Calcium stone fragility is predicted by helical CT attenuation values

Area of Science:

• Medical Imaging
• Urology
• Nephrolithiasis Research

Background:

• Helical computed tomography (CT) is the standard for imaging urinary calculi.
• Predicting shockwave (SW) requirements for lithotripsy using CT data would be beneficial.

Purpose of the Study:

• To determine if helical CT data can predict the number of SWs needed to fragment urinary stones.
• To establish a correlation between CT attenuation values and SW requirements for comminution.

Main Methods:

• Calcium stones were subjected to comminution using SWs in an in vitro setting.
• The number of SWs required was measured and correlated with helical CT attenuation values obtained at different collimations (1-mm and 3-mm).

Main Results:

• SW requirement correlated with stone size and CT attenuation at 3-mm collimation, but not at 1-mm collimation.
• The correlation at 3-mm collimation was attributed to volume-averaging effects.
• A "half-attenuation rule" (SWs < 0.5 * CT attenuation) accurately predicted SW needs for 95% of tested calcium stones.

Conclusions:

• Helical CT attenuation values, particularly at 3-mm collimation, contain information about stone size and fragility.
• The "half-attenuation rule" shows promise for predicting effective SW dose prior to lithotripsy.