Dual Energy CT Characterization Of Urinary Calculi: In Vitro And Clinical Experience

Urolithiasis is a common and increasing problem in daily urological practice. Urinary stones have affected mankind since time immemorial, It would be fascinating to know that the first evidence of urinary stones dates back to 4800 B.C., The majority of stones occur in the kidneys or ureters in human beings. calcium oxalate is the most common mineral occurring in stones in human beings, Treatment for urolithiasis in human beings includes lithotripsy (shattering stones into smaller fragments) or surgery. Shock wave lithotripsy is considered to be the reference treatment for most kinds of calculi. On the other hand, shock wave lithotripsy may not be the technique of choice, nor a cost-effective option when alternative medical treatment options are suitable and potentially harmful shock waves for the renal parenchyma can be avoided. Regarding UA-containing urinary stones,medical dissolution by urinary alkalization demonstrates the reference management technique before other treatment options are considered. These diferent therapy approaches are the driving force behind the efforts to determine the UA-component of urinary stones prior to treatment. Concerning non-UA-containing stones, the differentiation seems to be of a lower value because the knowledge of the major stone component does not allow for the adequate prediction of its fragility in lithotripsy treatment.Unenhanced computed tomography (CT) of the urinarytract is widely recognized as the most accurate technique for the detection of urinary stones, with a reported sensitivity of 95% to 100%.It is accompanied by the advantage of prompt availability of diagnosis and the identification of alternative diagnoses.Non-enhanced CT of the urinary tract is recognized as the most accurate technique for the detection of urinary stones..the Dual Source CT scanner is composed of two x-ray tubes and two detector units arranged on the rotating gantry with an angular off set of 90°.When running both tubes at the same voltage, a high temporal resolution is achieved that is used primarily for the evaluation of coronary arteries.When operating the x-ray tubes at different tube voltages, two different x-ray spectra are simultaneously obtained that improve the characterization and differentiation of various tissues. Advantages of CT are the high sensitivity and specificity of the diagnosis and the simultaneous recognition of other associated pathologies.The purpose of this study was to assess the potential of virtual unenhanced DSCT scans from dual-energy data for the detection of urinary stone disease. Although MDCT can identify patients who suffer from urinary stone disease, it cannot reproducibly predict stone composition. Dual Energy CT has the potential to differentiate urinary stone compositions. This could be of high clinical relevance for proper medical management, keeping in mind that urinary alkalinisation is the therapy of choice in patients with uric acid stones, and shock waves can be avoided that potentially may harm the renal parenchyma.We assessed the potential of dual-energy computed tomography (CT) for the differentiation between uric acid (UA)-containing and non-UA-containing urinary stones. Further prospective studies are warranted in order to prove the feasibility of the chemical decomposition in an in-vivo setting and to assess the clinical value of the new technology.Part I Dual-energy CT for the differential diagnosis of urinary calculi in vitroObjectives:We assessed the potential of dual-energy computed tomography (CT) for the diferentiation between uric acid (UA)-containing and non-UA-containing urinary stones;It is also expected to further distinguish between different types of non-uric acid stones. the reliability of Chemical composition analysis by Dual-energy CT analysis and its accuracy were evaluated.Materials and methods:1.89 stones collected during surgical and percutaneous nephrolithotomy lithotomy were included in this study. A Chemical Compositive analysis of the stones was performed after CT examination. All stones are a mixture of different crystal, a certain chemical components accounting for more than 50% is defined as a pure urinary stone.81 stones have been identified as pure stonea by chemical rough qualitative analysis,47 calcium oxalate, phosphate stones in 23 (including hydroxy-apatite, calcium hydrogen phosphate, and magnesium ammonium phosphate stone), cystine stones 7 and uric acid 4,8 mixed urinary calculi.2. All stones were examined in an ex vivo work bench model placed on the dual-source CT scanner table. Stones were embedded in random order in Swine kidney was purchased from the market