Transverse Field MRI Apparatus Magic Angle Imaging
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Solution Overview
Problem
Conventional MRI systems face challenges in achieving homogeneous magnetic fields and optimal image contrast due to the magic angle effect, particularly in anisotropic structures like collagen in musculoskeletal tissues, which limits diagnostic imaging quality.
Innovation Solution
A transverse field MRI apparatus is designed with two magnet assemblies spaced apart to provide a transverse B0 imaging field, allowing rotation of the magnetic field relative to the object, enabling better control over image contrast and orientation of structures to minimize magic angle artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional cylindrical or open MRI magnets are used with B0 field aligned with net magnetisation, then the magnetic field is homogeneous and imaging can be performed, but the physical constraints prevent optimal positioning of anisotropic structures at magic angle orientations
Solution Approach 1:
Instead of aligning the B0 field with the net magnetisation direction (conventional approach), the patent inverts this relationship by aligning the B0 field transverse to the net magnetisation direction of the magnetic elements. This allows the magnet assembly to be positioned with its separation direction aligned to the structure of interest, enabling magic angle imaging while maintaining field homogeneity.
Solution Approach 2:
The patent employs an asymmetric magnet configuration where two magnet assemblies are positioned at opposite sides of the imaging region with their net magnetisation directions arranged asymmetrically relative to the B0 field direction. This asymmetric arrangement enables the B0 field to be transverse to the net magnetisation while providing sufficient space for positioning anisotropic structures at optimal orientations.
2Measurement precision
If structures are positioned at magic angle orientations to increase signal, then image contrast improves, but conventional magnet geometries cannot achieve the required orientations
Solution Approach 1:
The patent introduces rotational capability to the magnet assemblies, allowing dynamic adjustment of the B0 field orientation relative to the object being imaged. The magnet assemblies can be rotated about the imaging region axis, enabling the system to achieve magic angle orientations (54.7 degrees) for optimal signal from anisotropic structures while maintaining operational flexibility.
3Measurement precision
If B0 field is made transverse to magnet assembly separation direction, then magic angle effects can be exploited for better image quality, but achieving homogeneous field becomes more challenging
Solution Approach 1:
The patent applies local quality by using individual magnet assemblies with specific magnetisation patterns on each side of the imaging region. Each assembly can be independently configured and adjusted to contribute to the overall homogeneous B0 field while maintaining the transverse field configuration. This allows local optimization of field homogeneity in different regions of the imaging space.
Solution Approach 2:
The patent incorporates field adjustment mechanisms that can be tuned to compensate for inhomogeneities arising from the transverse field configuration. By using adjustable magnetic elements and feedback-based field optimization, the system maintains homogeneous B0 field conditions even when the field is oriented transverse to the magnet assembly separation direction.
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 image quality by allowing precise manipulation of the magnetic field orientation, reducing motion artifacts and improving signal-to-noise ratio, enabling more accurate imaging of anisotropic structures without the need to reposition the patient.
Implementation Method 1
two magnet assemblies spaced apart and arranged to provide a transverse B0 imaging field in an imaging region between them
Implementation Method 2
magnetic nuclei, such as water protons, bound in such structures are subject to dipolar interactions whose strength depends on the orientation of the structures with respect to the B0 field
Implementation Method 3
At angles where the term 3 cos2θ−1 is small these dipolar interactions are reduced with the result that the transverse relaxation time T2 of these tissues is increased. This so called 'magic angle' effect
Data Source
AI summary
The invention relates to an MRI apparatus and a method of MRI involving the acquisition of a first and a second MRI image with mutually different orientations between the BO magnetic field and the object to be investigated. For instance, when imaging structures such as a tendon, due to the magic angle effect, this results in a change in image contrast. According to the invention, a coregistration can be performed between the first and the second MRI image. Moreover, the orientation of a structure within the object can be determined on the basis of the different orientations and the image intensity in the first and the second MRI image. The invention further discloses an apparatus for carrying out the method and a method of shimming the BO magnetic field of the apparatus.