In-Vitro Comparison of Time-Domain, Frequency-Domain and Wavelet Ultrasound Parameters in Diagnostics of Cartilage Degeneration

Abstract

Quantitative ultrasound imaging (QUI) is a promising preclinical method for detecting early osteoarthrotic (OA) changes in articular cartilage. The aim of this study was to compare time-domain, frequency-domain and wavelet transform (WT) QUI parameters in terms of their performance in revealing degenerative changes in cartilage in vitro. Mankin score and Cartilage Quality Index ( CQI) were used as a reference for quantifying cartilage degeneration. Intact ( n = 11, Mankin score = 0) and spontaneously degenerated ( n = 21, Mankin score = 1–10, mean = 4) osteochondral samples (diameter 19 mm) from bovine patellae, prepared and scanned with an ultrasound instrument in our earlier study, were further analyzed. Ultrasound reflection coefficient ( R), integrated reflection coefficient ( IRC) and ultrasound roughness index ( URI) for cartilage surfaces were obtained from our earlier study. In the present study, maximum magnitude ( MM) and echo duration ( ED) for the cartilage surface were determined from the WT analysis. All ultrasound (US) parameters were capable of distinguishing intact and degenerated cartilage groups ( p < 0.01, Mann-Whitney U test). Significant correlations were established between all QUI parameters and CQI or Mankin score ( p < 0.01, Spearman’s correlation test). The receiver operating characteristic (ROC) analysis indicated that the simple time-domain parameters ( R and URI) were diagnostically as sensitive and specific as the more complex frequency-domain ( IRC) or WT ( MM, ED) parameters. Although QUI shows significant potential for OA diagnostics, complex signal processing techniques may provide only limited additional benefits for diagnostic performance compared with simple time-domain methods. However, certain technical challenges must be met before any of these methods can be used clinically. (E-mail: Erna.Kaleva@uku.fi)