Method and apparatus for specifying slice planes in X-ray computed tomography

Abstract: A method and an apparatus for specifying slice planes in an X-ray CT, capable of specifying a slice plane corresponding to the desired tomographic image easily and accurately. In the apparatus, scans of the body to be examined are carried out and the projection data are stored in the large capacity memory (11) first. Then, a scanogram of the body to be examined is displayed, on which a cursor (21,31,41) is controlled in order to specify the desired slice planes corresponding to the desired tomographic images to be reconstructed. Then, the desired tomographic images are reconstructed for the desired slice planes indicated by the cursor by using an appropriate part of the projection data stored in the memory (11) which corresponds to the desired slice planes indicated by the cursor (21,31,41). Either one of the helical scan and the multi-scan can be used for collecting the data to obtain the scanogram and the tomographic images (23,33).

Description: The present invention relates to an X-ray computed tomography (CT) apparatus and to a method of X-ray CT imaging. JP-A-2-196383 discloses an X-ray CT apparatus and method in which a memory means is used for storing 3-dimensional processed image data obtained from an image reconstruction means. A desired slice plane is specified by rotating or moving a frame cursor image in a three-dimensional memory region. The display means is used for indicating a three-dimensional image and the cursor image so that an operator can see the slice plane from which data of a slice image are obtained, wherein the slice image is simultaneously displayed along with the three-dimensional image and the cursor image. JP-A-2-196383 is not related to helical scanning or reconstruction from projection data. US-A-4,674, 046 discloses a system in which a slice position image is generated and displayed on the screen of a display device in superposition with three-dimensional data of a patient. Non-prepublished EP-A-0 464 645 having an earlier priority date discloses an X-ray CT apparatus including a X-ray scanner means for carrying out helical scans of a body to be examined within a predefined scanning region. Before acquiring projection data, a scanogram is obtained on which the desired tomographic image range are designated,the helical scanning of the designated region is then started including additional start and stop regions and the data are stored in a memory means. For performing a reconstruction, a desired slice position is designated on the scanogram displayed by a display means, using a cursor indicating a desired slice position. Thereupon, projection data corresponding to the slice position and an additional preceding and succeeding range are selected from the acquired data. The image reconstruction means then performs the image reconstruction based on the selected projection data. In another conventional X-ray CT apparatus, in order to carry out the multi-scan imaging, the slice planes for obtaining the tomographic images are specified by selecting projection data corresponding to the desired slice planes from a list of projection data displayed on a monitor display, according to the associated data such as the table positions. Also, in order to carry out the helical scan imaging, the projection data corresponding to the desired imaging region containing the desired slice plane are selected by using the numerical input of the table position and the number of rotations since the start of the scan. However, in such a conventional X-ray CT apparatus in which the slice planes are specified by selecting the corresponding projection data, precisely which portions of the body to be examined are located at the specified slice planes cannot be confirmed until the reconstructed tomographic image is obtained, so that it has been difficult to accurately specify the slice plane corresponding to the desired tomographic image. On the other hand, as disclosed in U.S. Patent No. 4,649,555 for example, there has been a conventional X-ray CT apparatus in which the desired slice places are specified on a scanogram of the body to be examined prior to the scanning, and then the scans are carried out in order to obtain the projection data necessary in reconstructing the tomographic images for the slice planes specified on the scanogram. In this type of a conventional X-ray CT apparatus, because the scanning and image reconstruction are carried out after the slice places are specified on the scanogram, it has been taking a considerable amount of time for the operator to inspect the reconstructed image in order to determine whether the obtained tomographic image is the desired one, i.e., if the slice planes had been specified appropriately. Moreover, in a case the obtained tomographic image is not the desired one, this time consuming process has to be repeated all over again, so that it is not only time consuming but also tedious, and as a consequence there has also been a problem that the amount of X-ray irradiated on the body to be examined would have to be increased considerably in such a case, which is potentially harmful to the body to be examined and therefore highly undesirable. Similarly, in a case this type of a conventional X-ray CT apparatus is used to carry out the helical scan imaging, when the slice planes are specified on the scanogram, the apparatus is controlled by the command indicating after how many rotations should the scanning start and for how many rotations should the scanning continue in order to cover the specified slice planes, so that it has been necessary for the operator to inspect the reconstructed image in order to determine whether the obtained tomographic image is the desired one, i.e., if the slice planes had been specified appropriately. Thus, just as in the case of the multi-scan imaging described above, there have been problems in a case of the helical scan imaging that it can be quite time-consuming and tedious for the operator to obtain the truly desired tomographic image, and that a large amount of X-ray has to be irradiated on the patient. It is therefore the object of the present invention to provide an apparatus and a method for specifying slice planes in an X-ray CT, capable of specifying slice planes correponding to the desired tomographic images easily and accurately. This is achieved by the features of claim 1 and claim 7, respectively. The present invention provides a method and an apparatus for specifying slice planes in an X-ray CT, while preventing the potentially harmful increase of the amount of X-ray to be irradiated on the body to be examined in a process of obtaining the desired tomographic images. Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic block diagram of one embodiment of an X-ray CT apparatus according to the present invention. Fig. 2 is a sequential illustration of a scanogram display for specifying a slice plane in the X-ray CT apparatus of Fig. 1 in a case of helical scan imaging. Fig. 3 is an illustration of a scanogram display for specifying the slice plane in the X-ray CT apparatus of Fig. 1, showing a possible modification to the methods of specifying a slice plane used in Fig. