Radial MRI Gradient Delay Correction via Calibration
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Solution Overview
Problem
Radial scanning in magnetic resonance tomography is hindered by unintended time delays in gradient fields, leading to image artifacts due to anisotropic gradient delays, which existing correction methods fail to adequately address for clinical use.
Innovation Solution
A method involving calibration measurements to determine gradient moment differences between assumed and actual gradient moments, allowing for precise correction of pixel shifts in k-space, enabling isotropic or anisotropic corrections of gradient delays by shifting scan points based on calculated pixel shifts, and incorporating cross-correlation analysis for robust phase modulation correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If radial scanning is used to reduce movement sensitivity and enable ultra-short echo times, then imaging capabilities are improved, but gradient field time delays cause image artifacts that reduce diagnostic value
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements before the actual radial scanning to determine gradient delay characteristics. The system measures the relationship between assumed and actual gradient moments during calibration, stores this information as correction data, and then applies these corrections during image acquisition. This preliminary characterization of system behavior enables subsequent compensation without interfering with the actual imaging process.
Solution Approach 2:
The patent implements feedback by continuously comparing assumed gradient moments with actual gradient moments measured during calibration, determining correction factors based on this comparison, and then applying these corrections to compensate for gradient delays during radial scanning. The system uses the measured discrepancies to generate correction data that feedback into the image reconstruction process, thereby eliminating artifacts.
2Measurement precision
If calibration measurements are performed to determine gradient moment differences, then gradient delay correction precision is improved, but measurement time and system complexity increase
Solution Approach 1:
The patent applies self-service by having the system perform calibration measurements automatically without requiring external intervention or manual setup. The calibration process uses the system's own gradient coils and detection capabilities to measure gradient moments and determine correction factors. This self-contained calibration approach eliminates the need for separate calibration equipment or manual procedures, reducing overall time while maintaining precision.
Solution Approach 2:
The patent utilizes parameter changes by varying gradient moment parameters during calibration measurements to characterize the system's response across different conditions. By measuring gradient moments at different parameter settings and determining the relationship between assumed and actual moments, the system creates correction data that accounts for variations in gradient delay. This parameter-based approach enables precise correction without requiring extensive time-consuming measurements.
3Reliability
If gradient delays are corrected using existing correction methods, then some artifact reduction is achieved, but correction is insufficient for clinical use in morphological examinations
Solution Approach 1:
The patent replaces existing mechanical or hardware-based correction approaches with a computational method that operates in the data processing domain. Instead of attempting to physically correct gradient delays through hardware adjustments, the system measures the actual gradient moment deviations and applies computational corrections during image reconstruction. This substitution of physical correction mechanisms with information-processing methods achieves superior correction accuracy suitable for clinical morphological examinations.
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
The method effectively corrects gradient delays, improving image quality by reducing artifacts and making radial scanning suitable for clinical use, particularly in morphological examinations, without requiring extensive user interaction or prior calibration.
Implementation Method 1
the gradient fields generated in the scanning that lead to a deviation between the assumed and the actual scanned coordinate of the Fourier-transformed data entries
Implementation Method 2
a raw data space (also known as a measurement space or k-space) is typically scanned line by line
Data Source
AI summary
In a magnetic resonance apparatus and method to generate an image data set by means of a radial scanning of a raw data set, at least one calibration measurement is implemented for at least one predetermined spoke of the radial scan, and a gradient moment difference between an assumed gradient moment and an actually applied gradient moment is determined along the at least one predetermined spoke. Readout of all spokes of the predetermined raw data set ensues by activating multiple magnetic field gradients in spatial directions in order to respectively read out scan points of a respective spoke. The position of each scan point of each spoke is corrected depending on the gradient moment difference, by the position of the respective scan point that is assumed based on the respective activated magnetic field gradients being shifted by the gradient moment difference.