prediction of chemical composition of urinary calculi in-vivo based on computed tomography...

PREDICTION OF CHEMICAL COMPOSITION OF URINARY CALCULI IN-VIVO BASED ON

COMPUTED TOMOGRAPHY ATTENUATION VALUES

Abstract Id: IRIA - 1050

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.

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

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.

• GE Dual Slice– 120 kVp– Automated tube current modulation– Pitch 1.5:1– Slice thickness – 3 mm

• Sample size – 51 stones

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

• 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

• 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

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

RESULTS• Demographics – predominantly middle-aged and male

18-20 21-30 31-40 41-50 51-60 >600

5

10

15

20

25

30

35

5.9

17.6

31.4

21.6

15.7

7.8

Age Distribution

Age in years

Perc

enta

ge o

f tot

al su

bjec

ts

26%

75%

Gender Distribution

Female

Male

Calcium Oxalate Monohydrate Calcium Oxalate Dihydrate Uric Acid Hydroxyapatite0

5

10

15

20

25

30

35

27.5

33.3

27.5

11.8

Chemical Composition Distribution

Chemical composition

Perc

enta

ge o

f tot

al st

ones

• Mean maximal cross-sectional diameter of stones – 7 mm

HU Mean HU Median HU Maximum Periphery HU Core HU Periphery HU - Core HU

-400.00

-200.00

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

1600.00Comparison of attenuation parameters among stones of different chemical compositions

Calcium Oxalate Monohydrate Calcium Oxalate Dihydrare Uric Acid Hydroxyapatite

Mean HU

Calcium Oxalate Monohydrate

Calcium Oxalate Dihydrare

Uric Acid Hydroxyapatite0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

1006.43

710.35

452.43

1274.33

HU Mean

Chemical composition

Mea

n att

neua

tion

(HU)

Calcium oxalate monohydrate

1006 ± 135 HU

Calcium oxalate dihydrate 710 ± 114 HU

Uric Acie 452 ± 80 HU

Hydroxyapatite 1274 ± 55 HU

P < 0.001

Median HU




200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

1019.07

719.12

499.36

1292.00

HU Median

Chemical Composition

Med

ian

HU

•Calcium oxalate monohydrateCalcium oxalate monohydrate

1019 ± 135 HU


Uric ACid 499 ± 141 HU


P < 0.001

Maximum HU




200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

1600.00

1257.93

862.18

542.36

1454.00

HU Maximum


HU M

axim

um


1258 ± 184 HU


Uric acid 542 ± 76 HU


P < 0.001

Difference between Periphery and Core HU

Calcium O

xalate M

onohydrate

Calcium O

xalate Dihyd

rare

Uric Acid

Hydroxya

patite

-160.00

-140.00

-120.00

-100.00

-80.00

-60.00

-40.00

-20.00

0.00

Periphery HU - Core HU


Perip

hery

HU

- Cor

e HU


-83 ± 201 HU

Calcium oxalate dihydrate -126 ± 69 HU

Uric acid -58 ± 42 HU

Hydroxyapatite -148 ± 58 HU

P = 0.284

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 %

• 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 monohydrate Calcium oxalate dihydrateGupta et al. 1008 HU 748 HUZarse et al. 1707 – 1925 HU 1416 – 1938 HUPatel et al. 879 ± 230 HU 517 ± 203 HU

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

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

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prediction of chemical composition of urinary calculi in-vivo based on computed tomography...

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