JPS60254375A - X-ray ct picture processor - Google Patents

Abstract

PURPOSE:To attain simple beam hardening correction of a bone by contracting a binary picture and a weight function indicating the bone by 1/N in the vertical and horizontal directions, repeating two-dimensional addition of the weight function by using the binary picture as its mask in all picture elements, then expanding the interpolation again by N times to add the expanded result to the original density image. CONSTITUTION:An X-ray CT reconstituted density image inputted from an external device to the 1st picture memory 1 is converted by a binary-coding device 2 and the converted result is stored in the 2nd picture memory 3. A masking adder 5 matches the center of the weight function obtained from a weight function memory 4 with a picture element position indicating the bone in the binary picture are having a high CT value to add and store the two-dimensionally expanded weight function to/in the 3rd picture memory 6. The picture obtained by repeatedly adding all the picture elements is added to the initially inputted reconstituted density image by a picture adder 7 and the beam hardening artifact of the bone is removed. Thus, the number of times of operation is reduced and rapid operation is attained by contracting the binary picture and the weight function indicating the bone by 1/N in the vertical and horizontal directions.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to X-ray CT (CT is COMPUtedT'
The present invention relates to an X-ray CT image processing apparatus that quickly removes bone beam artifacts that occur in images using only reconstructed images. (Prior Art) Bone beam hardening correction has been previously described in the literature of Joseph et al.
t'orCorrecting 3one Indu
ced Artifacts in Co'mputed
T omoaraphy S canners, J.
internal ofCompute+' △5sis
tetl T-omography Vo12p100
~1o8. As seen in Jan, 197B), the reconstructed image is scanned on the image and the correction amount is calculated from the path length of the soft tissue part and bone (separated by the zero value) included therein. Based on this, the actual scan data was corrected and then reconstructed again.

However, this method has the following problems.

Since 0.2 degree reconstruction and scanning on the image are required, the calculation time is enormous, and high-speed processing cannot be expected.

■Post-processing is not easy because actual scan data is required.

(Object of the Invention) The present invention has been made in view of the above points, and its purpose is to perform bone beam hardening correction quickly and easily from only image data without impairing the effect of removing artifacts. An object of the present invention is to provide an X-ray CT image processing device of 1q.

(Structure of the Invention) A first invention that achieves the above object includes a first image storage device capable of inputting and outputting a reconstructed gray scale image of XIICT to an external device, and this first image storage device. a second image storage device for storing this binary image, and a weight storing a weighting function. a function storage device; a mask adder that adds the weighting function using the binary image as a mask; a third image storage device that stores the addition result obtained by the mask addition adder; and an image adder that performs addition between the images in the image storage device and the third image storage device, and provides the addition result to the first image storage device, and includes an image adder that performs addition between the images in the image storage device and the third image storage device, and provides the addition result to the first image storage device, and adds all pixels representing the bone component of the reconstructed image. The beam hardening correction of the bone is performed by calculating the sum of two-dimensional weighting functions spread around this point as a correction image, and performing JIG calculations on the reconstructed image and the correction image. So, the second invention is to
a first image storage device capable of inputting and outputting a reconstructed grayscale image of a line CT; an image reduction device that reduces the image provided from the first image storage device both vertically and horizontally; and a first image storage device that stores the reduced image. This fourth image storage device has a binarization device that binarizes the given image based on a predetermined CT value, and stores this binary image. a second image storage device for storing weighting functions, a weighting function storage device storing weighting functions, a mask for adding the weighting functions using the binary image as a mask (-1 adder, and a second image storage device for adding the weighting functions to each other using the binary image as a mask); an image enlarging device that performs interpolation on the image provided from the third image storage device and enlarges it to its original size both vertically and horizontally; and an image adder that performs addition between the images of the image storage device and the image enlargement device and provides the addition result to the first image storage device,
After reducing the 1iji image and the weighting function to 1/N vertically and horizontally, the process of adding the weighting function two-dimensionally using the binary image as a mask is repeated for all pixels representing the bone, and the obtained /ζ addition image is calculated using interpolation. Is it true that beam hardening correction for the bones is performed by adding the image to the original reconstructed image after enlarging it N times vertically and horizontally? It is a sign of i.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of essential parts showing an embodiment of an X-ray C1-image processing apparatus according to the first invention. In this figure, 1 is a first image storage device that stores reconstructed grayscale images, 2 is a 2-viewing device, 3 is a second image storage device, 4 is a weighting function storage device, and 55 is a masking addition device. 6 is a third image storage device, and 7 is an image adding Q device.

The first image recording ffi device 1 is capable of inputting and outputting images to an external device (not shown). 2
The digitizing device 2 binarizes the image in the first image storage device 1 using a preset CT value as a threshold, and the second image storage device 3 records this binary image. It is something that The mask addition adder 5 has a weighting function storage device 4 and a second
The center of the weighting function is aligned with the pixel position of the high CT value representing the bone on the binary image.
The weighting functions spread across dimensions are added and stored in the third image storage device 6. The image adder 7 adds the image in the third image storage device 6 and the image in the first image storage device 1, and the added image is stored in the first image storage device 1. It has become.

