Method for spectrally selective B1 insensitive T2 preparation contrast enhancement for high field magnetic resonance imaging

Inventors

Nezafat, Reza • Derbyshire, J. Andrew • Ouwerkerk, Ronald • Stuber, Matthias • McVeigh, Elliot R.

Assignees

DEPARTMENT OF HEALTH AND HUMAN SERVICES GOVERNMENT OF United States, Secretary of • Johns Hopkins University • US Department of Health and Human Services

Abstract

A T2 preparation sequence uses a segmented BIR-4 adiabatic pulse with two substantially equal delays and is insensitive to B1 field variations and can simultaneously suppress fat signals with low specific absorption rate (SAR). An adiabatic reverse half passage pulse is applied followed by a predetermined delay. An adiabatic full passage pulse is applied followed by a substantially equal delay, followed by an adiabatic half passage pulse. Fat signal suppression is achieved by increasing or decreasing either the first delay or the second delay.

Core Innovation

The invention provides a T2 preparation sequence for magnetic resonance imaging that uses a segmented BIR-4 adiabatic pulse with two substantially equal delays. This sequence is insensitive to B1 field variations and can simultaneously suppress fat signals with a low specific absorption rate (SAR). It involves applying an adiabatic reverse half passage pulse, followed by a delay, then an adiabatic full passage pulse, another substantially equal delay, and finally an adiabatic half passage pulse. Fat signal suppression is achieved by adjusting either the first or second delay.

The problem addressed by this invention arises from the limitations of conventional magnetic resonance imaging methods, especially at high magnetic fields like 3 T. Higher fields improve signal-to-noise ratio but also increase off-resonance susceptibilities, magnetic field inhomogeneities, and SAR. Traditional T2 preparation sequences, such as those using Malcom-Levitt (MLEV) pulses, can compensate for B1 imperfections but result in increased SAR, limiting their use. Additionally, conventional fat suppression methods rely on chemically selective RF pulses which increase SAR and require longer acquisition times. Hence, an improved method is needed to achieve T2 weighting and fat suppression with reduced sensitivity to magnetic field imperfections and lower SAR.

The invention overcomes these problems by providing magnetic resonance imaging methods that use adiabatic pulses configured to be spectrally selective and B1 insensitive. The symmetric arrangement of the reverse adiabatic half passage (rAHP), matched adiabatic full passage (AFP), and matched adiabatic half passage (AHP) pulses with equal or nearly equal delays minimizes sensitivity to both B0 and B1 inhomogeneities. By introducing a difference between the two delay intervals, the sequence selectively suppresses fat signals by maintaining fat magnetization in the transverse plane while returning water magnetization to the longitudinal axis, allowing fat suppression via spoiling gradients. This approach provides fat saturation with a minimal increase in sequence duration and reduced SAR, facilitating improved T2-weighted imaging at high fields.

Claims Coverage

The patent contains several independent claims covering methods, computer-readable mediums, and apparatus configurations involving sequences of matched adiabatic pulses and time interval selections.

The independent claims collectively cover methods and apparatuses using sequences of matched adiabatic pulses with symmetrically or asymmetrically timed delays, enabling T2-weighted imaging with reduced B1 sensitivity and selective fat suppression based on frequency offset between constituents like water and fat.

Stated Advantages

Documented Applications