Ultrasonic diagnostic device

An edge detector executes a process to extract a surface of an inner wall of a left ventricle from a binarized image output from a binarization circuit. A telediastolic edge memory stores an intracardial surface image at the end of ventricular diastole from among intracardial surface images for time phases output from the edge detector. A displacement detector unit detects the amount of displacement for each site of the intracardial surface between time phases from the intracardial surface image at the telediastolic which is output from the telediastolic edge memory, a current intracardial surface image which is output from the edge detector, and a center-of-mass coordinate of the intracardial section at the telediastolic point which is stored in a telediastolic center-of-mass memory. A coloring processor unit applies a coloring process to each site of the surface of the current intracardial surface image based on the amount of displacement and outputs the result to an image synthesizer unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ultrasonic diagnostic device and in particular to a three-dimensional ultrasonic diagnostic device for measuring and diagnosing movement of a target tissue.

2. Description of the Related Art

Ultrasonic diagnosis devices are used for diagnosing abnormal movement of a target tissue, for example, abnormal expansion and retraction movements of a heart. In order to diagnose abnormal movement of a target tissue, it is desirable to use an ultrasonic diagnostic device which can precisely capture the movement of the target tissue. To achieve this object, in conventional ultrasonic diagnostic devices, a two-dimensional ultrasonic image in which the outline of the target tissue is clarified is obtained for each frame, a displacement image corresponding to a difference between an image of an earlier frame and an image of the most recent frame is time sequentially synthesized to form a displacement history image, and the displacement history image is displayed (refer to, for example, Japanese Patent No. 3045642). With a two-dimensional ultrasonic diagnostic device having such functionality, it is possible to detect abnormal movements of target issue and positions where an abnormality occurred in the target tissue with a high degree of sensitivity.

With the development of ultrasonic technologies, it has become possible to employ for diagnosis three-dimensional ultrasonic diagnostic devices which can three-dimensionally express a target tissue within a three-dimensional space. The advantages of such three-dimensional ultrasonic diagnostic devices are particularly significant in the ultrasonic observation and diagnosis of an organ such as the heart. For example, by observing the expansion and retraction movements of the heart using a three-dimensional diagnostic device, it is possible for a user to comprehend the three-dimensional shape of the heart, which is much more difficult with two-dimensional ultrasonic diagnostic devices. The advantages of the comprehension of the three-dimensional shape are also true in a displacement history image in the conventional ultrasonic diagnostic device as described above. That is, by realizing a display method in a three-dimensional ultrasonic diagnostic device which allows visual comprehension of the displacement of the target tissue, it is possible to more precisely diagnose abnormal movements of a heart.

SUMMARY OF THE INVENTION

The present invention advantageously provides a three-dimensional ultrasonic diagnostic device which can be used to precisely diagnose abnormal movements of a target tissue.

According to one aspect of the present invention, there is provided an ultrasonic diagnostic device comprising an echo data obtaining unit for transmitting and receiving an ultrasonic wave to and from a three-dimensional space including a target tissue and obtaining three-dimensional echo data for each time phase; a displacement information creator unit for creating displacement information by calculating an amount of displacement for each site on the surface of the target tissue based on the three-dimensional echo data for each of the time phases; a displacement-present image formation unit for forming, based on the three-dimensional echo data and the displacement information, a three-dimensional displacement-present image in which displacement of each site on the surface of the target tissue is shown on a tissue image three-dimensionally representing the target tissue; a two-dimensional display image formation unit for projecting the three-dimensional displacement-present image onto a plane to form a two-dimensional display image; and a display for displaying the two-dimensional image.

With this structure, because a three-dimensional displacement-present image represents an amount of displacement on a tissue surface, for example, by forming the three-dimensional displacement-present image with the inner wall of the left chamber of the heart as the tissue surface, the position of an infarction can be very easily identified.

According to another aspect of the present invention, it is preferable that the ultrasonic diagnostic device further comprises a straight line setting unit for setting a plurality of straight lines extending along a radial direction from the reference point which is the center of mass of the target tissue, and that the displacement information creator unit calculates a position of an intersection between each of the straight lines and the surface of the target tissue based on the three-dimensional echo data for each of the time phases and calculates the amount of displacement based on a change in the position of the intersection for the same straight line between time phases.

