JP3096817B2 - Ultrasound diagnostic equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus that obtains a tomographic image of a diagnostic site of a subject using ultrasonic waves, and particularly to an ultrasonic diagnostic apparatus that does not use a contrast agent. The present invention relates to an ultrasonic diagnostic apparatus capable of facilitating diagnosis of a structure of a real organ showing minute changes according to a cardiac cycle, such as a moving part such as a blood vessel wall or a heart, a liver, a pancreas, a kidney, or a cancer tissue.

[Conventional technology]

B-mode display, Doppler mode display, and the like are known as methods for real-time image display of a blood vessel wall, a heart, and the like in a subject using ultrasonic waves. Attempts to obtain a difference image by using the British Heart Journal 59 (1988), p.
19 (British Heart Journol 59 (1988) PP12-19). In this method, subtraction is performed between tomographic images before and after the injection of a contrast agent using a contrast agent, so that, for example, a region of interest of the heart can be observed with contrast.

That is, in this image display method, as shown in FIG. 11, first, before injecting the contrast agent into the subject, four frames are taken if the ultrasonic tomographic image is tilted, and the four frame images are averaged. Create a mask image, subsequently, inject the contrast agent into the subject, take in tomographic images with time from the time when the contrast agent arrives at the diagnostic site, and with the mask image and each tomographic image after the contrast agent injection And subtraction is performed sequentially to obtain a differential image. In this method, the density of each pixel of the image serving as the mask image is an average value of the density of the corresponding pixels of the four frames. The reason for this is to reduce the influence of random noise on the difference image and obtain a better difference image.

[Problems to be solved by the invention]

However, in the image display by such a conventional ultrasonic diagnostic apparatus, a contrast medium is injected into the blood of the subject, and a place where the blood moves, for example, a ventricle or an atrium, is intended to be drawn with enhanced contrast. Therefore, it has been difficult to obtain motion information of a site having a small blood flow, for example, a tissue itself. In addition, the state of exercise of the inner wall of the ventricle or atria can be grasped, but the state of exercise of the outer wall cannot be observed. Furthermore, since a contrast agent is injected into a subject, it cannot be applied to a person who cannot tolerate it.

Further, a difference image is formed by calculation between a plurality of tomographic images obtained over time. However, it is not possible to simultaneously display the tomographic image of the diagnosis site and the formed difference image on the same screen of the image display means. It was impossible. Therefore, it is difficult to know how the tomographic image showing the entire diagnostic part is displayed and how the differential image showing the moving part is displayed thereon, which makes it difficult to diagnose the moving part and requires skill. Was something.

Therefore, the present invention solves such a problem, enables the movement of a moving part such as a heart or a blood vessel wall in a subject to be drawn without using a contrast agent, and facilitates diagnosis of the moving part. It is an object of the present invention to provide an ultrasonic diagnostic apparatus capable of performing the above.

[Means for solving the problem]

In order to achieve the above object, an ultrasonic diagnostic apparatus according to a first aspect of the present invention provides an ultrasonic diagnostic apparatus that transmits and receives an ultrasonic wave to and from a moving tissue by using a reflected echo signal from the ultrasonic transmitting and receiving means. Tomographic scanning means for obtaining tomographic image data within the subject at a predetermined cycle including: and means for calculating difference image data obtained by calculating between the obtained time-series tomographic images,
In the ultrasonic diagnostic apparatus having image display means for displaying the formed difference image data, the tomographic image data and the difference image data are fetched and the tomographic image data to the image display means is synchronized with the display cycle of the image display means. Means for arbitrarily setting a boundary between the display area of the difference image data and a display area of the difference image data; and tomographic image data in one display area of the image display means divided by the set boundary, and in the other display area. Means for combining and outputting the difference image data.

The means for setting the boundary sets an arbitrary ultrasonic scanning line on one image displayed on the image display means as a boundary, and sets a boundary between the set ultrasonic scanning line and a tomographic image. The display of the difference image is switched.