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to Fig. 1, an embodiment of an X-ray CT apparatus according to the present invention will be described in detail. In this embodiment, the X-ray CT apparatus comprises: an X-ray tube 1 and a detector 2 for carrying out scans with respect to a body to be examined P within a prescribed scanning region; a data collection unit 3 for collecting signals detected by the detector 2 in order to obtain projection data of the body to be examined P within the prescribed scanning region; a central processing unit 4 for controlling the operations of the apparatus as a whole; an image reconstruction unit 5 for reconstructing a scanogram and tomographic images from the projection data collected by the data collection unit 3 under the control of the central processing unit 4; an image memory 6 for temporarily storing the image which is reconstructed by the image reconstruction unit 5 and is to be displayed; a display unit 7 for displaying the image stored in the image memory unit 6; a cursor position input unit 8 for allowing an operator to specify the desired slice plane on the scanogram displayed on the display unit 7 by moving a cursor on a display screen; a specified position calculation unit 9 for calculating a position on the scanogram indicated by the cursor controlled by the operator using the cursor position input unit 8, which is fed to the central processing unit 4; a high voltage power source unit 10 for supplying high voltage power to the X-ray tube 1; and a large capacity memory unit 11 for storing projection data collected by the data collection unit 3, from which the projection data are read out under the control of the central processing unit 4 according to the position calculated by the specified position calculation unit 9 on a basis of the position of the cursor specified by the cursor position input unit 8. In this X-ray CT apparatus, the scans by the X-ray tube 1 and the detector 2 are carried out for the prescribed scanning region first, and all the projection data obtained by the data collection unit 3 from the scans of the prescribed scanning region are stored in the large capacity memory unit 11. Then, the scanogram is reconstructed at the image reconstruction 5 and displayed on the display unit 7. On the displayed scanogram, the operator specifies the desired slice planes for which the tomographic images are desired to be reconstructed by controlling the cursor on the scanogram. Then, according to the desired slice planes specified on the displayed scanogram, the central processing unit 4 reads out the appropriate projection data required for reconstructing the tomographic images at the specified slice planes from the large capacity memory unit 11 and supplied these appropriate projection data to the image reconstruction unit 5, such that the desired tomographic images at the specified slice planes can be obtained by the image reconstruction unit 5. More specifically, in this X-ray CT apparatus of Fig. 1, when the helical scan imaging is to be carried out, in order to specify the desired slice plane, the central processing unit 4 controls the apparatus such that the display on the display unit 7 is sequentially changed as shown in Fig. 2. Namely, as shown in (A) of Fig. 2, the display unit 7 first displays the scanogram of the body to be examined P along with an indicator cursor 20 indicating an image reconstructible region for which the projection data necessary in reconstructing the tomographic images have been collected by the data collection unit 3. Then, as shown in (B) of Fig. 2, the operator is allowed to specify the slicing region including the slice planes corresponding to the desired tomographic images by using the cursor position input unit 8, such that the slicing region is indicated on the displayed scanogram by a cursor 21 located within the image reconstructible region indicated by the indicator cursor 20. Next, as shown in (C) of Fig. 2, the slice planes 22 for image reconstruction are displayed within the slicing region indicated by the cursor 21 on the displayed scanogram, according to the slice pitch entered by the operator through an input unit (not shown), so as to facilitate the operator's visual inspection of the slice planes for obtaining the tomographic images on the displayed scanogram in which the portions of the body to be examined P corresponding to the specified slice planes are apparent. Then, as shown in (D) of Fig. 2, when the image reconstruction function is specified by the operator through the input unit (not shown), the image reconstruction unit 5 reconstructs the tomographic images 23 at the specified slice planes 22 by using the projection data stored in the large capacity memory unit 11 which are read out by the central processing unit 4 according to the desired slice planes specified on the displayed scanogram. The reconstructed tomographic images are subsequently displayed by the display unit 7. Here, it is to be noted that the different image reconstruction functions can be specified for the different tomographic images to be reconstructed, if necessary. In this embodiment, the step of specifying the slice planes may be modified as follows. Namely, as shown in Fig. 3, each of the slice planes to be set up can be indicated by a line segment 40 whose length indicates a size of the tomographic image to be reconstructed for this slice plane, and which has a center dot 41 indicating a central position of the tomographic image to be reconstructed for this slice plane, such that each tomographic image can be obtained as a zooming image of a desired area on each slice plane. Thus, according to this embodiment, the operator can try out various possible plans for the slice planes set up, and confirm precisely which portion of the body to be examined is going to be imaged by the specified slice plane before the actual reconstruction of the tomographic images, so that it becomes possible to specify slice planes corresponding to the desired tomographic image easily and accurately. As a consequence, the present invention is particularly useful in a case in which a large number of tomographic images are to be reconstructed. Furthermore, according to the present invention, since the projection data for the entire scanning region are taken and stored in the large capacity memory unit before the desired slice planes are specified on the scanogram and the image is reconstructed by using the projection data stored in the large capacity memory unit, it becomes possible to specify the slice planes corresponding to the desired tomographic images easily and accurately, as well as to prevent the potentially harmful increase of the amount of X-ray to be irradiated on the body to be examined. It is to be noted that many modifications and variations of the above embodiment may be made without departing from the novel and advantageous features of the present invention. Accordingly, all such modifications and variations are intended to be included within the scope of the appended claims.

