Measurement of the sound speed in articular cartilage in-vitro

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Measurement of the sound speed in articular cartilage in-vitro


Author: Patil, Sushil G
Title: Measurement of the sound speed in articular cartilage in-vitro
Degree: M.Phil.
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations
Articular cartilage
Sound -- Speed
Department: Jockey Club Rehabilitation Engineering Centre
Pages: xvii, 120 leaves : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: Articular cartilage (artC) is a biphasic biological soft tissue that covers the end of articulating bones within synovial joints. It plays an important role for joint lubrication and load transmission, and mainly consists of an organic composite matrix filled with liquids. The change of artC thickness, measured by various devices such as X-ray has been widely used as an indicator for its degeneration status. Recently, ultrasound (US) has been widely used to investigate the change of thickness and acoustic and mechanical properties of the degenerated artC. The sound speed in artC is an essential parameter for the ultrasonic measurement, and its change is also an indicator of artC degeneration. Conventional methods of calculating the sound speed require the measurement of the artC thickness in addition to the detection of the flight time of sound. Therefore, different approaches including needle punching technique, optical measurements, magnetic resonance imaging (MRI), X-ray, etc., have to be used for the measurement of artC thickness, which increases the complexity of the assessment. The sound speed of artC can be affected by the variations of surrounding environment and its structure during in-vitro measurement. Environmental factors include the temperature and the concentration of saline surrounding the artC specimen, while the artC structural factors include its inhomogeneous structure, anatomic location, degeneration level and compression level. To better understand the variation of the sound speed in artC under various conditions is important to the US assessment of artC. In the present study we first developed a non-contact US approach to measure the sound speed and the thickness of artC simultaneously using US (50MHz) alone. After validation using different materials, this approach was then used to investigate the variations of the sound speed in artC at different tissue depths (n = 18 x 3) and locations (n = 10 x 25), treated with different enzymes (n = 20 x 5), and under different temperature (n = 20) and saline concentrations (n = 19). ArtC specimens from bovine patellar models were used in these in-vitro studies. The strain-dependence (n = 20) of the sound speed in artC was studied using a custom-designed US compression device, which allowed simultaneous measurement of the applied force, artC deformation, and US signal reflected from the artC surface. Results showed that the sound speeds of artC at superficial, middle and deep regions were 1518+-17 (mean+-SD), 1532+-26 and 1554+-42 m/s with the US beam parallel to the artC surface, and 1562+-23, 1623+-33 and 1703+-50 m/s with the US beam perpendicular to the artC surface, respectively. The differences among the different depths and between the two measurement directions were both significant (p < 0.001). The sound speed in artC ranged from 1681+-50 m/s to 1816+-54 m/s with the saline concentrations varied from 0M to 2.5M, while the sound speed in saline changed from 1521+-03 to 1674+-03 m/s. The sound speed in artC changed from 1430+-39 to 1667+-68 m/s when the temperature varied from 15 C to 40 C. In case of the digested specimens the sound speed in artC significantly (p < 0.001) decreased from 1653+-40 m/s to 1577+-32, 1564+-33 and 1575+-38 m/s in specimens digested by chondrotinase, collagenase and trypsin, respectively. It was noted that the sound speed in artC varied from 1507 - 1830 m/s at the 25 locations tested on the patella. Significant (p < 0.01) site dependence of the sound speed in artC was demonstrated between the inner region and the surrounding region of the patellae. It was also revealed that the sound speed in artC increased from 1581+-36 m/s at 0% compression to 1671+-56 m/s at 20% compression. The sound speed in artC almost linearly increased at a rate of 11 m/s per 1 C increase in temperature. The overall mean of the sound speed in full-thickness artC was (1648+-75 m/s, ranged from 1438 -1984, 327 specimens and 87 patellae). The present study introduced a non-contact approach to measure the sound speed in artC in-vitro. The results revealed that the sound speed in artC varied significantly with the variations in artC structure, environmental and pathological conditions. It is concluded that these variations play important roles in defining the accuracy and reliability of the ultrasonic measurements of artC and should be well considered during the experimental designs. Though the results were obtained in-vitro using bovine patellar models, they should also have reference values for the ultrasonic assessment of human artC in-vitro or in-vivo.

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