Further, the ultrasonic diagnostic apparatus according to the second aspect of the present invention is an ultrasonic diagnostic apparatus that transmits and receives ultrasonic waves to and from an object, and an ultrasonic diagnostic apparatus that includes a moving tissue using a reflected echo signal from the ultrasonic transmitting and receiving means. Tomographic scanning means for obtaining tomographic image data at a predetermined period, means for calculating difference image data by calculating between the obtained time-series tomographic images, and image display means for displaying the formed difference image data. A first storage unit that stores the tomographic image data in association with one half scan of a display scan line of the image display unit, and a display scan line of the image display unit that stores the differential image data. A second storage unit that stores the image data in association with the other half-scan, and captures the tomographic image data and the difference image data from the first and second storage units and displays the image in accordance with the display cycle of the image display unit. Means for arbitrarily setting the boundary between the display area of the tomographic image data on the column and the display area of the differential image data, and the display scanning line from the half-scan tomographic image data and the differential image data from the means for setting the boundary. Means for forming full scans and outputting the image data to image display means.

(Operation)

An ultrasonic diagnostic apparatus according to a first aspect of the present invention captures tomographic image data from a tomographic scanning unit and differential image data from a differential image data generating unit, and matches the tomographic image to the image displaying unit in accordance with the display cycle of the image displaying unit. The boundary between the data display region and the difference image data display region is arbitrarily set, and the tomographic image data is divided into the one display region of the image display means divided by the set boundary, and the difference is displayed in the other display region. It operates to combine and output image data. Thereby, the tomographic image and the difference image can be simultaneously displayed on the same screen of the image display means. In this case, the motion of a moving part such as a heart or a blood vessel wall in the subject can be drawn without using a contrast agent by the difference image.

Further, the ultrasonic diagnostic apparatus according to the second invention stores the tomographic image data from the tomographic scanning means in the first storage means in association with one half scan of the display scanning line of the image display means, and stores the differential image data The difference image data from the generation unit is stored in the second storage unit in association with the other half scan of the display scan line of the image display unit, and the tomographic image data and the difference image from the first and second storage units are stored. The boundary between the display area of the tomographic image data and the display area of the differential image data on the image display means is arbitrarily set in accordance with the display cycle of the image display means by taking in the data, and a half scan from the means for setting this boundary From the tomographic image data and the differential image data, and operates to output the image data to the image display means. Thus, for example, in the first half of the horizontal scanning cycle, tomographic image data can be displayed, and in the second half, differential image data can be displayed. As a result, the screen of the image display means can be divided into, for example, left and right, and a tomographic image can be displayed in one half and a differential image of the same time phase as the other half in parallel.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention. This ultrasonic diagnostic apparatus obtains a tomographic image of a diagnostic part of a subject using ultrasonic waves,
As shown in the figure, a probe 1, an ultrasonic transmitting / receiving circuit 2,
A digital scan converter (hereinafter abbreviated as "DSC") 3, a subtracter 4, a D / A converter 5, and an image display 6
And a selection circuit 7 and an image memory 8.

The probe 1 transmits and receives ultrasonic waves to and from the subject 9 by mechanically or electronically performing beam scanning. Although not shown, the probe 1 is a source of ultrasonic waves and includes a reflected echo. There is a built-in vibrator that receives the signal. The ultrasonic transmission / reception circuit 2 sends a driving pulse to the probe 1 to generate an ultrasonic wave and to process a received reflected echo signal. , A transmission delay circuit, a reception amplifier, a reception delay circuit, an adder, and the like. The probe 1 and the ultrasonic transmission / reception circuit 2 constitute an ultrasonic transmission / reception unit, and the probe 1 causes the ultrasonic beam to scan in the body of the subject 9 in a certain direction. One tomographic image is obtained.

The DSC 3 obtains tomographic image data in the subject including the moving tissue using the reflected echo signal output from the ultrasonic transmission / reception circuit 2 in the ultrasonic transmission cycle and reads out the data in the television cycle to display the data. And the means for controlling the system.
A / D to convert reflected echo signal from
A converter 10 and a digital signal output from the A / D converter 10 are repeatedly written to and read from a line memory for each scanning line or a plurality of scanning lines of an ultrasonic beam, and transmitted to a frame memory 12 described later. Scan converter
It comprises a frame memory 12 composed of, for example, a semiconductor memory capable of storing one frame of image data output from the scan converter 11, and a controller 13 for controlling the operation of these components.

