Purpose: To establish whether information would be lost if slice reconstruction thickness was increased from 3 to 5 mm, and whether this altered how difficult it was to interpret the examinations.
Material and Methods: Twenty-three consecutive patients referred with suspected or known urinary stones were included. All examinations were performed without intravenous contrast media. The original series, with effective mAs 50, were reconstructed with slice thickness 3 and 5 mm, respectively. All demographic and examination data were removed and the series reviewed in PACS by two independent radiologists. Objective findings, i.e. number and size of stones, signs of obstruction, and evaluation of interpretation difficulty, were registered.
Results: Identical findings were registered in 18 of the series of 3 mm (n = 23) and 19 of the series of 5 mm (n = 23). In two series reconstructed with 3 mm slice thickness and in one series with 5 mm slice thickness, the observers disagreed on the presence of urinary stones. Main reasons for interpretation difficulties were given as “lack of intra-abdominal fat” and “many phleboliths in the pelvic region”, but never “disturbing noise”.
Conclusion: To determine the presence and size of urinary stones at low-dose computed tomography, 5 mm reconstruction algorithm seems equal to 3 mm. Patient-related factors influence the interpretation more than image quality.
