Patent Description:
Heretofore, as a method for displaying a cardiac function, a bull's eye display method has been used. As illustrated in <FIG>, the bull's eye display method is a method in which a heart is approximated with an ellipsoid model and images Q<NUM>, Q<NUM>, ----- Qi, ----- Qn representing evaluations of the cardiac function on planes P<NUM>, P<NUM>, ----- Pi ----- Pn provided by slicing the ellipsoid at a regular interval in a direction traversing the major axis of the ellipsoid are concentrically arranged and displayed (<FIG>). In the bull' s eye display method, the function on plane P<NUM> near one of the major vertices of the ellipsoid model is disposed in Q<NUM> located near the center of the concentric circles and the function on plane Pn near the other of the major vertices of the ellipsoid model is disposed in Qn located outer side of the concentric circles.

This display method is mainly used with functional images. The functional images include images directly photographed by myocardium scintigraphy (SPECT) and images representing functions obtained from analysis results of CT/MRI images.

In the mean time, it has become possible to discover a narrowed section of a blood vessel by injecting a contrast agent into a cardiac blood vessel and geometrically analyzing the state of the vessel with an angiography system or the like. When a narrowed section of a blood vessel is discovered by the angiography system, however, it has not been possible to confirm with the functional image to what extent it has an adverse effect, because the position of the blood vessel and the position of the functional image are not matched. Otherwise, it has not been possible to understand that an abnormal section appearing on the functional image corresponds to which part of the blood vessel.

Consequently, a method that allows observation by relating the state observed on a functional image to the position of a blood vessel is proposed as described, for example, in <CIT> in which a coronary artery is extracted from three-dimensional image data and a coordinate transformation is performed on the pass of the extracted coronary artery to display the vessel shape in a superimposing manner on the bull's eye functional image.

The method described in <CIT> in which a line is written on a bull's eye functional image by performing a coordinate transformation on the pass of a coronary artery, however, does not represent the morphology of the blood vessel actually running around the heart, so that it is difficult to determine which part of the coronary artery is observed.

<CIT> discloses a cardiac function display apparatus according to the preamble of claim <NUM>.

In view of the circumstances described above, it is an object of the present invention to provide a cardiac function display apparatus capable of accurately evaluating the performance of a heart by clearly representing morphology of a blood vessel of the heart. It is a further object of the present invention to provide a program for causing a computer to function as the cardiac function display apparatus.

A cardiac function display apparatus of the present invention is an apparatus, including the features of claim <NUM>.

A program of the present invention is a program for causing a computer to function as defined by claim <NUM>.

The term "a function of a heart in each position" as used herein refers to an operation of the heart in each position. Specific example may be the thickness of the myocardium in each position, that is, a variation in the thickness of the myocardium in the diastolic phase and systolic phase which allows estimation of the operation of the heart in each position. The term "functional image" as used herein refers to an image in which a function of the heart in each position is represented in a visually recognizable manner. More specifically, for example, the display color may be changed according to the function or the function of the heart in each position may be displayed by a numeric value.

The term "morphology" as used herein refers to the appearing shape or state, and the term "morphology of the blood vessel" as used herein refers to the shape or running state of the blood vessel.

Preferably, the functional image is an image in which images representing functions of the heart on a plurality of slice planes cut in a direction traversing a major axis extending from a cardiac base toward a cardiac apex of the heart are arranged concentrically.

Further, preferably, the functional image is an image in which an image representing a function of a slice plane near the cardiac base of the heart is disposed near the center of the concentrically arranged images and an image representing a function of a slice plane closer to the cardiac apex of the heart is disposed in a position farther away from the center.

Still further, the morphological image may be an image generated by performing MIP processing on voxel data present within a predetermined distance from the outer myocardial wall of the heart, which includes the blood vessel along the outer myocardial wall, and a blood vessel present in the predetermined distance is projected in the image.

Still further, the range of the blood vessel on the heart depicted in the morphological image may be wider than the range of the functions of the heart represented by the functional image.

