Using Helical CT to Predict Stone Fragility in Shock Wave Lithotripsy (SWL)

Area of Science:

• Urology
• Medical Imaging
• Biophysics

Background:

• Urinary stone response to shock wave lithotripsy (SWL) varies significantly, even for stones of the same mineral composition.
• Current methods to predict SWL success often rely on computed tomography (CT) stone number (Hounsfield units), but this is influenced by scan resolution and stone size.
• Existing studies correlating CT number with SWL failure are limited by unaddressed confounding factors like stone size.

Purpose of the Study:

• To investigate whether analyzing the internal structure of urinary stones using CT imaging can better predict their fragility to SWL compared to traditional CT number measurements.
• To evaluate the potential of micro-CT imaging to reveal structural characteristics of calcium oxalate monohydrate (COM) stones that correlate with SWL outcomes.

Main Methods:

• Review of studies linking stone CT number (Hounsfield units) to SWL outcomes, highlighting limitations due to stone size and CT resolution.
• Preliminary analysis of calcium oxalate monohydrate (COM) stones using micro-CT to assess internal structures such as voids and apatite regions.
• Comparison of shock wave requirements for complete fragmentation between COM stones with heterogeneous structures and those with homogeneous structures.

Main Results:

• Stone CT number (Hounsfield units) is an unreliable predictor of SWL success due to its dependence on factors like stone size and CT slice width.
• Calcium oxalate monohydrate (COM) stones exhibiting internal structural variations (e.g., voids, apatite inclusions) fragmented significantly faster than homogeneous COM stones.
• Stones with observable internal structure required approximately half the number of shock waves for complete fragmentation compared to structurally uniform stones.

Conclusions:

• Urinary stone structure, as visualized by CT, is a more promising predictor of SWL fragility than simple CT number values.
• Utilizing CT to assess stone internal morphology offers a novel approach to enhance the prediction of SWL treatment success.
• Further clinical studies are warranted to validate the correlation between CT-observed stone structure and in vivo SWL stone fragility.