Ultrasound in Med. & Biol. Vol. 18, No. 1, pp. 51-58, 1992 0301-5629/92 $5.00 + .00 Printed in the U.S.A. © 1992 Pergamon Press plc OOriginal Contribution QUANTITATIVE ASSESSMENT OF CARTILAGE SURFACE ROUGHNESS IN OSTEOARTHRITIS USING HIGH FREQUENCY ULTRASOUND RONALD S. ADLER, t DALE K. DEDRICK, $ TIMOTHY J. LAING,* EDWARD H. CHIANG, t CHARLES R. MEYER, t PEYTON H. BLAND t and JONATHAN M. RUaIN t University of Michigan Medical Center, Department of Radiology, t Orthopaedic Research Laboratories, Orthopaedic Surgery and Department of Internal Medicine, Rheumatology Division,: Department of Internal Medicine, Rheumatology Division,* 1500 E. Medical Center Drive, Ann Arbor, MI 49109/0030, USA (Received 19 June 1991; in final form 17 September 1991) Abstraet--Osteoarthritis (OA) is a common disease which affects nearly 50% of people over age 60. Histologic evaluation suggests that fibrillations ~20-150 ttm. are among the earliest changes in the articular cartilage. We propose a technique to quantify these surface fibrillatory changes in osteoarthritie articular cartilage by consider- ing the angular distribution of the envelope-detected backscattered pressure feld from an incident 30-MHz focused transducer. The angular distribution of the scattered acoustic field from an insonifyiag source will directly relate to the distribution of surface fibrillatory changes. Data are presented for three different grades (400, 500 and 600 grit) of commercially available emory paper and three samples of osteoarthritic femoral head articular cartilage, which were visually assessed as having smooth, intermediate and rough surfaces, respectively. Our preliminary results indicate a probable monotonic relationship between articular cartilage roughening and the degree of broadening in the angle-dependent pressure amplitude. When applied to the emory paper, the technique indicates sensitivity to differences as small as ~5-10 ~tm in mean roughness. This procedure may provide an extremely sensitive and reproducible means of quantifying and following the cartilage changes observed in early osteoarthritis. Key Words: Acoustics, Ultrasonics, Ultrasonic backscatter, Articular cartilage roughness, Osteoarthritis. INTRODUCTION Osteoarthritis (OA) is a very common disease and the early morphologic and biochemical changes in the ar- ticular cartilage are well known. However, the initiat- ing factors and exact sequence of events involving the subchondral bone and synovium remains conjectural (Mankin and Lippiello 1970; Minns et al. 1977; Bland and Cooper 1984). At present, treatment is lim- ited to relatively advanced disease in part because of the inability to detect and monitor OA in its early presymptomatic stages. The development of a nonin- vasive technique to identify and follow early OA has important implications for assessing therapeutic regi- mens advocated for the treatment of the arthritis and Address correspondence to: Ronald S. Adler, M.D., Ph.D., University of Michigan Medical Center, Dept. of Radiology, 1500 E. Medical Center Drive, Ann Arbor, MI 48109/0030. Portions of this research supported in part by NIH Grant #'s K11-AR01793 and 5P60-20557. the prevention of disability (Paulus 1989; Bran& 1990). Histologic evaluation (Minns et al. 1977; Bland and Cooper 1984) suggests that fibrillations --~20-150 um in height are among the earliest changes in the articular cartilage. These distance scales are particu- larly conducive to quantification by relatively high- frequency acoustic scattering (10-30 MHz), which is within the range of commercially available trans- ducers. In particular, the angular distribution of scat- tered acoustic radiation from some insonifying source will directly relate to variations in surface height, or roughness, resulting from the distribution of surface fibrillatory changes. In the simplest case, in which the surface fibrillations are sufficiently small relative to the acoustic wavelength, the angular scattering is a direct measure of surface root-mean-square (RMS) roughness (Thorne and Pace 1984). Similar surface phenomena have been extensively investigated within the nondestructive testing and laser speckle literature 51