The subtracter 4 serves as a means for performing calculation between the time-series tomographic images obtained by the above-mentioned DSC 3 and generating difference image data of the tomographic images. The subtraction is performed between two pieces of tomographic image data with the obtained image, and is configured using standard logic. The D / A converter 5 converts the difference image data output from the subtracter 4 into an analog signal. Further, the image display 6 is
A video signal is input from the D / A converter 5 and displayed as an image, and is, for example, a television monitor. And
The D / A converter 5 and the image display 6 constitute an image display means.

Here, in the present invention, on the output side of the subtractor 4, a selection circuit 7 is provided and an image memory 8 is provided. The selection circuit 7 takes in the tomographic image data and the difference image data and displays the tomographic image data on the image display means (5, 6) and the difference image data in accordance with the display cycle of the image display means (5, 6). Is a means for arbitrarily setting a boundary with the display area of the tomographic image. The tomographic image data output from the DSC 3 and the difference image data output from the subtracter 4 are taken in, and the display cycle of the image display 6 is set. In addition, either the tomographic image data or the differential image data is selected and output, and in order to simultaneously display both image data on the image display 6, one of the image data is temporally displayed. It is designed to output. Also,
Means for synthesizing tomographic image data in one display area and differential image data in the other display area of the image display means (5, 6) divided by the set boundary; In this case, either one of the tomographic image data and the differential image data is selected and output in time by the operation of the selection circuit 7, and the image data for one frame is stored. I have. The image memory 8 synchronizes with the image display means (5, 6).

Next, the operation of the ultrasonic diagnostic apparatus thus configured will be described with reference to FIG. 2 and FIG. First,
The probe 1 shown in FIG. 1 is brought into contact with a position corresponding to a diagnostic site of the subject 9 and transmits ultrasonic waves to the diagnostic site. At this time, the ultrasonic wave transmitted from the probe 1 is formed into a narrow beam at the diagnosis site by the transmission delay circuit in the ultrasonic transmission / reception circuit 2. The reflected echo of the transmitted beam hitting the diagnostic site is received by the probe 1 and taken in via a reception delay circuit and an adder in the ultrasonic transmission / reception circuit 2 to form a reception beam. You. Then, the ultrasonic wave transmission / reception direction is sequentially changed from the probe 1 at a predetermined cycle, and transmission / reception of the ultrasonic wave is repeated, and scanning of the diagnostic site is performed.

The reflected echo signal output from the ultrasonic transmission / reception circuit 2 is input to an A / D converter 10 in the DSC 3, converted into a digital signal, and transmitted to the next scan converter 11.
The scan converter 11 has a plurality of line memories, and is controlled by the controller 13 to switch between writing and reading each time the ultrasonic transmission / reception direction changes. 12 and to the subtractor 4 and the selection circuit 7. The frame memory 12 can store one frame of tomographic image data, and always stores image data of one frame before, that is, the previous ultrasonic scan. In this state, immediately before new image data is written from the scan converter 11 to the frame memory 12, the image data at the time of the previous scan stored in the same storage area is read out and sent to the subtracter 4. Therefore, the subtractor 4 receives the image data between the preceding and succeeding frames in the same part as the image data at the time of the current scan from the scan converter 11 and the image data at the previous scan from the frame memory 12. The Rukoto. After that, the subtracter 4 performs a subtraction between the two image data and sends out the obtained difference image data to the selection circuit 7.

As a result, tomographic image data directly from the scan converter 11 and difference image data calculated by the subtractor 4 are input to the selection circuit 7. Then, the selection circuit 7 selects and outputs tomographic image data or difference image data in accordance with the display cycle of the image display 6. That is, during the ultrasonic scanning for one frame, the tomographic image data Da of the same pixel and the differential image data Db are input to the selection circuit 7 as shown in FIG. , between first from time 0 of T ₁ in FIG. 2 selects and outputs the tomographic image data Da, followed by the period from the time T ₁ to T ₂ selects and outputs the difference image data Db, further from time T ₂ 1
Until the end time T of the frame, the tomographic image data again
Selectively output Da. The image data sequentially selected and output as described above is written to the image memory 8 at the subsequent stage. The image data read from the image memory 8 under the control of the controller 13 is converted into an analog signal by the D / A converter 5 and then input to the image display 6 to be displayed as an image. At this time, as shown in FIG.
The tomographic image Ia and the difference image Ib are simultaneously displayed on the same screen with arbitrary ultrasonic scanning lines l ₁ and l ₂ on one image displayed on the image display 6 as boundaries.

