Dilatation of the collecting system is a classical phenomenon during pregnancy, due to hormonal and extrinsic compressive factors. Imaging has to differentiate a physiological dilatation and a pathological obstruction due to urolithiasis. Presently, sonography, using both, B-mode and color Doppler, has the potential to demonstrate the physiological compression of ureters at the level of the pelvic brim. A pathological obstruction is considered either when a stone is detected above the usual site of compression or when the ureter appears dilated beyond. Color Doppler helps in localizing the site of ureteral compression against the vessels and in differentiating ureters from veins. Magnetic resonance urography, with strongly T2-weighted sequences, also may show the site and type of obstruction without contrast agent administration. These two non-radiating techniques make it possible to avoid the use of X-rays in most cases for management of these patients. The type of treatment is based mostly on the level of pain and the presence or absence of stone.

Dilatation of the collecting system during pregnancy: physiologic vs obstructive dilatation.

The mechanism of the twinkling artifact (TA) that occurs during Doppler ultrasound imaging of kidney stones was investigated. The TA expresses itself in Doppler images as time-varying color. To define the TA quan- titatively, beam-forming and Doppler processing were performed on raw per channel radio-frequency data collected when imaging human kidney stones in vitro. Suppression of twinkling by an ensemble of computer- generated replicas of a single radio frequency signal demonstrated that the TA arises from variability among the acoustic signals and not from electronic signal capture or processing. This variability was found to be random, and its suppression by elevated static pressureand return when the pressurewas releasedsuggest that the presence of bubbles on the stone surface is the mechanism that gives rise to the TA. (E-mail: olegs@apl.washington. edu) Published by Elsevier Inc. on behalf of World Federation for Ultrasound in Medicine & Biology.

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Evidence for trapped surface bubbles as the cause for the twinkling artifact in ultrasound imaging.

To assess the ability of the color Doppler twinkling artifact to detect renal stones relative to acoustic shadowing, we scanned seven uric acid calculi embedded in a tissue mimicking phantom and in sheep kidneys using a high frequency linear array and a standard curved linear array ultrasound scanheads (L12-5 and C5-2; Philips Ultrasound, Bothel, WA, USA) The stones were scanned in and out of focus The scans were optimized for shadow formation in gray-scale imaging and for color twinkling in color Doppler imaging The images were analyzed using Image J (http://rsbinfonihgov/ij/) We calculated the contrast to noise ratios (C/N) for the acoustic shadows and the color twinkling artifact compared with background These measurements were then evaluated using a single factor analysis of variance (ANOVA) and paired two-tailed t tests With these comparisons, the C/Ns for twinkling were significantly higher than for acoustic shadowing On average, twinkling produced 192 dB greater C/Ns for stones in the phantom and 176 dB more for the stones in the kidneys In addition, ANOVA showed that twinkling is resistant to focusing and scanning frequency differences The results suggest that the twinkling artifact is a robust method for detecting the presence of renal calculi The color signature is easier to detect than is acoustic shadowing Twinkling may be relatively resistant to many of the problems that plague ultrasound examinations for renal stones, ie, out-of-focus scans that might be caused by beam aberration effects due to patient body habitus

Comparison Between Color Doppler Twinkling Artifact and Acoustic Shadowing for Renal Calculus Detection: An In Vitro Study

The aim of the study was to investigate the diagnostic value of the colour Doppler twinkling artefact (TA) in renal stone disease. To enhance the evidence of TA, a preliminary in vitro study was performed to optimise the setting of colour Doppler sonography. In the in vitro study, an oxen kidney was examined using an high-frequency (12.5 MHz) linear array probe in a water bath before and after the inoculation of an aliquot of powder obtained by fragmentation of a calcium oxalate stone. In the clinical study, 67 patients with diagnosis of urinary stone based on B-mode sonography and 67 matched control subjects were examined with colour Doppler sonography using a low-frequency (2.5 MHz) curvilinear phased array probe. In vitro, the injection of calcium oxalate powder in a bovine kidney sample induced the appearance of spots without any back shadowing appearance on B mode but with a large number of TA on colour Doppler. In vivo, TA was much more frequent in patients with stone disease (95.5%) compared to controls (9.0%) (P < 0.001). TA was highly associated to renal stone disease and was also present in renal areas where a stone was undetected with B mode approach suggesting its diagnostic role although further studies are needed to confirm its accuracy. The type of instrumentation and its setting is crucial to obtain reproducible results.

Diagnostic value of colour Doppler twinkling artefact in sites negative for stones on B mode renal sonography

Techniques of Ureteral Imaging Normal Ureter Ureteral Malformations Ureteral Obstruction Ureteral Lithiasis Ureteral Tumors Inflammatory Diseases of Ureter Miscellaneous Extrinsic Pathology of Ureter Interventional Radiology of Ureter Strategy for Ureteral Imaging Subject Index List of Contributors.

Clayman Rv

Papers

Characterization of urinary calculi: in vitro study of "twinkling artifact" revealed by color-flow sonography.