color doppler twinkling artifacts in various conditions...

Color Doppler Twinkling Artifacts inVarious Conditions During Abdominaland Pelvic Sonography

Hyun Cheol Kim, MD, Dal Mo Yang, MD, Wook Jin, MD,Jung Kyu Ryu, MD, Hyeong Cheol Shin, MD

Objective. The aims of this study were to describe the mechanisms likely to be responsible for colorDoppler twinkling artifacts and their associated machine factors and to illustrate the various conditionsthat cause twinkling artifacts and those pitfalls. Methods. We evaluated various sonographic machine-associated factors that influence artifact appearance and identified various conditions that display twin-kling artifacts during abdominal and pelvic sonography. Results. The presence of twinkling artifacts wasfound to be dependent on focal zones, gray scale gains, color write priorities, and pulse repetition fre-quencies. Twinkling artifacts were found to be associated with calcified lesions in the liver, gallbladderadenomyomatosis, hepatic bile duct hamartoma, gallstones and choledocholithiasis, chronic pancreatitis,urinary stones, encrusted indwelling urinary stents, bowel gas, and metallic foreign bodies. However,some of the twinkling artifacts were found to be associated with false-negative and -positive results.Conclusions. Color Doppler twinkling artifacts are additional useful sonographic signs in the diagnosisof calcified lesions, urinary and biliary stones, gallbladder adenomyomatosis, and some miscellaneousconditions. Key words: abdomen; color Doppler sonography; pelvis; sonography; twinkling artifact.

Received September 13, 2009, from the Departmentof Radiology, East-West Neo Medical Center, Collegeof Medicine, Kyung Hee University, Seoul, Korea(H.C.K., D.M.Y., W.J., J.K.R.); and Department ofDiagnostic Radiology, Soonchunhyang University,Cheonan Hospital, Chungcheongnam-do, Korea(H.C.S.). Revision requested October 21, 2009.Revised manuscript accepted for publicationNovember 4, 2009.

Address correspondence to Hyun Cheol Kim, MD,Department of Radiology, East-West Neo MedicalCenter, Kyung Hee University, 149 Sangil-dong,Gangdong-gu, Seoul 134-727, Korea.

e-mail: [email protected]

AbbreviationsCT, computed tomography

olor Doppler sonography is commonly usedto assess tissue vascularity rapidly.1 However,any tissue or fluid motion can generate aDoppler signal; thus, a variety of artifacts can

be produced. Among these artifacts, color Doppler twin-kling artifacts are regarded as useful diagnostic signs.2

These artifacts appear as rapidly alternating red and bluesignals behind certain highly reflective structures (Figure1A) and may mimic flow.3 Spectral Doppler analysisproduces a fine heterogeneous broadband signal withouta discernable spectrum (Figure 1B).3 Twinkling artifactshave been mainly reported in association with urinarycalculi,4,5 but they have also been encountered duringabdominal and pelvic sonography in association withcalcifications in various tissues, biliary stones, encrustedindwelling urinary stents, gallbladder adenomyomatosis,and bile duct hamartomas.6–11 Although twinkling arti-facts do not occur in every case with the above-mentionedconditions, their visualization can improve diagnosticconfidence and facilitate lesion detection.

© 2010 by the American Institute of Ultrasound in Medicine • J Ultrasound Med 2010; 29:621–632 • 0278-4297/10/$3.50

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In this study, we describe the possible mecha-nisms responsible for twinkling artifacts and thevarious sonographic machine factors that influ-ence their appearances. On the basis of ourexperiences with the clinical use of twinklingartifacts during abdominal and pelvic sonogra-phy, we present various conditions that causetwinkling artifacts and some of the correlationsbetween twinkling artifacts and the findings ofother imaging modalities, such as simple radio-graphy, computed tomography (CT), and mag-netic resonance imaging. The pitfalls of using atwinkling artifact as a diagnostic sign are alsodiscussed.

