Figure 2 Schematic diagram illustrating the three perfusion modes of At-PI in thyroid nodules. The left image depicts the US image in the double-image condition, while the right image illustrates the At-PI image. The white arrow indicates the target nodule. (A) The US reveals a solid hypoechoic lesion in the right lobe of the thyroid gland, characterized by irregular edges, a regular shape, and uniform echogenicity. This nodule is classified as C-TIRADS category 4b. The At-PI demonstrates a centripetal perfusion pattern, with yellow and green hues on the periphery (indicating earlier arrival) and purple in the center (indicating late arrival). (B) The US shows a solid hypoechoic lesion in the left lobe of the thyroid gland with well-defined boundaries and a regular shape; however, the echogenicity is uneven, and this nodule is categorized as C-TIRADS 4a. The At-PI reveals a centrifugal perfusion pattern, featuring orange and yellow colors in the center (indicating earlier arrival) and purple at the periphery (indicating later arrival). (C) The US displays a solid hypoechoic lesion in the right lobe of the thyroid gland with poorly defined boundaries and indistinct edges. The aspect ratio is greater than 1, and this nodule is classified as C-TIRADS category 4c. The At-PI indicates a diffuse perfusion pattern. Figure was generated using PowerPoint version 2016 (Microsoft Corporation, Washington, USA).