Question 15#

The following are true of extracorporeal shock wave lithotriptors, except:

a. The Dornier HM1 lithotriptor, developed in 1980, was the first lithotripter to be used to treat renal calculi in vivo
b. The Stortz Modulith® is an example of a electromagnetic lithotripter, where magnetic energy is applied to crystals to generate the shockwave
c. Electrohydraulic lithotriptors often incorporate an angulated hemispherical dish to focus shock waves created by an underwater spark gap
d. Piezoelectric lithotriptors utilise multiple ceramic crystals arranged around a hemispherical dish
e. The Dornier HM3 lithotriptor, the first commercial device, required immersion of the fully anaesthetised patient in a water bath

Correct Answer is B


Answer B

The HM1 (Human Machine 1) lithotriptor was developed in 1980 by the German aerospace company Dornier following research into the effects of shock waves on metal parts of supersonic aircraft. Four years later, the HM3 lithotriptor was introduced into clinical practice and remains amongst the most effective devices to fragment renal calculi. Its main drawback is that it requires general anaesthesia and immersion of the patient in a water bath. The shock waves are generated when a high-voltage electrical current passes across an underwater spark-gap electrode, creating a vaporisation bubble, which then rapidly collapses. The shock waves are focussed by an elliptical dish, angulated to avoid interference of the bubbles with transmission of the shock wave energy through the water to the patient.

Second-generation lithotriptors commonly use piezoelectric or electromagnetic generators as the energy source. These devices are more portable that the electrohydraulic lithotriptors such as the HM3 machine. In electromagnetic lithotriptors, such as the Stortz Modulith®, electrical energy applied to a magnetic coil results in the generation of a shock wave. Shock waves are focussed to a small focal zone (F2), which has the advantage of minimising collateral damage but may compromise fragmentation rates as the kidney and stone move with respiration. Shock wave generation in piezoelectric lithotriptors, for example the Wolf Piezolith 3000®, is achieved through the application of electricity to multiple ceramic crystals arranged around a hemispherical dish.