Hounsfield unit density in the determination of urinary stone composition

Area of Science:

• Radiology
• Nephrology
• Urology

Background:

• Noncontrast computed tomography (NCCT) is the standard for diagnosing acute flank pain.
• In vitro studies suggest NCCT radiodensity (Hounsfield units, HUs) can predict urinary stone composition.
• The in vivo predictive capability of NCCT for stone composition requires further investigation.

Purpose of the Study:

• To evaluate if in vivo analysis of urinary stones using NCCT can predict their composition.
• To compare the efficacy of Hounsfield units (HUs) versus HU density in differentiating stone types.

Main Methods:

• 100 pure urinary stones visualized by NCCT were analyzed retrospectively.
• Radiodensity was measured in Hounsfield units (HUs).
• HU density was calculated by dividing HU by the stone's largest transverse diameter (mm) to account for size-related radiodensity variations.

Main Results:

• Calcium stones (n=87) could not be differentiated from other types based on Hounsfield units alone.
• HU density showed less overlap than HUs, distinguishing calcium stones from uric acid stones (P=0.006).
• No non-calcium stone exhibited an HU density greater than 76 HU/mm.

Conclusions:

• HU density is a more effective metric than Hounsfield units alone for differentiating urinary stone radiodensities in vivo.
• Calcium and uric acid stones can be distinguished using HU density.
• Neither HU value nor HU density reliably identified all urinary stone types in vivo.