Single-Sided NMR Sensor Microscopic Depth Resolution
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Solution Overview
Problem
Single-sided magnetic resonance imaging (MRI) sensors suffer from poor depth resolution due to lateral gradients in the magnetic field produced by open magnets, limiting the ability to discriminate heterogeneities based on relaxation times and self-diffusion coefficients, and requiring complex and expensive magnet geometries to achieve flat sensitive volumes.
Innovation Solution
A hand-held single-sided NMR sensor with a magnet system comprising four permanent magnet blocks and a coil system for producing a uniform magnetic field, allowing for selective RF excitation and mechanical repositioning to achieve a flat sensitive slice with microscopic resolution, enabling contrast by NMR parameters like relaxation times and self-diffusion coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a field with a strong gradient is used in open magnets, then volumes at different depths can be accessed by retuning excitation frequency, but depth resolution deteriorates due to lateral gradients defining a curved sensitive slice
Solution Approach 1:
The patent changes the magnetic field configuration from a strong gradient field to a homogeneous field region. This parameter change allows the sensitive slice to become flat rather than curved, improving depth resolution while maintaining the ability to access different depths through frequency retuning.
Solution Approach 2:
Instead of accepting the curved sensitive slice that results from strong gradient fields, the patent inverts the approach by designing a magnet geometry that produces a homogeneous field region, thereby inverting the field profile characteristic to achieve a flat sensitive slice with improved depth resolution.
2Manufacturing precision
If magnet geometry is optimized to improve flatness of sensitive volume, then depth resolution improves slightly, but device complexity and cost increase due to complicated magnet geometries
Solution Approach 1:
The patent segments the magnet system into a specific configuration of permanent magnet blocks arranged to create a homogeneous field region. This segmentation allows achieving flat sensitive volume without requiring overly complex integrated geometries, balancing performance with manufacturability.
Solution Approach 2:
The patent changes the field homogeneity parameter achieved through optimized magnet geometry to produce a homogeneous field region, which naturally provides a flat sensitive slice without requiring excessive geometric complexity.
3Adaptability or versatility
If frequency retuning is used to select planar slices at different depths, then depth profiling is enabled, but measurement precision deteriorates due to systematic errors in T2eff from B0 and B1 field variations
Solution Approach 1:
The patent changes the magnetic field uniformity parameter by creating a homogeneous field region, which eliminates the B0 and B1 field variations that cause systematic errors in T2eff measurements, thereby improving measurement precision while maintaining depth profiling capability through frequency retuning.
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 solution achieves microscopic resolution of about 25 μm with a low-cost, simple magnet system, comparable to high-resolution stray field imaging methods, while reducing constraints on magnet optimization and eliminating background signals from the RF coil housing.
Implementation Method 1
a magnet system for producing a magnetic field constant in a plane external to the body
Implementation Method 2
a coil system for producing an oscillating magnetic field substantially transverse to the magnetic field
Implementation Method 3
Single-sided nuclear magnetic resonance (NMR) sensors are used to characterize large size objects
Data Source
AI summary
A low-cost single-sided NMR sensor to produce depth profiles with microscopic spatial resolution is presented. The open geometry of the NMR sensor provides a non-invasive and non-destructive testing method to characterize the depth structure of objects of arbitrary size. The permanent magnet geometry generates one plane of constant magnetic field intensity parallel to the scanner surface. By combining the highly uniform static gradient with selective RF excitation, a thin flat sensitive slice can be defined. By moving the relative position between the slice and the object, one-dimensional profiles of the near surface of large samples are produced with high spatial resolution.