Image analysis on the structure of the Achilles tendon

Abstract: The Achilles tendon is the largest tendon of the human body which makes injuries of it very painful and incapacitating. A common factor of the pain are heterotopic ossifications, which are mineral deposits occurring inside the normal tendon tissue. Why and how heterotopic ossifications occur are somewhat unknown. To investigate this, many different methods of study have been trialed by scientists to create a complete understanding of the underlying causes. As new scientific methods and principles are developed, the understanding of our inner structures are increased. In this project, image analysis methodologies have been applied to high resolution images taken of rat Achilles tendons. The rats either had an forced unloading of their right leg, had their tendon microinjured by needling or was part of a control group. These animal experiments and image production was not done as part of this thesis but of a larger Achilles tendon project. The animal experiments were performed by Dr. Malin Hammerman and the imaging was done by Dr. Maria Pierantoni. This thesis has focused on producing a segmentation of the whole tendon as well as the hetrotopic ossification minerals. Different image analysis methods have been tried to achieve this, including different filters and morphological operations. Different pipelines had to be developed for extracting the soft tendon tissue and the hard mineral since they intrinsically look different on an x-ray image. The segmented mineral and tendons were then compared in relation to their testing group. To compare them different metrics were extracted; the volume and placement of the mineral as well as the volume of the tendon. No substantial differences were found between any of the groups, but tendencies in mineral volume and placement could distinguish the groups. With regards to the segmentation, there are specific places within the data sets that segments well and others that segment worse. This study does not answer the question on why hetrotopic ossifications occur, although the observations are not conclusive, there are still some points that can indicate a relationship connecting loading and microinjuries to heterotopic ossification of the tendon. This was observed as the variance, in the groups that were not part of the control, had generally less variation within their groups in many of the trialed metrics. Hetrotopic ossifications were evidently present in all but one of the trialed tendons, hence it is surely a common part of the natural tendon.