Recent developments in computed tomography for urolithiasis: diagnosis and characterization

THE USE OF LOW-DOSE CT WITH ADAPTIVE STATISTICAL ITERATIVE RECONSTRUCTION FOR THE DIAGNOSIS OF URINARY CALCULI

This study aimed to explore the diagnosis of urinary calculi through utilisation of low-dose computed tomography (LDCT) with adaptive statistical iterative reconstruction (ASIR). Data from 140 patients that had undergone pathological or operative diagnosis with urinary calculi were analysed. Patients were divided into two groups based on whether they received conventional-dose computed tomography (CDCT) or LDCT, respectively, followed by filtered back projection or ASIR. Average CDCT radiation doses were roughly 4-fold higher than LDCT doses. Despite this difference, there were no significant differences between groups with respect to stone size or location, image quality (P = 0.261), image noise (P = 0.153) and diagnostic efficacy (P = 0.371). LDCT is an effective approach to urinary calculi diagnosis, performing to ASIR while decreasing the effective radiation dose, improving the safety of this procedure.

Dose and Image Quality in Low-dose CT for Urinary Stone Disease: Added Value of Automatic Tube Current Modulation and Iterative Reconstruction Techniques

The aim of this study was to compare dose and image quality (IQ) of a baseline low-dose computed tomography (CT) (fix mAs) vs. an ultra-low-dose CT (automatic tube current modulation, ATCM) in patients with suspected urinary stone disease and to assess the added value of iterative reconstruction. CT examination was performed on 193 patients (103 baseline low-dose, 90 ultra-low-dose). Filtered back projection (FBP) was used for both protocols, and Sinogram Affirmed Iterative Reconstruction (SAFIRE) was used for the ultra-low-dose protocol only. Dose and ureter stones information were collected for both protocols. Subjective IQ was assessed by two radiologists scoring noise, visibility of the ureter and overall IQ. Objective IQ (contrast-to-noise ratio, CNR) was assessed for the ultra-low-dose protocol only (FBP and SAFIRE). The ultra-low-dose protocol (ATCM) showed a 22% decrease in mean effective dose (p < 0.001) and improved visibility of the pelvic ureter (p = 0.02). CNR was higher for SAFIRE (p < 0.0001). SAFIRE improves the objective IQ, but not the subjective IQ for the chosen clinical task.

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

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.