Original ar ticle
Image Register ed Gastroscopic Ultrasoun d (IRGUS) in
human subjec ts : a pilot study to assess feasibilit y
3,
2,3,
V. D . Patil, I . S . Spo f ford
5, 4M . B .
Ryan
2,
B . I . Lengyel, R .
Shams6
C . C . Thompson5
Institutions Institutions are listed at the end of ar ticle.
submit ted 20 July 2010
accepted af ter revision 10
December 2010
Bibliography DOI ht
tp://dx.doi.org/ 10.1055/s
-0030-1256241 Published
ahead of print Endoscopy ©
G eorg Thieme Verlag KG
Stut tgar t · New York ISSN
0013- 726X
Correspondi ng author C . C .
Thompso n, MD Brigham and Wo
men’s H ospital Division of
Gastroenterol ogy 75 Francis Stre
et Boston MA 02115 USA Fa x :
+1-617-264-63 42 ccthompson
@par tner s.org
Introduc tion
!
!
"
Authors K. L. Obstein1, R . S . J . Estépar2, J . Jayender3
, K. G . Vosburgh
computed tomography ( C T ) scan. Pat ients who
were scheduled to undergo convent ional EUS were
randomly chosen to undergo their procedure with
IRGUS. Main outcome m easures included feasibilit y,
ease of use, system f unc-
Background and study aims : Endoscopic ult rasound
(EUS) is a complex procedure due to the subtleties of
ult rasound interpretat ion, the small f i el d o f obser
vation, and the uncer taint y o f probe posit ion and or
ientat ion. Animal stud ies demonst rated that Image
Registered Gast roscopic Ult rasound (IRGUS) is
feasible and may b e super ior to convent ional EUS in
ef f icienc y and image interpretat ion. This st udy
explores w hether these att r ibutes o f I RGUS will be
evident in human subjec ts, with the aim of assessing
the feasibilit y, ef fe c t iveness, and ef f icienc y o f I
RGUS in patients with suspected pancreatic lesions.
Patients and methods : This wa s a prospect ive
feasibilit y s t udy at a ter t iar y care academic medical
center in human pat ients with pancreat i c lesions on
Image guidance technolog y has revolut ionized
diagnostic and therapeut ic modalit ies by providing
physicians with the mean s t o n av igate throughout
the body guided by three-dimensio nal (3D) images [1,
2]. Image guidance has been shown to improve t radit
ional surgical disease manageme n t in the abdomen
through more accurate int ra-operative d ef init ion of
therapeut ic targets and by reducing the
aggressiveness o f t reatment [3 – 15]. Image data can
be const r ucted, registered, and displaye d t o provide
t ion, validated task load (TLX) assess ment inst r u
ment , and IRGUS experience quest ionnaire. Results
: Five patients under went IRGUS without complication
. L ocalizat ion of pancreatic lesions wa s
accomplished ef f iciently and accurately (TLX
temporal demand 3.7 %; TLX ef fo r t 8.6 %). Image
synchronizat ion and regist ration wa s accomplished
in real t i me without procedure delay. The mean
assessment score fo r endoscopist experience with
IRGUS wa s posit ive (66.6 ± 29.4). Realt i me display
o f C T i mage s i n the EUS plane and
echoendoscope or ientat ion were the most benef icial
character ist ics. Conclusions : IRGUS appears
feasible and safe i n human subjec ts, and ef f icient
and a ccurate at ident if icat ion of pr obe positi on and
image interpretat ion. IRGUS has the potent ial to
broaden the adoption of EUS techniques and shor ten
EUS lear ning cur ves. Clinical st udies compar ing
IRGUS with convent ional EUS are ongoing.
t ionally, the IRGUS system demonst rated the
potential to shor ten the EUS lear ning cur ve and to
broaden the adoption of the EUS technique by gast
roenterologists [16]. The cur rent st udy aimed to
explore whether the att r ibutes o f the IRGUS system
will be ef fe c t ive, ef f icient , and feasible in human
pat ients with pancreatic lesions who are scheduled to
undergo EUS.
Patients and methods
Pat ients with suspected pancreat i c lesions on
computed tomography ( C T ) scan and who were
scheduled fo r E US were ident if ied fo r inclusion.