Mechanisms

Two hypotheses have been proposed to explaintwinkling artifacts. The first was offered byRahmouni et al,3 who suggested that a twinklingartifact is an artifact generated by a stronglyreflecting medium with a rough interface. Whenan incidental ultrasound beam is reflected by aflat interface, the acoustic waves are reflected bythe interface at the same time, which results inthe production of short-wave sound signals.However, when a beam impinges on a roughinterface composed of individual reflectors, theacoustic wave is split into a complex beam pat-tern caused by multiple reflections in the medi-

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Color Doppler Twinkling Artifacts on Abdominal and Pelvic Sonography

Figure 1. Appearance of color Doppler twinkling artifacts. A, Color Doppler sonogram showing a rapidly changing mix of red andblue behind a stone in the lower pole of the left kidney. B, Spectral Doppler sonogram showing a broadband signal without a dis-cernable spectrum.

A B

Figure 2. Effect of focal zone on twinkling artifacts. A, Color Doppler sonogram showing prominent twinkling artifacts from the bal-loon of a Foley catheter when the focal zone (oval) was located below the balloon. B, When the focal zone (oval) was located abovethe balloon, the twinkling artifacts weakened.

A B


um, accounting for the prolonged pulse durationof the transmitted sound signal. This is interpret-ed by Doppler units as movement and thus isassigned different colors. The second hypothesiswas offered by Kamaya et al,12 who proposed thata twinkling artifact is caused by a narrow band ofintrinsic sonographic machine noise, referred toas “phase jitter,” which is probably generated byslight random time fluctuations in the pathlengths of transmitted and reflected acousticwaves. It was proposed that at a strong reflectorwith a rough interface, these slight time fluctua-tions are amplified to produce apparent aliasedDoppler shifts.

Machine Parameters and TwinklingArtifacts

The detection of twinkling artifacts is highlydependent on machine settings.4,12 Lee et al,4

reported that the location of a focal zone caninfluence the occurrences and intensities oftwinkling artifacts. When a focal zone is locatedbelow a rough reflecting surface, the twinklingartifact becomes more obvious (Figure 2A).However, when a focal zone is located abovesuch a surface, the twinkling artifact is weakened(Figure 2B). The appearance of a color Dopplersignal is affected by several machine settings,such as color write priority, gray scale gain, and

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Figure 3. Effect of color write priority on twinkling artifacts. A, Color Doppler sonogram at the upper level of the color write priori-ty (oval) showing a prominent twinkling artifact from gallbladder adenomyomatosis. B, However, when the color write priority (oval)was reduced, the twinkling artifact disappeared.

A B

Figure 4. Effect of gray scale gain on twinkling artifacts. A, Color Doppler sonogram showing prominent twinkling artifacts from theballoon of a Foley catheter at a gray scale receiver gain of 49% (oval). B, When the gray scale receiver gain was increased to 75%(oval), the twinkling artifacts were substantially weakened.

A B


pulse repetition frequency.12 Color write prioritydecides whether a pixel should be depicted ascolor or as gray scale, and increasing the colorwrite priority causes more color information to bedisplayed and thus twinkling artifact enhance-ment (Figure 3). Similarly, but conversely, increas-ing the gray scale gain reduces the amount ofcolor in an image (Figure 4). Therefore, a twin-kling artifact usually increases on increasing thecolor write priority and reduces when the grayscale gain is increased. However, this rationaledoes not hold in all situations. With regard to thepulse repetition frequency, a reduction mayincrease the twinkling artifact intensity and pro-duce a strong broadband signal (Figure 5).

However, in particularly strong areas of a twin-kling artifact, spectral broadening is present at allpulse repetition frequencies.

Conditions That Display TwinklingArtifacts

Calcified Lesions in the LiverHepatic calcifications may be encountered ininflammatory lesions and in benign and malig-nant tumors. Inflammatory conditions such asgranulomatous diseases (eg, tuberculosis andhistoplasmosis) are the most common causes ofcalcified hepatic lesions.13 Most of these calcifica-tions are small and have a rough surface; thus,twinkling artifacts are observed because of reflec-tions from the surfaces of calcifications (Figure 6).The recognition of the association between hep-atic lesions and twinkling artifacts is importantbecause the presence of color might be erro-neously interpreted as real blood flow and mightlead to suspicions of a hypervascular mass.7

Gallbladder AdenomyomatosisGallbladder adenomyomatosis is characterizedby benign hyperplasia of the gallbladder mucosawith thickening of the muscular layer,14 and itssonographic appearance is focal or diffusethickening of the gallbladder wall. Intramuralechogenic foci cause V-shaped reverberation arti-facts and are highly specific for adenomyomato-sis; in fact, they represent the acoustic signatureof cholesterol crystals within Rokitansky-Aschoff

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Figure 5. Effect of pulse repetition frequency on twinkling artifacts. A, Color Doppler sonogram showing twinkling artifacts from theballoon of a Foley catheter at a pulse repetition frequency of 1100 Hz (oval). B, When the pulse repetition frequency was increasedto 5500 Hz (oval), the twinkling artifacts reduced slightly.

