Excitation-and-collection geometry insensitive fluorescence imaging of tissue-simulating turbid media

Abstract

We present an imaging technique for the correction of geometrical effects in fluorescence measurement of optically thick, turbid media such as human tissue. Specifically, we use the cross-polarization method to reject specular reflection and enhance the diffusive backscattering of polarized fluorescence excitation light from the turbid media. We correct the nonuniformity of the image field caused by the excitation-and-collection geometry of a fluorescence imaging system by normalizing the fluorescence image to the cross-polarized reflection image. The ratio image provides a map of relative fluorescence yield, defined as the ratio of emerging fluorescence power to incident excitation, over the surface of an imaged homogeneous turbid medium when fluorescence excitation-and-collection geometries vary in a wide range. We investigate the mechanism of ratio imaging by using Monte Carlo modeling. Our findings show that this technique could have a potential use in the detection of early cancer, which usually starts from a superficial layer of tissue, based on the contrast in the tissue fluorescence of an early lesion and of the surrounding normal tissue.

Fast and noninvasive fluorescence imaging of biological tissues in vivo using a flying-spot scanner

“…In the case of 9L glioma tumor, the fluorescence image was divided by the corresponding reflectance image. Qu et al [20] have reported the use of F/R imaging to correct geometrical artifacts during fluorescence imaging of tissue phantoms. They were able to correct their fluorescence images more effectively by normalizing them to the diffuse reflection image rather than to the total reflection image (diffuse and specular reflection).…”

Angular distribution of diffuse reflectance in biological tissue

“…Specifically, we measured the angular distribution of diffuse reflectance in real biological tissues, and compared the results with those obtained from tissue equivalent phantoms. In addition, we found that a diffuse model of light transport can be applied to explain the skewing effects [6,7] observed under oblique incidence. We conducted measurements in two different kinds of bi-ological tissues: isotropic and anisotropic.…”

“…Their results showed that the distribution was very close to the Lambertian distribution except for locations proximate to the incident point. In a later study, Qu et al [6] also found that when they used Monte Carlo simulation, the angular profile of diffuse reflectance was almost Lambertian under a normal incidence of a broad beam. However, under oblique incidence, the angular distribution was different from the Lambertian distribution.…”

“…In many applications, optical fibers are used to deliver and receive light because they are flexible and can be easily incorporated into endoscopes. Since a fiber optic probe has a limited acceptance angle, its geometrical design [5], and the spatial and angular distribution [6,7] of the light signals may affect the amount of light that is detected, and need to be characterized. In addition, the angular profile of diffuse reflectance from the tissue surface is an important factor for the realistic rendering of biological tissues in computer graphics [8].…”

A high-efficiency fiber-based imaging system for co-registered autofluorescence and optical coherence tomography

“…For endoscopic imaging such as in lung, the need for fiber optic catheters creates additional challenges. Fiber-based catheters that use separate adjacent fibers for the two modalities have been developed [17][18][19][20][21][22][23][24]. However, this approach compromises co-registration of the two modalities.…”