Multislice CEST MRI improves the spatial assessment of tumor pH

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering
• Medical Physics

Background:

• Accurate mapping of extracellular pH (pHe) is essential for understanding tumor and organ heterogeneities.
• Existing methods for pHe measurement have limitations in spatial resolution and coverage.

Purpose of the Study:

• To develop and validate a multislice chemical exchange saturation transfer (CEST) MRI method for in vivo pHe mapping.
• To assess the spatial heterogeneity of pHe in tumors and normal tissues.

Main Methods:

• Adapted the phase offset multiplanar (POMP) method for CEST fast imaging with steady-state free precession (FISP) MRI.
• Modified Bloch-McConnell equations to incorporate pH-dependent chemical exchange for the contrast agent iopamidol.
• Estimated pixel-wise pHe values from multislice acidoCEST MR images in a MDA-MB-231 tumor model.

Main Results:

• Successfully mapped a pHe gradient from 6.73 to 6.81 in a tumor.
• Mapped a pHe gradient from 6.56 to 6.97 across the mouse kidney.
• Measured a pHe of 6.3 in the bladder.

Conclusions:

• Multislice acidoCEST MRI with POMP acquisition and Bloch-McConnell analysis enables robust pHe mapping.
• This multislice approach facilitates the assessment of spatial heterogeneity in tissue pHe.
• The developed method provides valuable insights into the physiological microenvironment of tumors and organs.