|
|||||||
|
MR Imaging (MRI) - HeadWhat is MR Imaging (MRI) of the Head?MRI (magnetic resonance imaging) uses radio waves and a strong magnetic field rather than An MRI exam causes no pain, and the magnetic fields produce no known tissue damage of any kind. The MR scanner may make loud tapping or knocking noises at times during the exam; using earplugs prevents problems that may occur with this noise. You will be able to communicate with the technologist or radiologist at any time using an intercom. What are some common uses of the procedure?MRI is the most sensitive exam for brain tumors,strokes, and certain chronic disorders of the nervous system such as multiple sclerosis. In addition, it is a useful means of documenting brain abnormalities in patients with dementia, and it is commonly used for patients with disease of the pituitary gland. MRI can detect tiny areas of tissue abnormality in patients with disease of the eyes or the inner ear. How should I prepare for the procedure?Because the strong magnetic field used for MRI will pull on any metal object implanted in the body,
MRI staff will ask whether you have a prosthetic hip, heart pacemaker (or artificial heart valve), implanted port (brand names
Port-o-cath, Infusaport, Lifeport), intrauterine device (IUD), or any metal plates, pins, screws, or surgical staples in your body.
Tattoos and permanent eyeliner may also create a problem. You will be asked if you have ever had a bullet or shrapnel in your body, or
ever worked with metal. If there is any question of metal fragments, you may be asked to have an The radiologist or technologist may ask about drug allergies and whether head surgery has been done in the past. If you might be pregnant, this should be mentioned. Some patients who undergo MRI of the head in an enclosed unit may feel confined or claustrophobic. If you are not easily reassured, a sedative may be administered. Roughly 1 in 20 patients will require medication. What does the equipment look like?The conventional MRI unit is a closed cylindrical magnet in which the patient must lie totally still
for several seconds at a time, and consequently may feel Examples of the radiography equipment that may be used are shown at the top of this page. How does the procedure work?MRI is a unique imaging method because, unlike the usual radiographs How is the procedure performed?
When the exam is over the patient is asked to wait until the images are examined to determine if more images are needed. How will I prepare for my MRI exam?You will typically receive a gown to wear during your MRI study. Before entering the examining room, any friend or relative accompanying you will be asked questions regarding the presence of implants and will be instructed to remove all metal objects from pockets and hair. Additionally, this individual will need to fill out a screening form to ensure that he or she may safely enter the MR system room. Before the exam you will be asked to fill out a screening form asking about anything that might create a health risk or interfere with imaging. Items that may create a health hazard or other problem during an MRI exam include:
Items that need to be removed by patients and individuals before entering the MR system room include:
Objects that may interfere with image quality if close to the area being scanned include:
Some patients who have MRI in an enclosed scanner may feel confined, closed-in, and frightened. Perhaps one in twenty will require a sedative to remain calm. Today, many patients avoid this problem when examined in one of the newer MRI units that have a more "open" design. Some MRI centers permit a relative or friend to be present in the MR system room, which also has a calming effect. If patients are properly prepared and know what to expect, it is almost always possible to complete the examination even if a conventional MRI system is used. Pregnancy and MRI In general, there is no known risk of using MRI in pregnant patients. However, MRI is reserved for use in pregnant patients only to address very important problems or suspected abnormalities. In any case, MRI is very likely safer for the fetus than imaging with x-rays. You should be sure to inform your radiologist if you are breast-feeding at the time of a scheduled
MRI study and are to receive an MR contrast agent. One option under this circumstance is to pump breast milk before the study, to be
used until injected contrast material has cleared from the body, which typically takes about 24 hours. What will I experience during the procedure?MRI causes no pain, but there may be discomfort from being closed in or from the need to remain still. You may notice a warm feeling in the area under examination; this is normal, but if it bothers you the radiologist or technologist should be told. If a contrast injection is needed, there may be discomfort at the injection site, and you may have a cool sensation at the site during the injection. Most bothersome to many patients are the loud tapping or knocking noises heard at certain phases of imaging. Ear plugs may help. When the knocking and the slight vibration that may accompany it stops, you can reposition your arms. Who interprets the results and how do I get them?A radiologist, who is a physician experienced in MRI and other radiology examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician. The personal physician's office will inform the patient on how to obtain their results. New technology also allows for distribution of diagnostic reports and referral images over the Internet at some facilities. What are the benefits vs. risks?Benefits
Risks
What are the limitations of MRI of the Head?Bone is better imaged by conventional The powerful magnetic field of the MR system will attract iron-containing (also known as ferromagnetic) objects and may cause them to move suddenly and with great force. This can pose a possible risk to the patient or anyone in an object's flight path. Great care is taken to be certain that objects such as "ferromagnetic" screwdrivers and oxygen tanks are not brought into the MR system area. It is vital that you remove any metallic belongings in advance of an MRI exam, including watches, jewelry, and items of clothing that have metallic threads or fasteners. The powerful magnetic field of the MR system will pull on any iron-containing object in the body, such as certain medication pumps or aneurysm clips. Every MRI facility has a protocol that, when carefully followed, will ensure that the MRI technologist and radiologist knows about the presence of metallic implants and materials so that special precautions can be taken. In some unusual cases the exam may have to be canceled. An example is MRI of the head when a "ferromagnetic" aneurysm clip is present, because there is a risk of the clip moving or being dislodged. The magnetic field may damage an external hearing aid or cause a heart pacemaker or electrical stimulator to malfunction. If you have a bullet or other metallic fragment in your body there is a potential risk that it could change position, possibly causing injury. A metallic implant or other object may distort the MR images or make it difficult for the MRI system to "tune" to your body. This may be unavoidable, but if the radiologist knows about it, allowance can be made when interpreting the images. For some MRI studies a contrast material called gadolinium may be injected into a vein to help interpret the exam. Unlike contrast agents used in x-ray studies, a gadolinium contrast agent does not contain iodine and therefore rarely causes an allergic reaction or other problem.
|
The patient is placed on a sliding table
and a radio antenna device called a surface coil is positioned around the upper part of the head. After positioning the patient
with the head inside the MRI gantry, the radiologist and technologist leave the room and the individual MRI sequences are performed.
The patient is able to communicate with the radiologist or technologist at any time using an intercom. Also, many MRI centers allow a
friend or, if a child is being examined, a parent, into the room. Depending on how many images are needed, the exam will generally
take from 15 to 45 minutes, although a very detailed study may take longer. You will be asked not to move during the actual imaging
process, but between sequences some movement is allowed. Patients are generally required to remain still for only a few seconds at a
time. Some patients will require an injection of a contrast material to enhance the visibility of certain tissues or blood vessels. A
small needle connected to an intravenous line is placed in an arm or hand vein. A saline solution will drip through the intravenous
line to prevent clotting until the contrast material is injected about 