When displacements on straight lines extending along a radial direction from the center of mass are observed, the structure can be preferably used for diagnosis of abnormal movements of an organ which expands from and retracts to the center such as, for example, a heart.

According to another aspect of the present invention, it is preferable that, in the ultrasonic diagnostic device, a coloring process using colors determined for the amount of displacement of each site is applied.

With this structure, the coloring process allows for identification of a region where the amount of displacement is very small, which is preferable for diagnosis of, for example, a site of a myocardial infarction.

According to yet another aspect of the present invention, there is provided an ultrasonic diagnostic device comprising a reference point identifier unit for identifying a reference point corresponding to the structure of the target tissue and a movement calculator unit for calculating an amount of movement of the target tissue between time phases based on the identified reference point.

With such a structure, because the amount of displacement of each site can be determined with the amount of overall movement of the target tissue corrected, or, more preferably, completely cancelled out, the structure is very effective for observing movements of the target tissue itself without the overall movement of the target tissue associated with, for example, a deviation of a probe for transmitting and receiving the ultrasonic waves or the overall movement of the target tissue caused by movements of other tissues.

DESCRIPTION OF PREFERRED EMBODIMENT

A preferred embodiment of the present invention will now be described while referring to the drawings.

FIG. 1is a block diagram showing an overall structure of an ultrasonic diagnostic device according to a preferred embodiment of the present invention. A transceiver unit12transmits and receives an ultrasonic wave via a probe10into and from a space including a left ventricle of a heart which is a target tissue. Echo data within a three-dimensional space including the left ventricle of the heart is obtained for each volume in each time phase and stored in a three-dimensional data memory14. An inversion and binarization processor16applies an inversion process and a binarization process to an echo value in the echo data in each voxel stored in the three-dimensional data memory14. More specifically, voxels corresponding to an intracardial section within the left ventricle having relatively small echo values are set as voxels having a high brightness value and voxels corresponding to other sections having relatively large echo values are set as voxels having a low brightness value. A noise remover unit18, a smoothing processor unit20, a line correlation unit22, and a frame correlation unit24, apply image processes, primarily for the purpose removing a high frequency noise component, is applied to the high and low brightness value voxels to which inversion and binarization processes are applied.

The noise remover unit18determines a voxel as a noise when the voxel is spatially isolated and has a different brightness value from surrounding voxels, and converts the brightness value of the noise voxel. For example, when the brightness value of a target voxel differs from the brightness value of all 26 surrounding voxels spatially adjacent to the target voxel, the brightness value of the isolated target voxel having a different brightness value is converted to the same brightness as that of the surrounding voxels. The smoothing processor unit20calculates an average value of brightness values among a target voxel and 26 surrounding voxels adjacent to the target voxel for each brightness value of voxel output from the noise remover unit18and newly sets the calculated result as the brightness value of the target voxel. The line correlation unit22applies an averaging process between lines to the brightness value of each voxel output from the smoothing processor unit20in a two-dimensional frame forming a volume at a particular time phase. The frame correlation unit24applies an averaging process to the brightness value of each voxel between two-dimensional frames forming a volume at a particular time phase. The brightness values of voxels converted into various brightness values in the smoothing processor unit20, line correlation unit22, and frame correlation unit24are output to a coordinate converter unit26. The coordinate converter unit26converts the coordinate values of the voxels from an R, θ, φ coordinate system with the probe as the reference to an X, Y, Z coordinate system with a cube as the reference.

A binarization circuit30includes a comparator and etc., applies a binarization process based on a predetermined threshold value to an ultrasonic image output from the coordinate converter unit26made of voxels having various brightness values, to form a binarized image made of two types of voxels, one corresponding to the intracardial section of the left ventricle and the other corresponding to the other regions, and outputs the binarized image to an edge detector34and a center-of-mass detector unit36. The output of the binarization circuit30may instead be input to the edge detector34and the center-of-mass detector unit36through a translational and rotational movement canceling processor unit32. The details of the translation and rotational movement canceling processor unit32will be described below with reference toFIG. 8.

The edge detector34performs an extraction process for extracting the surface of the inner wall of the left ventricle from the binarized image output from the binarization circuit30. The edge detector34will now be described with reference toFIG. 2.

