CEST MRI Contrast Agents Using Salicylic Acid Derivatives
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Solution Overview
Problem
Current MRI contrast agents for molecular imaging lack sensitivity and effective contrast enhancement, particularly in detecting biomarkers at low concentrations, due to limitations in chemical exchange saturation transfer (CEST) technology.
Innovation Solution
Development of novel MRI contrast agents, such as salicylic acid and its derivatives, which exhibit strong CEST contrast at shifts greater than 5.5 ppm, enabling improved sensitivity and contrast effects through Chemical Exchange Saturation Transfer (CEST) or frequency labeled exchange (FLEX) imaging techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional MRI contrast agents are used, then anatomical imaging is achieved, but sensitivity for detecting low-concentration biomarkers is insufficient
Solution Approach 1:
The patent introduces exchangeable protons as an intermediary between the contrast agent and water protons. The contrast agent's exchangeable protons transfer magnetization to abundant water protons, amplifying the detection signal. This mediator mechanism enables detection of low-concentration biomarkers by leveraging the high abundance of water protons in the body.
Solution Approach 2:
The patent exploits changes in chemical shift parameters of exchangeable protons to achieve contrast. By selecting contrast agents with specific chemical shifts (e.g., 6.0-15.0 ppm from water) and using frequency-selective saturation pulses, the system can selectively detect biomarkers at low concentrations through parameter-based differentiation.
2Measurement precision
If CEST MRI technique is applied to detect low-concentration biomarkers, then detection sensitivity improves, but the contrast enhancement effect is insufficient without adequate signal amplification
Solution Approach 1:
Water protons serve as a signal amplifier and intermediary. The exchangeable protons on the contrast agent transfer their saturated magnetization state to the abundant water protons, which then produce a detectable signal change. This amplification through water protons provides reliable contrast enhancement even when the contrast agent concentration is low.
Solution Approach 2:
The patent employs periodic radiofrequency saturation pulses applied at the resonance frequency of exchangeable protons. This periodic saturation, combined with the continuous exchange process, builds up magnetization transfer effect over time, enhancing the contrast signal reliability through repeated cycles of saturation and exchange.
3Speed
If exchangeable protons are saturated rapidly to detect low-concentration agents, then detection speed improves, but radio-frequency power requirements increase
Solution Approach 1:
The patent utilizes the continuous exchange process between exchangeable protons and water protons to maintain saturation. Instead of requiring repeated high-power pulses, the system applies continuous low-power saturation that is sustained by the ongoing chemical exchange, reducing overall RF power requirements while maintaining detection speed.
Solution Approach 2:
The patent optimizes the chemical shift parameter of exchangeable protons to achieve larger frequency separation from water protons (6.0-15.0 ppm). This parameter optimization allows for more efficient saturation with lower RF power by reducing the required bandwidth and enabling more selective, lower-power irradiation at the specific resonance frequency.
4Measurement precision
If high chemical shift separation is used to resolve exchangeable protons from water, then spectral resolution improves, but the exchange rate must be slow which reduces saturation efficiency
Solution Approach 1:
The patent carefully optimizes the chemical shift parameter to achieve an optimal balance. By selecting exchangeable protons with chemical shifts of 6.0-15.0 ppm from water, the system achieves sufficient spectral resolution for selective saturation while maintaining exchange rates that are fast enough for efficient magnetization transfer. This parameter optimization resolves the contradiction between resolution and efficiency.
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
These agents provide significantly enhanced MRI contrast at shifts ranging from 6.0 to 15.0 ppm, improving the detection of biomarkers and metabolic changes, with potential applications in tumor detection, receptor imaging, and metabolic monitoring, while offering lower toxicity and ease of modification compared to traditional agents.
Implementation Method 1
CEST MRI is a technique in which low-concentration marker molecules are labeled by either saturating or labeling their exchangeable protons spins by radio-frequency (RF) irradiation. If such saturation or labeling can be achieved rapidly (i.e., before the spin exchanges), exchange of such labeled spins with water leads to transfer of the magnetization
Implementation Method 2
These exchangeable protons can be 'magnetically tagged' using a radiofrequency saturation pulse applied at their resonance frequency
Implementation Method 3
The tagged protons exchange with the protons of surrounding water molecules and consequently reduce the MRI signal. This in and of itself would not be visible at the low concentrations of solute, but the exchanged protons are replaced with fresh, unsaturated protons and the same saturation process is repeated. Over time (e.g., several seconds) this repetition results in signal amplification
Data Source
AI summary
Compositions and methods for chemical exchange saturation transfer (CEST) based magnetic resonance imaging (MRI) or frequency labeled exchange (FLEX) imaging are disclosed. Beta-hydroxycarboxylate and beta-aminocarboxylate derivatives including salicylic acid, salicylates, salicylic acid prodrugs, N-alkyl/aryl/acyl/sulfonyl-anthranilic acid analogs, and any aromatic compound with OH/NH group ortho to the carboxylic acid group are disclosed. Such compounds can be used as general MRI organic contrast agents and produce significantly improved contrast in MR images detectable through CEST or FLEX.