What Is the Difference Between a CT Scan and a Colonoscopy?
- CT scans utilize X-rays to form images of organs and tissues inside the body (for example, abdominal organs, brain, chest, lungs, heart) while colonoscopy is a procedure that can visualize only the inside surface of the colon.
- CT scans use radiation (X-rays) to form images while colonoscopy uses a flexible instrument equipped with a light and camera to form images, and it may be used to collect biopsy of colon tissues and/or polyp removal.
- CT scans are quick, painless, noninvasive and do not require extensive preparations; in contrast, colonoscopy is invasive (the flexible instrument is inserted through the anus) and usually requires a person to modify their diet for a time while following instructions about how to clean out the colon before starting.
- Individuals undergoing colonoscopy usually are sedated, while most patients undergoing a CT do not require sedation.
- Both procedures are relatively safe; CT does expose you to radiation (at a safe level) and if IV contrast dye is used to enhance CT images, some people may be allergic or have the possibility of kidney damage. A colonoscopy carries the risk of bowel perforation and allergic reaction to anesthesia drugs.
- Side effects of colonoscopy may include a short period of crampy pain and abdominal swelling; if a biopsy is performed, there may be some blood in stool. If perforation of the bowel occurs, infection and/or bleeding can also happen. For CTs, side effects may include allergic reactions to IV dye, damage to the kidneys from the IV dye and leakage of dye at the IV site.
- CT scans can be done on individuals at almost any age, while the majority of colonoscopy procedures are done on adults.
What Is a CT Scan?
CT, or CAT scans, are special X-ray tests that produce cross-sectional images of the body using X-rays and a computer. CT scans are also referred to as computerized axial tomography. CT was developed independently by a British engineer named Sir Godfrey Hounsfield and Dr. Alan Cormack. It has become a mainstay for diagnosing medical diseases. For their work, Hounsfield and Cormack were jointly awarded the Nobel Prize in 1979.
CT scanners first began to be installed in 1974. CT scanners have vastly improved patient comfort because a scan can be done quickly. Improvements have led to higher-resolution images, which assist the doctor in making a diagnosis. For example, the CT scan can help doctors to visualize small nodules or tumors, which they cannot see with a plain film X-ray.
CT Scan Facts
- CT scan images allow the doctor to look at the inside of the body just as one would look at the inside of a loaf of bread by slicing it. This type of special X-ray, in a sense, takes "pictures" of slices of the body so doctors can look right at the area of interest. CT scans are frequently used to evaluate the brain, neck, spine, chest, abdomen, pelvis, and sinuses.
- CT is a commonly performed procedure. Scanners are found not only in hospital X-ray departments, but also in outpatient offices.
- CT has revolutionized medicine because it allows doctors to see diseases that, in the past, could often only be found at surgery or at autopsy. CT is noninvasive, safe, and well-tolerated. It provides a highly detailed look at many different parts of the body.
- If one looks at a standard X-ray image or radiograph (such as a chest X-ray), it appears as if they are looking through the body. CT and MRI are similar to each other, but provide a much different view of the body than an X-ray does. CT and MRI produce cross-sectional images that appear to open the body up, allowing the doctor to look at it from the inside. MRI uses a magnetic field and radio waves to produce images, while CT uses X-rays to produce images. Plain X-rays are an inexpensive, quick test and are accurate at diagnosing things such as pneumonia, arthritis, and fractures. CT and MRI better to evaluate soft tissues such as the brain, liver, and abdominal organs, as well as to visualize subtle abnormalities that may not be apparent on regular X-ray tests.
- People often have CT scans to further evaluate an abnormality seen on another test such as an X-ray or an ultrasound. They may also have a CT to check for specific symptoms such as pain or dizziness. People with cancer may have a CT to evaluate the spread of disease.
- A head or brain CT is used to evaluate the various structures of the brain to look for a mass, stroke, area of bleeding, or blood vessel abnormality. It is also sometimes used to look at the skull.
- A neck CT checks the soft tissues of the neck and is frequently used to study a lump or mass in the neck or to look for enlarged lymph nodes or glands.
- CT of the chest is frequently used to further study an abnormality on a plain chest X-ray. It is also often used to look for enlarged lymph nodes.
- Abdominal and pelvic CT looks at the abdominal and pelvic organs (such as the liver, spleen, kidneys, pancreas, and adrenal glands) and the gastrointestinal tract. These studies are often ordered to check for a cause of pain and sometimes to follow up on an abnormality seen on another test such as an ultrasound.
- A sinus CT exam is used to both diagnose sinus disease and to detect a narrowing or obstruction in the sinus drainage pathway.
- A spine CT test is most commonly used to detect a herniated disc or narrowing of the spinal canal (spinal stenosis) in people with neck, arm, back, and/or leg pain. It is also used to detect a fracture or break in the spine.
What Is a Colonoscopy Procedure?
