JP3488497B2 - Radiation computed tomography equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation computed tomography apparatus (hereinafter, referred to as a "radiation CT apparatus"), and more particularly to a slice CT having an arbitrary thickness. The present invention relates to a radiation CT apparatus capable of obtaining an image. 2. Description of the Related Art In an X-ray CT apparatus which is one of conventional radiation CT apparatuses, a slice thickness of a CT image is, for example, 1,
Selection is made from a slice thickness prepared in advance by the apparatus, such as 2, 5, 10 mm. A doctor selects an optimal slice thickness according to a diagnostic method and a scan site, and performs a CT scan. However, in such an X-ray CT apparatus, when obtaining images having different slice thicknesses at the same slice position, it is necessary to perform a plurality of CT scans at the same position. Also,
It was not possible to obtain an image of an arbitrary slice thickness other than the previously prepared thickness. In order to obtain tomographic images having different slice thicknesses at the same slice position in one scan or to obtain tomographic images having an arbitrary slice thickness, image data of a plurality of thin slice thickness tomographic images can be obtained. Are appropriately added to generate an image having a large slice thickness. For example, by adding the tomographic image Q ₁ to Q ₅ in the five thin slice thickness as shown in (a) of FIG. 4, shown in FIG. 4 (b)
A tomographic image Q having a large slice thickness is created as shown in FIG. In this case, the organ M that is not clear due to a small slice thickness is formed as a tomographic image having a large slice thickness, so that the organ M is clear and a more accurate diagnosis can be performed. When a tomographic image with a large slice thickness is obtained by adding image data of a tomographic image with a small slice thickness, the number of added images and an appropriate weighting value have been specified. The slice thickness of the created tomographic image is calculated from the slice position and the slice thickness of the first and last tomographic images by the following equation. [0005] _{D = (D a / 2 +} D b / 2) + (S b -S a) ... (1) where, D slice thickness of a tomographic image that has been created, D _a and S _a first tomographic image The slice thickness and slice position of
D _b and S _b represents the slice thickness and the slice position of the last tomogram. [0006] In addition, 3 collected by a helical scan or the like.
There is also a method of using projection data with a small slice thickness for creating a two-dimensional image. [0007] A tomographic image having a large slice thickness is obtained from the above-described conventional tomographic image having a small slice thickness.
The line CT apparatus has the following problems. That is,
Equation (1) has a problem that a slice thickness based on a general definition of a slice thickness of a CT image required by a doctor at the time of diagnosis cannot be obtained. In general, the slice thickness is determined on the basis of a slice profile which is a shape of a CT value when an X-ray is irradiated to an object of uniform quality. The slice profile has a shape peculiar to the apparatus, and the slice thickness refers to the thickness of a half value of the maximum CT value indicating the slice profile. Therefore, for example, in the case of the slice profiles S _{1 to} S ₃ as shown in FIG. 5, the slice thickness is the thickness W _{1 to} W ₃ of the half width portion. In FIG. 5, the horizontal axis indicates the slice position, and the vertical axis indicates the ratio of the CT value to the maximum value. Here, as shown in FIG. 6, S ₄ and S ₅
Simply adding a tomogram having a slice profile shown in, the tomographic image having a slice profile as shown in S _6. At this time, even if the half widths W ₄ and W _{5 of} the slice profile shown in S ₄ and S ₅ and the slice position are substituted into the equation (1), they do not match the half width W ₆ of the slice profile shown in S _6. There was a problem. Further, when data is collected by helical scan, since the bed is constantly moving, the exact slice thickness cannot be known, so that there is a problem that the slice thickness cannot be calculated by the equation (1). SUMMARY OF THE INVENTION It is an object of the present invention to provide a radiation CT apparatus capable of obtaining a tomographic image having an arbitrary slice thickness based on the position and slice thickness definitions designated by an operator. It is another object of the present invention to provide a radiation CT apparatus capable of similarly obtaining a tomographic image from projection data obtained by helical scanning. According to the present invention, there is provided a means for collecting projection data using an X-ray source for irradiating X-rays and a detector for detecting X-rays transmitted through a subject; Means for reconstructing data of a plurality of tomographic images based on the collected projection data, tomographic image storage means for storing data of the reconstructed tomographic images, and a slice profile corresponding