Sagittal MR images of the lumbar spine through the intervertebral foraminae (between short arrows). (A) The fat within the foramen (star) is of high intensity on the T1-weighted image. It provides a bright background to the low intensity of the exiting nerve root (long arrow). Note the radicular veins in the lower third of the foramen (vertical arrow). (B) On sagittal T2WI through the lateral recesses, the obliquely oriented nerve roots are demonstrated on their course toward the intervertebral foraminae.
3. Scan time is prolonged compared with CT.
4. Contraindications prevent certain patients from entering the MRI system.
5. Patients with claustrophobia cannot tolerate the study and need anesthesia.
Contraindications for MR imaging are dictated by the strong magnetic field in the system and by the electromagnetic radiation involved. They include both passive and active implants. The passive implants are usually made of metal, and the active include electromagnetic devices implanted in the body. At present absolute contraindications include cochlear implants, certain pacemakers, and electromagnetic devices such as neurostimulators and automatic cardioverters.
Most other implanted medical devices have become MRI-compatible during the past 20 years. Certain cardiac pacemakers have been recognized as safe under the MR system influence, and there is ongoing research to ascertain the compatibility of other active electromagnetic devices with MRI exposure. Nevertheless specific precautions are still needed prior to the patient's entrance into the MRI system. Exact details of any implants should be thoroughly checked.
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