JP4891541B2 - Vascular stenosis rate analysis system - Google Patents

Description

  The present invention uses a three-dimensional image data of a blood vessel imaged by an X-ray CT apparatus, a magnetic resonance imaging apparatus, an ultrasonic diagnostic apparatus, etc. as a useful index for diagnosis of the range and extent of the blood vessel stenosis. The present invention relates to a blood vessel stenosis rate analysis system capable of color display as a three-dimensional image.

  In recent years, blood vessels are extracted from three-dimensional image data taken with an X-ray CT apparatus, a magnetic resonance imaging apparatus, an ultrasonic diagnostic apparatus, etc., and the stenosis rate is automatically calculated using morphological information inside the blood vessels. A method of displaying on a three-dimensional image has been developed.

  The stenosis rate is calculated using the shape of the stenotic blood vessel and the blood vessel shape in a normal state. In addition, the blood vessel shape in the normal state is an estimated blood vessel in the normal state before the stenosis (hereinafter referred to as a temporary normal blood vessel) using the blood vessel shape of the normal part excluding the stenosis portion from the stenotic blood vessel It is.

  In the conventional method, the stenosis rate is calculated for each cross section perpendicular to the blood vessel running (hereinafter referred to as a blood vessel orthogonal cross section) using the blood vessel diameter of the temporary normal blood vessel and the blood vessel diameter of the constricted blood vessel. In other words, according to the conventional method, the calculated diameter, position, and calculation result with respect to the blood vessel axis direction can be uniquely determined for the blood vessel using the projection diameter (minimum value), and the following formula (1) or ( 2) Calculate the stenosis rate.

Stenosis rate = (blood vessel diameter of normal part-blood vessel diameter of stenosis part) / blood vessel diameter of normal part (1)
Stenosis rate = (cross-sectional area of normal part-cross-sectional area of stenosis part) / cross-sectional area of normal part (2)
As shown in FIG. 16, the stenosis rate calculated in this way is calculated by displaying the cross-sectional shapes of the blood vessel and the provisional normal blood vessel on the cross section of the blood vessel used for calculating the stenosis rate as shown in FIG. The direction is displayed as a straight line, and the stenosis rate is displayed as a numerical value. On the other hand, on the three-dimensional image, as shown in FIG. 17, the position of the orthogonal cross section of the blood vessel where the stenosis rate is calculated is marked and displayed on the three-dimensional blood vessel shape, and the color is determined according to the value of the stenosis rate. The stenosis rate is visually indicated by displaying each color.

  However, there are the following problems in observing blood vessel stenosis in a conventional blood vessel stenosis rate analysis system, for example.

  First, the stenosis rate is calculated using the projected minimum diameter of the normal blood vessel diameter estimated as the stenotic blood vessel diameter on the blood vessel orthogonal cross section. Therefore, only one stenosis rate can be calculated for one blood vessel orthogonal cross section, and the stenosis rate in the blood vessel contour direction (or the local stenosis rate including the circumferential direction of the blood vessel) on the blood vessel orthogonal cross section cannot be acquired. .

  Second, when the stenosis rate is displayed on a two-dimensional image, the direction and shape of the stenosis calculated on the cross section of the blood vessel can be known, but the position and range of the stenosis with respect to the vascular axis direction can be grasped. Can not. On the other hand, when the stenosis rate is displayed in color on a three-dimensional image, only one stenosis rate can be calculated for the cross section of the blood vessel, so only the cross section can be displayed. The position, range, and degree of stenosis in all directions of the blood vessel including the circumferential direction cannot be grasped intuitively and locally.

In addition, as a well-known document relevant to this application, there exist the following, for example.
JP 11-164833 A

  The present invention has been made in view of the above circumstances, and by calculating a local stenosis with respect to the irregularity of the blood vessel and displaying it in a predetermined form, the position of the stenosis with respect to the entire blood vessel and the stenosis in the circumferential direction of the blood vessel An object of the present invention is to provide a blood vessel stenosis rate analysis system capable of presenting the position, the range of stenosis, and the degree (degree) of stenosis in a form that can be intuitively grasped.

  In order to achieve the above object, the present invention takes the following measures.

The invention according to claim 1 is based on storage means for storing image data collected by a medical imaging device, extraction means for extracting a blood vessel shape based on the image data, and on the basis of the extracted blood vessel shape. , Blood vessel information generating means for generating blood vessel information including a blood vessel core line and a plurality of blood vessel contour points on a cross section of the blood vessel orthogonal to the blood vessel core line, and correcting the twist of the blood vessel shape based on the blood vessel information Correction means;
Setting means for setting a stenosis range based on the corrected blood vessel information, and a temporary normal blood vessel shape indicating a blood vessel shape of a normal part excluding the stenosis part from the stenotic blood vessel based on the corrected blood vessel information And a combination of the provisional normal blood vessel shape contour point corresponding to each direction and the extracted blood vessel shape blood vessel contour point on each of the blood vessel orthogonal cross sections. A calculation unit that calculates a plurality of local stenosis rates, an image generation unit that generates a blood vessel image to which a different color is assigned according to the value of each stenosis rate, and the blood vessel image is displayed in a predetermined form A blood vessel stenosis rate analyzing system.

