The value of dual-energy computed tomography (DECT) in the diagnosis of urinary calculi: a systematic review and meta-analysis of retrospective studies

Introduction

Urolithiasis is a common cause of colicky pain and urinary tract obstruction (Quhal & Seitz, 2021). The clinical treatment of urolithiasis differs according to the stone components and thus the identification of these components before treatment would assist both the clinical treatment and prognosis of patients (Bartges & Callens, 2015). Conventional nonenhanced CT (CNCT) is currently the gold standard for diagnosing urinary calculi. However, some patients still need CT urography (CTU) to evaluate urinary obstruction and bilateral renal function after CNCT, resulting in increased radiation dose and potential nephrotoxicity, and limiting the application of CTU (Brisbane, Bailey & Sorensen, 2016). Dual-energy computed tomography (DECT) imaging provides a novel direction and method for the analysis of stone composition, resulting in the acquisition of several quantitative parameters that reflect tissue-related information and energy images that differ from those obtained by traditional imaging and which can be used for stone composition analysis (Murray et al., 2019). DECT uses high (140 kV) and low (80 kV, 100 kV) energy for synchronous scanning, allowing the acquisition of original CT values using two kinds of energy. The two sets of data allow simulation of the attenuation coefficient of matter in the energy range of 40 −190 keV, and the acquisition of single-energy images of 151 groups of keV and the curve of the energy spectrum (Kaza et al., 2017).

Previous studies have found that enhanced scanning using dual-energy CT in the diagnosis of urinary calculi could reduce the scanning times and the effective radiation dose by 20% to 50% (Megibow, Kambadakone & Ananthakrishnan, 2018). Both retrospective and prospective cohort studies on the use of DECT for the detection of urinary calculi have shown high diagnostic sensitivity and specificity (Kordbacheh et al., 2019; Lazar et al., 2020), although others have reported disappointing results (Mansouri et al., 2015; Ahn, Oh & Seo, 2015). Thus, there is no consensus on the accuracy of DECT in diagnosing urinary calculi and whether it can be used effectively in clinics. Thus, an elucidation of whether the diagnostic accuracy of DECT is sufficient for detecting urinary calculi is necessary. In this meta-analysis, we systematically evaluated the accuracy of DECT in the detection of urinary calculi from the point of view of evidence-based medicine through meta-analysis, using CNCT as the gold standard.

Materials & Methods

Results

Characteristics and selection of the included studies

Figure 1 illustrates the search process. The initial searches of the online databases identified 225 potentially relevant studies. Of these, 136 were found to be duplicates and, together with 24 irrelevant articles, were excluded. After reading the full texts of the studies, a further 44 were found not to satisfy the inclusion criteria, and these together with 11 studies with insufficient data for construction of the contingency tables, were excluded. Ultimately, 10 articles were included in the meta-analysis. The characteristics of the included articles are shown in Table 1.

Table 1:

Characteristics of all studies involved in this meta-analysis.

Study	Country	Number of patients	CT (kV)	Number of stones	Study center
Jepperson et al. (2013) (Lazar et al., 2020)	USA	89	80,140	27	Department of Radiology, Mayo Clinic, USA
Elisabeth et al. (2021) (Mansouri et al., 2015)	Germany	70	80,140	34	Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, Germany
Mehmet et al. (2023) (Ahn, Oh & Seo, 2015)	Turkey	115	100,140	83	Department of Radiology, Faculty of Medicine, İnönü University, Malatya, Turkey
Botsikas et al. (2014) (Zieliński, Zieba & Byś, 2021)	Switzerland	116	80,140	23	Radiology Department, Geneva University Hospital, Geneva, Switzerland
Katherine et al. (2022) (Botsikas et al., 2014)	Australia	1760	80,140	1740	Faculty of Medicine and Health, University of Sydney, Camperdown, Australia
Jung et al. (2016) (Schönberg, Budjan & Hausmann, 2018)	Korea	296	80/100,140	148	Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul
Ascenti et al. (2016) (Cruz et al., 2019)	Italy	84	80,140	75	Department of Radiological Sciences, University of Messina, Messina, Italy
Chen et al. (2016) (Hamid et al., 2021)	China	171	80,140	45	Department of Medical Imaging, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan
Karlo et al. (2013) (Tatsugami et al., 2022)	Switzerland	100	80,140	104	Department of Radiology, University Hospital Zurich, Switzerland
Moon et al. (2014) (Sajja et al., 2020)	Korea	29	100,140	62	The Department of Radiology and Centre for Imaging Science, Sungkyunkwan University School of Medicine, Seoul

DOI: 10.7717/peerj.16076/table-1

Risk-of-bias and quality assessment

The data from the studies were extracted, analyzed, and evaluated by QUADAS-2. Figure 2 showed the assessment of bias risk. A high risk of index text bias was detected in six studies. Thus, the quality of the articles met the requirements of the meta-analysis.

