Robert K. Zeman, MD #{149}William J. Davros, PhD #{149}Brian Steven C. Horii, MD #{149}Paul M. Silverman, MD #{149}Edward Wendelin S. Hayes, DO #{149}Cirrelda J. Cooper, MD

S Garra, MD #{149}Jo Anne L. Cattau, Jr, MD #{149}

Relationship between Stone Targeting, and Fragmentation during Experimental Biliary In vitro experiments in an anthropomorphic phantom were performed to clarify the relationship between stone motion, targeting, and fragmentation. Stone motion was minimized by pinning the stone against the dependent wall of a mock gallbladder cavity during shock wave treatment. Fragmentation was most effective (probably due to increased cavitation effects) when the shock wave traversed fluid at the point of its impact with a stone. The results suggest that treatment with the patient in the supine or oblique position may produce a better outcome than treatment in the prone position. Buoyant stones exhibited the greatest motion, which was often to-and-fro in nature. Although restricting the size of the mock gallbladder cavity reduced stone motion, maintaining a 1-cm fluid path was beneficial for achieving optimal pulverization. Index

terms:

Gallbladder, 762.1299

Radio!ogy

Gallbladder, interventional

#{149} Lithotripsy,

1990;

calculi, 762.289 procedures,

#{149}

762.1299 176:125-128

LTHOUGH

wave gational, cholelithiasis

been

with

fective targeting, fragmentation

from the patient with ment stones (patient The Lithostar Plus

shock

treated

this

otriptor

for

modality.

Ef-

stone motion, appear to have

and a corn-

was

used

system

has

electromagnetic

Medical to perform

three

pig-

Table).

shock

lith-

Systems,

Iselin,

lithotnipsy.

That

wave

generators:

under the treatment to biplane fluoroscopic

plex relationship, which gives rise to significant implications for the planning and performance of the lithotnipsy procedure. To elucidate the patterns of stone movement during lithotnipsy and how they may relate to targeting and fragmentation, in vitro ultrasonographic (US) and videofluonoscopic observations were made during fragmentation of stones

guidance.

The

third

overhead

module,

housed

ments, the stones were thropomorphic phantom phantom is made of an

in an anthropomorphic

MATERIALS A total patients

From the Departments of Radiology (R.K.Z., W.J.D., B.S.G., JAG., S.C.H., P.M.S., W.S.H., C.J.C.) and Medicine (Gastroenterology Division) (E.L.C.), Georgetown University Medical Center, 3800 Reservoir Rd NW, Washington, DC 20007. From the 1988 RSNA annual meeting. Received October 3, 1989; revision requested November 3; revision received March 12, 1990; accepted March 28. Address reprint requests to R.K.Z. RSNA, 1990

NJ)

(Siemens

predominantly

3 in the

Two are housed and are linked

phantom.

I

#{149}

Lithotripsy’

extracorponeal

have

RN

Motion,

lithotripsy is still investiseveral thousand patients

worldwide

Goldberg,

AND

of 35 stones at the

time

from

wave

the

11

of cholecystectomy

were

the

level

For the

shock were

properties

(and

-

m/sec

MHz.

therefore

phantom custom

had a diameter designed so that

dominantly

gallbladder

cavity

could

the

of the

phantom

all

came

of 1,000 expeni-

speed

1,540

shock to those

stones

generators

housed in an an(Fig 1). This agar and graphite

support similar

The

wave

fragmentation

were used in the fragmentation expeniments. The stones from 10 patients were predominantly composed of cholesterol, while those from one patient were prepigment.

at a

to 19 kV

A total

an approximate of dB/cm

used

given.

in vitro

transmission tion of 0.5

US

at full power, was

380 bar).

waves

an

in-line

equivalent

under-table

(approximately shock

used

module

power

in

uses

the purpose of these in the under-table shock

overhead

reduced on

For

generators

and

gel with

METHODS

harvested

for targeting. vitro experiments,

is contained

which

table

of sound

and

attenua-

Its acoustic its ability

wave transmission) of liver pamenchyma.

to are The

of 24 cm and a mock 50-mL

be carved

was

out

of

from single composition “families” (ie, had visually similar morphology and pigment content) and were of matched size (diameter, 1.0-1.6 cm). Prior baseline experiments had suggested that stones from

of the focal zone of the lithotriptor (1-3). Of the 35 stones treated, 31 were fragmented in the 50-mL mock gallbladder in normal saline or 7.5% or 15% urogmaphic

a single

contrast

composition

family

break

at com-

parable power levels with comparable degrees of pulverization. Between two and five matched stones were obtained from each patient. Three stones were obtained

interior

Abbreviation:

material.

