Rigid & elastic composite registration of 3D T1-weighted MR images for strain analysis

Strain analysis of deformation field is a crucial step for scientific analysis of muscle structures in MRI data sets. They are commonly used for different types of data analysis such as force transmission among muscles which is one of the popular topics in recent years. Especially there is a popular trend of research concentrating on force transmission among lower leg. For successfully carrying out these types of tasks, a correct and effective deformation field of the MRI data must be obtained in order to get the expected corresponding strain assessments. These deformation fields are usually obtained by registration framework, in which two groups of data sets were registered to one another, one serving as moving data set, which is transformed to the other target, static data set. Formerly, in registration framework, the whole region of MRI, including bones, is elastically registered to each other. However, bone tissues are relatively hard comparing to those soft muscles, elastically registering these hard tissues which yields non-zero deformation values among these regions could negatively affect the correctness of the obtained final result. For that, we can think of keeping these bone regions as fixed, and then elastically register the remaining parts to obtain a deformation field in which there would be zero deformations in the bone regions. In this work, T1-weighted MR images of lower leg of human body in undeformed and deformed states are selected as test data. We first segment the bone regions, keep them as fixed, then perform elastic registration on the remaining parts on MR images of lower legs, and compare the obtained strain analysis of deformation field results with those from unconstraioned elastic registration method. We expect to see the final result would be better than the one obtained by unconstrained elastic registration.