Alternating Diffusion Gradient Polarity in MR Systems
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Solution Overview
Problem
Current magnetic resonance (MR) diffusion-weighted imaging techniques face challenges in reducing measurement times while preventing artifacts caused by eddy currents, which are exacerbated by the limitations of power electronics in MR systems.
Innovation Solution
The method involves alternating the polarity of diffusion gradients in consecutive diffusion preparation phases, allowing for maximally antiparallel diffusion encoding directions. This approach reduces the load on polarity-sensitive hardware components and minimizes eddy-current-induced artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If diffusion gradients are switched with high amplitude to improve diffusion weighting, then diffusion contrast is enhanced, but measurement time increases due to additional pauses required by power electronics load limits
Solution Approach 1:
The patent applies periodic action by alternating the polarity of diffusion gradients in consecutive diffusion preparation phases. This creates a periodic pattern where gradients with opposite polarities are applied in succession, allowing the system to utilize hardware components that can handle alternating load directions without requiring extended pause times between each gradient application, thereby reducing total measurement time while maintaining diffusion weighting effectiveness
Solution Approach 2:
The patent changes the polarity parameter of diffusion gradients between consecutive diffusion preparation phases. By inverting the polarity alternately, the system optimizes the load distribution on power electronics components, enabling continuous operation with reduced pause times while preserving the necessary diffusion encoding capability for image contrast
2Productivity
If diffusion gradients are applied repeatedly to reduce measurement time, then productivity increases, but eddy-current-induced artifacts are exacerbated
Solution Approach 1:
The patent converts the harmful eddy-current effects into a beneficial outcome by alternating gradient polarity. The eddy currents generated by gradients with opposite polarities have opposite directions and temporal profiles, causing them to partially cancel each other out when accumulated across multiple diffusion preparation phases. This allows rapid repeated gradient application for high productivity while mitigating the harmful artifact generation
Solution Approach 2:
The patent applies preliminary anti-action by proactively alternating gradient polarity before eddy-current artifacts can accumulate to problematic levels. The alternating pattern pre-compensates for eddy-current effects by ensuring that subsequent gradients generate opposing eddy currents that cancel previous ones, preventing artifact buildup while maintaining high acquisition speed
3Reliability
If pauses are inserted between diffusion gradients to respect hardware load limits, then device reliability is maintained, but measurement time increases
Solution Approach 1:
The patent uses periodic action with alternating gradient polarity to create a rhythmic load pattern on hardware components. This periodic alternation allows the system to operate continuously at high intensity without requiring long pause periods, as the alternating load directions prevent cumulative thermal buildup and stress on power electronics, thereby maintaining reliability while minimizing measurement time
Solution Approach 2:
The patent achieves continuity of useful action by eliminating unnecessary pause times between diffusion gradients through polarity alternation. The alternating gradient pattern allows the system to maintain continuous operational flow, keeping hardware components actively engaged in useful diffusion encoding work without idle pause periods, thus improving time efficiency while preserving hardware reliability through intelligent load management
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 method effectively reduces the overall measurement time for diffusion-weighted data acquisition while preventing eddy-current-related artifacts, thereby improving the efficiency and diagnostic quality of MR imaging.
Implementation Method 1
Diffusion means the Brownian motion of molecules in a medium. In diffusion imaging multiple images with different diffusion directions and weightings are generally acquired and combined with one another.
Implementation Method 2
The resultant diffusion contrast is becoming clinically of ever greater significance and applications now extend well beyond the traditional early recognition of ischemic stroke. However, the need for data to be acquired—for example acquisitions with a plurality of different diffusion encodings (weightings, directions, temporal operational sequences, etc.)—and thus the need to speed up the measurements
Implementation Method 3
the object under examination is positioned in a magnetic resonance device in a comparatively strong static, homogeneous constant magnetic field, also called a B0 field
Implementation Method 4
For position encoding of the measurement data, the constant magnetic field is overlaid by rapidly switched magnetic gradient fields, called gradients for short
Implementation Method 5
To trigger nuclear spin resonances measurable as signals, radio-frequency excitation pulses (RF pulses) are irradiated into the object under examination, the triggered nuclear spin resonances are measured as so-called k-space data
Data Source
AI summary
In a method for the optimized acquisition of diffusion-weighted measurement data of an object under examination using a magnetic resonance (MR) system, a first set of diffusion-weighted measurement data is captured by excitation, and, in an acquisition phase, acquisition of at least one position-encoded echo signal, where prior to the acquisition phase, diffusion gradients are switched for diffusion encoding of the diffusion-weighted measurement data in a diffusion preparation phase, and at least one further set of diffusion-weighted measurement data is captured by excitation, and, in an acquisition phase, acquisition of at least one further position-encoded echo signal, where prior to the acquisition phase, diffusion gradients are switched for diffusion encoding of the diffusion-weighted measurement data in the associated diffusion preparation phase. The diffusion gradients switched in consecutive diffusion preparation phases may have an inverted polarity.