JP2012245106A - Apparatus and program for extracting region where heart is present - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and program for extracting a region where heart is present, capable of automatically extracting a region of the heart without including the auricle of right atrium or the auricle of left atrium within a space constructed with medical image data.SOLUTION: A core line L of the auricle of right atrium is found based on the medical image data, and a closed surface enveloped by the core line L is optimized by an RBS technique to approximate an optionally selected function by a linear sum of a plurality of radial basis functions based on the positional information of the core line, and the optimized closed surface is set as a closed surface W for masking. An inner region of the closed surface W for masking is extracted as the region where heart is present, and by applying a volume rendering method to the extracted region where heart is present, a VR image of the whole heart corresponding to the internal region of the closed surface for masking is formed.

Description

  The present invention relates to a technique for supporting image diagnosis, and in particular, in a space constructed based on medical image data obtained by an image diagnosis apparatus such as X-ray CT (Computed Tomography), MRI (Magnetic Resonance Imaging) or the like. The present invention relates to a heart presence region extraction apparatus and program for extracting a region where a heart is present.

  Constructed on the basis of the obtained three-dimensional image data in accordance with the fact that high-precision three-dimensional image data (volume data) can be obtained in a short time by an image diagnostic apparatus such as X-ray CT or MRI. It is used for various purposes, such as extracting regions of living body parts such as organs and tumors in space, making them easy to see and using them for explanations for patients and academic purposes, and making surgical plans. Demand is increasing.

  Conventionally, in areas such as the lung field and brain where contours and lesions are relatively easy to extract, research has been actively conducted to automatically extract living body areas using computers such as computers. Even in the heart region where automatic extraction has been difficult until now, research for automatically extracting a predetermined region such as the entire heart or a coronary artery is in progress.

  For automatic extraction of coronary arteries, after identifying the position of the coronary artery core line (center line) based on the image signal value (voxel value) corresponding to each voxel of the three-dimensional image data, in a plane perpendicular to the core line A technique for identifying the contour of a coronary artery (see, for example, Patent Document 1 and Non-Patent Document 1 below) has been developed, and only a medical image obtained by a CT apparatus (hereinafter referred to as “CT image”) can be used. In addition, a highly accurate extraction result can be obtained even in a medical image (hereinafter referred to as “MRI image”) obtained by an MRI apparatus.

JP 2011-25005 A

Stephen R. Aylward, Member, IEEE and Elizabeth Bullitt, “Initialization, Noise, Singularities, and Scale in Height Ridge Traversal for Tubular Object Centerline Extraction” IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. 21, NO.2, FEBRUARY 2002

  On the other hand, as a method for automatically extracting the entire heart, a method using CT image data of a chest taken by injecting a contrast medium is known. In this method, the existence area of the heart is roughly specified in the space constructed by the CT image data, unnecessary tissues such as bones and lung fields located outside the existence area are deleted, and each data of the CT image data is deleted. Based on the value (CT value) or the like, a coronary artery portion into which a contrast medium is injected and a soft tissue portion (myocardium or right heart system) adjacent thereto are selected and extracted as a heart.

  According to this method, the right atrial appendage and the left atrial appendage that exist so as to cover a part of the coronary artery are also extracted as a part of the heart (see FIG. 9B described later). It is anatomically correct to have the right and left atrial appendages as part of the heart, but if you want to observe the running state of the coronary arteries, the presence of the right or left atrial appendage hinders confirmation of coronary running. Therefore, there is a desire to delete these from the image.

  However, since the right atrial appendage and the left atrial appendage are in close contact with the coronary arteries and have similar CT values to other cardiac tissues such as the myocardium, the right atrial appendage and the left atrial appendage are not included. It was difficult to extract the region automatically. Therefore, conventionally, doctors who have anatomical expertise have also deleted the right atrial appendage and the left atrial appendage from the image by manual operation based on visual observation. Therefore, it takes a lot of time to generate an image, and there is a possibility of adversely affecting the travel information of the obtained coronary artery.

  In addition, the above-described automatic heart extraction method has been developed so that it can be applied to CT image data from which a predetermined image signal value (CT value) can be obtained without being affected by imaging equipment or imaging conditions. When applied to MRI image data in which the image signal value varies greatly depending on the photographing device and photographing conditions, it has been difficult to obtain a stable extraction result (see FIG. 10B described later).

