Comparison of clinical characteristics of stones in the stone-free group (n = 51) and non-stone-free group (n = 21). Patients in the non-stone-free group (n = 21) had significantly larger diameter (a), surface area (b), and volume (c) but not higher density (d) or larger high-density (>1,000 HU) volume (e), compared to patients in the stone-free group (n = 51). *Indicates statistically significant difference.