NOE-weighted imaging in tumors using low-duty-cycle 2π-CEST

Area of Science:

• Biomedical Imaging
• Magnetic Resonance Imaging
• Chemical Exchange Saturation Transfer (CEST)

Background:

• Nuclear Overhauser enhancement (NOE)-mediated CEST imaging at -3.5 ppm is clinically relevant for tumor diagnosis.
• Conventional quantification of NOE using multiple-pool Lorentzian fit is time-consuming.
• Asymmetric analysis of CEST signals offers a faster alternative but suffers from amide proton transfer (APT) contamination at 3.5 ppm.

Purpose of the Study:

• To introduce a novel 2π-CEST imaging method utilizing asymmetric analysis of a low-duty-cycle pulsed-CEST sequence.
• To reduce the contribution of APT at 3.5 ppm in NOE-mediated CEST imaging.
• To provide a faster and more accurate quantification of NOE for tumor diagnosis.

Main Methods:

• Simulations were conducted to assess the 2π-CEST method's ability to mitigate APT.
• Experiments were performed on animal tumor models to compare 2π-CEST with conventional asymmetric analysis.
• Phantom studies using phospholipids and proteins were employed to investigate the molecular origins of the NOE at -3.5 ppm.

Main Results:

• The 2π-CEST method demonstrated a reduced contribution from APT.
• NOE signals in tumor regions acquired with 2π-CEST appeared more homogeneous than those from conventional methods.
• Phantom studies confirmed that both phospholipids and proteins contribute to the NOE at -3.5 ppm.

Conclusions:

• The NOE at -3.5 ppm possesses a distinct contrast mechanism compared to APT and other CEST/NOE effects.
• The proposed 2π-CEST method offers improved accuracy over conventional asymmetric analysis for NOE detection.
• 2π-CEST significantly reduces scan time compared to the multiple-pool Lorentzian fit method.