation is calculated and a further step is provided, in which an angle deviation between an estimated velocity in the border region and a wall tangent is determined and compared to a threshold. If the angle deviation is below the threshold, the correction (or correction factor or degree of correction) is zero in step b), and the flow estimation from the uncorrected flow estimation is used for the border region for steps c) and d). Or if the angle deviation is above the threshold, a first correction, or first degree of the correction, or first correction factor, is chosen for step b) and a first constrained flow is estimated for the border region. The first constrained flow is provided back to step above of the estimation to a threshold, and, if necessary, a second and further correction, or second or further correction factor or correction degree, is/are chosen until the angle deviation is below the threshold. The respective second or further corrected flow estimation is used for the border region for steps c) and d).

The term "uncorrected" relates to a result of a flow estimation, which result is not adjusted or corrected by applying a correction to align velocities or flow vectors in the border region. A correction of zero may relate to a correction without any further

modification of the vector or velocity.

In an example, for the sub- step of the second option above, applying the first and further correction, it is provided to perform a correction on the velocity field for the border region provided by flow estimation. In an example, for the sub-step of this option, it is provided to perform a correction on the full flow estimation step for the border region.

According to an example, before step b) it is provided to determine different anatomy portions based on different anatomical structures and to determine different segments of the border region based on the different anatomy portions. In step b), the constrained flow is determined for the different segments of the border region.

The "anatomical structure" relates to different parts of a vessel, such as a vessel root or starting point, a bifurcation, an aneurysm or the like.

The "anatomical structure" may also relate to areas or regions of the vessel having different diameters along the length. In an example, the border regions of the different segments have different extensions. In another example, different degrees of correction are applied for the different segments.

In another exemplary embodiment of the present invention, a computer program or a computer program element is provided that is characterized by being adapted to execute the method steps of the method according to one of the preceding embodiments, on an appropriate system.

The computer program element might therefore be stored on a computer unit, which might also be part of an embodiment of the present invention. This computing unit may be adapted to perform or induce a performing of the steps of the method described above. Moreover, it may be adapted to operate the components of the above described apparatus. The computing unit can be adapted to operate automatically and/or to execute the orders of a user. A computer program may be loaded into a working memory of a data processor. The data processor may thus be equipped to carry out the method of the invention.

This exemplary embodiment of the invention covers both, a computer program that right from the beginning uses the invention and a computer program that by means of an up-date turns an existing program into a program that uses the invention.

Further on, the computer program element might be able to provide all necessary steps to fulfill the procedure of an exemplary embodiment of the method as described above.

According to a further exemplary embodiment of the present invention, a computer readable medium, such as a CD-ROM, is presented wherein the computer readable medium has a computer program element stored on it which computer program element is described by the preceding section.

A computer program may be stored and/or distributed on a suitable medium, such as an optical storage medium or a solid state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.

However, the computer program may also be presented over a network like the World Wide Web and can be downloaded into the working memory of a data processor from such a network. According to a further exemplary embodiment of the present invention, a medium for making a computer program element available for downloading is provided, which computer program element is arranged to perform a method according to one of the previously described embodiments of the invention.

It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application.

However, all features can be combined providing synergetic effects that are more than the simple summation of the features.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A device (10) for correcting flow estimation inside an anatomy, comprising:

a data provision unit (12);

a processor (14); and

a display (16);

wherein the data provision unit is configured: to provide a temporal sequence of at least two images of an anatomy comprising data of an identifiable fluid; wherein the anatomy comprises at least one lumen within enclosing walls and filled with a flowing fluid; and to provide data of a border region inside the anatomy along the enclosing walls and data of a remaining main region inside the at least one lumen;

wherein the processor is configured: to estimate a flow inside the lumen based on the temporal sequence of at least two images; wherein the estimation comprises an estimation of a constrained flow for the border region; wherein in the constrained flow, flow vectors of the estimated flow are corrected by a correction; and to combine the constrained flow and an estimated flow in the main region to form a corrected flow field; and

wherein the display is configured to display the corrected flow field.

2. Device according to claim 1, wherein the border region is located inside the lumen and extends from the inner side of a vessel's wall into the lumen.

3. Device according to claim 1 or 2, wherein, for the correction of the estimated flow, the processor is configured to at least partly correct an angle deviation between an estimated velocity vector and a wall tangent such that the angle deviation is reduced;

wherein, preferably, the processor is configured to reduce the angle deviation to a deviation of 0° such that the corrected velocity vector is aligned with the wall tangent.

4. Device according to claim 1, 2 or 3, wherein the display:

i) is configured to visualize the border region to indicate in which region the estimated flow is corrected; and/or ii) is configured as a graphical user interface (18) for user interaction to:

- determine the degree of correction; and/or

- determine an extent of the border region.

5. A medical imaging system (50), comprising:

an image acquisition device (52); and

a device (54) for correcting flow estimation inside an anatomy according to one of the preceding claims;

wherein the image acquisition device is configured to provide image data comprising at least a temporal sequence of at least two images; and

wherein the device for correcting flow estimation inside an anatomy is configured to compute flow estimation based on the image data.

6. A method (100) for correcting flow estimation of a fluid inside an anatomy, comprising the following steps:

al) providing (102) a temporal sequence of at least two images of the anatomy comprising data of an identifiable fluid; wherein the anatomy comprises at least one lumen within enclosing walls and filled with a flowing fluid;

a2) providing (104) data of a border region inside the anatomy along the enclosing walls and data of a remaining main region inside the at least one lumen;

b) estimating (106) a flow inside the lumen based on the temporal sequence of at least two images; wherein the estimation comprises: estimating a constrained flow for the border region; wherein in the constrained flow, flow vectors of the estimated flow are corrected by a correction;

c) combining (108) the constrained flow and an estimated flow in the main region to form a corrected flow field; and

d) displaying (110) the corrected flow field.

7. Method according to claim 6, wherein the border region is located inside the lumen and extends from the inner side of a vessel's wall into the lumen.

8. Method according to claim 6 or 7, wherein, for the correction of the estimated flow, in step b) an angle deviation between an estimated velocity vector and a wall tangent is at least partly corrected such that the angle deviation is reduced; and

wherein, preferably, for the correction of the estimated flow, in step b) the angle deviation is reduced to a deviation of 0° such that the corrected velocity vector is aligned with the wall tangent.

9. Method according to claim 6, 7 or 8, wherein:

before step a2), a segmentation of the anatomy is provided (112); and/or before step a2), the border region is determined (114); and/or step b) also comprises a sub-step bl) of estimating (116) a main flow for the remaining main region; and in step c), the constrained flow is combined with the main flow to form the corrected flow field.

10. Method according to one of the claims 6 to 9, wherein step b) comprises a determination of the degree of correction by user interaction.

11. Method according to one of the claims 6 to 10, wherein, for step a2) it is provided to determine an extent of the border region and the remaining main region by user interaction.

12. Method according to one of the claims 6 to 11, wherein in step b), the flow vectors of the estimated flow are corrected by the correction dependent on a distance to the enclosing walls; wherein a weighting of the correction is applied in relation to the distance.

13. Method according to one of the claims 6 to 12,

wherein, before step b), the following steps are provided:

determining different anatomy portions based on different anatomical structures;

determining different segments of the border region based on the different anatomy portions; and

wherein in step b), the constrained flow is determined for the different segments of the border region.

14. Computer program element for controlling an apparatus according to one of the claims 1 to 5, which, when being executed by a processing unit, is adapted to perform the method steps of one of the claims 6 to 13.

15. Computer readable medium having stored the program element of claim 14.