According to the present invention, a functional image representing a function of a heart in each position and a morphological image depicting morphology of a blood vessel are displayed in a superimposing manner such the each position of the heart in the functional image corresponds to each position of the heart in the morphological image, thereby allowing an observation of the heart by relating each function to the anatomical position.

Further, images representing functions of the heart at a plurality of slice planes cut in a direction traversing a major axis extending from the cardiac base toward the cardiac apex of the heart are arranged concentrically, and an image of a slice plane near the cardiac base is disposed near the center of the concentrically arranged images and an image representing a function of a slice plane closer to the cardiac apex of the heart is disposed at a position farther away from the center, whereby a coronary artery of the morphological image displayed in a superimposing manner branches from the center toward the outside, so that an image allowing easy understanding of the anatomical position of the heart may be generated.

Further, generation of a morphological image by performing MIP processing (maximum intensity projection) on voxel data present within a predetermined distance from an outer myocardial wall of the heart which includes a blood vessel along the outer myocardial wall allows an image representing detailed morphology of the blood vessel to be generated and the anatomical position of the heart becomes more understandable.

Still further, the wider range of the blood vessel on the heart depicted in the morphological image than the range of the functions of the heart represented by the functional image may provide a portion in which the anatomical position of the hear can be confirmed without being restricted by the display area of the functional image when the morphological image and functional image are displayed in a superimposing manner, thereby facilitating understanding of the correspondence between the position and function of the heart.

Hereinafter, an embodiment of the cardiac function display apparatus of the present invention will be described in detail with reference to the accompanying drawings. <FIG> is a schematic configuration diagram of the cardiac function display apparatus of the present invention. The configuration of cardiac function display apparatus <NUM> shown in <FIG> is realized by executing a cardiac function display processing program, read in an auxiliary storage device, on a computer. Here, the cardiac function display processing program is stored in recording medium, such as a CD-ROM or the like, or distributed through a network, such as the Internet, and installed on the computer.

Cardiac function display apparatus <NUM> of the present invention includes first storage means <NUM> for storing first voxel data <NUM> of a three-dimensional medical image obtained by photographing a subject; functional image generation means <NUM> for generating functional image <NUM> representing a function of a heart in each position using voxel data <NUM>; second storage means <NUM> for storing second voxel data <NUM> of a three-dimensional medical image obtained by photographing the subject; morphological image generation means <NUM> for generating, using a portion of second voxel data <NUM> corresponding to an area which includes a blood vessel along an outer myocardial wall of the heart, a morphological image depicting morphology of the blood vessel; alignment means <NUM> for aligning the position of first voxel data <NUM> with the position of second voxel data <NUM>; and superimpose display means <NUM> for displaying morphological image <NUM> and functional image <NUM> on display means <NUM> in a superimposing manner.

First voxel data <NUM> and second voxel data <NUM> are data of three-dimensional images obtained by CT (Computed Tomography) or MRI (Magnetic Resonance Imaging). First voxel data <NUM> are used to generate functional image <NUM>, and second voxel data <NUM> are used to generate morphological image <NUM>.

Each of first storage means <NUM> and second storage means <NUM> is a large capacity storage device, such as a hard disk or an image server. They store first voxel data <NUM> or second voxel data <NUM> obtained by photographing a subject with a CT or MRI system.

Functional image <NUM> is an image of distributed evaluation values representing functional evaluations of a heart according to the cardiac movement, diameter of a ventricle, or thickness of the myocardium. Specific examples of functional images include a ventricular diameter image representing the diameter of a ventricle in a certain phase, an end-diastolic ventricular diameter image representing the diameter of the ventricle in a diastolic phase, an end-systolic ventricular diameter image representing the diameter of the ventricle in a systolic phase, a local ejection fraction image representing an ejection fraction of each segmented area, a wall thickness image representing the thickness of the myocardium in a certain phase, an end-diastolic wall thickness image representing a thickness of the myocardium in a diastolic phase, an end-systolic wall thickness image representing a thickness of the myocardium in a systolic phase, a wall thickness variation image representing the difference in thickness of the myocardium from a diastolic phase to a systolic phase, a wall thickness increase rate representing a value of (B-A) /A, in which A indicates a thickness of the myocardium in a diastolic phase, and B indicates the thickness of the myocardium in a systolic phase, a wall movement image representing the difference in ventricular diameter from a diastolic phase to a systolic phase, a myocardial scintigraphic image, and the like.

