Utilization of Dual Energy CT to Characterize Renal Stones and Effects on Patient Management

posted by Savvas Nicolaou, M.D. | Sep 15, 2008

The following study was presented at the UBC Radiology Scientific Day, June 2008 & Stanford Radiology’s 10 th Annual International Symposium on Multidetector CT In May 2008.

Purpose: To investigate whether DECT can accurately determine composition of renal calculi at acceptable dose. To observe how this information changes patient management in the ER setting and urological practice.

Methods & Materials: Sixty consecutive patients presenting with renal colic and microscopic hematuria  (43 male, 17 female; mean age 57 ± 18; range 19-83)  underwent non-contrast dual-energy CTKUB examination. Patients were recruited form the emergency department, inpatient ward referrals and urological referral in patients pre ESWL /PNL. Scanning was performed with a Somatom DSCT Definition unit (Siemens Medical Solutions, Germany) with the following parameters:  80 and 140 kVp, 255 and 60 mAs, respectively; collimation, 14 × 1.2 mm; pitch, 0.9, 4D care dose on. Images were reconstructed to 3 and 5mm axially and 3mm in the coronal plane. Two dual energy trained radiologists, blinded to one another’s results and stone type,  prospectively determined the composition of calculi on the dual energy viewing station by applying the three material decomposition algorithm and utilizing  overlay values. DECT  stone overlay values   were correlated pathologically  with the same stones following intervention (ESWL/PNL) or spontaneous passage. Both invivo and in vitro correlation was performed.

Results: Pathologically correlation was obtained in 33 stones. DECT  calculations  revealed (n=19,  color coded blue; n=14,  color coded red) in the patient population. Mean stone diameter was 5.0 mm (range, 1.0-33.0 mm). The blue color coded  stones were composed of calcium oxalate  (n=13), struvite (n=6).  The red color coded  stones were composed of cystine (n=5) and uric acid (n=9).  The mean patient anteroposterior abdominal diameters were measured to be 24.7 ± 3.3 cm (range, 15.3-30.8 cm). Mean DLP was 393.0 ± 95.4 mGy•cm (range, 242.0 – 633.0 mGy•cm). Overlay mean values were as follows calcium oxalate was 22.5  SD 6.9 , struvite 12.9  SD 1.4, cystine –6.5 SD1.2, uric acid -26.5 SD 6.9. Initial  comparison of the  mean values was performed  with ANOVA  in which there was statistical significant difference with a p value <0.0001. Subsequent  pairwise analysis between the different stone types was performed using pairwise comparisons (Boneferroni) in which the different types of stones could be differentiated form each other  based on the overlay  values that was statistically significant using 95% confidence intervals.

Conclusion: Dual-energy CTKUB permits accurate differentiation of four types of urinary calculi at low doses, effectively streamlining  diagnostic and therapeutic pathways. This has significant clinical revelance  for  the management of stone disease. Cystine stones are ESWL resistant thus acutely these types of stones would be stratified into ureteroscopy or PNL depending on location and size. Chronic cystine  and uric acid stones can be treated medically bypassing surgical treatment  and   high doses of intravenous antibiotics are needed pre ESWL for struvite stones as there is an increased incidence of urosepsis post ESWL in the treatment of struvite stones.

Authors: S. Nicolaou, A. Eftekhari, M. Rivers-Bowerman, L. Louis, M Hydri,R. Patterson, B. Chew, C. Ziewerich

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