MRI is a noninvasive imaging procedure that creates detailed, high resolution images of your body’s organs, tissues and skeletal system. MRI uses a magnetic field and radio waves to construct these images. No radiation is involved. The MRI machine is a large, tube-shaped magnet. When you lie inside the machine, the magnetic field temporarily aligns all the water molecules in your body. Radio waves cause these aligned particles to produce very faint signals, which are used to create cross-sectional images of your body — like slices in a loaf of bread. The MRI machine can combine these slices to produce 3-D images that may be viewed from many different angles.
The strength of the magnet is a key element to MRI scanning. Tesla (T) is the unit of measurement used to quality the strength of the MRI magnetic field. The stronger the magnet, the higher the image quality.
| Memorial Hermann Imaging Centers offer cutting-edge MRI technology, including: |
| 3.0T |
3.0T Open Bore |
| 1.5T |
1.0 Open |
With twice the strength of a conventional magnet, 3.0T MRI produces images with extreme detail and clarity while revealing fine changes in body structures of physiological processes. It can often pick up early chemical changes that other tests may not find. Our new 3T MRI services feature the Philips InteraAchieva 3.0T MR system and the Siemens Magnetom Verio Open Bore. Both machines allow for more precise diagnosis, better pre-surgical plannign and enhanced patient care.
3T MRI is used for these applications:
- Breast biopsy
- Breast MRI
- Neurological
- Musculoskeletal
- Whole body imaging
The Magnetom Verio Open Bore 3T MRI at our Richmond Avenue location is the only one of its kind in Texas. The bore - or the long tube - is over 2 feet wide and only 4 feet long. This means that your head can remain outside of the bore during procedures not involving your head, neck or upper spine. But for those procedures, the wider bore gives you about a foot of headroom so you won’t feel like you are nose-to-nose with the top of the machine.
This larger bore size makes the Verio 3T MRI an ideal choice for children, or for patients who are claustrophobic, anxious, obese or elderly.
The Verio 3T MRI also uses a contrast-free technique, optimized for imaging the kidneys — a distinct benefit for patients with renal failure.
Our 1.5T MRI systems provide state-of-the-art diagnostic efficiency and image accuracy. The 1.5T strength results in high-quality images for diagnostic confidence, 3x greater power that the conventional open MRI.
Patient comfort is a hallmark of our Philips Panorama 1.0T Open MRI. Unlike the standard closed MRI an Open MRI is more focused on patient comfort. Because it is open an all sides, you may find this scanner easier to tolerate. The Open MRI eliminates any anxiety or claustrophobic effects you may find with traditional MRI scanners.
Magnetic resonance imaging; Nuclear magnetic resonance (NMR) imaging
You may be asked to wear a hospital gown or clothing without metal fasteners (such as sweatpants and a t-shirt).
You will be asked to lie on a narrow table, which slides into the middle of the MRI machine. If you have a fear of confined spaces (claustrophobia), tell your doctor before the exam. You may be prescribed a mild sedative, or your doctor may recommend an "open" MRI, in which the machine is not as close to the body.
Small devices, called coils, may be placed around the head, arm, or leg, or other areas to be studied. These devices help send and receive the radio waves, and improve the quality of the images.
Certain exams require that a special dye (contrast) be given before the test. The dye is usually given through an intravenous line (IV) in your hand or forearm. The contrast helps the radiologist see certain areas more clearly.
During the MRI, the person who operates the machine will watch you from a room next door. Several sets of images are usually need, each taking from 2 to 15 minutes. Depending on the areas being studied and type of equipment, the exam may take 1 hour or longer.
An MRI can be performed immediately after other imaging studies. Depending on the area of interest, the patient may be asked to fast for 4 - 6 hours prior to the scan. Other preparations are usually not needed.
The strong magnetic fields created during an MRI can interfere with certain implants, particularly pacemakers. Persons with cardiac pacemakers can not receive an MRI and should not enter an MRI area.
If you have any of the following metallic objects in your body, you should not get an MRI:
- Inner ear (cochlear) implants
- Brain aneurysm clips
- Certain artificial heart valves
- Older vascular stents
- Recently placed artificial joints
You will be asked to sign a consent form that says you do not have any of these items in your body.
Before an MRI, sheet metal workers or any person that may have been exposed to small metal fragments should receive a skull x-ray to check for metal in the eyes.
Because of the strong magnets, certain metallic objects are not allowed into the room.
- Items such as jewelry, watches, credit cards, and hearing aids can be damaged.
- Pins, hairpins, metal zippers, and similar metallic items can distort the images.
- Removable dental work should be taken out just prior to the scan.
- When the MRI magnet is turned on, pens, pocketknives, and eyeglasses may fly across the room. This can be dangerous, so such items are not allowed into the scanner area.
An MRI exam causes no pain. Some people may become anxious when inside the scanner. If you have difficulty lying still or are very anxious, you may be given a mild sedative. Excessive movement can blur MRI images and cause errors.
The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises when turned on. Ear plugs are usually given to help reduce the noise.
An intercom in the scanner allows you to speak to the person operating the exam at any time. Some MRIs have televisions and special headphones that you can use to help the time pass.
There is no recovery time, unless sedation was necessary. After an MRI scan, you can resume your normal diet, activity, and medications.
Combining MRIs with other imaging methods can often help the doctor make a more definitive diagnosis.
MRI images taken after a special dye (contrast) is delivered into the body may provide additional information about the blood vessels.
An MRA, or magnetic resonance angiogram, is a form of magnetic resonance imaging, which creates three-dimensional pictures of blood vessels. It is often used when traditional angiography cannot be done.
There is no ionizing radiation involved in MRI, and there have been no documented significant side effects of the magnetic fields and radio waves used on the human body to date.
The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. The person operating the machine will monitor your heart rate and breathing as needed.
MRI is usually not recommended for acute trauma situations, because traction and life-support equipment cannot safely enter the scanner area and the exam can take quite a bit of time.
People have been harmed in MRI machines when they did not remove metal objects from their clothes or when metal objects were left in the room by others.
For more information, see the specific MRI topics: