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

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).

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.

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%).

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

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.