A B

Figure 6. Hepatic parenchymal calcifications in a 54-year-oldwoman. The gray scale sonogram (left) shows echogenic cal-cifications (arrows) in the liver. The corresponding colorDoppler sonogram (right) shows twinkling artifacts behind thecalcifications.


sinuses.14 Some echogenic intramural foci arecomposed of calcifications or cholesterol deposi-tions with rough interfaces, and these are likelyto cause twinkling artifacts.10 A twinkling artifactmay facilitate the detection of adenomyomatosisin the gallbladder fundus, which is affected byreverberation artifacts arising from the subcuta-neous layer (Figure 7). In addition, the presenceof a twinkling artifact can also provide an impor-tant diagnostic clue that allows the differentia-tion of gallbladder adenomyomatosis andgallbladder cancer (Figure 8).

Hepatic Bile Duct HamartomasBile duct hamartomas of the liver are composedof cystic dilatation of the bile duct accompaniedby variable amounts of collageneous stroma.15

Sonographically, these hamartomas have aninhomogeneous coarse echo texture resemblingcirrhosis, multiple small hyperechoic or hypo -echoic nodules, or multiple bright spotty echoeswith comet tail artifacts.11 Bile duct hamartomasare clinically important because they can mimiccirrhosis or metastasis on imaging studies.16

Twinkling artifacts can also be produced by bileduct hamartomas due to multiple reverberations

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Figure 7. Gallbladder adenomyomatosis in a 50-year-old man with accompanying gallbladder stones. A, Color Doppler sonogram(right) showing a twinkling artifact from the wall of the gallbladder fundus. The V-shaped reverberation artifact was indefinite on thegray scale sonogram (left). B, Contrast-enhanced axial oblique CT showing focal wall thickening with enhancement (arrow) in thegallbladder fundus. This patient underwent an operation for accompanying gallbladder stones. The fundus lesion was later confirmedas adenomyomatosis.

A B

Figure 8. Gallbladder adenomyomatosis in a 43-year-old man. A, Contrast-enhanced axial CT showing stones with surrounding gall-bladder wall thickening (arrows), suggestive of gallbladder cancer. B, Subsequently obtained color Doppler sonogram showing a twin-kling artifact from gallbladder wall thickening. This patient was confirmed to have adenomyomatosis at surgery.

A B


from cholesterol crystals within cystic dilatationsof bile ducts (Figure 9) and are similar to thoseobserved in gallbladder adenomyomatosis.11

Cholelithiasis and CholedocholithiasisTwinkling artifacts are often observed in gall-stones but have little or no diagnostic impact inthis context because gallstones are readily diag-nosed by gray scale sonography.6 The productionof twinkling artifacts by gallstones is related tobiochemical composition. Most mixed stonesand about half of cholesterol stones producetwinkling artifacts, whereas most pigment stonesdo not (Figure 10).17 Thus, gallstone composi-

tions can be predicted on the basis of the pres-ence of twinkling artifacts, although this is of lit-tle use clinically. However, the identification ofcommon bile duct stones is challenging becausethey are sometimes obscured by bowel gas dur-ing gray scale sonography; thus, the presence of atwinkling artifact sometimes provides a usefulmeans of detection (Figure 11).

Chronic PancreatitisChronic pancreatitis is often associated withpunctate calcifications in parenchyma, whichcan be subtle on gray scale sonography whenthey are small and posterior acoustic shadowing

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Figure 9. Bile duct hamartoma in a 58-year-old man. A, Gray scale sonogram (left) showing spotty echogenic foci (arrows) with sub-tle comet tail artifacts. The corresponding color Doppler sonogram (right) shows twinkling artifacts behind the echogenic foci. B, Contrast-enhanced axial CT showing numerous tiny hypoattenuating lesions in the entire liver, suggestive of bile duct hamartoma.No biopsy was conducted in this case.

