Medical Tests
Common Medical Tests:
Colonoscopy is a procedure that enables an examiner (usually a gastroenterologist) to evaluate the appearance of the inside of the colon (large bowel). This is accomplished by inserting a flexible tube that is about the thickness of a finger into the anus, and then advancing it slowly, under visual control, into the rectum and through the colon. It is performed with the visual control of either looking through the instrument or with viewing a TV monitor. This test may be done for a variety of reasons. Most often it is done to investigate the finding of blood in the stool, abdominal pain, diarrhea, a change in the bowel habits, or an abnormality found on colon x- ray or a CT scan. Certain individuals with previous history of polyps or colon cancer and certain individuals with family history of particular malignancies or colon problems may be advised to have periodic colonoscopies because they are at a greater risk of polyps or colon cancer.
CT scan
A computerized axial tomography scan is more commonly known by its abbreviated name, CT scan or CAT scan. It is an x-ray procedure which combines many x-ray images with the aid of a computer to generate cross-sectional views and, if needed, three-dimensional images of the internal organs and structures of the body. A CT scan is used to define normal and abnormal structures in the body and/or assist in procedures by helping to accurately guide the placement of instruments or treatments. A large donut-shaped x-ray machine takes x-ray images at many different angles around the body. These images are processed by a computer to produce cross-sectional pictures of the body. In each of these pictures the body is seen as an x-ray “slice” of the body, which is recorded on a film. This recorded image is called a tomogram. “Computerized Axial Tomography” refers to the recorded tomogram “sections” at different levels of the body.
Imagine the body as a loaf of bread and you are looking at one end of the loaf. As you remove each slice of bread, you can see the entire surface of that slice from the crust to the center. The body is seen on CT scan slices in a similar fashion from the skin to the central part of the body being examined. When these levels are further “added” together, a three-dimensional picture of an organ or abnormal body structure can be obtained.
MRI scan
An MRI (or magnetic resonance imaging) scan is a radiology technique that uses magnetism, radio waves, and a computer to produce images of body structures. The MRI scanner is a tube surrounded by a giant circular magnet. The patient is placed on a moveable bed that is inserted into the magnet. The magnet creates a strong magnetic field that aligns the protons of hydrogen atoms, which are then exposed to a beam of radio waves. This spins the various protons of the body, and they produce a faint signal that is detected by the receiver portion of the MRI scanner. The receiver information is processed by a computer, and an image is produced.
The image and resolution produced by MRI is quite detailed and can detect tiny changes of structures within the body. For some procedures, contrast agents, such as gadolinium, are used to increase the accuracy of the images.
Ultrasound
An ultrasound test is a radiology technique, which uses high- frequency sound waves to produce images of the organs and structures of the body. The sound waves are sent through body tissues with a device called a transducer. The transducer is placed directly on top of the skin, which has a gel applied to the surface. The sound waves that are sent by the transducer through the body are then reflected by internal structures as “echoes.” These echoes return to the transducer and are transmitted electrically onto a viewing monitor. The echo images are then recorded on a plane film and can also be recorded on videotape. After the ultrasound, the gel is easily wiped off.
The technical term for ultrasound testing and recording is “sonography.” Ultrasound testing is painless and harmless. Ultrasound tests involve no radiation and studies have not revealed any adverse effects.
Tuberculosis Skin Test
The tuberculosis skin test (also known as the tuberculin or PPD test) is a test used to determine if someone has developed an immune response to the bacterium that causes tuberculosis (TB). This response can occur if someone currently has TB or if they were exposed to it in the past. The tuberculin skin test is based on the fact that infection with M. tuberculosis produces a delayed-type hypersensitivity skin reaction to certain components of the bacterium. The components of the organism are contained in extracts of culture filtrates and are the core elements of the classic tuberculin PPD (also known as purified protein derivative). This PPD material is used for skin testing for tuberculosis. Reaction in the skin to tuberculin PPD begins when specialized immune cells, called T cells, which have been sensitized by prior infection, are recruited by the immune system to the skin site where they release chemical messengers called lymphokines. These lymphokines induce induration (a hard, raised area with clearly defined margins at and around the injection site) through local vasodilation edema, fibrin deposition, and recruitment of other inflammatory cells to the area.
