Laboratory for Photonics Research of Bio/nano Environments (PROBE), Department of Electrical and Computer Engineering,University of Illinois Urbana-Champaign, 1406 W Green Street, Urbana, Illinois 61801, USA.
Fourier transform second-harmonic generation (SHG) microscopy has been applied to quantitatively compare the information content between SHG images obtained from the forward and backward direction for three tissue types: porcine tendon, sclera, and ear cartilage. Both signal types yield consistent information on the preferred orientation of collagen fibers. For all specimens, the Fourier transform of the forward and backward SHG images produces several overlapping peaks in the magnitude spectrum at various depths into the tissues, indicating that some information present in the forward SHG images can be extracted from the backward SHG images. This study highlights the potential of backward SHG microscopy for medical diagnostics.
"Other collagen-based tissues with biological or clinical interest were also investigated. These include dermis connective tissue [22,23], tendons [24–26], ear cartilage , sclera [24,27] and breast tissue  among others. Most of these studies used the FT to extract numerical information from collagen fiber organization. "
[Show abstract][Hide abstract] ABSTRACT: The spatial organization of stromal collagen of ex-vivo corneas has been quantified in adaptive-optics second harmonic generation (SHG) images by means of an optimized Fourier transform (FT) based analysis. At a particular depth location, adjacent lamellae often present similar orientations and run parallel to the corneal surface. However this pattern might be combined with interweaved collagen bundles leading to crosshatched structures with different orientations. The procedure here reported provides us with both principal and crosshatched angles. This is also able to automatically distinguish a random distribution from a cross-shaped one, since it uses the ratio of the axes lengths of the best-fitted ellipse of the FT data as an auxiliary parameter. The technique has successfully been applied to SHG images of healthy corneas (both stroma and Bowman's layer) of different species and to corneas undergoing cross-linking treatment.
"In order to examine SHG microscopy's potential for assessing bone structure, we choose an example study where we quantify the structural changes in the collagen fiber organization of bone due to age. For quantification, we employ an approach called Fourier transformsecond harmonic generation (FT-SHG) imaging— recently developed for quantifying collagen fiber organization in biological tissues   . Here, relative collagen fiber orientation is considered as a parameter for quantification. "
[Show abstract][Hide abstract] ABSTRACT: We propose the use of second-harmonic generation (SHG) microscopy for imaging collagen fibers in porcine femoral cortical bone. The technique is compared with scanning electron microscopy (SEM). SHG microscopy is shown to have excellent potential for bone imaging primarily due its intrinsic specificity to collagen fibers, which results in high contrast images without the need for specimen staining. Furthermore, this technique's ability to quantitatively assess collagen fiber organization is evaluated through an exploratory examination of bone structure as a function of age, from very young to mature bone. In particular, four different age groups: 1 month, 3.5 months, 6 months, and 30 months, were studied. Specifically, we employ the recently developed Fourier transform-second harmonic generation (FT-SHG) imaging technique for the quantification of the structural changes, and observe that as the bone develops, there is an overall reduction in porosity, the number of osteons increases, and the collagen fibers become comparatively more organized. It is also observed that the variations in structure across the whole cross-section of the bone increase with age. The results of this work show that quantitative SHG microscopy can serve as a valuable tool for evaluating the structural organization of collagen fibers in ex vivo bone studies.
Bone 12/2011; 50(3):643-50. DOI:10.1016/j.bone.2011.11.013 · 3.97 Impact Factor
"Second-harmonic generation (SHG) images of collagen fibers in keratoconic corneas have shown both significant thinning and a decrease in the number of collagen lamellae in the stroma as well as breaks in the lamellae of the Bowman's layer as shown in Fig. 3 (Morishige et al., 2007). SHG microscopy, in recent years has become a popular imaging technique to study the structural organization of collagen fibers (Ambekar Ramachandra Rao et al., 2009a,b; Campagnola and Loew, 2003). Thinning of the collagen lamellae has been attributed to the decrease in the number of cross-links (bonds between and within collagen fibrils) (Meek et al., 2005). "
[Show abstract][Hide abstract] ABSTRACT: Keratoconus is an eye disorder wherein the cornea weakens due to structural and/or compositional anomalies. This weakened cornea is no longer able to preserve its normal shape against the intraocular pressure in the eye and therefore bulges outward, leading to a conical shape and subsequent distorted vision. Changes in structure and composition often manifest as a change in shape (or geometry) as well as in mechanical and optical properties. Thus, understanding the properties and structure of keratoconic corneas could help elucidate etiology and pathogenesis, to develop treatments, and to understand other diseases of the eye. In this review, we discuss the changes in structure, composition, and mechanical and optical properties of the cornea with keratoconus. Current treatments for keratoconus and a novel proposed treatment using two-photon excitation therapy are also discussed. The intended audiences are mechanical engineers, materials engineers, optical engineers, and bioengineers.
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