Adiabatic T2 Preparation for MRI B1 Inhomogeneity

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Solution Overview

Problem

Current magnetic resonance imaging (MRI) techniques face limitations in signal-to-noise ratio (SNR) and specific absorption rate (SAR) issues, particularly with T2-weighted imaging for coronary MRA, due to magnetic field inhomogeneities and RF field imperfections, which restrict the use of high magnetic fields and lead to imaging artifacts.

Innovation Solution

The implementation of adiabatic T2 preparation sequences, which combine amplitude and frequency modulation of RF pulses to rotate magnetization independently of RF field strength, reducing sensitivity to magnetic field inhomogeneities and improving image quality by using a system controller to define adiabatic pulses and apply them in specific pulse sequences for T2-weighted imaging.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional T2 prep sequences with MLEV pulses are used, then robustness to B1 inhomogeneities is improved, but specific absorption rate (SAR) increases

Engineering Contradiction:

Improverobustness to B1 inhomogeneitiesVSAvoidspecific absorption rate

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent changes the parameters of RF pulses by using adiabatic pulses with time-varying amplitude and frequency instead of conventional fixed-parameter pulses. This allows achieving the same T2 preparation effect with reduced SAR while maintaining robustness to B1 inhomogeneities through the adiabatic condition that makes the pulse effects independent of B1 field strength variations.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If higher magnetic fields are applied, then signal-to-noise ratio is improved, but magnetic field inhomogeneities and SAR increase

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidmagnetic field inhomogeneities

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies adiabatic pulses whose effects are independent of B1 field strength over a substantial range, making the imaging sequence robust to magnetic field inhomogeneities. This allows utilizing higher magnetic fields for improved SNR while the adiabatic condition compensates for the increased field inhomogeneities and SAR concerns.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If more MLEV pulses are used, then compensation for B1 imperfections is improved, but specific absorption rate increases

Engineering Contradiction:

Improvecompensation for B1 imperfectionsVSAvoidspecific absorption rate

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

Instead of increasing the number of MLEV pulses to improve B1 compensation, the patent uses adiabatic pulses with specific amplitude and frequency modulation profiles. These pulses inherently provide robustness to B1 imperfections through the adiabatic condition while maintaining lower SAR compared to multiple MLEV pulses.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Adiabatic T2 preparation sequences enhance image contrast and reduce artifacts, improving SNR and SAR, enabling more effective T2-weighted imaging with better visualization of coronary arteries and surrounding tissues without the limitations of conventional MLEV-based methods.

Implementation Method 1

adiabatic pulses combine amplitude and frequency modulation of the RF designed to create a rotation of the magnetization in a way that is independent of the RF field strength

Methodology Applied

Scientific EffectAdiabatic passage:

Implementation Method 2

Magnetic resonance (MR) imaging systems generally use a static magnetic field (B0) and a radio frequency magnetic field (B1) to produce images

Methodology Applied

Scientific EffectMagnetic resonance:

Implementation Method 3

The T2 relaxation between the two 90° pulses provides the desired alteration of contrast between components of the sample with different T2 relaxation rates

Methodology Applied

Scientific EffectT2 relaxation:

Data Source

PatentUS7787930B2Adiabatic T2 preparation sequence for magnetic resonance imaging with reduced B1 sensitivity

Publication Date: 2010.08.31 JOHNS HOPKINS UNIVERSITY

AI summary

Adiabatic pulses that define an amplitude modulation and a frequency modulation are applied in a sequence of pulses to obtain a T2 weighted magnetic resonance image. Such an adiabatic T2 prep sequence typically includes a first 90° pulse, an even number of adiabatic pulses, and a second 90° pulse. Adiabatic pulses can be selected based on function pairs, or can be defined numerically. A magnetic resonance imaging (MRI) system includes a library of adiabatic pulse waveforms, and is configured to select a waveform and apply an RF magnetic field based on the selected pulse waveform.