Technology and Engineering

Evaluation of 16 New Holmium:Yttrium-Aluminum-Garnet Laser Optical Fibers forUreteroscopy

Erin C. Akar and Bodo E. Knudsen

OBJECTIVE To test the performance of 16 new single-use holmium:yttrium-aluminum-garnet (YAG) laser

Financial Disclosure: Bodo E.Boston Scientific. Erin Akar declFrom the Department of Urol

versity, Columbus, OHAddress correspondence to: Bo

Urology, Wexner Medical CenteRd., Ste. 2000, Columbus, OHSubmitted: August 28, 2014,

ª 2015 Elsevier Inc.All Rights Reserved

fibers.

MATERIALS ANDMETHODS

Small and medium core fibers were evaluated for flexibility, true diameter, connector temperature,and failure threshold. A flexible ureteroscope was deflected with the fiber in the working channel

to measure flexibility. Diameter was measured by micrometer and connector temperature byinfrared thermometer. Failure threshold was determined by bending the fiber to 180�, beginningwith a radius of 1.25 cm. A 100 W holmium:YAG laser was operated at 1.2 J/10 Hz for 30 secondsor until fiber fracture. The radius was decreased in 0.25-cm increments until a minimum bendradius of 0.4 cm was attained or until fiber fracture.

RESULTS Of the small core-fibers, the Cook-HLF-S150 (Cook Medical) had the smallest diameter and the

Flexiva TracTip 200 (Boston Scientific) the largest. The Cook-HLF-S150 and S200 were themost flexible and the SlimLine EZ200 (Lumenis) the least. The SlimLine EZ200 failed at thelargest bend radius, whereas the Flexiva 200 and Flexiva TracTip 200 did not fracture. Of themedium-core fibers, the ScopeSafe 300 had the smallest diameter and the Flexiva 365 the largest.The ScopeSafe 300 was the most flexible and the SlimLine 365 the least. The ScopeSafe 365failed at the largest radius of 1.25 cm, and the Flexiva 365 did not fail in 6 of 9 trials at the tightestradius.

CONCLUSION Performance characteristics of these new holmium:YAG optical fibers differed significantly but

performance was on par or better than historical controls. UROLOGY -: -e-, 2015. � 2015Elsevier Inc.

he ideal laser fiber is flexible, thin, and durable,maximizing maneuverability within the collect-

Ting system, allowing for adequate irrigation flow

rate to maintain visibility and to transmit energy in astraight or deflected configuration without the fiber frac-turing. Fiber fracture can lead to costly damage to thescope, increased operating room time, and a potentialretained foreign body, the fractured fiber tip.1 Flexibility,energy transmission, and fracture thresholds differ amonglaser fibers.2 In addition, the true measured fiber diametersare significantly larger than the stated fiber core sizebecause of the additional girth of the fiber cladding andjacket, which may be misleading to some users.3 In thisstudy, we evaluated 16 new laser fiber types in effort todefine their performance characteristics.

Knudsen is a paid consultant to Olympus Surgical andares no relevant financial interest.ogy, Wexner Medical Center, The Ohio State Uni-

do E. Knudsen, M.D., F.R.C.S.(C), Department ofr, The Ohio State University, 915 Olentangy River43210-1228. E-mail: bodo.knudsen@osumc.eduaccepted (with revisions): April 8, 2015

h

MATERIALS AND METHODS

True diameter, flexibility, connector temperature, durability,and energy transmission were evaluated in 16 new single-usefiber types. Three samples of each fiber included in the studywere tested. Flexibility was measured at 1 point along the fiberby maximally deflecting a Stryker U-500 ureteroscope with thefiber in the working channel. Diameter was measured by adigital micrometer (Mitutoyo Japan) at 3 points along the fiberand averaged. Energy transmission was measured using anelectronic detector in mJ set to detect the average energy of 50pulses. Three measurements of each individual fiber’s energytransmission were tested and then averaged among 3 fibers ofthe same type for a total of 9 measurements. A 100 Wholmium:yttrium-aluminum-garnet (YAG) laser (LumenisVersaPulse, Santa Clara, CA) was operated at 0.5 J/10 Hz for50 pulses. Energy transmission was measured with the fiberstraight and the fiber bent at 180� with fixed radius of 1.25 cm.Durability testing was performed with the fibers submergedunder water and secured by silicone tubing attached to rareearth magnets that permitted fine adjustment of the bendradius. The laser fiber was threaded through the tubing andactivated underwater. Power was set at 1.2 J/10 Hz for 30 sec-onds or until fiber fracture, observed as the entire fiberbreaking.

