Thermal effects of high-field (1.5 tesla) magnetic resonance imaging of the spine. Clinical experience above a specific absorption rate of 0.4 W/kg.
Current safety guidelines recommend limiting the exposure to radiofrequency (RF) radiation used for clinical magnetic resonance imaging to a whole body average specific absorption rate (SAR) of 0.4 W/kg. Since it may be desirable to image with SARs that exceed this level during MRI of the spine, we evaluated the thermal responses associated with these procedures. Body and skin temperatures were determined in 25 patients immediately before and after MRI. Since the eye is particularly susceptible to thermal injury, corneal temperature was also measured. High-resolution thermography was performed on three subjects to evaluate the surface heating pattern and identify potential thermal 'hot spots'. A 1.5 tesla/64 MHz MRI system with quadrature transmission and reception was used iN this study. The whole body average specific absorption rate ranged from 0.5 to 1.3 W/kg. Ambient conditions were room temperature 20-24 degrees C and relative humidity between 40 and 50 per cent. There was a slight but statistically significant (p less than 0.01) increase in body temperature after MRI (36.5 +/- 0.4 to 36.7 +/- 0.4 degrees C). Temperatures of the hand (30.4 +/- 1.4 to 31.2 +/- 1.0 degrees C), positioning isocenter (32.1 +/- 0.6 to 32.9 +/- 0.5), and cornea (32.5 +/- 0.6 to 32.9 +/- 0.5 degrees C) also increased a statistically significant amount. Thermographic imaging revealed normal heating patterns with no surface 'hot spots'. We conclude that the temperature changes associated with MRI of the spine at the SARs we studied were well below known thresholds for adverse effects and do not appear to be harmful to patients.
Shellock
F G
FG
Department of Diagnostic Radiology, Cedars-Sinai Medical Center, Los Angeles, CA.
Schaefer
D J
DJ
Grundfest
W
W
Crues
J V
JV
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001831:Body Temperature; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D013131:Spine / Q000033:anatomy & histology*; D013817:Thermography