Multi-Point Dixon MR Imaging Calibration
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Solution Overview
Problem
Conventional MR imaging techniques struggle with achieving optimal magnetic field homogeneity, particularly at high field strengths, leading to suboptimal fat suppression and image quality due to the lack of detailed analysis of fat tissue distribution and inadequate compensation for B0 inhomogeneities.
Innovation Solution
A method utilizing a multi-point Dixon technique for calibration, which involves acquiring low-resolution calibration data to derive parameters for optimizing shim settings, reconstructing water and fat images, and determining shim settings to maximize B0 homogeneity in both water and fat regions, thereby improving image quality through enhanced fat suppression and field homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional MR imaging techniques are used, then the imaging process is simple and fast, but magnetic field homogeneity is poor leading to suboptimal fat suppression and image quality
Solution Approach 1:
The patent applies preliminary action by performing a calibration scan before the actual diagnostic imaging. During this calibration scan, multiple echoes are acquired at different echo times to estimate B0 inhomogeneities and fat/water distribution. These preliminary estimates are then used to optimize shim settings and guide the main imaging sequence, thereby improving magnetic field homogeneity and fat suppression without significantly increasing the complexity of the overall imaging process.
Solution Approach 2:
The patent implements feedback by using the calibration data to adjust shim settings and imaging parameters. The estimated B0 inhomogeneities and fat/water distribution from the calibration scan are fed back into the imaging system to optimize the main imaging sequence. This feedback mechanism allows continuous improvement of image quality and field homogeneity based on actual patient-specific characteristics.
2Measurement precision
If high field strength MR imaging is used, then image quality and resolution are improved, but off-resonance effects and B0 inhomogeneities become more severe
Solution Approach 1:
The patent converts the harmful effect of B0 inhomogeneities into a beneficial diagnostic tool. Instead of merely correcting for field inhomogeneities, the calibration scan uses the multi-echo signal data to estimate the actual B0 distribution and fat/water composition. These estimates are then used to optimize imaging parameters and shim settings, turning the previously harmful inhomogeneities into useful information for improving image quality and achieving better fat suppression at high field strengths.
3Manufacturing precision
If detailed fat tissue distribution analysis is performed, then fat suppression is improved, but imaging time and complexity increase
Solution Approach 1:
The patent performs preliminary fat/water distribution analysis during a calibration scan before the main imaging sequence. By acquiring multiple echoes at different echo times during this preliminary scan, the system estimates fat and water distribution throughout the field of view. This preliminary action provides the necessary information for optimizing fat suppression parameters in the main imaging sequence, thereby improving fat suppression without requiring time-consuming detailed analysis during the actual diagnostic imaging.
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 significantly improves image quality by providing detailed fat and water distribution information, enabling better shim settings that enhance B0 homogeneity, leading to improved diagnostic MR images with enhanced fat suppression and reduced artifacts.
Implementation Method 1
The spectral difference between fat and water spins are made use of for the purpose of separating MR signals emanating from water containing tissue and MR signals emanating from fat tissue
Implementation Method 2
multiple acquisitions of k-space are repeated with different echo times... The fat magnetization in the second acquisition is out of phase relative to the first acquisition at the respective echo times
Implementation Method 3
The magnetic field B0 produces different energy levels for the individual nuclear spins in dependence on the magnetic field strength which can be excited (spin resonance) by application of an electromagnetic alternating field (RF field) of defined frequency (so-called Larmor frequency, or MR frequency)
Implementation Method 4
the magnetization performs a precessional motion about the z-axis. The precessional motion describes a surface of a cone whose angle of aperture is referred to as flip angle
Implementation Method 5
The variation of the magnetization can be detected by means of receiving RF coils which are arranged and oriented within an examination volume of the MR device in such a manner that the variation of the magnetization is measured in the direction perpendicular to the z-axis
Implementation Method 6
linear magnetic field gradients extending along the three main axes are superposed on the uniform magnetic field B0, leading to a linear spatial dependency of the spin resonance frequency
Data Source
Figure 1
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AI summary
The invention relates to a method of MR imaging of at least a portion of a body (10) of a patient positioned in an examination volume of a MR device (1). It is an object of the invention to provide a method that enables improved fat saturation. The method of the invention comprises the steps of: -subjecting the portion of the body (10) to a calibration sequence comprising RF pulses and switched magnetic field gradients controlled in such a manner that a calibration signal data set is acquired by means of a multi-point Dixon technique at a first image resolution; -deriving calibration parameters from the calibration signal data set; -controlling the MR device (1) according to the derived calibration parameters; -subjecting the portion of the body (10) to an imaging sequence comprising RF pulses and switched magnetic field gradients controlled in such a manner that a diagnostic signal data set is acquired at a second image resolution which is higher than the first image resolution; and -reconstructing a diagnostic MR image from the diagnostic signal data set. Moreover, the invention relates to a MR device (1) for carrying out the method and to a computer program to be run on a MR device (1).