CEST MRI pH Imaging via Dual RF Power Levels
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Solution Overview
Problem
Current chemical exchange saturation transfer (CEST) MRI methods for pH imaging are limited by their dependence on contrast agent concentration, relaxation rates, and experimental conditions, which compromise pH specificity, especially when using agents with only one exchangeable site or under suboptimal radio frequency (RF) power levels.
Innovation Solution
A method and system using magnetic resonance imaging (MRI) that acquires signals at two different RF power levels in a CEST pulse sequence to derive pH values and exchange rates, independent of contrast agent concentration, by calculating the ratio or inverse difference of CEST effects, thereby optimizing sensitivity and range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CEST imaging is used, then pH imaging can be performed, but the measurement is dependent on contrast agent concentration and relaxation rates, compromising pH specificity
Solution Approach 1:
The patent changes the parameter of RF power level by acquiring CEST signals at multiple different RF power levels (e.g., low power and high power). This parameter change enables the system to distinguish between concentration-dependent effects and pH-dependent effects, thereby achieving concentration-independent pH measurement while improving pH specificity.
2Adaptability or versatility
If ratiometric CEST imaging is used to reduce concentration effects, then pH determination is simplified, but the method is limited to agents with at least two chemically distinguishable exchangeable sites
Solution Approach 1:
Instead of relying on multiple exchangeable sites, the patent changes the RF power level parameter to achieve concentration independence. This approach works with agents having only one exchangeable site by utilizing the power-dependent behavior of the CEST effect, thereby expanding adaptability to various contrast agents regardless of their exchangeable site configuration.
3Ease of operation
If the same B1 field is used for multiple exchangeable sites, then the procedure is simplified, but the power level is not optimal for any site, compromising pH measurement precision
Solution Approach 1:
The patent acquires CEST signals at multiple different RF power levels, allowing the system to optimize the B1 field strength for each specific exchangeable site. By comparing signals at different power levels, the system can determine the optimal saturation condition for each site, thereby improving pH measurement precision while maintaining operational simplicity through automated multi-level acquisition.
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 concentration-independent pH imaging with improved sensitivity and range, reducing the impact of RF power variations and relaxation rates, and accurately determining pH values regardless of the number of exchangeable sites in the contrast agent.
Implementation Method 1
Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) is one of the methods to increase the MRI sensitivities by exploiting CEST effects, where the signals of water protons change due to the exchange between exchangeable protons and water protons.
Implementation Method 2
a magnetic gradient system including a plurality of magnetic gradient coils configured to apply at least one magnetic gradient field to the polarizing magnetic field
Implementation Method 3
a RF system configured to apply an RF field to the subject and to receive MR signals therefrom
Data Source
AI summary
Systems and methods for indicating pH in a subject using a magnetic resonance imaging (MRI) system are provided. The method includes selecting a contrast agent, generating a chemical exchange saturation transfer (CEST) pulse sequence, performing the pulse sequence with the saturating pulse at a first power level, and performing the pulse sequence again with the saturating pulse at a power level different from the first power level. The method also includes generating values indicating pH of the subject, and generating a report indicating the pH using those values.