Quiet MR Imaging Gradient Echo Sequences
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Solution Overview
Problem
Conventional MR imaging techniques generate significant acoustic noise due to mechanical oscillations of magnetic field gradient coils, causing discomfort to patients and requiring hearing protection, while existing silent radial centre-out k-space encoding techniques only provide proton-density weighted contrast.
Innovation Solution
The method involves gradually varying the magnetic field gradient vector during RF pulse radiation and MR echo signal acquisition, sampling a spherical volume in k-space, and reconstructing images to achieve T2 or diffusion-weighted contrast, thereby reducing acoustic noise and enabling quiet MR imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional MR imaging techniques are used, then high image quality and diagnostic accuracy are achieved, but significant acoustic noise is generated causing patient discomfort and requiring hearing protection
Solution Approach 1:
The patent replaces the conventional mechanical gradient switching system with a gradient echo-based system that uses RF pulse sequences to generate images. By using gradient echoes instead of conventional spin echoes, the system eliminates the need for high-amplitude gradient switching that causes acoustic noise, while maintaining image quality through alternative signal acquisition methods
Solution Approach 2:
The patent changes the imaging parameters by using low-flip-angle RF pulses and gradient echo sequences instead of conventional high-flip-angle spin echo sequences. This parameter change allows for rapid image acquisition with reduced acoustic noise while maintaining diagnostic image quality through optimized echo train length and repetition time
2Object-affected harmful factors
If silent radial centre-out k-space encoding techniques are used, then acoustic noise is reduced, but only proton-density weighted contrast is provided
Solution Approach 1:
The patent creates a multi-functional imaging system that can generate multiple types of contrast (T1-weighted, T2-weighted, proton-density weighted, and diffusion-weighted images) using the same silent gradient echo sequence framework. By adjusting RF pulse parameters, echo train length, and b-values, the system provides versatile contrast options while maintaining low acoustic noise levels
Solution Approach 2:
The patent employs dynamic parameter adjustment within the gradient echo sequence, allowing the operator to modify flip angles, echo times, and gradient strengths to achieve different contrast weightings. This dynamic adaptability enables the system to provide multiple contrast types without requiring separate imaging sequences, thereby expanding contrast options while maintaining silence
3Adaptability or versatility
If conventional spin echo sequences are used, then T2-weighted contrast is achieved, but high acoustic noise is generated
Solution Approach 1:
The patent substitutes the mechanical gradient switching required for conventional spin echo sequences with a gradient echo-based system that uses RF pulse manipulation to generate T2-weighted contrast. This substitution eliminates the high-amplitude gradient switching that causes acoustic noise while achieving the desired T2-weighted image contrast through optimized echo train parameters
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 limits acoustic noise and allows for the production of T2 or diffusion-weighted MR images, enhancing imaging quality without the need for hearing protection and expanding contrast options beyond proton-density weighted images.
Implementation Method 1
The Lorentzian forces induced when an electrical current is applied to the gradient coils make them physically move.
Implementation Method 2
The magnetic field produces different energy levels for the individual nuclear spins in dependence on the magnetic field strength. Transitions between these energy levels can be excited (spin resonance) by application of an electromagnetic alternating field
Implementation Method 3
After termination of the RF pulse, the magnetization relaxes back to the original state of equilibrium, in which the magnetization in the z direction is built up again with a first time constant T1 (spin lattice or longitudinal relaxation time), and the magnetization in the direction perpendicular to the z direction relaxes with a second time constant T2 (spin-spin or transverse relaxation time)
Data Source
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AI summary
The invention relates to a method of MR imaging of an object (10) positioned in an examination volume of a MR device (1). It is an object of the invention to enable 'silent' MR imaging with T2∗ -weighted or diffusion-weighted contrast. The invention proposes that the method comprises the steps of: - subjecting the object (10) to an imaging sequence comprising: a) gradually varying a magnetic field gradient vector (GX, GY, GZ) from an initial position (A) to an end position (B) over a plurality of intermediate positions while a number of RF pulses (20) is radiated in the presence of the magnetic field gradient; b) gradually varying the magnetic field gradient vector (GX, GY, GZ) again from the initial position (A) to the end position (B) over the plurality of intermediate positions while a number of MR echo signals is acquired in the presence of the magnetic field gradient; c) sampling a spherical volume in k- space by repeating steps a) and b) a number of times for different initial, intermediate, and/or end positions; - reconstructing a MR image from the acquired MR echo signals. Furthermore, the invention relates to a MR device (1) and to a computer program for a MR device (1).