Training benefits of virtual bronchoscopy prior to Endobronchial Ultrasound Guide sheath

doi:10.4236/ojcd.2011.13003

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Open Journal of Clinical Diagnostics, 2011, 1, 9-14

doi:10.4236/ojcd.2011.13003 Published Online December 2011 (http://www.SciRP.org/journal/ojcd/ OJCD

Published Online December 2011 in SciRes. http://www.scirp.org/journal/OJCD

Training benefits of virtual bronchoscopy prior to

endobronchial ultrasound guide sheath

D. Fielding, F. Bashirzadeh, P. Nguyen

Depart ment of Thoracic Medicine , Royal Brisbane an d Womens Hospital, Herst o n, Australia.

Email: [email protected]

Received 4 August 2011; revised 6 September 2011; accepted 16 September 2011.

ABSTRACT

Research questions: How does a virtual broncho-

scopy navigation system (VBNS) improve prediction

of candidate bronchus across a range of doctors in-

vestigating a range of lesions with endobronchial ul-

trasound (EBUS) guide sheath? To what extent do

benefits of virtual bronchoscopic pre-procedure

navigation apply to experienced versus inexperienced

bronchoscopists? Methods: Using archived EBUS

Guide sheath cases, a comparison was made between

identified candidate 4th order bronchus by Comput-

erised tomography (CT) evaluation versus that iden-

tified after virtual path creation. Results: From 7

archived cases, 14 doctors identified the correct

bronchus in 94 of 98 assessments (95%). Percentage

of cases where there was an improvement in localisa-

tion by 2 or more 4th order bronchi was 39.8% over-

all (28.6% - 51.0%), 26.6 for experienced and 53.1 for

inexperienced bronchoscopists (p < 0.02). The abso-

lute mean number of 4th order bronchi different be-

tween CT and VBNS was 2.0 ± 2.6 overall, 1.2 (range

0 - 6) for experienced, and 2.8 (range 0 - 11) for inex-

perienced bronchoscopists. Virtual Path software

calculation time was 8.1 ± 2.7 minutes, compared to

3.6 ± 2.1 minutes by CT. Conclusion: VBNS allowed

rapid accurate assessment with minimal software

training. Greatest benefits in reduction of procedure

time were obtained in inexperienced bronchoscopists,

and VBNS could allow more rapid skill development

in EBUS GS in these doctors.

Keywords: Virtual Bronchoscopy; Lung Neoplasms and

Solitary Pulmonary Nodule/Diagnosis; Transbronchial Bi-

opsy; Three-Dimensional Imaging; Endobronchial Ultra-

sonography

1. INTRODUCTION

Endobronchial Ultrasound Guide sheath (EBUS GS)

