Terahertz pulsed imaging of knee cartilage

Abstract

Osteoarthritis (OA) is a common form of arthritis caused by cartilage degeneration. In this paper, we investigate the potential use of terahertz (THz) pulsed imaging to quantitatively measure the early symptoms of OA in an animal model. THz images of excised rabbit femoral condyles were taken. We observe THz waves reflected off different layers within samples and demonstrate that the optical delay between reflections can give a quantitative measure of the thicknesses of particular tissues within cartilage.

Fig. 1

(a) Histology of a femoral condyle with pronounced OA symptoms and (b) The dashed blue box indicates the measured region and the cartilage layer thicknesses of interest.

Fig. 2

The processed data from a pixel in the image of a typical (a) left sample and (b) right sample.

Fig. 3

(a) B-scan of a right sample (IM86R), a cross-section view with y-axis showing the depth profile. The arrow points to the interface formed by the reflected trough. So the space between two dark lines indicates the hyaline thickness if the trough is reflected off the cartilage/calcified cartilage interface. (b) It is important that the sample makes good contact with the quartz window. This graph illustrates how the waveforms for a sample are affected by the sample contact made with the quartz window.

Fig. 4

Color map of a left sample (IM88L) with contrast representing the (a) peak-to-peak optical delay. The darker the blue represents a shorter peak-to-peak optical delay; and (b) the peak-to-trough optical delay.

Fig. 5

The histology from animal 2 (IM86) of the (a) left sample and (b) right sample. The total cartilage thickness varies much more in the left sample (279-474 µm) compared to the right sample (398-443 µm).

Fig. 6

A graph of the mean peak-to-trough THz optical delay against the mean total cartilage thickness from histology.