Quantitative 3D analysis of the canal network in cortical bone by micro‐computed tomography

Abstract

Cortical bone is perforated by an interconnected network of porous canals that facilitate the distribution of neurovascular structures throughout the cortex. This network is an integral component of cortical microstructure and, therefore, undergoes continual change throughout life as the cortex is remodeled. To date, the investigation of cortical microstructure, including the canal network, has largely been limited to the two-dimensional (2D) realm due to methodological hurdles. Thanks to continuing improvements in scan resolution, micro-computed tomography (muCT) is the first nondestructive imaging technology capable of resolving cortical canals. Like its application to trabecular bone, muCT provides an efficient means of quantifying aspects of 3D architecture of the canal network. Our aim here is to introduce the use of muCT for this application by providing examples, discussing some of the parameters that can be acquired, and relating these to research applications. Although several parameters developed for the analysis of trabecular microstructure are suitable for the analysis of cortical porosity, the algorithm used to estimate connectivity is not. We adapt existing algorithms based on skeletonization for this task. We believe that 3D analysis of the dimensions and architecture of the canal network will provide novel information relevant to many aspects of bone biology. For example, parameters related to the size, spacing, and volume of the canals may be particularly useful for investigation of the mechanical properties of bone. Alternatively, parameters describing the 3D architecture of the canal network, such as connectivity between the canals, may provide a means of evaluating cumulative remodeling related change.

Micro-channels in the mastoid anatomy. Indications of a separate blood supply of the air cell system mucosa by micro-CT scanning

“…Considering their mean diameter of 158 µm, the micro-channels could contain both small arterioles and venules, which have diameters around 30 µm and 10 to 60 µm, respectively (Boulpaep, 2009). Haversian canals are well known in bone providing a vascular supply for the tissue, but these canals are smaller up to 45 µm in diameter and usually only containing capillaries (Cooper et al, 2003); thus, such canals were below the resolution of our method (40-60 µm).…”

Assessment of bone vascularization and its role in bone remodeling

“…On the basis of synchrotron radiation mCT images of cortical bone, Schneider et al 74 reported mouse strain and sex-related differences in vascular channel structure and density. In human bone, Cooper et al 75 , using skeletonization techniques were able to image and quantify the density and connectivity of the cortical 'vascular' porosity. Their work suggests that threedimensional morphologic analysis of the canal network may provide novel insights into bone physiology that are not possible with two-dimensional approaches.…”

Anatomy of the Intracortical Canal System: Scanning Electron Microscopy Study in Rabbit Femur

“…The application of different methods of study based on histology [5,9,18,30,31] or micro-CT [6,7] has led to several three-dimensional models of the canal network. These reconstructions can be useful to give a general view of the architecture of the system but are limited by the loss of morphologic details and the sense of temporal development.…”