Abstract
A rigid surface–volume registration scheme is presented in this study to register computed tomography (CT) and free-hand tracked ultrasound (US) images of the talocrural joint. Prior to registration, bone surfaces expected to be visible in US are extracted from the CT volume and bone contours in 2D US data are enhanced based on monogenic signal representation of 2D US images. A 3D monogenic signal data is reconstructed from the 2D data using the position of the US probe recorded with an optical tracking system. When registering the surface extracted from the CT scan to the monogenic signal feature volume, six transformation parameters are estimated so as to optimize the sum of monogenic signal features over the transformed surface. The robustness of the registration algorithm was tested on a dataset collected from 12 cadaveric ankles. The proposed method was used in a clinical case study to investigate the potential of US imaging for pre-operative planning of arthroscopic access to talar (osteo)chondral defects (OCDs). The results suggest that registrations with a registration error of 2 mm and less is achievable, and US has the potential to be used in assessment of an OCD’ arthroscopic accessibility, given the fact that 51% of the talar surface could be visualized.
Highlights
A rigid surface–volume registration scheme is presented in this study to register computed tomography (CT) and free-hand tracked ultrasound (US) images of the talocrural joint
The mean of the d f RMS values averaged over all successful registrations in “Sweep Type I” and “Sweep Type II” were, respectively, 0.9 mm ± 0.5 mm and 0.8 mm ± 0.3 mm
Results of the Test I are displayed as plots of d f RMS vs. di RMS for the US sweeps showing the best (i.e., 99% for both the “Sweep Type I” and “Sweep Type II”) and worst success rate (i.e., 1% for the “Sweep Type I” and 0% for the “Sweep Type II”) at a total of 100 registrations each (Figure 6a,b)
Summary
A rigid surface–volume registration scheme is presented in this study to register computed tomography (CT) and free-hand tracked ultrasound (US) images of the talocrural joint. Bone surfaces expected to be visible in US are extracted from the CT volume and bone contours in 2D US data are enhanced based on monogenic signal representation of 2D US images. The proposed method was used in a clinical case study to investigate the potential of US imaging for pre-operative planning of arthroscopic access to talar (osteo)chondral defects (OCDs). To understand the nature of cartilage healing in-vivo and in turn to devise treatment scenarios, longitudinal monitoring of OCDs of patients in short intervals could be helpful [7,8]
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