According to the grades of echogenicity to evulated thyroid nodules is a subjective process and is thus influenced by the observer's judgement. The investigators first proposed the ultrasound gray-scale ratio (UGSR) to explore its efficacy for differentiating papillary thyroid microcarcinomas from small nodular goiters.

Echogenicity is a common ultrasonic parameter to evaluate thyroid nodules. The echogenicity of the thyroid nodule was divided into 5 grades according to gray scale. Of the five categories, the diagnostic values of the hypoechoic and markedly hypoechoic categories have been widely accepted for thyroid malignant nodules. However, distinguishing between hypoechoic and markedly hypoechoic categories is a subjective process and is thus influenced by the observer's judgement. A more objective method should be proposed to differentiate papillary thyroid microcarcinoma(PTMC) from small nodular goiter(NG).

The investigators suspect the echo intensity of nodules could be reflected by values, as CT values reflecting the nodule density. The investigators first proposed the ultrasound gray-scale ratio (UGSR), namely, the ratio of lesion gray-scale value to surrounding normal thyroid tissue, and the previous study showed UGSR can better display the relationship of gray scale of PTMC or NG with surrounding normal thyroid tissue, and can make objective judgment of the nodules through quantitative results.

As the absolute ultrasound grayscale value is affected by the apparatus, scan gain, dynamic range, frequency, and operators. The investigators would collected different data acquired from different parameters to explore their potential relations.

Inclusion Criteria:

• patients diagnosed as thyroid nodule.
• homo-echogenicity of normal thyroid tissue.
• able and willing to comply with all study requirements.

Exclusion Criteria:

• nodules are mainly cystic or calcified.
• pathology confirmed Hashimoto's thyroiditis.
• unable or unwilling to comply with all study requirements.

Patients diagnosed with thyroid nodules by ultrasound or incidentally noted on other imaging tests.