From these patients, f i ve who were scheduled to
undergo convent ional EUS were randomly chosen
to undergo their procedure with the IRGUS system (
●Table 1 ). The IRGUS system provides clinicians
with a real-t ime display that shows endoObste in KL et al. Imag e Register ed Gastroscopic U ltrasound (IRGUS) i n h umans … Endoscopy
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easily used and int uit ive suppor t i n endoscopic
procedur es. Image guidance technolog y has been ut
ilized in endoscopy in a porcine model through the
Image Registered Gastroscopic Ul t rasound (IRGUS)
system, w hich wa s found to be super ior to convent
ional endoscopic ult rasound (EUS) in accuracy of
endoscope posit ion and in image interpretat ion [16].
Addi-
Age,
Sex Race I ndication for E US
yea r
s
1 53 Female C au casi an 57 × 43 mm mixed densi t y l e si on i n
total cost, depending on the size of the display, of under US $ 1 9
the h ead o f the p an creas
000. Pr ior to the procedure, a standard pat ient st retcher wa s outf
2 6 8 M al e C au casi a n 39 × 3 2 m m il l - d efi n ed hypodense
mass withi n the hea d of t he pan c reas
3 86 M al e C au casi a n 31 × 14 m m pr e d omi na tely
hypodense l esion i n th e t a il o f t he pa ncr eas extending an t
eriorly
4 40 Fema le C au casi a n 29 mm low a t t en ua tion lesi on with
thick r im and l ack of o bvi ous en ha nce men t in the t ail of t he
pancreas
5 54 M al e C au casi a n 7 m m hyp od ens e l e si on projecting
superiorly in the ne c k o f t he pa ncr eas
scope posit ion and ult rasound plane or ientation within the pr
eprocedure volumetr ic C T images. For these f i ve patients, t wo
synthetic images (a 3D model o f the reference anatomy and a
single oblique planar slice that matches the plane sampled by the
ult rasound t ransducer) were created from the C T images ut ilizing
advanced customized visualization sof t ware (3D Slicer,
www.slicer. org). The IRGUS system uses established techniques
fo r the visualizat ion of the probe posit ion a n d i mage regist
ration, but implements them in real t i me by using recent advances
i n m iniaturized posit ion-t racking technolog y ( microBIR D; As
cension Technolog y Cor p, Milton, Ve r m ont , U SA). The t racking
sensors are small (1 mm in diameter, 6 m m i n length) and have
been tested to meet Inter national Elec t rotechnical Commission
(IEC) 6060101 standards ( ●Fig. 1). The mini-sensors were ster
ilized within 24 h o f the procedure according t o the guidelines fo r
surgical inst r u ments and equipment at our center, by using the
STER R A D sterilization system (A dvanced Sterilization Produc ts,
Ir vine, Califor nia, USA) . All components (t racker system, inter
faces, personal computer wit h displays) are commercially available,
with a
"
Fig. 1 Trac king
Sensor.
it ted with an elec t romagnet i c f lat-plate t ransmit ter ( ●""Fig. 2).
The pat ient wa s the n placed over the embedded t ransmit ter and,
immediatel y p r ior to patient sedat ion in the endoscopy suite, one
miniature sens or wa s attached to the distal t i p o f a standard
linear echoendoscope (GF-UC-140P-AL5, Olympus, To k yo,
Japan) using a combinat ion of Steri-St r ips and Tegader ms (3M,
St . Paul, Minnesota, USA) . The echoendoscope with attached
sens or wa s then inser ted into an Alo ka SSD - a 10 ult rasound
console (Aloka Inc., To k yo, Japan) ( ●Fig. 3 ) and calibrated using
an addit ional nonattached sensor. The calibration def ines the
coordinates of the ult rasound plane with respec t t o the coordinate
frame o f the attached sensor. Calibration wa s per fo r m ed by
touching the distal point of the echoendoscope to the nonattached
sensor. The 3D body model o f the patient wa s then registered to
the C T coordinate system by scanning the pat ient ’s torso with the
nonattached sensor to obtain a ser ies of points. Those points were
aligned to a 3D model o f the patient ’s ski n extrac ted from the C T
using the iterat i ve closest point algorithm [17].
Obstein KL et al. Image Registered G astroscopic U ltrasound (IRGUS) i n humans … Endoscopy
Fig. 2 Standard patient stretcher outfit ted with the elec tromagnetic f
lat-plate transm it ter. a The transmit ter (white arrow) i s p osition ed on the
stretcher. b Padding is then used to cover the transmit ter, m akin g i t
comfo r table for patient s t o lie upon.
