Variable Density Wave-CAIPI Pulse Sequences for Faster MRI
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Solution Overview
Problem
Current Wave-CAIPI methods for magnetic resonance tomography systems do not achieve optimal acquisition speed, limiting the efficiency of MR imaging processes.
Innovation Solution
A pulse sequence method for CAIPIRINHA readout that includes varying readout gradients and encoding gradients with periodic waveforms, allowing for dynamic sampling density and amplitude modulation to enhance k-space sampling, particularly concentrating higher density near the k-space center.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If constant amplitude gradients are used in Wave-CAIPI methods, then the gradient system operates at maximum performance, but the acquisition speed is not optimal
Solution Approach 1:
The patent applies dynamics by making the gradient amplitudes variable rather than constant. Specifically, the readout gradient amplitudes are dynamically adjusted during different readout processes, and the encoding gradient amplitudes are dynamically varied to achieve variable-density k-space sampling. This dynamic adjustment enables optimal acquisition speed by adapting gradient strengths to the specific sampling requirements at different k-space locations.
Solution Approach 2:
The patent implements parameter changes by varying the amplitudes of both readout gradients and encoding gradients. The readout gradient amplitudes are changed across different readout processes, and the encoding gradient amplitudes are modified to create variable-density sampling patterns. These parameter changes directly improve acquisition speed while maintaining image quality through optimized k-space coverage.
2Loss of time
If uniform k-space sampling is used, then the sampling process is simple, but the scan time is prolonged
Solution Approach 1:
The patent applies local quality by implementing variable-density sampling where different regions of k-space are sampled at different densities. The center region of k-space is sampled with higher density while the peripheral regions are sampled with lower density. This local differentiation reduces the total number of samples required while maintaining image quality, thereby reducing scan time without requiring uniformly complex sampling across the entire k-space.
Solution Approach 2:
The patent employs periodic action through the use of Wave-CAIPI encoding gradients that periodically modulate the k-space sampling positions. This periodic modulation, combined with variable-density sampling, creates an efficient sampling pattern that covers k-space more rapidly than uniform sampling, reducing scan time while maintaining image reconstruction quality.
3Loss of time
If higher acceleration factors are achieved, then the scan time is reduced, but the image coherence increases which may degrade image quality
Solution Approach 1:
The patent uses parameter changes in the encoding gradient amplitudes to maintain image quality at higher acceleration factors. By varying the encoding gradient amplitudes according to the variable-density sampling scheme, the patent ensures that the incoherence of the sampling pattern is maintained even when using higher acceleration factors. This prevents excessive image coherence and associated artifacts while achieving reduced scan times.
Data Source
AI summary
In a method for creating a pulse sequence for controlling a magnetic resonance tomography apparatus as part of a CAIPIRINHA readout method for generating magnetic resonance image data of an examination object, two or more readout gradients and encoding gradients are used, wherein a readout gradient is positioned on a gradient axis and an encoding gradient is positioned on another gradient axis so as to occur simultaneously with the readout gradient. The encoding gradient has a periodic waveform. This positioning is repeated at different times in the pulse sequence, with the sampling density of a readout gradient being varied during a readout process, and/or the amplitude of the encoding gradients and/or of the readout gradients being varied for different readout processes.