A B

Figure 10. Twinkling artifact and gallbladder stone composition. A, Gray scale sonogram (left) showing an echogenic stone (arrow)with posterior acoustic shadowing in the gallbladder. The corresponding color Doppler sonogram (right) shows a twinkling artifactbehind the stone. The stone was confirmed as a cholesterol stone after surgery. B, An echogenic stone in the gallbladder did not pro-duce a twinkling artifact on the color Doppler sonogram. This stone was found to be a pigmented stone after surgery.

A B

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is absent. However, they can become obvious inthe color Doppler mode because of the presenceof twinkling artifacts8; thus, twinkling artifactscan help establish a diagnosis of chronic pancre-atitis (Figure 12).

Urinary StonesThe detection of renal stones by sonography canbe problematic when they are obscured by indis-tinct echogenicity caused by renal sinus fat orwhen their posterior acoustic shadowing is indis-crete. However, 80% of renal stones exhibit twin-kling artifacts, and in most cases these artifactsare easily detected (Figure 13).4 Furthermore, in

cases of hydronephrosis and hydroureter causedby ureteral stones, it is sometimes difficult todetect stones by gray scale imaging because ofthe obscuring effects of bowel gas. However, atwinkling artifact facilitates stone detection, andits presence strongly supports a diagnosis of aureteral stone (Figure 14).18 Therefore, a twin-kling artifact can be considered a major diagnos-tic sonographic finding in this context. Chelfouhet al,5 reported that stone composition has amajor influence on twinkling artifacts. For exam-ple, stones composed of calcium oxalate dehy-drate or calcium phosphate produce twinklingartifacts, whereas most of those composed pre-

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Figure 11. Common bile duct stone in a 39-year-old woman. A, Gray scale sonogram (left) obtained in a sagittal scan showing anechogenic stone (arrow) with posterior acoustic shadowing in the common bile duct. The corresponding color Doppler sonogram(right) shows a prominent twinkling artifact behind the stone. B, Contrast-enhanced coronal CT showing a hyperattenuating stone(arrow) in the distal common bile duct.

A B

Figure 12. Chronic pancreatitis in a 70-year-old man. A, Gray scale sonogram (left) showing increased echogenicity with uncertainposterior acoustic shadowing in the pancreas body and tail. The corresponding color Doppler sonogram (right) shows prominent twin-kling artifacts in the regions of increased echogenicity. B, Nonenhanced axial CT showing multiple tiny parenchymal calcificationsinvolving the whole pancreas, suggestive of chronic pancreatitis.

A B


dominantly of calcium oxalate monohydrate orurate do not.

Bowel GasIntraluminal echogenic gas in the bowel can alsobe recognized by a twinkling artifact (Figure 15),which might be due to the rough surfaces of bowelcontents. However, a twinkling artifact caused bythe bowel lumen can obscure an artifact from alesion of the gallbladder or urinary system.

Encrusted Indwelling Urinary StentsIndwelling urinary stents are widely used torelieve urinary obstructions, but encrustation of

a stent tip can obstruct the urinary system.Encrustation rates vary and depend on the bio-chemical composition of urine and on stentmaterials. The calcium phosphate or calciumoxalate deposits responsible for these encrusta-tions cause stent surfaces to become irregular orcrystalline and produce twinkling artifacts(Figure 16).9 Thus, the presence of a twinklingartifact enables encrustation to be identified.

Metallic Foreign BodiesTwinkling artifacts can also aid the identificationof needle tracts during sonographically guidedbiopsies,6 probably because entrapped air and

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Figure 13. Right renal stone in a 51-year-old woman with a co-occurring proximal ureteral stone. A, Gray scale sonogram (left) show-ing no echogenic focus or posterior acoustic shadowing. The corresponding color Doppler sonogram (right) shows a prominent twin-kling artifact in the lower pole of the right kidney. B, Conventional abdominal radiograph showing a stone (arrow) in the lower poleof the right kidney and a proximal ureteral stone (arrowhead).

