Body Computed Tomography
Body CAT, body CT scan, body CAT (computerized axial tomography) scan
*Computed tomography (or computerized axial tomography) is an examination that uses X-ray to obtain a cross sectional image of the human body.
*When X-rays are irradiated on the human body, some of the rays are absorbed and some pass through the body to produce an image. In plain X-ray imaging, the film directly absorbs penetrated X-rays. In CAT scanning, an electronic device called a "detector array" absorbs the penetrated X-rays, measures the X-ray amount, and transmits the data to a computer system. A sophisticated computer system, in turn, calculates and analyzes data from each detector in each level, and finally reconstructs multiple, two-dimensional, cross-sectional images. An X-ray source and a CAT scan detector rotate around the patient to obtain each cross-sectional image.
*CT scan images represent the density and atomic number of human tissue just like general X-ray imaging, such as chest and bone X-rays. The denser the tissue, and the higher the atomic number, the whiter the CAT image is. Bone and calcium appear white; air in the lungs appears black; water, blood, and internal organs such as liver, kidneys, and intestines appear gray; and fat tissue appears dark gray.
*Types of body CAT scans:
1.Chest CAT scan
2.Abdominal CAT scan
3.Pelvis CAT scan
Provides detailed, two-dimensional images with great clarity. This method provides higher quality images of many types of tissue, including those of the lungs, bones, soft tissue, and blood vessels.
Fast. In case of trauma, CAT scan can reveal internal bleeding and other life-threatening injuries quickly.
Simple, painless, and non-invasive
Sensitive in detecting traumatic injuries, cancer, and many other diseases
Cost-effective imaging tool for a wide range of clinical problems (when compared to MRI)
It can distinguish normal from abnormal structures accurately. It is useful in guiding biopsies, in fluid removal/aspiration, in drainage of abscesses, and in other minimally invasive procedures and radiotherapy.
It can make three-dimensional images.
Diagnosing many different cancers of the lungs, liver, kidneys, and pancreas. It can be used to confirm the presence of a tumor, measure its size, precise location, nature, and the extent of the tumor's involvement with nearby tissue. CAT scanning can be used to distinguish between benign and malignant tumors (cancer) in some cases. (But confirmative diagnosis should be made by a biopsy or other tests.)
Planning radiation therapy for cancer
Guiding biopsies, fluid withdrawal, etc.
Screening trauma victims. CAT scan can be used to detect internal hemorrhaging and injuries to the spleen, liver, kidneys, lungs, or other internal organs, as well as fractures, especially of the spine and small bones
Measuring bone mineral density to detect osteoporosis
Evaluating vascular diseases
Detecting abscesses, infections, inflammations
Detecting congenital anomalies and birth defect
To further diagnose the abnormalities shown on chest and abdominal X-ray
Chest CAT scan:
1. Lung cancer
6. Traumatic injuries, fractures
7. Pleural effusion
8. Pericardial effusion
Abdominal CAT scan:
1. Cancer/tumor of internal organs such as liver, kidney, colon, stomach, pancreas, spleen, gallbladder, intestine, colon, and peritoneum
2. Traumatic injuries
5. Bowel obstruction
6. Inflammatory bowel disease
Pelvis CT scan:
1. Tumor/cancer of pelvic organs such as uterus, uterine cervix, ovaries, bladder, prostate gland, seminal vesicles
2. Pelvic fluid collection
3. Traumatic injuries, fracture
5. Congenital anomalies
You will be asked to lie on the CAT table.
Your arms will be raised above your head.
After proper positioning, the technologist will move to the console room, and start exposing X-ray to your body.
Once the X-ray tube rotates around your body 360 degrees to take one cross- sectional image, the table will move a little bit to get the next slice.
You will be asked to hold your breath at each scanning.
You will be alone in the exam room during X-ray exposure, but you can talk and listen to your technologist using the intercom, or by raising your hands to communicate. The technologist will watch you during the scanning through a glass window and video camera.
If a contrast medium is required to make organs and blood vessels stand out, it will be injected into your vein during the exam.
The exam usually takes from ten minutes to one half hour.
Wear comfortable, loose-fitting clothing.
Take off your clothes in the examining room and put on hospital gown. Any metal objects, such as zippers, snaps, and accessories around your body can interfere with quality imaging.
For contrast enhanced CAT scanning, you should not eat or drink for one or more hours before the exam. A contrast agent will be injected into your blood stream a moment before scanning. If you have had any allergic reactions to the contrast medium, certain medications, iodine, and foods, or if you have a history of kidney problems, asthma, thyroid problems, diabetes, or a heart condition, you will be asked to inform your technologist or doctor.
For abdominal/pelvic CAT scanning, you may need to avoid food or drink for several hours. You may be asked to swallow a liquid contrast agent to better see the stomach, small bowel, and colon. Sometimes, the contrast agent will be administered via enema for studying your colon, or by vaginal tampon to evaluate the uterine cervix.
Lie still on the examining table until the technologist asks you to get down.
If you are pregnant or suspect pregnancy, you should inform your doctor, technologist, or radiologist.
A radiologist (a physician specialist trained to interpret CAT images or other radiology exams, such as X-ray, MRI, mammography, etc.) reviews the CAT scan and reports the results to your personal doctor.
The physician's office informs patients when the results are in, and what the results are. The office uses the results as a reference in evaluating and treating patients.
Radiation exposure. Radiation exposure during a CAT examination is equal to a year's worth of natural background radiation (i.e., from radon gas in our homes, soil, or from cosmic rays.) It is much more than the radiation exposure from general X-ray studies, such as chest and skull X-rays, but it is less than that from a barium enema, an upper GI series, or cardiac catheterization. The benefits of CT study outweigh the risk of radiation exposure. But in the case of children, special care should be taken to expose them to only necessary amounts of radiation, because growing children are more sensitive to radiation hazard.
Adverse reactions to contrast agents given intravenously:
1. Allergic reactions such as rash, hives, itching. Usually self-limiting; antihistamine can be given.
2. Anaphylactic reaction -- causing difficulty breathing, swelling in the throat, or other parts of the body -- is potentially life threatening. It is treated with epinephrine, corticosteroids, and antihistamine. It is very rare. Radiology departments are well trained to deal with anaphylactic reactions.
3. Kidney failure, especially if the patient is taking Glucophage (metformin) for diabetes.
Nursing mothers cannot start breast-feeding for 24 hours after receiving the contrast medium intravenously.
Bone, air, fat, and other tissue are easily distinguished with CAT scanning because they appear distinctly due to different densities. But it is difficult to distinguish body organs, tumor, cancer, blood vessels, muscle, and fluid from one another. Injection of a contrast medium can increase the capability of differentiating soft tissue. Sometimes MRI can be a better imaging method for evaluating soft tissue.
CAT scans only provide axial cross-sections. When the longitudinal cross- sections are needed to evaluate a problem, such as the extent of prostate cancer growth or cervix cancer spread, CAT scan can play only a limited role. MRI may be needed instead.