Comparison of articular cartilage images assessed by high-frequency ultrasound microscope and scanning acoustic microscope

Purpose The purpose of this study was to compare images of a newly developed high-frequency ultrasound imaging system (HFUIS) and scanning acoustic microscope (SAM) and to calculate their Pearson product moment correlations with a view to applying HFUIS for clinical use. Methods Cylindrical cartilage–bone complexes from adult male Sprague-Dawley rats were obtained. The specimens were immersed in normal saline and scanned by HFUIS. Intensity by HFUIS was normalised by reflection from a steel plate at the same distance. After the scanning, specimens were fixed with paraformaldehyde, decalcified and embedded in paraffin. Thinly sliced tissues were prepared for SAM evaluation. After the scanning, three layers of articular cartilage (superficial, middle and deep) were independently evaluated and their relationships calculated. Results The superficial and deep layers indicated high relative intensity, whereas the middle layer showed nonhomogeneous relative intensity by HFUIS. A high relative intensity by HFUIS and high sound speed area by SAM had strong correlations (Pearson product moment correlation, superficial layer 0.704, middle layer 0.731). Conclusions HFUIS produced high-resolution images of the articular cartilage and its intensity was strongly correlated with sound speed by SAM.