Functional image <NUM> representing myocardial scintigraphy is an image of data obtained by injecting a medical agent that concentrates in a myocardium into a subject's arm and externally measuring the distribution of the medical agent. The state of blood flow within the myocardium, metabolism of myocardial tissue, work of the nerves, and the like can be represented by using different medical agents.

When representing the evaluations of cardiac movement by functional image <NUM>, the heart in motion is imaged in a plurality of different phases, then evaluation values of heart function are obtained from the difference between the images, and functional image <NUM> is generated based on the evaluation values. When the heart is imaged in a plurality of different phases as described above, it is desirable to generate functional image <NUM> from images obtained by an MRI system, which do not irradiate the subject, in a plurality of different phases.

In the mean time, morphological image <NUM> is an image representing morphology of a vessel along the surface of an outer myocardial wall of a heart. It is desirable that morphological image <NUM> be generated from a three-dimensional image obtained by a CT system, in which the structure of each organ is clearly represented.

Preferably, voxel data generated from tomographic images obtained by a CT or MRI system at a fine pitch (e.g., an interval of <NUM>) are used as the second voxel data to be used for generating morphological image <NUM> in order to finely represent the morphology. On the other hand, when the photographing is required in a plurality of phases according to the movement of a heart in order to generating functional image, there may be a case in which the photographing can not be performed in a plurality of phases if it is performed at a fine pitch. Therefore, voxel data generated from tomographic images obtained by an MRI system or the like at a coarse pitch (e.g., an interval of <NUM> to <NUM>) are commonly used as the first voxel data.

Functional image generation means <NUM> generates functional image <NUM> from first voxel data <NUM> stored in first storage means <NUM>. Here, a detailed description will be made of a case in which cardiac function image <NUM> representing the wall thickness of a myocardium is generated in bull's eye display method.

First, a surface model is approximated with ellipsoidal shape E shown in <FIG> from first voxel data <NUM>, and major axis A<NUM> and minor axis A<NUM> of the heart are determined. Major axis A<NUM> is determined so as to extend from the cardiac base to the cardiac apex of the heart and pass through a central portion of the ventricular area. Minor axis A<NUM> is determined so as to be orthogonal to major axis A<NUM>.

Then, cross-sectional images on slice planes P<NUM>, P<NUM>, -----, Pi, -----, Pn-<NUM>, Pn obtained by cutting the heart in a direction traversing the major axis A<NUM> (direction of minor axis A<NUM>) at a regular interval are generated from voxel data <NUM> and wall thicknesses of the myocardium are obtained. For example, contours of the endocardium and epicardium are extracted from the cross-section on slice plane Pi shown in <FIG> and the distance between the contours of the endocardium and epicardium on each of lines l<NUM>, l<NUM>, l<NUM>, ----- ljlm is obtained as wall thickness d.

When wall thicknesses of the myocardium are displayed in bull's eye representation, different colors are used according to wall thickness d of the myocardium, and wall thicknesses d on slice planes P<NUM>, P<NUM> ----- located near the cardiac base are displayed in concentric circles near the center and wall thicknesses d on slice planes Pn, Pn-<NUM> ----- located near the cardiac apex are displayed in concentric circles on the circumferential side remote from the center. Further, a minor axis image is generated, in which wall thickness d on slice plane Pi is displayed in concentric circle Q<NUM> by relating wall thickness d on each of lines l<NUM>, l<NUM>, l<NUM> ----- lj, ----- lm to angle θ between reference line Z and each of lines l<NUM>, l<NUM>, l<NUM>lj, ----- lm. The minor axis image displayed in concentric circles Q<NUM>, Q<NUM> ----- Qi, ----- Qn-<NUM>, Qn produced in the manner illustrated in <FIG> is superimposed to generate functional image <NUM> in bull' s eye representation. <FIG> shows an example of wall thicknesses of a myocardium in bull' s eye representation. In <FIG>, each area is an area separated according to wall thickness d. Preferably, each area is displayed with a different color according to the wall thickness d. Otherwise, an arrangement may be adopted in which the thickness of an area is displayed by a numeric value when a mouse or the like is move to the area.

