Image-based non-contact method to measure cross-sectional areas and shapes of tendons and ligaments

Abstract

In determining the mechanical properties of biological tissues, accurate measurements of such geometrical attributes as cross-sectional area, volume and shape are needed. For soft tissues a non-contact technique is advantageous in determining these. A low cost, image-based, non-contact solution has been developed, suitable for determining the cross-sectional profiles of soft tissues with quasi-prismatic shapes such as tendons and ligaments. Digital processing of images of the object, illuminated by a sheet of laser light, is used to obtain cross-sectional ‘slices’ through it. The method was validated by using it to measure several rigid reference objects: two circular cylinders, a hex key and torx key, whose shape and dimensions had also been obtained by independent metrology. The smooth circular cross-sectional shape of the cylinder, the flat parallel faces of the hex key and the concave faces of the torx key were all reproduced by the laser-slice method. Their linear dimensions were correctly resolved to within 0.15 mm or less, and cross-sectional areas to within 0.17 mm2 or less. The method has been applied successfully to a selection of bovine digital extensor tendons. Some contained concavities on their surfaces, and their cross-sectional areas ranged from 14 mm2 to 49 mm2. The new method provides an accuracy and resolution better than or comparable to previous non-contact approaches, while avoiding some of their disadvantages.