MRI Multi-Shot Navigator Signal Phase Correction
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Solution Overview
Problem
Magnetic resonance imaging (MRI) 'multi-shot' methods face challenges with movement-induced artifacts due to phase distribution changes during data acquisition, leading to image distortions, particularly in diffusion-weighted imaging, where strong field gradients exacerbate these issues.
Innovation Solution
A method involving a 'multi-shot' acquisition sequence with additional navigator signals to assess the breadth of signal value distribution across the k-space matrix, allowing for phase correction and repeated acquisitions if the distribution exceeds a tolerance range, ensuring accurate phase determination and reduced artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multi-shot acquisition methods are used to improve image quality by scanning k-space in segments, then manufacturing precision of image data is improved, but reliability is worsened due to increased sensitivity to movement artifacts and phase distribution changes
Solution Approach 1:
The patent applies preliminary action by acquiring navigator signals before the actual imaging data to detect and correct movement-induced phase distributions. The navigator signals are acquired in advance to characterize the phase distribution, allowing correction to be applied before the imaging data is reconstructed, thereby preventing movement artifacts from degrading image quality
Solution Approach 2:
The patent uses navigator signals as an intermediary to mediate between the imaging data and the reconstruction process. These navigator signals serve as a separate measurement channel that characterizes the phase distribution caused by patient movement, allowing the system to correct the imaging data without being directly affected by the movement artifacts that would otherwise corrupt the reconstruction
2Reliability
If navigator signals are acquired to detect phase distribution changes, then reliability is improved by reducing movement artifacts, but loss of time increases due to additional signal acquisition
Solution Approach 1:
The patent applies partial action by acquiring navigator signals that sample only a portion of k-space (typically the central region) rather than the entire k-space matrix. This partial sampling provides sufficient information to characterize the phase distribution caused by movement while significantly reducing the time penalty compared to acquiring full imaging data for the same purpose
Solution Approach 2:
The patent implements periodic action by acquiring navigator signals at regular intervals between imaging data acquisitions. This periodic sampling of phase information allows the system to track and correct movement-induced phase changes throughout the multi-shot acquisition sequence without continuously acquiring full imaging data
3Manufacturing precision
If strong field gradients are used in diffusion-weighted imaging to improve measurement precision, then manufacturing precision is improved, but object-generated harmful factors increase due to exacerbated movement-induced artifacts
Solution Approach 1:
The patent applies feedback by using the navigator signals to continuously monitor the phase distribution caused by patient movement during the diffusion-weighted imaging acquisition. The measured phase distributions are fed back into the reconstruction process to correct the imaging data, creating a closed-loop system that actively compensates for movement artifacts that are exacerbated by the strong field gradients used in diffusion weighting
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 enables the reconstruction of high-quality MRI images with minimized artifacts by accurately accounting for movement-induced phase distributions, particularly in diffusion-weighted imaging, by repeating partial acquisitions with complex phase distributions, thereby improving image fidelity.
Implementation Method 1
the phase of the transverse magnetization of the excited spins changes when excited spins move along magnetic field gradients
Implementation Method 2
After the end of a radio-frequency (RF) excitation pulse, the nuclear spins precess at a frequency that is known as the Larmor frequency, which depends on the strength of the basic magnetic field
Implementation Method 3
These nuclei are excited to a precessional movement around direction of the basic magnetic field by means of radio-frequency excitation pulses
Data Source
AI summary
In a method and magnetic resonance apparatus for acquisition of image data for a magnetic resonance image, the image data are acquired with an acquisition sequence, in which a k-space matrix corresponding to the image data is scanned in segments with at least two partial acquisitions and in which each of the partial acquisition includes a navigator signal in addition to the measurement signal with which a specific k-space segment is scanned, with which navigator signal a same navigator segment of the k-space matrix is scanned. In one of the partial acquisitions a measure is determined that characterizes the breadth of the distribution of signal values of the navigator signal with regard to the k-space matrix and the partial acquisition is repeated if and when the measure lies outside of a tolerance range.