Contrast Ratio during Visualization of Subsurface Optical Inhomogeneities in Turbid Tissues: Perturbation Analysis Topics: Biophotonics; Image Processing Methods; Medical Imaging and Diagnosis; Quantitative Bioimaging; Ultrasound and Optical Imaging In Proceedings of the 14th International Joint Conference on Biomedical Engineering Systems and Technologies - Volume 2: BIOSTEC, 94-102, 2021