Value of in-line and out-of-line ultrasound targeting in extracorporeal shock wave lithotripsy

Acoustic inhomogeneities of body tissue may deflect diagnostic ultrasound waves as well as therapeutic shock waves. The influence of incorrect ultrasound targeting and shock wave application due to these deflection effects has been examined quantitatively by means of a two-dimensional physical model. The accuracy of in-line and out-of-line targeting has been determined. Calculations on 2 stone patients show that in-line deflection effects remain below 2 mm, while they reach values up to 6 mm for out-of-line systems. These results, confirmed by first clinical observations done by others, indicate that in-line ultrasound targeting is superior to out-of-line targeting.