impaired upper urinary tract urine flow is often caused by ureter obstruction due to retro - peritoneal metastatic cancer .
obstruction generally begins with pain , then with loss of renal function due to long - lasting congestion , acute or chronic renal insufficiency and/or hydronephrosis of the infected kidneys and may end with generalized sepsis . indwelling ureter splints consisting of polyurethane , silicon , or other polymers
are placed to restore urine flow from the renal pelvis to the bladder but gradually become incrusted with crystalline deposits , which can ultimately result in renewed flow obstruction .
routinely , indwelling ureter splints are monitored sonographically or by x - ray to detect renewed urinary congestion due to stent obstruction by crystalline deposits . however
, early crystalline implant deposits can not be detected by x - ray , presumably due to low spatial resolution and radiolucency of the deposited material .
forgotten incrusted dj - stents have been described and continuous monitoring of implanted material and removal or exchange as early as possible is recommended . in vascular doppler sonography ,
the  glittering artifact (= twinkling artifact , ta ) appears as a color doppler signal at atheromatous plaque , calcified cardiac valves [ 2 , 3 ] , and also at other calcified body structures . here
, the doppler signal falsely indicates turbulent current , thus limiting the correct assessment of vascular circulation .
however , twinkling artifacts were employed in 2013 to detect early incrustation of a nephrostomy catheter by ta   and , with minor sonographic parameter modification in the color doppler mode , they can be used to detect minimal ureter splint incrustation .
ureter splints are particularly susceptible to crystalline deposits in patients with tumor lysis syndrome ( tls ) . during tls
the high filtration rate of uric acid exerts a severe burden on the kidneys and becomes a decisive factor contributing to impaired renal function that can culminate in renal failure .
clinically manifested tls is a life - threatening complication of tumor chemotherapy and results in a high dialysis rate .
one option of lowering uric acid is to inhibit xanthine oxidase with allopurinol , as far as the nephrotoxicity of allopurinol will allow , at which point the allopurinol dosage must be reduced .
another option is to employ rasburicase , a synthetic recombinant urate oxidase , transforming uric acid into the more water - soluble allantoin . in 2001
although treatment with rasburicase significantly reduces renal complications , including the necessity for dialysis , the high therapeutic cost of rasburicase limits preventive application prior to the occurrence of tls .
therefore , an easily applied , inexpensive technique to identify stent incrustation in time to prevent complications is important . the present study aimed to employ ta to detect early ureter splint incrustation in oncologic patients and to follow blood and urine parameters , which might correlate with ureter splint incrustation .
twenty - six oncologic patients with implanted dj stents ( dj - stent ; 7/28 dj , optimed , ettlingen , germany ) and receiving chemotherapy or combined radio / chemotherapy and at high risk for developing tumor lysis syndrome ( tls ) were included in the investigation . the patients were hospitalized due to routine change of their ureter splints or to change their ureter splints because of presenting complications such as flank pain .
sonographic examination employing twinkling artifacts took place the day after implantation and then at weekly intervals .
serum creatinine and uric acid as well as urine ph were also measured on the day of stent implantation and weekly thereafter .
patients with initially evident tls , increased blood levels of uric acid ( > 6 mg / dl ) or manifest symptoms of tls were excluded from the study .
removal of the newly implanted stent was not influenced by the detection of tas , but was initiated according to customary diagnostic procedure .
all procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 helsinki declaration and its later amendments or comparable ethical standards .
ultrasonography was carried out with an acuson sequoia 512 ultrasound system with the following transducers : 4v1 ( range 4/3/1.75 ) , 4c1 ( range 4/3/175 ) , 6c2 ( range 5/3.5/2.5 used for very slim patients ) ( siemens , mnchen , germany ) ( normal frequency on color doppler in mhz ) .
the following defined parameters and structured procedure ensured targeted , reproducible tas , which could be distinguished from signals stemming from blood flow .
depending on the transducer , the nominal frequency was selected at the lowest possible mhz level .
a high pulse repetition frequency ( prf , cm / sec ) was selected on the velocity scale .
transmitting focus on a particular site is essential at highest acoustic energy and post - processing with color variance ( cdvv ) must be turned on to distinguish ta arising from blood vessels .
these parameters were not only employed for implanted stents in patients , but also in a water bath for new , unused dj - stents and stents after removal from the urinary tract .
infrared spectroscopy ( ft / ir 4100 , jasco , gro - umstadt , germany ) was used to analyze the incrustation material scratched from ureter splints after explantation .