The difference image Ib at this time is a difference image for each pixel between the two preceding and succeeding images. Therefore,
If the tissue at the diagnostic site in the subject moves during the time elapsed between the time of capturing the image at the previous scan and the image at the time of the current scan, the portion of the moved tissue is moved between the previous image and the current image. A difference occurs in the image data, and for the portion of the stationary tissue, the image data is the same between the two images, the difference data becomes zero, only the moving tissue is displayed as an image, and no portion of the stationary tissue is displayed. That is, as the image displayed on the image display unit 6 as the difference image Ib, only the part that has moved from the time when the previous image was captured to the time when the current image was captured is displayed.

Thereafter, when an image obtained by repeatedly performing the above operation is continuously displayed on the image display 6, a real-time image of only the moving tissue of the diagnosis site is obtained. At this time, it is necessary to consider the moving speed of the moving tissue for the frame rate of the display on the image display 6. Then, in order to obtain a tomographic image with a high frame rate in order to obtain a differential image of a moving tissue faster than the standard frame rate of the image on the image display 6, as an ultrasonic transmission / reception technique, for example, Japanese Patent No. 109537
The technique described in the specification of No. 7 (Japanese Patent Publication No. 56-20017) may be used in combination.

In FIG. 2, the time T ₂ −T ₁ corresponds to the display width of the difference image Ib shown in FIG. 3, time T ₁ represents a switching point from the tomographic image Ia to the difference image Ib, and time T 1 Reference numeral ₂ denotes a switching point from the difference image Ib to the tomographic image Ia. Then, the display width of the difference image Ib as a variable, a keyboard or joystick provided in the operation console of the time T ₁ for example device, by enabling change by using the track ball, the left and right of the differential image Ib Can be steered.

FIG. 4 is a block diagram showing a second embodiment of the present invention. In this embodiment, a tomographic image memory 14a for storing tomographic image data sent from a scan converter 11 therein is provided on the output side of the DSC 3, and the subtracter 4 is provided on the output side of the subtracter 4. A difference image memory 14b for storing difference image data sent from the
A selection circuit 7 is provided on the output side of a, 14b. The tomographic image memory 14a and the difference image memory 14b
Under the control of the controller 13, writing is performed in the transmission / reception cycle of ultrasonic waves, and reading is performed in the output cycle of the image display means (5, 6).

Next, the operation of the second embodiment configured as described above will be described with reference to FIG. 5 and FIG. First, as shown in FIG. 1, tomographic image data output from the scan converter 11 in the DSC 3 is sent to the frame memory 12, the subtracter 4, and the tomographic image memory 14a. Then, the subtracter 4 performs the same operation as described above to generate difference image data, and sends the difference image data to the difference image memory 14b. At this time,
The image data input to the tomographic image memory 14a and the difference image memory 14b, respectively, is controlled under the control of the controller 13 so that their transmission and reception directions are sequentially associated with each ultrasonic beam to form one tomographic image or difference image. Written to form. Next, from the tomographic image memory 14a and the difference image memory 14b in which each image data is written,
The tomographic image data and the difference image data are read out and input to the selection circuit 7. Then, this selection circuit 7
Selects and outputs tomographic image data or difference image data in accordance with the display cycle of the image display 6. The switching timing between the tomographic image data and the difference image data in the selection circuit 7 at this time is, as shown in FIG.
During horizontal scanning, for example, a method of switching at a time phase corresponding to the AA 'line in the vertical direction, a method of switching at a time phase corresponding to the BB' line in the horizontal direction, and a diagonal direction by combining the above two methods And a method of switching at a time phase corresponding to the line CC ′. As a result, FIG.
As shown in (b) and (c), a tomographic image is formed on one side with an arbitrary line segment AA ', BB', CC 'of the image display 6 as a boundary.
Ia and the difference image Ib on the other side are simultaneously displayed on the same screen.

