Predicting the Composition of Urinary Stone by Non-enhanced Spiral Computed Tomography

Seo Yong Park; Jeong Hee Hong; Seong Soo Jeon

doi:10.4111/kju.2006.47.7.717

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Park, Hong, and Jeon: Predicting the Composition of Urinary Stone by Non-enhanced Spiral Computed Tomography

Original Article

Korean J Urol 2006;47(7):717-721.

Published online: 18 December 2006

DOI: https://doi.org/10.4111/kju.2006.47.7.717

Predicting the Composition of Urinary Stone by Non-enhanced Spiral Computed Tomography

Seo Yong Park, Jeong Hee Hong, Seong Soo Jeon

¹From the Department of Urology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea

Corresponding Author: Jeon Seong-su Sungkyunkwan University College of Medicine Department of Urology, Samsung Seoul Hospital 50, Ilwon-dong, Gangnam-gu, Seoul ? 135-710 TEL: 02-3410-3555 FAX: 02-3410-3027 E-mail: seongsoo.jeon@ samsung.com

Received 6 March 2006 Accepted 22 April 2006

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose:

We attempted to develop a more accurate set of tools for predicting the composition of urinary stone with using Hounsfield units (HUs) in non-enhanced spiral computed tomography (NESCT).

Materials and Methods:

We evaluated 141 stones, and each of which was determined to contain the predominant stone component more than 70% (84 calcium oxalate, 35 uric acid, 16 carbonate apatite, 4 cystine and 2 brushite). NESCT was conducted at different collimations that varied between 3.75mm, 5mm and 7mm through the stones. One region of interest (ROI) was acquired for the plane that passed through the widest transverse diameter of the stone at the bone window setting. The mean size of the ROI in which the highest attenuation area was located was determined to be 2.0±0.5mm², and we recorded the mean and maximum HU values. In order to assess the partial volume effects, we used the S/C ratio (stone size/collimation ratio).

Results:

As the S/C ratio increased, both mean and maximum HU values increased, as did the ability to differentiate between different stone compositions. Also, under conditions in which the S/ C ratio exceeded 2, we proved to be able to differentiate uric acid stones from other stones, with no overlap in attenuation. Maximum HU values also proved to be effective tools for determining stone composition, as compared with the mean HU values.

Conclusions:

In situations in which the S/ C ratio exceeded 2, CT HUs proved to be a useful and accurate measurement for predicting uric acid stones. (Korean J Urol 2006;47:717-721)

Keywords: Tomography, Calculi, Urinary tract

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Fig. 1.

Stone composition and Hounsfield unit distributions. (A) Mean Hounsfield unit distributions of each the stone component in all the stones. (B, C) Mean (B) and maximum (C) Hounsfield unit distributions of each stone component on the condition that the S/C was >2.

Fig. 2.

Schematic illustration that shows the relationship between stone size and the collimation width of the computed tomography. (A) In the case in which the stone is smaller than the collimation width (S/C ratio < 1). (B, B’) In the cases in which the stone is larger than the collimation width, but smaller than double the collimation width(1<S/C ratio <2). (C, C’) In the cases in the which the stone is larger than double the collimation width (S/C ratio >2).

Table 1.

Patient and stone characteristics

No. of patients	141
Mean age±SD (range)	51.2±15.6(3-82)
No. of gender (%)
Male	98 (69.5)
Female	43 (30.5)
Mean calculous size±SD (range)	10.6±11.7 (3-65)
No. of calculous sites (%)
Kidney	28 (19.9)
Ureter	113(80.1)
No. of treatment method (%)
URS	84 (59.6)
ESWL	25 (17.7)
PNL	22 (15.6)
Spontaneous passage	9 (6.4)
Anatrophic nephrolithotomy	1 (0.7)

URS: ureteroscopic removal of stones, ESWL: extracorporeal shock wave lithotripsy, PNL: percutaneous nephrolithotomy

Table 2.

Mean and maximum Hounsfield unit (HU) of each stone's components

Stone type	No.	Mean HU at stone size/collimation				Max HU at stone size/collimation
Stone type	No.	S/C<1	1≤S/C>2	S/C<2	p-value	S/C<1	1≤S/C>2	S/C≥2	p-value
Ca. Oxalate	84	420±101	791±279	1,271±238	<0.001∗	503±92	873±276	1,298±220	<0.001∗
Uric acid	35	216±99	378±61	466±73	<0.001∗	240±47	421±18	495±68	<0.001∗
Car. apatite	16	274± 104	-	1,125±274	0.004^†	295±62	-	1,177 ± 278	0.004^†
Cystine	4	-	497	774±49		-	572	823±33
Brushite	2	394	-	1,700		438	-	1,801

Data were expressed as mean± SD. ∗Kruskal-Wallis test, ^†Mann-Whitney U test

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