MRI Pulse Sequence Integration for Motion Correction
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Solution Overview
Problem
Current MRI systems face challenges in reducing scan time while maintaining image quality, particularly in neuroimaging applications, where motion artifacts are a significant issue due to lengthy acquisition times and limited effectiveness of existing motion correction methods, especially with short TR protocols.
Innovation Solution
The integration of a volume navigator pulse sequence using echo-planar imaging (EPI) with the imaging pulse sequence in MRI systems, coordinating the navigator repetition time (TR) with the imaging TR to preserve a steady state of magnetization, allowing for prospective motion correction and improved motion estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If gradient echo sequences (SPGR/FLASH) are used for neuroimaging, then image quality is improved, but scan time becomes excessively long (several minutes)
Solution Approach 1:
The patent divides the imaging process into multiple segments by implementing multi-band excitation that simultaneously excites multiple slices or volumes within a single TR period. This segmentation approach allows parallel acquisition of multiple imaging datasets, effectively reducing the total scan time while maintaining the image quality characteristics of gradient echo sequences.
2Reliability
If navigator sequences are inserted to track motion, then motion correction capability is improved, but the steady state of magnetization is disrupted and acquisition time increases
Solution Approach 1:
The patent merges the navigator sequence with the imaging sequence by using the same RF excitation pulses and gradient structures for both purposes. The navigator data is extracted from the same signal acquisition used for imaging, eliminating the need for separate navigator acquisitions and preserving the steady state of magnetization while providing motion tracking capability.
3Measurement precision
If navigator sequences are used for motion tracking, then motion estimation is improved, but image quality deteriorates due to disruption of steady state magnetization
Solution Approach 1:
The patent implements a multi-functional pulse sequence where the same RF and gradient system serves dual purposes: generating imaging signals and generating navigator signals for motion tracking. This universal approach ensures that both imaging and motion estimation functions operate within the same steady state conditions, preventing image quality deterioration while maintaining accurate motion estimation.
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 effective prospective motion correction during MRI scans, reducing scan time without significantly extending acquisition times and improving image quality by accurately tracking and correcting for patient motion, even in 3D FLASH/SPGR sequences.
Implementation Method 1
MRI uses the nuclear magnetic resonance (NMR) phenomenon to produce images. When a substance such as human tissue is subjected to a uniform magnetic field (main magnetic field), B0, the individual magnetic moments of the nuclei in the tissue attempt to align with this magnetic field, but precess about it in random order at their characteristic Larmor frequency, ω.
Implementation Method 2
A signal is emitted by the excited nuclei, or spins, after the excitation magnetic field, B1, is terminated. The emitted signal may be received and processed to form an image.
Data Source
AI summary
A system and method for directing an MRI system to form echo signals from spins in a volume-of-interest (VOI) includes creating an integrated pulse sequence that integrates a volume navigator pulse sequence with an imaging pulse sequence by coordinating a navigator TR with an imaging TR to preserve a steady state of magnetization in the VOI associated with the imaging pulse sequence. The integrated pulse sequence includes performing the imaging pulse sequence to acquire imaging data from the VOI, performing the navigator pulse sequence to acquire navigator data VOI, processing the navigator data to generate motion estimates of motion in the VOI, creating an updated imaging pulse sequence that prospectively corrects for the motion in the VOI using the motion estimates, and repeating these steps using the updated imaging pulse sequence.