  As described above, according to the present invention, by calculating the local stenosis for the irregularity of the blood vessel and displaying it in a predetermined form, the position of the stenosis with respect to the entire blood vessel, the position of the stenosis with respect to the circumferential direction of the blood vessel, the range of the stenosis, It is possible to realize a blood vessel stenosis rate analysis system that can present the degree of stenosis and the like in a form that can be intuitively grasped.

  Hereinafter, a blood vessel stenosis rate analysis system according to an embodiment of the present invention will be described with reference to the drawings. In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

  The vascular stenosis rate analysis system is set as a single device, and various medical images such as an image reference device (viewer), a medical workstation, an X-ray CT device, a magnetic resonance imaging device, and an ultrasonic diagnostic device. It can also be built in equipment. In the present embodiment, in order to make the description more specific, the case where it is built in a medical workstation is taken as an example.

  FIG. 1 is a block diagram of a vascular stenosis rate analysis system 1 according to this embodiment. As shown in the figure, the vascular stenosis rate analysis system 1 includes a storage unit 11, a control unit 12, an image processing unit 13, a transmission / reception unit 14, a display unit 15, and an operation unit 16.

  The storage unit 11 stores three-dimensional image data captured by an X-ray CT apparatus, a magnetic resonance imaging apparatus, an ultrasonic diagnostic apparatus, or the like. The storage unit 11 also stores a dedicated program for executing a stenosis rate analysis process including calculation of a stenosis rate, which will be described later, and three-dimensional color display of the stenosis rate.

  The control unit 12 reads out the program stored in the storage unit 11 and develops it on the memory, and controls each unit or the entire system statically or dynamically according to these.

  Under the control of the control unit 12, the image processing unit 13 executes each process related to stenosis rate analysis described later.

  The transmission / reception unit 14 transmits / receives various image data to / from other devices such as an X-ray CT apparatus via a network.

  The display unit 15 converts the image data received from the image processing unit 13 into a video signal, and displays in vivo morphological information and blood flow information as an image based on the video signal. In particular, the display unit 15 displays an image in which the local stenosis rate is displayed in a three-dimensional color according to the content described later.

  The operation unit 16 includes an input device such as a keyboard, a trackball, a mouse, and a dedicated interface for executing a stenosis rate analysis process described later.

(Stenosis analysis processing)
Next, stenosis rate analysis processing including calculation of the stenosis rate and three-dimensional color display of the calculated stenosis rate, which is realized by the present vascular stenosis rate analysis system 1, will be described. This stenosis rate analysis process uses the 3D extracted blood vessel extracted from 3D image data and the 3D temporary normal blood vessel estimated from the extracted blood vessel to calculate the displacement amount of the corresponding position (point) of the extracted blood vessel and the temporary normal blood vessel. Based on this, the local stenosis rate with respect to the irregularity of the blood vessel including the blood vessel circumferential direction is calculated. In addition, the color of the irregularity of the blood vessel is determined (mapped) according to the degree of stenosis based on the calculated stenosis rate, and the degree of local stenosis is displayed in color in a three-dimensional blood vessel shape.

  By this stenosis rate analysis processing, not only information such as the position of the stenosis with respect to the vascular axis direction but also stenosis such as the position of the stenosis with respect to the entire blood vessel, the position (direction) of the stenosis with respect to the peripheral direction of the blood vessel, the range of stenosis, the degree of stenosis, etc. New clinical information can be acquired. In addition, it is possible to present new clinical information related to stenosis in a form that facilitates intuitive grasping by color display of the local stenosis rate.

  FIG. 2 is a flowchart showing the flow of the stenosis rate analysis process executed by the vascular stenosis rate analysis system 1. As shown in the figure, this analysis process can be broadly divided into a blood vessel extraction process A and a stenosis rate calculation / display process B.

(Blood vessel extraction processing)
As shown in FIG. 2, first, under the control of the control unit 12, the image processing unit 13 reads image data obtained by photographing a target blood vessel from the storage unit 11 (step S <b> 1). Here, the image data is a three-dimensional image photographed over a certain distance in the opposite axis direction using helical CT, but if it is three-dimensional image data including a blood vessel to be analyzed, a magnetic resonance imaging apparatus or other medical device is used. Subsequent processing is the same for other types of images such as image data captured by an imaging device.

  Next, based on the read image data, three-dimensional blood vessel data (blood vessel core and blood vessel surface) is extracted from the three-dimensional image data as a three-dimensional blood vessel shape extraction process (step S2). As the method, Onno Wink, Wiro J. et al. Niessen, “Fast Delineation and Visualization of Vessel in 3-D Angiographic Images”, IEEE Trans. Med. Imag. , Vol. 19, No. 4, 2000 describes a method of automatically tracking the inside of a blood vessel from a specified point and extracting the center line and surface of the blood vessel (Bessel tracking method). G. D. Rubin, D.C. S. Paik, P. C. Johnston, S. Napel, “Measurement of the Aorta and Its Branches with Helical CT,” Radiology, Vol. 206, no. 3, pp. 823-9, Mar. 1998. Describes a method for thinning the extraction region of a luminal organ. In the present embodiment, an existing extraction method using the former Bessel tracking method is used. More specifically, the following processing is executed.