Contrast

AP

at the

material

center

was

anteroposterior.

125

C

B

A

Figure Figure and

1. Treatment C an under-table

dent

or nondependent

tation

geometries shock wave

used in fragmentation generator (SWG)

position.

tangentially.

When

used,

experiments. used with

was

the US probe

With stones

tion size

geometries A in either a depen-

was positioned

to view

tiveness waves.

fragmen-

With

geometry B an overhead module was used for generating shock waves; stones were treated in the dependent position and were imaged with an in-line US probe. Of the 31 stones treated, 20 were treated with the shock wave traversing fluid to the point of stone impact (17 with geometry A, three with geometry B). Eleven stones were treated with geometry C. This does not include the stones treated in the smaller cavities.

administered

because

only

in biplane

to assist

geting

but

also

it could

be fluoroscopic

to manipulate

used

the

to buoyancy

not tar-

stone

position

due

effects.

tnibution ronment

of stones treated in each envifrom patients 1-11 is shown in

Table. Ten of the 1 1 stones trast material floated. contrast material, and

The

dis-

the

line.

Of

the

treated in 15% conFour floated in 7.5% three floated in sa-

17 floating

stones,

three

were

suspended in fluid and did not rise to the roof of the mock gallbladder. The pigment stones tended to become dependent in contrast

material.

graphic in two

evidence of the three

saline.

Stone

There

was

of gas stones

buoyancy

in

radio-

internal clefts that floated in

was

important

in

determining the position of a stone in me!ation to an incoming shock wave (Fig 1). Continuous

fluonoscopic

or

US

moni-

toring of the fragmentation process was performed and videotaped for review. The shock wave path was continuously readjusted so that the stone on largest dominant fragment was centered in the focal zone. If no dominant fragment was seen, the center of the mock gallbladder was targeted. Stone and fragment motion was rated on a crude motion scale: 0, no movement; 1, excursion of 1 cm or less; 2, brisk

motion.

The

actual

measurement

was made with use of an electronic grid, corrected for magnification and displayed on the viewing monitors. Motion was observed

with

genera! tion

each

trend. in

shock

The

relation

wave

direction

to the

and

mo-

surrounding

mcdi-

um and stone position were also noted. Measurements were performed 20 times each in the anteropostenior (AP) and oblique (craniocaudal) fluoroscopy planes or transverse

and

longitudinal

US

planes.

The stones and fragments were inspected at 200-shock wave intervals. At the conclusion

stone, 126

of fragmentation

the

fragments

Radiology

#{149}

were

for

each

segregated

and

photographed.

by

They

graded on a scale the effectiveness grade 2, excellent

mm,

abundant

were

3-5-mm

fragments);

0, poor fragmentation (failure stone breakage on fragments 80% of the original played little role mentation

matched

grade

Size frag-

stone

size were classification

5

to produce in excess of

stone diameter). determining

in

because

homogeneous jective, this

then

most fragments fragmentagreater than

used. does

sets

of

Albeit allow

sub-

crude grading of the effectiveness of fragmentation. The motion and fragmentation data treatment

will be presented separately geometries A, B, and C. The

Student significance

t test

the means indexes.

Seven

for motion

from

stone

and

additional

patients sets

for

was used to determine of the difference between

were

the

(from

four

or five

obtained)

were

volume

bladder mL

of the

cavity

or 6 mL.

With

was 1 cm or 1-2 in the near field

face for

with the

tro

mock

was

these

the stone. 15-mL

experiment

cavity.

Geometry The

conducted were

US

gall-

respectively, wave inter-

B was

in

used

visual

in the other repeated

15

there

and

in vi-

this

model.