  The present invention has been made in view of such circumstances, and in a space constructed based on medical image data obtained by a CT apparatus or an MRI apparatus, an existing region of the heart that does not include the right atrial appendage and the left atrial appendage is obtained. It is an object of the present invention to provide a heart presence region extraction apparatus and program that can be automatically extracted.

  In order to achieve the above object, a heart presence region extraction apparatus and program according to the present invention are configured as follows.

That is, the heart presence region extraction device according to the present invention is
A heart presence region extraction device that extracts a region where a heart exists in a space constructed based on medical image data (for example, CT image data or MRI image data),
A closed curved surface setting means for setting a closed curved surface enveloped by the traveling line as a closed curved surface for a mask based on position information of the traveling line of the coronary blood vessel obtained based on the medical image data;
And an area extracting means for extracting an internal area of the closed curved surface for the mask as an area where the heart exists.

In the heart presence region extraction apparatus according to the present invention,
The closed curved surface setting means uses a control point setting means for setting a plurality of control points along the travel line and a method of approximating an arbitrary function by a linear sum of a plurality of radial basis functions. A closed surface optimization unit that optimizes a closed surface that satisfies a condition of passing a point, and the closed surface optimized by the closed surface optimization unit is set as the closed surface for a mask Can be configured.

  Further, an image forming unit that forms a volume rendering image corresponding to the internal region of the mask closed curved surface using a volume rendering method may be provided.

In addition, the heart presence region extraction program according to the present invention is
In a space constructed based on medical image data, a heart presence region extraction program for causing a computer to execute processing for extracting a region where a heart exists,
A mask closed surface setting step for setting a closed curved surface enveloped by the travel line as a mask closed curved surface based on position information of the travel line of the coronary blood vessel obtained based on the medical image data;
An area extracting step of extracting an internal area of the closed curved surface for mask as an area where the heart exists is executed in the computer.

  The above “coronary blood vessel” means a blood vessel that runs along the outer surface of the heart, and is a concept that includes a coronary vein in addition to a coronary artery.

  The “coronary blood vessel running line” means each line indicating the three-dimensional running state of the coronary blood vessels such as the coronary arteries. In addition to the core line (center line) of the coronary blood vessels, It is a concept including a line along the line.

  The above-mentioned “closed curved surface enveloped by the travel line” means a closed curved surface enclosed by the entire travel line while contacting a part of each travel line. It does not exclude the case where a part is included.

  The heart presence region extraction apparatus and program according to the present invention sets a closed curved surface enveloped by a running line as a closed curved surface for a mask based on position information of a running line of a coronary blood vessel obtained based on medical image data, The internal area of the mask closed curved surface is extracted as an area where the heart exists, and the following effects are obtained.

  That is, since coronary blood vessels such as coronary arteries run along the outer surface of the heart, the closed curved surface enveloped by the running line of the coronary blood vessel has a shape that approximates the outer shape of the heart, Will include the main part of the heart (myocardial part). On the other hand, the right atrial appendage and the left atrial appendage are not included in the inner region of the closed curved surface because they are anatomically located at a position covering a part of the coronary artery, that is, outside the running line of the coronary artery.

  Moreover, it is possible to automatically calculate the position information of the running line of the coronary blood vessel, whether it is CT image data or MRI image data, and further, a closed curved surface enveloped by the running line can be obtained. The calculation can also be automatically performed by applying a three-dimensional curved surface generation method conventionally used in image processing technology. Moreover, in order to execute the calculation for obtaining the closed curved surface, only the position information of the travel line is required, and the distribution information of the image signal value (voxel value) of the medical image data is not required. For this reason, it is possible to automatically obtain a closed curved surface for both CT image data and MRI image data.

  Therefore, according to the present invention, the closed curved surface enveloped by the running line of the coronary blood vessel is set as the closed curved surface for the mask, and the internal region of the closed curved surface for the mask is extracted as the region where the heart exists. In the space constructed based on the CT image data or the MRI image data, it is possible to automatically extract the existing region of the heart that does not include the right atrial appendage and the left atrial appendage.

  In addition, according to the present invention, since an artificial operation that has been conventionally performed to delete the right atrial appendage and the left atrial appendage from an image becomes unnecessary, appropriate information (coronary artery running information) can be efficiently and stably obtained. Etc.) can be generated.