First, when the designated points P _S (start point), P _E (end point), and P _B (passage point) are designated in the blood vessel displayed on the display unit 15 with the mouse of the operation unit 16, the image processing unit 13 Using the Bessel tracking method, the inside of the blood vessel between P _{S and} P _E is automatically tracked based on the designated point, and after extracting the core line, the blood vessel contour point on the cross section orthogonal to the core line is extracted as the blood vessel surface.

  FIG. 3 is a diagram schematically showing core lines and blood vessel contour points extracted by the Bessel tracking method. As shown in the figure, the extracted three-dimensional blood vessel data is represented by a blood vessel core line and a blood vessel contour point on a cross section orthogonal to the core line.

  When the direction in which the blood vessel travels is the axial direction and the direction along the blood vessel contour point on the orthogonal section is the circumferential direction, the blood vessel core line is a smooth curve in the axial direction, and the blood vessel contour point is a smooth curve in the circumferential direction. . The blood vessel contour points are associated in the axial direction between the blood vessel contour points on each blood vessel orthogonal cross section, and a smooth curve is also drawn in the axial direction (dotted line in the figure). In this way, by correlating blood vessel contour points in the axial direction, it is easy to create a mesh (or patch) for surface display of extracted blood vessels and normal blood vessels, and to facilitate color map display of stenosis (degree) described later. . Further, the blood vessel contour points are also associated between the sample points of the extracted blood vessels and the sample points of the temporary normal blood vessels. By this association, the change in stenosis at each point on the blood vessel contour can be calculated from the difference between the blood vessel diameter of the temporary normal blood vessel and the blood vessel diameter of the stenotic blood vessel, as will be described later.

Next, torsion correction is performed on the extracted blood vessel (step S3). First, as shown in FIG. 4, a circle Q having a sample point corresponding to each blood vessel contour point and the radial direction around the blood vessel core point is created on each blood vessel orthogonal cross section perpendicular to the blood vessel axis direction. Next, two continuous circles arranged in the direction of the blood vessel axis are taken out, and the sum of the distances of the points associated between the two circles is calculated. For example, in the example of the circle Q ₁ and the circle Q ₂ on the left side of FIG. 5, between Q ₁ , ₀ −Q ₂ , _0, between Q ₁ , ₁ −Q ₂ , ₁ ,..., Q ₁ , ₅ −Q _{2, 5} The sum of the distances between them is calculated.

  In this association, a number is assigned to each blood vessel contour point on the basis of a (reference) vector B (Bx, By, Bz) that determines the direction of the blood vessel orthogonal cross section. At the initial stage (for example, at the stage of blood vessel surface extraction processing), the points in the reference vector Bx direction of each blood vessel orthogonal cross section are set to 0, and the cross sections are associated with each other. Here, the direction of the reference vector is a direction that coincides with the Vy (t) direction of the Volume coordinate where the blood vessel exists.

  Next, while fixing one circle and rotating the other circle, the sum of distances at each angle is calculated, and the angle θ at which the sum of distances is minimized is detected. Finally, the associated position (number) is shifted by the detected angle θ and reflected on the original blood vessel contour point as shown on the right side of FIG.

  In the case where the mechanical association is performed without considering the running or bending direction of the blood vessel during the blood vessel extraction processing as in the past, as shown on the left side of FIG. 5, the blood vessel is twisted, and the wire frame or surface is used. When displaying a blood vessel, the blood vessel shape is distorted. Further, since the shape of the blood vessel is distorted, the degree of stenosis cannot be calculated from the irregularity of the blood vessel and displayed in color.

  In this method, it is possible to remove the distortion of the blood vessel shape and display the blood vessel shape with less distortion as shown on the right side of FIG. Is possible. Further, in this method, the correction of the twist corrects not only the twist of the blood vessel but also the association of the blood vessel contour points. Therefore, the extracted normal blood vessel and the temporary normal blood vessel are estimated by estimating the temporary normal blood vessel using the corrected blood vessel data. Correspondence between the blood vessel contour points can be appropriately performed. The subsequent processing can be similarly performed on blood vessel data obtained by resampling / smoothing the core points and blood vessel contour points in the axial direction / circumferential direction. Accordingly, it is possible to estimate a temporary normal blood vessel with less distortion, and an appropriate local stenosis rate (degree) can be calculated from changes in the blood vessel contour point and the blood vessel contour point of the temporary normal blood vessel.

Next, when the blood vessel shape is extracted and the torsion correction is performed, the extraction result is displayed, and at the same time, the minimum diameter curve is displayed as an index for knowing the unevenness of the three-dimensional blood vessel shape. S4). Here, the minimum diameter curve, the distance along the blood vessel core from the starting point P _S to the arbitrary position in the vessel axial direction of the extraction range on the horizontal axis, the vertical axis of the vessel minimum diameter of each position, the vessel axis Is a graph showing a change in the minimum blood vessel diameter (an example is shown in FIG. 9 and the like described later).