early morning. After scanning, the stones were sent to the laboratory for chemical analysis.3. The examinations of the model were performed on a dual-source CT scanner (Deffnition, Siemens Medical Solutions, Germany) in the dual-energy mode. After positioning of conventional scanned, Conventional non-enhanced CT scan was executed, Scanning parameters:120kv/130mAs, slice collimation 0.6 mm and pitch 0.60. next, enter the dual-energy CT scan mode, The tube voltages were set at 80 and 140 kV, and the tube current time products at 404 and 95 mAs/rotation. Slice thickness and pitch the same as with conventional CT scanning that has been completed;Scan data will be transmitted to the workstation.4. The images from the 140/80kv scan were reconstructed on the regular image reconstruction system of the CT scanner.Additional reconstructions from the raw spiral projection data of both tubes were performed on an external prototype workstation (Multi Modality Workplace, Syngo multimodality AG2008 Software, Siemens). The dual-energy data reconstruction was per-formed with a speciffcally designed soft tissue convolution kernel (D30f) in order to avoid changes of voxel informa-tion at objects'edges. CT value of each urinary calculi at different scanning conditions were measured.5. urinary calculi were analysised byDual-energy CT-processing software(Siemens Medical Solutions, Forchheim, Germany). This software automati-cally calculates differences of attenuation between the 80 and 140 kV data sets and displays the results in a colour-coded fashion on fused multi-planar reformations. But also, the software displays calcified structures like cortical bone and calcified stones in blue, and UA stones in red color. Stone differentiation based on color coding only was then compared with differentiation byDEI.6. Statistical analysis:The data obtained earlier were analysised by using of SPSS statistical software, The results were expressed as absolute numbers, frequen-cies, and means±SDs. The non-parametric Wilcoxon Signed Rank Test was performed to evaluate signiffcant differences between the 80 and 140-kV series attenuation measurements, between scans, and between readers. Differences in attenuation at 80 and 140 kV were assessed using the t test between different types of urinary stones. A P level of<0.05 was con-sidered statistically signiffcant. The sensitivity, speciffcity, positive predictive value, and negative predictive value were calculated from Chi-Square tests of contingency. all statistical analysis was conducted using SPSS software.Results:1. All 89 stones were clearly visible at 80,120, and 140kVp and on the dual energy images scanned at 80 and 140 kVp.The CT values of urinary stones gradually decreased as the tube voltage increased except for Uric acid stones. uric acid stones and non-uric acid stones can be distinguished by Non-enhanced CT scanning. the difference of CT values in calcium oxalate and calcium phosphate is no significant statistical difference. there is no overlap between the dual energy indices of UA and other types of calculi, and there is very little overlap between mixed UA and calcified stones.2. the major advantage of DECT scanning for evaluation of urinary calculi is that the UA,cystine, struvite, and calcifications, which are the most clinically important components of renal calculi, can be differentiated by DEI, The information from the dual energy scan, namely the DEI, is needed to reliably differentiate between different stone materials.Conclusion:With dual energy CT techniques,the UA,cystine,struvite, and mixed renal calculi can be differentiated from other types of stones ex vitro. Our study has confirmed that a differentiation of renal calculi is feasible in vitro and in vivo and can be combined in DECT with stone detection in a single fast acquisition. DECT is an accurate, noninvasive test in patients with suspected or known urinary calculi. As opposed to intravenous urography,it does not require an intravenous contrast agent injection. Previous studies had shown the feasibility of a differentiation of calculi in vitro and to some extent in vivo. The information from the dual energy scan, namely the DEI, is needed to reliably differentiate between different stone materials. According to our results, the major advantage of DECT scanning for evaluation of urinary calculi is that the UA,cystine, struvite, and calcifications, which are the most clinically important components of renal calculi, can be differentiated by DEI. the DEI is useful to reflect the spectral behavior of a substance in a single unit.In conclusion, DECT can provide a fast and noninvasive detection and differentiation of renal calculi. The DEI characterizes the dual energy