MRI Phase Encoding Gradient Correction via Dual Pre-Scan Sampling
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Solution Overview
Problem
Conventional Fast Spin Echo (FSE) methods in magnetic resonance imaging (MRI) face challenges in correcting phase differences caused by phase encoding gradient magnetic fields, leading to image quality deterioration due to sensitivity unevenness and 'ghost' phenomena.
Innovation Solution
The MRI apparatus employs a dual pre-scan approach using distinct pulse sequences to calculate and correct phase differences in the phase encoding direction, applying sampling gradient magnetic fields during the first pre-scan and a representative phase encoding gradient during the second pre-scan to adjust the main scan pulse sequence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional FSE method with phase encoding gradient magnetic fields is used, then imaging speed is improved, but phase differences occur causing image quality deterioration
Solution Approach 1:
The patent applies preliminary action by performing pre-scans before the main imaging scan to measure and calculate phase difference correction amounts. The pre-scan pulse sequences are executed prior to the main scan, allowing the system to pre-determine correction parameters that will be applied during the actual imaging process, thereby resolving phase differences before they degrade image quality.
Solution Approach 2:
The patent implements feedback by measuring actual phase differences during pre-scans and using these measurements to calculate correction amounts that are fed back into the pulse sequence control. The system continuously monitors phase differences and adjusts the pulse sequence parameters accordingly, creating a closed-loop correction system that maintains image quality while preserving imaging speed.
2Measurement precision
If pre-scan with stimulated echo cancellation is performed, then phase differences in readout and slice directions are corrected, but phase differences in phase encoding direction remain uncorrected
Solution Approach 1:
The patent applies segmentation by dividing the phase difference correction process into separate components: first correcting readout and slice direction phase differences using conventional pre-scan methods, then separately correcting phase encoding direction phase differences using specialized pre-scan pulse sequences with sampling gradient magnetic fields. This segmented approach allows each correction type to be optimized independently, improving overall measurement precision without unnecessarily complicating the entire pulse sequence.
Solution Approach 2:
The patent uses an intermediary approach by introducing sampling gradient magnetic fields as a mediator to measure phase differences in the phase encoding direction. These sampling gradients act as a bridge, allowing the system to indirectly measure and quantify phase encoding direction phase differences without requiring complex direct correction mechanisms, thereby improving correction accuracy while managing pulse sequence complexity.
3Manufacturing precision
If multiple pre-scan pulse sequences are executed, then comprehensive phase difference correction is achieved, but scan time increases
Solution Approach 1:
The patent applies partial action by executing only the necessary pre-scan pulse sequences required for comprehensive phase difference correction. Rather than performing all possible pre-scans, the system selectively executes pre-scan sequences that target specific phase difference components (readout direction, slice direction, and phase encoding direction), achieving sufficient correction accuracy without the time penalty of excessive or redundant scanning.
Solution Approach 2:
The patent utilizes parameter changes by varying pulse sequence parameters (such as gradient magnetic field strength, echo timing, and RF pulse phases) during different pre-scan executions to optimize the measurement of different phase difference components. By dynamically adjusting these parameters, the system achieves comprehensive phase difference correction while minimizing the total time required for pre-scans.
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 prevents image quality deterioration by accurately correcting phase differences in the phase encoding direction, improving the overall quality of MRI images.
Implementation Method 1
applying a plurality of gradient magnetic fields for sampling in a phase encoding direction, applying a sampling gradient magnetic field at the same echo signal as in the first pulse sequence, and applying a representative phase encoding gradient magnetic field among the phase encoding gradient magnetic fields applied in a pulse sequence for a main scan
Implementation Method 2
a flip pulse is a Radio Frequency (RF) pulse used for exiting atomic nuclear spins within the examined subject. The flop pulses are RF pulses used for refocusing phases of the atomic nuclear spins
Data Source
AI summary
A magnetic resonance imaging apparatus according to an embodiment includes an executing unit, a calculating unit, and a correcting unit. The executing unit executes a first pre-scan in which a readout gradient magnetic field and a phase encoding gradient magnetic field are not applied and sampling gradient magnetic fields is applied in a phase encoding direction and a second pre-scan in which the readout gradient magnetic field is not applied, the sampling gradient magnetic field is applied at the same echo signal as that in the first pre-scan, and a representative phase encoding gradient magnetic field in a main scan. The calculating unit calculates the amount of correction from phase differences between the echo signals collected by the first pre-scan and between the echo signals collected by the second pre-scan. The correcting unit corrects the pulse sequence for the main scan on the basis of the calculated amount of correction.