Morphological image generation means <NUM> generates morphological image <NUM> from second voxel data <NUM> stored in second storage means <NUM>. In morphological image <NUM>, information of the coronary artery running along the outer myocardial wall is important, and hence a cardiac surface model that includes the coronary artery will be built. First, from a hear having the shape shown in <FIG>, the coronary artery running along the outer myocardial wall is extracted (<FIG>), and a continuous curved surface is estimated by interpolating between core lines or applying a spline function or the like, whereby a surface model is built. An example of generated surface model is shown in <FIG>. Further, with reference to the surface model, a surface model is approximated with ellipsoidal shape E shown in <FIG>, as in functional image generation means <NUM>, and the directions of major axis A<NUM> and minor axis A<NUM> of the heart are determined.

As illustrated in <FIG>, slice plane Pi traversing major axis A<NUM> is generated. As a blood vessel has a large pixel value, it can be proj ected by performing MIP processing on voxel data including the blood vessel. Thus, as illustrated in <FIG> (which is a partially enlarged view of <FIG>), MIP processing is performed using voxel data present within certain distance D in which the lines radially extending to each direction from the center C (where the slice plane intersects major axis A<NUM>) of slice image Pi intersects the surface model. Then, a maximum pixel value (hereinafter, MIP value) obtained by searching within distance D of each of lines l<NUM>, l<NUM>, l<NUM>, -----, lj, -----, lm by MIP processing is projected to provide bull's eye representation. Distance D is determined based on the diameter of blood vessel B obtained when extracted so that a blood vessel structure is obtained. The running states of a blood vessel along the outer myocardial wall, such as a coronary artery, can be observed in detail by providing slice planes P<NUM>, P<NUM>, -----, Pi, -----, Pn-<NUM> Pn with an interval as small as possible and then performing MIP processing. If MIP values of slice planes P<NUM>, P<NUM>, ----- near the cardiac base are displayed in concentric circles near the center and MIP values of slice planes Pn, Pn-<NUM>, ----- near the cardiac apex are displayed in concentric circles on the circumferential side remote from the center, branches of the coronary artery along the outer myocardial wall are branched from the center of the concentric circles toward the outside, as shown in <FIG>, so that the coronary artery running from the cardiac base toward the cardiac apex along the outer myocardial wall can be observed more easily. Further, the use of MIP processing allows the morphology of a blood vessel to be represented finely.

Alignment means <NUM> aligns the position of a heart of first voxel data <NUM> with the position of a heart of second voxel data <NUM>. For example, when first voxel data <NUM> represent an image of a heart obtained by a MRI system while second voxel data <NUM> represent an image of the heart obtained by a CT system, it is difficult to position the heart at exactly the same position in the two different images even though the same subject is photographed. Consequently, in order to project morphology of a blood vessel present around the heart at the position of the corresponding heart of functional image <NUM>, the position of the heart shape of first voxel data <NUM> is aligned with the position of the heart shape of second voxel data <NUM>.

The alignment may be implemented by various types of so-called registration. Here, an example case in which point xA in image A of first voxel data <NUM> is transformed to point xR in image R of second voxel data <NUM> will be discussed in detail.

If the transform function used is assumed to be T, T can be expressed as follows.

If a heart is regarded as a rigid body, the transform function can be expressed by movements (tx, ty, tz) in X, Y, and Z axis directions in a three-dimensional space and rotations (α, β, γ) of the axes as shown below.

