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E l e c t r o m a g n e t i cN a v i g a t i o n
Yehuda Schwarz, MD, FCCPa,b,*
The first bronchoscopic procedure was performed
in 1897 by Gustav Killian using a laryngoscope and
a rigid esophageal tube to remove a foreign body
from the trachea.1 During the next century, bron-choscopy evolved from being a rigid technique
to one that uses a flexible bronchoscope devel-
oped by Ikeda and colleagues2 in 1968, opening
new horizons in the diagnosis and treatment of
pulmonary diseases. Flexible bronchoscopy is
a minimally invasive procedure, obviating general
anesthesia and eliminating potential associated
complications. New technological developments
emerged in the 80s to improve the yield in diag-
nosis; these innovations included videobroncho-
scopy, endobronchial ultrasonography (EBUS),autofluorescence bronchoscopy, and lately,
narrow-band imaging.3,4 Endoscopic therapeutic
procedures have also kept pace with these devel-
opments, with the introduction of laser photore-
section, cryotherapy, electrocautery, and stent
technology.5 The field of imaging also underwent
technological transformation at the same time.
The incidence of peripheral non-smallcell lung
cancer (NSCL, adenocarcinoma subgroup) has
also increased significantly during the last 30
years; probably because of the introduction and
use of filtered cigarettes and the subsequent distaldelivery of smaller cigarettes particles.
Patients with pulmonary nodules and masses
are routinely referred to pulmonologists, radiolo-
gists, and thoracic surgeons for evaluation and
tissue diagnosis. The rapidly increasing use of
chest computed tomography (CT) for screening
and ruling out pulmonary embolism and various
other indications has led to a significant increase
in the detection of lung nodules.6 More than 6.5
million CT scans of the chest were performed in
the United States alone in 2001, highlighting the
gravity of this clinical scenario.7Choosing the invasive diagnostic procedures to
perform a biopsy for tissue diagnosis in cases of
small peripheral nodules or opacities remains
a clinical challenge. The main options are bron-
choscopy, percutaneous needle aspiration, and
thoracoscopic lung biopsy. Percutaneous needle
aspiration biopsy still plays an important role in
the diagnosis of peripheral lung cancers, yet the
associated pneumothorax (20%34%) and
hemoptysis are unacceptable.811 The high inci-
dence of pneumothorax in percutaneous tech-niques can be partially explained by the fact that
most patients diagnosed with a peripheral lung
lesion also may have some degree of emphysema-
tous changes and poor pulmonary function from
smoking. Thoracoscopic and open surgical biopsy
have the obvious disadvantages of the procedures
being invasive, the patients having to undergo
general anesthesia, and the need to tolerate
single-lung ventilation during the procedure. The
rate of mortality for this procedure can be 0.5%
to 5.3%.12
In patients with a high probability of lung cancerand good lung function, it is often not necessary to
obtain tissue diagnosis. For all others, however,
there is a need for an approach with a low compli-
cation rate, especially in those with multiple
nodules and compromised lung function. Cohort
studies have demonstrated that most nodules so
detected are benign.13 As such, surgery, with its
associated morbidity and mortality, is not
a
Department of Pulmonology, Tel-Aviv Sourasky Medical Center, 6 Weisman Street, Tel-Aviv, 64239, Israelb Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel* Department of Pulmonology, Tel-Aviv Sourasky Medical Center, 6 Weisman Street, Tel-Aviv, 64239, Israel.E-mail address: [email protected]
KEYWORDS
Electromagnetic navigation bronchoscopy Peripheral lung lesion Transbronchial needle aspiration Fiducial markers Stereotactic radiosurgery
Clin Chest Med 31 (2010) 6573doi:10.1016/j.ccm.2009.08.0050272-5231/10/$ see front matter 2010 Published by Elsevier Inc. c
hestmed.t
heclinics.c
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mailto:[email protected]://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/http://chestmed.theclinics.com/mailto:[email protected] -
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indicated for most patients who present with inci-
dentally discovered pulmonary nodules. Tissue
diagnosis, on the other hand, is frequently
essential.12
The conventional flexible bronchoscopy proce-
dure is of limited diagnostic value in peripheral
lung nodules, that is, those located at the periph-eral third of the lung. Biopsy success is further
compromised if the lesion is smaller than 2 cm in
diameter.14 The main limitation of the broncho-
scopic approach is the difficulty in reaching
peripheral lesions with the biopsy tools. The tools
used to obtain biopsy tissue are difficult to steer
to the desired location. Once extended beyond
the tip of the bronchoscope, the physician per-
forming the bronchoscopy is faced with the diffi-
culty of precisely localizing the lesion under
fluoroscopy, whereas the alternatives of CT-
guided bronchoscopy and EBUS are more techni-
cally demanding and require special training.
EBUS enables the operator to see the lesion
but it cannot provide guidelines to the bronchos-
copist for choosing the correct airway to reach
a given peripheral lesion.
