Radio frequency inhomogeneity compensation technology

Summary

Applications to High Field MRI (3T)

Nuclear magnetic resonance in the forms of magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) is used for research and diagnostic purposes. Problems can occur with either MRI or MRS when the RF coil generates an inhomogeneous field (also known as the B1 magnetic field), causing a decreased signal-to-noise ratio and a subsequent reduction in the measurement accuracy.

Current methods for correcting this problem are based on the modulation of RF waveform or the use of multiple coils. RF-based compensation requires pulses that are either longer and/or require more power than uncompensated pulses.

The disadvantage is that an increased RF power deposition increases the safety risk and the chance that the person being imaged will be heated to a point of discomfort or danger. The disadvantage of using multiple coils is that there is often not enough space for more than one coil, as is the case with clinical imaging of the head.

Researchers at the NRC have developed two approaches to compensate for inhomogeneous B1 fields generated by RF coils.

The first approach involves a Bz field where the spatial variation is correlated with that of the B1 field (U.S. patent 5,914,599). The advantage to this approach is that it can operate over a wide bandwidth and range of B1 intensities without modification of the B1 pulse. The second approach utilizes a rapid oscillatory phase modulation to an existing RF pulse waveform (U.S. patent 6,049,206). This approach does not require an additional Bz field, but it also does not have the minimum RF power advantage of the first approach.

Advantages

  • Compensates for RF inhomogeneity (an increasing problem with high field MRI)
  • Modulation of the Bz field does not increase the RF power deposition which is crucial for high field MRI
  • Simplifies the RF sequence and shortens the pulse sequence

Opportunity

The opportunity lies in the development of unique low power applications for high field MRI. The technology is available for exclusive or non-exclusive license.

Contact

Claude Larose, Portfolio Business Advisor
Telephone: 514-496-6173
EmailClaude.Larose@nrc-cnrc.gc.ca