Some bowel cancers can be detected by CT, but not all bowel cancers can be detected by CT. Usually, it is necessary for the patient to do colonoscopy, so that early bowel cancers can be detected, because when bowel cancers start to develop, the foci are usually relatively small, so under this circumstance, it is usually not possible to detect the lesions inside the intestinal tract by doing CT. Only when the intestinal cancer is bigger, or invades deeper into the intestinal wall, which may lead to localized narrowing of intestinal lumen, or thickening of intestinal wall, or may even cause incomplete intestinal obstruction, then abdominal CT will be able to find out the lesions inside the intestines, which means that intestinal cancer can be detected. In addition, it is also necessary to do colonoscopy to take pathological examination to further confirm the diagnosis, so that the diagnosis can be further clarified, so for a part of the patients who have abdominal pain, or hidden pain, frequent bowel movements and blood in stools, it is necessary to do colonoscopy or CT to carry out the examination.