CT window technology
Window technology is a display technology used to observe normal tissues or lesions with different densities in CT examination, including window width and window level. Since various tissue structures or lesions have different CT values, when it is desired to display the details of a certain tissue structure, the window width and window level suitable for observing the tissue or lesion should be selected to obtain the best display.
The window width is the range of CT values displayed on the CT image, and the tissues and lesions within this range of CT values are displayed in different simulated grayscales. Tissues and lesions with CT values higher than this range, no matter how much higher the degree is, are displayed as white shadows, and there is no gray difference; on the contrary, tissue structures lower than this range, no matter how low the degree is Displayed in black shadows, there is no grayscale difference. When the window width is increased, the range of CT values shown in the image will increase, and the number of tissue structures with different densities will increase, but the gray level difference between the structures will decrease. When the window width is reduced, the displayed tissue structure decreases, but the gray level difference between each structure increases. For example, the window width for observing brain matter is usually -15 to +85H, that is, various structures with densities in the range of -15 to +85H, such as brain matter and cerebrospinal fluid spaces, are displayed in different gray scales. Tissue structures above +85H, such as bone and intracranial calcification, although there is a difference in density, are all displayed as white shadows, with no gray scale difference; while tissue structures below -15H, such as subcutaneous fat and gas in the mastoid Displayed in black shadows, there is no grayscale difference between them.
The window level is the center position of the window. For the same window width, due to the difference of the window level, the CT value of the included CT value range is also different. For example, if the window width is 100H, when the window level is 0H, the CT value ranges from -50 to +50H; if the window level is +35H, the CT value ranges from -15 to +85H. Usually, to observe the structure of a certain tissue and the lesions that occur, the CT value of the tissue should be used as the window level. For example, the CT value of brain matter is about +35H, so when observing brain tissue and its lesions, it is appropriate to choose a window position of +35H.
It can be seen from the above that at the same CT scanning level, various gray-scale images for observing different tissue structures can be obtained due to the selection of different window widths and window levels.
Common CT values correspond to the list of organs:
Window Width and Window Level in Image Processing
The window width is the range of grayscale displayed by the image. The grayscale range of a general display is 256 levels, and the grayscale range of medical images is much larger than this range, so the display is not enough to display all the grayscale levels, and the window width needs to be used to define the grayscale range to be displayed; in
general , when the grayscale value is higher than the maximum value of the window width range, the pixel value is displayed as a white value (255); when the grayscale value is lower than the minimum value of the window width range, the pixel value is displayed as a black value (0 ); increasing the window width range can display more different gray-scale tissue structures, but will reduce the contrast between the tissues; reducing the window width range can reduce the different gray-scale tissue structures displayed, which also increases the tissue structure The contrast between them;
the center position of the window width when the window level is used; the window width only determines the range of visualization on the pixel, which is a specific value. The upper limit and lower limit of this range cannot be determined by relying on the window width alone, and cooperation is required. Use the window level to determine; for example, in the previous code: the window width is 2000, which can only indicate that the window width range is 2000, but cannot indicate whether it is from 0 to 2000, or -1000 to 1000. When the window level is set to 500, the window width 2000, it can indicate that the visible gray scale range is from -500 to 1500; 
when manually converting the gray value of pixels, you can refer to the above picture.
