Collagen is one of the most abundant proteins
in the body. It is essential for the structure, functionality, and
strength of the connective tissue such as skin, bone, tendon,
and cornea. It is known that a change in the arrangement
or morphology of these fibrillar structures relates to multiple
dysfunctions including corneal diseases and various cancer types.
Due to their critical roles in wide-range abnormalities, there
is an increasing interest in the pattern analysis of collagen
arrangements. In recent years, Second Harmonic Generation
(SHG) microscopy is proven to be an efficient imaging modality
for visualizing unstained collagen fibrils. There are plenty of
studies in the literature on the analysis of collagen distribution
in SHG images. However, the majority of these methods are
limited to detecting simple, statistical and non-local properties
such as pixel intensity and orientation variance. There is a
need for a method to detect the local structural properties of
collagen bundles. This paper is to introduce an automated method
to detect collagen bundles in 3-dimensional SHG microscopy
images. The origin of the proposed method is based on multiscale
directional representation systems. The proposed method detects
the collagen bundles by measuring the dominant orientation
of local regions and an orientation-based connected component
analysis. Through more local analysis and the detection of
collagen bundles separately, the proposed method would lead to
the extraction of more detailed structural information on collagen
bundle distribution.