  The conventional blood vessel diameter calculation method is extracted because it calculates the diameter passing through the blood vessel center (or core point) on the cross section of the blood vessel (the distance between the two intersections where the straight line passing through the blood vessel center and the blood vessel contour intersect). The blood vessel diameter varied depending on the position of the blood vessel center and could not be calculated as an objective value. In the vascular stenosis analysis system 1 according to the present embodiment, the projection diameter is calculated as the vascular diameter calculated regardless of the vascular center, and the minimum value (minimum projection diameter) is used, thereby objectively independent of the position of the vascular center. Value is calculated.

  The minimum projection diameter is calculated based on the position information of each blood vessel contour point by rotating the projection direction by θ = 0 to 180 degrees to calculate the projection diameter d (θ) in each direction. Is defined as the minimum value min (d (θ)). Therefore, depending on the number of projection directions and the number of blood vessel contour points, the number of processes may become very large and a long processing time may be required. Considering such a case, in the present embodiment, as shown in FIG. 6, a step of calculating a projection direction (one direction) that minimizes the projection diameter by optimization using the Brent method, and the calculated projection direction A high-speed and high-precision calculation method comprising a step of calculating a minimum diameter is used.

  That is, in the step of determining the projection direction, the initial value of the Brent method is calculated (step S41), and the projection direction that minimizes the diameter is determined using the method (step S42). Here, the Brent method is a method of calculating a minimum x coordinate of a given function f (x) by performing a convergence operation by inverse parabolic interpolation using arbitrary three points on the function (Technical Review). NUMERICAL RECIPES in C, quoted on pages 289-292).

  FIG. 7 is a conceptual diagram for explaining the Brent method, and shows the convergence of the function f (x) to the minimum value by the method. As shown in the figure, first, a parabola g (x) passing through three points a, b, and c on a given function f (x) is drawn, and the minimum d is set as the current best point. When f (d) is compared with f (a), f (b), and f (c), the maximum point c is discarded and three new points a, d, and b are determined. Draw a parabola h that passes through three new points, and set the minimum e as the new best point. By repeating this process, the minimum of a given function is narrowed down. When the convergence condition is tol, this process is repeated until the distance between the minimum in the previous state and the current minimum is smaller than tol, and the minimum reaches the center between two points sandwiching the minimum.

In the present embodiment, the parabola of the projection diameter d (θ) calculated with respect to the projection angle θ is assumed to be the function f (x), the minimum value of the parabola is obtained, and the projection angle θ at the minimum value is obtained. Is calculated by the Brent method. The initial value, a projection diameter d (θ _i) is the minimum projection angle theta _i and angle theta _i-1 before and after when calculated at 10 degree intervals projection size to the projection direction 0-180 degrees, Using θ _{i + 1} , the range of [θ _i−1 , θ _{i + 1} ] is the application range of the Brent method.

  Next, as shown in FIG. 6, in the step of calculating the minimum diameter, after calculating the projection distance of each contour point (step S43), the blood vessel projection diameter in the projection direction determined by the Brent method is calculated (step S44). ). Here, the blood vessel projection diameter is a distance between two straight lines that are in contact with the blood vessel contour and perpendicular to the projection direction, as shown in FIG. In this embodiment, after setting the reference point to an arbitrary position, each projection distance l (θ) when the blood vessel contour point is projected on a line that passes through the reference point and is perpendicular to the projection direction is calculated, and these projection distances are calculated. The blood vessel projection diameter d (θ) is calculated from the following formula (3) from the maximum value and the minimum value.

Projection diameter d (θ) = | Max (l (θ)) | + | Min (l (θ)) | (3)
As described above, in the present embodiment, the blood vessel projection diameter is calculated, and the blood vessel diameter independent of the blood vessel center point or the core point is uniquely determined. Can be calculated. Further, by optimizing using the Brent method for speeding up the blood vessel diameter calculation process, the number of times of the projection diameter calculation process can be reduced and the processing time for the blood vessel minimum diameter calculation can be reduced. Therefore, in order to improve the accuracy of the blood vessel diameter calculation process, the parabola d (θ) to be optimized is considered as a continuous function, so the step size Δθ that is the sample interval for calculating the value is considered. Therefore, it is possible to calculate the minimum value with higher accuracy. Furthermore, the minimum diameter curve created using the projected minimum diameter can be considered as an index indicating the unevenness of the three-dimensional blood vessel, in order to determine the target range of subsequent blood vessel analysis processing (here, stenosis rate analysis). It is also effective as an indicator of Note that the same processing can be performed in the case of a blood vessel cross-sectional area instead of the blood vessel minimum diameter.

  Based on the results obtained by the processes described above, display of the three-dimensional extracted blood vessel is executed (step S5 in FIG. 2). That is, as a result of 3D blood vessel extraction and blood vessel minimum diameter (or blood vessel cross-sectional area) calculation processing, a 3D image of an extracted blood vessel (blood vessel core and blood vessel surface), a minimum diameter curve (or cross-sectional area curve), and an arbitrary position The blood vessel orthogonal cross section is displayed.

FIG. 9 is a diagram illustrating an example of a display screen of a three-dimensional extracted blood vessel provided by the blood vessel extraction processing A. In the figure, _{P 1} is a three-dimensional image of the extraction vessel, _{P 2} is the minimum diameter curve, _{P 3} is a vascular orthogonal cross-sectional images (PV image).

