Polarization response of second-harmonic images for different collagen spatial distributions

Abstract

The response to polarization of second-harmonic generation (SHG) microscopy images of samples with different collagen distributions (quasialigned, partially organized, and nonorganized) has been analyzed. A linear decay relationship between the external arrangement and polarization sensitivity was found. SHG signal from nonorganized samples presented a large structural dispersion and a weak dependence with incident polarization. Polarization dependence is also associated with the internal organization of the collagen fibers, directly related to the ratio of hyperpolarizabilities ρ. This parameter can experimentally be computed from the modulation of the SHG signal. The results show that both external and internal collagen structures are closely related. This provides a tool to obtain information of internal properties from the polarimetric response of the external spatial distribution of collagen, which might be useful in clinical diagnosis of pathologies related to changes in collagen structure.

Quantifying external and internal collagen organization from Stokes-vector-based second harmonic generation imaging polarimetry

“…It is well known that SHG signal emerging from a sample is polarization dependent. Moreover, it has also been reported that the modulation of the SHG signal for linear polarization is maximized when the sample under study presents a quasiparallel external structure, that is DoI values >0.70 [12]. When the sample presents a lower external organization (i.e.…”

“…However the use of elliptical states might provide improved SHG signal and relevant information [16][17][18]. Whereas the dependence of quasi-parallel collagen structures and linear polarization is well understood (theoretical and experimentally), the combination of samples with non-regular arrangements and incident elliptical polarized light is still a topic of interest [12,19]. Moreover, some polarization parameters such as the dichroic ratio [12,20] or the anisotropy factor [21] have been defined taking into account only linear polarization.…”

“…Whereas the dependence of quasi-parallel collagen structures and linear polarization is well understood (theoretical and experimentally), the combination of samples with non-regular arrangements and incident elliptical polarized light is still a topic of interest [12,19]. Moreover, some polarization parameters such as the dichroic ratio [12,20] or the anisotropy factor [21] have been defined taking into account only linear polarization. As recently reported, this fact might lead to incomplete results under certain experimental circumstances (for instance, when the specimen does not show a well-organized collagen arrangement) [19].…”

Polarimetric multiphoton microscopy for the analysis of ocular structures

“…Por otra parte, el signo de  determina la forma de la distribución de intensidad: para valores negativos aparece un máximo secundario en torno al estado de polarización vertical [16].. En las muestras aquí utilizadas el tejido de escleral presenta valor positivo de , mientras que la córnea muestra una distribución de intensidad correspondiente a valores negativos de . Mapas de  para dichas muestras (derecha).…”

“…• Construcción de un modelo teórico para analizar la sensibilidad a la polarización de la señal SHG en colágeno tipo I, permitiendo obtener una expresión analítica para el cálculo de la organización interna o a escala molecular [15]. La comprobación experimental permitió obtener por primera vez la relación entre la organización interna y externa del colágeno [16]. La sensibilidad a la polarización fue propuesta como método de diagnóstico clínico de la patología corneal conocida como queratocono.…”