sampling of peripheral lung nodules is an accepted

method in bronchoscopy [1,2]. Finding small peripheral

lesions is difficult [3] and EBUS GS has substantially

improved procedural yields [4]. It involves pre proce-

dure scrutiny of the CT chest to predict which bronchus

is likely to harbour the lesion into which the probe is

passed. However due to a number of factors the selection

of the correct bronchus can be difficult. These include

the presence of endobronchial variations, difficulty in

interpreting segmental pulmonary anatomy on CT, and

the experience of the operator [5,6]. In recent years a

number of virtual navigation tools have improved the

ability to extract info rmation from a CT scan which pre-

viously would only have been used for axial and coronal

imaging [7,8]. Now CT reconstruction is used to create

“fly through” images showing endobronchial appear-

ances [9,10]. Some systems have enough definition to

enable correct path tracking in up to 14 branches from

the trachea out to a peripheral lesion [11]. The majority

identify 5 - 8 branches [9]. This information is particu-

larly useful when combined with EBUS GS because the

selection of the bronchus is so critical, thereby reducing

procedure time. This has been demonstrated in a limited

number of centres, usually by operators highly experi-

enced in the field [12,13]. In Asano’s series combining

EBUS GS with a CT virtual bronchoscopy navigation

system (VBNS) the system automatically produced vir-

tual images to a median of fifth- (third- to seventh-) or-

der bronchi [12]. In all patients, the thin bronchoscope

could be guided along the planned route, and observa-

tion to a median of fifth- (third- to seventh-) order bron-

chi was possible. Thirty lesions (93.8%) were success-

fully visualized by EBUS, and 27 (84.4%) could be

pathologically diagnosed. In lesions < or =30 mm in size,

the EBUS visualization yield was 91.7% (22/24), and the

diagnostic yield was 79.2% (19/24). Shinagawa com-

pared use of VBNS with real time in-procedure tracking

with EBUS GS to a historical series of VBNS assisted

biopsies where the bronchoscopist had to remember the

D. Fielding et al. / Open Journal of Clinical Diagnostics 1 (2011) 9-14

images [10]. Here there were slight improvements in

diagnostic sensitivity for a similar sized cohort of lesions,

as well as a 5 minute reduction in the overall procedure

time. This was attributed to the benefits of the VBNS in

quickly identifying the correct bronchus. In a recent

multicentre study by Asan o comparing CT to VB guided

EBUS GS there were significant improvements in diag-

nostic yield (81% for VB versus 67% for CT) and reduc-

tions in examination times [14]. VBNS is not a real time

tracking device in itself, that is it does not track the ac-

tual bronchoscope; however it has the advantage of sim-

plicity in that it is not directly connected to the patient

and does not require additional bronch oscopic hardware.

It is almost real time in the sense that the proceduralist

can easily progress the stored virtual images ahead of the

actual bronchoscopic images to allow the correct path to

be followed. It utilises existing CT imaging.

Learning endobronchial anatomy is difficult, particu-

larly when combined with the challeng e of matching CT

segmental anatomy to endobronchial appearances [9].

Sakurada et al have noted great inter-individual differ-

ences in subsegmental bronchial angulation, and diffi-

culties due to bronchial movement during respiration [5].

Conversely actually doing the biopsies and manipulation

of the EBUS miniprobe in EBUS GS is no different to a

standard transbronchial biopsy, and this part of the pro-

cedure does not require any real new skills [4]. There-

fore for doctors starting out in EBUS GS assistance in

obtaining the correct bronchial anatomy would greatly

enhance their results, and indeed possibly their overall

motivation to learn the technique.

We wanted to determine the practical aspects of a vir-

tual bronchoscopic navigation system- how easy was it

to use, how much time does it take to learn to use it, and

how much longer preparation time is involved. We also

wanted to know to what extent it could quickly bring

inexperienced bronchoscopists up to the level of their

more experienced colleagues in finding the correct

bronchus into which they might pass the EBUS GS

probe.

2. MATERIALS AND METHODS

2.1. Subjects

Subjects were bronchoscopists with an interest in EBUS

guide sheath TBLB. There were seven experienced and

seven inexperienced in EBUS GS. In the experienced

group all were at consultant level and the mean number

EBUS GS cases was 100, range 10 - 250. Inexperienced

bronchoscopists had a year of standard bronchoscopy

training during which they had observed EBUS GS pro-

cedures and were about to start their own procedural

learning of this. All had received endobronchial anatomy

tuition as part of their standard bronchoscopy training.

2.2. Study Design

A prospective single blind crossover study. Only ar-

chived de-identified bronchoscopy data and CT images

were used from procedures which were part of a normal

patient workup and as such no ethics committee submis-

sion was made. A prospective single blind crossover

study. Only archived de-identified bronchoscopy data

and CT images were used from procedures which were

part of a normal patient workup and as such no ethics

committee submission was made.

2.3. Methods

See Figure 1 for a flow diagram of the study design.

