P5A-9 Depth Dependent High Frequency Backscatter Analysis of Degenerated Cartilage

The aim of this study was to relate depth- dependent high-frequency backscatter parameters to histological alterations of degenerated human articular cartilage. Biopsies from femoral condyles of 19 patients with the indication for alloplastic joint replacement and 4 normal samples were investigated in-vitro at 40-MHz with a custom scanning acoustic microscope (SAM200Ex). The backscattered signals were measured in two dimensions with a spatial increment of 20 mum. A sliding time-gate analysis was performed to derive apparent integrated backscatter amplitude (AIB), average scatter spacing and the frequency dependent backscatter amplitudes as a function of the distance from the cartilage surface. The degree of degeneration (Mankin score) was evaluated by histological and immunohistochemical analyses. The Mankin score of 55 evaluated biopsies ranged from 0 to 13. In intact cartilage the superficial, intermediate and deep zones could be identified based on distinct attenuation coefficients. Progressive stages of degeneration were associated with several alterations of acoustic parameters, i.e. increased surface roughness, decreased surface reflection and AIB amplitudes, increased attenuation coefficients, and a decrease of the superficial zone thickness. High frequency backscatter analysis provides information of ultrastructural tissue alterations induced by OA. Early degenerative processes may be detected by ultrasound prior to an apparent surface roughening or cartilage softening.