In such a configuration, a reconstructed grayscale image of X-ray CT input from an external device to the first image storage device 1 is compared with a preset threshold value in the binarization device 2 and binarized. Ru. These binary images are sequentially stored in the second image storage device 3. The mask (=I) receives the binary image from the second image storage device 3 and assigns a weight from the weighting function storage device 4 to the pixel position with a high CT value representing the upper bone of the binary image. A weighting function that spreads two-dimensionally by merging the centers of the functions is added and stored in the third image storage device 6.The initial storage value of the third image storage device 6 is set to zero. The addition process is repeated for all pixels having a value of 0 at the threshold value.

The image created in this way is sent to the image adder 7.
- is added to the initially manually reconstructed grayscale image (stored in the first image storage device 1). This results in
The beam hardening of the bone can be removed, and the image is written anew to the first image storage device 1 and output to an external device as required.

FIG. 2 is an explanatory diagram showing another embodiment of the present invention. 1st
The difference from the figure is that the third image storage device 6 and image adder 7 are omitted. In FIG. 2, instead of taking the sum of the weighting functions and adding them later between the two images, the weighting functions are added directly to the corresponding positions of the reconstructed image and the results are stored in the first image storage device. Depending on the configuration, the bone beam hardening artifact L- can be removed and covered in the same manner as described above.

In addition, the same weighting function is added to pixels with a certain CT value (a or more, but the C
It is also possible to configure so that weighting functions modulated by the T value are added.

Further, the mask addition adder 5 can perform a two-dimensional convolution of the binary image in the second image storage device 3 and the weighting function in the weighting function storage device 4.

In the embodiment of the first invention described above, two-dimensional weighting functions are added for the number of pixels representing bones, which may result in a considerable amount of calculation depending on the case. Therefore, if we reduce the weight function of the bone to 1/N vertically and horizontally, use the binary image as a mask, add the weight function two-dimensionally, and repeat the addition for all pixels representing the bone. The amount of calculations can be reduced, and high-speed processing can be achieved accordingly.

FIG. 3 is a configuration diagram showing an embodiment of the X-ray CT image processing apparatus according to the second invention, which is designed to achieve such high-speed processing. In FIG. 3, parts equivalent to those in FIG. 1 are given the same reference numerals. Components different from those in FIG. 1 are the image reduction device 31
．． They are a fourth image recording fIA device 321, an image enlargement device R33, and a fifth image storage device 34.

The image reduction device 31 receives the image in the first image storage device 1 and reduces it to 1/N in both the vertical and horizontal directions, and the result is stored in the fourth image storage device 32. The output of the fourth image storage device 32 is led to the binarization device/device 2.

The image enlarging device 33 multiplies the reduced image stored in the third image storage device 6 by N times and enlarges the reduced image to the original size. The enlarged image is once stored in the fifth image storage device @34 and then sent to the image adder 7.

The operation in such a configuration will be explained next.

The reconstructed grayscale image of the X-ray CH input from the external device into the first image storage device 1 is reduced to 1/N in both vertical and horizontal directions by the image reduction device 31, and is stored in the fourth image storage device @32. be done. Note that N is usually an integer.

The reduced image in the storage device 32 is binarized by the binarization device 2 according to a preset CT value, and is stored in the second image enlarging device 3.

It is assumed that the weighting function of the weighting function storage device 40 has also been reduced in advance to 1/N in the vertical and horizontal directions corresponding to the above-mentioned reduction rate of 1/N.

In the mask adding adder 5, the weighting function of the weighting function storage device 4 is added to the third image storage device 6 by centering the bones of the binary image (storage device 3) for each pixel. Ru. Note that the initial storage value of the third image storage device 6 is set to zero.

The result of performing this addition process on all pixels that do not represent bones is a corrected image that overlaps the reduced image, so this is multiplied by N in the image enlarging device 33 and restored to the original large serrations. For this expansion, linear interpolation is used to shorten the division time, and two-dimensional interpolation is performed in two stages for each dimension. The enlarged image is stored in the fifth image storage device @34, and this enlarged corrected image is two-dimensionally added to the input image on the first image recorder 18 in the image adder 7, and the result is added to the first image storage device @34. The image data is output onto the image storage device 1 of the image storage device 1.

FIG. 4 is an explanatory diagram illustrating enlarged interpolation when N=4. Based on the known value (○ mark), first calculate the value at the X mark from the value at the Q mark sandwiching it using the following formula.

f (i > = f (1) + (i /4)・(f (
2)-f (1)) Here, ==1.2.3 Next, the value at the * mark is extracted from the values at the X marks on the left and right sides thereof using the following formula.

