Patent Number: 055880363
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus and a radiographing method for setting radiographing conditions at a time of radiographing by using the X-ray CT apparatus. 2. Related Prior Art An X-ray CT (computerized tomography) apparatus has been widely used as a medical diagnosis apparatus for providing a tomographic image of a body of a subject such as a patient. When radiographing operation is performed by using an X-ray CT apparatus, various radiographing conditions such as a scan speed, tube voltage, tube current, slicing width, scan pitch, and tilt angle are entered in advance as previous informations, and a scanning operation is then carried out in accordance with the entered radiographing conditions to obtain a desired tomographic image. In such medical use, there is a case where a particular region of a patient is repeatedly radiographed at regular intervals in order to determine time-dependent changes such as progress or healing of a disease of a patient. In such a case, the radiographing has been often carried out under nearly the same radiographing conditions as those by which the previous radiographing was carried out for the reason that the subject, the region to be diagnosed, the type of disease, etc. are the same. In a conventional X-ray CT apparatus, however, the radiographing conditions must be reset each time the radiographing is performed. This is extremely troublesome to an operator and causes the examination efficiency to be lowered. SUMMARY OF THE INVENTION An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art and to provide an X-ray CT apparatus and a radiographing method using the X-ray CT apparatus capable of automatically setting radiographing conditions in accordance with past exposure information of a subject. This and other objects can be achieved according to the present invention by providing, in one aspect, an X-ray CT apparatus for performing a radiographing operation to a subject lying on a bed, comprising: a bed drive means for moving a bed to a predetermined position; PA1 an X-ray tube irradiating an X-ray to the subject; PA1 a detecting means for detecting an irradiated X-ray; PA1 a gantry means on which the X-ray tube and the X-ray detecting means are mounted; PA1 a gantry drive means for rotationally driving the gantry means; PA1 an exposure information file means into which past exposure information for the subject is stored; and PA1 a main controller for setting a radiographing condition in accordance with the past exposure information stored in the exposure information file and for controlling at least one of the X-ray tube, the bed drive means and the gantry drive means in accordance with the set radiographing condition. PA1 preparing an information of the subject; PA1 entering the information into the main controller; PA1 indexing the past exposure information of the subject from the exposure information file; PA1 confirming whether the past exposure information is indexed; PA1 displaying the indexed past exposure information as numerical data in a case where the past exposure information is indexed; PA1 confirming whether a radiographing condition is set in accordance with the displayed exposure information; PA1 setting and storing the radiographing condition in a case where the radiographing condition is set in accordance with the displayed exposure information; and PA1 performing a scan operation with the set radiographing condition. PA1 preparing an information of the subject; PA1 entering the information into the main controller; PA1 carrying out a scanographing operation and displaying the scanographic image on the monitor; PA1 indexing the past exposure information of the subject from the exposure information file; PA1 confirming whether the past exposure information is indexed; PA1 converting a slice information in the indexed past exposure information into a slice information image data in a case where the past exposure information is indexed; PA1 displaying the indexed past exposure information as numerical data and displaying the slice information as slice information image data; PA1 confirming whether a radiographing condition is set in accordance with the displayed exposure information; PA1 inversely converting the slice information image data into the slice information; PA1 setting and storing the radiographing condition in a case where the radiographing condition is set in accordance with the displayed exposure information; and PA1 performing a scan operation with the set radiographing condition. In a preferred embodiment in this aspect, the apparatus further comprises a bed drive means controller, a gantry drive means controller and a high-voltage controller, through which the bed drive means, the gantry drive means and the X-ray tube are controlled, respectively, by the main controller. The main controller comprises a central processing unit, a scan control means for controlling the high-voltage controller, the bed drive means controller and the gantry drive means controller, an input/output control means for the exposure information file means and means for converting a slice information data within the exposure information into a slice information image data and controlling the data for display, the scan control means, the input/output control means and the converting means are operatively connected to the central processing unit. A monitor is operatively connected to the data converting and controlling means of the main controller, the monitor means including a main monitor for displaying a scanographic image and a sub-monitor for displaying the exposure information as numerical data. In another aspect of the present invention, there is provided a method for performing a radiographing operation by using an X-ray CT apparatus of the characters described above, wherein a radiographing condition according to which the radiographing operation is performed is set in accordance with a past exposure information stored in the exposure information file and at least one of the bed, the X-ray tube, and the gantry in accordance with the set radiographing conditions. In one preferred embodiment, the radiographing operation is performed by the steps of: In this embodiment, the radiographing operation further comprises the steps of modifying a numerical data of the radiographing condition in the displayed exposure information. In a case where the past exposure information is not indexed, the radiographing condition is set manually and stored and the scan is then performed with the set radiographing condition. In a case where the radiographing condition is not set, it is confirmed whether further index is to be continued and in a case where the index is continued, another past exposure information for the subject is further indexed, and in a case where the index is not continued, the radiographing condition is set manually and stored. In another preferred embodiment, the radiographing operation is performed through a previous setting of a radiographing position and region of the subject by the steps of: In this embodiment, the radiographing operation further comprises the step of modifying a numerical data of the radiographing condition and the slice information image data in the displayed exposure information. In a case where the past exposure information is not indexed, the radiographing condition is set manually and stored and the scan is then performed with the set radiographing condition. In a case where the radiographing condition is not set, it is confirmed whether further index is to be continued and in a case where the index is continued, another past exposure information for the subject is further indexed, and in a case where the index is not continued, the radiographing condition is set manually and stored. In the above embodiments, a predetermined number of a plurality of past exposure informations for the subject are stored in accordance with the time order and when a new radiographing condition is stored as exposure information, an oldest past exposure information automatically vanishes. According to the embodiments of the present invention, the past exposure information on a particular subject such as a patient is indexed from the exposure information file, which stores exposure information. Then, the radiographing conditions are set based on the indexed past exposure information. Scan is then carried out while controlling at least one of the bed, the X-ray tube, and the gantry in accordance with the set radiographing conditions. According to the preferred embodiment of the present invention, scanography is performed to produce a scanographic image before implementing the scan. The slice information such as the slicing pitch in the slicing operation and the tilt angle of the gantry is converted to slice information image data, and the converted slice information image data are displayed on a monitor as an image which is superimposed on the scanographic image. At this point, no relationship of relative position has been established between the slice information image and the scanographic image on the monitor. Next, the slice information image is modified so that the radiographing will be carried out at a desired point on the scanographic image and at a desired tilt angle. As a mode of modifying the slice information image, the whole slice information image is moved on the monitor with respect to the scanographic image. Such a modifying operation on the monitor establishes the relationship of relative position between the slice information image and the scanographic image. Then, the modified slice information image data are inversely converted to the slice information data, and the inversely converted slice information data and numerical data, which have been modified separately, are used as the radiographing conditions for carrying out the scan. During the scan, the gantry, the bed, and the X-ray tube are controlled in accordance with the radiographing conditions. The nature and further features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.