Evaluation of the accuracy of low dose CT in the detection of urolithiasis in comparison to standard dose CT

Soliman, Amany Ahmed; Sakr, Lobna Khaled

doi:10.21608/aimj.2020.22462.1082

Evaluation of the accuracy of low dose CT in the detection of urolithiasis in comparison to standard dose CT

Document Type : Original Article

Authors

al-zahraa university hospital

10.21608/aimj.2020.22462.1082

Abstract

Objective: This study aims to evaluate the sensitivity, specificity, and accuracy of low dose CT in the detection of urolithiasis in comparison with standard-dose CT as a reference test.
Materials and Methods: This prospective randomized study was conducted on 30 patients with suspected renal colic undergone standard and low dose CT from September 2018 to September 2019 at AL-Zahraa University Hospital. The patients were scanned by the Toshiba CT system, 160 slices using automated tube current modulation; the computed tomography was performed without oral or intravenous contrast.
Results: This study enrolled 30 patients who had renal colic symptoms and signs and had a urinary stone that detected in standard-dose CT, the mean of age was (43.83±11.45). The male percentage was (56.7%) while the female percentage was (43.3%). This study was revealed that 55 stones were detected by SDCT and 53 stones were detected by LDCT, so there was a statistically significant agreement between the two modalities in the detection of urolithiasis with Kappa value of (0.868) and p-value(<0.001**). The mean current tube was (416.0±79.1) and (135.2±25.7) in SDCT and LDCT respectively. The radiation dose was (120 and 80) in SDCT &LDCT respectively. Sensitivity was (96.4%) and specificity was (100%) in LDCT.
Conclusion: This study revealed that LDCT was an effective technique in the detection of urolithiasis with high sensitivity and specificity despite a significant reduction in radiation dose exposure to SDCT.

Keywords

Full Text

INTRODUCTION

Renal colic is a common situation affecting 1 in 1,000 persons per year¹. Non-contrast computed tomography scan of the kidney, ureter, and bladder (CT KUB) is the investigation of choice for patients with suspected urolithiasis, and it is recommended by the European Association of Urology and the American Urological Association^{2, 3.}

The usage of non-contrast computed tomography reveals the presence of a stone, its size, location, density and the presence of hydronephrosis⁴; it gives us information for selecting the appropriate therapeutic approach.⁵. However, renal colic affects frequently adults with a high incidence of recurrence about 50%^6.The regular usage of SDCT increases the ethical concern about the exposure dose of radiation ^7,8.

Today, there is an improvement in computed tomography technique that has marked a decrease in the exposure dose and allowed the provision of clear images. Low-dose CT（LDCT) is a method that has been developed to reduce the exposure dose associated with the examination, and is mainly performed for lung cancer screening^{9, 10.} LDCT is recommended as an examination for urinary tract stones ^{11, 12}. Our study aims to

evaluate the sensitivity, specificity, and accuracy of LDCT in the detection of urolithiasis compared to SDCT as a reference test.

MATERIALS AND METHODS

A prospective randomized study approved by the Local Ethical Committee and patients informed about the study and acquired their consent to undergo additional CT scans. It is conducted from September 2018 to September 2019 on 30 patients with the mean age (43.83±11.45) which done in the CT unit of the radiological department of Al-Zahraa University Hospital.

The patients had a history of urinary stone and referred from the consultant clinic of urology, patients with documented urinary stone by SDCT were included. The patients were scanned by the Toshiba CT system, 160 slices using automated tube current modulation; all CT scans were done without oral or intravenous contrast. CT scan started from the diaphragm to lower symphysis pubis with standard- dose CT has first done to patients, and then after detection of stone the patient was undergone LDCT in a limited area (only the site of stone). In SDCT, tube voltage of 120 kV and tube current- time product of mean in all patients of the mean (416.0±79.1) is shown in Figure (1,2,3 a). While in

LDCT, tube voltage of 80 kV and tube current- time product of mean (135.2±25.7) mAs is shown in Figure (1,2,3 b).

Fig. 1: (A, B): CT of the urinary tract revealed left renal lower calyceal stone. (a) Stone appeared by standard dose

2. a

2.bb

Computed tomography (120 kV, 420 mAs). (b) The same stone appeared by low dose computed tomography (80 kV, 130 mAs)

Fig. 2: (A, B): CT of the urinary tract revealed left lower Ureteric stone. (a) Stone appeared by standard dose computed tomography (120 kV, 420 mAs). (b) The same stone appeared by low dose computed tomography (80 kV, 130 mAs).

