A versatile look-up algorithm for mapping pH values and magnesium ion content using ³¹P MRSI

Area of Science:

• Biophysics
• Biochemistry
• Medical Imaging

Background:

• Phosphorus-31 Magnetic Resonance Spectroscopic Imaging (31P MRSI) non-invasively maps pH and magnesium (Mg) using chemical shifts of inorganic phosphate and adenosine-5'-triphosphate (ATP).
• Conventional calibration equations for 31P MRSI are often limited to physiological conditions, posing challenges for analyzing diseased tissues with altered biochemical environments.

Purpose of the Study:

• To develop and validate a condition-independent multi-parametric look-up algorithm for determining pH and Mg using 31P MRSI.
• To improve the accuracy and applicability of 31P MRSI in diverse biochemical conditions, including disease states.

Main Methods:

• A multi-parametric look-up algorithm was developed utilizing multiple quantifiable 31P spectral properties simultaneously.
• A look-up table was generated using measurements from 114 model solutions at 9.4 T, with entries expanded via interpolation using a Hill equation-based function.
• pH and Mg determination incorporated probability distributions accounting for measurement uncertainties, estimating the most plausible values.

Main Results:

• The algorithm was successfully applied to in vivo 3D 31P MRSI data from healthy volunteers' leg muscles and glioblastoma patients' brains at 7 T.
• Generated volumetric maps of pH and Mg showed plausible values and highlighted differences compared to conventional calibration methods.
• The proof-of-concept demonstrated the algorithm's capability in real-world clinical and research scenarios.

Conclusions:

• The proposed multi-parametric look-up algorithm enables condition-independent determination of pH and Mg using 31P MRSI.
• This novel approach enhances the reliability of 31P MRSI for studying biochemical parameters in both healthy and diseased tissues.
• The findings suggest improved diagnostic potential for 31P MRSI in conditions with altered biochemical environments.