MRI Preparation Pulse Adaptation for Field Inhomogeneity
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Solution Overview
Problem
Magnetic resonance tomography scanners face challenges in achieving optimal chemical selectivity and image quality due to field inhomogeneities, particularly when larger scanning volumes are involved, leading to reduced image contrast and quality.
Innovation Solution
The method involves varying the coil current and pulse parameters of the preparation pulse based on the position of scanning slices within the scanning volume, optimizing chemical selectivity by subdividing the volume into smaller subgroups and using chemically selective preparation pulses to minimize the influence of molecular species like fat molecules, allowing for improved signal suppression and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If chemically selective preparation pulses are used to suppress fat molecules, then chemical selectivity is improved, but image quality deteriorates due to field inhomogeneities in larger scanning volumes
Solution Approach 1:
The scanning volume is divided into multiple scanning slices, and the preparation pulse is applied selectively to each slice rather than uniformly across the entire volume. This segmentation allows optimization of field homogeneity and chemical selectivity for each individual slice, overcoming the limitation of field inhomogeneities in large scanning volumes.
Solution Approach 2:
Different parameters of the preparation pulse (such as frequency, amplitude, or phase) are adjusted locally for each scanning slice based on its specific position and field characteristics. This local optimization ensures that each slice receives a tailored preparation pulse that maximizes chemical selectivity while maintaining image quality, rather than using a single uniform pulse for the entire volume.
2Device complexity
If a single preparation pulse is used for the entire scanning volume, then device complexity is reduced, but chemical selectivity deteriorates due to field inhomogeneities
Solution Approach 1:
The scanning volume is divided into multiple scanning slices, and the preparation pulse is applied selectively to each slice rather than uniformly across the entire volume. This segmentation allows optimization of field homogeneity and chemical selectivity for each individual slice, overcoming the limitation of field inhomogeneities in large scanning volumes.
Solution Approach 2:
The parameters of the preparation pulse are made dynamic and adaptable to each scanning slice's specific conditions. By adjusting pulse characteristics based on local field inhomogeneities detected in each slice, the system maintains high chemical selectivity without requiring overly complex fixed sequences, achieving a balance between adaptability and simplicity.
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 enhances chemical selectivity and image quality by adapting the preparation pulses to local field inhomogeneities, reducing unwanted excitation and signal contributions, and enabling efficient acquisition of scanning volumes with improved temporal and spatial resolution.
Implementation Method 1
a field correction coil (25), in particular a shim coil, for reducing a local inhomogeneity of the basic magnetic field in the scanning volume
Implementation Method 2
water and fat molecules, in particular CH— and CHO— groups, have slightly different resonance frequencies. The chemical shift is in the region of 3.5 ppm
Implementation Method 3
an excitation takes place by radiation of a chemically selective preparation pulse in the whole scanning volume
Implementation Method 4
the existing transverse magnetization is completely dephased by a spoiler gradient
Data Source
AI summary
In a magnetic resonance tomography scanner and an operating method therefor, a scanning volume is subdivided in a slice direction into multiple scanning slices, and the scan data of each of the scanning slices are acquired by a scan sequence allocated to the respective scanning slice. Each scan sequence has at least one preparation pulse allocated to the scanning slice, which causes nuclear spin excitation throughout the whole scanning volume. At least two scan sequences are implemented that differ with regard to a coil current fed during the preparation pulse to a field correction coil of the scanner for reducing a local inhomogeneity of a basic magnetic field, or that differ with regard to at least one pulse parameter of the preparation pulse. The respective coil current and/or pulse parameter is determined depending on the position of the scanning slice allocated to the respective scan sequence in the scanning volume.