Single-Shot MR Imaging with K-Space Segmentation and Correction
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Solution Overview
Problem
Current MR imaging techniques, such as EPI, face challenges in achieving high-resolution images due to image distortion caused by main magnetic field inhomogeneity, T2 relaxation, and chemical shift effects, while also requiring high RF energy deposition, which exceeds safety limits.
Innovation Solution
A method that generates a sequence of MR echo signals using a single RF pulse and multiple switched magnetic field gradients, with subsampling in the phase encoding direction to produce sub-sequences traversing different k-space trajectories, and uses phase/amplitude correction maps to compensate for image distortions, minimizing RF power transmission and SAR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If EPI sequence is used for high-resolution imaging, then image resolution is improved, but image distortion increases due to T2 relaxation, magnetic field inhomogeneity, and chemical shift effects
Solution Approach 1:
The patent divides the k-space trajectory into multiple segments or shots, where each segment traverses a portion of k-space. This segmentation allows the use of shorter echo trains per segment, reducing the accumulation of T2 decay, field inhomogeneity, and chemical shift effects that cause image distortion, while still achieving high-resolution imaging through composite reconstruction of all segments
Solution Approach 2:
The patent applies preliminary phase and amplitude correction maps to compensate for T2 relaxation, magnetic field inhomogeneity, and chemical shift effects before final image reconstruction. These correction maps are generated in advance based on the known physics of the imaging sequence, allowing pre-compensation of expected distortions
2Reliability
If multi-shot EPI or GRASE is used to resolve EPI problems, then image distortion is reduced, but RF energy deposition (SAR) increases beyond safety limits
Solution Approach 1:
The patent segments the k-space acquisition into multiple shots with subsampling in the phase encoding direction, where each shot uses a single RF pulse followed by a shortened echo train. This reduces the RF energy deposition per shot compared to conventional multi-shot EPI or GRASE, while still achieving complete k-space coverage through combination of subsampled data from multiple shots
Solution Approach 2:
The patent uses subsampling in the phase encoding direction, acquiring only a portion of the required k-space lines in each shot. This partial action allows reduction of the echo train duration and RF energy deposition, with the understanding that complete image reconstruction requires combining data from multiple such partial acquisitions
3Productivity
If conventional EPI is used for fast imaging, then acquisition speed is improved, but image resolution deteriorates due to required long echo train duration
Solution Approach 1:
The patent segments the k-space trajectory into multiple shorter passes with subsampling, where each pass uses a shortened echo train that can be completed within the T2 decay time window. This maintains fast acquisition speed while enabling higher resolution by reducing the echo train duration that would otherwise be required for a single-shot full-resolution acquisition
4Use of energy by moving object
If single RF pulse with subsampled k-space trajectory is used, then RF energy deposition is minimized, but complete k-space coverage requires multiple sub-sequences
Solution Approach 1:
The patent divides complete k-space coverage into multiple sub-sequences or shots, where each shot uses a single RF pulse and traverses a subsampled portion of k-space. This segmentation minimizes RF energy deposition per shot while the systematic organization of multiple sub-sequences manages the overall sequence complexity through structured k-space sampling patterns
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
Enables high-resolution single-shot MR imaging with reduced image distortions and minimal RF energy deposition, efficiently compensating for T2 decay, magnetic field inhomogeneity, and chemical shift effects, while maintaining fast image acquisition.
Implementation Method 1
means for establishing a substantially homogeneous main magnetic field in the examination volume
Implementation Method 2
means for generating switched magnetic field gradients superimposed upon the main magnetic field
Implementation Method 3
means for radiating RF pulses towards the body
Implementation Method 4
means for receiving and sampling MR signals
Data Source
AI summary
MR imaging of a body (7) placed in an examination volume includes establishing a substantially homogeneous main magnetic field in the examination volume, generating switched magnetic field gradients superimposed upon the main magnetic field, radiating RF pulses towards the body (7), controlling the generation of the magnetic field gradients and the RF pulses, receiving and sampling MR signals, and forming MR images from the signal samples. A sequence of MR echo signals is generated by subjecting at least a portion of the body (7) to a single RF pulse and a plurality of switched magnetic field gradients. The switched magnetic field gradients are controlled to produce at least two sub-sequences of MR echo signals. Each sub-sequence traverses a different trajectory in k-space with subsampling in the phase encoding direction (ky) MR echo signals are acquired and sampled. An MR image is reconstructed from the signal samples and from phase/amplitude correction maps associated with the sub-sequences of MR echo signals.