The 3-dimensional image P ₁ of the extraction vessel, a straight line indicating the position of the blood vessel cross section perpendicular to I, linear indicating the range of the blood vessel extraction processing S, linear E is displayed. Further, the straight line I is also displayed at the corresponding position on the minimum diameter curve P _2. Vascular orthogonal cross-sectional images P ₃ is an image at the position of the straight line I. On the blood vessel cross section perpendicular to the image P _3, as shown in FIG. 9, it is preferable to display the position or direction was calculated vascular径最diameter by arrows.

Further, when a straight line I in the three-dimensional image P ₁ of the extraction vessel to Drag and therewith also move linearly I on minimum diameter curve, PV image is also updated on the blood vessel cross-sectional image relative to the position of the straight line I after movement Is done. This simplifies the work of grasping the position of the abnormal site with respect to the entire blood vessel using the minimum diameter curve and the work of confirming the internal state of the blood vessel with the PV image.

  Here, the extracted blood vessel is displayed as a surface-rendered image. However, the present invention is not limited to this, and it is also possible to display a wire frame in which the core line and the blood vessel contour point are connected by a smooth curve. In addition, a minimum diameter curve can be used as an index for seeing the change in irregularities in the direction of the blood vessel axis. When only the extraction result of the three-dimensional blood vessel shape is displayed and the minimum diameter curve is not displayed, the calculation of the minimum diameter or the blood vessel cross-sectional area can be performed as necessary in the subsequent analysis processing. .

(Stenosis analysis processing)
Next, the stenosis rate analysis process B executed by the present vascular stenosis rate analysis system will be described. This stenosis rate analysis process is performed using the blood vessel data and the value of the minimum blood vessel diameter with respect to the cross section of the blood vessel, but basically only the three-dimensional extracted blood vessel data is necessary. If the minimum blood vessel diameter for each blood vessel orthogonal cross section has not been calculated after blood vessel extraction, determination of the analysis range, which is the first processing of the stenosis rate analysis processing, is started after calculating the minimum diameter.

As shown in FIG. 2, in the stenosis rate analysis process, the analysis range is first set (step S6). Analysis range, for example above 3-dimensional image P ₁ of the extraction vessel after the blood vessel extraction process shown on FIG. 9 (or minimum diameter curve P ₂ above), carried out using a linear S and the straight line E. That is, when the straight line S is designated by the pointer and an operation such as long pressing of the click button is performed, a straight line S ′ that is a duplicate of the straight line S is created and can be dragged. The straight line S ′ is moved to a predetermined position by dragging between the straight lines S-E, and a duplicate straight line E ′ of the straight line E is created and moved by the same operation. The final straight line S′- _E ′ after the movement is set as an analysis target range R _S -R _E. When the straight lines S and E are not moved, the extraction target range is applied as it is as the analysis range. When the straight line S ′ and the straight line E ′ are created, the straight line S ′ and the straight line E ′ are displayed not only on the three-dimensional image P ₁ of the extracted blood vessel but also on the minimum diameter curve, and the unevenness of the minimum diameter curve While observing the above, it is possible to move these straight lines on the minimum diameter curve to determine the analysis range. This has an effect of facilitating the determination of the analysis target range after confirming the vascular abnormality site.

  Next, automatic extraction of a normal site | part and a stenosis site | part is performed (step S7). In the present embodiment, since the minimum diameter curve is created using the projected minimum diameter in the blood vessel extraction processing A, it can be considered as an index indicating three-dimensional unevenness in the blood vessel axis direction. Therefore, in the present embodiment, the normal region and stenosis region extraction processing is performed using the minimum diameter curve.

  FIG. 10 is a flowchart showing the flow of each process executed in the extraction of the normal site and the stenosis site. As shown in FIG. 11, after extracting the three-dimensional blood vessel shape, when the minimum diameter curve is created and the analysis range is determined, first, as shown in FIG. 11A, the regression line is obtained for the minimum diameter curve. (Step S11).

  Next, when comparing the minimum curve with the value obtained by multiplying the value indicated by the regression line by a certain ratio (1-α), the portion where the value of the minimum curve is smaller (dent) The remaining part is regarded as a normal part and extracted (step S72). Note that the value α is an allowable rate when deleting data corresponding to the stenosis (a value that determines how much data is deleted from the regression line), and 10% is used in this embodiment. In addition, data having an allowable rate of 10% or less is automatically deleted.

  Next, a regression line is calculated again using data corresponding to the normal part (remaining data) (step S73b). The regression line is calculated until there is no fluctuation of the regression line as shown in FIG. 11 (b) by the convergence condition that the residual ratio of the data is β% and the residual ratio is β% or until the position of the regression line does not change. The data deletion is repeated (steps S74 and S75). Note that β represents the number (ratio) of data necessary for calculating an appropriate regression line, and for example, β = 20% is used.

  On the other hand, in the determination of the inclination 0.1 in step S72, if the inclination of the regression line calculated in step S71 is γ (here, γ = 0.1 is used) or more, one end of the analysis range is a stenotic blood vessel. The average value (straight line indicating the average value without inclination) is calculated instead of the regression line (step S73a), and the data of the stenosis site is deleted using this (step S74), and the process proceeds to step S75 and described above. Repeat the process.