None of the three stones treated with geometry B showed this effect, which occurred in only one of 1 1 stones

treated suggest

neal-time

with that

parallel

geometry this type

to the

C. These data of movement

direction

of shock

wave travel requires stone The three stones that were but

did

not

rise

nondependent

all

the

Off-center fragments

buoyancy. buoyant

way

surface

gallbladder showed tion. The rhomboid lanly shaped stones gyrate and tumble four instances.

but

to the

of the

mock

brisk level 2 moand more imnegucould be seen to end over end in

hits caused to be deflected

the stones laterally.

on

for 16 of 17 stones geometry A (Fig 3), one

treated

was not Treatment

for 17 stones motion index

duced 1.53

with

essential geometry

fluoro-

scopic and US guidance revealed that incoming shock waves caused stones and fragments to exhibit substantial motion within the mock gallbladder.

for

was

B, and

it. A was

used

and resulted in a mean of 1.88 ± 0.11. It pro-

a mean ± 0.26.

geometry

fragmentation For

this

ometry C. The mean was 0.55 ± 0.27, and

of

of stones

and very efFor the three

use of geometry index was 0.33 ± fragmentation in-

2.0 ± 0.0. This

lent fragmentation motion in this small stones were treated

index

group

there was brisk motion fective fragmentation.

dex of the

surface of the mock in 13 of 17 cases (Fig 3).

stones treated with B, the mean motion 0.33, and the mean

RESULTS Videotape

geometry but off the

of three

to either

mm of fluid, at the shock

shock

seven of 1 1 treated with geometry C. The extent of movement was included in the motion index calculations. Buoyancy favored lateral movement

fragment-

volumes

1,000

matched

elliptical

reduced

after

by

the four

ed in normal saline in a phantom identical to that already described except that the

nondependent gallbladder

This occurred treated with

fragmentation

stones

whom

of fragmentation

Directly centered hits with A caused little lateral motion caused the stone to ricochet

of 0-2 with regard to of fragmentation (Fig 2): fragmentation (no frag-

ments greater than 5 mm, 2-3 mm); grade 1, moderate tion (one to five fragments

observations

as a

of stone

size

2. Example of grade 1 fragmentaillustrates stratification of fragments for the purpose of determining effec-

meant

excel-

with little stone group. Eleven with use of ge-

motion index the mean fragJuly

1990

ThIGBL.m..

114GB 1.....

I

I

ri

I

i-.-

_________________________________________________

TM

GB

1..,,,,

,I

H15

a.

c.

b. 3.

vector representation of stone movement within tissue-mimicking mock gallbladder (TM GB). CC with stone recoil is greatest when an off-center hit drives the stone laterally within the AP viewing stones were also subject to random deflections off the nondependent wall of the mock gallbladder cavity. This movement the lateral deflections depicted in a. (c) Dependent stones treated with use of under-table shock wave generators exhibited than buoyant stones. This movement was in the general direction of shock wave propagation. Figure

Schematic

=

(a) Lateral movement

mentation index was 0.91 ± 0.09. This indicated moderate fragmentation with little to moderate stone movement. Student t tests were performed on motion and fragmentation mean indexes cant

to determine differences

whether signifiexisted between the

treatment geometries. For fragment motion, geometry A produced significantly greaten motion than geometries B and C (P < .001, t 6.74, 1.33).

stones

were

viewing

due

deflected

plane,

out

they

to partial

of the

were

volume

less

a second

ducen tudinal

and switching between and axial orientation,

were

able

out-of-line

to include

By

US

trans-

bongiwe

out-of-plane

motion in the index calculations. With both in-plane and out-of-plane motion, stones were seen to exhibit to-and-fro movement. After receiving an incoming shock wave, a stone

There was no significant difference in mean motion index between geometries B and C (P > .5, t = 0.635). For fragmentation, geometry B was

would be be drawn

found

all treatment geometries but was most pronounced with geometry A for buoyant stones. Recoil movement

to be marginally

superior

geometry

A (P < .5, t

try

superior

A was

1.54).

C in

producing fragmentation at the P .01 level (t 3.60), and geometry was superior to geometry C at the < .001 level (t 6.09). Five stones showed an unusual fragment spatial distribution that fected targeting. Two of the three

stones

that

internal

gas

floated

in saline

sank

to a dependent

effect

Geome-

to geometry

and

< B P

af-

had po-

sition immediately after being fnagmented. Radiognaphs of specimens of the fragments showed an absence of internal gas that had previously been present.