3:a

3:b

Fig.3: (A, B): CT of the urinary tract revealed left lower Ureteric stone. (a) Stone appeared by standard dose computed tomography (120 kV, 420 mAs). (b) The same stone appeared by low dose computed tomography (80 kV, 130 mAs).

Fig. 4: Bar chart between standard and low dose according to stone size (mm).

Statistical analysis:Recorded data were analyzed using the statistical package for social sciences, version 20.0 (SPSS Inc., Chicago, Illinois, USA). Quantitative data were expressed as mean± standard deviation (SD). Qualitative data were expressed as frequency and percentage. Independent-samples t test using to compare two means. Kappa measure of agreement between standard dose and low dose in detecting the level of stone. A value of: 0 – 0.20 indicates slight agreement; 0.21– 0.40, fair agreement; 0.41– 0.60, moderate agreement; 0.61– 0.80, substantial agreement; and 0.81–1.00, almost perfect agreement. The confidence interval was set to 95% and the margin of error accepted was set to 5%. So, P-value <0.05 was considered significant, P-value <0.001 was considered as highly significant, and P-value >0.05 was considered insignificant.

RESULTS

A prospective randomized study included 30 patients who had renal colic and a stone was detected in the urinary tract in standard- dose CT. General Character of patients showed in (table1).

Demographic data	Total (n=30)
Age (years)
Range	22-a63
Mean ±SD	43.83±11.45
Gender
Male	17 (56.7%)
Female	13 (43.3%)

Table 1: Demographic data distribution of the study group. This table shows that the ranged age 22-63 with mean 43.83 regarding age, while the male (56.7%) and female (43.3%) of sex.

Stone distribution	No.	%
Renal stone	25	45.5%
Upper calyx
Left	4	7.3%
Middle
LT	5	9.1%
RT	1	1.8%
Lower
LT	8	14.5%
RT	4	7.3%
Pelvis
RT	3	5.5%
Ureteric	30	54.5%
Right
Lower	11	20%
Mid	4	7.3%
Left
Lower	7	12.7%
Mid	8	14.5%
Bladder
Mural
0	0	0.0%
Luminal
0	0	0.0%
Total	55	100.0%

Table 2: Stone distribution of the study group.

Renal stones were 25 (LT:17 and RT:8)(45.5%) and

Ureteral stones were 30(LT:15 and RT:15)(54.5%).

Stone size (mm)	Standard	Low dose
3-5mm	8 (14.5%)	6 (11.3%)
6-10mm	28 (50.9%)	28 (52.8%)
11-15mm	16 (29.1%)	16 (30.2%)
16-20mm	3 (5.5%)	3 (5.7%)
> 20mm	0 (0.0%)	0 (0.0%)
Total stones	55 (100.0%)	53 (100.0%)
*Kappa test*	0.868
*p-value*	<0.001**

Table 3: Comparison between standard and low dose according to stone size (mm).Using: Kappa test; **p-value Statistical analysis of these results showed significant agreement between the two modalities in the detection of stone. Comparison of standard and low dose a yielded weighted Kappa value of 0.868

	Standard	Low dose	t-test	p-value
Tube current (mAs)
Range	170-560	81-191	12.862	<0.001**
Mean±SD	416.0±79.1	135.2±25.7	12.862	<0.001**
Diameter of stone (mm)
Range	5-20	5-20	0.921	0.482
Mean±SD	7.3±1.4	7.5±1.31	0.921	0.482
Stone density (HU)
Range	120-1444	120-1297	1.482	0.097
Mean±SD	726.20±424.70	676.58±404.55	1.482	0.097
Radiation dose (KV)
Mean	120	80	17.914	<0.001**

Sensitivity		96.4%
Specificity		100.0%

Table 4: Comparison of finding between standard doses

Computed tomography and low dose computed tomography.

Using: Independent Sample t-test; p-value >0.05 NS: Using: Independent Sample t-test; p-value >0.05 NS: **p-value

There was a significant difference in tube current between two procedures in SDCT scan the mean of tube current was (416.0±79.1) mAs, while in LDCT scan the mean was (135.2±25.7) mAs. There was no statistically significant difference in diameter and density of stone between the two procedures (P=0.482) and (P=0.097) respectively. Also, there was a statistically significant difference in radiation dose between two procedures (kV) (P<0.001). The sensitivity of LDCT was (96.4%) and specificity was (100%) in comparison with SDCT.

