Ⅰ. INTRODUCTION
Urinary stone appears in lifetimes of approximately 12% of population. The rate of recurrence of urinary stones in ten years reaching 50% is relatively higher than other diseases, and 87% of patients suffering from urinary stone appeal pains in flank; it accompanies other symptoms such as hematuria, nausea, and vomiting[1-3].
Treatment for urinary stones exhibited extraordinary improvement through advancements in extracorporeal shock wave lithotripsy (ESWL) and urology.
However, the causes of urinary stone are yet to be clarified and therefore the recurrence rate is still high.
In particular, it turned out to see approximately 14% in a year, 35% in five years, and 52% in 10 years in a study related with the rate of recurrence of urinary stones[4].
The symptoms, size, and composition of urinary stones are very important as definite factors of the treatment[5]. Among those factors, the information on composition of urinary stones plays a crucial role for the effective treatment; the information also enables the prediction on disintegration of urinary stones[6-8].
In 1983, Mitcheson et al. reported an experimental study that the measurement of Hounsfield Unit (HU) vafter conducting computed tomography (CT) can be exploited to distinguish composition in the other urinary stone[9].
Therefore, We intended to identify the accuracy and the clinical feasibility of the composition analysis of urinary stones through using dual-energy computed tomography (DECT).
Ⅱ. MATERIAL AND METHODS
1 Subjects
Urinary stones were collected after the ESWL for urinary stones of patients who had been diagnosed on DECT. To simulate the conditions of urinary stones embedded in human body, the flesh of pork (length: 555 mm, width: 358 mm, height: 176 mm) was prepared wherein small plastic bottle (diameter: 10 mm, length: 45 mm) containing urinary stones was inserted for the examination as illustrated in Fig. 1.
Fig. 1. Pork which embeds the urinary stone to simulate situation.
2 Examination and Measurement
The mode of dual-energy(DE) of 640 slices multi-detector computed tomography(MDCT, Aquilion ONE, Canon Medical Center, Japan) enabling DECT was employed for the examination with the following parameters: Beam Collimation 0.5×320 mm, tube voltage of 135+80 kV, tube current of 50+290 mA, Rotation Time of 0.5 sec, D-FOV(Display-Field of View) 99.8 (S-FOV(Scan-Field of View): SS), and Volume Scan were used.
The values of HU were measured by using DE software (“DE stone Analysis” software version 48.3, Canon Medical Center, Japan) from the two images obtained as illustrated in Fig. 2-3, thereafter the compositions of uric acid stone and non-uric acid stone were analyzed, respectively.
Fig. 2. Measurement of the HU value of a Urinary stone.
Fig. 3. Dual-energy Analysis of urinary stones by plotting the two HU value of high and low kV.
3 Statistical Analysis
The SPSS software (Version 21.0; SPSS Inc., Chicago) was used for the statistical analyses the means and standard deviations of measurement of HU of urinary stones which varied according to of the tube voltage.
The t-test over the corresponding samples was carried out to determine the presence of significant differences between the HU values of a uric acid stone and a non-uric acid stone which corresponds to of p<0.05.
Ⅲ. RESULT
1. Gender of Patients & Composition of Urinary Stones
The patients (10 males and 7 females) participated in the present study and compositions of urinary stones are as presented in Table 1. The urinary stones collected from the patients consisted of six uric acid stones (35.29%) and 11 non-uric acid stones (64.71%).
Table 1. Gender of Patients and Compositions of Urinary Stones
2. HU values of Urinary Stones
As presented in Table 2, the measurement of HU of uric acid stone appeared at each level of voltage: 135 kV for 348.87±166.37, 100 kV for 345.33±151.18, and 80 kV for 337.94±172.77. Whereas the mean HU ± standard deviation (SD) of non-uric acid stone appeared as in the following: 135 kV for 551.93±297.09, 100 kV for 747.04±351.31, and 80 kV for 958.19±424.72. The values of HU, corresponding to the values of tube voltage, appeared constantly for the cases of uric acid stone, whereas the values of HU of non-uric acid stone appeared higher in accordance with lower tube voltage.