There were 7 cases for the doctors to review. Each case

had previously had an EBUS GS procedure so the cor-

rect bronchus was known from that. The task for each

doctor look at the CT scan with the lesion and nominate

the correct bronchus they thought would reach that le-

sion. Then they would use the VBNS software with the

same CT images and use that to nominate the correct

bronchus. They did not use the name of the bronchus,

rather just indicate on a picture of an endobronchial view

which bronchus they had chosen. (The endobronchial

pictures were prepared for each case from fly through

images obtained from the CT of each case. Therefore it

was more of a real life situation, rather than just having

the doctors mark a single standard anatomical chart.)

Each doctor received 45 minutes of tuition in the use of

the VBNS system. Each doctor therefore placed 2 points

on the same bronchial picture for each case—one for the

estimate by CT viewing, the other from viewing the

VBNS fly-through path leading to th e lesion. Th e pictur e

was of all bronchi within the bronchial tree, not just the

likely candidate lobe. Doctors were asked to mark the

bronchus at the 4th order level. Each doctor therefore

marked 7 pictures. These pictures were scored by com-

paring the two marked bronchi to the actual known cor-

rect bronchus—were they the same or different, and if

different by how many 4th order bronchi were they in-

correct? An integer for each doctor for each of the 7

cases was therefore derived. This was 0 if they were

correct and 1, 2 or 3 and so on depending on how many

4th order bronchi they were incorrect by. Within a lobe

the number of bronchi different was counted directly

back towards the nearest correct bronchus. For example

marks on RB1a for CT and RB1b for VBNS would be a

score of 1. Where the identified bronchus was in a dif-

ferent lobe from the correct one then all of the 4 th order

bronchi in that lobe were counted in addition to co unting

the number in the correct lobe. Figure 2 gives an exam-

ple of creation of a path for 1 lesion. A supplemental

video shows the fly through for that case. Figure 3 gives

an example of a score sheet for 1 case for 1 doctor. To

D. Fielding et al. / Open Journal of Clinical Diagnostics 1 (2011) 9-14 11

Figure 1. Study design.

Figure 2. Example of a path created to a lesion in RML using

VBNS software. The CT panels ((a) Axial, (b) Coronal, (c)

Sagittal) show the blue “bronchogram” which shows a bron-

chus leading to the lesion. This blue bronchus is clicked by the

operator which then leads to the creation of the virtual path

down which the operator can scroll ((d) still image from the

flythough). The green dot seen in the still example in lower

right panel indicated the direction of the lesion.

estimate the added time of missing the correct bronchus

by only using CT we timed how long it took to unsuc-

cessfully interrogate a 4th order bronchus in 6 conven-

tional EBUS GS cases, not used in the localisation part

of this study.

2.4. Equipment

CTs were viewed on Osirix free ware, with both axial

and coronal images available. The virtual bronchoscopy

system was Olympus VBNS system (Olympus Tokyo

2008). This system inputs Diagnostic Imaging and Com-

miunication in Medicine (DICOM) CT images of 1mm

thickness overlapping at 0.5 mm intervals. The method

is as described in Asano, but briefly the operator identi-

fies the lower trachea as the start point, then identifies

Figure 3. Figure 2 Example of a score sheet of one doctor for

one case. The marked bronchus by CT (*) is RB3B. The

marked bronchus by VBNS (**) is RB1b. This is a difference

of 4 4th order bronchi and a score of 4 is given.

Table 1. Details of archived cases.

Case numberLesion size, mmLobe 4thorder bronchus

1 70 RLL Rb6a

2 18 Lingula LB4a

3 23 LUL LB 1&2c

4 11 LLL LB 9a

5 20 RML RB4a

6 10 RUL Rb1a

7 29 RUL RB1b

Mean 25.9 ± 20.6

the pulmonary nodule in question, then identifies the

closest bronchus leading to the lesion. The pathway so

derived is then presented as a fly through or as a series

of thumbnail images at branch points. Archived EBUS

GS cases had been performed with Olympus 20 - 20 or

20 - 17 EBUS mini-probes with 4.9 or 6.4 mm diameter

bronchoscopes.

2.5. Analysis

Standard statistical comparison of CT versus VBNS

such as t tests could not be applied because the data were

clumped at zero and skewed above zero.

