In vivo comparison of radiation exposure of dual-energy CT versus low-dose CT versus standard CT for imaging urinary calculi

Abstract

Purpose: Dual-energy computed tomography (DECT) is an emerging imaging modality with the unique capability of determining urinary stone composition. This study compares radiation exposure of DECT, standard single-energy CT (SECT), and low-dose renal stone protocol single-energy CT (LDSECT) for the evaluation of nephrolithiasis in a single in vivo patient cohort.

Materials and methods: Following institutional review board (IRB) approval, we retrospectively reviewed 200 consecutive DECT examinations performed on patients with suspected urolithiasis over a 6-month period. Of these, 35 patients had undergone examination with our LDSECT protocol, and 30 patients had undergone examination of the abdomen and pelvis with our SECT imaging protocol within 2 years of the DECT examination. The CT dose index volume (CTDIvol) was used to compare radiation exposure between scans. Image quality was objectively evaluated by comparing image noise. Statistical evaluation was performed using a Student's t-test.

Results: DECT performed at 80/140 kVp and 100/140 kVp did not produce a significant difference in radiation exposure compared with LDSECT (p=0.09 and 0.18, respectively). DECT performed at 80/140 kVp and 100/140 kVp produced an average 40% and 31%, respectively, reduction in radiation exposure compared with SECT (p<0.001). For patients imaged with the 100/140 kVp protocol, average values for images noise were higher in the LDSECT images compared with DECT images (p<0.001) and there was no significant difference in image noise between DECT and SECT images in the same patient (p=0.88). Patients imaged with the 80/140 kVp protocol had equivocal image noise compared with LDSECT images (p=0.44), however, DECT images had greater noise compared with SECT images in the same patient (p<0.001). Of the 75 patients included in the study, stone material was available for 16; DECT analysis correctly predicted stone composition in 15/16 patients (93%).

Conclusion: DECT provides knowledge of stone composition in addition to the anatomic information provided by LDSECT/SECT without increasing patient radiation exposure and with minimal impact on image noise.

FIG. 1.

Axial (A) dual-energy computed tomography (DECT) material-specific (B) diagnostic and (C) conventional single-energy low-dose renal stone protocol images through the left kidney in the same patient demonstrate a small renal calculus. The calculus is purple on the material-specific dual-energy images indicating a nonuric acid stone. The arrow in each image is pointing to the stone.

FIG. 2.

Axial (A) DECT diagnostic image and (B) conventional single-energy image through the abdomen in the same patient. A region of interest is drawn in the aorta for comparison of image noise.