Ultra-Low-Dose CT: An Effective Follow-Up Imaging Modality for Ureterolithiasis

Classically, abdominal X-ray (KUB), ultrasound, or a combination of both have been routinely used for ureteral stone surveillance after initial diagnosis. More recently, ultra-low-dose CT (ULD CT) has emerged as a CT technique that reduces radiation dose while maintaining high sensitivity and specificity for urinary stone detection. We aim to evaluate our initial experience with ULD CT for patients with ureterolithiasis, measuring real-world radiation doses and stone detection performance. We reviewed all ULD CT scans performed at the Veterans Affairs Palo Alto Health Care System between 2016 and 2018. We included patients with ureteral stones and calculated the mean effective radiation dose per scan. We determined stone location and size, if the stone was visible on the associated KUB or CT scout film, and if hydronephrosis was present. We performed logistic regression to identify variables associated with visibility on KUB or CT scout film and hydronephrosis. One hundred eighteen ULD scans were reviewed, of which 50 detected ureteral stones. The mean effective radiation dose was 1.04 ± 0.41 mSv. Of the ULD CTs that detected ureterolithiasis, 38% lacked visibility on KUB/CT scout film and had no associated hydronephrosis, suggesting that they would be missed with a combination of KUB and ultrasound. Larger stones (odds ratio [OR]: 1.40, 95% confidence interval [CI]: 1.08, 1.96 for every 1 mm increase in stone size) were more likely to be detected by KUB/CT scout film or ultrasound, while stones in the distal ureter (OR: 0.18, 95% CI: 0.03, 0.81) were more likely to be missed by KUB/CT scout film or hydronephrosis. Based on our institutions' initial experience, ULD CT detects small and distal ureteral stones that would likely be missed by KUB or ultrasound, while maintaining a low effective radiation dose. An ULD CT protocol should be considered when reimaging for ureteral stones is necessary.