Publication Info

• Author
  C. Hänisch
  B. Hohlmann
  K. Radermacher 
• Conference
  CAOS
• Publisher
  EPiC Series in Health Sciences
• Date
  2017
• Link
  http://doi.org/10.29007/rbgl
• PDF IPASM 2018

Project Description

In applications such as biomechanical simulations or implant planning, bone surfaces of the knee are most often reconstructed from computed tomography or magnetic resonance imaging data. Here, ultrasound (US) might serve as an alternative imaging modality. However, established methods cannot directly be transferred to US due to differences in imaging quality and underlying physics.

In this paper, we present a generalisation of the well-known active shape model search algorithm (ASM) that allows for segmenting various structures in US volume images that are too large to be captured with a single recording. The multi-view segmentation approach uses a-priori knowledge in the form of a statistical shape model (SSM) as is the case with the classical ASM. This allows to extrapolate missing information and to generate shapes that comply with the underlying distribution of some training data. The main differences are, however, that the SSM is not only adapted to a single image but to multiple images and that the adaption process is interleaved. As a result, within each iteration the surface information of all sub-volumes is propagated and used in all subsequent steps.

In-silico tests were conducted to investigate how this algorithm would perform in real tracked US data. US volume images were split in slightly overlapping sub-volumes, noise was added, and the alignment was distorted. We could show that the algorithm is capable of reconstructing shapes in the lower millimetre range and for some cases even with submillimetric accuracy. The algorithm is hardly affected by orientation errors below 5 degrees and displacement errors below 5 mm; above these limits, the average absolute SDE as well as its associated variance increases.

Visualization of the IPASM search algorithm. The principle setup with a tracked probe and tracked bones is shown in sub-figure 1. The correspondence search and the subsequent alignment of all shapes are shown in sub-figures 2 and 3. If only part of the bone is visible it may be undecidable whether a sub-volume needs to be aligned or whether the mode weights have to be adapted (sub-volume 4). Initializing the SSM in the IPASM search algorithm by prior adaption to a few landmark points solves this problem.