Then the preparations before inspection mainly include:
1. Remove high-density objects on the body surface, and strive for the patient's cooperation as much as possible during the examination.
2. There was no barium meal examination of digestive tract and no history of swallowing high-density films one week before the examination.
3. If contrast examination requires contrast agent allergy test, etc.
Followed by CT parameters:
1. Density resolution. Density resolution is affected by scanning layer thickness, noise, photon number, object size and detector sensitivity, in which noise is the most important factor.
2. Time resolution. Time resolution: refers to the time required for CT equipment to collect and reconstruct a complete layer of image data. The shorter the time, the higher the time resolution.
3. Spatial resolution. It is influenced by pixel, focus, detector size, reconstruction range and matrix, scanning slice thickness, pitch and reconstruction algorithm. Spatial resolution is closely related to the size of pixels. The larger the pixels, the fewer the number, and the lower the spatial resolution. On the contrary, the smaller and more pixels, the higher the spatial resolution.
4. Noise. Noise shows that the CT value of each pixel in a uniform object image is uneven, and the image is granular, which reduces the density resolution.
5. Artifacts. Mainly in two aspects: (1) equipment reasons; (2) Patients' causes: motion artifact and harness hardening artifact.
6. Selection of window width and window level.
7. Appropriate scanning range.