What anatomical structures are well seen with US  

Solid organs including the liver, kidneys and spleen are nicely seen with US.

Superficial structures can be seen with excellent resolution, including the thyroid gland and testicles. The above right image is of a testicle. The black, or anechoic structure posterior to it, depicted with the star, is an abnormal collection of fluid around the testicle. This is called a hydrocele. Deeper structures can't be seen with the same level of resolution because of the number of scattered, absorbed and reflected sound waves occuring, leaving less sound available to penetrate deeper tissues and reflect back to the transducer to create the image. As an example, look at the kidney on the left image. The inferior pole of the kidney, on the right side of the image, is more superficial than the superior pole. Note the inferior pole is seen with better resolution than the superior pole.