JPH0333328B2 - - Google Patents

Description

[Detailed description of the invention]

[Field to which the invention pertains] The present invention relates to, for example, CT (Computerizud
The present invention relates to a CT image display device used in a CT tomography (CT) device, which converts image data into luminance data when displaying a reconstructed image. [Prior Art] CT apparatuses that obtain tomographic images of a subject using radiation such as X-rays have been known. In this CT device, for example, an X-ray tube and an X-ray detection device are placed facing each other with a subject in between, and the X-ray tube and detection device rotate integrally around the subject. The specimen is exposed to X-rays, the intensity of the X-rays passing through the specimen is detected at each rotation angle, and this is collected in the storage unit as projection data.Then, each part of the tomographic plane of the specimen is analyzed by a computer. The X-ray absorption rate is calculated and the tomographic plane is reproduced with a gradation level corresponding to the absorption rate. In this case, the structure of each part of the tomographic plane can be analyzed in as many as 3,000 gradations depending on the X-ray absorption rate. This CT display data, so-called CT value, is expressed in 3000 gradations, with 0 being the black level and +3000 being the white level, but when it is ultimately displayed on a display screen such as a CRT, the values shown in Figure 1. As shown in Figure 2, a CT value (a to b) in a specific range of interest is determined from among the 3000 levels of CT values,
The CT values in this range are divided into gradations that can be displayed by the display device, so-called luminance data gradations (up to 256 gradations can be classified), and displayed on the screen. However, in conventional devices, when converting luminance data to gradation, the memory capacity becomes large because it has a conversion table covering the entire input data range, and the CT value of a specific range is It is specified by the level value, which is the center value of the CT value range, and the width of the CT value range, which is the window width (for example, 100).
Each time the level value or window width changes, the table is rewritten accordingly using only software, so an extra buffer memory of the same capacity as the table is required. to work
The drawback was that the CPU was occupied. Furthermore, the brightness gradation distribution within the window width is usually uniform (the CT value and the brightness data are in direct proportion). A uniform brightness gradation distribution is effective for images such as the abdomen, but a brightness gradation distribution that emphasizes contrast at the center of the window width is more effective for images such as the head. It would be very convenient if the brightness gradation distribution could be changed depending on the target area in this way. There are some systems that have a variable brightness gradation distribution, but the problem is that only a limited number of gradation distributions are available, and it is not possible to obtain an arbitrary distribution, making them not very effective. . [Object of the Invention] An object of the present invention is to provide a CT image display device that can solve all of the above drawbacks and problems at once. [Summary of the Invention] To achieve such an object, the present invention provides a rewritable luminance data table with a capacity sufficient for the maximum width of a window, and a comparison between the lower limit value of the window and input reconstructed image data. and a table rewriting circuit for rewriting the luminance data table. , is equipped with a rewritable brightness gradation distribution table that reads out the final brightness output data by addressing with intermediate output brightness data from the previous brightness data table, reducing the capacity of the brightness data table and changing the table according to various changes. This makes it possible to reduce the burden on hardware and software for rewriting. [Example] Hereinafter, the present invention will be explained in detail using the drawings.
FIG. 2 is a block diagram of main parts showing an embodiment of a data conversion device according to the present invention. In the figure, 10 is a data area boundary value comparator (hereinafter simply referred to as a comparator);
20 is a first switch, 30 is a brightness data table, 40 is a second switch, 50 is a table rewriting circuit, and 60 is a brightness gradation distribution table. The comparator 10 compares input data with a window area lower limit value. This input data is image data expressed in CT values,
This image data is image data reconstructed by a computer (not shown). By the way, in the present invention, several kinds of specific widths (for example, CT value) are used as the window width.
20, 40, 60,…, 500, 1000) are available.
Any one of these can be designated by a code number. The maximum window width (in this example,
1000). The comparator 10 compares the input data with the window lower limit value, but as shown in FIG. 3, if the input data is within a range smaller than the lower limit value, the output terminal
The lower limit value of luminance data is outputted from _D2 , and conversely, the upper limit value of luminance data is outputted from the output terminal _D2 in a range larger than the value obtained by adding the CT value width of the table area to the lower limit value. Furthermore, when the input data exactly falls within the range of the table area, the deviation from the window lower limit value can be sent out from the output terminal _D1 . The first switch 20 connects the output terminal D ₁ of the comparator 10
The output from the comparator 10 is selected and outputted from either the output from the table rewriting circuit 50 or the rewriting address sent from the table rewriting circuit 50. When displaying images by television system, the output from the comparator 10 is used except during the blanking period. During the blanking period, the address outputs of the table rewriting circuit 50 are selected and can be applied to the table 30 as address signals. The brightness data table 30 is displayed in the window.
As the CT value increases, the color changes from black to white up to 2
The data of 56 gradations is set correspondingly.
The output of the switch 20 can be addressed and its contents can be read out. Also,
The contents of the table can be rewritten, and the rewriting data is provided by a table rewriting circuit 50. The second switch 40 switches between the intermediate output data of the table 30 and the comparator 10.
This selects one of the D ₂ outputs and sends it out as the luminance data output. When the comparator 10 sends out the D ₂ output, the D ₂ output is selected, and when the D ₁ output is sent out, the table 30 It is now possible to select the output of The table rewrite circuit 50 sends a rewrite address and rewrite data for rewriting the contents of the table 30 when the level value and window width are changed. FIG. 4 is a block diagram showing the details of one embodiment, in which 51 is an address counter, 52 is a step programm, 53 is an adder, 54 is a latch, and 55 is a switch. The address counter 51 increments the table address by one address and outputs it. The step program 52 stores gradation data increment values corresponding to each window width in a ROM of 16 steps each. For example, in the case of a window width of 20, intermediate gradation data is output. The data increase value is as shown in Table 1, and the configuration is such that the data increase value can be output by specifying the window width code and address.

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Claims (1)

[Claims] 1 The reconstructed image on the CT device is
It is a CT image display device that divides reconstructed image data into predetermined gradations and converts it into luminance data in order to display it on the screen with appropriate contrast only around the value. A brightness data table that has a memory capacity sufficient for the maximum width and in which intermediate brightness data can be written and read is compared with the lower limit value of the window and the input reconstructed image data, and the image data is compared to the lower limit of the window. If it is less than the window upper limit, the data for the brightness data lower limit is output; if it is greater than the window upper limit, the data for the brightness data upper limit is output; if the image data is between the window lower limit and upper limit, the brightness is output. Comparison means configured to output the deviation from the window lower limit value as an address of a data table, and information regarding intermediate luminance data for a large number of windows stored in advance and written to the luminance data table when a desired window is designated. a table rewriting circuit that sequentially outputs the address of the window and intermediate brightness data of the window, and a rewritable circuit that can read the final brightness output data by addressing with the intermediate output brightness data from the brightness data table. A CT image display device characterized by comprising a brightness gradation distribution table.