Letter to the Editor

Pulse Oximetry in MRI Units To the Editor: Magnetic Resonance Imaging (MRI) is a developed, noninvasive diagnostic technique that employs a strong magnetic field and radio frequency pulses to generate high-contrast images. During MRI, patients are out of view, and a means of continuous monitoring becomes necessary, especially in critically ill patients and in children who require sedation or general anesthesia. Thus, patient monitoring during scanning causes problems because the ferrous metal contained in most monitoring equipment and the radio frequency energy emitted from light-emitting diodes, electrical wires, and monitors distort the magnetic field and interfere with the formation of MRI images. We have designed a simple technique for radio frequency isolation of a standard pulse oximeter for use in a 1.5T MRI unit (Magnetom, Siemens, Erlangen, West Germany). In standard pulse oximeters, two light-emitting diodes, red and infrared, are used to generate dual light beams that are recorded by a photodetector. The relative amount of each color adsorbed by the pulsing arterial blood indicates the amount of arterial hemoglobin saturation (Nellcor Inc., Product Information Division, Haywood, CA). In this study, continuous arterial saturation was monitored by a pulse oximeter (Nellcor 100, Haywood, CA) in 20 patients, ages 3 months to 60 years, undergoing MRI examination. A disposable light-emitting diode sensor was attached to the patient’s toe, and its short electrical line was attached to a preamplifier. The preamplifier cable was connected to the oximeter by a second 6-meter wire. The cable never touched the patient and was kept parallel to the magnet. The preamplifier and the oximeter were placed at 1 meter and 5 meters, respectively, from the middle of the scanner within the magnet room. The monitor was placed behind the observers’ window. The preamplifier and the connections between wires were wrapped with aluminum foil. The oximeter had no aluminum radio frequency shielding and ran on a battery. No oxygen or sedative drugs were used in the study. The 1.5T MRI unit did not interfere with the operation of the pulse oximeter. Oxygen saturation was monitored before the patient entered the magnet room, and SaO, values remained constant throughout the examination. An EKG monitor (Sirecust 404, Siemens, Erlangen, West Germany) validated the heart rate shown on the oximeter. All images were free of artifacts, and their quality was indistinguishable from studies in which the oximeter was not used. J. Clin. Anesth., vol. 2, Jan/Feb 1990

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Letter to the Editor

We concluded that pulse oximetry can be used to detect harmful conditions and prevent injury in a MRI unit.

potentially

Ida Salvo, MD Associate Professor Sergio Colombo, MD Resident Tania Capocasa, MD Resident Giorgio Torri, MD Professor Department of Anesthesiology Istituto Scientifico S. Raffaele Universita di Milan0 Milano, Italy

ANNOUNCEMENTS

Third Annual International Monitoring and Related Technology Conference: March 18-23, 1990, Orford, Quebec, Canada, Cheribourg Resort. Information: Yolande Bourassa-Auger, Department of Anaesthesia, University of Sherbrooke School of Medicine, 3001, 12th Avenue North, Fleurimont (Quebec), JIH 5N4 Canada Tel: (819) 563-5555, ext. 4950. The meeting is sponsored by the Department of Anaesthesia of the University of Sherbrooke School of Medicine, with support from related health care product manufacturers. Sixth International Symposium on Computing in Anesthesia and Intensive Care, President, Tsutomu Oyama, M.D.: April 15-18, 1991, Hamamatsu, Japan. Information: the Organizing Anesthesiology, Medicine, 3600 431-31, Japan.

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Kazuyuki Ikeda, M.D., Chairman of Committee, c/o Department of Hamamatsu University School of Handa-cho, Hamamatsu, Shizuoka,

J. Clin. Anesth.,

vol. 2, Jan/Feb

1990

17th Annual Harvard Medical School Course on Intensive Care Medicine: June 24-27, 1999, Omni Parker House Hotel, Boston, MA. “The Art and Science of Critical Care.” Information: Bart Chernow, M.D., FACP (Course Director), Department of Anaesthesia, Harvard Medical School/Massachusetts General Hospital, 32 Fruit Street, Boston, MA 02114 Tel: (617) 726-2858. Fourth International Symposium of Anesthesia and Intensive Care: November 7-9, 1990, Dead Sea, Israel. Information: Dr. G. Gurman, Division of Anesthesiology, Soroka Medical Center, Beer-Sheva 84 101, Israel. A program of international speakers, plus a chance to enjoy the unique facilities of the Dead Sea and surroundings.

Pulse oximetry in MRI units.

Letter to the Editor Pulse Oximetry in MRI Units To the Editor: Magnetic Resonance Imaging (MRI) is a developed, noninvasive diagnostic technique tha...
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