to a slice thickness. A slice profile storage unit for storing a plurality of slice profiles; and a unit for weighting and adding the plurality of reconstructed tomographic images with a weight value corresponding to a slice profile corresponding to a slice thickness designated by an operator. [0015] As a result of taking the above-mentioned measures, the following effects are produced. If the slice profile of the tomographic image of the thick slice thickness created by adding the tomographic images of the thin slice thickness matches the slice profile of the tomographic image when the tomographic image of the thick slice thickness is created from the beginning, two tomographic images are obtained. The images are equivalent. Therefore, if the image data is added so that the slice profile having the designated slice thickness and the slice profile of the created tomographic image match, the slice thickness of the created tomographic image is based on the general definition of the slice thickness. It becomes the slice thickness. Therefore, a tomographic image suitable for a doctor's diagnosis can be obtained. Further, by displaying the slice profile of the created tomographic image, comparison with the designated slice profile becomes possible. Furthermore, a tomographic image having a specified slice thickness can be obtained by adding the data so as to obtain a specified slice profile using projection data obtained by the helical scan, and projection for forming a three-dimensional image can be obtained. Data can be collected. FIG. 1 is a block diagram showing the configuration of an X-ray CT apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart for specifying a slice thickness in the present apparatus. An example is shown. The X-ray CT apparatus includes a gantry 10 rotatably supported, a bed 11 on which a subject P is placed, an X-ray tube 20 fixed to the gantry 10 and exposing X-rays, Detector 30 for detecting X-rays emitted from tube 20 and transmitted through subject P
It has. An X-ray dose detector 31 and an X-ray collimator 32 are arranged between the X-ray tube 20 and the detector 30. The gantry 10 and the bed 11 are controlled by a gantry / bed controller 12, and the X-ray tube 20 is connected to the X-ray controller 2.
1 is controlled. Mount / bed controller 12 and X
The line controller 21 is connected to the control device 40, and is controlled by an operator's command via a console 41. The projection data detected by the detector 30 and the X-ray data detected by the X-ray detector 31 are connected to a computer 60 via a signal processing unit 50. The computer 60 is connected to the control device 40, the storage device 61, and the monitor 62. The computer 60 reconstructs a tomographic image by designating a slice position and a slice thickness inputted via the console 41 based on projection data collected by scanning or image data stored in the storage device 61 and the like. It has the function to do. In the X-ray CT apparatus configured as described above,
A tomographic image having a slice thickness of an arbitrary thickness is created according to the procedure shown in FIG. Here, a case where a tomographic image having an arbitrary slice thickness is created from image data of a tomographic image having a small slice thickness stored in the storage device 61 will be described. First, image data is read from the storage device 61 via the computer 60 (ST11). Next, a slice position required for diagnosis and a slice thickness value suitable for diagnosis (hereinafter, referred to as “creation conditions”) are input by the operator (ST12). Note that an allowable range is also input for the input creation conditions. Next, the shapes of a plurality of slice profiles having the above-described slice thickness are displayed on the screen of the monitor 62. As for these slice profiles, a plurality of slice profiles are stored in the computer 60 for each slice thickness. A slice profile suitable for diagnosis is designated by the operator from the displayed slice profiles, and the designated slice profile is determined (ST13). It is determined by changing the weighting value or the like whether or not a tomographic image conforming to the creation conditions input in ST12 and having the designated slice profile designated in ST13 can be created. If it can be created, the process proceeds to ST15. If it cannot be created, the process proceeds to ST20 (ST14). At this time, the above-described error is considered. In ST15, the designated slice profile and the created slice profile of the tomographic image to be created are superimposed and displayed on the monitor 62 (ST15), and the process proceeds to ST16. On the other hand, in ST20, an addition condition for changing the weighting value of the image data for obtaining a tomographic image having a profile whose shape is closest to the selected profile, which satisfies the creation conditions described above, is calculated. The shape of the slice profile and the creation conditions are displayed on the screen of the monitor 62, and the process proceeds to ST21. In ST21, the monitor 62
It is determined by the operator whether or not the display can be performed based on the creation condition displayed in step ST16.
