Final answer:
When tilting the transducer toward the leg in a parasternal short axis view (PSAX), parts of the descending aorta or closer thoracic structures may become visible instead of the ascending aorta.
Step-by-step explanation:
When tilting the transducer toward the leg in parasternal short axis view (PSAX), the ascending aorta will no longer be visible, and instead, possibly parts of the descending aorta will come into view. The parasternal short axis view is positioned at the level of the heart, with the base of the aorta being one of the main structures visible. Tilting the transducer inferiorly (towards the leg) moves the imaging plane downwards, likely bringing into view the thoracic aorta, which descends from the aortic arch.
The aorta itself is the largest artery in the body, originating from the left ventricle and comprising several parts: the ascending aorta, the aortic arch, and the descending thoracic and abdominal aorta. Given that the thoracic aorta runs posteriorly near the bodies of the vertebrae and through the aortic hiatus in the diaphragm, tilting the transducer downward in the PSAX view may reveal portions of this part of the aorta or closer thoracic structures.