Kidney stones – Lesion characterization

Benefit of the GSI histogram

Testimonial by Dr. Fekir
Radiologist at Hôpital Bicêtre (Kremlin-Bicêtre - 94)

Clinical case

Patient history

  • Patient age 30
  • Recurring kidney stone disease since childhood
  • Left hyperalgesic renal colic
  • Renal function degradation


  • Urinary GSI
  • Abdominopelvic spiral without injection
  • GSI targeted spiral in the region of interest containing the stone
  • Rotational speed: 0.7 s/rot
  • 375 mA

GSI Data Management

  • GSI Viewer Software
  • Analysis of monochromatic images at 70 keV, axial
  • Setup of an ROI within the stone
  • Calculation of the average effective atomic number (Z eff): quantitative analysis
  • Obtaining the density in Hounsfield Units
  • Obtaining a histogram: distribution of the Z of each pixel within the ROI according to the known Z eff of various stone compositions (uric acid, struvite, cystine, calcium oxal


Clinical benefit

  • GSI is a urological treatment strategy suitable for the composition of the stone46; indeed, a study conducted at the Rouen CHU demonstrated the possibility of recognizing uric acid and cystine stones.
  • With conventional imaging, a biochemical analysis of the stone (gold standard) requires that the stone be retrieved invasively.
  • GSI, that is, fast, low-radiation, dual-energy acquisition, together with material decomposition allow for a simple and reproducible non-invasive method that is available from the very start of patient care, allowing the composition of the kidney stone to be determined.
  • The qualitative approach makes it possible to classify the stone visually according to the different categories of known compositions.

In this case, most of the pixels have an atomic number (Z-eff) close to that of cystine, which allowed us to deduce the composition of the stone in this patient.