Note that arbitrary line segments AA ′, BB ′, and CC ′ that are boundaries between the tomographic image Ia and the difference image Ib are, for example, a keyboard, a joystick, and a track provided on a console of the apparatus. What is necessary is just to be able to freely move using a ball etc. Further, two or more boundary lines may be set for one screen.

FIG. 7 is a block diagram of a main part showing a third embodiment of the present invention. This embodiment corresponds to one horizontal scan of the image display 6 in the embodiment of FIG. 4 after the tomographic image memory 14a and the difference image memory 14b and before the selection circuit 7. Line memories 15a and 15b are provided respectively. In this case, the line memory 15a
Is the first storage means for storing the tomographic image data from the tomographic image memory 14a in association with one half scan of the display scanning line of the image display 6, and the line memory 15b is provided from the difference image memory 14b. And a second storage unit for storing the difference image data of the image display device 6 in association with the other half scan of the display scan line of the image display 6. And each of the above line memories
As shown in FIG. 8, the tomographic image memories 14a and 15b
In addition, tomographic image data Da and differential image data Db corresponding to one horizontal scan read from the differential image memory 14b are stored. In order to read out the image data from these line memories 15a and 15b and display them on the image display 6, first, as shown in FIG. Image data from an arbitrary position D in the memory 15a to a position D 'corresponding to half of one horizontal scan is output, and subsequently, the same D- data as in the second line memory 15b in which the difference image data Db is stored.
The image data between D 'is output. The tomographic image data Da and the difference image data Db are displayed on the image display 6 via the D / A converter 5, and at this time, as shown in FIG. For example, control is performed so that the first half displays tomographic image data Da and the second half displays differential image data Db. That is,
The D / A converter 5 and the controller 13 form a full scan of a display scanning line from half-scan tomographic image data and difference image data from the selection circuit 7 and output the image data to the image display 6. Becomes As a result, as shown in FIG. 10, the screen of the image display 6 is divided into, for example, left and right.
In one half, a tomographic image Ia is displayed in parallel, and in the other half, a difference image Ib of the same time phase is displayed in parallel.

〔The invention's effect〕

Since the present invention is configured as described above, according to the invention according to claim 1, tomographic image data from the tomographic scanning means (3) and difference image data from the difference image data generating means (4) are fetched. The boundary between the display area of the tomographic image data and the display area of the difference image data on the image display means is arbitrarily set in accordance with the display cycle of the image display means (5, 6), and is divided by the set boundary. The tomographic image data can be combined in one display area of the image display means and the difference image data can be combined and output in the other display area. Thereby, the tomographic image Ia and the difference image Ib can be simultaneously displayed on the same screen (6) of the image display means. In this case, the motion of a moving part such as a heart or a blood vessel wall in the subject can be drawn without using a contrast agent by using the difference image Ib. In addition, the same screen (6) of the image display means shows how the tomographic image Ia showing the entire diagnostic region is displayed, and how the difference image Ib showing the moving region is displayed thereon. It can be understood, and diagnosis of the above-mentioned exercise site can be facilitated.

According to the second aspect of the present invention, the tomographic image Ia and the difference image Ib are bounded by any one of the ultrasonic scanning lines l ₁ and l ₂ on one image displayed on the image display means (5, 6). Can be switched. From this, only the moving tissue in the tomographic image of the differential image display is displayed in association with the tomographic image, and it becomes easier to obtain the motion information of the tissue itself.