the command variable ( time for twinkling artifacts to appear after implantation , revealing incrustation ) and cause variables ( sex , age , ph of urine , uric acid and creatinine ) were correlated by spearman correlation and nonparametric biserial correlation ( sex ) .
since three censored data existed ( time to appearance of incrustation > 12 weeks after implantation ) the significance of the five cause variables was calculated by cox - regression including backward elimination ( wald - statistics ) .
twenty - six oncologic patients with implanted dj stents ( dj - stent ; 7/28 dj , optimed , ettlingen , germany ) and receiving chemotherapy or combined radio / chemotherapy and at high risk for developing tumor lysis syndrome ( tls ) were included in the investigation . the patients were hospitalized due to routine change of their ureter splints or to change their ureter splints because of presenting complications such as flank pain .
sonographic examination employing twinkling artifacts took place the day after implantation and then at weekly intervals .
serum creatinine and uric acid as well as urine ph were also measured on the day of stent implantation and weekly thereafter .
patients with initially evident tls , increased blood levels of uric acid ( > 6 mg / dl ) or manifest symptoms of tls were excluded from the study .
removal of the newly implanted stent was not influenced by the detection of tas , but was initiated according to customary diagnostic procedure .
all procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 helsinki declaration and its later amendments or comparable ethical standards .
ultrasonography was carried out with an acuson sequoia 512 ultrasound system with the following transducers : 4v1 ( range 4/3/1.75 ) , 4c1 ( range 4/3/175 ) , 6c2 ( range 5/3.5/2.5 used for very slim patients ) ( siemens , mnchen , germany ) ( normal frequency on color doppler in mhz ) .
the following defined parameters and structured procedure ensured targeted , reproducible tas , which could be distinguished from signals stemming from blood flow .
depending on the transducer , the nominal frequency was selected at the lowest possible mhz level . a high pulse repetition frequency ( prf , cm / sec ) was selected on the velocity scale .
transmitting focus on a particular site is essential at highest acoustic energy and post - processing with color variance ( cdvv ) must be turned on to distinguish ta arising from blood vessels .
these parameters were not only employed for implanted stents in patients , but also in a water bath for new , unused dj - stents and stents after removal from the urinary tract .
infrared spectroscopy ( ft / ir 4100 , jasco , gro - umstadt , germany ) was used to analyze the incrustation material scratched from ureter splints after explantation .
the command variable ( time for twinkling artifacts to appear after implantation , revealing incrustation ) and cause variables ( sex , age , ph of urine , uric acid and creatinine ) were correlated by spearman correlation and nonparametric biserial correlation ( sex ) .
since three censored data existed ( time to appearance of incrustation > 12 weeks after implantation ) the significance of the five cause variables was calculated by cox - regression including backward elimination ( wald - statistics ) .
no twinkling artifacts were detected in new , unused dj - stents investigated in a water bath .
after incrusted implanted stents had been removed from the urinary tract and were investigated in a water bath , tas exclusively and reproducibly were visible where crystals had been deposited and did not appear on the stent material itself ( figures 1a and 1b ) .
minor stent incrustation at the distal end ( urinary bladder ) of a dj - stent , removed six weeks after implantation ( upper picture ) .
twinkling artifacts ( tas ) appear as colored spots on the pigtail , but not on the polyurethane stent itself ( lower picture ) .
sonography in water bath . b. minimal stent incrustation of intra - renal pigtail ( upper picture ) .
incrustation is not apparent . c. distinct ta at the distal intra - vesical pigtail of the ureter splint ( urinary bladder ) with detectable incrustation in the intramural course of the ureter ( extra - luminary ) .
e : x - ray image of the same explanted ureter splint ( d ) showing no visible incrustation .
one to four weeks after implantation minimal ta activity was apparent at the indwelling splints in all patients ( figure 1b ) .
appearance of twinkling artifacts ( tas ) in indwelling ureter splints as well as urine ph and serum levels of uric acid and creatinine rcc 
condition after kidney transplantation ; ca  carcinoma ; leukemias ( among others ) , ml , all , cll , nhl , aml ; cup  cancer of unknown primary ; gist  gastrointestinal stroma tumor extremely early incrustation of the ureter splint was found in one patient ( metastasizing urothelial carcinoma ) with uric acid increased to 11.7 mg / dl , slightly acidic urine ( ph 6.0 ) and compensated renal insufficiency of a single kidney with serum creatinine of 2.9 mg / dl .
after one week of implantation , the indwelling ureter splint already displayed distinct tas at the distal end of the stent inside the bladder and in the intramural course of the ureter ( figure 1c ) .