FIG. 2is a block diagram showing an internal structure of an edge detector. The edge detector34has two frame memories (1) and (2), six line memories (1) through (6), a voxel data memory70, and a surface extraction processor unit72. The output from the binarization circuit30is output as a voxel data array in the order of abutting on the image in units of echo values (voxel data) for voxels forming a volume in each time phase. In other words, in a voxel data array forming a particular volume, voxel data is arranged, in order, from a first frame to the last frame forming the volume, and, in each frame, the voxel data is arranged in order from a first line to the last line forming the frame.

The frame memory is a memory for storing the voxel data array in units of frames and for outputting the stored data. Thus, the frame memory functions as a delay buffer for one frame. The line memory is a memory for storing the voxel data array in units of lines and for outputting the stored data. Thus, the line memory functions as a delay buffer for one line. That is, the output of the frame memory (1) is voxel data for the frame just before the voxel data output from the binarization circuit30and the output of the frame memory (2) is voxel data for the frame which is two frames before the voxel data output from the binarization circuit30. In this manner, current voxel data, voxel data which for the previous frame, and voxel data for the frame before the previous frame are all input into the voxel data memory70.

Similarly, the output of the line memory (1) is voxel data one line before the voxel data output from the binarization circuit30, the output of the line memory (2) is voxel data two lines before the voxel data output from the binarization circuit30, the output of the line memory (3) is voxel data one line before the voxel data output from the frame memory (1), the output of the line memory (4) is voxel data two lines before the voxel data output from the frame memory (1), the output of the line memory (5) is voxel data one line before the voxel data output from the frame memory (2), and the output of the line memory (6) is voxel data two lines before the voxel data output from the frame memory (2). In this manner, to the voxel data memory70, voxel data of a total of 9 lines are input, 3 lines which abut within the current frame, 3 corresponding lines within the previous frame, and 3 corresponding lines within a frame which is two frames prior.

The voxel data memory70has a total of 27 latches, three for each of the 9 lines. The three latches corresponding to each line are for extracting data for 3 sequential voxels on a line.

In this manner, the voxel data output from the latch (14) is set as a target voxel and a group of 27 voxel data in which 26 voxel data adjacent to the target voxel are added is output to the surface extraction processor unit72.

The surface extraction processor unit72determines the target voxel as a surface voxel of an intracardial section when the data of the target voxel is voxel data corresponding to the intracardial section and at least one of 26 adjacent surrounding voxel data is voxel data corresponding to the other sites. By finding surface voxels with every voxel within a volume of each time phase as a target voxel, a group of voxels forming the surface of the intracardial section in each volume, that is, an intracardial surface image (outline image of the inner wall of ventricle) is obtained. The intracardial surface image formed for each volume is output to a telediastolic edge memory (reference numeral38inFIG. 1) or the like.

Referring again toFIG. 1, the telediastolic edge memory38stores the intracardial surface image at the telediastolic point of the ventricle, selected from among the intracardial surface images of each time phase output from the edge detector34. An R wave of the cardiographic waveforms is input to the telediastolic edge memory38and the telediastolic moment is determined based on the R wave generated at ventricular diastole. A past edge memory40is a memory for temporarily storing an intracardial surface image at each time phase output from the edge detector34for each time phase. A selector42selects one of an intracardial surface image at the telediastolic point output from the telediastolic edge memory38and an intracardial surface image at a past time phase output from the past edge memory40, and outputs the selected image to a displacement detector unit50. The selection operation by the selector42is performed based on instructions from a user.

A binarized image output from the binarization circuit30is also input to the center-of-mass detector unit36, which then calculates the coordinates of the center of mass of the intracardial section based on the input image. In some cases, the image of the intracardial section may not have a shape wherein the outer surface is completely closed. In such a case, the calculation of the center of mass may be performed with the target being a region of interest which is set in advance to surround the intracardial section. A telediastolic center-of-mass memory44stores the coordinates of the center of mass of the intracardial section at the point of telediastolic of the ventricle. The R wave of the cardiographic waveform is input to the telediastolic center-of-mass memory44, and the telediastolic center-of-mass memory44determines the telediastolic point based on the R wave generated at the end of ventricular diastole.

A displacement detector unit50is provided for detecting an amount of displacement between time phases for each section within the intracardial surface. One of the intracardial surface images output from the telediastolic edge memory38and an intracardial surface image of a past time phase output from the past edge memory40are input to the displacement detector unit50via the selector42. A current intracardial surface image output from the edge detector34is also input to the displacement detector unit50, and the coordinates of the center of mass of the intracardial section at the telediastolic point which is stored in the telediastolic center-of-mass memory44is input to the displacement detector unit50. The displacement detector unit50detects the amount of displacement based on this input information. A detection method of the amount of displacement by the displacement detector unit50will now be described referring toFIG. 3.