Table 2. HU Values of Urinary Stones
3. Comparison of Respective Values of HU of Urinary Stones at Each Tube Voltage
At each level of 135 kV and 100 kV of tube voltage, the values of HU of uric acid and non-uric acid stones exhibited no statistically significant differences (P>0.05), whereas at the level of tube voltage of 80 kV, the difference between HU values of uric acid and non-uric acid stones revealed statistically significant differences (P<0.05) (Table 3).
Table 3. Comparison of Respective Value of HU of Urinary Stones at Each Tube Voltage
4. Comparison of HU Values at 135 kV and 80 kV of Uric acid and non-uric acid Stones
For the case of uric acid stone, the values of HU at 80 kV and 135 kV were not statistically different (p>0.05), whereas for the case of non-uric acid stone, the values of HU at 80 kV and 135 kV were statistically significantly different (p<0.05) (Table 4).
Table 4. Comparison of HU Values of 135 kV and 80 kV of Uric acid and non-uric acid Stones
Ⅳ. DISCUSSION
The discovery of stones in the bladder dates to 4,800 years B.C. in Egypt, and the urolithiasis of which prevalence varies according to regions and environment is found on the increasing trend along with the westernization of dietary lives wherein the overweight, hyperlipidemia, and excessive uptake of animal protein etc. are frequently found[10-12].
Urinary stone is a consequence of disease that appears in approximately 12% of population in their lifetimes[1]. Approximately 87% of patients experience acute side abdominal pains thereby come to hospitals together with symptoms of nausea, vomiting, and visually observable urinary bleeding. The patients of acute side abdominal pain as chief complaint are frequently put into radiological examination to discriminate the presence of diseases associated with urinary stone.
For the patients suspected with the presence of urinary stone, the ‘unenhanced helical CT’ has been reported as more prompt, safer, and accurate diagnostic alternative than conventional urography for internal jugular vein or ultrasonic examination[13]. In addition, the ‘unenhanced helical CT’ has additional advantages of diagnosing radiolucent urinary stones and finding causes of the acute side abdominal pains by urinary stones, simultaneously[14,15].
Since the employment of CT by Mitcheson et al. in 1998 to distinguish compositions of urinary stone, the values of HU have been employed in many studies to distinguish compositions of urinary stone[9].
Mostafavi et al. reported that the uric acid stones were distinguished easily from stones of calcium, cystine, brushite, and struvite by CT imaging of 1mm thickness of urinary stones, and the employment of dual voltage CT was reported that it would show significant differences in values of HU of respective compositions at the level of significance of p<0.03 except for the uric acid stone[16].
Newhouse et al. conducted the study in laboratory with the spacing of 2 mm and reported that uric acid stones and stones of cystine can be distinguished from other components of urinary stone; Deveci et al. captured images of 107 urinary stones by the spacing of 1 mm in their study conducted in the laboratory and reported that they could distinguish all kinds of uric acid stones except for calcium oxalate dehydrate[17,18].
In the results obtained from the present study, the uric acid stones exhibited no differences at both levels of tube voltage of 135 kV and 100 kV except for the level of 80 kV wherein the decrease by the difference of 10.93 was observed. However, the difference between two values was not significant with the level of significance on p>0.05 (Table 3). On the contrary, the varied level of energy from 135 kV to 80 KV and 100 kV rendered the increase in values of HU by 406.26 and 195.11 respectively suggesting significant differences(p<0.05) (Table 4). That is, for the case of uric acid stone, the difference in values of HU almost did not appear despite differences in levels of energy. On the contrary, for the case of non-uric acid stones, the values of HU varied greatly according to variation in level of energy thus it was possible to distinguish two stones in DECT by using such properties.
Limitations of this study would be the small number of the entire samples, and it would be hard to generalize the results of this study with only six uric acid stones. Due to such limitations, it would be improbable to use in clinical guidelines. However, the results obtained from this study would be of help for further large scaled prospective studies in the future.
Ⅴ. CONCLUSIONS
In the phantom experimental study using urinary stones extracted after the procedure, uric acid stones and non-uric acid stones could be distinguished by the difference in the HU value which was changed differently according to the energy value investigated using DECT. Uric acid and non-uric acid stones was distinguished by non-invasive examination. In the case of uric acid stone, the stone may be treated through the treatment of alkalinization of urine rather than invasive. These results may help to treatment methods for urinary stone patients.
In the future, If the study of DE and reconstruction methods will in progress, the DECT test is expected to be useful for the treatment of urinary stones.
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