Let me talk about what is the value of CT
CT image reflects on the X-ray absorption coefficient of the human body, but we are concerned that the density differences of the organizational structure, ie, the relative density, if a tissue lesions, the density will change, but due to relatively absorption coefficient it is very complicated, so the tissues and organs Heinz absorption coefficient of X-ray CT in terms of value, the unit is Hu. 0Hu CT value of water, various other tissue density are compared with it. Density much positive than water, small water ratio is negative. Human body CT value shown in FIG.
Image normalization encounter problems during the processing of medical images, standardization of in general 1 (each pixel by subtracting the mean and dividing by the standard deviation); 2. Normalized (such as normalized to 0 ~ 255).
problems in the second step.
If the whole picture is normalized to 0 to 255, it will lose a lot of information. Because the medical image pixel wide distribution, such as -1000 to 2000, if normalized to 0 to 255, then each pixel after normalization is equivalent to the original image 11.7, many of the details will be lost.
There is also a range of our target area of the pixel normalized to 0 to 255. For example, this range is set to less than 0, greater than this range is set to 255. This relates to the window width and position. Window width (window width, ww) is a CT image pixel range, the window bit (window level, wl) is the window width center CT value.
Example: (I arbitrary CT value is written)
We divided the eyeball to head CT images, CT range is assumed that the eye such as 50 to 60, in order to highlight the eye, we wl to 55, ww to 10, value is set to 50 ~ 60 normalized to 0 to 255. 0 is less than 50, greater than the value set to 60 255. such information can be clearly displayed eye.
Window width in pixels can clearly show, while the outside of the window is not wide difference in gradation can not be displayed.
Of course, there are other organizations CT value may be 50 to 60, but does not affect.
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Author: sunyao_123
Source: CSDN
Original: https: //blog.csdn.net/sunyao_123/article/details/73195332
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