It is a block diagram which shows schematic structure of the heart presence area | region extraction apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the functional structure of the arithmetic processing unit shown in FIG. It is a flowchart which shows the flow of the process which the arithmetic processing unit shown in FIG. 1 performs. It is a flowchart which shows the flow of the closed curved surface setting process for masks. It is a figure which shows the calculated | required travel line of the coronary artery. It is a figure which shows the setting aspect of the some control point set on the running line of a coronary artery. It is a figure which shows the closed curved surface enveloped by the running line of a coronary artery. It is a figure which shows a coronary artery extraction image. It is a figure ((A) is based on the method of this invention, (B) is based on a conventional method) which shows an example of the heart extraction image based on CT image data. It is a figure ((A) is based on the method of this invention, (B) is based on a conventional method) which shows an example of the heart extraction image based on MRI image data.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the above-mentioned drawings. First, a heart presence region extraction apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  1 extracts a region where a heart exists in a space constructed based on medical image data (hereinafter referred to as “image data space”), and extracts a heart located in this region. The whole image is formed, and includes an arithmetic processing device 10 formed of a computer or the like, an input device 20 formed of a mouse or a keyboard, and an output device 30 formed of an image display device.

  As shown in FIG. 2, the arithmetic processing apparatus 10 includes medical image data storage means 11, travel line specifying means 12, closed curved surface setting means 13, area extracting means 14, and image forming means 15, and is set to a closed curved surface. The means 13 includes a control point setting means 131 and a closed curved surface optimization means 132. These means include a CPU for performing various arithmetic processes, a storage device such as a hard disk and a ROM, a control program stored in the storage device (including a heart existing region extraction program according to an embodiment of the present invention), a RAM, and the like This is a conceptual illustration of a temporary storage device or the like.

  The medical image data storage means 11 includes three-dimensional medical image data (CT image data or MRI image data) of a subject's chest obtained by an X-ray CT apparatus or an MRI apparatus, the above-described running line specifying means 12, Various data obtained by the curved surface setting means 13, the area extraction means 14, and the image forming means 15 are stored.

  The travel line specifying means 12 specifies the entire travel line of the coronary blood vessel (coronary artery in this embodiment) of the heart in the image data space, and obtains its three-dimensional position information.

  The closed curved surface setting means 13 obtains a closed curved surface enveloped by the running line based on the position information of the running line of the coronary artery obtained by the running line specifying means 12, and sets this as a closed curved surface for the mask. Is. Specifically, the control point setting unit 131 sets a plurality of control points along the travel line, and a closed surface that satisfies the condition of passing through the plurality of control points is determined as the closed surface optimization unit 132. The optimized closed surface is set as the mask closed surface.

  The area extracting unit 14 extracts the internal area of the mask closed curved surface set by the closed curved surface setting unit 13 as a region where the heart exists.

  The image forming means 15 forms a volume rendering image (hereinafter referred to as “VR image”) of the entire heart corresponding to the internal region of the mask closed curved surface using a volume rendering method.

  Next, the procedure for extracting the heart existing area and the procedure for forming the VR image of the entire heart by the heart existing area extracting apparatus 1 according to the present embodiment will be described with reference mainly to FIGS. The heart presence region extraction procedure described below is executed according to the heart presence region extraction program according to an embodiment of the present invention.

  <1> Medical image data (CT image data or MRI image data) of the subject's chest is acquired (medical image data acquisition step; see step S1 in FIG. 3). In the present embodiment, it is assumed that necessary medical image data is stored in advance in the medical image data storage unit 11 (see FIG. 2), but is recorded in an information storage medium such as a CD or a DVD. You may make it read medical image data as needed.

  <2> Based on the acquired medical image data, in the image data space constructed by the medical image data, the entire running line of the cardiac coronary artery is specified and its three-dimensional position information is obtained (running line Specific step; see step S2 in FIG. 3 and FIG. In the present embodiment, the core line (center line) of the coronary artery is specified as the running line by the method disclosed in the aforementioned Non-Patent Document 1.

  Specifically, first, based on each data value (voxel value) of medical image data, a point estimated to be located on the core line of the coronary artery in a local region in the image data space (hereinafter referred to as “via point”). Set. Next, the eigenvalue of the Hesse matrix in the local region including the via point is calculated, the principal axis direction of the coronary artery core line (the direction in which the core line extends) is obtained based on the calculated eigen value, and a new via point is calculated in the main axis direction. Set. By repeating this procedure, a large number of via points are set in order, and the set via points are smoothly connected to each other, thereby specifying the entire core line L (see FIG. 5) of the coronary artery.