FIG. 3is an explanatory diagram of method of detecting an amount of displacement performed by a displacement detector unit (reference numeral50inFIG. 1) and shows an intracardial surface image80at the point of telediastolic and a current intracardial surface image82. A coordinate A (X1, Y1, Z1) represents the coordinates of the center of mass of the intracardial section at the point of telediastolic.

First, the displacement detector unit identifies surface sections within the current intracardial surface image for which an amount of displacement is to be measured. Various methods can be employed to identify the surface sections. For example, it is possible to sequentially move a point of interest from an origin (0, 0, 0) in the X direction, Y direction, and Z direction to detect surface sections and set all detected surface sections as a target. Alternatively, it is also possible to set sample points from the detected surface sections. It is still further possible for the user to identify surface sections while viewing the ultrasonic wave imaged is played on a display. A surface section determined through any method is set as a coordinate B (X2, Y2, Z2).

The coordinates C (X3, Y3, Z3) of an intersection of a straight line84passing through point A (a point at coordinate A) and point B (a point at coordinate B) and an intracardial surface image80at the telediastolic point are calculated. By then finding then distance between point B and point C (the point at coordinate C) determined in this manner, the displacement of the surface section (point B) from the telediastolic is determined. In some cases, the outer surface of the image of the intracardial section may not be a completely closed shape, and the coordinate C of the intersection between the straight line84and the intracardial surface image80at the point of telediastolic therefore cannot be calculated. In such a case, it is determined that the amount of displacement cannot be calculated, and other points A and B are set to continue calculation of the amount of displacement. When the output of the past edge memory (reference numeral40inFIG. 1) is selected by the selector (reference numeral42inFIG. 1), the above-described detection method of displacement can be applied in a similar manner by replacing the surface image indicated by the reference numeral80inFIG. 3by the intracardial surface image of a past time phase.

Referring again toFIG. 1, the amounts of displacement in each section within the surface of the intracardial section detected by the displacement detector unit50are stored in a displacement memory52. A color determiner54determines colors for each site within the surface of the intracardial section based on the amount of displacement. In other words, the color determiner54reads the amount of displacement of a target surface site from the displacement memory52and sets the color absolutely determined in advance for each amount of displacement as the color of this target site. A color determination method by the color determiner54will now be described referring toFIG. 4.

FIG. 4is a diagram showing example colors absolutely determined for each amount of displacement. As shown inFIG. 4, when the displacement of a site is within a range of 30 mm to 31 mm, a color “red” is assigned and when the displacement is within a range of 29 mm to 30 mm, a color “light red” is assigned. When the displacement is a negative displacement, a “blue” color is assigned. The amount of displacement becomes negative when the displacement is in the expansion direction while the ventricle is retracting or when the displacement is in the retraction direction while the ventricle is expanding. The correspondence relationship between the amounts of displacement and the colors may also be determined based on an external setting by a user. For example, it is possible to set the amount of displacement corresponding to “red” to be within a range from 40 mm to 41 mm or to set the amount of displacement corresponding to “yellow” to be within a range from 30 mm to 31 mm. The color determined in this manner for each section of the surface of the intracardial section is output to a coloring processor unit (reference numeral56inFIG. 1).

Referring again toFIG. 1, the coloring processor unit56applies a coloring process to the current intracardial surface image output from the edge detector34based on the color of teach section of the surface determined by the color determiner54and outputs the result to an image synthesizer58. The image synthesizer58synthesizes a three-dimensional image output from the coordinate converter unit26which includes the intracardial section and the colored intracardial surface image output from the coloring processor unit56to form a three-dimensional image. A display image formation unit60forms a two-dimensional display image in which the three-dimensional image is projected onto a plane. When the display image formation unit60projects the three-dimensional image onto a plane, a rendering calculation may be performed based on a volume rendering method to form a two-dimensional display image in which the inside of the target tissue is transparently displayed. For example, the method disclosed in Japanese Patent Laid-Open Publication No. Hei 10-33538 may be preferably employed as the rendering calculation based on the volume rendering method. The method described in this reference can be briefly summarized as follows. First, a plurality of rays (which match, for example, the ultrasonic beam) are set in a three-dimensional space. For each ray, echo values are referenced in order and a rendering calculation is performed for each echo value in sequence. In parallel to this operation, multiplication with each opacity (degree of non-transparency) is performed. When the multiplied value becomes 1 or greater, the rendering calculation for the ray is completed and the rendering calculation result at this point is determined as the two-dimensional display pixel value corresponding to the ray. By determining a pixel value for each ray, a two-dimensional display image in which the inside of the target tissue is transparently displayed can be formed as a collection of the pixel values.