A B

Figure 14. Left mid ureter stone in a 49-year-old man. A, Gray scale sonogram (left) showing the echogenic focus (arrow) with uncer-tain posterior acoustic shadowing in the left mid ureter. The corresponding color Doppler sonogram (right) shows a prominent twin-kling artifact behind the echogenic focus, strongly indicative of a ureteral stone. B, Nonenhanced axial CT showing a stone (arrow) atthe left midureteral level.

A B


the metallic needle along the biopsy tract cause arough interface (Figure 17). Twinkling artifactscan also be helpful for identifying metallic for-eign bodies with rough rusty surfaces (Figure 18).

Pitfalls of Using Twinkling Artifacts asDiagnostic Signs

Although twinkling artifacts are frequentlyobserved behind calcifications with a rough sur-face, some calcifications do not produce artifacts.We have found that cases of gallbladder adeno-myomatosis of the fundal type or cases withoutcholesterol crystal deposition do not producetwinkling artifacts (Figure 19). Furthermore,although bowel gas frequently produces twin-kling artifacts, biliary air does not (Figure 20).

During kidney sonography, echogenic foci withtwinkling artifacts do not always suggest stones. Infact, calcifications of the renal artery, renal tumor,renal cyst, and renal parenchyma may producetwinkling artifacts.6 These can usually be differen-tiated from renal stones because they tend to pul-sate and because of their locations and patienthistory. A renal arteriovenous fistula is a well-known complication of renal biopsies andappears as an abnormally high velocity with local-ized turbulent flow on color Doppler images.19

This turbulent flow produces perivascular vibra-tions, which result in combined red and blue sig-nals that resemble twinkling artifacts (Figure 21).However, an arteriovenous fistula usually can bedifferentiated from a twinkling artifact by Dopplerspectra and by a history of renal biopsy.

Conclusions

Color Doppler twinkling artifacts are additionalsonographic signs that can be useful during thediagnoses of calcified lesions, urinary and biliarystones, gallbladder adenomyomatosis, and othermiscellaneous conditions. Our experiences indi-cate that the recognition of twinkling artifactsduring abdominal and pelvic sonography canimprove diagnostic confidence for a consider-able number of clinical conditions.

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Figure 15. Prominent bowel gas in a 79-year-old man. A, Gray scale sonogram showing echogenic materials in the mid abdomen.B, Color Doppler sonogram showing prominent twinkling artifacts from echogenic materials.

A B

Figure 16. Encrusted indwelling urinary stent in the left proxi-mal ureter in a 53-year-old woman. The gray scale sonogram(left) shows an echogenic line (arrows) indicating the stent with-in the ureter. The corresponding color Doppler sonogram (right)shows twinkling artifacts from the echogenic stent.


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Figure 19. Gallbladder adenomyomatosis in a 39-year-old woman. A, Gray scale (left) and color Doppler (right) sonograms showingfocal wall thickening (arrows) of the gallbladder fundus without twinkling artifacts. B, Magnetic resonance cholangiography showinga grapelike cystic lesion (arrow) in the fundus of the gallbladder, suggestive of adenomyomatosis. This patient underwent surgery andwas confirmed to have adenomyomatosis.

A B

Figure 18. Small-bowel perforation due to the swallowing of a metallic needle in a 16-year-old boy. A, Gray scale sonogram (left)showing an echogenic line (arrows) indicating the metallic needle in the small-bowel loop. The color Doppler sonogram (right) showstwinkling artifacts from the echogenic line. B, Conventional abdominal radiograph (left) showing the needle in the left side of theabdominal cavity and the rusty needle retrieved during surgery (right).

A B

Figure 17. Liver biopsy in a 70-year-old woman with hepatitis. A, Gray scale sonogram showing an echogenic line (arrows) along themetallic needle tract in the liver. B, Color Doppler sonogram showing twinkling artifacts from the needle tract.

A B


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Figure 21. Arteriovenous fistula after renal biopsy in a 55-year-old woman. A, Gray scale sonogram (left) failing to visualize an abnor-mal lesion in the left kidney. On the other hand, the corresponding color Doppler sonogram (left) shows rapidly alternating red andblue signals in the lower pole of the left kidney, resembling a twinkling artifact. B, Spectral Doppler sonogram showing turbulent flowwith a decreased resistive index (0.47), suggestive of an arteriovenous fistula.

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