Reporting of quantitative oxygen mapping in EPR imaging

Area of Science:

• Medical Imaging
• Biophysics
• Cancer Research

Background:

• Oxygen (pO2) mapping is vital for cancer treatment, as hypoxic regions exhibit 3-4x resistance to therapy.
• Electron paramagnetic resonance spectral-spatial imaging (EPRI) combined with MRI offers precise pO2 mapping.
• Co-registration of EPR and MR images can exaggerate spatial resolution, hindering accurate distinction between hypoxic and normoxic tissues.

Purpose of the Study:

• To describe pO2 maps based on the intrinsic spatial resolution of EPRI.
• To address limitations in distinguishing hypoxic from normoxic regions caused by image co-registration.
• To highlight the importance of intrinsic resolution and uncertainty quantification in EPRI-based pO2 mapping.

Main Methods:

• Utilizing spectral parameters like Full Width at Half Maximum (FWHM) of the EPR absorption line to define intrinsic EPRI resolution.
• Considering transverse relaxation times (T(2)(*)) and excitation pulse delay times (t(p)) that limit resolution in frequency-encoded and single-point imaging.
• Analyzing the impact of spectral uncertainties and blurring on pO2 level interpretation.

Main Results:

• The intrinsic spatial resolution of EPRI is determined by spectral parameters such as FWHM and T(2)(*).
• Co-registration with MRI can lead to exaggerated spatial resolution, blurring boundaries and misrepresenting pO2 levels.
• Blurring effects can cause apparent increases in pO2 in hypoxic regions, complicating interpretation.

Conclusions:

• Accurate pO2 mapping requires utilizing the intrinsic resolution of EPRI, not solely relying on co-registered MRI resolution.
• Understanding and specifying EPRI's intrinsic resolution and associated pO2 uncertainties are essential for reliable interpretation.
• Precise distinction of hypoxic regions is critical for effective cancer treatment monitoring and planning.