MRI Image Formation with Fourier Background Noise Subtraction
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Solution Overview
Problem
Existing MRI devices, particularly portable ones, face challenges in reducing correlated noise signatures that mask image details due to limitations in main magnetic field intensity, leading to noisy and low-quality images.
Innovation Solution
A method involving a basic sequence with echo and background signal measurements, followed by Fourier image processing to subtract background signals, using techniques like spectral subtraction and principal component analysis, to form an image devoid of background noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If a main magnetic field of limited intensity (≤60 mT or ≤200 mT) is used in portable MRI apparatuses, then the mass and bulk of the device are reduced, but the signal-to-noise ratio deteriorates and correlated noise signatures appear in the images
Solution Approach 1:
The patent extracts the correlated noise component from the total signal by using a secondary coil positioned to detect only the correlated noise signature without detecting the body signal. This separated noise measurement allows for its subsequent removal from the main image data, thereby improving measurement precision without requiring higher magnetic field intensity.
Solution Approach 2:
The patent introduces a secondary coil as an intermediary device that specifically detects the correlated noise component. This intermediary measurement channel enables the separation and subsequent elimination of noise from the primary imaging data, resolving the contradiction between using low-field magnets and maintaining image quality.
2Measurement precision
If a secondary coil is positioned close to the RF coil to detect correlated noise, then the noise detection sensitivity is improved, but the coil becomes sensitive to the body signal which introduces error
Solution Approach 1:
The patent applies local quality by positioning the secondary coil in a specific location where it has different sensitivity characteristics compared to the primary RF coil. The secondary coil is placed to be sensitive to correlated noise while being insensitive to the body signal, creating localized detection zones with different functional properties.
Solution Approach 2:
The patent uses asymmetry in the positioning and configuration of the secondary coil relative to the primary RF coil and the body. This asymmetric arrangement ensures that the secondary coil detects correlated noise with high sensitivity while remaining insensitive to the body signal, thereby avoiding the harmful effect of signal interference.
3Measurement precision
If mathematical processing is performed on Fourier images to subtract background signals, then background noise is reduced, but processing time and computational complexity increase
Solution Approach 1:
The patent performs preliminary action by measuring the correlated noise signature in advance using the secondary coil before the main imaging sequence. This pre-measured noise characterization is then used in the Fourier domain to efficiently subtract the noise from the body signal, reducing the need for complex iterative processing and thereby minimizing processing time while maintaining image quality.
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 effectively eliminates background noise signatures, enhancing image quality in low-field MRI devices, including portable ones, without introducing approximations.
Implementation Method 1
a magnet intended to impose on the body a static magnetic field (called main magnetic field), under the effect of which the nuclear spins associated with the hydrogen nuclei contained in the water molecules forming part of this body polarize
Implementation Method 2
the magnetic moments associated with these spins are preferentially aligned along an axis called the z axis, determined by the orientation of the main magnetic field so as to create a magnetization of the body
Implementation Method 3
gradient coils configured to produce magnetic fields of small amplitude and varying in space when a current is applied thereto
Implementation Method 4
the at least one radio frequency coil is configured to emit RF energy pulses of a frequency equal to or close to the resonant frequency of the hydrogen nuclei spins and that is at least partially absorbed by these nuclei
Implementation Method 5
As soon as the RF emission is interrupted, the nuclear spins relax to return to their initial energy state and in turn emit an RF signal capable of being collected by at least one RF coil
Implementation Method 6
repeating the basic sequence as many times as necessary to form, in Fourier space, a Fourier image of the body from the echo signals and a Fourier image of the background from the background measurements
Data Source
AI summary
A method for imaging a body, implements a basic sequence that includes:—generating at least one echo signal of a sequence of RF pulses produced by an RF coil;—performing an echo measurement of the at least one echo signal by the RF coil; and—performing a background measurement by the RF coil representative of a background signal. The method includes the following steps: a) repeating the basic sequence as many times as necessary so as to form a Fourier image of the body and a Fourier image of the background from the background measurements; and b) processing the Fourier image of the body and of the background so as to obtain an image of the body in which a signature of the one or more background signals is reduced or even eliminated.