Study type: Medical/biological study (experimental study)

Superficial- and deep-tissue temperature increases in anesthetized dogs during exposure to high specific absorption rates in a 1.5-T MR imager. med./bio.

Published in: Radiology 1988; 167 (2): 551-554

Aim of study (acc. to author)

To measure superficial- and deep-tissue heating in dogs during high specific absorption rate radiofrequency irradiation to see whether significant temperature changes could be produced by a 1.5-T clinical magnetic resonance imager. The radiofrequency power output employed was 6.3 times that required for routine imaging.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 64 MHz
Exposure duration: 25.6 min
Exposure 2: 64 MHz
Exposure duration: 25.6 min
Exposure 3: 64 MHz
Exposure duration: 25.6 min
Exposure 4: 64 MHz
Exposure duration: 25.6 min
Exposure 5: 64 MHz
Exposure duration: 35.6 min

Exposure 1

Main characteristics
Frequency 64 MHz
Type
Exposure duration 25.6 min
Exposure setup
Exposure source
  • 1.5T MRI with quadrature coil, 150 cm long.
Setup Dogs placed in the magnet bore within the confines of the RF coils.
Parameters
Measurand Value Type Method Mass Remarks
SAR 5.9 mW/g mean calculated - -
power 16 W maximum - - -
magnetic flux density 1.5 T - - - -

Exposure 2

Main characteristics
Frequency 64 MHz
Type
Exposure duration 25.6 min
Exposure setup
Exposure source
  • 1.5T MRI with quadrature coil, 150 cm long.
Setup Dogs placed in the magnet bore within the confines of the RF coils.
Parameters
Measurand Value Type Method Mass Remarks
SAR 6.5 mW/g mean calculated - -
power 16 W maximum - - -
magnetic flux density 1.5 T - - - -

Exposure 3

Main characteristics
Frequency 64 MHz
Type
Exposure duration 25.6 min
Exposure setup
Exposure source
  • 1.5T MRI with quadrature coil, 150 cm long.
Setup Dogs placed in the magnet bore within the confines of the RF coils.
Parameters
Measurand Value Type Method Mass Remarks
SAR 8.1 mW/g mean calculated - -
power 16 W maximum - - -
magnetic flux density 1.5 T - - - -

Exposure 4

Main characteristics
Frequency 64 MHz
Type
Exposure duration 25.6 min
Exposure setup
Exposure source
  • 1.5T MRI with quadrature coil, 150 cm long.
Setup Dogs placed in the magnet bore within the confines of the RF coils.
Parameters
Measurand Value Type Method Mass Remarks
SAR 10.5 mW/g mean calculated - -
power 16 W maximum - - -
magnetic flux density 1.5 T - - - -

Exposure 5

Main characteristics
Frequency 64 MHz
Type
Exposure duration 35.6 min
Exposure setup
Exposure source
  • 1.5T MRI with quadrature coil, 150 cm long.
Setup Dogs placed in the magnet bore within the confines of the RF coils.
Parameters
Measurand Value Type Method Mass Remarks
SAR 8.3 mW/g mean calculated - -
power 16 W maximum - - -
magnetic flux density 1.5 T - - - -

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • before exposure
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

In each dog, there was a linear temperature increase of several degrees during radiofrequency irradiation; the maximal average change was 4.6°C in the urinary bladder. The temperature elevation was slightly greater in deep tissues than in superficial tissues. The calculated specific absorption rate averaged 7.9 W/kg for all five dogs.
These data argue for continued caution in the design and operation of imagers capable of high specific absorption rates, particularly when they are used for imaging infants or patients with altered thermoregulatory capability.

Study character:

Study funded by