Effects of ultrasound beam angle and surface roughness on the quantitative ultrasound parameters of articular cartilage.

High-resolution arthroscopic ultrasound imaging provides a potential quantitative technique for the diagnostics of early osteoarthritis. However, an uncontrolled, nonperpendicular angle of an ultrasound beam or the natural curvature of the cartilage surface may jeopardize the reliability of the ultrasound measurements. We evaluated systematically the effect of inclining an articular surface on the quantitative ultrasound parameters. Visually intact (n = 8) and mechanically degraded (n = 6) osteochondral bovine patella samples and spontaneously fibrillated (n = 1) and spontaneously proteoglycan depleted (n = 1) osteochondral human tibial samples were imaged using a 50-MHz scanning acoustic system. The surface of each sample was adjusted to predetermined inclination angles (0, 2, 5 and 7 degrees ) and five ultrasound scan lines along the direction of the inclination were analyzed. For each scan line, reflection coefficient (R), integrated reflection coefficient (IRC) and ultrasound roughness index (URI) were calculated. Nonperpendicularity of the cartilage surface was found to affect R, IRC and URI significantly (p < 0.05). Importantly, all ultrasound parameters were able to distinguish (p < 0.05) the mechanically degraded samples from the intact ones even though the angle of incidence of the ultrasound beam varied between 0 and 5 degrees among the samples. Diagnostically, the present findings are important because the natural curvature of the articular surface varies, and a perfect perpendicularity between the ultrasound beam and the surface of the cartilage may be challenging to achieve in a clinical measurement.

Minimally invasive ultrasound method for intra-articular diagnostics of cartilage degeneration.

Quantitative ultrasound imaging (QUI) can be used to evaluate the integrity of articular cartilage and for diagnosing the early signs of osteoarthritis (OA). In this study, we applied a minimally invasive ultrasound imaging technique and investigated its ability to detect superficial degeneration of bovine knee articular cartilage. Intact (n=13), collagenase-digested (n=6) and mechanically degraded (n=7) osteochondral samples (dia.=25 mm) and custom-made phantoms with different degrees of surface roughness (n=8) were imaged using a high-frequency (40 MHz) QUI system. For each sample and phantom, the ultrasound reflection coefficient (R), integrated reflection coefficient (IRC) and ultrasound roughness index (URI) were determined. Furthermore, to evaluate the clinical applicability of intra-articular ultrasound (IAUS) in diagnostics, one intact bovine knee joint was investigated ex vivo using a simulated arthroscopic approach. Differences in the surface characteristics of the phantoms were detected by monitoring changes in the reflection and surface roughness parameters. Both mechanically- and enzymatically-induced degradation were sensitively diagnosed by decreased (p<0.05) reflection (R and IRC) at the cartilage surface. Furthermore, mechanical degradation was detected in the increased (p<0.05) surface roughness (URI). The intra-articular investigation of a bovine knee joint suggested that the IAUS technique may enable minimally invasive, straightforward diagnostics of the degenerative status of the articular surfaces. We conclude that quantitative IAUS imaging can be used for detecting collagen disruption and increased roughness of the articular surface. This quantitative in vivo ultrasound technique could have great clinical value in the diagnostics of joint diseases.

In-vitro comparison of time-domain, frequency-domain and wavelet ultrasound parameters in diagnostics of cartilage degeneration.

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.