Monte Carlo-Based Analysis of Wavelength Penetration in Thyroid Tissue

Diffuse Reflectance Spectroscopy (DRS) is a promising non-invasive optical method for assessing thyroid functionality through light-tissue interactions. This study evaluates the diagnostic potential of 860 nm, 890nm, and 1020 nm based on their interaction with key chromophores involved in thyroid hormone regulation. Photon transport simulations modeled the thyroid as a six-layer structure, including skin, subcutaneous tissue, platysma muscle, investing fascia, strap muscles, and the thyroid gland. The results indicate that oxyhemoglobin and deoxyhemoglobin absorb strongly at 860 nm and 890 nm, leading to higher reflectance in superficial vascularized regions. In contrast, lipids and water exhibit strong absorption at 1020 nm, correlating with deeper penetration (2.8 mm) into thyroid tissue. Photon penetration depth analysis confirmed that 860 nm penetrates 1.8 mm, making it suitable for surface-level vascular assessment, while 890 nm reaches 2.2 mm, balancing penetration and contrast. 1020 nm, with the deepest penetration of 2.8 mm, is ideal for deeper tissue evaluation. CNR analysis showed the highest contrast at 860 nm (CNR = 2.1), followed by 890 nm (CNR = 1.7) and 1020 nm (CNR = 1.2), while SNR measurements identified 1020 nm as the most reliable (SNR = 30 dB), 890 nm as balanced (SNR = 22 dB), and 860 nm as the noisiest (SNR = 15 dB). These spectral characteristics enable a multi-depth diagnostic approach, where 860 nm aids surface-level vascular detection, 890 nm ensures balanced tissue evaluation, and 1020 nm facilitates deep tissue assessment, enhancing overall thyroid diagnostic accuracy.