Echocardiography

Each standard transthoracic window exploits a region where the ultrasound beam avoids lung (air) and rib (bone), both of which scatter and attenuate the signal; the parasternal window uses an intercostal space adjacent to the sternum, the apical window uses the point of maximal impulse, and the subcostal window transmits through the liver as an acoustic pathway. Higher-frequency transducers improve axial resolution but penetrate less deeply, which is why adult transthoracic imaging typically uses 2-4 MHz. Doppler measurements additionally require the ultrasound beam to be aligned as parallel as possible to the direction of blood flow, which is why apical views are preferred for Doppler interrogation of LVOT and mitral inflow, while parasternal views are preferred for 2D structural detail.