MRI Scan: Traditional versus open


When Karla had an MRI scan a decade ago, she was warned that she might feel claustrophobic inside the large tunnel-like machine. In fact, she was more bothered by the loud jackhammer noises that bombarded her periodically.

When Karla's four-year-old son had an MRI, she had no concern about either claustrophobia or clanging noises. He sat on her lap watching television while the scan was taken.

MRI stands for magnetic resonance imaging, a procedure that has assumed an important role in medical imaging in the past two decades. As the technology evolves, MRI scanners have become increasingly versatile and useful in detecting and diagnosing disease throughout the body while making the experience less stressful to the patient.

Medical imaging, starting with the introduction of the X-ray in 1895, was a major breakthrough, allowing doctors to look inside the body to visualize a broken bone in the leg or a tumor in the lung.

On their own, X-rays are best at detecting problems in bones and joints, but imaging capability was significantly expanded with the introduction of computer tomography or CT scans and the use of radio-dense contrast materials to allow the visualization of less dense anatomical structures. This technology is now able to create a sequence of X-ray images, giving doctors a high-quality, detailed image of tissue anywhere in the body.

For the majority of cases, the X-ray remains the most practical and inexpensive option and new digital techniques are making X-rays sharper, clearer and easier to store, but the MRI has emerged as another major development in medical imaging.

No dangerous radiation

A traditional MRI scanner is a tube surrounded by a giant circular magnet. After removal of jewelry, watches and all other metal objects, the patient is placed on a bed that is inserted into the tube and asked to remain as motionless as possible while the scan is performed, sometimes an hour or longer.

The strong magnetic field of the MRI machine aligns hydrogen atoms in the body, which respond to radio waves that are then processed by a computer into detailed, high-contrast images in any plane, greatly improving a physician's ability to visualize the brain or any other body part.

Using magnetism rather than potentially dangerous radiation, an MRI scan adds an important measure of safety and medical imaging. An MRI scan has no known adverse effects and can be repeated any number of times with no danger to the patient or staff.

In addition, MRI is very sensitive, capable of picking up lesions and tumors that may not show up, even on a CT scan.

Magnetic resonance imaging is more expensive than other procedures and because of the strong magnetic field, cannot be used on patients with metal in their bodies, such as pacemakers, shrapnel, artificial joins or inner ear implants.

The major drawback, until recently, was the configuration of MRI machines, requiring the patient to lie supine and motionless for a long period in a confined area within the large magnetic tube.

Individuals with claustrophobic tendencies may not be able to tolerate a traditional MRI scan, at least without sedation. An obese person will not fit comfortably within the tube and an uncooperative child will not remain still long enough.

Responding to this drawback, scientists have developed open configuration MRI scanners. Although these machines were available as early as the late 1980s, they have only recently become widely used.

There are various configurations, but all provide some open space around the patient to reduce anxiety and in some cases, allow the physician to perform surgical procedures.

Open MRI machines are clearly more user friendly. They virtually eliminate the threat of claustrophobia and the disconcerting clanging of traditional machines is replaced by a soft tap.

Whereas a traditional MRI may be large enough to require its own building or a semi-trailer truck, one open MRI model is small enough and light enough to be installed in a physician's office. The C-shaped magnet in these machines is useful for diagnosis of arm or leg injuries.

The MRI used for Karla's son consists of a room-sized magnet, allowing family members to accompany the patient during the procedure. Its manufacturer calls it "the most patient-friendly scanner in the world," with colorful backdrops of Disney characters and beach and mountain scenes.

Another version of this scanner is an MRI operating room which allows doctors to walk inside and perform surgical procedures.

A standup MRI, introduced in the fall of 2000, allows diagnosis of problems that only show up during weight-bearing activities. If you have pain only while you're standing in a certain position, for example, the standup MRI can show what is happening to soft tissues in that position.

Another important use of this scanner is cardiovascular: Obtaining images of the beating heart while the patient is standing rather than lying down. The manufacturer recently demonstrated a prototype of an MRI-compatible treadmill for use inside this upright MRI scanner.

Many open configuration machines, particularly the early ones, have less powerful magnetic fields and, as a result, produce less accurate and detailed images. In most cases, doctors prefer traditional closed machines for more precise uses such as early stroke detection or examination of the central nervous system. For some orthopedic uses, on the other hand, the less powerful magnetic field of an open scanner may offer advantages in visualizing non-fatty tissues.

Some of the newer open-configuration MRI scanners have addressed this limitation, offering image resolution comparable to that of traditional machines. The standup MRI, in fact, uses the same magnet as a traditional MRI, and some doctors say the image is actually superior because it allows the patient, who is more relaxed because of the reduction of anxiety, to assume the precise position that is causing the pain.

MRI technology is rapidly changing. The patient benefits from the less threatening environment of the open scanners while the doctor, regardless of which type of MRI is used, can be assured of getting high-quality images that allow precise diagnosis and effective treatment.

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