By measuring the adult human head during carotid endarterectomy, we investigate the depth sensitivity of two methods for deriving the absorption coefficient changes \left(\Delta {\text{μ}}_a\right) from time-resolved reflectance data to absorption changes in inhomogeneous media: (1) the curve-fitting method based on the diffusion equation (DE-fit method) and (2) the time-independent calculation based on the modified Lambert–Beer law (MLB method). Remarkable differences in the determined values of \Delta {\text{μ}}_a caused by clamping the external carotid artery and subsequently clamping the common carotid artery were observed between the methods. The DE-fit method was more sensitive to {\text{μ}}_a changes in cerebral tissues, whereas the MLB method was rather sensitive to {\text{μ}}_a changes in the extracerebral tissues. Our results indicated that the DE-fit was useful for monitoring the cerebral blood circulation and oxygenation during neurosurgical operations. In addition, the combined evaluation of {\text{μ}}_a changes with the DE-fit and MLB methods will provide us with more available information about the hemodynamic changes in the depth direction.