... = Z2 Greater the difference between Z1 and Z2 → ↑IRC IRC (%) = [(Z − Z1 )/(Z2 + Z1 ) ]2 11 Physics of ultrasound v1 v1 i t i t v2 > v1 when t > i v1 > v2 when i > t v2 v2 sine t / sine i = v2 / ... 2. 5 3 1.5 1 .2 Half value layer thickness (HVLT) HVLT = depth at which I falls by 1 /2 = −3 dB Units = cm (also called penetration depth and half boundary layer) TOE HVLT = 0 .25 2 cm (Table 1 .2) ... Determined by sound source and medium λ influences axial resolution Velocity (v), frequency ( f ) and wavelength (λ) associated by the equation v = fλ Transoesophageal Echocardiography A Amplitude...