this ureter splint required change at this time , since renewed obstruction of the upper urinary tract was diagnosed with conventional ultrasonography .
incrustations scratched from the ureter splints were predominantly identified as phosphates ( struvite , apatite ) , uric acid and oxalates ( whewellite , weddelite ) .
repeated x - ray examination of clearly incrusted stents , which had been explanted , revealed no deposits .
incrustation had previously been identified by ta while these splints were indwelling ( example : figures 1d , 1e ) .
a significant correlation was apparent between the serum creatinine level and the time it took after stent implantation for tas to appear , indicating incrustation ( correlation coefficient of -0.54 ) ( figure 2 ) .
all other cause variables had no significant influence on the time it took after stent implantation to identify incrustation by tas .
time between stent placement and appearance of twinkling artifacts ( tas ) as a function of serum creatinine .
conventional x - ray imaging can not be used to detect stent incrustation since uric acid crystals are x - ray translucent .
conventional sonographic monitoring of the kidneys in patients with an indwelling stent can only differentiate between renewed urinary congestion due to obstruction by stent incrustation or manifest urolithiasis . during conventional color doppler sonography
it was noted that colored spots , dubbed twinkling artifacts , appeared on crystalline surfaces such as arterial plaque or kidney stones [ 5 , 10 , 11 ] .
these artifacts are common enough to cause considerable misinterpretation of flow where atheromatous vascular plaque occurs . however , with specific defined sonographic parameter selection it is possible to utilize twinkling artifacts to locate even minor incrustation in indwelling ureter splints .
patients with impaired urine flow of the upper urinary tract and severe tumor load , require ureter splint implantation , and face increased risk of splint incrustation .
tumor lysis syndrome ( tls ) , resulting from the breakdown of dying cells induced by successful cancer treatment manifests itself with high phosphate and uric acid levels in both blood and urine .
resulting splint incrustation from crystalline deposits can lead to severe urinary tract complications , including lumen obstruction and renewed kidney congestion .
incrustation and protein precipitates in the implant can also lead to an infected biomatrix , possibly causing a urinary tract infection culminating in sepsis , particularly in immunocompromised patients .
this investigation shows that serum creatinine negatively correlates with the time it takes for tas to become apparent during examination of the ureter stent : the higher the creatinine , the less time it takes for tas revealing incrustation to appear .
this implies that patients with normal kidney function have a significantly lower risk for dj - stent incrustation , while patients with renal insufficiency could require more frequent monitoring by means of ta .
removing a highly incrusted dj - stent can cause complications including mechanical strain to the urothelium , injuries , consecutive strictures , bleeding , impossible stent removal or ureter avulsion . since tas appear as a result of minute incrustation , but minute incrustation does not obstruct urine flow , identification and establishment of the rate of increase can facilitate decisions about removal , so that complications do not become manifest .
this investigation shows that the use of sonographic twinkling artifacts may be especially useful in cases where a high rate of ureter stent incrustation can be expected , such as in patients at risk for tumor lysis syndrome .
 introductionureter obstruction caused by a retro - peritoneal tumor is treated by inserting an indwelling ureter splint ( dj - stent ) . 
 indwelling duration is limited by cumulative crystalline deposits into the splint , eventually causing the repeated impairment of urine flow . 
 deciding when a dj - stent must be replaced is important since belated removal can be accompanied by severe complications . 
 x - ray or conventional sonography do not allow satisfactory evaluation of early incrustation , therefore , the use of sonographic twinkling artifacts ( ta ) to provide accurate stent surveillance was investigated.material and methods26 patients with indwelling ureter splints carrying a high risk of developing tumor lysis syndrome ( tls ) , which is often accompanied by early splint incrustation , were investigated utilizing ta the day after dj - stent implantation and weekly thereafter . 
 serum creatinine , uric acid , and urine ph were measured at all ta exams.resultsearly incrustation of the ureter splint was detected by ta in all patients 14 weeks after implantation . 
 incrustation occurred sooner with increased uric acid levels , and high creatinine or acidic urine accelerated early implant incrustation.conclusionsta can be used to monitor early crystalline deposits in implanted ureter splints , before they can be detected by conventional sonography or x - ray imaging and before complications occur . 
INTRODUCTION
MATERIAL AND METHODS
Material
Twinkling artifact ultrasonography
Infrared spectroscopy
Statistics
RESULTS
DISCUSSION
CONCLUSIONS
CONFLICTS OF INTEREST