If not, the process returns to ST12. In ST16, the operator selects whether or not to create a tomographic image. If the tomographic image is to be displayed, the process proceeds to ST17; otherwise, the process ends. In ST17, weighted addition is performed, and a tomographic image and a creation condition are displayed. Also, a slice profile is displayed at the same time. The doctor diagnoses the subject with reference to the created tomographic image and the creation conditions and the slice profile. [0026] Figure 3 is a slice profile S _a tomographic image obtained by changing the weighting values multiplied to the image data to be _{added, S b, S c, S} d, shows the S _e, respectively W _{a, W b, W c, W d} , tomographic images having a slice thickness of W _e are obtained. As described above, in the X-ray CT apparatus of the present embodiment, the input of the preparation conditions and the selection of the slice profile can be performed in an interactive manner for comparing the designated slice profile with the prepared slice profile. It is possible to create a tomographic image having a different slice thickness. Further, even when tomographic images having a plurality of slice thicknesses are required at the same position, only one X-ray exposure is required, so that the dose is not increased and the exposure is safe. Since the slice thickness can be specified interactively without relying on experience, the burden on the operator can be reduced. The present invention is not limited to the above embodiment. That is, in the above embodiment, the tomographic image of the desired slice thickness is added from the data of the collected tomographic image of the thin slice thickness, but the tomographic image is reconstructed from the addition result of the projection data in the helical scan or the like. An image may be created. Further, by registering the creation conditions, the slice thickness, and the slice profile, the processing time can be reduced when a large amount of tomographic images having the same slice thickness are required. In addition, it goes without saying that various modifications can be made without departing from the spirit of the present invention. According to the present invention, it is not necessary to repeat the scan every time the slice thickness is changed, so that the inspection time is shortened, and the radiation dose is reduced, thereby minimizing the effect on the human body. Of course, the image data is added so as to have the specified slice profile, so that an image having an arbitrary slice thickness according to the general definition can be obtained. Further, an image having a small slice thickness for a three-dimensional image and a tomographic image having a large slice thickness for diagnosis can be simultaneously obtained by helical scanning.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an X-ray CT apparatus according to one embodiment of the present invention. FIG. 2 is a flowchart showing a procedure of a tomographic image creation process in the apparatus. FIG. 3 is a diagram showing a change in slice thickness in a profile of a tomographic image created by the same apparatus. FIG. 4 is an explanatory diagram showing the concept of a conventional tomographic image creation process. FIG. 5 is a view showing a definition of a slice thickness in a slice profile. FIG. 6 is a view showing a slice profile in a tomographic image creation process in a conventional X-ray CT apparatus. [Description of Signs] 10 ... Stand 11 ... Couch 12 ... Stand / Couch controller 20 ... X-ray tube 21 ... X-ray controller 30 ... Detector 31 ... X-ray dose detector 32 ... X-ray collimator 40 ... Control device 41 ... Console 50 ... Signal processing unit 60 ... Computer 61 ... Storage device 62 ... Monitor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-224736 (JP, A) JP-A-57-64047 (JP, A) JP-A-61-109551 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) A61B 6/03

Claims (1)

(57) Claims: means for collecting projection data using an X-ray source for irradiating X-rays and a detector for detecting X-rays transmitted through a subject; Means for reconstructing data of a plurality of tomographic images based on the obtained projection data, tomographic image storing means for storing data of the reconstructed tomographic images, and storing a plurality of slice profiles corresponding to slice thicknesses A radiation profile computer comprising: a slice profile storage unit for performing a weighting operation on a plurality of reconstructed tomographic images with a weighting value corresponding to a slice profile corresponding to a slice thickness designated by an operator. Tomography equipment.