Figure 2a. US images depict ice ball formation. At maximum size, ice ball is an oval mass with echogenic anterior surface and dense posterior acoustic shadowing. Distance between margin of ice ball and skin (arrowheads) was greater on b because of injection of sterile saline, which was intermittently instilled between ice ball and skin to maintain an ice ball-to-skin distance of at least 5 mm to prevent hypothermic injury to skin. (a) Longitudinal and (b) transverse orientation of US transducer relative to ice ball.