Abstract: Background and purpose: Three-dimensional power Doppler angiography (3D-PDA) is a new technique to investigate the vessels in the organs, but the research in thyroid is limited. The purpose of this research was to investigate three-dimensional power Doppler angiography (3D-PDA) in differentiating malignant from benign thyroid nodules. Methods: This study prospectively evaluated 103 lesions in 94 patients who were scheduled for surgery. The patients underwent preoperative 3D-PDA scanning. Analysis of the 3D-PDA characteristics includes blood flow pattern, the number of blood vessels, the shape of vessels, the spatial distribution of the vessels, the existence of rich local blood flow within nodules or in the parenchyma surrounding the nodules. This study also analyzed the difference between the benign lesions and the malignant lesions. Results: There were 50 benign lesions and 53 malignant lesions. The sensitivity and specificity of irregular vessels, the asymmetry spatial distribution, rich local blood flow within nodules or in the parenchyma surrounding the nodules were 64.2%, 96.0%; 56.0%, 88.0%; 54.7%, 96.0%; 60.4% and 94.0%, respectively. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 3D-PDA were 83.0%, 94.0%, 93.6%, 83.9% and 90.3%, respectively. Conclusion: 3D-PDA provides a useful tool to investigate vascularization of thyroid leisions．This technique is feasible for clinical application and plays an important role in diagnosis of thyroid nodules.

Key words: Thyroid nodule, Three-dimensional power Doppler angiography, Diagnosis