Magnetic Resonance Imaging

Definition

A noninvasive technique, skeletal magnetic resonance imaging (MRI) produces clear and sensitive images of bone and soft tissue. The scan provides superior contrast of body tissues and allows imaging of multiple planes, including direct sagittal and coronal views in regions that can’t be easily visualized with X-rays or computed tomography scans. MRI eliminates any risks associated with exposure to X-ray beams and causes no known harm to cells.

There are two types of MRI. Closed MRI uses scanning equipment that resembles a tunnel like chamber. While open MRI uses more sophisticated equipment. During open MRI, the patient can comfortably see the surroundings from all views while the scan is in progress. This is ideal for patients who are claustrophobic or anxious, children, elderly, and the very obese.

Purpose

• To evaluate bony and soft-tissue tumors.
• To identify changes in bone marrow composition.
• To identify spinal disorders.

Patient Preparation

1. Make sure the scanner can accommodate the patient’s weight and abdominal girth.
2. Explain to the patient that skeletal MRI assesses bone and soft tissue. Tell him who will perform the test and where it will take place.
3. Explain that the test takes 30 to 90 minutes.
4. Explain to the patient that although MRI is painless and involves no exposure to radiation from the scanner, a contrast medium may be used, depending on the type of tissue being studied.
5. If the patient is claustrophobic or if extensive time is required for scanning, explain to him that a mild sedative may be administered to reduce anxiety. Open scanners have been developed for use on the patient with extreme claustrophobia or morbid obesity, but tests using such machine take longer.
6. An anesthesiologist may need to be present to monitor a heavily sedated patient.
7. Tell the patient that he must lie flat, and describe the test procedure.
8. Explain to the patient that he’ll hear the scanner clicking, whirring, and thumping as it moves inside its housing.
9. Reassure the patient that he’ll be able to communicate with the technician at all times.
10. Instruct the patient to remove all metallic objects, including jewelry, hairpins, or watches.
11. Stop I.V. infusion pumps, feeding tubes with metal tips, pulmonary artery catheters, and similar devices before the test.
12. Ask whether the patient has any surgically implanted joints, pins, clips, valves, pumps, or pacemakers containing metal that could be attracted to strong MRI magnet. If he does, he won’t be able to have the test.
13. Note and report all allergies.
14. Make sure that the patient or a responsible family member has signed an informed consent form, if required.

MRI Procedure

1. At the scanner room door, check the patient one last time for metal objects.
2. The patient is placed on a narrow, padded, nonmetallic table that moves into the scanner tunnel. Fans continuously circulate air in the tunnel, and a call bell or intercom is used to maintain verbal contact.
3. Remind the patient to remain still throughout the procedure.
4. While the patient lies within the strong magnetic field, the area to be studied in stimulated with radio-frequency waves.
5. If the test is prolonged with the patient lying flat, monitor him for orthostatic hypotension.
6. Provide comfort measures and pain medication as needed and ordered because of prolonged positioning in the scanner.
7. After the test, tell the patient that he may resume his usual activity.
8. Provide emotional support to the patient with claustrophobia or anxiety over his diagnosis.

Nursing Interventions for MRI

1. Provide patient with comfort measures as needed.
2. Tell the patient to resume his normal diet and activities unless otherwise indicated.
3. Monitor vital signs.
4. Monitor the patient for orthostatic hypotension.

MRI Precautions

1. Be aware that MRI can’t be performed on a patient with a pacemaker, intracranial aneurysm clip, or other ferrous metal implants. Ventilators, I.V. infusion pumps, oxygen tanks, and other metallic or computer based equipment must be kept out of the MRI area.
2. If the patient is unstable, make sure an I.V. line without metal components is in place and that all equipment is compatible with MRI imaging. If necessary, monitor the patient’s oxygen saturation, cardiac, rhythm, and respiratory status during the test. An anesthesiologist may be needed to monitor a heavily sedated patient.
3. Make sure that the technician maintains verbal contact with the conscious patient.

MRI Interpretation

Normal Results

• MRI should reveal no evidence of pathology in bone, muscles, and joints.

Abnormal Findings

• MRI is excellent for visualizing disease of the spinal canal and cord and for identifying primary and metastatic bone tumors. It’s beneficial in anatomic delineation of muscles, ligaments, and bones. The image show superior contrast of body tissues and sharply defines healthy, benign, and malignant tissues.

Interfering Objects

• Metal objects, such as I.V. pumps, ventilators, other metallic equipment, or computer-based equipment, in the MRI area.

MRI Complications

• Orthostatic hypotension
• Anxiety
• Claustrophobia