Multispectral imaging of the Olfactory Bulb activation: Influence of realistic differential pathlength correction factors on the derivation of oxygenation and total hemoglobin concentration maps

摘要

In vivo multispectral reflectance imaging has been extensively used in the somatosensory cortex (SsC) in anesthetized rodents to collect intrinsic signal during activation and derive hemodynamics signals time courses. So far it has never been applied to the Olfactory Bulb (OB), although this structure is particularly well suited to the optical study of brain activation due to the its well defined organization, the ability to physiologically activate it with odorants, and the low depth of the activated layers. To obtain hemodynamics parameters from reflectance variations data, it is necessary to take into account a corrective factor called Differential Pathlength (DP). It is routinely estimated using Monte Carlo simulations, modeling photons propagation in simplified infinite geometry tissue models. The first goal of our study was to evaluate the influence of more realistic layered geometries and optical properties on the calculation of DP and ultimately on the estimation of the hemodynamics parameters. Since many valuable results have been obtained previously by others in the SSc, for the purpose of validation and comparison we performed Monte Carlo simulations in both the SSC and the OB. We verified the assumption of constant DP during activation by varying the hemoglobin oxygen saturation, total hemoglobin concentration and we also studied the effect of a superficial bone layer on DP estimation for OB. The simulations show the importance of defining a finite multilayer model instead of the coarse infinite monolayer model, especially for the SSc, and demonstrate the need to perform DP calculation for each structure taking into account their anatomofunctional properties. The second goal of the study was to validate in vivo multispectral imaging for the study of hemodynamics in the OB during activation. First results are presented and discussed.