title: Towards Optical Coherence Tomography-based elastographic evaluation of human cartilage.
abstract: Optical Coherence Tomography (OCT) is an imaging technique that allows the surface and subsurface evaluation of semitransparent tissues by generating microscopic cross-sectional images in real time, to millimetre depths and at micrometre resolutions. As the differentiation of cartilage degeneration remains diagnostically challenging to standard imaging modalities, an OCT- and MRI-compatible indentation device for the assessment of cartilage functional properties was developed and validated in the present study. After describing the system design and performing its comprehensive validation, macroscopically intact human cartilage samples (n=5) were indented under control of displacement (δ1=202µm; δ2=405µm; δ3=607µm; δ4=810µm) and simultaneous OCT imaging through a transparent indenter piston in direct contact with the sample; thus, 3-D OCT datasets from surface and subsurface areas were obtained. OCT-based evaluation of loading-induced changes included qualitative assessment of image morphology and signal characteristics. For inter-method cross referencing, the device׳s compatibility with MRI as well as qualitative morphology changes under analogous indentation loading conditions were evaluated by a series of T2 weighted gradient echo sequences. Cartilage thickness measurements were performed using the needle-probe technique prior to OCT and MRI imaging, and subsequently referenced to sample thickness as determined by MRI and histology. Dynamic indentation testing was performed to determine Young׳s modulus for biomechanical reference purposes. Distinct differences in sample thickness as well as corresponding strains were found; however, no significant differences in cartilage thickness were found between the used techniques. Qualitative assessment of OCT and MRI images revealed either distinct or absent sample-specific patterns of morphological changes in relation to indentation loading. For OCT, the tissue area underneath the indenter piston could be qualitatively assessed and displayed in multiple reconstructions, while for MRI, T2 signal characteristics indicated the presence of water and related tissue pressurisation within the sample. In conclusion, the present indentation device has been developed, constructed and validated for qualitative assessment of human cartilage and its response to loading by OCT and MRI. Thereby, it may provide the basis for future quantitative approaches that measure loading-induced deformations within the tissue to generate maps of local tissue properties as well as investigate their relation to degeneration.
authors.affiliation: Department of Orthopaedics, Aachen University Hospital, Aachen, Germany; Institute of Anatomy and Cell Biology, RWTH Aachen University, Germany. Electronic address: snebelung@ukaachen.de.
authors.forename: Sven
authors.initials: S
authors.lastname: Nebelung
authors.affiliation: Fraunhofer Institute for Production Technology, Aachen, Germany. Electronic address: nicolai.brill@ipt.fraunhofer.de.
authors.forename: Nicolai
authors.initials: N
authors.lastname: Brill
authors.affiliation: Fraunhofer Institute for Production Technology, Aachen, Germany. Electronic address: felix.mueller@rwth-aachen.de.
authors.forename: Felix
authors.initials: F
authors.lastname: Müller
authors.affiliation: Department of Orthopaedics, Aachen University Hospital, Aachen, Germany. Electronic address: mtingart@ukaachen.de.
authors.forename: Markus
authors.initials: M
authors.lastname: Tingart
authors.affiliation: Institute of Anatomy and Cell Biology, RWTH Aachen University, Germany. Electronic address: tpufe@ukaachen.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Pufe
authors.affiliation: Institute of Imaging & Computer Vision, RWTH Aachen University, Aachen, Germany. Electronic address: Dorit.Merhof@lfb.rwth-aachen.de.
authors.forename: Dorit
authors.initials: D
authors.lastname: Merhof
authors.affiliation: Fraunhofer Institute for Production Technology, Aachen, Germany; Laboratory for Machine Tools and Production Engineering, RWTH Aachen University, Aachen, Germany. Electronic address: robert.schmitt@ipt.fraunhofer.de.
authors.forename: Robert
authors.initials: R
authors.lastname: Schmitt
authors.affiliation: Department of Orthopaedics, Aachen University Hospital, Aachen, Germany. Electronic address: hjahr@ukaachen.de.
authors.forename: Holger
authors.initials: H
authors.lastname: Jahr
authors.affiliation: Department of Diagnostic and Interventional Radiology, Aachen University Hospital, Aachen, Germany. Electronic address: dtruhn@ukaachen.de.
authors.forename: Daniel
authors.initials: D
authors.lastname: Truhn
mesh_terms: D000328:Adult; D000368:Aged; D002356:Cartilage / Q000166:cytology* / Q000000981:diagnostic imaging* / Q000502:physiology; D054459:Elasticity Imaging Techniques; D004867:Equipment Design; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008422:Materials Testing / Q000295:instrumentation*; D008875:Middle Aged; D041623:Tomography, Optical Coherence; D016474:Weight-Bearing
keywords: Cartilage; Functional properties; Indentation; Optical Coherence Tomography; Qualitative evaluation