ttp://dx.doi.org/10.1016/j.urology.2015.04.0170090-4295/15

1

Figure 1. True fiber diameter (mm) of (A) small-core fibers (core <300 mm) and (B) medium-core fibers (core �300 mm).Flexibility (�) of (C) small-core fibers (core <300 mm) and (D) medium-core fibers (core �300 mm).

Durability was determined by bending the fiber to 180�,beginning with a radius of 1.25 cm. These parameters have beenpreviously described and were selected to represent the higherend of clinical settings that might be used to treat stones in thekidney.4 The magnets were brought closer together in 0.25-cmincrements until a bend radius of 0.4 cm was attained or thefiber fractured, whichever occurred first.

Energy transmission was again measured with the fiberstraight after the durability testing had been completed using thesame settings and measurement protocol for predurability energytransmission testing. The temperature of the connector wasmeasured using an infrared thermal detector (Rosewill, City ofIndustry, CA) over a period of three 30-second intervals andcompared with room temperature. Fibers from Bard (Endo-Beam), Boston Scientific (Flexiva), Lumenis (SlimLine EZ),Cook Medical (Cook-HLF), and Storz (ScopeSafe) were tested.All fibers were considered off the shelf and donated by each ofthe manufacturers.

Analysis included paired 2-tailed t tests done comparing en-ergy transmitted before and after durability testing for each fibertype. Analysis of variance and Tukey tests were performed todetect significant differences in the change in energy trans-mitted after durability testing and differences in fracture radius.Pearson correlation plots were also done to assess relationships

2

among the different performance parameters evaluated. SPSSsoftware (IBM Corp.) was used for data analysis.

RESULTS

True DiameterThe Cook-HLF-S150 has the smallest true diameter, at274 mm, and the Cook-HLF-S273 has the largest, at 422mm. Notably, the Flexiva TracTip 200 and Flexiva 200have 240-mm core sizes, and the SlimLine 200 has a272-mm core, despite “200” being included in the mar-keting name (Fig. 1A). The ScopeSafe 300 has a measureddiameter of 465 mm. The fibers with core sizes of 365 rangefrom the EndoBeam 365, with the smallest diameter of541 mm, to the Flexiva, with the largest of 604 mm (Fig. 1B;Table 1).

FlexibilityThe Cook-HLF-S150 and -S200 were the most flexible at254� deflection. The SlimLine 200 was the least flexibleat 218� (Fig. 1C). The ScopeSafe 300 had maximumdeflection at 220�. There was not much variation in

UROLOGY - (-), 2015

Table1.Sum

maryof

fibe

rpe

rforman

cech

arac

teristics

Produ

cer

Lase

rType

Max

Defl

ection

(�)

Avg

Rad

iusat

Frac

ture

(cm)

Mos

tCom

mon

Frac

ture

Rad

ius(cm)

Frac

turing

atTh

atRad

ius(%)

Worst

Frac

ture

Rad

ius(cm)

Ene

rgy

Drop(%)

True

Diameter

(mm)

