NMR Spectral Resolution in Inhomogeneous Magnetic Fields

Solution Overview

Problem

Nuclear magnetic resonance (NMR) spectral resolution is limited by inhomogeneous magnetic fields in existing well-logging tools, making it difficult to distinguish between chemical shifts of water and hydrocarbons, which differ by only a few parts-per-million.

Innovation Solution

A method involving the generation of magnetic pulses and gradient pulses to produce a reconstructed high-resolution NMR spectrum by determining the spatial dependence of the inhomogeneous magnetic field, allowing for the correction and summation of spectra to improve spectral resolution without requiring more homogeneous magnetic fields.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the magnetic field homogeneity is improved to achieve high spectral resolution, then the spectral resolution is improved, but the device complexity and manufacturing cost increase significantly

Engineering Contradiction:

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

A gradient pulse is introduced as an intermediary element to modulate the magnetic field during the NMR measurement process. This gradient pulse enables spatial encoding of the magnetic field inhomogeneity, allowing the system to achieve high spectral resolution without requiring a perfectly homogeneous magnetic field from the magnet itself

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system changes the magnetic field parameters dynamically by applying gradient pulses with varying strengths and directions during different time periods of the NMR sequence. This allows the magnetic field to be intentionally made inhomogeneous during measurement while still achieving high resolution through mathematical reconstruction

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If the magnetic field homogeneity is improved to achieve high spectral resolution, then the spectral resolution is improved, but the manufacturing cost increases

Engineering Contradiction:

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The invention converts the harmful effect of magnetic field inhomogeneity into a beneficial tool for achieving high spectral resolution. By intentionally applying controlled gradient pulses that exploit the spatial variation in the magnetic field, the system transforms what was previously a limitation into a feature that enables chemical shift measurement without requiring expensive high-precision magnets

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Measurement precision

If gradient pulses are applied to improve spectral resolution in inhomogeneous fields, then the spectral resolution is improved, but the signal-to-noise ratio may deteriorate

Engineering Contradiction:

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The gradient pulse is applied periodically during specific time intervals (first time period and second time period) within the NMR sequence, rather than continuously. This periodic application allows the system to maintain spectral resolution improvement while managing the impact on signal strength through controlled timing

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The gradient pulse is applied in advance during the first time period before the main signal acquisition, preparing the spin system with appropriate phase encoding. This preliminary action enables subsequent signal reconstruction that maintains both resolution and signal-to-noise ratio

Inventive Principle:

Principle #10Preliminary action

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 enables high-resolution NMR measurements by effectively reducing the impact of magnetic field inhomogeneities, allowing for accurate differentiation of chemical shifts and maintaining signal-to-noise ratio, even in complex field distributions.

Implementation Method 1

Nuclear magnetic resonance (NMR) spectroscopy is one of the most used methods for the characterization of molecular species, functional groups and structures

Methodology Applied

Scientific EffectNuclear magnetic resonance: Magnetic Field

Implementation Method 2

The B1 antenna should be capable of transmitting and receiving signals at the Lamor frequency, fL, given by the equation: fL = □B0/2π

Methodology Applied

Scientific EffectLamor precession: Precession

Implementation Method 3

during the first time period, generating a gradient pulse

Methodology Applied

Scientific EffectMagnetic field gradient: Magnetic Field

Data Source

PatentUS7683615B2Method and apparatus to improve NMR spectral resolution in an inhomogeneous magnetic field

Publication Date: 2010.03.23

AI summary

A method and apparatus for improving spectral resolution of an NMR measurement in the presence of an inhomogeneous magnetic field. According to one embodiment, a method producing a high resolution nuclear magnetic resonance (NMR) spectrum for a sample in an inhomogeneous magnetic field may comprise generating a first magnetic pulse and a second magnetic pulse, the first and second magnetic pulses being separated in time by a first time period, during the first time period, generating a gradient pulse, repeating the steps of generating the first and second magnetic pulses and generating the gradient pulse N times for different values of a field strength of the gradient pulse, wherein N is an integer greater than one, after each second magnetic pulse, acquiring a signal from the sample, and producing a reconstructed high resolution NMR spectrum from the acquired signals.