Attenuation Estimation and Acoustic Characterization of Mouse Lymph Node Tumor Using High-frequency Ultrasound

Purpose: Lymph node (LN) biopsy is the gold standard for diagnosing metastasis. While ultrasound imaging is a non-invasive method for real-time LN metastasis diagnosis and tumor assessment, its accuracy depends on operator skill and system settings. Quantitative ultrasound can characterize tissue microstructure changes due to tumors, offering operator-independent parameters, and one of the quantitative ultrasound methods, the backscatter coefficient, is necessary to compensate for tissue attenuation. However, the change in the attenuation coefficient (AC) in the tumor growth is uncertain. Using in vivo high-frequency ultrasound (25 MHz) measurement and scanning acoustic microscopy (80 and 300 MHz) for ex vivo samples, we aim to investigate how tumor growth is linked to the attenuation and acoustic properties such as acoustic impedance and speed of sound related to ultrasonic wave propagation. Procedures: FM3 A-Luc mammary carcinoma cells were inoculated into the subiliac LNs of mice, and tumor progression was monitored over time. Bioluminescence imaging was used to assess tumor growth, while ultrasound measurements focused on estimating AC and other acoustic properties. Results: Results indicated that the mean of AC decreased, and its standard deviation increased as tumors grew, correlating with bioluminescence intensity. Furthermore, acoustic impedance and speed of sound varied between normal and tumor tissues, revealing differences in tissue microstructure from the histopathological images. Conclusions: The finding of a decrease in AC observed with tumor growth may play a crucial role in enhancing the accuracy of quantitative ultrasound on attenuation compensation, potentially improving the differentiation between metastatic and non-metastatic LNs.