| Background and objectiveUrinary stone is a common health problem in China. It may be caused by environment, inherit, diet, drug, metabolic disorder or urinary tract deformity. Recently, the incidence rate of urinary stone is inclined to rise. The unrelieved urinary stone and susceptibility factors in urinary tract not only often leads to urinary tract infection or obstruction, but also can leads to renal failure. A rapid diagnosis and proper treatment are needed to be established to the urinary stone. When urinary stone is large, it can be detected easily. However, in clinical practice, we encounter many equivocal cases in which it is difficult to determine whether a urinary stone is present or not because it is small or not has atypical clinical symptoms. Conventional radiography, including both Kidney, Ureter, Bladder(KUB)with tomograms and intravenous pyelography(IVP)evaluation, they have the advantages of showing the stones located at any level in the urinary system, and giving physiological information on the degree of obstruction. However, they may not show some small urinary stones because of their low attenuation value or bowel superimposition. Non-contrast enhanced helical computed tomography(CT)has a high accuracy and reliability in detecting urinary calculi. Currently, CT is the preferred modality for evaluating patients with urinary stone, but it is high radiation exposure dose and cost. Ultrasonography is a safe, rapid, inexpensive and repeatable technique. However, when a renal stone is poorly distinguished from echogenic renal sinus fat or has faint or absent posterior acoustic shadowing, especially small stones, it is difficult to determine its presence on sonography. The twinkling artifact is a color Doppler artifact, which is produced at or behind the surfaces of rough, strongly reflecting objects. Recent in vitro and in vivo studies have shed some light toward understanding the twinkling artifact in association with urinary stone. In our study, with CT as a reference standard, our purpose was to study the twinkling artifact and acoustic shadowing of renal stones on Doppler sonography, and to evaluate the clinical significance of twinkling artifact in the diagnosis of renal stones.Materials and methods1. Patients dataBetween January and October 2009, A prospective study was performed in 71 patients with 118 renal stones,39 male and 32 female, ranged in age from 16 to 72 years(mean 44.2). The renal stones were confirmed with CT at the radiology department of the Qilu Hospital of Shandong University. The height and weight of each patient was recorded, and body mass index (BMI) was calculated(mean height 1.66m; mean weight 65.9kg). Subjects were grouped as normal, overweight, obesity based on BMI values.2. CT scanningAll CT scans were performed with GE LightSpeedl6,5 millimeter slices with 0.5 pitch(120kV,230mA)were obtained, The scan range was from liver dome to the level of symphysis pubis. Images were reconstructed at 1.25mm intervals when necessary. The size, number and location of the stones were all the evaluated by 2 experienced radiologists, the diagnosis was made by consensus. Renal stones were classified into groups of smaller than 5 mm,5～10 mm and greater than 10 mm by measuring the longest axis of the stones. On CT, all high-density foci in the renal pelvis or calices were diagnosed as stones.3. Ultrasound scanning All sonographic examinations were performed using the Phillips IU22 ultrasonography system with 3.5MHz color Doppler transducer. The size, echo difference between stone and adjacent tissue, and posterior acoustic shadowing of renal stones were analyzed. After gray-scale images of the stones were obtained, examinations were used for color sonography and pulsed Doppler sonography for spectral analysis. In all cases, the values of Doppler gain, velocity range, color filters, focal depth, and depth of the field were varied during color scanning to evaluate the presence or the pattern of the twinking artifact.4. Statistical analysisAll the data were evaluated using SPSS 16.0 software. A signifcant difference was considered when the P value was less than 0.05.Results1. On gray-scale sonography 59 of 118 renal stones had obvious posterior shadowing,24 renal stones had faint posterior shadowing,35 renal stones had no shadowing.2. On color Doppler sonographyThe twinkling artifact was generated from 103 of 118 stones,15 renal stones did not have these Doppler artifact. On power Doppler sonography, spectra with noise and saturated amplitude were obtained from all 103 stones with the color Doppler twinkling artifact. The spectrum was composed of close vertical bands without a definable waveform.3.The detection rate of twinking artifact was much higher than that of acoustic shadowing in all groups. When echogenic foci with obvious acoustic shadowing and with twinkling artifact that were seen in the renal pelvis or calices on sonography were used for the diagnosis of renal stones, the sensitivity in groups of smaller than 5 mm and 5～10 mm increased from 24.5% to 87.8% and from 56.1% to 82.9%, respectively. There was distinctly significant between the two groups (P＜0.01), while there was no distinctly significant in the greater than 10 mm group(P>0.05).4. No relationship between the twinkling artifact and BMI was found (P＞0.05). 5. The stone size that meaured by CT and Ultrasound were compared, it is showed that they had good concordance(P>0.05).Conclusions The detection rate of twinking artifact was much higher than that of acoustic shadowing in all groups. The twinkling artifact is not influenced by stone size and BMI. It is useful in the diagnosis of renal stones, especially small or residual stones with faint or absent posterior acoustic shadowing. |
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