Individu

alFibe

rCon

nectorsIncrea

sed

inTe

mp

Coo

kCoo

k-HLF-S200

254

0.489

0.5

89

0.5

11

374

No

Coo

k-HLF-S273

230

0.433

0.4

67

0.5

6422

No

Coo

k-HLF-S365

201

0.5

0.5

100

0.5

13

547

No

Coo

k-HLF-S150

254

0.389

0.4

56

0.5

24

274

Yes

Bard

End

oBea

m200

244

0.4

0.4

100

0.4

17

377

No

End

oBea

m272

231

0.444

0.4

56

0.5

9392

Yes

End

oBea

m365

199

0.778

0.75

44

116

541

No

Bos

ton

Scien

tific

Flexiva200

242

0Nofailu

re100

Nofailu

re3

443

No

Flexiva365

202

0.211

Nofailu

re67

111

604

No

Flexiva

Trac

Tip200

243

0Nofailu

re100

Nofailu

reGaine

d1%

460

No

Storz

Sco

peSafe200

249

0.089

Nofailu

re78

0.4

24

374

Yes

Sco

peSafe272

236

0.489

0.5

89

0.5

2420

No

Sco

peSafe300

220

0.528

0.5

89

0.75

8465

No

Sco

peSafe365

199

0.639

0.5

67

1.25

3551

No

Lumen

isSlim

Line

200

218

0.765

144

15

421

No

Slim

Line

365

198

0.506

0.5

67

0.75

1543

No

UROLOGY - (-), 2015

flexibility among the larger-diameter fibers measured(Fig. 1D; Table 1).

DurabilityOf the small-core fibers, the SlimLine 200, ScopeSafe272, and Cook-HLF-S200 were the least durable, whereasthe Flexiva 200, TracTip 200, and ScopeSafe 200 werethe most durable (Fig. 2A). Of the medium-core fibers,the EndoBeam 365 and ScopeSafe 365 were the leastdurable, and the Flexiva 365 was the most durable(Fig. 2B). Most common and worst fracture radii wererecorded for each fiber type (Table 1). The ScopeSafe365 had the largest fracture radius of all fibers measured,at 1.25 cm, and the Flexiva 200 and Flexiva TracTip 200did not fracture. The ScopeSafe 200 did not fracture in78% of measurements but fractured at 0.4 cm. TheFlexiva 365 did not fracture in 67% of measurements;however, its worst fracture radius was 1 cm (Table 1). Ofall variables evaluated on laser performance, a significantcorrelation was found between increasing core size andincreasing fracture radius.

Energy TransmissionOf the small-core fibers, the ScopeSafe 200 had thegreatest loss of energy transmission, at 24%, and theFlexiva TracTip maintained energy transmission(Fig. 2C). Of the medium-core fibers, the EndoBeam 365lost the most energy transmission, at 16%, whereas theSlimLine 365 only had a 1% drop in energy transmission(Fig. 2D). The top 4 energy losers were the Cook-HLF-S150, ScopeSafe 200, EndoBeam 200, and EndoBeam365 (Table 1). Of all variables evaluated in laser perfor-mance, a significant correlation was found betweendecreasing core size and increasing energy loss afterdurability testing.

Connector TemperatureMost of the laser fiber connectors did not increase intemperature from the average room temperature duringtesting. The Cook-HLF-S150 fibers heated up the most,and 1 even fractured at the connector site during laseractivation. The ScopeSafe 200 was second to the Cook-HLF-S150 in heat generation at the connector. Inter-estingly, the Cook-HLF-S150 and ScopeSafe 200 fibershad the highest drops in energy of all fiber types(Table 2), suggesting energy loss during coupling at theconnector.

COMMENTLaser fibers were evaluated for their true diameter, flexi-bility, durability, and energy transmission after durabilitytesting. These parameters, taken as a whole, make up theperformance characteristics of the fiber. The fiber evalu-ations revealed that no single fiber excels in all categoriesand that tradeoffs occur as manufacturers tweak their fiberdesigns.

3

Figure 2. Durability (cm) of (A) small-core fibers (core <300 mm) and (B) medium-core fibers (core �300 mm). Decrease inenergy (mJ) after durability testing in (C) small-core fibers (core <300 mm) and in (D) medium-core fibers (core >300 mm).

