Safety considerations in MR imaging

Article Abstract:

Magnetic resonance (MR) imaging is a diagnostic technique that applies magnetic fields to areas of the body for measuring different magnetic properties inherent in elements. From the measurements obtained, images of tissues, flow rates, and other information can be constructed. A number of safety concerns, both for the patient and the practitioner, should be considered when using MR in the clinical setting, and these are reviewed. The biologic effects of static magnetic fields constitute an area of great controversy. There is only indirect evidence that the application of magnetic fields during MR can cause any biologic damage. The physical effects of magnetic fields are well known. Objects in the MR area may be attracted to the field and even small objects may become hazardous projectiles. While patients with metal implants should be safe, patients with implants that are sensitive to magnetism in their operation, such as pacemakers, should not undergo MR imaging or be near it. Magnetic shielding and the use of metal detectors can reduce the hazards of static magnetic fields. Exposure to MR causes rapid switching of magnetic fields in the body, which can produce electrical currents. This may result in thermal (heat) effects that are not significant and nonthermal effects such as stimulation of nerve or muscle cells. MR imaging can produce noise of an intense level. Earplugs are useful when using MR and ways of reducing this noise are being researched. MR machines themselves present possible hazards. Superconductive MR systems use liquid helium that could possibly be released in extreme circumstances. The psychological effects of undergoing MR imaging should also be considered. Contrast agents such as gadopentetate dimeglumine (Gd-DTPA) have potential side effects and patients should be aware of them, especially pregnant women and patients with kidney problems. No definitive indications of excess danger to these people has been shown, however. There are a number of safety factors to be considered when using MR and an understanding of them can reduce possible hazards to patients and health care workers. (Consumer Summary produced by Reliance Medical Information, Inc.)

Safety and security measures, Complications and side effects, Medical imaging equipment, editorial

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Patellar tracking abnormalities: clinical experience with kinematic MR imaging in 130 patients

Article Abstract:

Patellar tracking abnormalities (malalignment of the knee) are a common cause of knee pain for which a precise diagnosis is often difficult. Knee symptoms and the findings of clinical examinations can be the same for various knee diagnoses and an individual patient may have more than one problem. Researchers developed a kinematic (biomechanical movement over time) magnetic resonance (MR) imaging technique to obtain multiple images of the patellofemoral (knee to upper leg) joint during early stages of knee flexion. This MR technique permits evaluation of alignment of the patella when the knee is at less than 30 degrees flexion. This crucial range of motion has not been detectable with other imaging methods. One hundred and thirty patients who had symptoms of patellar tracking abnormalities (a total of 235 symptomatic knees) and 14 healthy control subjects (28 asymptomatic knees) participated in the study. Normal patellar tracking was observed with kinematic MR imaging in all of the control subjects. Of the symptomatic knee joints 93 percent were found to have patellar malalignment. Kinematic MR imaging demonstrated patellar malalignment in 87 percent of the 23 symptomatic patellofemoral joints that previously had been operated on to correct abnormal patellar position. This percentage of abnormally aligned postoperative patellofemoral joints suggests that surgical intervention for realignment of the patella may not always be successful. It was concluded that kinematic MR imaging of the patellofemoral joint is useful in evaluating treatments and in selecting patients who would be most likely to benefit from particular forms of therapy.

Methods, Joints, Abnormalities, Biomechanics, Range of motion, Patella

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Knees of trained long-distance runners: MR imaging before and after competition

Article Abstract:

Magnetic resonance (MR) imaging is a diagnostic technique that uses the unique magnetic properties of each element to differentiate among chemicals, cells and tissues in the body. It can either provide visual images of the body part or it can measure signal intensities for various substances and denote amounts of activity or changes in them. A recent study using MR found that signal intensities increased in the menisci (crescent-shaped pieces of cartilage in the joint) of the knee after subjects jogged on a treadmill for 30 minutes. These changes indicate that the jogging caused fluid to accumulate in the knee joint, which could eventually lead to degenerative changes if such stress continued on a chronic basis. The current study examined the knees of trained long-distance runners, using MR imaging, before and after a long-distance running competition. The knees of five runners were examined with MR to measure signal intensities in the menisci and to examine the knee ligaments. Results showed that the knee ligaments in all runners were normal both before and after the running. The meniscal signal intensities were absent in three runners, grade I in one runner, and grade II in the other runner prior to their runs. The intensities were unchanged following the run. No increases in knee joint fluid levels were detected after the running. These results indicate that trained runners have adapted to the stress of their running, and that their knees are not adversely affected by the activity. (Consumer Summary produced by Reliance Medical Information, Inc.)

Injuries, Physiological aspects, Knee injuries, Runners (Sports)

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