Sensitivity studies for imaging a spherical object embedded in a spherically symmetric, two-layer turbid medium with...

Area of Science:

• Biomedical Optics
• Medical Imaging
• Photonics

Background:

• Layered biological tissues are modeled as two-layer spherical media.
• Embedded spherical objects simulate pathologies like tumors.
• Tissue optical properties (absorption and scattering) are within reported ranges.

Purpose of the Study:

• Develop analytic expressions for photon-density waves in complex media.
• Evaluate optical imaging system sensitivity to absorption and scattering inhomogeneities.
• Determine optimal modulation frequencies for detecting embedded objects.

Main Methods:

• Solved the inhomogeneous Helmholtz equation using the normal-mode-series method in spherical coordinates.
• Applied boundary conditions for a two-layer spherical model.
• Compared optical fields with and without an embedded object to assess sensitivity.

Main Results:

• Enhanced sensitivity to embedded objects occurs when the outer layer is more absorbing or scattering.
• Sensitivity generally increases with modulation frequency, with exceptions for highly absorbing outer layers.
• Amplitude measurements are more sensitive to absorption changes; phase measurements are more sensitive to scattering changes and better at distinguishing perturbations.

Conclusions:

• Phase measurements offer superior capability for differentiating absorption from scattering perturbations in optical imaging.
• Optimizing modulation frequency and understanding layer properties are crucial for sensitive detection of pathologies.
• This model provides insights into designing optical imaging systems for tissue diagnostics.