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Zhao, Shukui, De-yu Li, Yi Zheng, Li-xue Yin, Chang-qiong Zheng, Tian-fu Wang, Chunmei Li, Yan Deng, and Guang-fu Yin. "Quantitative Analysis of Sinoatrial Node Using Doppler Tissue Images." IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on, IEEE Trans. Ultrason., Ferroelect., Freq. Contr. 50, no. 10 (2003): 1336-1341. https://doi.org/10.1109/TUFFC.2003.1244750.

Zhao, Shukui, et al. "Quantitative Analysis of Sinoatrial Node Using Doppler Tissue Images." IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on, IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 50, no. 10, 2003, pp. 1336-1341, https://doi.org/10.1109/TUFFC.2003.1244750.