Absolute oxygen R1e imaging in vivo with pulse electron paramagnetic resonance

Area of Science:

• Biophysics
• Medical Imaging
• Cancer Research

Background:

• Tissue oxygen levels (pO2) are critical cellular stimuli and key determinants of cancer therapy response.
• Accurate measurement and imaging of pO2 are vital for biological understanding and medical applications.
• Existing in vivo EPR O2 imaging methods often face confounding self-relaxation issues.

Purpose of the Study:

• To introduce a novel pulse electron paramagnetic resonance (EPR) imaging technique for accurate pO2 measurement in tissues and tumors.
• To utilize a nontoxic, injected triaryl methyl (trityl) spin probe for enhanced O2 sensing.
• To overcome the limitations of transverse relaxation rate (R2e) based EPR O2 imaging.

Main Methods:

• Development of a pulse EPR imaging technique using a trityl spin probe.
• Measurement of pO2 based on the longitudinal electron spin relaxation rate (R1e) of the trityl probe.
• Comparison of R1e imaging with existing R2e-based methods for O2 sensitivity and accuracy.

Main Results:

• The trityl probe's R1e is significantly less susceptible to self-relaxation compared to R2e.
• R1e imaging demonstrates improved accuracy in determining absolute pO2 values.
• EPR O2 images generated using R1e exhibit greater precision.

Conclusions:

• R1e imaging provides a more accurate method for assessing oxygenation in both cancerous and normal tissues in animal models.
• This technique enables rapid, noninvasive O2 imaging, crucial for understanding oxygen biology.
• The enhanced imaging capability will aid in elucidating the relationship between oxygenation patterns and therapy outcomes.