  Next, the regression line calculated using the data (data satisfying the convergence condition) that is finally left by the repetition from step S73b to step S75 is compared with the minimum diameter curve, and the minimum diameter curve is more than the regression line. The range existing below is automatically extracted as the stenosis range (step S76a).

  In addition, as shown in FIG. 12A, in the case of a blood vessel in which one end of the analysis range is constricted (hereinafter referred to as one end constriction), normal region data is also deleted by the regression line, so that it is properly normal. The site and stenosis site cannot be extracted. However, in this method, it is determined whether or not the stenosis is one end by the slope of the regression line. If it is determined that the stenosis is one end, as shown in FIG. Set the stenosis range. Therefore, it is possible to extract a normal part / stenosis part of one end of stenosis.

  By automatically extracting the stenosis range using this method and automatically determining the site and direction for calculating the stenosis rate, after estimating the temporary normal blood vessel, the stenosis part of the extracted blood vessel and the temporary normal blood vessel at the same position The stenosis rate can be calculated using the blood vessel diameter (or cross-sectional area). Further, it is possible to calculate the objective value without changing the position of the stenosis site designated by the difference in the user who performs the analysis or changing the value to be calculated.

Note that the automatically extracted stenosis range Z _S -Z _E is between the straight line Z _S and the straight lines Z _E , Z _S -Z _E on the three-dimensional image of the blood vessel and the minimum diameter curve, as shown in FIG. It is displayed as a distance (numerical value) along the blood vessel core line. It is also possible to modify the constriction range manually by moving by dragging the displayed linear Z _S and the straight line Z _E on the image. After correction, recalculate the distance of the analysis range and update the numerical value. As another method of correcting the stenosis range, it is possible to return to the analysis range setting process, correct the analysis range, and recalculate.

  Next, estimation of temporary normal blood vessels is performed based on the extracted blood vessel data corresponding to the normal site (step S8). That is, first, a radius curve is created using points associated in the axial direction between blood vessel contour points on each blood vessel orthogonal cross section. Here, the radius is the distance between the core point and the blood vessel contour point on the blood vessel orthogonal cross section. In this embodiment, a radius curve is created for all blood vessel contour points on the orthogonal cross section. Therefore, when 24 blood vessel contour points exist on one orthogonal cross section, 24 radius curves are created. Become. Next, when a radius curve is created, a regression line is calculated using only data corresponding to the normal region, and the temporary normal blood vessel is estimated by using the data on the regression line as the radius of the temporary normal blood vessel. Although a regression line is used here, it is possible to approximate with a smooth curve in addition to linear approximation.

  Next, when the provisional normal blood vessel is estimated, the unevenness change of the three-dimensional blood vessel shape is detected using the two blood vessel data of the provisional normal blood vessel and the extracted blood vessel, and the stenosis (degree) is calculated (step S9).

  That is, first, the projection average diameter Sr of the temporary normal blood vessel is calculated. Next, as shown in FIG. 13, the distance Si between the blood vessel contour points is calculated from the blood vessel contour point of the temporary normal blood vessel corresponding to the blood vessel contour point of the extracted blood vessel on the same orthogonal cross section (where i is 1 ≦ 1). n is an integer satisfying i ≦ n, and n corresponds to the total number of blood vessel contour points.) Finally, the degree of deformation of the diameter due to stenosis with respect to the projected average diameter using the distance between the corresponding blood vessel contour points is expressed by the following equation: The local stenosis rate Stenosis (blood vessel diameter) corresponding to each blood vessel contour point is calculated by (4).

Stenosis = 100 · Si / Sr (4)
In this way, from the distance between the corresponding two points of the blood vessel contour point indicating the blood vessel shape of the extracted blood vessel and the blood vessel contour point indicating the blood vessel shape of the temporary normal blood vessel, the shape change of the blood vessel after stenosis from the normal state is obtained. Detect locally. Therefore, a plurality of stenosis rates can be calculated for one vascular cross section, and the stenosis rates in the blood vessel contour direction on the vascular cross section can be acquired. In addition, by displaying in color according to the local stenosis (degree) on the three-dimensional blood vessel, the unevenness of the three-dimensional blood vessel can be confirmed, and at the same time, not only the position in the blood vessel axis direction but also the position of the stenosis in the circumferential direction of the blood vessel It is possible to observe the degree of distribution and stenosis.

The direction θ _{min in} which the projected diameter d (θ) of the blood vessel shape is minimized is calculated as the stenosis rate for each blood vessel orthogonal cross section, and the blood vessel diameter in the same direction θ _min with respect to the temporary normal blood vessel on the same blood vessel orthogonal cross section Fr (θ _min ) may be calculated, and the minimum stenosis rate for each cross section of the blood vessel may be calculated from d (θ _min ) and Fr (θ _min ).

  Next, three-dimensional color mapping of the calculated local stenosis rate is executed (step S10). This color display is realized by assigning a color according to the value of the stenosis rate (0 to 100%) at each obtained position. Here, in order to express the change of the stenosis rate with a red-blue gradation, the RGB values are calculated by the following formulas (5) to (7) (when the stenosis rate is x%) and the mapping is executed.