Downloaded by: Harvard University Library. Copyrighted material.
Pa
Original ar ticle
Table 1 Patient charac teristics. tient
Fig. 3 Trac king sensor
(arrow) a t tached to the
distal tip of a standard
linear echoendoscope.
The echoendoscope with the IRGUS system wa s then ut ilized fo r the
endoscopic examinat ion of the f i ve patients by a single attending p
hysician sk illed in EUS and advanced endoscopic techniques.
Following each procedure, a validated task load (TLX) assessment inst
r u ment (NA SA Task L oad Index v1.0, NA SA Ames Research
Center, Mof fett Field, Califor nia, USA) and an IRGUS experience
quest ionnaire were completed. The TLX is a subject ive workload
assessment technique commonly used in human factors resea rch to
assess perceived workload based on a m ult idimensional const r u c t
of six subscales: mental demand (h ow much mental and perceptual
ac t ivit y was required?), physical demand (h ow much physica l a c t
ivit y was required?), temporal demand (h ow hur r ied or r ushed wa s
the pace of the task?), per fo r m ance (h ow successf u l were yo u i n
accomplishing w hat yo u were aske d t o do?), ef fo r t (h ow hard did
yo u h ave t o work to accomplish your level of per fo r m ance?), and
fr ust ration level (h ow insecure, discouraged, ir r itated, st ressed,
and annoye d were you?) [18 – 20]. The TLX has been used to assess
workload in t ranspor tation (ground and aviat ion), endurance tasks,
healthcare, teaching, and powe r plants [20 – 27]. The TLX can be we
ighted or unwe ighted, and each subscale ranges from 0 t o 100. We
chose to use the unwe ighted TLX subscale scores i n this research st
udy, a s they have been more commonly used and there is high
correlation bet ween the we ighted and unwe ighted scores [28, 29]. All
cases were recorded in .avi fo r m at, de-ident if ied, and stored on a
secure, encr ypted, workstat ion at the medical center fo r review and
analysis. This research st udy was approve d by the center’s Inst itu t
ional Review Board (IR B) and wa s f unded through a grant from the
National Cancer Inst itute under award R42 C A115112-03, the
National Center fo r I mage Guided Therapy under award U41 R
R019703, and the Center fo r Integration of Medicine and Innovative
Technolog y (CIMI T).
Results
!
The f i ve human
pat ients under
went their
procedure wit h use
of the IRGUS
system safely and
without
complication . All
procedures were
per fo r m ed in the
endoscopy suite
with int ravenous
sedation (propofol
administered by an
"
anesthesiologist [n
= 2 ] o r midazolam
and fentanyl
administered by the
endoscopy team [n
= 3]). Endoscopic
examinat ion
(including Doppler
evaluation) wa s car
r ied out with
complete explorat
ion of the pancreas
(head, body, a nd
tail). L ocalizat ion
of the pancreatic
lesion wa s a
ccomplished ef f
iciently and
accurately ( ●Table
2). Image
synchronizat ion
and regist ration wa
s accomplished by
a shor t calibration
process at the
beginning of the
procedure, pr ior to
the inser t ion of the
echoendoscope.
Synchronization wa
s a c-
Table 2 Unweighted Task Load Index subscale rating for Image Registered
Gastroscope Ultrasound (IRGUS). All subscales range from 0 (“ ver y low ” )to
100 ( “ver y high” ); the exception is the subsca le of “ Per formance” , w here
0 i s “ per fect” and 100 is “failu re ”.
the most benef icial characterist ics of IRGUS ( ●
Discussion
!
