CT KUB / Renal Stone (Non-Contrast)

Indications

• Acute flank pain; suspected urolithiasis (renal/ureteral calculi)
• Stone burden assessment and follow-up; hematuria initial evaluation
• Hydronephrosis evaluation

Patient prep

• No oral or IV contrast (stones obscured by contrast)
• No specific NPO; full bladder helpful for distal ureteral/UVJ stones
• Remove metal from field

Contrast

Technique

• Supine (prone optional to distinguish UVJ stone vs bladder stone)
• Coverage top of kidneys through pubic symphysis (include entire urinary tract)
• Low-dose protocol: 120 kV with reduced mAs and iterative reconstruction; or low kV in thin patients
• Thin collimation; 2.5-3 mm axial review with thin recon and coronal reformats
• Coronal reformats aid stone localization along ureter

Series / Sequences

Key points

• Low-dose technique appropriate—most stones are high-contrast; reserve standard dose for body habitus needs
• Report stone size, location, density (HU), and secondary signs: hydronephrosis, perinephric/periureteral stranding, ureteral dilation, tissue rim sign
• Dual-energy CT can characterize uric acid vs calcium stones
• Prone or delayed imaging helps confirm UVJ stone vs bladder stone
• Indinavir stones are radiolucent on CT

References