Magnetic Resonance Imaging of Low Concentration Solutes via Label Transfer
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Solution Overview
Problem
Current magnetic resonance imaging (MRI) methods face limitations in detecting low concentrations of solutes with exchangeable protons, as they require radio-frequency (RF) saturation, which is inefficient and prone to interference from direct water saturation and tissue magnetization transfer effects.
Innovation Solution
The method employs frequency-selective RF pulses to selectively excite and magnetically label exchangeable solute protons, allowing them to exchange with water protons, thereby enhancing sensitivity and separating agent signals from background noise through label-transfer-modules (LTM) based approaches like frequency transfer, inversion transfer, and dephasing transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RF saturation is used to detect exchangeable solute protons, then the detection method is simple, but the sensitivity is insufficient and interference from direct water saturation and tissue magnetization transfer effects occurs
Solution Approach 1:
The method segments the RF pulse sequence into distinct modules: a frequency-selective RF pulse module for selective excitation of solute protons, an exchange period for proton transfer to water, and a detection module for measuring the water signal. This segmentation allows independent optimization of each module's parameters to achieve high sensitivity while minimizing interference from direct water saturation and magnetization transfer effects.
Solution Approach 2:
The patent uses water protons as an intermediary carrier to detect solute protons. Instead of directly detecting the weak solute proton signal, the method transfers magnetization from solute protons to water protons through chemical exchange, then measures the changes in the abundant water signal. This intermediary approach amplifies the detection signal and eliminates the need for direct solute proton detection, resolving the sensitivity issue.
2Measurement precision
If frequency-selective RF pulses are used to selectively excite solute protons, then sensitivity enhancement is achieved, but the method complexity increases
Solution Approach 1:
The method applies local quality by using frequency-selective RF pulses with specific carrier frequencies and bandwidths tailored to the resonance frequency and spectral width of solute protons. The RF pulse parameters (frequency offset, bandwidth, pulse duration) are locally optimized for the specific solute being detected, allowing selective excitation of solute protons while minimizing excitation of water protons and other tissues, thereby achieving sensitivity enhancement without excessive complexity.
3Adaptability or versatility
If multiple solute proton species are imaged simultaneously, then imaging versatility is improved, but signal separation becomes more difficult
Solution Approach 1:
The method introduces frequency as an additional dimension for signal separation. By using frequency-selective RF pulses with different carrier frequencies or bandwidths for different solute proton species, and by measuring the spectral content of the detected water signal, the method can simultaneously image multiple solute types while maintaining signal separation. The frequency domain provides an orthogonal space that allows independent characterization of each solute species without interference from others.
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 achieves several orders of magnitude sensitivity enhancement, enabling the detection of low-concentration solutes while preserving specific frequency information, allowing for simultaneous imaging of multiple solute proton species without the need for RF saturation.
Implementation Method 1
selectively exciting exchangeable solute protons or protons of exchangeable solute-based water molecules in a subject using at least one frequency-selective radio frequency (RF) pulse, wherein the at least one frequency-selective RF pulse has a corresponding frequency response covering a frequency range, wherein the frequency range encompasses characteristic resonance frequencies of the exchangeable solute protons
Implementation Method 2
allowing a portion of the magnetically labeled exchangeable solute protons to exchange with the water protons
Data Source
AI summary
An embodiment of the current invention provides a method for magnetic resonance (MR) imaging or spectroscopy, comprising: (a) selectively exciting exchangeable solute protons or protons of exchangeable solute-based water molecules within a frequency range in a subject using at least one frequency-selective radio frequency (RF) pulse, wherein the frequency range encompasses characteristic resonance frequencies of the exchangeable solute protons or protons of exchangeable solute-based water molecules, wherein the frequency range is substantially non-overlapping with a characteristic resonance frequency of bulk water protons in the subject, wherein the at least one frequency selective RF pulse performs a substantially minimal excitation on the bulk water protons, and wherein the at least one frequency-selective RF pulse, sometimes in combination with a time period that separates the at least one frequency-selective RF pulse, magnetically labels the exchangeable solute protons or the exchangeable solute-based water molecules; (b) allowing a portion of the magnetically labeled exchangeable solute protons to exchange with the bulk water protons or allowing the magnetically labeled exchangeable solute-based water molecules to exchange with bulk water molecules;(c) repeating (a) and (b) a plurality of times to enhance a population size of the magnetically labeled exchangeable solute protons or the magnetically labeled exchangeable solute-based water molecules; (d) irradiating the subject under observation with a water excitation RF pulse that is adapted to excite the bulk water protons; (e) recording a magnetic resonance (MR) signal from the subject under observation in response to the water excitation RF pulse; and (f) analyzing the recorded MR signal to estimate a quantity associated with the exchangeable solute protons or the exchangeable solute-based water molecules.