When a heart is regarded as a non-rigid body, the shape of the heart varies, the degree of freedom is increased and T is expressed by a complicated function which includes a polynomial equation or a spline function.

More specifically, the transform function may be obtained by detecting a certain number (e.g., three) of anatomical points representing characteristics of a heart. Alternatively, the transform function may be obtained by determining the contour of one image and repeating fitting such that the distance of a point sequence corresponding to the surface of another image becomes the smallest. Otherwise, the transform function may be obtained in a superimposed manner by examining the similarity using the pixel value of each voxel in images. The use of each pixel value in images may cancel out noise component of the pixel so that relatively stable results may be obtained (for example, <NPL>).

The alignment may be implemented by any of the registration methods described above. Here, for example, the alignment is implemented by regarding the heart as a rigid body and performing evaluation using a correlation coefficient calculated from first and second voxel data <NUM>, <NUM>, and obtaining amounts of displacement, such as rotations and movements, when performing transformation from the coordinate system of the morphological image to that of the functional image.

Superimpose display means <NUM> displays functional image <NUM> shown in <FIG> and morphological image <NUM> shown in <FIG> by superimposing morphological image <NUM> on functional image <NUM>. Morphological image <NUM> is superimposed on functional image <NUM> such that the position of the heart in functional image <NUM> corresponds to the position of the heart in morphological image <NUM> using the amounts of displacement obtained by alignment means <NUM> when transforming from the coordinate system of the morphological image to the coordinate system of the functional image. <FIG> shows an example of superimposed display of functional image <NUM> shown in <FIG> and morphological image shown in <FIG>. As shown in <FIG>, the superimposed display allows the observation of which function of the heart is normal or abnormal based on the position of the blood vessel. Further, by placing images located near the cardiac base near the center of the concentric circles and images located near the cardiac apex on the outer side of the concentric circles, the coronary artery branches from the cardiac base toward the cardiac apex, so that the running state becomes more recognizable, whereby understanding of the state of heart function at an anatomical position and each position is facilitated.

Next, a processing flow when an image in which morphological image <NUM> is superimposed on functional image <NUM> is displayed using cardiac function display apparatus <NUM> will be described according to the flowchart of <FIG>.

First, the heart of a subject is imaged by a CT system and the image is stored in first storage means <NUM> as first voxel data <NUM> (S100). Further, an image of the same subject obtained by a MRI system is stored in second storage means <NUM> as second voxel data <NUM> (S101).

Functional image <NUM> in which the function of the heart is displayed in bull' s eye representation is generated from first voxel data <NUM> by functional image generation means <NUM> (S102).

Next, using second voxel data <NUM>, morphological image <NUM> is generated by morphological image generation means <NUM>. A MIP calculation is performed using voxel data including a blood vessel within a certain distance D on each of lines l<NUM>, l<NUM>, l<NUM>, -----, lm radially extending from a point where the major axis intersects with each slice plane, and morphological image <NUM> in bull's eye representation is generated by projecting MIP values obtain by the MIP calculation (S103).

The position of the heart in first voxel data is aligned with the position of the heart in second voxel data by alignment means <NUM>. More specifically, for example, the heart may be evaluated using a correlation coefficient calculated from voxel data <NUM> and voxel data <NUM> by regarding the heart as a rigid body and amounts of displacement, such as rotations and movements, when performing transformation from the coordinate system of the morphological image to that of the functional image may be obtained (S104).

Then, by superimpose display means <NUM>, the coordinate system of functional image <NUM> is transformed to the coordinate system of morphological image <NUM> such that the position of the heart in functional image corresponds to the position of the heart in morphological image using the amounts of displacement obtained by alignment means <NUM>, and functional image <NUM> and morphological image <NUM> are superimposed on top of each other and displayed (S105).

Although the description has been made of a case in which the first and second voxel data are different, but the same voxel data may be used. When the same voxel data are used, the alignment is not required.

