NMR Phase Offset Map Calculation for Magnetic Field Shimming
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Solution Overview
Problem
Current NMR measurement methods require multiple measurements with different phase evolution periods, leading to prolonged time for generating magnetic field maps.
Innovation Solution
A nuclear magnetic resonance measurement apparatus that calculates a phase offset map independently of the inhomogeneous magnetic field component and phase evolution period, allowing for the reduction of measurement time by using a ratio-based calculation of phase maps from pulse sequences with varying shim coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple measurements with different phase evolution periods are performed to generate magnetic field maps, then measurement precision is improved, but measurement time is prolonged
Solution Approach 1:
The patent applies preliminary action by calculating and storing the phase offset map before the actual magnetic field map measurement. The phase offset map, which contains information about phase offsets independent of the inhomogeneous magnetic field component, is computed in advance using Equation (4) from phase maps acquired during preliminary execution of pulse sequences. This preliminary calculation allows the main measurement to use a simplified formula (Equation (5)) that only requires one phase map, thereby reducing measurement time while maintaining precision through the pre-computed offset correction.
2Measurement precision
If multiple measurements with different phase evolution periods are performed to generate magnetic field maps, then calculation accuracy is improved, but the number of measurements increases
Solution Approach 1:
The patent performs preliminary calculation of the phase offset map using Equation (4) which involves phase maps from multiple pulse sequence executions. This preliminary action separates the offset calculation from the main magnetic field map generation, allowing the subsequent measurement to use Equation (5) with only a single phase map acquisition. The preliminary computation stores the offset information that would otherwise require multiple measurements to extract, thus improving productivity without sacrificing calculation accuracy.
Solution Approach 2:
The patent segments the magnetic field map generation process into two independent parts: (1) preliminary calculation of the phase offset map using Equation (4) which handles the offset component, and (2) calculation of the inhomogeneous magnetic field component using Equation (5) which handles the field map proper. This segmentation allows each part to be optimized independently - the offset calculation uses multiple phase maps for accuracy, while the main measurement uses a single phase map for efficiency, thereby resolving the contradiction between measurement precision and productivity.
3Measurement precision
If phase offset maps are calculated for each measurement, then measurement precision is maintained, but device complexity increases
Solution Approach 1:
The patent applies universality by creating a single phase offset map that serves multiple measurement conditions. The offset map calculated from Equation (4) using phase maps with different phase evolution periods (short τ and long τ) is a universal correction that can be applied to subsequent magnetic field map calculations regardless of the specific pulse sequence parameters. This universal offset map eliminates the need to recalculate offsets for each measurement, reducing device complexity while maintaining precision through consistent offset correction across all measurements.
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 reduces the number of measurements needed for magnetic field map generation, improving measurement precision and calculation accuracy, and enables efficient shimming of static magnetic fields.
Implementation Method 1
The present disclosure relates to a nuclear magnetic resonance (NMR) measurement apparatus, and in particular to correction of a static magnetic field.
Data Source
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AI summary
An offset map is determined in advance by a preliminary measurement process. A phase map is generated by execution of a long τ pulse sequence. A magnetic field map is calculated based on a phase map and a phase offset map. A shim adjustment is performed based on the magnetic field map. The offset map is calculated based on a first phase map acquired by execution of a first pulse sequence, a second phase map acquired by execution of a second pulse sequence, and a ratio α related to phase evolution periods.