The nodule aspect ratio is used in the measurement of thyroid volume, in which the measurement is made transversely and then longitudinally. 4 mm is the transverse measurement length and 3 mm is the longitudinal measurement length, and the aspect ratio is calculated as 3 mm/4 mm, which is less than 1. The result of the aspect ratio is a reference value used to assess the benignity and malignancy of the nodule. An aspect ratio greater than 1 is an indication of a malignant nodule, but the aspect ratio is only a reference value and does not determine the outcome of the lesion. Other parameters should be analyzed, such as the size of the nodule, whether the nodule boundary is clear, whether the shape is regular, the relationship with the surrounding tissues, whether there is calcification inside the nodule, whether there is blood supply inside, etc. Further treatment can be performed according to the examination results.