Magnetic R~SOIWZCS? Imaging. Vol. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 10, pp. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 689-694. 1992 Printed in the USA. All rights reserved. 0730-725X/92 $5.00 + .OO C o p yrig ht 0 1592 Pergamon Press Ltd. l zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Original Contribution zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA BIO-EFFECTS OF HIGH MAGNETIC FIELDS: A STUDY USING A SIMPLE ANIMAL MODEL JEREMY WEISS, * RICHARD C. HERRICK,*~ KATHERINE H. TABER, *t CHARLES CONTANT,$ AND GORDON A. PLISHKER*$ *Baylor College of Medicine, Magnetic Resonance Center, The Woodlands, TX 77380, USA Departments of tRadiology, SNeurosurgery, and $Neurology, Baylor College of Medicine, Houston, TX 77030, USA zyxwvutsrqp The desire to do clinical imaging and spectroscopy at magnetic field strengths greater than 2 Tesla (T) necessi- tates investigation of possible bioeffects at these high fields. A simple T-maze was utilized to evaluate the aver- sive effects of exposure to three levels of static magnetic field (0,1.5, and 4 T). The right arm of the maze extended into the center of a 30-cm horizontal bore magnet, while the left arm extended into a mock magnet bore with the same dimensions. The self-shielded design of the magnet reduces the fringe field to zero within 1 m of the bore, placing the start box of the maze outside the 5-G line of the magnet. Each rat performed a total of ten trials at each level of magnetic field strength. A follow-up subset was run at 4 T with the maze reversed. At 0 T, the rats entered the magnet freely. No significant differences from the control were observed at 1.5 T. At 4 T, however, in 97% of the trials the rats would not enter the magnet. In the maze-reversed subset a majority of the rats turned toward the magnet, indicating that they had learned an aversive response from the previous trials at 4 T. How- ever, in only 4 decisions out of 58 did the rats actually enter the magnet. Eighteen decisions to turn around were made at the edge of the magnet in a region of strong field gradients (up to 13 T/m) and a field strength up to 1.75 T. We propose that the aversive response is most likely due to magnetic induction effects caused by motion in a strong magnetic field gradient. Keywords: Magnetic resonance; Biosafety; Static magnetic field effects. There is a growing concern over the bioeffects of ex- posure to high magnetic fields, fueled in part by re- ports that technicians working around 4-T magnets sometimes experience dizziness, nausea, vertigo, and visual phosphenes.’ In addition, it has been known for some time that high magnetic field pulses can be used to directly stimulate nerves and brain.2 Recently, direct muscle stimulation has been reported during an MRI scan with magnetic field time rate of change zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA (dB/dt) of 61 T/sec.3 Experimental demonstration of the effects of expo- sure to the magnetic fields used in magnetic resonance imaging (MRI) on spatial orientation performance have been difficult to obtain. No effects have been found at very low (0.15 T) or intermediate (1.5 T) magnetic field strength on spatial memory.4 How- ever, short term exposure (3-4 hr) at 1.6 T increased investigatory behavior in rats, while exposure to 0.3 T depressed investigatory behavior. 5 The large fringe field associated with the higher field strength magnets has made standard radial and T maze testing impossible in the past. The recent in- troduction of a high field (up to 4.5 T) self-shielded magnet with virtually no fringe field has made such studies possible. In the present study, the behavior of rats in a standard T maze is evaluated. These experi- ments are designed to simulate the exposure of a hu- man patient entering a magnet for diagnostic purposes. METHODS Adult male Long Evans Hooded rats (50-57 days of age, 200-225 g, n = 32) were housed in groups of four under standard conditions. Within each group, the rats were distinctly marked with iodine tincture to maintain individual identification. Prior to a testing period, each group was transported to the testing site (“2 miles). Four rats were eliminated from the study due to lack of cooperation. A simple T maze was constructed from clear acrylic, RECENED g/24/91; ACCEPTED3/16/92. Magnetic Resonance Center, 9450 Grogan’s Mill Rd., Suite Address correspondence to Dr. Richard Herrick, Baylor 110, The Woodlands, TX 77380, USA. 689