DISCUSSION

Urolithiasis affects a wide range of age groups from adults to elderly patients. In the U.S., the incidence of recurrence of urinary calculi was 75% which needs treatment and follow-up for a long time^{13, 14}. Multiple recent studies demonstrated the effectiveness of low dose CT in the detection of urinary stones^{15, 16, 17}.

In our study, the mean age was (43.83±11.45) and the age range from (22-63) years, which is nearly similar to Moore et al¹⁸.in 2005 reported mean of age( 44± 2.6), and Poletti et al¹¹.reported in 2006 age range from (19-80) years and mean age( 45±5.1), while Fracchia et al¹⁹ reported 53 years mean age.

In our study, the male constitutes (56.7%), while in other reported studies revealed high male incidence Hamm et al 74%.²⁰, and Moore et al¹⁸ recorded 52% of male incidence.

Our study revealed 45.5% of stones were located in the kidney, while 54.5% of stones were presented in the ureter, which is nearly similar to the study reported stone location as 50% in the kidney and 30% within the distal ureter and 20% located in the proximal ureter²¹, while another study by William Sohn detected that ureteral stones were demonstrated in 38 (36%) of 106 patients¹⁶.

In this study, there was a statistical significant difference between the two procedures in tube current and radiation dose, in SDCT the tube current mean was (416.0±79.1mA)and the radiation dose was 120(KV), while in LDCT, the tube current mean was (135.2±25.7 mA) and the radiation dose was 80 (KV)(P<0.001),which agree with a study demonstrated by Heneghan et al²².That detected CT done with a reduced tube current of 100 mA resulted in an approximately 25%-42% reduction in dose when compared with the SDCT, without a significant change in the accuracy. Spielmann et al²³.recorded excellent detection of stones, even with significant reductions in the tube current (range 170-20 mA) and nearly 75% reduced in radiation dose. Indeed, many stones were visualized at a mA as low as 20.

Our study demonstrated that the sensitivity and specificity of LDCT in relation to SDCT as a reference test was (96.4%) and (100%) respectively, our results were similar to study by Niemann et al²⁴.that revealed sensitivity of 96% & specificity of 94.9%, and another study by Moore et al¹⁸. detected a sensitivity of the reduced protocols 90.3% and 99% specificity. Some studied revealed 100% sensitivity and specificity of low dose CT ^{15, 25}.

Several factors may affect the accuracy of LDCT, such as the size of stone. In our study some small stones < 3mm were not detected by LDCT which may affect the sensitivity and specificity of LDCT, these agree with the results of a study by Rob et al²⁶, which reported lower sensitivity and specificity in the diagnosis of stones<3mm.

In our study, there was no statistically significant difference in the diameter of stones between the two procedures (p=0.482), which agree with the results of Kwon et al¹⁵. And Sohn et al¹⁶. Revealed that no difference in the measurement of stones between LDCT and SDCT. In our study there is no significant difference in the attenuation values of stones detected in LDCT compared to that in SDCT, this agrees with a study by Alsyoufet al ²⁷, reported similar attenuation values of stones detected in LDCT (regarding stone composition) compared with Conventional/standard-dose CT with only a slight increase in variability. A study by Sohn et al¹⁶supported this observation.

CONCLUSION

This study revealed that LDCT was an effective technique in the detection of urolithiasis with high sensitivity and specificity despite significant reduction in radiation dose exposure in to SDCT.