3. RESULTS

Fourteen doctors examined 7 cases, giving a total of 98

sets of data for comparison between CT and VNBS pre-

dicted bronchus. Table 2 shows the times taken to re-

view CT data and then create a VBNS path. Overall

D. Fielding et al. / Open Journal of Clinical Diagnostics 1 (2011) 9-14

Table 2. Times (in minutes) for review of CT and creation of

VBNS path.

All

Experienced

bronchoscopist Inexperienced

bronchoscopist

CT 3.6 ± 2.1 4.2 ± 2.5 2.9 ± 1.4

VBNS 8.1 ± 2.7 8.8 ± 2.9 7.4 ± 2.4

VBNS added approximately 4 minutes of procedure

preparation time. On average experienced broncho-

scopists spent a minute long er on reviewing the CT scan ,

whereas inexperienced bronchoscopists were on average

a minute faster in deriving the virtual path candidate

bronchus. Overall from the 98, 94 (95%) correctly iden-

tified the candidate bronchus by VBNS. Of the 4 where

this was incorrect there was only a single 4th order

bronchus different. Figure 1 gives an example of the

data sheet for one doctor for one case, with the points for

CT and VBNS identification of the candidate bronchus.

Video 1 (supplemental data) is an attachment of a typical

virtual bronchoscopic path and bronchus identification.

The mean number of 4th order bronchi different between

CT and VBNS was as follows: for all cases it was 1.98 ±

2.6, for experienced bronchoscopists it was 1.2 ± 1.7,

range 0 - 6, and fo r inex p erien ced br onch osco p ists it was

2.8 ± 3.1, range 0 - 11. In a series of 6 cases where ac-

tual EBUS GS was done and a 4th order bronchus was

unsuccessfully interrogated we timed that interrogation

to take 96 seconds ± 62. Using this figure, and applying

it to cases where an incorrect candidate bronchus was

identified, the approximate maximum time difference at

a potential bronchoscopy before the lesion was correctly

found would be 9 minutes (6 × 90 seconds) for experi-

enced bronchoscopists, and potentially 15 minutes (11 ×

90 seconds) for an experienced bronchoscopist. No sig-

nificant differences in improvement were noted when

comparing improvements in localisation of upper lobe

lesions versus middle and lower lobe lesions. From the

98 sets of data, the percentage of cases where there was

an improvement in localisation by 2 or more 4th order

bronchi was a follows: All cases 39.8, experienced

bronchoscopists 26.6 and inexperienced 53.1 (p < 0.02

for experienced versus inexperienced). Using McNemars

test, confidence intervals for all cases showed a range of

28.6% to 51.0%. Therefore it is likely to be a minimum

30% of procedures in a wider population where some

benefit would accrue from using VBNS, in the form of a

change of candidate bronchus of 2 or more 4th order

bronchi.

4. DISCUSSION

The main result of this study was that after a single brief

tuition session with the software the correct candidate

bronchus could be defined by VBNS in 95% of cases.

