MRI Pseudorandom RF Pulses for Low Power Imaging

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Solution Overview

Problem

Conventional MRI techniques suffer from low duty cycle, high RF energy exposure due to high flip angles, and limitations in utilizing powerful image reconstruction algorithms, particularly in achieving multiple-contrast images without prolonged magnetization/RF exposure.

Innovation Solution

Implementing a new class of pulse sequences with pseudorandom phase low flip angle RF pulses and gradient waveforms that generate pseudorandom spatial excitation, enabling high steady state transverse magnetization and efficient data acquisition, compatible with compressed sensing reconstruction methods.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If high flip angle RF pulses are used for excitation, then signal magnitude is improved, but RF power deposition increases

Engineering Contradiction:

Improvesignal magnitudeVSAvoidRF power deposition

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

The patent applies periodic RF pulses with randomized phases at high repetition rates (duty cycle up to 99%) with low flip angles (e.g., 2°), replacing conventional periodic high flip angle excitations. This periodic low flip angle excitation with randomization maintains signal magnitude while dramatically reducing RF power deposition compared to conventional high flip angle sequences.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent changes key parameters: flip angle (from high to low, e.g., 2°), phase (from deterministic to randomized), and duty cycle (from 20-50% to up to 99%). These parameter changes enable maintaining signal magnitude while reducing RF power deposition by approximately 15 times compared to conventional 30° pulses.

Inventive Principle:

Principle #35Parameter changes

2Illumination intensity

If conventional MRI sequences are used for excitation, then signal magnitude is maintained, but duty cycle is limited to 20-50%

Engineering Contradiction:

Improvesignal magnitudeVSAvoidduty cycle

Core Design Contradiction:

Illumination intensityVSProductivity

Solution Approach 1:

The patent implements continuous data acquisition with RF pulses applied at very high repetition rates, achieving duty cycles up to 99%. The gradient waveform continuously moves in a recirculating path through k-space, enabling nearly continuous data acquisition without the intermittent excitation periods required by conventional sequences, thereby maximizing productivity.

Inventive Principle:

Principle #20Continuity of useful action

3Manufacturing precision

If gradients are used for excitation and movement around k-space in balanced SSFP, then spatial encoding is achieved, but at least 50% of time is spent on non-data acquisition

Engineering Contradiction:

Improvespatial encoding accuracyVSAvoiddata acquisition efficiency

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The patent uses periodic RF pulses with randomized phases combined with a recirculating gradient waveform that continuously traverses k-space. This periodic excitation with randomization allows data acquisition at every gradient echo, eliminating the need for separate excitation and movement phases, thereby achieving both spatial encoding and maximum data acquisition efficiency.

Inventive Principle:

Principle #19Periodic action

4Loss of information

If multiple-contrast images are acquired without prolonged exposure, then diagnostic information is improved, but RF power deposition and exposure time must be reduced

Engineering Contradiction:

Improvediagnostic informationVSAvoidRF power deposition

Core Design Contradiction:

Loss of informationVSObject-affected harmful factors

Solution Approach 1:

The patent performs preliminary randomization of RF pulse phases and timing to create incoherent excitation patterns that encode multiple tissue contrast information (T1, T2, proton density) simultaneously in the acquired data. This preliminary randomization enables subsequent reconstruction of multiple-contrast images from a single continuous acquisition without prolonged exposure, thereby obtaining comprehensive diagnostic information while minimizing RF power deposition.

Inventive Principle:

Principle #10Preliminary action

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

This approach achieves high signal-to-noise ratio efficiency, reduces RF power deposition, and allows for nearly continuous data acquisition, enabling efficient use of gradients and simultaneous estimation of proton density, T1, and T2 images with improved image quality and reduced exposure time.

Implementation Method 1

a gradient waveform is applied to generate a k-space trajectory in a subject

Methodology Applied

Scientific EffectMagnetic resonance: Magnetic Field

Implementation Method 2

Radio frequency (RF) pulses having a pseudorandom phase distribution are applied, such that the RF pulses are applied to the subject

Methodology Applied

Scientific EffectRadio frequency excitation: Electromagnetic Induction

Data Source

PatentUS9285445B2Magnetic resonance imaging using randomized radio frequency pulses

Publication Date: 2016.03.15 RGT UNIV OF CALIFORNIA

AI summary

Methods, systems and apparatus for magnetic resonance imaging that facilitate applying a gradient waveform to generate a k-space trajectory in a subject, applying radio frequency (RF) pulses having a pseudorandom phase distribution, such that the RF pulses are applied to the subject at a plurality of non-uniform locations near a center of the k-space trajectory and collecting, based on the applied RF pulses and the applied gradient waveform, imaging data from the subject.