Assessment of correlation between urinary stone Hounsfield units in CT scan and quantitative stone density in KUB images

Abstract

Non-contrast abdominopelvic computer tomography (CT) scan represents the diagnostic test of choice for evaluation of patients with urolithiasis. This is a result of CT superiority to identify renal stones when compared with kidney-ureter-bladder (KUB). Hounsfield unit (HU) values measured in CT scan could predict stone clearance in extracorporeal shock wave lithotripsy (ESWL). However, radiation exposure is more in CT scan than KUB. Aim: To assess the correlation between HU in CT scan and stone brightness in KUB images Materials and methods: We reviewed the medical records of 43 patients admitted in Imam Reza hospital in recent 5 years for surgical urinary stone management. CT scan films were reviewed to identify stone HU. We used Adobe Photoshop application to evaluate quantitative values of each stone brightness and its ratio to 12th rib, liver and iliac crest brightness. Results: Fourty-three patients were evaluated and mean HU was 770±320. The Spearman’s correlation coefficients between HU and stone, 12th rib, liver and iliac crest brightness were 0.606, 0.14, 0.146 and 0.176 (p<0.001, p=0.431, p=0.425 and 0.305), respectively. The Spearman’s correlation coefficients between HU and stone/12th rib, stone/liver and stone/iliac crest brightness ratios were 0.483, 0.461 and 0.463 (p=0.004, 0.008 and 0.004), respectively. Brightness ratios of stone/12th rib > 1.1, stone/liver >1.3 and stone/iliac crest > 1.05 were related to HU > 1000 (p=0.026, 0.001 and 0.018), respectively.