Differentiation Of Urinary Stone Compositions By Color Doppler Twinkling Artifact:an Experimental Study

Objectives1. To quantitatively analyze the effect of urinary stone composition on the color Doppler twinkling artifact (TA) by using artificial urinary stones.2. To evaluate the ability of color Doppler TA to differentiate urinary stone compositions.Materials and methodsPreparation of artificial stonesFour kinds of pure chemical materials including calcium oxalate monohydrate (COM), hydroxyapatite, cystine, and uric acid and egg white were used to manufacture artificial stones in this study. A single-punch tablet press (Shandong medical instrument factory, Zibo, China) with tablet diameter of8.5mm and thickness of5.0mm was used to create artificial stones.Phantom constructionOne hundred gram gelatin powder (Sinopharm Chemical Reagent Co., Ltd, Jinan, China) was mixed with1000mL water to form a uniform solution by a S81-2magnetic stirrer (Shanghai Sile Instrument Co., Ltd, Shanghai, China). This matrix was poured into a rectangular plastic food container measured (25cm×15cm×10cm) to form a bottom layer at least3cm thick. It was then cooled in a refrigerator until becoming firm. This echogenic gelatin matrix layer prevented strong reflection of plastic bottom that may influence the quality of sonogram. A pig kidney obtained from a local meat market was placed on the surface of the bottom layer of gelatin matrix. A linear slice was made through the cortex of the kidney and extended to the depth of the sinus. The artificial stone was inserted into the pig kidney within or adjacent to the sinus to simulate the in vivo situation, one at a time. Preparation of the kidneys, insertions of the stones, subsequent scans and data analysis of these kidneys were identical to what was operated in the first pig kidney.Ultrasound ScanningAll scans were performed on a Philips iU22ultrasound scanner (Philips Medical Systems, Bothel, WA, USA) using an L12-5linear array probe. The probe was mounted on a ring stand during scanning to prevent motion and to keep a fixed distance between the surface of the probe and the stones. Ten grey images of each stone were saved for further analysis. Machine parameters were set as the most suitable for showing of TA. Once the point of maximum twinkling was detected, a cine loop of TA was acquired and saved. The length and width of TA (TAL, TAW) were measured and recorded.Image processingPhotoshop CS5and Image J (http://rsb.info.nih.gov/ij/) were used to calculate the number of TA color pixels representing twinkling artifact intensity (TAI) and the top ten of each cine loop were chose for statistical analysis.Statistical analysis Single factor analysis of variance (ANOVA) was performed on all data to determine if there were significant differences among four kinds of stone compositions. Students-Newman-Keuls (SNK-q) test was conducted to decide if there was significant difference between any two kinds of stone compositions. The relationships between the TAW and TAI, TAL and TAI were assessed by linear correlation and regression. The receiver operating characteristic (ROC) curve was used to evaluate the diagnostic ability of TAI, TAL and TAW. Numerical variable was reported as the mean value and standard deviation (SD). Statistical analyses were performed with the SPSS19.0software package (SPSS Inc, Chicago, IL) and medcalc11.4software (MedCalc Software bvba, Ostend, Belgium). A P value<0.05was considered as having statistical significance.Results1. TAI, TAL and TAW were significantly correlated with stone diameter (r=0.976,0.940,0.974respectively, P<0.05) for all four types of stone phantoms. The ANOVAs for the differences of TAI, TAL and TAW among four chemical compositions were highly significant (FTAI=80.310, FTAI=55.608, FTAW=67.451, P <0.01).2. TAI could be helpful in differentiating calcium oxalate monohydrate (COM) stone, hydroxyapatite, cystine stone and uric acid stone. Uric acid stone showed the strongest twinkling artifact, followed by cystine stone and hydroxyapatite stone, and the twinkling artifact of COM stone was the weakest. The ROC curve displayed that the area under the curve (AUC) of TAI on diagnosing COM stone and uric acid stone were bigger than the others. TAL and TAW were independent factors of TAI. Conclusions1. Urinary stone composition was an influence factor for color Doppler TA. There were significant differences of TAI, TAL and TAW among these four kinds of stones.2. Color Doppler TA was helpful in urinary stone analysis in vitro, especially in distinguishing COM stone and uric acid stone from the others. Both TAL and TAW were fine predictive factors for TAI.