Application of Ultrasound Backscatter Technique in Quantitative Tendon Characterization

Academic Background

Tendinopathy is a common musculoskeletal disease characterized by alterations in the microstructure, composition, and cellular organization of tendons, leading to pain and decreased function. Tendinopathy is typically initiated by overuse and may be accompanied by various pathological changes such as vascular proliferation, inflammation, and disorganized collagen fibers. Although early diagnosis of tendinopathy is crucial, existing diagnostic methods largely depend on physicians’ experience and lack quantitative and objective evaluation. While ultrasound imaging has been used in diagnosing tendinopathy, it relies heavily on subjective judgment and cannot provide quantitative data. Therefore, developing a non-invasive, quantitative diagnostic method is of great significance for the early detection and treatment of tendinopathy.

The ultrasound backscatter technique (ultrasound backscatter technique) is a quantitative method based on the analysis of ultrasound signals and has been widely applied in characterizing tissues such as bone and myocardium. Studies have shown that ultrasound backscatter parameters are highly sensitive to microstructural changes in tissues, thus holding potential application value in assessing tendinopathy. However, there is limited research on the relationship between ultrasound backscatter parameters and tendon health status, and standardized measurement methods are lacking. The aim of this study is to explore the feasibility of using ultrasound backscatter techniques for quantitative tendon characterization and to analyze their correlation with tendon elastic and mechanical properties.

Paper Source

This paper was jointly completed by researchers from the Department of Biomedical Engineering, School of Information Science and Technology, Fudan University—Qian Zheng, Min He, Ying Li—and Mengyao Liu and Lixin Jiang from the Department of Ultrasound, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine. The first author of the paper is Qian Zheng, and the corresponding author is Dean Ta from the Department of Rehabilitation Medicine, Huashan Hospital, Fudan University. The paper was published in 2025 in the journal IEEE Transactions on Biomedical Engineering under the title “Quantitative Ultrasonic Backscatter Evaluation of Elastic and Mechanical Property in a Rabbit Tendinopathy Healing Model.”

Research Process

1. Experimental Design and Animal Model

The study selected 66 New Zealand white rabbits, which were randomly divided into three groups: the normal control group (NC group, n=6), the model control group (MC group, n=30), and the low-intensity pulsed ultrasound treatment group (LT group, n=30). The MC and LT groups induced tendinopathy models by injecting prostaglandin E2 (PGE2), while the NC group received an equal volume of PBS solution as a control. After modeling, the LT group received low-intensity pulsed ultrasound (LIPUS) treatment, the MC group received sham ultrasound treatment, and the NC group received no treatment. The experiment was assessed at five time points (1, 4, 7, 14, and 28 days post-intervention), with six animals per group at each time point.

2. Ultrasound Shear Wave Elastography (SWE) Measurements

Shear wave elastography was performed using the Aixplorer ultrasound system to measure the shear modulus and shear wave velocity of the rabbit Achilles tendon. Tendon structure was evaluated through 2D grayscale imaging, and quantitative parameters were extracted in the elastography mode. To ensure accuracy, multiple measurements were taken, and the average values were used for subsequent analysis.

3. Mechanical Testing

Mechanical tests were conducted in vitro on tendon samples, including measurements of maximum load, stiffness, maximum stress, and tensile modulus. A tensile test was carried out using the Instron 5965 electronic universal material testing machine, recording the load-displacement curve and calculating relevant parameters.

4. Ultrasound Backscatter Measurements

Ultrasound backscatter signal acquisition was performed using a custom-made diagnostic instrument with a frequency of 3.5 MHz. Signals were collected both in vitro and in vivo, and the signal of interest (SOI) of the Achilles tendon was extracted. The Hilbert transform and moving average filter were used to process the signals, dynamically locating the peak of the reflected wave and extracting the SOI.

5. Backscatter Parameter Calculation

Four backscatter parameters were calculated: average integrated backscatter (AIB), spectral centroid shift (SCS), frequency slope of apparent backscatter (FSAB), and frequency intercept of apparent backscatter (FIAB). These parameters reflect microstructural changes in the tendon and their correlation with elastic and mechanical properties.

Main Results

1. Correlation Between Elastic and Mechanical Parameters

The study found that the shear modulus positively correlates with mechanical parameters (e.g., maximum load, stiffness, maximum stress, and tensile modulus), with the strongest correlation being between the shear modulus and tensile modulus (r = 0.61, p < 0.0001). This indicates that ultrasound elastic parameters can effectively characterize the mechanical properties of tendons.

2. In Vitro Backscatter Signal Assessment

Backscatter parameters (AIB, SCS, FSAB) showed a significant negative correlation with the shear modulus, with AIB showing the strongest correlation (r = -0.72, p < 0.0001). This suggests that these parameters can sensitively reflect microstructural changes in the tendon, especially during injury and repair processes.

3. In Vivo Backscatter Signal Assessment

The results of the in vivo experiments were consistent with those of the in vitro experiments, with AIB, SCS, and FSAB showing a significant negative correlation with the shear modulus. Notably, AIB exhibited higher stability in the in vivo experiments and could simultaneously characterize the elastic and mechanical properties of the tendon.

Conclusion

This study validates the feasibility of using ultrasound backscatter techniques for quantitative tendon characterization. Parameters such as AIB, SCS, and FSAB can effectively reflect microstructural changes in the tendon and their correlation with elastic and mechanical properties. Particularly, AIB demonstrated stable assessment capabilities in in vivo experiments, providing new insights for non-invasive diagnosis of tendinopathy.

Research Highlights

1. Innovative Methodology: This study is the first to apply ultrasound backscatter techniques to quantitative tendon characterization and proposes an SOI extraction method based on multi-layer tissue models.
2. Multi-Parameter Analysis: Comprehensive evaluation of the tendon’s microstructure and its relationship with elastic and mechanical properties was achieved by analyzing multiple backscatter parameters such as AIB, SCS, FSAB, and FIAB.
3. Clinical Application Value: The research findings offer quantitative and objective evaluation tools for the early diagnosis and treatment of tendinopathy, with important clinical application value.

Other Valuable Information

One limitation of this study is the lack of a gold standard for tendon diagnosis. Future research can further explore the impact of different ultrasound frequencies on backscatter signals and optimize SOI extraction techniques to improve accuracy. Additionally, the research results provide a theoretical foundation for the development of tendon diagnostic devices based on ultrasound backscatter.

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Through the detailed introduction of this study, we can clearly see the immense potential of ultrasound backscatter techniques in quantitative tendon characterization. This technology not only provides new tools for the diagnosis of tendinopathy but also lays a solid foundation for future clinical applications.