In

the

three

stones, the fragments ing out at different

remaining

were stratifylevels within the

mock gallbladder (one in 15% contnast material, one in 7.5% contrast material, and one in saline). Fragments from a single stone may have varying specific gravities due to their

composition, seek

different

which

causes

levels

within

them

to

than

with

US.

cross-sectional Volume

176

Because

nature Number

#{149}

of the

of US, when 1

was

was

present

position seen

(Fig

in all

in an

less

then

motion between

or fragmentation the results

mL cavities from treated

the

when

with

direction

for

Fragmentation effective

was in the

±

was in

was found in the 50- and

same composition with comparable 6-mL

15-

stones family geometry

considerably

B.

less

cavity.

DISCUSSION Targeting is a critical part of gallstone lithotripsy. This series of in vitro experiments sought to clarify the relationship between targeting, stone movement,

and

fragmentation.

motion

center

in the

stones

showed

wave

Al-

was

AP plane. the to the

B and

C un-

clearly

off

Buoyant

greatest

stones

rise

of stones

geometries

shock

that

motion.

did

not

corn-

nondependent

wall of the mock gallbladder showed the briskest motion and were most apt to migrate from the focal zone. Shock waves are longitudinal waves. Theoretically, stones could be propelled forward parallel to the dinection

of wave

propagation

during

the

compressive (positive-pressure) half cycle. This may account for the lack of stone motion with geometry B, wherein the stone is pinned against the mock gallbladder wall. The same logic would have predicted little motion with geometry A; however, this was not the case. Stones

the 0.33

index difference

comparing

the

pletely

12 stones and in a lateral direction for five. The limited experiments performed in a 6-mL cavity with each of four stones laterally surrounded by a thin 1-2-mm layer of saline revealed virtually no stone motion. A fragmentation index of 1 .25 ± 0.5 was achieved, meaning that fragmentation was effective but by no means

0.2, and the fragmentation 2.0 ± 0.0. No significant

with

Free-floating

and

complete. In the 15-mL cavity, mean stone motion index was

little

treated

3). This

media

axial

relatively

fluid.

This posed a challenge in targeting fragments separated from each other by several centimeters. Stone motion was better evaluated subjectively with biplane fluoroscopy

deflected and would back (often incompletely)

to its original

to

though US guidance is used for clinical lithotnipsy, we found that motion was more conveniently assessed in the laboratory with fluoroscopy than with US. Fluomoscopy allowed classification of complex motion because it is not cross-sectional in nature. The in vitro results demonstrated

visible

averaging.

using

craniocaudal. plane. (b) Buoyant was not as great as less movement

treated

showed the greatest ment, which, more ment

with

with

geometry

A

stone movethan the move-

geometries

B and

C, could

be described as to-and-fro. Although gravity may contribute to this peculiar motion in the axial direction, it is not likely to cause lateral recoil in a nondependent direction. There are three other possible reasons why during treatment stones may be dniven away from their original position and then pulled back. In addition to their compressive (positive-pressure) component, shock waves also have a ranefactive

ponent pressure localized

(negative-pressure)

(4,5). The component vacuum

corn-

latter

negativecould create effect, drawing Radiology

a

127

#{149}

stones

and

fragments

back

fragmentation should be maximized if stones can be kept in the shock wave focal zone by minimizing their

toward

the shock wave path after their initial deflection. Since the forces involved may be small, this effect may be obvi-

movement.

ous only for buoyant stones with melatively little inertia to overcome. A second possible explanation is that as negative pressures are created, cavitation bubbles are drawn out of solution (6,7). As these bubbles oscillate, are associated with jet formation, and ultimately collapse, they

may

exert

sufficient

buoyant

stones

A third shock

possible

waves

a cavity

may

nection ry wave.

force

to move

or small

fragments.

explanation

reflected

off

displace

stones

opposite to that We know that

are reflected just waves. Reflected

is that the

walls

of

in a di-

of the shock

primawaves

like other acoustic shock waves are not

uncommon and are responsible for most of the damage to in-line diagnostic US probes used in clinical lithotnipsy.

The vealed

in vitro experiments some unexpected

considerations. contain gas may release

ken.

Buoyant stones that in their internal fissures that gas after being bro-

Following

buoyancy sink into

below

the

concentrated

target

and latter

of this

gas,

may

in a stone

zone.