Table 2. Individual fibers with increased connectortemperatures during testing

FiberAvg ConnectorTemp (�C)

Avg RoomTemp (�C)

EnergyLost (%)

Scope Safe 200 - 2 24.5 20.9 17.4Scope Safe 200 - 3 26.1 20.5 33.7Cook-HLF-S150 -1 27.4 17.1 27.2Cook-HLF-S150 -2 28.8 18.5 39.7Cook-HLF-S150 -4 Fiber fractured 19.3 7.21EndoBeam 272 -1 23.2 20.3 12.2

The small-core fibers, defined as fibers with core sizes ofless than 300 mm, are the smallest and most flexible fibersand are typically used for flexible ureteroscopic caseswhere deflection of the fiber an important consideration.However, with deflection comes the risk of the fiberbreaking, usually at the point of maximum deflection. Ofthe small-core fibers, the Flexiva 200 and Flexiva TracTipwere the most durable, not fracturing at the tightest bendradius tested, 0.4 cm, which is a smaller radius of deflec-tion than currently available flexible ureteroscopes. Thetradeoff is that these fibers have larger diameters and areless flexible than several other fibers in their category.This may affect irrigation flow and visibility and alsomake deflection into the lower pole more difficult. Lessflexible fibers may also tax the deflection mechanism ofthe delicate flexible ureteroscope, potentially decreasingthe interval between repairs. The Cook-HLF-S150 hasthe smallest diameter and was the most flexible fiber inthis study. However, it was less durable, and energytransmission decreased by 24% after durability testing.Why the energy decrease occurred is not entirely clear butsuggests an interruption of energy transmission in the fi-ber connector or along the length of the fiber. This fiberalso experienced heating at the connector end, whichwould lend support to the conclusion that the connectorwas causing the issue.

Medium-core fibers have core sizes of w365 mm. Theyare less flexible, limit the deflection of ureteroscopes

4

within the kidney, and increase the strain on thedeflection mechanism of delicate flexible ureteroscopes.We advocate limiting the use of medium-core fibers tosemirigid ureteroscopes or situations where deflection ofthe flexible ureteroscope is not required to reach theintended target. The Flexiva 365 is the most durable ofthe medium-core fibers, but the tradeoff is the largerdiameter and some loss of energy transmission afterdurability testing (Table 1). The SlimLine 365 is not asflexible or as durable as the Flexiva 365 but lost the leastamount of energy, suggesting it could be used at acuteangles with less risk of reducing energy transmission.However, we do not advocate using the larger 365 fiberswhen significant deflection is anticipated due to the po-tential for increased wear on the delicate deflectionmechanism of the ureteroscopes. The ScopeSafe 300 wasnot as durable as the Flexiva 365 but provided greater

UROLOGY - (-), 2015

energy transmission after durability testing and has asmaller diameter, making it a more flexible fiber withimproved irrigation flow.

Durability should be given the highest priority whendeciding on a laser fiber to use, because fiber fracture canlead to catastrophic scope damage from the laser beingactivated in the working channel. Furthermore, a fiber tipthat breaks off in the patient can be very difficult toremove. Failure to remove the fiber tip could lead toencrustation and subsequent stone formation. Therefore,a more durable fiber that is resistant to fracture should besought.5

Connector temperature was monitored during testingbecause failure to confine energy to the laser fiber coremay lead to costly damage of equipment.5 Prior testinghas shown that certain fibers may not be compatible withall available lasers and that misalignment can lead tocatastrophic failure.6 Manufacturers are aware of this issueand have heat sinks built into some connectors to rapidlydisperse heat in an effort to prevent catastrophic fiberfailure. Fibers may fail at the connector for a number ofreasons, including concentricity error, misalignment withthe connector, or the design of the heat sink leading toenergy lost as heat, poor energy transmission, and fiberfracture.5

In the current study, there appeared to be good couplingof the fibers with the laser in most cases. Howeverincreasing connector temperatures were recorded with 6individual fibers from 3 different manufacturers (Table 2).The Cook-HLF-S150 fiber demonstrated the mostconsistent increase in temperature, including 1 fiber thatfractured at the connector. The Cook-HLF-150 is a non-tapered fiber with a subminiature version A connector.The small 150-mm core size is a technical challenge tocouple with the laser. The energy beam must be funneledinto the small fiber core, and this may lead to poor couplingwith resultant heat generation.5 If enough heat is generatedand not dissipated quickly enough, fiber failure at theconnector may occur.

