MRI Gradient Coil Prescan for Center Frequency Drift Correction
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Solution Overview
Problem
The degradation of MR image quality due to changes in the center frequency of nuclear spin magnetic resonance caused by temperature fluctuations in gradient coils during MRI scanning, which can be exacerbated by the application of gradient magnetic fields.
Innovation Solution
A method involving multiple prescan settings to measure temperature and frequency variations in gradient coils along different axes, followed by calculating correction coefficients to adjust the center frequency of RF pulses during the main scan, ensuring accurate frequency alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gradient magnetic fields are applied during scanning, then spatial positional information is added to MR signals, but temperature of gradient coil changes causing center frequency shift
Solution Approach 1:
The patent applies preliminary action by measuring temperature variation of the gradient coil before the main scanning process and using this pre-acquired data to calculate and apply center frequency correction. This allows the system to compensate for frequency shifts caused by temperature changes before they degrade image quality, resolving the contradiction between applying gradient fields for spatial information and managing the resulting temperature-induced frequency drift.
2Reliability
If center frequency is corrected based on temperature change, then image quality is maintained, but scanning time increases due to additional measurement and calculation steps
Solution Approach 1:
The patent applies partial action by measuring temperature variation at selected prescan settings rather than continuously throughout the entire scanning process. The system acquires temperature data at specific intervals and uses this partial information to calculate center frequency correction, maintaining image quality while avoiding the time penalty of continuous monitoring and correction.
3Measurement precision
If multiple prescan settings are used to measure temperature and frequency variations, then correction accuracy is improved, but process complexity increases
Solution Approach 1:
The patent applies universality by using the same gradient coil unit to generate gradient magnetic fields for both the prescan measurement process and the main scanning process. This multi-functional use of the gradient coil allows the system to acquire temperature variation data under actual scanning conditions without requiring additional specialized equipment, thereby improving measurement accuracy while limiting the increase in device complexity.
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 effectively maintains MR image quality by correcting for frequency shifts, enhancing the effectiveness of fat-suppression pulses and improving image clarity.
Implementation Method 1
When a gradient coil is supplied with a pulse current from a gradient magnetic field power supply during scanning, the gradient coil generates a gradient magnetic field
Implementation Method 2
as the pulse current is repeatedly supplied, the gradient coil generates heat, which changes the temperature of a gradient coil unit
Implementation Method 3
A magnetic resonance imaging (MRI) apparatus is an imaging apparatus that excites nuclear spin of a subject placed in a static magnetic field with a radio frequency (RF) pulse of a Larmor frequency, executes scanning to collect magnetic resonance (MR) signals generated from the subject due to excitation
Data Source
AI summary
A method in magnetic resonance imaging according to an exemplary embodiment includes acquiring a first temperature variation amount as a variation amount of a temperature of a gradient coil unit which includes a gradient coil corresponding to an X-axis; a gradient coil corresponding to a Y-axis; and a gradient coil corresponding to a Z-axis; and a first frequency variation amount as a shift amount of a center frequency at which nuclear spin of a subject causes magnetic resonance, the first temperature variation amount and the first frequency variation amount being caused by execution of a first sequence based on a first setting in which a readout gradient magnetic field is applied in a direction of the X-axis by the gradient coil unit; acquiring a second temperature variation amount as the variation amount of the temperature of the gradient coil unit and a second frequency variation amount as the shift amount of the center frequency, the second temperature variation amount and the second frequency variation amount being caused by execution of the first sequence based on a second setting in which the readout gradient magnetic field is applied in a direction of the Y-axis by the gradient coil unit; acquiring a third temperature variation amount as the variation amount of the temperature of the gradient coil unit and a third frequency variation amount as a shift amount of the center frequency, the third temperature variation amount and the third frequency variation amount being caused by execution of the first sequence based on a third setting in which the readout gradient magnetic field is applied in a direction of the Z-axis by the gradient coil unit; and acquiring a fourth temperature variation amount as the variation amount of the temperature of the gradient coil unit caused by execution of a second sequence to be executed after the first sequence, and calculating a value corresponding to the shift amount of the center frequency in the second sequence, based on the first temperature variation amount, the first frequency variation amount, the second temperature variation amount, the second frequency variation amount, the third temperature variation amount, the third frequency variation amount, the fourth temperature variation amount, and a weighting value corresponding to a gradient magnetic field to be applied in the second sequence.