Tar-

complicated according Most stones

pigment be

rim

cornfocally

or nidus

(8). If that is the case, fragments from that area may seek greater dependency than those with greater relative cholesterol content. Aiming at fragments distributed oven several centimeters is problematic. They generalby must be treated separately unless they can be made to lie in the long axis of the shock wave focal zone. It might be assumed that stone

128

Radiology

#{149}

suit

in

This

study.

was

not

Geometry

fragmentation

strictly C did

as

true not

me-

effective

as

that

with geometries A and B. GeomA resulted in good fragmentation despite much stone motion. Stones treated with geometry B (although a small group) showed excellent fragmentation with little movement. Comparable results were obtamed in the l5-mL cavity with use of this same geometry. These data suggest that shock waves produce more effective fragmentation if they traverse fluid up to the point of impact with a stone. This may indicate that a supine on oblique treatment position may result in better fragmentation than a prone treatment position with stones resting on the dependent gallbladder wall. The mesults of the limited fragmentation experiments conducted in the 6- and l5-mL cavities suggest that fragmentation can occur if stones are bathed in a small amount of fluid (1-mm fluid interface); greater quantities of surrounding fluid (i-cm fluid inter-

etry

however,

to

cabby contracting the gallbladder reduce stone motion, but if the bladder is contracted too much, effectiveness of fragmentation be compromised. The presence surrounding fluid may promote tation effects, which are known participate in stone fragmentation

stones

move

in the

exposed ometry

surface can

of a stone.

be achieved

This while

be

authors

frag-

thank

Yvonne

preparation

of this

References 1.

Davros

WJ,

Zeman

mimicking the

effects

(abstr). 2.

Choyke

PL,

Pahira

an in vitro 170:39-44. man

BS, Davros

using

4. 5.

7.

8.

to 9.

Davros

WJ,

Nilges

E,

Radiology

WJ, Lack

1989;

EE, Horii

of gallstone and

SC, Ze-

fragments

fluoroscopy:

implica-

tions for monitoring of gallstone lithotripsy. Radiology 1990; 174:343-347. Reichenberger H. Lithotripter systems. Proc IEEE 1988; 76:1236-1246. Coleman AJ, Saunders JE. A survey of the acoustic

6.

gallstones

Renal calculi after US evaluation with

Visibility

ultrasound

Tissue-

l69(P):380.

JH,

phantom.

RK.

BS.

in studying

on

1988;

AJ, Mun 5K. wave lithotripsy:

Garra

Garra

for use

of lithotripsy

Radiology

Dwyer shock

3.

RK,

phantom

output shock Bio!

of commercial wave

1989;

extracor-

lithotripters.

Ultrasound

15:213-227.

Ter Haar G, Daniels 5, Eastaugh KC, Hill CR. Ultrasonically induced cavitation in vivo. Br J Cancer 1982; 45(suppl):l51-i55. Coleman AJ, Saunders JE, Crum LA, Dyson M. Acoustic cavitation generated by an cxtracorporeal shockwave lithotripter. Ultrasound Med Biol 1987; 13:69-76. Trotman BW, Morris TA, Sanchez HM, So!oway RD. Ostrow JD. Pigment versus cholesterol

due

path

effective

The

Med

the impact of shock waves and often recoil. This type of movement is most common for buoyant stones. Fragmentation is most effective when shock waves traverse fluid up to the

fluid

Acknowledgment:

poreal

may gallthe may of cavito

a i-cm

to produce U

Carew for assistance manuscript.

(9). In conclusion,

that

maintained mentation.

face) allow better fragment pulvemization. Theoretically, pharmacobogi-

and fragments position well

be further of fragments gravity.

cholesterol

ponents;

escape

original

geting may by layering their specific

have

the

is reduced a dependent

the

also metargeting

our

in

same time limiting movement of nonbuoyant stones by pinning them against the dependent surface of the gallbladder. Limiting the amount of fluid surrounding a stone (as would occur with pharmacologic contraction of the gallbladder) can reduce stone movement. It is recommended,

cholelithiasis:

identification

and quantification py. Gastroenterology Delius MK, Brendel tion in extracorporeal

by infrared spectrosco1977; 72:495-498. W. Mechanisms of acshockwave lithotrip-

sy.

Delius

In:

Ferrucci

MJ, eds. Biliary Book Medical,

JT,

lithotripsy. 1989; 31-42.

MK,

Burhenne

Chicago:

Year

geat the

July

1990

Relationship between stone motion, targeting, and fragmentation during experimental biliary lithotripsy.

In vitro experiments in an anthropomorphic phantom were performed to clarify the relationship between stone motion, targeting, and fragmentation. Ston...
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