A colonoscopy is a procedure to look at the inside of the colon. The colon is the large intestine and the last part of the digestive system. The colon dries, processes, and eliminates the waste left after the small intestine has absorbed the nutrients in food. The colon is about 3 to 5 feet long. It travels from the lower right corner of the abdomen (where the small intestine ends) up to the liver, across the body to the spleen in the upper left corner and then down to form the rectum and anus.
The doctor will use an instrument called the colonoscope to perform a colonoscopy. It is a long (about 5 feet), thin (about 1 inch), flexible fiberoptic camera that allows the doctor to visualize the entire colon.
A doctor may order a colonoscopy to investigate many different diseases of the colon.
Colonoscopy is best known for its use as a screening tool for the early detection of colorectal cancer.
- Colorectal cancer is the second leading cause of cancer deaths in the United States.
- Colon cancer develops from growths within the wall of the intestine such as polyps or tumors.
- These growths often take 5 to 10 years to develop and may not cause many symptoms.
- A person may not have any symptoms of colon cancer, but having a close relative with the disease increases the risk for the disease compared to the general public.
- Most people develop polyps after age 50, so the American College of Gastroenterology (the digestive specialists) recommends screening examinations every 10 years for early detection and removal of these cancer-causing growths after that age.
Colonoscopy is also used to investigate other diseases of the colon.
- Colonoscopy may be used to find the place and cause of bleeding as well as to check areas for irritation or sores in the colon.
- These colon problems can cause unexplained changes in bowel habits.
- Pain, bloody diarrhea, and weight loss can be caused by inflammation of the bowel, which may be the result of Crohn's disease or ulcerative colitis.
- These inflammatory digestive diseases tend to occur in young adults and, if undetected, can produce chronic symptoms and increase the risk of colon cancer.
Colonoscopy is used when there is concern a disease of the colon may exist.
- The doctor may recommend this test if other screening tests such as a manual rectal examination, a fecal occult blood test (a test that detects blood in the feces), or a barium enema (a test in which barium is used to make the colon visible on an X-ray) suggest that further information is needed to make a diagnosis.
- A colonoscopy may be required when symptoms of digestive disease or other warning signs are present.
- Rectal bleeding (which may appear as bright red, very dark, or black)
- Pain in the lower abdomen
- Changes in bowel habits
- Non-dietary weight loss
- A new test called Cologuard, a stool-based colorectal screening test that detects the presence of red blood cells and DNA mutations, may indicate the presence of certain kinds of abnormal growths that may be cancers such as colon cancer or precursors to cancer. If this test reveals the possibility of colon cancer, a colonoscopy may be necessary.
Only doctors who specialize in the study of digestive or rectal diseases, have special training in endoscopy, and are certified to perform colonoscopy qualify to perform this procedure.
- The American Society for Gastrointestinal Endoscopy suggests that a doctor perform at least 200 procedures to become technically competent at diagnostic colonoscopy.
What Are the Risks of a CT Scan vs. a Colonoscopy?
CT Scan Risks
CT scan is a very low-risk procedure.
- The patient will be exposed to radiation when undergoing a CT scan. However, it is a safe level.
- The biggest potential risk is with a contrast (also called dye) injection that is sometimes used in CT scanning. This contrast can help distinguish normal tissues from abnormal tissues. It also helps to help distinguish blood vessels from other structures such as lymph nodes. Like any medication, some people can have a serious allergic reaction to the contrast. The chance of a fatal reaction to the contrast is about 1 in 100,000. Those at increased risk may require special pretreatment and should have the test in a hospital setting. Anyone who has had a prior contrast reaction or severe allergic reaction to other medications, has asthma or emphysema, or has severe heart disease is at increased risk for a contrast reaction and is referred to a hospital X-ray department for the exam. Besides an allergic reaction, the intravenous dye can damage the kidneys, particularly if an individual already has marginal kidney disease. Usually, the patient is advised to drink plenty of fluids to help flush the dye out of their system.
- Any time an injection is done into a vein, there is a risk of the contrast leaking outside of the vein under the skin. If a large amount of contrast leaks under the skin, in rare cases, this can cause the skin to break down.
As with any procedure, there are risks associated with a colonoscopy. Before obtaining your consent for the procedure, the doctor will tell you about the potential risks.
- The most common side effects are cramping pain and abdominal swelling caused by the air used to inflate the colon during the procedure. This air is expelled shortly after the procedure, and these symptoms generally resolve without medical treatment.
- If a biopsy is performed during the procedure, the patient may see small amounts of blood in the bowel movements after the examination. This may last a few days.
- Though rare, there is potential for the colonoscope to injure the intestinal wall, causing perforation, infection, or bleeding.
- Although this test is very helpful in finding the cause of many digestive diseases, abnormalities can go undetected. Factors that can affect this include the completeness of the bowel preparation before the procedure, the skill of the operator of the colonoscope, and the patient's anatomy.
- When this test is performed, the patient will be given sedating medications to make the test more comfortable. Whenever a medication is given, a risk of an allergic reaction or side effect of the medication itself is present. These IV medications are given under medical supervision, and the patient will be monitored during the procedure to lessen the risk of medication-related complications.
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