Quantitative synthesis

Significant heterogeneity in the sensitivity, specificity, and PLR of DECT in the diagnosis of urinary stones (I² = 74.5%, 62.2%, 70.1%, all P < 0.1) was found in the included studies. Using the random effects model, the sensitivity of DECT in the diagnosis of urinary calculi was found to be 0.94 (95% CI [0.92–0.96], Fig. 3), with a PLR of 0.91 (95% CI [0.88–0.94], Fig. 4) and an NLR of 0.08 (95% CI [0.05–0.11], Fig. 5). The specificity of DECT in detecting urinary calculi was 0.91 (95% CI [0.88–0.94], Fig. 6). The AUC under the SROC curve was 0.9875, demonstrating excellent diagnostic performance (Fig. 7). Furthermore, there was no significant heterogeneity in the sensitivity, specificity, PLR, and NLR of DECT in the diagnosis of urinary stones with diameters <3 mm(I² = 16.3%, 0%, 0%, 29.5%). Using the fixed effects model, the sensitivity of DECT in the diagnosis of urinary calculi with diameters <3 mm was 0.94 (95% CI [0.91–0.96], Fig. 8) with a PLR of 10.79 (95% CI [5.25 to 22.17], Fig. 9) and an NLR of 0.08 (95% CI [0.05–0.13], Fig. 10). The specificity of DECT for detecting urinary calculi with diameters <3 mm was 0.91 (95% CI [0.87–0.94], Fig. 11). The AUC under the SROC curve was 0.9772, indicative of superior diagnostic performance (Fig. 12).

Discussion

Urolithiasis is a common disease that is frequently observed in clinics, and its incidence is increasing. There are significant differences in the clinical treatment of stones with different components, and thus evaluating the stone composition before treatment would assist both the clinical treatment and prognosis of patients. The recurrence rate of urolithiasis is high, and patients often need to undergo partial exclusion diagnostic examination (except for urinary neoplastic lesions), resulting in repeated examination (Schönberg, Budjan & Hausmann, 2018). In recent years, CT urography (CTU) has been widely used in examinations of urinary calculi. The overall scanning time of CTU is long, the radiation dose is high, and there is potential nephrotoxicity. Therefore, there is a need for radiologists to reduce the radiation dose while obtaining high-quality images and meeting the needs of the patients (Cruz et al., 2019). The overall scanning time of CTU is long, the radiation dose is high, and there is nephrotoxicity. Therefore, it is the direction of radiologists to reduce the radiation dose while obtaining high-quality images and meeting the needs of clinical and patients.

DECT imaging uses two sets of mutually perpendicular ball tubes and detectors in the rotating frame, with two tube voltages of 140 kV and 80 kV140 kV. After data conversion, the discs are transformed by enhanced scanning (Hamid et al., 2021). The virtual single-energy spectrum imaging by DECT can draw different contrast-to-noise ratio (CNR) curves by using the different sound and image characteristics of the different stone components to identify the composition of the stones before treatment. Because the CT values of different substances differ under different X-ray energy levels, the CT values of iodine agents vary significantly between the 80-kV and 140-kV images (Tatsugami et al., 2022). After data conversion, the iodized substances are removed from the enhanced scanning images, thus achieving material separation. A comparative investigation of DECT and CNCT in terms of image quality, tissue, organ structure, and CT values, amongst others, by Sajja et al. (2020) indicated that DECT could replace the diagnostic role of CNCT. In the CTU excretion phase images, urinary calculi are often indistinguishable from iodized contrast agents. Dual-energy CT can provide information about the size and location of urinary calculi by removing iodized substances from the CT images (Schyns et al., 2017). Thus, using a one-stop dual-energy CT examination, the information of both plain scan and CTU images can be obtained at the same time (Fernández-Pérez et al., 2022).

The image noise of dual-energy CT is higher than that of CNCT, and DECT requires more time and expertise to process image data and generate images (Sodickson et al., 2021). One of the factors limiting the broad application of DECT in CTU is the incomplete subtraction of the high concentration of iodized contrast medium excreted in the urine; the “marginal artifact” produced by this high concentration of iodized contrast agent can conceal the stone, resulting in a false-negative result (Xu et al., 2021). In addition, the focus without deiodination may be mistaken for the stone, resulting in a false positive (McCollough et al., 2015). A total of 10 articles were included in this meta-analysis. The results of the meta-analysis showed that dual-energy CT had good sensitivity and specificity for the detection of urinary calculi, especially for urinary calculi <3 mm in diameter. In addition, subgroup and sensitivity analyses were performed to explore the source of heterogeneity. Firstly, we extracted the data from three subgroups, and no source of heterogeneity was observed in subgroup analysis. Moreover, the sensitivity analysis showed that the study by Botsikas et al. (2014) significantly impacted the heterogeneity. The reason for this may be related to the preliminary design of the study (the delay period occurred at 10 min after 100 mL administration, and the lack of observed small stones may have been due to attenuation of contrast medium in the urinary system). Furthermore, the number of articles included in the meta-analysis was relatively small, and there were differences in the sample size and quality of the different articles, thus requiring additional confirmation by well-designed and high-quality studies in the future.

In the articles included in this study, the DECT phase was the delayed phase. There was no unified standard for studying the DECT phase, and the phases used by different researchers also differ. Thus, the detection sensitivity of urinary calculi with lengths <three mm was high (Spek et al., 2016). A previous study found that most ureteral stones with lengths of less than three mm can be excreted by themselves, although even if the length of the stone is less than three mm, it can cause pain and microscopic hematuria (Singh et al., 2020).

This meta-analysis has several strengths as well as some limitations. While the document retrieval was broad, it was limited to studies reported in English. There was slight heterogeneity between the included studies, which might have affected the results. The samples and diagnostic tests involved in the meta-analysis were relatively limited, so further multicenter studies with large samples are needed to clarify these factors.

Conclusions

In brief, the meta-analysis showed that dual-energy CT had high diagnostic sensitivity and specificity in the diagnosis of urinary calculi. It could thus replace conventional CT in CTU examinations and reduce the radiation dose, suggesting its potential in clinical applications. After post-processing, dual-energy CT can produce enhanced scan images and iodine maps, which not only allow the detection of stone and their compositions but also provides more clinical information.

Supplemental Information