Where the first voxel data and the second voxel data are those obtained by a CT system and a MRI system respectively or those obtained both by a CT system or a MRI system but with different slice intervals, the alignment is implemented using the registration methods described above. When myocardium scintigraphy is used, however, the alignment may not be successfully implemented by a registration method using correlation between pixels, because the purposes of the images are different and the relationship between the morphological image and the functional image is small. Consequently, in such a case, characteristic points may be selected from each image and a registration may be performed between the points to calculate the amounts of rotation and movement.

Further, although the description has been made of a case in which the coordinate system of functional image <NUM> is transformed to the coordinate system of morphological image <NUM>. But the coordinate system of morphological image <NUM> may be transformed to the coordinate system of functional image <NUM> or both coordinate systems may be changed if the transformation or the changes are performed such that each position of the heart is aligned.

Alternatively, either functional image <NUM> or morphological image <NUM> may be generated first, and then the other image may be written on the corresponding positions of the generated image using the alignment information.

Still further, the description has been made of a case in which morphologies and functions of slice planes traversing the major axis are displayed in equal interval concentric circles as morphological and functional images. But, as shown in <FIG>, values of functional and morphological images may be disposed in relation to the distances of lines S<NUM>, S<NUM>, S<NUM>, and S<NUM> radially extending along the surface of a heart as shown in <FIG>, whereby a bull's eye display dependent on the distances of surface shapes becomes possible. The bull's eye display dependent on the distances of surface shapes may provide an image like that shown in <FIG>.

Further, the bull's eye display in which images located near the cardiac base are displayed near the center of the concentric circles and images located near the cardiac apex are displayed on the outer side of the concentric circles has been described. But, as in the conventional method, a bull's eye display in which images located near the cardiac apex are displayed near the center of the concentric circles and images located near the cardiac base are displayed on the outer side of the concentric circles is also possible.

In <FIG>, the description has been made of a case in which the heart range represented by morphological image <NUM> and the heart range represented by functional image <NUM> are substantially the same. But, as shown in <FIG>, the range of the blood vessel depicted in morphological image <NUM> may be wider than the range of the functions on the heart represented by functional image <NUM>. The wider range of the heart represented by morphological image <NUM> than that represented by functional image <NUM> may provide a portion in which the anatomical position of the heart can be confirmed without being restricted by the display area of functional image <NUM> when morphological image <NUM> and functional image <NUM> are displayed in a superimposing manner, thereby facilitating understanding of the correspondence between the position and function of the heart.

<FIG> shows a case in which morphological image <NUM> outside of the concentric circles is wider than functional image <NUM>. But morphological image inside of the concentric circles may be wider than functional image <NUM>. Further, morphological image <NUM> both in inside and outside of the concentric circles may be wider than functional image <NUM>.

Claim 1:
A cardiac function display apparatus, comprising
a functional image generation means (<NUM>) for generating a functional image (<NUM>) representing a function of a heart in at least one position using first voxel data (<NUM>) of a three-dimensional medical image obtained by photographing a subject;
a morphological image generation means (<NUM>) for generating, using a portion of second voxel data (<NUM>) of a three-dimensional medical image obtained by photographing the subject, which are identical to or different from the first voxel data (<NUM>), corresponding to an area which includes a blood vessel along an outer myocardial wall of the heart, a morphological image (<NUM>) depicting morphology of the blood vessel, including a width of the blood vessel, and morphology of a tissue along the outer myocardial wall other than the blood vessel; and
a superimpose display means (<NUM>) for displaying the functional image (<NUM>) and the morphological image (<NUM>) in a superimposing manner such that at least one position of the heart in the functional image (<NUM>) corresponds to at least one position of the heart in the morphological image (<NUM>), characterized in that
the functional image (<NUM>) is an image in which images representing functions of the heart on a plurality of slice planes cut in a direction traversing a major axis extending from a cardiac base toward a cardiac apex of the heart are arranged concentrically, and
the functional image (<NUM>) is an image in which an image representing a function of a slice plane near the cardiac base of the heart is disposed near the center of the concentrically arranged images and an image representing a function of a slice plane closer to the cardiac apex of the heart is disposed in a position farther away from the center.