Furthermore, according to the invention of claim 3, the first storage means associates the tomographic image data from the tomographic scanning means (3) with one half scan of the display scanning line of the image display means (5, 6). (15a), and associates the difference image data from the difference image data generation means (4) with the other half scan of the display scanning line of the image display means (5, 6) in the second storage means (15b). The tomographic image data and the difference image data from the first and second storage means are taken in, and the display area of the tomographic image data to the image display means and the difference image data are displayed in accordance with the display cycle of the image display means. A boundary with the display area is arbitrarily set, a full scan of a display scanning line is formed from half-scan tomographic image data and difference image data from the means (7) for setting this boundary, and the image data is displayed on an image display means. (5,6)
Can be output to Thus, for example, in the first half of the horizontal scanning cycle, tomographic image data can be displayed, and in the second half, differential image data can be displayed. As a result, the screen (6) of the image display means is divided into, for example, left and right, and a tomographic image Ia is provided in one half and a differential image having the same time phase as the other half.
Ib can be displayed in parallel.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention, FIG. 2 is a timing diagram for explaining an operation of reading image data from a frame memory, and FIG. FIG. 4 is a block diagram showing a second embodiment of the present invention, and FIG. 5 is a boundary showing switching timing between a tomographic image and a difference image on an image display. FIG. 6 is an explanatory diagram showing another example of a display state of a tomographic image and a difference image on an image display, and FIG. 7 is a main part showing a third embodiment of the present invention. , FIG. 8 is a timing diagram for explaining an operation of reading out tomographic image data and differential image data from a line memory, and FIG. 9 is a timing diagram showing a state of display control of image data on an image display. Diagram, Figure 10 shows tomographic image to image display Further explanatory view showing another example of the display state of partial images, FIG. 11 is an explanatory diagram for explaining the display operation of the difference image in the conventional example. 1 ... probe, 2 ... ultrasonic transmitting and receiving circuit, 3 ... DSC,
4 ... Subtractor, 5 ... D / A converter, 6 ... Image display,
7 ... Selection circuit, 8 ... Image memory, 9 ... Subject, 12
…… Frame memory, 14a …… Tomographic image memory, 14b ……
Difference image memory, 15a, 15b …… Line memory, Da ……
Tomographic image data, Db ...... difference image data, l _1, l ₂ ...... ultrasonic scanning lines, Ia ...... tomogram, Ib ...... difference image.

──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Jun Tauchi 1-11-1, Mukoyo-cho, Higashinada-ku, Kobe-shi, Hyogo 141-119 (72) Inventor Toshihiko Kono 2-1 Shinjuyo-212, Kashiwa-shi, Chiba Co., Ltd. Hitachi Medical Corporation Osaka Plant Kashiwa Branch Plant (72) Inventor Shinji Kishimoto 2-1 Shinjyuyo, Kashiwa City, Chiba Prefecture Hitachi Medical Research Laboratory Co., Ltd. (56) References JP-A-59-77841 (JP, A) JP-A-61-135641 (JP, A) JP-A-63-111839 (JP, A) JP-A-1-218432 (JP, A) JP-A-1-270861 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) A61B 8/00-8/15

Claims (3)

(57) [Claims] An ultrasonic transmitting / receiving means for transmitting and receiving an ultrasonic wave to / from a subject, and tomographic image data in the subject including a moving tissue are obtained at a predetermined period using reflected echo signals from the ultrasonic transmitting / receiving means. Tomographic scanning means, means for calculating difference image data by calculating between the obtained time-series tomographic images,
In the ultrasonic diagnostic apparatus having image display means for displaying the formed difference image data, the tomographic image data and the difference image data are fetched and the tomographic image data to the image display means is synchronized with the display cycle of the image display means. Means for arbitrarily setting a boundary between the display area of the difference image data and a display area of the difference image data; and tomographic image data in one display area of the image display means divided by the set boundary, and in the other display area. Means for combining and outputting difference image data. 2. The means for setting the boundary sets an arbitrary ultrasonic scanning line on one image displayed on the image display means as a boundary, and uses the set ultrasonic scanning line as a boundary. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein the display of the tomographic image and the display of the difference image are switched. 3. An ultrasonic transmitting and receiving means for transmitting and receiving ultrasonic waves to and from a subject, and tomographic image data in a subject including a moving tissue are obtained at a predetermined period using reflected echo signals from the ultrasonic transmitting and receiving means. Tomographic scanning means, means for calculating difference image data by calculating between the obtained time-series tomographic images,
An ultrasonic diagnostic apparatus having image display means for displaying the formed differential image data, wherein the first tomographic data is stored in association with one half scan of a display scan line of the image display means. Second storage means for storing the difference image data in association with the other half scan of the display scanning line of the image display means; tomographic image data and difference image data from the first and second storage means Means for arbitrarily setting the boundary between the display area of the tomographic image data and the display area of the difference image data on the image display means in accordance with the display cycle of the image display means, and a half of the means for setting the boundary. Means for forming a full scan of a display scanning line from tomographic image data and differential image data of the scan and outputting the image data to an image display means.