The two-dimensional display image formed by the display image former unit60is displayed on a display62.

FIG. 5is a diagram showing a display image including a displacement-present image obtained by the ultrasonic diagnostic device ofFIG. 1and shows the intracardial section of the left ventricle of a heart. Images (A) and (B) are display images of the same three-dimensional image seen from different viewpoints, and one or both images (A) and (B) are shown on the display.FIG. 5shows images to which the coloring process has been applied using colors based on the amount of displacement of each section of the surface of the intracardial section (refer toFIG. 4). The section86is displayed in “black” to indicate a displacement within a range of −1 mm to 1 mm. Thus, it can be seen that the section86is moving very slowly and can be deduced as a diseased section affected by an infarction or the like.

FIG. 6shows another form of the color determiner54ofFIG. 1. The color determiner54shown inFIG. 6determines color, for each site within the surface of the intracardial section, based on a relative magnitude of displacement of each site with respect to displacements of a plurality of sites. The color determiner54ofFIG. 6includes a maximum absolute value detector unit88and a color table creator unit89. The maximum absolute value detector unit88detects a displacement having a maximum absolute value from among the amounts of displacement stored in the displacement memory (reference numeral52ofFIG. 1). For example, when the displacement is distributed between −5 mm to 18 mm, an absolute value of “18 (mm)” is detected as the maximum absolute value from comparison between “18 (mm)” and “5 (mm)”.

The color table creator unit89sets a relative displacement region based on the maximum absolute value detected by the maximum absolute value detector unit88and sets “(maximum absolute value) X (−1)” as a minimum value and the “maximum absolute value” as a maximum value. That is, when the maximum absolute value is “18 (mm)”, the relative displacement region becomes −18 mm to +18 mm. Then, the color table creator unit89generates a color table in which displayable color gradations are distributed between the maximum and minimum values of the relative displacement region.FIG. 7shows an example of a color table created by the color table creator unit89.

In the example shown inFIG. 7(A), the displacement AL is distributed between −5 mm and +18 mm, and the maximum and minimum displayable color gradations are respectively “red (+32)” and “blue (−31)”. In this case, the range of gradations from +32 to −31 is assigned to a range of displacements of +18 mm to −18 mm. In the example shown inFIG. 7(B), the displacement AL is distributed between −10 mm and +3 mm, and the maximum and minimum displayable color gradations are “red (+32)” and “blue (−31)”. In this case, the range of gradations from +32 to −31 is assigned to a range of displacements from +10 mm to −10 mm. By determining color for each site based on the displacements of all sites in this manner, it is possible to maximize the efficiency of use of the displayable color gradations. The generated color table is output to the coloring processor unit (reference numeral56ofFIG. 1). In the coloring processor unit, a coloring process is applied based on the color table to color the current intracardial surface image output from the edge detector (reference numeral34ofFIG. 1) using a color corresponding to the displacement of each site.

FIG. 8is a block diagram showing an internal structure of a translational and rotational movement canceling processor unit shown inFIG. 1. A ventricular ROI (region of interest) generator90generates coordinates of an ROI forming the periphery of the ventricle of a heart, which is a target tissue. The ROI for a ventricle may, for example, have an elliptical shape, and the user will set the initial values such as the lengths of the major and minor axes, position of the center, and slope of the ellipse while viewing the ultrasonic image so that the image of the ventricle fits within the ROI. In this process, the user determines, using a trackball or the like, the initial values while viewing the ultrasonic wave image and observing movement of one heartbeat so that the ROI includes the left ventricle of the heart in all frames. The setting of the ROI is not limited to manual setting by a user, but may also be automatically set based on the movement of the ventricle.