This was true for both experienced and inexperienced

bronchoscopists and represents quickly acquired accu-

rate information prior to a procedure. In fact inexperi-

enced bronchoscopists on average took a minute less to

gain the information, demonstrating quicker uptake of

use of the software in this group. The degree of im-

provement is modest and as expected there was greater

benefit for inexperienced bronchoscopists. However in

calculating the improvement and a potential time saving

we assume that the bronchoscopist would move towards

rather than away from the correct bronchus, so poten-

tially the improvements could be an underestimate of

benefit. We estimated using the VBNS saves on average

around 2 to 3 minutes. This is in keeping with recently

published data from a group experienced in VB assisted

EBUS GS [10,18]. In the ore recent Shinagawa study

virtual planning did in fact reduce EBUS GS procedure

time by approximately 2 minutes- that study was done

by 3 experienced bronchoscopists and our study pro-

vides unique information about the potential benefit to

trainees as well. As such there would be definite benefits

to patient comfort when the predicted bronchus could be

improved by up to 6 bronchi in experienced and up to 11

bronchi in inexperienced proceduralists. The strength of

our study is the use of actual cases where the gold stan-

dard of comparison was the candidate bronchus which

had localised the lesion in a real bronchoscopy. Other

studies have repeatedly used one endobronchial model

simulation for all cases, only varying the target lesion

[15]. Merritt et al reported a series of image guided

bronchoscopy where lesions had been artificially created

on CT. Having created the lesions the 10 broncho-

scopists then used the same phantom to reach each of the

10 lesions. Our cases had real lesions which were obvi-

ously matched to the real bron chial tree leading to them,

and therefore a fully new virtual bronchial path had to be

created each time. Nonetheless this group still demon-

strated benefits with VB improving overall localisation

from 43% to 94 % for 10 lesions. Interestingly there was

no difference between their inexperienced and experi-

enced group in terms of improvement with addition of

virtual bronchoscopy. What is the trade off for reducing

the procedure time overall by approximately 3 minutes

compared to approximately 8 minutes of VBNS prepara-

tion beforehand? At least part of the preparation time

could be deducted if we subtract the time normally taken

for reading the CT, which here was 4 minutes. In addi-

tion we believe any time saved with the bronchoscop e in

situ constitutes a benefit for a patient, although this of

course is difficult to quantitate. A procedure shortened

by 2 - 3 minutes would likely constitute a comfort bene-

fit to patients, particularly given less manipulation of the

D. Fielding et al. / Open Journal of Clinical Diagnostics 1 (2011) 9-14 13

EBUS GS probe in the bronchus searching for the cor-

rect bronchus.

Overall our inexperienced candidates scored very well

on their knowledge of CT and endobronchial anatomy

before applying VBNS. This may in part reflect their

exposure to others performing the procedure and better

learning tools now available for training bronchoscopists

[16]. In one other series of both experienced and inexpe-

rienced bronchoscopists Dolina reported a simulation

study where 10 lesions were artificially created at endo-

bronchial sites between 3rd and 5th order bronchi [17].

These lesions were therefore considerably easier to iden-

tify and locate than the lesions in this study which were

placed at non bronchoscopically visible locations typi-

cally at 8th order bronchus level. Similar to our study

bronchoscopists recorded their results on a paper deci-

sion sheet in this case it was the bronchoscope path to

the lesion. Results were that without VB assistance the

correct path was only found in 14%, which improved to

49% with the addition of VB assistance. With a com-

puter tracking tool, perhaps more accurate in terms of

the subjects’ decisions, there was an improvement from

40% to 96% in reaching the target. With either method

the basic results for their subjects withou t the aid of vir-

tual bronchoscopy were therefore lower than our group.

A limitations of our study was that only two of the

cases had endobronchial variations, and cases where

more variations had been present may well have shown a

bigger improvement with VBNS. Also we were not test-

ing manipulation of a bronchoscope to arrive at a certain

bronchus as has been done in other mannequin studies.

Sakurada et al. [5] noted that some bronchi are more

difficult to gain access to such as RB3a and LB 1 & 2c,

however we did not include manual dexterity for access

in this study. In terms of the input of CT data into the

VBNS system a significant number of cases could not be

performed because the CT had not been acquired with

thin enough slices, thereby severely reducing definition

of virtual images.

In summary we have showed virtual bronchoscopy is

an easily aquired skill which improves bronchial local-

isation, even with a high baseline knowledge of anatomy.

Inexperienced bronchoscopists quickly acquire the skill

and this affords them greater potential in-procedure

benefit. This is in line with the use of virtual tools for a

range of bronchoscopic skills [18]. We believe this sim-

ple method should be available to all proceduralists do-

ing EBUS GS, but particularly inexperienced broncho-

scopists as a compliment to their learning of the EBUS

GS method.

5. ACKNOWLEDGEMENTS

Supply of VNS software prototype by Olympus Medical Systems

Tokyo.

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