void ConvertDigitImageToGrayImageByWindowLevelAndWindowWidth(short* digitImage, short* grayImage, int size, int window_level, int window_width){
double rate = 256.0 / window_width;
for (size_t i = 0; i < size; i++){
int tmp = 128.0 + (digitImage[i] - window_level)*rate;
if (tmp < 0){
tmp = 0;
}
else if (tmp > 255) {
tmp = 255;
}
grayImage[i] = tmp;
}
}
Window width and level information in DICOM files
| tag value | meaning |
|---|---|
| 0028,1050 | window level |
| 0028,1051 | window width |
| 0028,1052 | Intercept b of CT Numerical Scaling Thread Transformation |
| 0028,1053 | Slope k of CT numerical scaling thread transformation |
Commonly used window width and window level table
| parts | window width | window level |
|---|---|---|
| head scan | 90 | 35 |
| skull augmentation | 85 | 40 |
| skull window | 1600 | 450 |
| joint bone window | 1600 | 550 |
| joint soft tissue window | 350 | 35 |
| sinus soft tissue window | 2000 | 450 |
| mastoid | 4000 | 650 |
| intervertebral disc soft tissue window | 350 | 40 |
| intervertebral disc bone window | 2000 | 450 |
| lung window | 1500 | -400 |
| mediastinal window | 350 | 40 |
| lung high resolution | 1500 | -500 |
| liver | 200 | 50 |
| kidney | 350 | 40 |
| Chest | 400 | 40 |
| bone window | 1500 | 300 |
| Blood vessel | 600 | 300 |
| abdomen | 400 | 60 |
1. During chest CT examination, the window width and window position of lung window and mediastinal window are:
(1) lung window WW1500—2000HU, WL-450—600HU
(2) mediastinal window WW250—350HU, WL30—50HU
2. Bone window, soft tissue window window width, window level
(1) Bone window WW1000—1500HU, WL250—350HU
(2) Soft tissue window WW300—500HU, WL40—60HU
3. Window width and window level settings
Use different window widths for different parts It can fully reflect the anatomical content and image appearance of lesions: head
: the window width of brain tissue is set at 80 Hu~100 Hu, and the window level is 30 Hu~40 Hu; the window width of
pituitary and sella region lesions should be set at 200 Hu ~250 Hu, window level 45 Hu~50 Hu;
patients with cerebral hemorrhage can change the window width to 80 Hu~140 Hu, window level 30 Hu~50 Hu;
patients with cerebral infarction usually use narrow window 60 Hu, which can improve the detection rate of lesions , to clearly show infarction and softening lesions.
The maxillofacial orbital window width is set at 150 Hu~250 Hu, and the window level is 30 Hu~40 Hu.
When observing bones, the window width is 150 Hu~2 000 Hu, and the
window The window width and window level of the neck, nasopharynx, and throat are usually set at 300 Hu~350 Hu and 30 Hu~50 Hu, which can meet the anatomy and display of lesions in this part. Chest: The mediastinal window and
lung The mediastinal window can observe the position of the heart and great vessels, the size of the lymph nodes in the mediastinum, the mass in the mediastinum and the adjacent relationship of these structures. The available window width of the mediastinum window is set to be 300 Hu~500 Hu, and the window level is 30 Hu~50 Hu ,
The lung window width is 1 300 Hu~1 700 Hu, and the window level is -600 Hu~-800 Hu. On the basis of the above-mentioned basic window width, if the pulmonary fissure and pulmonary blood vessels are observed, the window width can be narrowed and the window level can be lowered. The lung window is clearer than the mediastinal window for the observation of mass shape, lobulation, pleural indentation, and spiculation.
Abdomen: The window width is usually set at 300 Hu~500 Hu for abdominal examination, and the window level is 30 Hu~50 Hu
. In spleen CT examination, the window width should be appropriately narrowed to better detect lesions. The window width is 100 Hu~200 Hu, and the window level is 30 Hu~45 Hu. Because of the high water content in the kidney, the commonly used window width is 200 Hu~300 Hu
. , the window level is 25 Hu~35 Hu,
the pancreas is generally 300 Hu~350 Hu, the window level is 35 Hu~50 Hu, the narrow window is 120 Hu~150 Hu and 30 Hu~40 Hu, spine and limbs: conventional spine scan
shows For soft tissue next to the spine, the window width is 200 Hu~350 Hu, and the window level is 35 Hu~45 Hu. The
bone window is 800 Hu~2 000 Hu wide, and the window level is 250 Hu~500 Hu. , the muscle is about 40 Hu, and the fat is mostly below -50 Hu.
References
1. CT value and commonly used CT window width and window level