Final answer:
ESWL uses focused ultrasound to fragment kidney stones through cavitation. The procedure can sometimes damage kidney tissue and is one of several treatment options, including stent placement and surgery.
Step-by-step explanation:
Extracorporeal Shock Wave Lithotripsy (ESWL) is a non-invasive medical procedure used to treat kidney stones that are too large to pass through the urinary tract on their own. High-intensity ultrasound pulses are focused on the stone to break it into smaller fragments. This is achieved through a process known as cavitation, in which the ultrasound waves create vapor cavities in a fluid. These cavities collapse with great pressure, effectively fragmenting the stone.
Despite its non-invasive nature, ESWL can potentially cause damage to the kidney tissues. This is due to the high energy carried by the ultrasound waves, which at focused intensities of 10³ to 10⁵ W/m² can alter cell permeability or even rupture cell walls. For stones causing a blockage, an alternative is to insert a ureteral stent to facilitate passage of the stone and urine. If required, surgical intervention may be the method of choice for physically removing a particularly large stone.
Ultrasound's role in medical therapy extends beyond lithotripsy, including localized heating for physical therapy and targeted treatments for cancer. However, in the context of ESWL, ultrasound is specifically used for its mechanical disruptive effects on kidney stones.