Protoporphyrin IX delayed fluorescence imaging: a modality for hypoxia-based surgical guidance

Area of Science:

• Biomedical Optics
• Molecular Imaging
• Cancer Research

Background:

• Tumors often exhibit hypoxia, characterized by low oxygen partial pressure (pO2) and chaotic blood flow, complicating surgical guidance.
• Imaging tissue pO2 is crucial for understanding cellular metabolism and disease states, but has been technically challenging.

Purpose of the Study:

• To demonstrate the utility of protoporphyrin IX (PpIX) delayed fluorescence (DF) as a novel hypoxia imaging agent for surgical guidance.
• To develop a time-gated imaging system for real-time pO2 mapping using PpIX DF.

Main Methods:

• Utilized a time-gated imaging system to capture PpIX delayed fluorescence (DF) signals.
• Acquired both prompt and DF signals sequentially for pO2 imaging, independent of PpIX concentration.
• Achieved video-rate acquisition of pO2 images for real-time metabolic information.

Main Results:

• Successfully imaged hypoxia signals from PpIX in a pancreatic cancer model.
• Achieved >5X contrast for hypoxic tumor regions compared to normal oxygenated tissues.
• Demonstrated signal amplification and intuitive temporal contrast through tissue palpation, linked to neoangiogenic blood flow.

Conclusions:

• Protoporphyrin IX (PpIX) delayed fluorescence (DF) offers a novel intrinsic contrast mechanism for tumor visualization.
• This technique shows significant potential for translation to human oncologic surgical guidance.
• Real-time pO2 imaging provides critical metabolic information for surgical decision-making.