  Anatomically, coronary arteries are broadly divided into right coronary arteries (RCA) and left coronary arteries (LCA) that branch from the enormous part of the aortic root. The right coronary artery passes through the right atrioventricular groove, branches down the right edge of the heart and branches into the posterior descending branch and atrioventricular branch at the interventricular groove, and each branch is further finely branched. The left coronary artery is branched into a left anterior descending branch (LAD) descending to the front side of the heart from the vicinity of the root and a left circumflex branch (LCX) wrapping around the back side, and each branch is further finely branched. The specification of the core line L is preferably performed in detail up to the tip of each branch of the coronary artery, but may be omitted as appropriate within a range that does not hinder the specification of the closed curved surface described later, such as only the main branch. Good.

  <3> Based on the obtained positional information of the core line L of the coronary artery, a closed curved surface enveloped by the core line L is obtained, and a mask closed curved surface setting process for setting this as a mask closed curved surface is executed (mask closed Curved surface setting step; see step S3 in FIG.

  Specifically, first, a plurality of control points P are set on the core line L (control point setting step; see step S31 in FIG. 4 and FIG. 6). The setting of the control point P can be appropriately performed at an arbitrary interval along the core line L. However, according to the present embodiment, according to the curvature of each part of the core line L, the interval is narrow and the curvature is narrow. In small parts, the interval is widened, and on average, control points P are automatically set every several millimeters in terms of actual size. In FIG. 6, the control point P is schematically indicated by “•” (a symbol “P” is attached to a part of the control point), but in reality, the control point P is denser than the illustrated state. Is set.

  Next, a condition that an arbitrary function is approximated by a linear sum of a plurality of radial basis functions (hereinafter referred to as “RBF method”) is satisfied, and the condition that the control points P are passed is satisfied. The closed curved surface to be optimized is optimized, and the optimized closed curved surface is set as the mask closed curved surface W (closed curved surface optimization step; see step S32 in FIG. 4, FIG. 7). In FIG. 7, the outline of the mask closed curved surface W is simplified by a one-dot chain line.

  The RBF method approximates an arbitrary curved surface by an implicit function expression of s (x) = 0 using a function s (x) of an arbitrary point x (x is a vector (three-dimensional point)) in a three-dimensional space. This is a technique for expressing, and has the advantages that various curved surface expressions with a high degree of freedom are possible and that the local smoothness of the curved surface can be easily adjusted.

  The function s (x) used for the RBF method is expressed by the following equation (1).

  As the radial basis function φ (r), a thin-plate function, a Gaussian function, a multi-quadratic function, a bi-harmonic function, a tri-harmonic function, or the like can be used. In this embodiment, the radial basis function is used. A bi-harmonic function is used as φ (r). In this case, the radial basis function φ (r) is expressed by the following equation (2), and the polynomial function p (x) is expressed by the following equation (3).

  In the present embodiment, in order to obtain the mask closed surface W (see FIG. 7) that satisfies the above-described condition of passing through the plurality of control points P, the coordinate values (x, y) of each point x in the above equation (1) are obtained. , Z), the coordinate value of each control point P is substituted, and arithmetic processing for obtaining vectors Λ and e defined by the following equations (4) and (5) may be performed.

  This calculation process is known to be equivalent to solving the linear equation of the following equation (7) under the additional condition of the following equation (6) (see Reference 1 below).

  Reference 1: Yoshitaka Masutani Image Computing and Analysis Laboratory, Department of Radiology, University of Tokyo (UT-RAD / ICAL) “RBF-based Representation of Volumetric Data: Application in Visualization and Segmentation”, MICCAI 2002, LNCS 2489, pp. 300-307

  <4> Extract the internal region of the mask closed curved surface W obtained by the arithmetic processing using the RBF method described above as a region where the heart exists (hereinafter referred to as “heart existence region”) (region extraction step; step of FIG. 3) (See S4).

  <5> A volume rendering method is applied to the extracted heart existing region to form a VR image of the entire heart corresponding to the inner region of the mask closed curved surface W (VR image forming step; step S5 in FIG. 3) reference). Note that the volume rendering method is a method for imaging each voxel of the three-dimensional medical image data by assigning a color or opacity to the image signal value.

