The pH sensitivity of APT-CEST using phosphorus spectroscopy as a reference method.

Area of Science:

• Biomedical Imaging
• Magnetic Resonance Imaging
• Physiological Monitoring

Background:

• Intracellular pH is a crucial biomarker altered in diseases like cancer.
• Phosphorus magnetic resonance spectroscopic imaging (³¹ P MRSI) is a standard for pH measurement.
• Amide Proton Transfer-Chemical Exchange Saturation Transfer (APT-CEST) MRI is a promising alternative for pH quantification.

Purpose of the Study:

• To evaluate the efficacy of APT-CEST MRI techniques for pH quantification.
• To compare two analysis methods: Magnetization Transfer Ratio asymmetry (MTR_asym) and Lorentzian Difference Analysis (LDA).
• To correlate APT-CEST derived pH values with those from ³¹ P MRSI in glioblastoma patients.

Main Methods:

• APT-CEST MRI and ³¹ P MRSI were performed on 14 glioblastoma patients and 12 healthy controls.
• Z-spectrum analysis was conducted using both MTR_asym and LDA methods.
• Statistical analysis, including two-sample t-tests, was used to compare results across different regions and groups.

Main Results:

• Both MTR_asym and LDA showed good correspondence with ³¹ P MRSI-derived pH values.
• Significant differences in MTR_asym, LDA, and pH were observed in glioblastoma, contralateral, and white matter regions (P < 0.001).
• LDA demonstrated a slightly stronger correlation (r=0.78) with pH compared to MTR_asym (r=0.70).

Conclusions:

• Both MTR_asym and LDA methods are suitable for monitoring pH changes using APT-CEST MRI.
• The LDA approach offers enhanced suitability for pH quantification due to its improved correlation with direct pH measurements.
• APT-CEST MRI, particularly with LDA, shows potential for noninvasive pH monitoring in clinical settings, especially for tumor characterization.