MRI Scans Diagnostic

Date: 2015-10-07; view: 459.

Magnetic resonance imaging (MRI) uses computer-generated radio waves and a powerful magnetic field to produce detailed images of body structures including tissues, organs, bones, and nerves. Neurological uses include the diagnosis of brain and spinal cord tumors, eye disease, inflammation, infection, and vascular irregularities that may lead to stroke. MRI can also detect and monitor degenerative disorders such as multiple sclerosis and can document brain injury from trauma.

The equipment houses a hollow tube that is surrounded by a very large cylindrical magnet. The patient, who must remain still during the test, lies on a special table that is slid into the tube.

MRI scanning equipment creates a magnetic field around the body strong enough to temporarily realign water molecules in the tissues. Radio waves are then passed through the body to detect the “relaxation” of the molecules back to a random alignment and trigger a resonance signal at different angles within the body. A computer processes this resonance into either a three-dimensional picture or a two-dimensional “slice” of the tissue being scanned, and differentiates between bone, soft tissues and fluid-filled spaces by their water content and structural properties. A contrast dye may be used to enhance visibility of certain areas or tissues. Depending on the part(s) of the body to be scanned, MRI can take up to an hour to complete. Due to the incredibly strong magnetic field generated by an MRI, patients with implanted medical devices such as a pacemaker should avoid the test.

Positron emission tomography (PET) scans provide two- and three-dimensional pictures of brain activity by measuring radioactive isotopes that are injected into the bloodstream. PET scans of the brain are used to detect highlight tumors and diseased tissue, measure cellular or tissue metabolism, show blood flow, evaluate patients who have seizure disorders that do not respond to medical therapy and patients with certain memory disorders, and determine brain changes following injury or drug abuse, among other uses. A low-level radioactive isotope, which binds to chemicals that flow to the brain, is injected into the bloodstream and can be traced as the brain performs different functions. The patient lies still while overhead sensors detect gamma rays in the body's tissues. A computer processes the information and displays it on a video monitor or on film. Using different compounds, more than one brain function can be traced simultaneously.

Single photon emission computed tomography (SPECT), a nuclear imaging test involving blood flow to tissue, is used to evaluate certain brain functions. The test may be ordered as a follow-up to an MRI to diagnose tumors, infections, degenerative spinal disease, and stress fractures. As with a PET scan, a radioactive isotope, which binds to chemicals that flow to the brain, is injected intravenously into the body. Areas of increased blood flow will collect more of the isotope. As the patient lies on a table, a gamma camera rotates around the head and records where the radioisotope has travelled. That information is converted by computer into cross-sectional slices that are stacked to produce a detailed three-dimensional image of blood flow and activity within the brain.

5. Answer the questions according to the text:

1. What can MRI detect?

2. What does the equipment house?

3. 3. Is the procedure of MRI complex?

4. How is it performed?

5. How long does it take?

6. What does PET provide?

7. Why is SPECT important for diagnostic imaging?

6. Read about ultrasound diagnostic and answer the following questions:

1. What is ultrasound?

2. Is ultrasound effective for diagnostic?

3. How is ultrasound performed?

4. How long does the test take?

5. Why do scientists develop diagnostic research?