A ventricular gate circuit92is a circuit which allows only the echo data within the ROI for the ventricle to pass through. In other words, coordinates of an ROI output from the ventricular ROI generator90is input to one of the input terminals of the ventricular gate circuit92so that only the echo data of coordinates within the ventricle ROI are extracted from a binarized image input to the other input terminal. The extracted data is output to an intracardial extractor unit94. The intracardial extractor unit94extracts an intracardial image within the ventricle from the binarized image in the ROI. A ventricle center-of-mass calculator unit96calculates, for each frame, the coordinates of a center of mass in an image of the inside of the ventricle output from the intracardial extractor unit94. The calculated coordinates of the center of mass of the ventricle are output to a read address generator112and a ventricle center-of-mass memory98.

A valve ring ROI (region of interest) generator100generates coordinates of an ROI forming a periphery of a valve ring section positioned on the end of a ventricle. The ROI for valve ring has, for example, an elliptical shape, and the user sets the initial values such as the lengths of the major and minor axes of the ellipse, position of the center, and slope of the ellipse while viewing the ultrasonic wave image so that the valve ring section fits into the ROI. In this process, the user determines, using a trackball or the like, the initial values while viewing the ultrasonic wave image and observing movement for one heart beat so that the ROI includes the valve ring section in all frames. The setting of the ROI is not limited to a manual setting by the user and may also be mechanically set based on the movement of the valve ring.

A valve ring gate circuit102is a circuit which allows only the echo data within the valve ring ROI to pass through. That is, coordinates of the ROI output from the valve ring ROI generator100are input to one of the input terminals of the valve ring gate circuit102, so that just the echo data of the coordinates within the valve ring ROI are extracted from a binarized image input to the other input terminal. The extracted echo data is output to a valve ring section extractor unit104. The valve ring section extractor unit104extracts an image of the valve ring section from the binarized image within the ROI. A valve ring center-of-mass calculator unit106calculates coordinates of the center of mass of the valve ring section for each frame of a valve ring image output from the valve ring extractor unit104. The calculated coordinates of the center of mass of the valve ring section are output to the read address generator112and a valve ring center-of-mass memory108.

The ventricle center-of-mass memory98stores coordinates of the center of mass of ventricle at the point of telediastolic. As a trigger used to inform the telediastolic, an R wave of the cardiographic waveform is used. In other words, using the R wave obtained at the point of telediastolic as a trigger, the coordinates of the center of mass of the ventricle output from the ventricle center-of-mass calculator unit96are stored as the coordinates of the center of mass of ventricle at its telediastolic point. Similarly, the coordinates of the center of mass of the valve ring at the telediastolic is stored from the valve ring center-of-mass calculator unit106to the valve ring center-of-mass memory108using the R wave as the trigger.

A read controller unit110comprises a read address generator112and a memory controller unit114, and reads echo data from the binarization circuit (reference numeral30inFIG. 1) so as to form an ultrasonic wave image in which the translational and rotational movements of the ventricle between volumes are cancelled. More specifically, the read address generator112obtains the coordinates of the center of mass of the ventricle at the point of telediastolic from the ventricle center-of-mass memory98and coordinates of the center of mass of the valve ring section at the point of telediastolic from the valve ring center-of-mass memory108. The read address generator112further obtains the coordinates of the center of mass of the ventricle in the current volume from the ventricle center-of-mass calculator unit96and the coordinates of the center of mass of the valve ring section in the current volume from the valve ring center-of-mass calculator unit106.

The read address generator112calculates a read address so that the center of mass of the ventricle of the current volume overlaps the center of mass of the ventricle at the telediastolic, and, at the same time, a straight line passing through the center of mass of the ventricle and the center of mass of the valve ring in the current volume overlaps a straight line passing through the center of mass of the ventricle and the center of mass of the valve ring at the telediastolic point.

In the volume memory116, a copy of the echo data output from the binarization circuit30is stored for each volume, along with the address of the original image. The memory controller unit114reads the echo data from the volume memory116according to the read address calculated by the read address generator112and outputs the read data to the edge detector (reference numeral34inFIG. 1) and the center-of-mass detector unit (reference numeral36inFIG. 1). As a result, the echo data output from the volume memory116is output in the form of an image in which the translational and rotational movements have been cancelled.

A preferred embodiment of the present invention has been described. It should be understood, however, that the above-described embodiment is for exemplifying purpose only and is not in any way intended to limit or restrict the scope of the present invention.