4D MRI Respiratory Motion Characterization via Self-Gating
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Solution Overview
Problem
Current imaging methods for free-breathing radiotherapy, such as 4D-CT and 4D-MRI, face challenges in accurately accounting for respiratory motion due to high radiation doses, suboptimal soft tissue contrast, and motion artifacts, particularly in irregular breathing patterns, which can lead to inaccurate determination of treatment margins for tumors and healthy tissues.
Innovation Solution
A 4D-MRI technique using a spoiled gradient echo sequence with 3D radial sampling and one-dimensional projection-based self-gating, combined with conjugate gradient sensitivity encoding, allows for high isotropic spatial resolution and frequent respiratory motion sampling, enabling retrospective data sorting and reconstruction of respiratory phase-resolved images that accurately depict tumor and tissue motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If 4D-CT is used to acquire respiratory phase-resolved images, then treatment planning information can be obtained, but high dose of ionizing radiation is delivered to the patient
Solution Approach 1:
The patent replaces CT-based imaging with MRI technology, substituting one physical imaging modality with another that uses different physical principles (magnetic resonance instead of ionizing radiation). This allows acquisition of respiratory phase-resolved images without delivering high doses of ionizing radiation to the patient, while maintaining the capability to obtain treatment planning information.
2Loss of information
If 4D-CT is used for imaging, then respiratory phase information is obtained, but manifest motion artifacts occur due to breathing pattern variation
Solution Approach 1:
The patent implements self-gating by embedding gating information directly within the MRI signal itself. The k-space trajectory is designed to pass through a specific point (e.g., center of k-space) at regular intervals, and the signal at these points contains respiratory motion information. This self-contained approach eliminates the need for external gating devices and ensures that the gating information is inherently synchronized with the image acquisition, thereby reducing motion artifacts while preserving respiratory phase information.
3Measurement precision
If real-time 3D-MRI is used to achieve high spatial resolution, then isotropic resolution is obtained, but the sampling rate is insufficient for fast-moving structures
Solution Approach 1:
The patent segments the k-space sampling into multiple trajectories or segments that are acquired sequentially. Each segment captures a portion of the respiratory cycle, and by combining multiple segments with different temporal sampling rates, the system achieves both high spatial resolution (from the 3D radial sampling) and high temporal sampling rate (from the multiple segments captured at different time points). This segmentation allows the system to capture fast-moving structures while maintaining isotropic spatial resolution.
4Loss of time
If 2D-MRI is used to reduce scan time, then acquisition time is reduced, but 3D motion characterization is incomplete
Solution Approach 1:
The patent transitions from 2D slice imaging to 3D volumetric imaging by acquiring data in k-space with encoding in two spatial dimensions plus the temporal dimension. The 3D radial sampling trajectory in k-space, when combined with temporal encoding through self-gating, produces four-dimensional information (three spatial dimensions plus time). This dimensional expansion allows complete 3D motion characterization while maintaining reasonable scan times through efficient k-space sampling strategies.
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 provides accurate characterization of respiratory motion, improving the determination of internal target volume and optimizing radiation treatment planning by reducing motion artifacts and maintaining image quality across respiratory phases, even in irregular breathing patterns.
Implementation Method 1
magnetic resonance imaging (MRI)
Data Source
AI summary
Magnetic resonance imaging utilizing a continuous spoiled gradient echo sequence with 3D radial trajectory and 1D self-gating for respiratory motion detection can be used to characterize respirator motion in the abdomen. The resulting image data is acquired and is retrospectively sorted into different respiratory phases based on their temporal locations within a respiratory cycle, and each phase is reconstructed via a self-calibrating conjugate gradient sensitivity encoding (CG-SENSE) program.