In the cur rent st udy, I RGUS appears feasible and safe i n human
subjects . All pat ients tolerated the examinat ion well without pr
ocedural delay. The system did not encumber the endoscopist or
Subscale Unweighted rating, median (range)
the endoscopy suite staf f. The system uses pre-exist ing
equipment in the endoscopy suite (patient st retchers,
M e nta l Dema nd 65 ( 25 – 90) Physic al
echoendoscopes, mouth-guards) and wa s simple to assemble
Dem an d 45 ( 2 0 – 75) Temporal De man d
55 ( 25 – 75) Pe r for man ce 3 0 ( 10 – 80)
immedi atel y p r ior to the procedure without dif f icult y. In shor t ,
Ef for t 35 (20 – 80) Fr us tra t i on 20 ( 15 –
the IRGUS system has the potent ial to be prac t ical in the “
80)
real-life” high-volume endoscopy suite sett ing. The IRGUS system
wa s ef f icient and accurate at ident if ication of probe posit ion and
imag e interpretat ion. This allowe d the endoscopist to quickly
"Figs. 4, 5).complished in 3 – 4 s , and regist ration wa s accomplished
visualize anatomic st r u c t ures without losing echoendoscope
in 2 – 4 m in. Retroper itoneal st r u c t ures remained localized in
image o r ientation (especially when the echoendosonographic
positi on relative t o stable st r u c t ures such as the aor ta. The
image i s degraded by calcif ications, ar t i fa c ts, or poor sur face
precise regist ration of the 3D imag e and endoscope posit ion wa s m contact). This may promote shor tened procedure t i mes, therefore
inimally distor ted fo r s t r uc t ures in the r ight upper quadrant when decreasing sedation requirements, and improving pat ient safet y.
the pat ient wa s i n the lef t-lateral decubit us posit ion. The distort ion Use of the IRGUS system may also lead to improve ment in lesion
or target ing er ror, def ined as the distance bet ween the line def ined target ing fo r echoendoscopic biopsy or f ineneedle aspirat ion, wit
by the needle and the lesion center, wa s 12.23 ± 0.45 mm fo r a
h the potent ial to enhance t issue sampling fo r better diagnosis of
lesion diameter of 21.38 mm. The accuracy of regist ration in the
disease. W hile retroper itoneal str uc t ures remained localized in
pancreas wa s a f fec ted by endoscope location, with improve d regist posit ion, the precise regist ration of the 3D image and endoscope
ration in the stomach compared with regist ration in the duodenum.
positi on were minim ally distor ted (12.23 ± 0.45 mm fo r a lesion
The mean assessment score fo r endoscopist experience with IRGUS diameter of 21.38 mm) fo r s t r uc t ures in the r ight upper
wa s positive (66.6 ± 29.4), and IRGUS wa s f avored as providing an quadrant when the patient wa s i n the lef t-lateral decubit us posit
advantage ove r convent ional EUS (65 ± 26.5). Realt i me display o f ion. This distor t ion or target er ror is wit hin the bounds that can
C T i mage s i n the EUS plane and echoendoscope or ientation were make the guidance
Obste in KL et al. Imag e Register ed Gastroscopic U ltrasound (IRGUS) i n h umans … Endoscopy
Downloaded by: Harvard University Library. Copyrighted material.
Original ar ticle
Obstein KL et al. Image Registered G astroscopic U ltrasound (IRGUS) i n humans …
Endoscopy
Fig. 4 The ac tual Image Registe red Gastroscope
Ultrasound (IRGUS) system real- time d isplay with:
a ultrasound image; b reformat ted computed
tomography ( C T ) i mage in the ultrasound-defined
plane; c 3D C T-based mo del of the patient, all on
the same m onitor for navigation and orientatio n.
The ultrasound image plane (*) cut s direc tly
through the pancreatic les ion (arrows). k, lef t
kidney ; s , spleen.
"Fig. 5 The ac tual Image Registe red Gastroscope
Ultrasound (IRGUS) system real- time d isplay
(different patient than ●Fig. 4). a The endoscopic
ultrasound probe tip, ultrasound plane (US p lane),
pancreatic lesion (PL), fine -needle aspiration
needle (FNA), lungs (blue), aor ta (red), and
kidneys (brown) are clearly visualized. b The
spleen (white arrows) can be seen on the
computed tomography image, 3D model, and
ultrasound image in the same plane as the
ultrasound. c The aor ta is demonstrated in the
image plane (white arrows). d The lef t kidney is
clearly visualized in the image plane (white
arrows). R, right; S, superior.
d material.
