Low-dose and standard computed tomography scans yield equivalent stone measurements.

Objective: To ascertain the reliability of low-dose computed tomography (CT) compared with standard CT in the determination of stone size, density, and skin-to-stone distance (SSD).

Materials And Methods: A total of 10 patients seen in the emergency room within a mean of 23 days (range 0-51) underwent both conventional CT and low-dose CT for the same stone. The radiation dose reduction was calculated according to the patient's body mass index. The CT scans were performed with 2-mm section cuts, and 3-dimensional reconstruction was performed to obtain the coronal views. The stone size was measured (ie, height, width, and length), and the Hounsfield units were calculated. In addition, the SSD was calculated for the nonmoving renal stones.

Results: No difference was found in stone size between the 2 dosage levels, as measured by the height, width, length, and volume of the stone (P = .9, P = .7, P = .8, and P = .8 respectively). In addition, no difference in Hounsfield units was appreciated between the 2 scan types (P = .6). Finally, no significant difference was found in the SSD (P = .5). Between the 2 scans, the average effective dose reduction was 73%, from 23 to 6 mSv (P = .002).

Conclusion: No significant difference was found in the measurement of stone size, Hounsfield units, or SSD between the low-dose and conventional-dose CT scans. However, the low-dose CT scans resulted in a marked reduction in the radiation dose to the patient.