  In this embodiment, since the core line L of the coronary artery is used as the running line, the mask closed curved surface W passes through a position that bisects the coronary artery in the radial direction. For this reason, in the VR image (hereinafter referred to as “whole heart image”) formed in the VR image forming step described above, the coronary artery cut along the core line L is depicted. When it is desired to form an image in which the surface portion of the coronary artery is depicted, only the coronary artery is extracted based on the method disclosed in the above-mentioned Non-Patent Document 1 when extracting the core line L in the above-described travel line specifying step. A VR image (hereinafter referred to as “coronary artery extracted image”) is formed, and this coronary artery extracted image (see FIG. 8) may be combined with the whole heart image. Alternatively, by expanding a part of the mask closed curved surface W along the core line L and setting so that the entire coronary artery is included in the heart existing region, an image in which the surface portion of the coronary artery is depicted is formed. You may make it do.

  According to the method of the present invention described above, it is possible to automatically extract the existence region of the heart not including the right atrial appendage and the left atrial appendage in the image data space constructed based on the CT image data or the MRI image data, An extracted image of the entire heart suitable for observing the running state of the coronary artery can be formed.

  Specifically, when CT image data is used, in the conventional method, as shown in FIG. 9 (B), it is an obstacle to observe the running state of the coronary arteries such as the right atrial appendage 32, the left atrial appendage 33, and the pulmonary artery 34. 9 (hereinafter referred to as “unnecessary tissue at the time of observation”) is drawn, according to the method of the present invention, these unnecessary tissues at the time of observation are drawn as shown in FIG. An extracted image of the whole heart can be formed.

  In FIG. 9A, the whole heart image corresponding to the internal region of the mask closed curved surface W and the coronary artery extracted image formed based on the technique disclosed in the above-mentioned Non-Patent Document 1 are combined. It is formed. In FIG. 9A, a part of the aorta 31 is depicted. This is because a part of the aorta is extracted when the coronary artery extraction image is formed. The same applies to FIG. 10A described below.

  Further, when MRI image data is used, in the conventional method, as shown in FIG. 10B, there is a high possibility that a large number of unnecessary tissues existing around the heart are drawn. According to the technique, as shown in FIG. 10A, an extracted image of the entire heart in which these unnecessary tissues during observation (including the right atrial appendage, the left atrial appendage, and the pulmonary artery) are not drawn can be formed.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A mode can be changed variously.

  For example, in the above embodiment, the above-described RBF method is used as a method for obtaining the mask closed curved surface enveloped by the core line (running line) of the coronary artery, but other methods such as a method of approximating the curved surface using a spline function are used. A closed curved surface for a mask may be obtained using a three-dimensional curved surface generation method.

  In the above embodiment, the method disclosed in Non-Patent Document 1 described above is used to obtain the core wire as the coronary artery running line. However, other methods are used to obtain the coronary artery running line. It may be.

DESCRIPTION OF SYMBOLS 1 Heart presence area extraction apparatus 10 Arithmetic processing apparatus 20 Input apparatus 30 Output apparatus 11 Medical image data storage means 12 Traveling line specification means 13 Closed surface setting means 14 Area extraction means 15 Image formation means 31 Aorta 32 Right atrial appendage 33 Left atrial appendage 34 Pulmonary artery 131 Control point setting means 132 Closed surface optimization means L Core wire (travel line)
P Control point W Masked closed surface

Claims (4)

A heart presence region extraction device that extracts a region where a heart exists in a space constructed based on medical image data,
A closed curved surface setting means for setting a closed curved surface enveloped by the traveling line as a closed curved surface for a mask based on position information of the traveling line of the coronary blood vessel obtained based on the medical image data;
An area extraction unit for extracting an internal area of the closed curved surface for a mask as an area where the heart exists.   The closed curved surface setting means uses a control point setting means for setting a plurality of control points along the travel line and a method of approximating an arbitrary function by a linear sum of a plurality of radial basis functions. A closed surface optimization unit that optimizes a closed surface that satisfies a condition of passing a point, and the closed surface optimized by the closed surface optimization unit is set as the closed surface for a mask The heart presence region extraction device according to claim 1, wherein the heart presence region extraction device is configured.   The heart presence region extraction apparatus according to claim 1, further comprising an image forming unit that forms a volume rendering image corresponding to an internal region of the closed curved surface for a mask using a volume rendering method. In a space constructed based on medical image data, a heart presence region extraction program for causing a computer to execute processing for extracting a region where a heart exists,
A mask closed surface setting step for setting a closed curved surface enveloped by the travel line as a mask closed curved surface based on position information of the travel line of the coronary blood vessel obtained based on the medical image data;
An area extraction step for extracting an internal area of the closed curved surface for a mask as an area where the heart is present is executed in the computer.