Maximum fluence for accurate functional photoacoustic microscopy.

Area of Science:

• Biomedical optics
• Medical imaging
• Photoacoustic microscopy

Background:

• Photoacoustic microscopy (PAM) offers high-resolution mapping of blood oxygen saturation (sO2).
• Transient thermal accumulation from laser irradiation in fast functional PAM may impact sO2 measurement accuracy, a factor not extensively studied.

Purpose of the Study:

• To investigate the impact of laser irradiation on sO2 accuracy in fast functional PAM.
• To develop a numerical model for estimating maximum laser fluence for accurate sO2 measurements.

Main Methods:

• Established a numerical model to estimate maximum laser fluence (Fmax) based on laser irradiation parameters.
• Conducted in vivo experiments using 532-nm and 558-nm wavelengths.
• Validated the model using a blood phantom and mouse brain samples.

Main Results:

• Determined the relationship between maximum fluence (Fmax) and repetitive laser pulse number (N) for accurate sO2 measurement: Fmax = 45N^-0.41 mJ·cm^-2.
• Validated the model's accuracy and stability under long-term scanning conditions.
• Demonstrated practical applicability in preclinical settings.

Conclusions:

• The developed maximum-fluence model offers crucial guidance for optimizing laser settings in fast functional PAM.
• Ensuring accurate sO2 measurements requires careful consideration of laser fluence and pulse repetition, especially in dynamic imaging scenarios.