Magnetic Resonance Imaging (MRI)
An equally impressive technology, magnetic resonance imaging or MRI, has greatly improved the sensitivity and specificity of diagnostic imaging, particularly in structures such as the liver, brain, spinal cord, and joint spaces. A great advantage of MRI is that the patient is not exposed to x-rays. The images are created with the use of strong magnetic fields, radiofrequency transducers (called coils), and computer assisted image processing. To date, no any side effects have been reported by use of superconducting magnets or radiofrequency pulses in the diagnostic range.
Solutions such as gadolinium are sometimes injected intravenously into an arm vein, as contrast agents to enhance lesions. Few adverse drug events are reported with these agents. Prior to the MR examination, patients are asked to fill out a screening questionnaire to identify any indwelling magnetic materials (metal fragments, shunt regulators, cardiac pacemaker, or other devices) that may not be safely placed in the magnetic field. Many devices, despite containing metal, can be safely imaged. During the examination, which takes an average of thirty minutes, a "knocking" sound can be heard. This is a normal effect of the gradient coils responding to the different fields. Despite this noise, most patients can easily tolerate the procedure. As with the CT scan, a technologist is always in close observation and intercom communication with the patient throughout the procedure.