-<r <2>-r (1)) Here, r = 1.2.3 Interpolation is performed in this way. The same applies to cases other than N=4.

Note that the present invention is not limited to the embodiment, and the following method may be used.

The 0-image reduction device 31 does not actually reduce the image, but integrates it with the binarization equipment 2 to binarize the image by pulling one sample every N pixels in both the vertical and horizontal directions.

(2) The image enlarging device 33 performs addition directly to the first image storage device without passing through the fifth image storage device 34.

(2) Replace the mask addition adder 5 with a two-dimensional conpolision device.

0 image reduction device 31. The binarization device 2 outputs N without using the fourth image storage device 32 and the second image storage device 3.
The adder 5 is turned on and off according to the value of +J.

(Effect of the Invention Song Dynasty) As explained in Part 1, according to the present invention, by appropriately setting the weighting function, Ji...1F:! It is possible to correct bone hardening equivalent to other conventional methods, and the image of the brain and skull + IJ! It is possible to obtain 1 q of clear images without bone cupping.

In addition, it requires a complex and huge amount of calculation to repeat the scan again with the conventional image - [:, examine the components in the path, correct the actual scan data accordingly, and reconstruct it again. Compared to conventional processing, it is extremely practical due to the simplicity of the algorithm and the small amount of calculations, such as the fact that processing can be performed by repeating simple calculations between images using the reconstructed image as a base (1).

For example, when using an image of 320 x 320 pixels and a pixel weighting function of 61 x 61 pixels, it took about 15 hours with other conventional methods, but according to the present invention, the processing time is about 50 minutes. nothing.

Furthermore, according to the present invention as shown in FIG. 3, the image is first reduced to 1/N2, and the reduced image is binarized and the weighting function is added. Since it is reduced to 1/N2 and an I-sized cylinder is used, the number of cylinders is M 2 ×f<
From <M/N) 2xk /N2 and 1. / Decrease to N4. Here, M2 is the area of the weighting function expressed in the number of pixels, and k is the number of pixels representing the bone.

In the simulation using Total III, N=4, M
= 61, the image quality deterioration is less than ±1 CT value, and the calculation time is 1/203 times that of the case without reduction.

This method is the result of skillfully exploiting the phenomenon that the beam hardening corrected image of tatami mats contains only low spatial frequency components.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the X-ray CT image processing apparatus according to the first invention, FIG. 2 is an explanatory diagram showing another embodiment of the first invention, and FIG. FIG. 4 is a block diagram showing one embodiment of the invention, and is an explanatory diagram for explaining enlargement interpolation. 1... First image storage device 2... 21m conversion device 3... Second image storage device 4... Weighting function storage device 5... Mask addition adder 6... Third Image storage device 7...image adder 31...image reduction! ! , location 32...Fourth image storage device 33...Image enlargement device 34...Fifth image storage device pP) 2 oxxx. X come to the US × × 1g spicy X X come to the US X

Claims (2)

[Claims] (1) A first image storage device capable of inputting and outputting reconstructed grayscale images of X-ray CT to an external device; A binarization device that performs binarization and stores this binary image.1. : a second image storage device, a weighting function notation 4Ja device that stores weighting functions, a mask addition adder that adds the weighting functions using the binary image as a mask, and an image obtained by this mask addition adder. a third image storage device that stores Iζ addition results; and an image adder that performs addition between images of the first image storage device and the third image storage device and provides the addition result to the first image storage device. The sum of the two-dimensional weighting functions spread around this point for all pixels representing the blue component of the reconstructed image is calculated as a corrected image, and the bone is calculated by adding the reconstructed image and the corrected image. An X\ACT image processing device characterized by performing beam hardening correction. (2) A first image storage device that can input and output a reconstructed grayscale image of X-ray CT to an external device, and an image reduction device that reduces the image provided from the first image storage device both vertically and horizontally. a fourth image storage device that stores this reduced image; a binarization device that converts the image provided from the fourth image storage device into 2(lIj) with a predetermined CT value; a second image storage device for storing value images; a weighting function storage device storing weighting functions;
a mask addition adder that adds the weighting function using the binary image as a mask; a third image storage device that stores the addition result obtained by the mask addition adder; an image enlarging device that performs interpolation to enlarge the image to the original size both vertically and horizontally; and an image enlarging device that performs addition between the images of the first image storage device and the image enlarging device, and stores the addition result in the first image storage. The device is equipped with an image adder that applies the image adder to the apparatus, and after reducing the binary image representing the bone and the weighting function to 1/N vertically and horizontally, the process of adding the weighting function two-dimensionally using the 21 images as a mask is performed on all pixels representing the bone. is repeated, and the resulting added image is enlarged vertically and horizontally by N times using interpolation, and then added to the original reconstructed I pale image to perform beam hardening correction for the bone. CTi1ii image processing device.