Cartesian-radial hybrid k-space trajectory for MRI volumetric imaging
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Solution Overview
Problem
Current MRI techniques, particularly 2D imaging, face limitations in temperature monitoring during focused ultrasound thermal therapy due to partial volume effects, field of view constraints, and motion artifacts, which are mitigated by 3D imaging but can lack sufficient temporal resolution with all-Cartesian k-space trajectories.
Innovation Solution
A hybrid Cartesian-radial k-space trajectory for MRI systems that combines 2D EPI projections in a first plane with radially shifted projections in other planes, allowing efficient 3D data sampling and improved temporal resolution, suitable for temperature monitoring and motion correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If all-Cartesian k-space trajectories are used in segmented 3D EPI, then T2*-weighting is maintained, but temporal resolution is insufficient for temperature monitoring
Solution Approach 1:
The k-space trajectory is segmented into multiple 2D EPI projections that are acquired in different planes. Each projection covers a portion of k-space, and multiple projections are combined to fill the complete 3D k-space volume. This segmentation allows for faster acquisition of each individual projection while maintaining overall image quality and T2*-weighting.
Solution Approach 2:
The patent transitions from traditional 2D Cartesian trajectories to a 3D volumetric approach by acquiring 2D EPI projections in multiple planes (different orientations and positions) that collectively sample the entire 3D k-space. This dimensional extension enables more efficient coverage of k-space while preserving T2*-weighting characteristics.
2Area of stationary object
If 2D MRI slices are used for temperature monitoring, then field of view is reduced, but coverage gaps and partial volume effects occur
Solution Approach 1:
The patent employs 3D volumetric imaging by acquiring 2D EPI projections in multiple planes that collectively cover the entire volume of interest. This volumetric approach eliminates coverage gaps between slices and reduces partial volume effects by providing continuous 3D sampling, thereby improving both field of view and temperature measurement reliability.
3Loss of time
If faster k-space traversal is implemented to improve temporal resolution, then T2*-weighting may be compromised
Solution Approach 1:
By segmenting the k-space acquisition into multiple rapid 2D EPI projections, each projection can be acquired quickly to maintain temporal resolution, while the cumulative effect of multiple projections preserves the T2*-weighting through proper timing and phase encoding across all projections.
Data Source
AI summary
An MRI system uses a Cartesian-radial hybrid k-space trajectory to capture three-dimensional k-space data and reconstruct an image of an area of interest of a subject. The MRI system performs a series of k-space acquisitions to collect the data. A first k-space acquisition includes acquiring a two-dimensional EPI projection in a first plane parallel to a frequency-encoding direction and acquiring additional two-dimensional EPI projections in planes that are radially shifted about a center axis parallel to the frequency-encoding direction with respect to the first plane, until a selected number of projections are acquired. Each subsequent k-space acquisition includes acquiring an additional set of two-dimensional EPI projections in all of the planes in which an EPI projection was acquired during the first k-space acquisition, each additional set of EPI projections being shifted along a respective plane in a direction perpendicular to the frequency-encoding direction.