MRI Diffusion Encoding Gradient Timing Optimization
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Solution Overview
Problem
Existing magnetic resonance imaging (MRI) methods for acquiring diffusion contrast in MR images are limited by inflexible gradient switching schemes, which restrict the minimum achievable echo time and diffusion time, and limit the parameter range of measurement protocols, thereby restricting image resolution and field of view.
Innovation Solution
A method for acquiring MR data with diffusion information using a magnetic resonance system that involves exciting a volume segment with an RF pulse, applying diffusion coding and decoding gradient pulse curves, and adjusting time intervals such as tshift, tF, tP1, and tP2 to optimize the chronological workflow, allowing for flexible selection of coding and diffusion times without altering the echo time, thereby enhancing image resolution and field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional gradient switching schemes are used to generate diffusion contrast, then diffusion information can be acquired, but the minimum achievable echo time and diffusion time are restricted, and the parameter range of measurement protocols is limited
Solution Approach 1:
The patent implements dynamic gradient switching schemes where the timing and amplitude of gradient pulses are made variable rather than fixed. The diffusion encoding gradient pulses can be adjusted in amplitude and duration independently, allowing the system to adapt to different measurement requirements while maintaining optimal echo times. This dynamic approach enables flexible selection of coding time δ and diffusion time Δ without being constrained by predetermined gradient sequences.
Solution Approach 2:
The invention changes the parameters of the gradient pulses, specifically allowing variable amplitude and duration for the diffusion encoding gradients. By modifying these parameters independently, the system can optimize for different diffusion times and coding times while maintaining a consistent echo time. This parameter flexibility resolves the contradiction by allowing the system to adapt to various measurement protocols without being locked into fixed time constraints.
2Adaptability or versatility
If the spin echo condition is satisfied at the point in time of the acquisition of the k-space center with fixed diffusion time, then diffusion contrast can be generated, but the flexibility in selecting coding time δ and diffusion time Δ is reduced
Solution Approach 1:
The patent segments the gradient waveform into distinct components: the diffusion encoding gradient pulses and the readout gradient. By separating these functions, the invention allows independent optimization of the diffusion encoding parameters (coding time δ and diffusion time Δ) while maintaining the spin echo condition at the k-space center acquisition time. This segmentation enables flexible selection of diffusion parameters without compromising the timing precision required for the spin echo condition.
3Object-affected harmful factors
If four gradient pulses with identical amplitude and ramp durations are used, then a double spin echo condition can be satisfied, but the parameter range of measurement protocols is limited and eddy current fields are generated
Solution Approach 1:
The patent employs asymmetric gradient pulse designs where the diffusion encoding gradient pulses have different amplitudes and/or durations rather than being identical. This asymmetry allows for more flexible measurement protocols and reduces eddy current effects by avoiding the symmetric switching patterns that generate strong eddy currents. The asymmetric design maintains the necessary diffusion encoding capability while mitigating harmful electromagnetic effects.
Solution Approach 2:
The invention converts the potential harm of gradient switching into benefit by carefully designing the gradient waveforms to minimize eddy current generation. By using asymmetric pulses with optimized rise and fall times, the system reduces eddy current effects while maintaining effective diffusion encoding. The gradient design transforms the constraint of avoiding eddy currents into an opportunity for more flexible and optimized pulse sequences.
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 allows for more flexible diffusion coding schemes, enabling the examination of time-dependent diffusion processes and improving image quality by reducing eddy current fields and shortening echo times, thereby enhancing the resolution and field of view in MRI images.
Implementation Method 1
excite the volume segment with an excitation module. The volume segment is thereby excited with an RF excitation pulse in order to generate a spin coherence in the volume segment
Implementation Method 2
A first gradient pulse curve is thereby radiated in the form of the diffusion coding module. A second gradient pulse curve that balances or cancels the phase change generated by the first part given unmoving spins is then radiated
Data Source
AI summary
In the acquisition of MR data with diffusion information nuclear spins in a volume segment are excited with radiation of a diffusion coding module and a subsequent diffusion decoding module, and at least one RF pulse is radiated after the excitation, and the MR data are read out. At least one of a time period that defines a time interval between a point in time at which the spin echo condition is satisfied, and the echo time, a first time interval that defines a minimum time interval between the end of the diffusion coding module and the start of the diffusion decoding module, and a second time interval that defines a minimum time interval between the end of the excitation module, and the start of the diffusion coding module, and a third time interval that defines a minimum time interval between the end of the diffusion coding module and the start of the readout of the MR data, is set.