behavior of substances and makes an immediate stone differentiation feasible.Stone differentiation is of importance for treatment planning and may render invasive stone removal dispensable in some patients.PartⅡClinical Imaging of Dual-energy CT for the urolithiasisObjectives:Ex-vivo studies have demonstrated that Dual Source, Dual Energy CT has the potential to differentiate urinary stone compositions. the purpose of this study is to explore the clinical value of the dual-energy CT in the differential diagnosis of urinary calculi.Materials and methods:1.53 patients suspected of urinary tract stone disease were included in this study, Patients receiving enhanced scan must have the following conditions:non-iodine contrast agent allergy history, no serious heart, lung, renal insufficiency; non-maternity; In addition, all patients had signed informed consent agreement.2. the patients included in the study were referred to perform abdom inal CT scan. Conventional (VNCT), portal phase enhanced scanning were performed with dual-energy mode (80kV/400mA and 140kV/96mA). The dedicated software of L iver VNC was used to reformat virtual nonen-hanced CT at the arterial and portal phase.Image quality, the average CT value, image quality, signal to noise ratio, and lesion detectability were compared by the SPPS statistical software. the data obtained from dual-energy stone analysis and chemical analysis were compared.Results:1. the Stone detection was no statistical difference between the general non-enhanced scanning and Dual-energy scanning, all urinary stones were detected.2. The average CT value of the kidney measured was no statistical difference between the general non-enhanced scanning and Dual-energy CT fusion images; Statistically significant difference among conventional nonenhanced CT and virtual nonenhanced CT at the portal phase (P<0.05).CT value of VNC was significantly lower than that of general CT scan.SNR of VNCT was much higher than that of conventional nonenhanced CT (P=0.00). Image quality of the VNCT was decreased compared with conventional nonenhanced CT (P=0. 00<0.05), but it had at least moderate image quality to meet imaging diagnosis.3. Dual-energy stone analysis:128 urinary stones were found from the inspection of the 53 patients; 13 stone samples were taken to surgery, all the stones through a chemical analysis, Statistical analysis was not carried out due to a small number of samples.of which calcium oxalate stones in 7, phosphate stones 5, cystine stones 1; In which two phosphate stones were mistaken for calcium oxalate stone by CT dual-energy analysis, the rest of the results coincide completely with the chemical analysis. Conclusion1. the stone detection rate of dual-energy CT scan is basically the same as the conventional CT scan, Dual-energy CT analysis is a reliable means of imaging for urolithiasis.2. CT value of VNC was significantly lower than that of general CT scan, in addition, Its image quality decreased significantly Just to meet the needs of clinical diagnosis; therefore, VNC can not entirely replace the non-enhanced scanning to minimize radiation exposure, VNC can help radiologists identify urinary stones from iodine contrast agent residue.3. Dual-energy chemical composition of urinary stones was a reliability technologies, but its accuracy needs to be improved..SummaryDECT is an accurate, noninvasive test in patients with suspected or known urinary calculi, our results show that identification of UA components in uroliths is feasible. We did not experience any mischaracterization of stones containing UA, Therefore, we have ample reason to believe that the reliability of dual-energy analysis techniques is 100% to different uric acid stones from non-uric acid stones. As opposed to intravenous urography,it does not require an intravenous contrast agent injection. With dual energy CT techniques, the UA, cystine,struvite, and mixed renal calculi can be differentiated from other types of stones in vitro and in vivo. This is of clinical relevance as UA uroliths may be treated pharmacologically rather than with surgical extraction or extracorporal shockwave lithotripsy. VNC is the useful technology to help radiologists identify urinary stones from iodine contrast agent. VNC can not entirely replace the non-enhanced scanning to minimize radiation exposure owing to its poor image quality and unreliable CT value.There are some limitations to our study that have to be acknowledged. One is the small sample sizes of stones in the in vitro experiments and the limited number of patients. Further studies with external validation encompassing more patients will be required to eventually establish stone differentiation in DECT as a valid method.