Steer-PROP MRI Sequence for k-Space Phase Correction
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Solution Overview
Problem
Magnetic resonance imaging (MRI) techniques face limitations in achieving high spatial resolution and minimizing motion artifacts, particularly at higher magnetic fields, due to constraints in k-space coverage and sensitivity to off-resonance effects and gradient anisotropy in existing pulse sequences like single-shot EPI and multi-shot EPI with PROPELLER sampling.
Innovation Solution
The implementation of a PROPELLER pulse sequence based on gradient and spin echo (GRASP) with a novel k-space traversal strategy and comprehensive phase correction scheme, allowing for minimal artifacts and reduced data acquisition times, by applying specific RF and gradient pulse trains to reposition k-space traversal points and independently correct phase errors among blades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If single-shot EPI is used for fast imaging, then data acquisition efficiency is improved and SAR is reduced, but spatial resolution is limited due to constraints on maximal k-space coverage
Solution Approach 1:
The patent divides k-space coverage into multiple segments or shots, where each shot covers a portion of k-space. By segmenting the acquisition into multiple shots with different phase-encoding ranges, the system can achieve both fast data acquisition (inheriting ss-EPI efficiency) and high spatial resolution (by covering more of k-space across multiple segments).
Solution Approach 2:
The patent introduces a new dimension to k-space sampling by using non-Cartesian trajectories (such as spiral or radial paths) combined with parallel imaging techniques. This dimensional approach allows efficient coverage of k-space while maintaining high resolution, overcoming the limitations of traditional single-shot EPI.
2Manufacturing precision
If multi-shot EPI is used to improve spatial resolution, then k-space coverage is improved, but sensitivity to motion is increased
Solution Approach 1:
The patent applies motion correction techniques before image reconstruction by using navigator echoes or field-map acquisitions to measure and compensate for motion artifacts. This preliminary correction ensures that multi-shot data can be accurately combined, maintaining both high resolution and motion robustness.
Solution Approach 2:
The patent incorporates real-time motion monitoring and feedback mechanisms where motion parameters are continuously measured during acquisition and used to adjust the imaging sequence or reconstruction process. This feedback loop reduces sensitivity to motion by dynamically compensating for patient movement.
3Reliability
If PROPELLER sampling is used to reduce motion sensitivity, then motion robustness is improved, but off-resonance effects and gradient anisotropy cause artifacts
Solution Approach 1:
The patent modifies the PROPELLER sequence parameters by optimizing the blade width, rotation angle, and echo spacing to minimize off-resonance artifacts. By carefully tuning these parameters, the system maintains motion robustness while reducing the impact of off-resonance effects and gradient anisotropy.
Solution Approach 2:
The patent replaces the traditional PROPELLER mechanical k-space traversal with an EPI-based approach that uses gradient switching and RF pulse sequences to achieve similar motion robustness. This substitution eliminates gradient anisotropy issues while maintaining the benefits of motion correction through alternative physical mechanisms.
4Manufacturing precision
If FSE or turbo spin echo is used for multi-shot imaging, then resolution is improved and motion sensitivity is reduced, but data acquisition time is considerably slower
Solution Approach 1:
The patent merges the advantages of FSE (fast spin echo) with EPI (echo planar imaging) techniques to create a hybrid sequence. This combination inherits the high resolution and motion robustness of FSE while achieving the rapid data acquisition speeds of EPI, thereby reducing total scan time significantly.
Solution Approach 2:
The patent implements continuous k-space filling through optimized gradient waveforms and echo train techniques that minimize idle time between acquisitions. By maintaining continuous useful action during the imaging process, the system achieves fast acquisition times without sacrificing the resolution benefits of multi-shot imaging.
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 enables the acquisition of high-resolution images with reduced artifacts and faster data acquisition compared to FSE-PROPELLER, while effectively addressing motion and off-resonance issues, thereby improving image quality and efficiency.
Implementation Method 1
The main magnetic field causes the atomic nuclei (spins) that possess a magnetic moment in the matter comprising the subject or object to become aligned in the magnetic field. The spins form a magnetization that precesses around the magnetic field direction at a rate proportional to the magnetic field strength. If the magnetization is perturbed by a small radio-frequency magnetic field, known as B1 magnetic field, the spins can emit radio frequency (RF) radiation
Implementation Method 2
The field gradients are typically applied along one or more orthogonal axes, (x, y, z), the z-axis usually being aligned with the B0, and introduce spatially-distributed variations in frequency and/or phase of the precessing nuclear spins
Data Source
AI summary
A GRASE-type PROPELLER sequence called Steer-PROP is disclosed. This sequence exploits a serious of steer blips together with rewinding gradient pulse to traverse k-space. Steer-PROP improves the scan time by a factor of 3 or higher compared to FSE-PROPELLER, provides improved robustness to off-resonance effects compared to EPI-PROPELLER, and addresses a long-standing phase correction problem inherent to GRASE based sequences. Steer-PROP also enables intra-blade, inter-blade, and inter-shot phase errors to be separately determined and independently corrected.