1. PREDICTION OF CHEMICAL COMPOSITION OF URINARY CALCULI IN-VIVO BASED ON COMPUTED TOMOGRAPHY ATTENUATION VALUES Abstract Id: IRIA - 1050

2. ADVANTAGES OF KNOWING STONE COMPOSITION IN-VIVO Avoid unnecessary and unsuccessful shock wave lithotripsy procedures. More directed diagnostic workup in recurrent stone formers. Information generally limited to patients who have stone retrieved – spontaneous passage/ surgery.

3. Stones show varying degrees of X-ray attenuation that is dependent on their chemical composition

4. AIMS AND OBJECTIVES Attenuation parameters (mean HU, median HU, maximum HU) of stone calculated on non-contrast CT study. Chemical composition of retrieved stone assessed with X-ray diffraction crystallography. Relationship between attenuation parameters and chemical composition sought.

5. GE Dual Slice – 120 kVp – Automated tube current modulation – Pitch 1.5:1 – Slice thickness – 3 mm Sample size – 51 stones

6. Parameters studied for each stone – Mean HU – Median HU – Maximum HU – Periphery HU – Core HU (Difference) – Chemical Composition

7. Slice with maximum stone width (for mean and median HU) Each slice showing stone assessed for maximum HU and highest selected Magnified Bone window with finer manual adjustment to better appreciate edges

8. 4 Region of Interest HU measurements – Mean, Median – Maximum – Periphery – Core Avoid periphery and consider adjacent slices (for mean and median HU) – Stones not oriented perpendicular – Avoid errors due to partial volume

9. Potential pitfalls and limitations Region of Interest selection – subject to intra-observer and inter-observer variability. Stones are not homogeneously dense. Stones were categorized according to major composition – but stones are not always pure. Small sample size

10. RESULTS Demographics – predominantly middle-aged and male

11. Mean maximal cross-sectional diameter of stones – 7 mm

13. Mean HU Calcium oxalate monohydrate 1006 ± 135 HU Calcium oxalate dihydrate710 ± 114 HU Uric Acie452 ± 80 HU Hydroxyapatite1274 ± 55 HU P < 0.001

14. Median HU Calcium oxalate monohydrate 1019 ± 135 HU Calcium oxalate dihydrate719 ± 115 HU Uric ACid499 ± 141 HU Hydroxyapatite1292 ± 57 HU P < 0.001

15. Maximum HU Calcium oxalate monohydrate 1258 ± 184 HU Calcium oxalate dihydrate862 ± 170 HU Uric acid542 ± 76 HU Hydroxyapatite1454 ± 64 HU P < 0.001

16. Difference between Periphery and Core HU Calcium oxalate monohydrate -83 ± 201 HU Calcium oxalate dihydrate-126 ± 69 HU Uric acid-58 ± 42 HU Hydroxyapatite-148 ± 58 HU P = 0.284

17. DISCUSSION 4 studied stone types showed statistically significant differences in – Mean HU – Median HU – Maximum HU – Hydroxyapatite > Ca oxalate monohydrate > Ca oxalate dihydrate > Uric Acid No significant pattern in Periphery- Core HU value differences – Although uric acid showed smaller differences consistent with literature that they are homogeneous Discriminant function analysis – prediction accuracy of 84.5 %

18. Hierarchy observed in density of stones in agreement with literature – Hydroxyapatite – densest – Uric acid – most lucent But absolute attenuation measurements are not in agreement with literature Calcium oxalate monohydrateCalcium oxalate dihydrate Gupta et al.1008 HU748 HU Zarse et al.1707 – 1925 HU1416 – 1938 HU Patel et al.879 ± 230 HU517 ± 203 HU

19. Attenuation measurements dependent on parameters other than characteristics of stone like – Stone size – Scan collimation – X-ray tube potential – Inter-scanner differences

20. CONCLUSION Significant relationship exists between chemical composition of a urinary stone and its CT attenuation values. Stones can be predicted IF – Database of attenuation characteristics is built (continually over time) for given CT machine and given protocol with stones of known chemical composition

21. Bibliography Hillman BJ, Drach GW, Tracey P, Gaines JA. Computed tomographic analysis of renal calculi. AJR Am J Roentgenol. 1984 Mar;142(3):549–52. Kuwahara M, Kageyama S, Kurosu S, Orikasa S. Computed tomography and composition of renal calculi. Urol Res. 1984;12(2):111–3. Mostafavi MR, Ernst RD, Saltzman B. Accurate determination of chemical composition of urinary calculi by spiral computerized tomography. J Urol. 1998 Mar;159(3):673–5. Saw KC, McAteer JA, Monga AG, Chua GT, Lingeman JE, Williams JC. Helical CT of urinary calculi: effect of stone composition, stone size, and scan collimation. AJR Am J Roentgenol. 2000 Aug;175(2):329–32. Tublin ME, Murphy ME, Delong DM, Tessler FN, Kliewer MA. Conspicuity of renal calculi at unenhanced CT: effects of calculus composition and size and CT technique. Radiology. 2002 Oct;225(1):91–6. Levi C, Gray JE, McCullough EC, Hattery RR. The unreliability of CT numbers as absolute values. AJR Am J Roentgenol. 1982 Sep;139(3):443–7. Groell R, Rienmueller R, Schaffler GJ, Portugaller HR, Graif E, Willfurth P. CT number variations due to different image acquisition and reconstruction parameters: a thorax phantom study. Comput Med Imaging Graph Off J Comput Med Imaging Soc. 2000 Apr;24(2):53–8.

22. THANK YOU