Multiple small- and medium-core fibers were evaluatedin prior studies.2,4 The 2009 report and our current studyboth tested durability at the same power of 1.2 J/10 Hz,whereas the 2005 report gradually increased energy from200 to 4000 mJ at 5 Hz. The Dornier LG 200 had the bestaverage energy transmission but the worst durability,fracturing at a 1-cm radius at only 200 mJ; however, arevised fiber had better durability in the 2009 study,fracturing at a 1-cm radius at 1200 mJ.4 The LumenisSlimLine 200 had the worst energy transmission at175 mJ but the best durability, fracturing at 0.5 cm and4000 mJ.2 This outcome was likely influenced by lowerenergy transmission. In the current study, we usedLumenis SlimLine EZ fibers, which are the single-useversion. The SlimLine EZ 200 had the worst durabilityof the small-core fibers, fracturing most commonly at a1-cm radius. This is in contrast to the 2009 report, inwhich the same brand fractured at a 0.5-cm radius.4

UROLOGY - (-), 2015

Overall, the SlimLine 200 was less durable, and theSlimLine 365 was more durable in our current resultscompared with their performance in the 2009 study.

There were differences measured between Boston Sci-entific’s older AccuFlex fiber line and the newer Flexivaline. The Flexiva 200 is less flexible and has a largerdiameter but is more durable than the AccuFlex 200,which fractured at 1.75 cm. The Flexiva 365 is lessflexible but has a smaller diameter and had a larger frac-ture radius of 1 cm compared with the AccuFlex 365.4 Itshould be noted that the Flexiva 365 did not fracture inmost cases, showing better overall durability; however,the most common fracture radius of the AccuFlex was notrecorded.4 In our study, no Flexiva 200 or TracTip failed,and 67% of the Flexiva 365 fibers did not fracture duringtesting. This is in line with prior durability testing of 100Flexiva 200 fibers in which only 13% of fibers failed at a0.5-cm radius.3 Our data indicate that the Flexiva 200 is avery durable single-use fiber, which, in our opinion, re-mains one of the most important considerations in fiberselection The Flexiva fibers do come with the tradeoff ofhaving a larger diameter, which can decrease irrigationflow.2

It is interesting to note that no correlation was foundbetween increasing true measured diameter and fractureradius in our data. One possibility of this observation isdifferences in the cladding material makeup and thick-ness. A thicker cladding material with a lower index ofrefraction may allow less thermal energy from higher-order beams to escape into the jacket, thus decreasingfracture rates and increasing durability.5 This is consistentwith the findings of the prior 2005 and 2009 studies.2,4

Our correlations analysis demonstrated an inverse rela-tionship between increasing core size and durability, withsmaller-core fibers breaking at smaller radii.4 Thesecomparisons illustrate a very critical point, namely, thatfiber performance is a moving target. Small changes in themanufacturing process, parts used (such as where the coreof the fiber is sourced from), and other variables likelyaffect fiber performance. Our ongoing evaluation of fibershas demonstrated not only differences in the performanceof fibers from different manufacturers but also differencesamong the same line of fibers over time.

It is important to mention that the names given tofibers by the manufacturers continue to be a point ofconfusion, even among experienced urologists. Withsome fibers, the name reflects the core size of the fiber butnot its true measured diameter. An example of this is theLumenis SlimLine 365, which has a 365-mm core but atrue measured diameter, which includes the core, jacket,and cladding, of 541 mm. Another example is the Cook-HLF fibers. On the Cook Medical Web site (https://www.cookmedical.com/product/-/catalog/optilite-holmium-laser-fibers-for-use-with-standard-sma-connections?ds¼uro_hlf_webds) the HLF single-use fiber diameter isexplicitly stated as 200 and 365 mm, respectively; how-ever, our data show the true fiber diameter is actually 374

5

and 547 mm, respectively. This is almost a 200-mm dif-ference between the reported and measured values. Hereat least the marketing name reflects the size of acomponent of the fiber, in this case the fiber core.