R (Red) = (x / 100) · 255 (5)
G (Green) = 0 (6)
B (Blue) = {(100−x) / 100} · 255 (7)
Next, three-dimensional color display of the local stenosis rate is performed according to the color mapping (step S11). FIG. 14 is a flowchart showing the flow of each process executed in the three-dimensional color display of the local stenosis rate in step S11. Here, two types of color display by surface rendering and volume rendering will be described using a rendering algorithm.

  When performing three-dimensional surface rendering, as shown in the flow on the left side of FIG. 14, first, the narrowed blood vessel is divided into triangular patches composed of three blood vessel contour points (step S111a), and the center of gravity of the patch is obtained. The distance between the position, the center of gravity and the blood vessel contour point is calculated (step S112a). Next, the color of the centroid position is calculated from the color value of each contour point and the weight of the distance between the centroid and each vascular contour point, and the calculated color is used as a patch (step S113a). Finally, a three-dimensional surface display is performed based on each patch (step 114a).

  It is also possible to resample the blood vessel in the axial direction and circumferential direction, take blood vessel contour points sufficiently finely, calculate the stenosis rate at each contour point, perform a color map, and display the surface in the same way is there.

  On the other hand, when performing volume rendering, as shown on the right side of FIG. 14, first, blood vessel contour points are calculated in units of pixels by resampling (111b), and the color for each contour point is interpolated (such as linear interpolation). Calculation is performed (step S112b), and based on this, three-dimensional volume display is performed (step S113b).

FIG. 15 is a diagram showing an example of a three-dimensional color display screen of a local stenosis rate provided by the vascular stenosis rate analysis system. As shown in the figure, the stenosis rate is displayed not only by color display on the three-dimensional image P ₁ of the extracted blood vessel but also by the minimum diameter curve P ₂ , the orthogonal cross-sectional image P ₃ , and each measurement result (numerical value) image P _4. Is done.

Further, a straight line indicating each position is superimposed and displayed at a position corresponding to the stenosis range Z _S -Z _E , the maximum stenosis rate, and the minimum diameter (MLD) on the three-dimensional image P ₁ and the minimum diameter curve P _{2 of} the extracted blood vessel. The Display linear I indicating the position of the blood vessel cross section perpendicular to the image on the three-dimensional image P ₁ of the extraction vessel and on minimum diameter curve P _2, on the orthogonal cross-sectional images P ₃ vascular contour extraction vessel and preliminary normal blood vessels The direction θ in which the stenosis rate (blood vessel diameter) is calculated is displayed with an arrow in a superimposed manner. Each measurement result of the maximum stenosis rate (diameter), maximum stenosis rate (area), stenosis range length Z _S -Z _E , and minimum diameter (MID) is displayed as a numerical value.

  Of these displays, the three-dimensional blood vessel shape (color) is displayed to color the entire blood vessel according to the degree of local stenosis, and the three-dimensional blood vessel shape (unevenness) along the blood vessel axis direction and the blood vessel circumferential direction. In addition to being able to observe, it is possible to intuitively and relatively grasp the position / distribution / degree of local stenosis rather than the cross section of the blood vessel by color difference. Further, on the PV image, the state inside the blood vessel such as the cross section of the blood vessel, the shape of the extracted blood vessel, and the shape of the temporary normal blood vessel can be confirmed. Each value can be quantitatively evaluated by displaying each measurement result as a numerical value.

  The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.

  For example, each function according to the present embodiment can also be realized by installing a program for executing the processing in a computer such as a workstation and developing these on a memory. At this time, a program capable of causing the computer to execute the technique is stored in a recording medium such as a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), an optical disk (CD-ROM, DVD, etc.), or a semiconductor memory. It can also be distributed.

  In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  As described above, according to the present invention, by calculating the local stenosis for the irregularity of the blood vessel and displaying it in a predetermined form, the position of the stenosis with respect to the entire blood vessel, the position of the stenosis with respect to the circumferential direction of the blood vessel, the range of the stenosis, It is possible to realize a blood vessel stenosis rate analysis system that can present the degree of stenosis and the like in a form that can be intuitively grasped.

