Phase contrast imaging X-ray computed tomography: quantitative characterization of human patellar cartilage matrix with topological and geometrical features

Abstract

Current assessment of cartilage is primarily based on identification of indirect markers such as joint space narrowing and increased subchondral bone density on x-ray images. In this context, phase contrast CT imaging (PCI-CT) has recently emerged as a novel imaging technique that allows a direct examination of chondrocyte patterns and their correlation to osteoarthritis through visualization of cartilage soft tissue. This study investigates the use of topological and geometrical approaches for characterizing chondrocyte patterns in the radial zone of the knee cartilage matrix in the presence and absence of osteoarthritic damage. For this purpose, topological features derived from Minkowski Functionals and geometric features derived from the Scaling Index Method (SIM) were extracted from 842 regions of interest (ROI) annotated on PCI-CT images of healthy and osteoarthritic specimens of human patellar cartilage. The extracted features were then used in a machine learning task involving support vector regression to classify ROIs as healthy or osteoarthritic. Classification performance was evaluated using the area under the receiver operating characteristic (ROC) curve (AUC). The best classification performance was observed with high-dimensional geometrical feature vectors derived from SIM (0.95 ± 0.06) which outperformed all Minkowski Functionals (p < 0.001). These results suggest that such quantitative analysis of chondrocyte patterns in human patellar cartilage matrix involving SIM-derived geometrical features can distinguish between healthy and osteoarthritic tissue with high accuracy.

Full-Field Strain Uncertainties and Residuals at the Cartilage-Bone Interface in Unstained Tissues Using Propagation-Based Phase-Contrast XCT and Digital Volume Correlation

“…This is vital, as previous phase-contrast SR-XCT on cartilage-bone plugs was successful in visualizing structural details in the articular cartilage (chondrocyte distribution) [25,45], although typical refraction brightness was visible in the articular cartilage matrix and entirely covered mineralized microarchitecture [25]. Such image gray-scale alteration and noise due to the use of phase-contrast may affect characterization [24], particularly at the cartilage-bone interface.…”

“…Visualization of articular cartilage as well as the majority of soft tissues using XCT still relies on the use of radiopaque staining (i.e., iodine potassium iodide, phosphotungstic acid) [16,17], but this type of staining can alter both morphology and mechanical properties of tissues mainly due to dehydration caused by the use of solvents such as ethanol, resulting in tissue shrinkage [18][19][20][21][22][23]. As a solution, in line phase-contrast using high-flux synchrotron radiation (SR-XCT) was used on native articular cartilage [24,25], aiming to enhance image contrast. To date, SR-XCT phase-contrast experiments enabling DVC computation of full-field strain on unstained musculoskeletal soft tissues has only been performed for intervertebral discs [26] and no literature is available on DVC strain changes in articular cartilage.…”

Propagation phase-contrast micro-computed tomography allows laboratory-based three-dimensional imaging of articular cartilage down to the cellular level

“…Articular cartilage is typically difficult to image by micro-CT due to poor absorption of X-rays owing to its composition of low-Z elements such as carbon, hydrogen, oxygen and nitrogen 5 . However, two methods that exist to increase contrast in cartilage are contrast agents 6 and phase-contrast imaging 7 .…”

“…PPC requires no such modification to the equipment used for typical absorption contrast as long as the beam is highly spatially coherent and the scanner allows for the detector to be positioned sufficiently far from the sample. Various attempts have been made to image articular cartilage with phase-contrast using relatively common laboratory micro-CT 23,24 as well as highly specialised synchrotron sources 7,25 . Data indicates PPC in the synchrotron is able to detect the structure of cartilage 26 , but lab micro-CT has not yet generated comparable images 25,27 .…”