Original ar ticle
system clinically
usef ul. A detailed
validation st udy of
target ing accuracy
is cur rently under
way. The precisio n
o f regist ration wa s
also af fe c ted by
endoscope
endolum inal
location, with
improve d regist
ration in the
stomach compared
with regist ration in
the duodenu m. The
3D reconstr uct ion
(segmentation)
process fo r the
procedure is
semi-automat ic (a
super vised
combinat ion of
imaging techniques)
and may b e
accomplished by an
individu al with
basic computer
literacy. Based on
the system used fo
r this research st
udy, the t i me fo r
segmentatio n
ranges from 30 min
t o 1.5 h, depending
on the f ile size of
the images. This t i
me may b e s t
reamlined to
approximatel y 1 5
m in by increasing
computer processor
speed and system
memor y. The 3D
reconstr uc t ion
simplif ies image
interpretat ion (both
C T images and ult
rasound images) fo
r the endoscopist
and may promote
shor tened procedur
e t imes. Due to the
int uit ive nature in
visualizing the 3D
anatomy, no lear
ning cur ve wa s
demonst rated and
no addit ional t
raining in 3D
anatomy i s
necessar y t o use
the image guidance
system. A potent ial
technical limitation
wa s the reg ist
ration er ror of the
synthesized oblique
C T image t o the
ultras ound imag e
planes of
approximatel y 5
mm. IRGUS
capabilit y does not
depend on absolute
imag e regist ration
accuracy, therefore
this minimal shift wa
s found to be suf f
icient , a s m ost
targets fo r o r
ientation are
considerably larger
and slight misregist
rations did not
appear to hamper
the use of the
system. Because
the 3D and C T
imag es of the
system are based
on a pre-procedure
C T scan, they are
static. Therefore,
when a pancreatic c
yst is drained, it
resolve s o n the ult
rasound image but
remains on the 3D
reconst r u c t ion
and C T images. W
hile it would provide
f u r ther infor
mation to have
dynamic radiologic
images, it would
also expose the pat
ient to addit ional
unnecessar y
radiation and be
more dif f icult fo r w
idespread system
adoption. Not h
aving the dynamic
images may also
prove to be an
advantage, as the
endosonographer is
able to visualize the
site of inter vent ion
as it looked before
inter vent ion. This
may assist the
endoscopist in
maintaining or
ientation and
allowing fo r a caref
u l examinat ion of
the area that wa s k
nown to have the f
inding of interest .
We also ant
icipated that the
motion of organs
induced by respirat
ion and gravit y
would compromise
the ut ilit y o f the
compar ison of the
preoperative C T i
mage with the real-t
ime ult rasound
image. This wa s
not the case, as ve
r y lit tle relative m
otion (~ 3 mm) bet
ween the C T
oblique image and
the US image was
obser ved. W hen
the patient wa s i n
the lef t-lateral
decubit us posit ion,
gravit y did cause
minimal distor t ion
bet ween the C T
image and the real-t
ime ult rasound
image for st r u c t
ures that were in
the lef t upper
quadrant . H
owever, all retroper
itoneal st r uct ures
and st r u c t ures in
the r ight side
remained in posit
ion without distort
ion. Finally, the cur
rent st udy wa s a
feasibilit y s t udy of
f ive human patients
and a single
endoscopist . L
arger, randomized,
clinical st udies
compar ing IRGUS
with convent ional
EUS with mult iple
operators are
ongoing. In summar
y, I RGUS appears
feasible and may b
e super ior to
convent ional EUS
in a ccuracy of
probe posit ioning
and in image
interpretat ion;
howe ver, these
compar isons are
limited i n the
current feasibilit y s
t udy. W h e n
consider ing these
results, as well as
the int uit ive
interface and the
ease of
implementation , i t i
s ant icipated that
such systems could
f ind ut ilit y i n m
any diagnostic and
therapeut ic
endoscopic
procedures,
including the potent
ial fo r the
development of new
procedures w ith
novel indicat ions.
These preliminar y
results also sug g
es t that IRGUS
technolog y may
shor ten the EUS
lear ning cur ve and
could broaden the
adopt ion of EUS
techniques.
Original ar ticle
Competing interests : None
Institutions
Surgical Planning Labor ator y, Brigham and Wo men’s H ospital,
Boston, Massachuset t s, USA
Center for Integratio n o f M edicin e and Innovative Technology Image
Guidance Laborator y, Massachuset ts General Hospital, Boston,
Massachuset t s, USA
Division of Pediatric Gastroenterolog y, Massachuset ts General Hospital,
Boston, Massachuset t s , USA
Division of Gastroenterolog y, Brigham and Wo men’s H o spital, Boston,
Massachuset t s, USA
College of Engin eering and Computer Scien ce, Australian National
Universit y, Canberr a, Austra lian Capital Territor y, Australia
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Obste in KL et al. Imag e Register ed Gastroscopic U ltrasound (IRGUS) i n h umans … Endoscopy
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