Comparing absorption and phase contrast modes in micro computed tomography measurements of osteochondral tissue of the human knee

Background
Among the clinically relevant imaging techniques, computed tomography reaches the best spatial resolution. The visualization of the soft tissue components in the vicinity of bone, however, is demanding. As an alternative to the established absorption contrast, many researchers proposed to better apply phase contrast methods (e.g. grating interferometry). In recent studies, grating interferometry has shown good results for soft tissue imaging, but has not yet been applied to a human joint.
Method
The present research was conducted on tissues of a human knee post-mortem. The knee was dissected stepwise and tomographically scanned after each step with a laboratory based μCT device. The images were compared. Osteochondral plugs were taken from designated regions of interest. Grating interferometry μCT measurements were conducted at synchrotron facilities. The results were compared to the absorption based measurements of the laboratory system.
Results
High resolution images of the laboratory μCT device offered detailed insights to the subchondral bone and the calcified cartilage region. However, weakly absorbing non-calcified cartilage could not be visualized with sufficient contrast. The grating interferometry based technique on the other hand presents the cartilage morphology in high resolution and reasonable contrast.
Discussion
Grating interferometry is a promising technique for the imaging of osteochondral tissue and of great potential for articular cartilage research. Simultaneous high-resolution imaging of bone and soft tissues is feasible. However, the current experimental effort is very high. Optimizations in both data acquisition and processing must be strived for.