Claims: An X-ray CT apparatus, comprising: scanner means (1) including an X-ray tube and a detector for carrying out helical scans of a body (P) to be examined within a prescribed scanning region; a data collection unit (3) for collecting signals detected by the detector (2) in order to obtain projection data of the body (P); image reconstruction means (5) for reconstructing desired tomographic images (23) of the body (P) to be examined from the projection data; memory means (11) for storing all projection data obtained in the helical scans within the prescribed scanning region carried out by the scanner means (1, 2, 3); display means (7) for displaying a scanogram of the body (P) to be examined; cursor control means (8) for controlling a cursor (21) on the scanogram displayed by the display means (7), the cursor (21) indicating desired slice planes (22) corresponding to the desired tomographic images (23) on the scanogram according to an operator specifiable slice pitch; and wherein only an appropriate part of the projection data corresponding to the desired slice planes (22) indicated on the scanogram by the cursor (21) is supplied from the memory means (11) to the image reconstruction means (5) such that the image reconstruction means (5) only reconstructs the desired tomographic images (23) for the desired slice planes (22) by using said appropriate part of the projection data supplied from the memory means (11). The X-ray CT apparatus of claim 1, wherein the display means (7) displays the scanogram along with an indication of the image reconstructible region and the cursor control means (8) controls the cursor (21) within the image reconstructible region. The X-ray CT apparatus of claim 1 or 2, wherein the image reconstruction means (5) reconstructs the desired tomographic images (23) according to an externally specifiable image reconstruction function. The X-ray CT apparatus of any of claims 1 to 3, wherein the display means (7) further displays a line segment on each of the desired slice planes (22), the line segment indicating a desired area to be covered by the desired tomographic image to be reconstructed by the image reconstruction means (5). The X-ray CT apparatus of claim 4, wherein the image reconstruction means (5) reconstructs a zooming tomographic image of the desired area indicated by the line segment for each of the desired slice planes. The X-ray CT apparatus of claim 4 or 5, wherein the display means (7) further displays a marking on each line segment indicating a central position of the desired area indicated by the line segment. A method of X-ray CT imaging, comprising the steps of: carrying out helical scans of a body (P) to be examined by using scanner means (1) including an X-ray tube and a detector, to obtain projection data of the body (P) to be examined within a prescribed scanning region; collecting signals detected by the detector in order to obtain projection data of the body (P); and reconstructing desired tomographic images (23) of the body (P) to be examined from the projection data; storing in memory means (11) all projection data obtained in the helical scans within the prescribed scanning region carried out by the scanner means (1); displaying a scanogram of the body (P)to be examined on a display means (7); controlling a cursor (21) on the displayed scanogram, the cursor (21) indicating desired slice planes (22) corresponding to the desired tomographic images (23) on the displayed scanogram according to an operator specified slice pitch; and supplying only an appropriate part of the projection data corresponding to the desired slice planes (22) indicated on the scanogram by the cursor (21) from the memory means (11) to the image reconstruction means (5) such that the image reconstruction means (5) only reconstructs the desired tomographic images (23) for the desired slice planes (22) at the reconstructing step by using said appropriate part of the projection data supplied from the memory means (11). The method of claim 7, wherein at the displaying step, the display means (7) displays the scanogram along with an indication of the image reconstructible region and at the controlling step the cursor (21) is controlled within the image reconstructible region. The method of claim 7 or 8, wherein at the reconstructing step, the desired tomographic images are reconstructed according to an externally specified image reconstruction function. The method of any of claims 7 to 9, wherein at the displaying step, the display means (7) further displays a line segment on each of the desired slice planes (22), the line segment indicating a desired area to be covered by the desired tomographic image to be reconstructed. The method of claim 9 or 10, wherein at the image reconstructing step, a zooming tomographic image of the desired area indicated by the line segment is reconstructed for each of the desired slice planes (22). The method of claim 10, wherein at the displaying step, the displaying means (7) further displays a marking (41) on each line segment indicating a central position of the desired areas indicated by the line segment.

Inventors: HAYASHIBARA MAKOTO, TOKI YUSUKE, HAYASHIBARA, MAKOTO, TOKI, YUSUKE
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: A61B6
IPC codes: A61B6, G01N23, H04N7