Monday, August 6, 2012

What is an MRI?

MRI is stand for Magnetic Resonance Imaging. An MRI 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 where the scanning is performed. The MRI unit looks like a large cylindrical (tube-shaped) with an open-ended tunnel running through the middle. MRI scanners, like X-rays machine and CT scanners, are basically doctors use to take images of your insides so that they can figure out what’s ailing you. An MRI can provides images of the human body as if it had been sliced like a loaf of bread. The slices can be in any direction, and can be a thin as a couple of millimeters.

Basically it involves a powerful but harmless magnetic field and radiowaves like the kind that transmit your favorite FM music. The combination of radio waves and magnetic field produces very clear images of body structures such as the brain, spine, knee, kidney, liver, blood vessels, heart and other important structures.

When you arrive at the MRI room, you will be asked to put on a patient gown and to remove all personal possessions such as your watch, wallet and car keys or metallic items such as dentures, pins, and put your things in a locker outside the scan room.
It's very important not to take those things to the scan room because the MRI scanner is a large magnet that is on all of the time and it could be affected by a magnet in the examining room. For example, the information on your credit cards will be erased if you have them in your pocket during the exam.

You'll be asked to lie down on the padded table.Then the radiographer will position you inside the magnet so that the appropriate part of your body is ready to be scanned. You'll be given a pair of earplugs to decrease the noise encountered. Your head, chest, and arms may be held with straps to help you stay still. During the exam, you will be able to talk with the radiographer/radiologist by an intercom and they will be able to watch you through a glass window (control panel).

You may hear very loud clanking and thumping sounds that the machine makes as the radiographer adjust the radio frequencies and other controls. These sounds are completely normal. What you have to do during the exam is lie as still as possible. People who get nervous in small places (claustrophobic) may need medicine to help them relax while having an MRI scan. Very active children may require some relaxing medication (sedation) prior to the exam to help them stay still.

An MRI scan can be used as an extremely accurate method of disease detection throughout the body. In the head, trauma to the brain can be seen as bleeding or swelling. Other abnormalities often found include brain aneurysms stroke, tumors of the brain, as well as tumors or inflammation of the spine.

Patients who have heart pacemakers, metal implants, or metal chips or clips in or around the eyeballs cannot be scanned with an MRI because of the risk that the magnet may move the metal in these areas. Similarly, patients with artificial heart valves, metallic ear implants, bullet fragments, and chemotherapy or insulin pumps should not have MRI scanning.

For some procedures, contrast agents, such as gadolinium, are used to increase the accuracy of the images. The MRI scanning time depends on the exact area of the body studied, but ranges from half an hour to an hour and a half. While the MRI procedure itself causes no pain, having to lie still for the length of the procedure might cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure such as surgery. The radiographer will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.

When your the scan has been completed, the table will slide out of the scanner and you will be assisted off the table. You should move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness from lying flat for the length of the procedure

MRI scan technique has not changed anything about your body or its chemistry, you’re free to move around and you can have as many MRI scans as often as is necessary to diagnose your ailment and track your recovery after treatment. There is no risk of ionizing radiation during an MRI procedure because radiation is not used.
The decision whether to use MRI or CT is based according to the density of the body tissue that needs to be seen. Softer tissues that have more water molecules or hydrogen atoms in them are better seen by MRI.

MR image of the brain

Advantages of MRI:
1) A CAT scan uses x-rays to build up a picture. MRI uses a magnetic field to do the same and has not known side effects related to radiation exposure. MRI scan does not expose either patient or radiographer to potentially harmful radiation.

2) MRI has much higher detail in the soft tissues.

3) One of the greatest advantages of MRI is the ability to change the sharpness of the black, white and gray of the images by making small changes in the radio waves and the magnetic fields. Different settings will highlight different types of tissue.

4) MRI offers the ability to change the imaging plane without moving the patient. Most MRI machines can produce images in any plane. CT cannot do this.

5) Contrast agents are used in both MRI and CT, however MRI contrast does not contain iodine. There are fewer documented cases of reactions to MRI contrast and it is considered to be safer than x-ray contrast, which is iodinated.

6) For purposes of tumor detection and identification, MRI is generally superior. However, CT usually is more widely available, faster, much less expensive, and may be less likely to require the person to be sedated or anesthetized.

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