References

1. Nice. Renal or Ureteric Colic-Acute-Summary.https://cks.nice.org.uk/renal-or-ureteric-colic-acute. Topic summary. Accessed April 2017.
2. European Urological Association Guidelines on Urolithiasis. Avilableat: https:// uroweb.org/wp-content/uploads/22-Urolithiasis_LR_full.pdf. Accessed April 2017.
3. Surgical Management of stones: American Urological Society/ Endourology Guidline. Available at: https://www.auanet.org/guidelines/surgical-management-of-stone#x3160. Accessed April 2017.
4. Vieweg J, Teh C, Freed K, Leder RA, Smith RH, Nelson RH, et al. Unenhanced helical computerized tomography for the evaluation of patients with acute flank pain. J Urol 1998; 160: 679-84.
5. Marsoul AD, Rasool HA, Judi MR. A comparison between low dose and standard dose computed tomography scan in the detection of urolithiasis. Med J Babylon 2018; 15: 258-62.
6. Sierakowski R, Finlayson B, Landes RR, Finlayson CD, Sierakowski N. The frequency of urolithiasis in hospital discharge diagnosis in the United States. Invest Urol 1978; 15:438-41.
7. Tamm EP, Silverman PM, Shuman WP. Evaluation of the patient with flank pain and possible ureteral calculus. Radiology 2003; 228: 319-29.
8. Katz SI, Saluja S, Brink JA, Forman HP. Radiation dose associated with unenhanced CT for suspected renal colic: Impact of repetitive studies. AJR. Am J Roentgenol 2006; 186: 1120- 4.
9. The National Lung Screening Trial Research Team. Reduced lung-cancer mortality with low-dose computed tomographic screening. N Engl J Med 2011; 365: 395-409.
10. Kobayashi T, Kibe Y, Hiura T, et al. Evaluation of the exposure dose in a low dose CT for lung cancer screening to its permitted image quality. J Thorac CT Screen 2014; 21: 30-35.
11. Poletti PA, Platon A, Rutschmann OT, et al. Low-dose versus standard-dose CT protocol in patients with clinically suspected renal colic. Am J Roentgenol.2007; 188: 927-933.
12. Ciaschini MW, Remer EM, Baker ME, et al. Urinary calculi: radiation dose reduction of 50% and 75% at CT- effect on sensitivity. Radiology. 2009; 251: 105-111.
13. Curhan GC. Epidemiology of stone disease. Urol Clin North Am. 2007; 34: 287-293.
14. Bartoletti R, Cai T, Mondaini N, et al. Epidemiology and risk factors in urolithiasis. UroInt 2007; 79:3-7.
15. Kwom JK, Chang IH, Moon YT, et al. Usefulness of low-dose nonenhanced computed tomography with iterative reconstruction for evaluation of urolithiasis: diagnostic performance and agreement between the urologist and the radiologist. Urology. 2015; 85: 531-538.
16. Sohn W, Clayman RV, Lee JY, et al. Low-dose and standard computed tomography scans yield equivalent stone measurements. Urology. 2013; 81: 231-234.
17. Park SH, Kim DK, Moon YT, et al. Pilot study of low-dose nonenhanced computed tomography with iterative reconstruction for diagnosis of urinary stones. Korean J Urol . 2014; 55:581-586.
18. Moore CL, Daniels B, Ghita M, Gunabushanam G, Luty S, Molinaro AM, et al. Accuracy of reduced-dose computed tomography for ureteral stones in emergency department patients. Ann Emerg Med. 2015; 65: 189-98.e2.
19. Fracchia JA, Panagopoulos G, Katz RJ, Armenakas N, Sosa RE, DeCorato DR. Adequency of low dose computed tomography in patients presenting with acute urinary colic. J Endourol. 2012; 26:1242-6.
20. Hamm M, Knopfle E, Wartenberg S, Wawroschek F, Weckermann D, Harzmann R, et al. Low dose unenhanced helical computerized tomography for the evaluation of acute flank pain. J Urol. 2002; 167: 1687-91.
21. Tack D, Sourtzis S, Delpierre I, de Maertelaer V, Gevenois PA. Low dose unenhanced multidetector CT of patients with suspected renal colic. AJR Am J Roentgenol. 2003; 180: 305-11.
22. Heneghan JP, McGuire KA, Leder RA, DeLong DM, Yoshizumi T, Nelson RC, et al. Helical CT for nephrolithiasis and ureterolithiasis: Comparison of conventional and reduced radiation- dose techniques. Radiology. 2003; 229: 575-80.
23. Spielman AL, Heneghan JP, Lee LJ, Yoshizumi T, Nelson RC. Decreasing the radiation dose for renal stone CT: A feasibility study of single- and multidetector CT. AJR Am J Roentgenol. 2002; 178: 1058-62.
24. Niemann T, Kollmann t, Bongartz G. Diagnostic performance of low-dose CT for the detection of urolithiasis: A meta-analysis. AJR Am J Roentgenol. 2008; 191:396-401.
25. Licheng J, Yidong F, Ping W, Keqiang Y, Xueting W, Yingchen z, et al. Unenhanced low-dose versus standard- dose CT localization in patients with upper urinary calculi for minimally invasive percutaneous nephrolithotomy ( MPCNL). Indian J Med Res. 2014; 139:386-92.
26. Rob S, Bryant T, Wilson I, Somani BK. Ultra-low-dose, low-dose, and standard-dose CT of the kidney, ureters, and bladder: Is there a difference? Results from a systemic review of the literature. ClinRadiol. 2016; 72:11-5.
  1. Alsyouf M, Smith DL, Olgin G, Heldt JP, Lightfoot M, Li R, et al. Comparing stone attenuation in low and conventional-dose non-contrast computed tomography. J Endourol. 2014; 28(6):704-7.