Effect of strong homonuclear proton coupling on localized (13)C detection using PRESS

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysical Chemistry
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• Proton coupling influences ¹³C incorporation measurements in MRI.
• Accurate quantification of ¹³C in biological systems is crucial for metabolic studies.
• Existing MRI sequences may be affected by homonuclear proton coupling.

Purpose of the Study:

• To investigate the impact of strong homonuclear proton coupling on ¹³C incorporation measurements.
• To evaluate both indirect (PRESS-POCE) and direct (PRESS-DEPT) detection methods at 3.0 Tesla.
• To quantify the potential errors introduced by proton coupling in ¹³C MRI.

Main Methods:

• Numerical simulations and experimental validation using glutamate at 3.0 T.
• Utilized PRESS sequences for proton localization.
• Incorporated Proton Observe Carbon Edited (POCE) for indirect detection and Distortionless Enhancement by Polarization Transfer (DEPT) for direct detection.

Main Results:

• Strong homonuclear proton coupling significantly modifies ¹³C measures from both PRESS-POCE and PRESS-DEPT sequences.
• Observed changes in MR lineshapes of ¹³C-bonded and non-bonded protons during ¹³C incorporation.
• Potential cross-contamination up to 30% between glutamate ¹³C(3) and ¹³C(4) in PRESS-POCE.
• DEPT enhancement reduction varied across glutamate carbons (¹³C(2), ¹³C(3), ¹³C(4)) and was exacerbated by PRESS localization.

Conclusions:

• Homonuclear proton coupling is a critical factor affecting the accuracy of ¹³C incorporation measurements in MRI.
• Both indirect and direct detection methods are susceptible to errors caused by proton coupling.
• Sequence parameters, particularly PRESS echo times (TE1, TE2), influence the extent of these errors in direct detection.