MR Slice Acquisition Using Multiple Phase-Encoding Gradients
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Solution Overview
Problem
Existing magnetic resonance imaging (MRI) techniques, such as TSE sequences, face significant increases in scanning time due to the need for additional phase coding steps to suppress metal artifacts, making clinical protocols impractical.
Innovation Solution
A method that reduces scanning time by applying multiple phase-encoding gradients and selection gradients without additional RF pulses, allowing multiple k-space lines to be selected from a single refocusing pulse, similar to the Turbo Gradient Spin Echo sequence, while accounting for previous gradient effects using additional phase-encoding gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional phase coding steps (SEMAC encoding) are applied to suppress metal artifacts, then metal artifact suppression is improved, but scanning time increases linearly
Solution Approach 1:
The patent divides the k-space acquisition into multiple lines that can be selected from a single refocusing pulse. By segmenting the phase encoding process and selecting multiple k-space lines without requiring additional RF pulses, the method reduces the number of repeated scanning cycles while maintaining metal artifact suppression capability.
Solution Approach 2:
The patent applies phase-encoding gradients and selects multiple k-space lines in advance from a single refocusing pulse. This preliminary action allows multiple pieces of information to be acquired simultaneously without requiring sequential RF pulses, thereby reducing scanning time while preserving the metal artifact suppression function.
2Reliability
If multiple SEMAC steps are used to suppress metal artifacts, then artifact suppression is improved, but scanning time increases to over 17 minutes
Solution Approach 1:
The patent merges multiple phase-encoding operations into a single refocusing pulse sequence. By combining the acquisition of multiple k-space lines from one refocusing pulse instead of requiring separate pulses for each SEMAC step, the method achieves both metal artifact suppression and improved scanning efficiency.
Solution Approach 2:
The single refocusing pulse is designed to serve multiple functions: it provides the necessary refocusing while also enabling the selection of multiple k-space lines for different phase-encoding states. This multi-functionality allows the system to achieve metal artifact suppression without proportionally increasing scanning time.
3Measurement precision
If conventional TSE sequences with long TR are used, then image quality is maintained, but scanning time becomes impractical for clinical protocols
Solution Approach 1:
The patent introduces dynamic gradient switching and phase-encoding manipulation that allows multiple k-space lines to be acquired from a single refocusing pulse. This dynamic approach enables the system to maintain image quality through proper gradient control while significantly reducing the overall scanning time by over a third compared to conventional methods.
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 significantly reduces scanning time by over a third and minimizes Specific Absorption Rate (SAR) exposure, making it suitable for clinical use, especially in areas with metallic implants or magnetic field inhomogeneities.
Implementation Method 1
Switching (activating) on a first slice selection gradient along a first direction or slice selection direction which is perpendicular to the slice
Implementation Method 2
Radiating an RF refocusing pulse to selectively excite the slice while the slice selection gradient is applied
Implementation Method 3
Applying a first phase-encoding gradient along the first direction. Applying this first phase-encoding gradient can also be referred to as SEMAC-encoding
Implementation Method 4
Applying a selection gradient along a third direction, which is perpendicular to the first and second direction
Data Source
AI summary
In a method and magnetic resonance (MR) apparatus for acquisition of MR data from a slice in a subject, a first slice selection gradient is activated in a first direction perpendicular to the slice, and an RF excitation pulse then selectively excites nuclear spins in the slice. A second slice selection gradient is activated along the first direction, and a refocusing pulse is radiated. A first phase encoding gradient along the first direction is activated, and a second phase encoding gradient is activated along a second direction perpendicular to the first direction. A selection gradient is activated along a third direction perpendicularly to the first and second directions, during which MR data are acquired from the slice. The acquired MR data are entered into multiple k-space lines that are selected starting from the refocusing pulse, without a further RF pulse being radiated.