For some fibers the label does not reflect the size of anypart of the fiber. The Flexiva 200 and TracTip 200 bothhave a 240-mm core and true diameters of 443 and460 mm, respectively. On the basis of previous studiesconducted assuming a 3.6F working channel, that in-crease would lead to a reduction in flow rates of w50%and 75%, respectively. This would reduce flow byapproximately an extra 25% in contrast to fiber diametersof the reported values.2

Cost is also an important aspect when purchasing afiber. Pricing is variable among the manufacturers,although the trend in the industry is moving towardsingle-use fibers. Although the debate between single useand reusable is outside the scope of this report, our owninstitution has transitioned to single-use fingers. Thedecision to do so was based on eliminating the humanresource component of sterilization and repacking as wellas having a new, ideally performing fiber for every case.

Our study has several limitations, including the smallsample size. Manufacturers contributed off-the-shelf fibersfree of charge for the independent testing, and we did testall fibers provided. We did not perform flow studiesbecause previous work showed that flow is proportional toPoiseuille’s law,2 and therefore, larger-diameter fibershave proportionally less flow at a fixed irrigation pressure.All testing was performed on a Lumenis VersaPulse100 W laser, and results might vary if other lasers wereused.

Another limitation is that only 3 fibers of each typewere tested. We relied on samples provided by themanufacturers for this study, with the exception of theBoston Scientific fibers, which were off-the-shelf fibersfrom our own surgical center. It is possible with a largersample size that greater intrafiber variability related tomanufacturing tolerances might have been seen.

6

CONCLUSIONOverall, the performance of fibers has improved and ismore consistent among fibers compared with prior testing,with fewer outliers. However, fiber performance differedamong those tested, and no one single fiber was the bestperformer in all categories. The best performing fiberdepends on the user’s priorities: flexibility and visibility,durability, or energy transmission. The results demon-strate that different fibers excelled in different categories.Fiber durability, with resistance to fracturing duringbending and energy transmission, is critical because abroken fiber can lead to endoscope damage and a possiblepiece of retained fiber in the patient. Therefore, a highlydurable fiber that still provides good performance in theother categories is our recommended fiber of choice. TheFlexiva 200 and Flexiva TracTip meet these criteria forthe small coreesized category. For the medium-core fi-bers, if the fibers are going to be used in a nontaxingstraight configuration (with a semirigid ureteroscope), awide variety of options are available. We do not advocateusing medium coreesized fibers during flexible uretero-scopy in the kidney due to the strain these fibers place onthe deflection mechanism of the ureteroscopes.

References

1. Landman J, Lee DI, Lee C, et al. Evaluation of overall costs ofcurrently available small flexible ureteroscopes. Urology. 2003;62:218-222.

2. Knudsen BE, Glickman RD, Stallman KJ, et al. Performance and safetyof holmium: YAG laser optical fibers. J Endourol. 2005;19:1092-1097.

3. Khemees TA, Shore DM, Antiporta M, et al. Evaluation of a new240 um single-use holmium:YAG optical fiber for flexible uretero-scopy. J Endourol. 2013;27:475-479.

4. Mues AC, Teichman JM, Knudsen BE. Evaluation of 24 holmium:YAG laser optical fibers for flexible ureteroscopy. J Urol. 2009;182:348-354.

5. Nazif OA, Teichman JM, Glickman RD, et al. Review of laser fibers:a practical guide for urologists. J Endourol. 2004;18:819-829.

6. Marks AJ, Mues AC, Knudsen BE, Teichman JM. Holmium:yttrium-aluminum-garnet lithotripsy proximal fiber failures from laser andfiber mismatch. Urology. 2008;71:1049-1051.

UROLOGY - (-), 2015