Pulsed photothermal temperature profiling of agar tissue phantoms

Area of Science:

• Biomedical Optics
• Thermal Analysis
• Non-invasive Sensing

Background:

• Accurate temperature depth profiling is crucial for understanding thermal processes in various applications.
• Pulsed photothermal radiometry (PPTR) offers a non-contact method for thermal analysis.
• Water-based samples, common in biological and industrial settings, present unique challenges for thermal measurements.

Purpose of the Study:

• To experimentally determine the accuracy of PPTR for temperature depth profiling in water-based samples.
• To compare the performance of PPTR using different spectral bands of the radiation detector.
• To evaluate the impact of spectral filtering on measurement accuracy and spatial resolution.

Main Methods:

• Utilized custom tissue phantoms with agar gel layers and thin absorbing layers.
• Employed two PPTR acquisition system configurations: a customary spectral band (3.0-5.5 µm) and a spectrally narrowed band (4.5-5.5 µm).
• Reconstructed laser-induced temperature depth profiles using a custom minimization algorithm and validated against optical coherence tomography (OCT) and histology.

Main Results:

• PPTR-derived temperature depth profiles showed excellent correlation with phantom geometry.
• Absorbing layer depth determination exhibited good repeatability, with spatial resolution decreasing with depth.
• Spectral filtering significantly improved accuracy and resolution, particularly for shallow layers (~120 µm) and multi-layered structures.
• The average full width at half maximum (FWHM) of temperature peaks was 23% of the layer depth.

Conclusions:

• PPTR is a highly accurate technique for temperature depth profiling in water-based media.
• Spectrally narrowed detection bands enhance PPTR's precision and resolution capabilities.
• The findings support PPTR's utility for detailed thermal characterization of complex layered materials.