Multi-nuclear MR Thermometry for Absolute Temperature Mapping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current magnetic resonance imaging (MRI) techniques face challenges in accurately measuring absolute temperature in vivo due to spatiotemporal variations in the main magnetic field and the lack of local internal frequency references, limiting their applicability, especially in scenarios with small thermal gradients and physiological noise.
Innovation Solution
A multi-nuclear MR thermometry method utilizing the unique frequency dependence of hydrogen and sodium nuclei, which provides a one-to-one mapping of their precession frequency difference to absolute temperature, overcoming the limitations of existing methods by using endogenous molecules like water and sodium ions, and a framework for absolute MR thermometry applicable with any pair of nuclei.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single-nuclear PRF thermometry is used, then temperature mapping can be performed, but measurement accuracy deteriorates due to B0 field variations and lack of internal reference
Solution Approach 1:
The patent introduces a second nucleus (such as sodium-23) as an intermediary reference system. This second nucleus serves as an internal frequency reference that experiences the same B0 field variations as the primary nucleus (proton), allowing differential measurement that cancels out common-mode B0 drift and improves temperature measurement accuracy.
Solution Approach 2:
The patent changes the measurement parameter from single-nucleus frequency shift to dual-nucleus frequency difference. By measuring the frequency difference between two nuclei with different gyromagnetic ratios and temperature dependencies, the system achieves both absolute temperature measurement and immunity to B0 field variations.
2Measurement precision
If internal frequency reference is introduced using traditional molecules like methanol or glycol, then absolute temperature measurement is enabled, but in vivo applicability is lost due to non-ubiquity in human body
Solution Approach 1:
The patent employs endogenous nuclei (protons from water and sodium ions) that are naturally present in biological tissues. These self-service internal references eliminate the need for exogenous contrast agents or temperature-sensitive molecules, enabling direct in vivo temperature measurement without modification of the biological system.
Solution Approach 2:
The patent utilizes the ubiquity of water and sodium in all biological tissues to create a universally applicable thermometry method. The dual-nucleus approach works across different organ systems and physiological conditions, providing broad in vivo applicability while maintaining absolute temperature measurement capability.
3Measurement precision
If NAA peak imaging is used for internal referencing, then absolute thermometry is achieved, but imaging time increases and SNR decreases due to low NAA concentration
Solution Approach 1:
The patent changes the reference mechanism from relying on low-concentration metabolites (NAA) to utilizing high-concentration endogenous nuclei (water protons and sodium ions). This parameter change in reference concentration enables faster signal acquisition and improved SNR while maintaining absolute temperature measurement accuracy.
4Measurement precision
If polynomial fit is used to estimate background B0 change, then localized heating measurement is improved, but distributed thermal change measurement fails due to assumption of localized heating
Solution Approach 1:
The patent introduces a second nucleus as a spatially distributed internal reference that experiences the same B0 field variations across the entire field of view. This intermediary reference system eliminates the need for polynomial fitting assumptions, enabling accurate measurement of both localized and distributed thermal changes throughout the imaging volume.
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
Enables accurate and robust measurement of absolute temperature with reduced sensitivity to macroscopic B0 inhomogeneities, as demonstrated in aqueous solutions, agarose gel samples, and ex vivo mouse tissues, with proof-of-concept experiments showing agreement with infrared measurements.
Implementation Method 1
A unique feature of magnetic resonance imaging (MM) is its contrast-sensitivity to temperature changes. For water, MR parameters such as the longitudinal relaxation time (T1), transverse relaxation time (T2), proton density (M0), diffusion coefficient (D) and chemical shift (CS) are all temperature-dependent. The chemical shift of protons, also known as the 'proton resonance frequency (PRF) shift' phenomenon, has been shown to have the greatest sensitivity to temperature fluctuations.
Implementation Method 2
The chemical shift of protons, also known as the 'proton resonance frequency (PRF) shift' phenomenon, has been shown to have the greatest sensitivity to temperature fluctuations.
Data Source
AI summary
System and methods that reconstruct absolute temperature using a multi-nuclear approach. Specifically, the methods and systems utilize independent NMR/MRI information provided by the precession frequency of two different nuclei to reconstruct a map of the absolute temperature.