FIG. 1 is a block diagram of a vascular stenosis rate analysis system 1 according to this embodiment. FIG. 2 is a flowchart showing a flow of a series of processing including main image processing and image display. FIG. 3 is a diagram schematically showing core lines and blood vessel contour points extracted by the Bessel tracking method. FIG. 4 is a conceptual diagram for explaining the extracted blood vessel twist correction processing. FIG. 5 is a conceptual diagram for explaining the extracted blood vessel twist correction processing. FIG. 6 is a flowchart showing the flow of processing executed in calculating the minimum projected diameter. FIG. 7 is a conceptual diagram for explaining the Brent method, and shows the convergence of the function f (x) to the minimum value by the method. FIG. 8 is a diagram for explaining a blood vessel projection diameter (a distance between two straight lines in contact with a blood vessel contour and perpendicular to the projection direction). FIG. 9 is a view showing an example of a display screen of a three-dimensional extracted blood vessel provided by the blood vessel stenosis rate analyzing system. FIG. 10 is a flowchart showing the flow of each process executed in the extraction of the normal site and the stenosis site. FIG. 11 is a conceptual diagram for explaining setting of a stenosis range using a regression line. FIG. 12 is a conceptual diagram for explaining setting of a stenosis range using a regression line or an average value line. FIG. 13 is a diagram for explaining the detection process of the unevenness change of the three-dimensional blood vessel shape based on the two blood vessel data of the temporary normal blood vessel and the extracted blood vessel. FIG. 14 is a flowchart showing the flow of each process executed in the three-dimensional color display of the local stenosis rate in step S11. FIG. 15 is a diagram showing an example of a three-dimensional color display screen of a local stenosis rate provided by the vascular stenosis rate analysis system. FIG. 16 is a diagram showing an example of conventional stenosis ratio display on a two-dimensional image. FIG. 17 is a diagram showing an example of conventional stenosis ratio display on a three-dimensional image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Vascular stenosis rate analysis system, 11 ... Memory | storage part, 12 ... Control part, 13 ... Image processing part, 14 ... Transmission / reception part, 15 ... Display part, 16 ... Operation part

Claims (10)

Storage means for storing image data collected by the medical imaging device;
Extraction means for extracting a blood vessel shape based on the image data;
Based on the extracted blood vessel shape, blood vessel information generating means for generating blood vessel information including a blood vessel core line and a plurality of blood vessel contour points on a blood vessel orthogonal cross section orthogonal to the blood vessel core line;
Correction means for correcting torsion of the blood vessel shape based on the blood vessel information;
Setting means for setting a stenosis range based on the corrected blood vessel information;
Based on the corrected blood vessel information, estimating means for estimating a plurality of contour points of a temporary normal blood vessel shape indicating a blood vessel shape of a normal portion excluding the stenosis portion from the narrowed blood vessel,
Calculation for calculating a plurality of local stenosis ratios using a combination of the contour points of the temporary normal blood vessel shape corresponding to each direction and the blood vessel contour points of the extracted blood vessel shape on the blood vessel orthogonal cross section Means,
Image generating means for generating a blood vessel image to which a different color is assigned according to the value of each stenosis rate ;
Display means for displaying the blood vessel image in a predetermined form;
A blood vessel stenosis rate analysis system comprising: Said image generating means, and the reference position in each of predetermined areas formed the vessel contour points present before Symbol stenosis range as the vertex, by weighting according to the distance between the vertices to form the respective predetermined areas Generating the blood vessel image by calculating the color of each predetermined area and performing surface rendering using the calculated color;
The blood vessel stenosis rate analysis system according to claim 1. The image generating unit, by executing the volume rendering using the volume data including a plurality of vessels contour points before Symbol color is assigned, to generate the blood vessel image,
The blood vessel stenosis rate analysis system according to claim 1. The correcting means detects an axial twist angle of the blood vessel shape based on the association of the blood vessel contour points between the adjacent blood vessel orthogonal cross sections,
The vascular stenosis rate analysis system according to any one of claims 1 to 3, wherein the association between the blood vessel contour points in the axial direction is corrected based on the detected angle.   The setting means is a graph showing a change in the minimum blood vessel diameter in the direction of the blood vessel axis with the distance along the blood vessel core line of the extracted blood vessel shape as the horizontal axis and the minimum blood vessel diameter of each blood vessel orthogonal section as the vertical axis. The stenosis rate analysis system according to any one of claims 1 to 3, wherein the stenosis range is set using a minimum diameter curve and a regression line related to the plurality of vascular contour points.   The setting means determines whether one end of the blood vessel shape is stenotic based on the slope of the regression line, and if it is determined that one end is stenotic, the setting means relates to the plurality of blood vessel contour points. 6. The blood vessel stenosis rate analysis system according to claim 5, wherein an average value is calculated and the stenosis range is set using the average value. The calculation means calculates a direction θ _{min in} which the projected diameter d (θ) of the blood vessel shape is minimum as the stenosis rate for each blood vessel orthogonal cross section, and is the same for the temporary normal blood vessels on the same blood vessel orthogonal cross section Calculate the blood vessel diameter Fr (θ _min ) in the direction θ _min , calculate the minimum stenosis rate for each of the blood vessel orthogonal cross sections from d (θ _min ) and Fr (θ _min ),
The display means displays the minimum stenosis rate for each of the blood vessel orthogonal cross sections in a predetermined form;
The blood vessel stenosis rate analysis system according to any one of claims 1 to 6.   8. The blood vessel stenosis rate analysis system according to claim 7, wherein the display unit displays the position or direction in which the minimum stenosis rate is calculated in a predetermined form.   The calculation means calculates the stenosis rate by determining the degree of deformation of the blood vessel shape from a blood vessel constricted on each blood vessel orthogonal cross section and a distance between two blood vessel contour points corresponding to the temporary normal blood vessel. The vascular stenosis rate analysis system according to any one of claims 1 to 6, wherein Further comprising changing means for changing the stenosis range,
The calculating means, when the stenosis range is changed by the changing means, calculating a local stenosis ratio in the changed stenosis range,
The blood vessel stenosis rate analyzing system according to any one of claims 1 to 9.

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