Multimodal measurement of acoustic properties in cartilage tissue

Abstract

In order to detect the disease and degeneration of cartilage early, evaluations of acoustic properties are expected, but the physical meaning should be clarified. On the other hand, we have proposed a multimodal method using ultrasound (US) and magnetic resonance (MR) images for in vivo SOS measurement. In this study, the method was applied for the tissue-engineered cartilage, and the SOS was compared with T1, T2, apparent diffusion coefficient (ADC), attenuation coefficient (ATT), and Young’s modulus (YM). All procedures were approved by the Animal Care and Use Committee of our institution. 12-week-old male rats were used, and five different types of tissue-engineered cartilage was subcutaneously implanted in the back of rat (n = 30). Under anesthesia, MR and US images including same cross-sections were acquired separately, by using a MR imager of 2 Tesla and a US device of 13 MHz. At this time, T1, T2, ADC were also measured. The SOS was determined by the thickness measurement using the MR image and the time-of-flight measurement using the US image. After that, the ATT and YM were measured by using the extracted samples of tissue-engineered cartilage. As a result, the SOS exhibits negative correlations with T1, T2, and ADC (R2 = 0.30, 0.93, 0.82), and positive correlations with ATT and YM (R2 = 0.98, 0.87). These results suggest the SOS of tissue-engineered cartilage strongly reflects the elasticity. Consequently, the physical meaning of SOS was clarified through the multimodal measurement.