Moderate sedation is the current practice in
standard bronchoscopy and the procedure is
safe in the hands of trained personnel. Because
the mortality for bronchoscopy is low (1 in 4000)
and the complication rate for pneumothorax with
transbronchial biopsy is also much lower than allthe other available approaches (
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Fig. 1. (A) The sensor (1 mm diameter and 8 mm length) mounted at the tip of a flexible metal cablethe LG. TheLG has a built-in bending mechanism for active steering in 8 directions that allows bending of the tip. Courtesy of
superDimension, Inc., Minneapolis, MN; with permission. (B) The LG with the sensor is integrated into theextended working channel (EWC). The EWC is left at the desired location once it has been reached with theaid of the sensor, enabling easy access for bronchoscopic accessories. (C) The monitor and computer are placedon a trolley to receive input and visualization of the sensors position on the monitor in all orientations (X, Y,and Z planes and roll, pitch, and yaw movements) in real time. Courtesy of superDimension, Inc., Minneapolis,MN; with permission. (D) Magnetic board placed under the mattress of the bronchoscopy bed.
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direction in which to bend the LG to move toward
the lesion (see Fig. 2). The fully retractable probe is
incorporated into a flexible catheter (the EWC
sheath) that is 130 cm long and 1.9 mm in diam-
eter. Once the area of interest is reached, the LG
is removed leaving the sheath in place. Various
tools and endoscopic accessories can now be
introduced through the catheter: these include
forceps for biopsy, needle, brush or curette, radial
EBUS (used by some researchers for confirmation
of the proximity of the sensor to the nodule), or to
place fiducials surrounding the diagnosed tumors.
Schwarz and colleagues15 performed the first
trial to determine the practicality, accuracy, and
safety of real-time EMB in locating artificial periph-
eral lung lesions in a swine model. The study
showed a registration accuracy of 4.5 mm on
average. No adverse effects, such as pneumo-
thorax or internal bleeding, were encountered in
any animal. The authors concluded that real-timeelectromagnetic positioning with previously
acquired CT scans is an accurate technology
that can augment standard bronchoscopy to
assist in reaching peripheral lung lesions and in
performing biopsies. The first human study was
a prospective controlled clinical investigation that
was opened in June 2003; its result was published
in 2006.16 Of 15 subjects, 13 underwent EMB for
peripheral lung lesions, ranging in size from 1.5
to 5 cm, that were beyond the optical reach of
a bronchoscope. Four of the lesions were in the
left upper lobe, 3 in the right upper lobe; 5 in the
right lower lobe, and 1 in the right middle lobe. A
definitive diagnosis was established in 9 (69%) of
the 13 subjects. No device-related adverse events
were reported during or up to 48 hours after the
study. A parallel study17 was performed in
Germany from July to December, 2003, which
also attained diagnostic yield of 69%. There were
no serious complications. Both studies concluded
that real-time EMB with CT images is a feasible
and safe method for obtaining biopsies of periph-
eral lung lesions.
At the end of the 2006, a larger prospectivestudy involving 60 patients was performed by
Gildea and colleagues18; the results showed an
improved yield of 74%, although 57% of lesions
were smaller than 20 mm in size. Their study
Fig. 2. The monitor depicting the reconstructed 3-dimensional CT scans (coronal, sagittal, and axial views), withthe position of the sensor probe at the tip-view showing a ring with an arrow giving an accurate direction tobend the LG for reaching the targeted lesion and 3-dimensional CT images of the focal sensors area.
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was the first to demonstrate another application
of the navigation system, that is, the diagnosisof mediastinal lymph nodes. By adding lymph
node sampling, they improved the overall patient
diagnosis accuracy to 80.3%. Complications
were limited to pneumothorax, which occurred
in 3.5% of the patients. By giving the bronchos-
copist access to the peripheral lung area, itbecame apparent that there are cases in which
the steerable probe cannot be advanced to all
the lesions, as the bronchus leading to the lesion
may not exist.
Fig. 3. (A) CT data represented by the system software in axial, sagittal, and coronal cuts and VB images. ( B)Carina and major bronchial bifurcations on the VB images marked as reference points for the registration phase.
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Fig. 4. Targeting the mediastinal lymph nodes for TBNA. The software on-demand shows a transparent VBimage of the tracheal wall, thus allowing a view of the previously marked mediastinal lymph node for aspiration.(A) R4 lymph node and (B) lymph node at the aortopulmonary window.
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Makris and colleagues19 described their experi-
ence using the same EMB system in 40 patients
with lesions between 17 to 39 mm in size. They
emphasized that the average of CT-to-body diver-
gence, which represents the radius of the
expected difference in location between the tip
of the sensor probe in the actual patient and where
the tip is expected to be was 4.6015 mm, whereas
the distance between sensor probe and the center
of the lesion was 8.7608 mm. The yield they
reached was 62.5% in 25 out of the 40 cases,
improving if the CT-to-body divergence was less
than 4 mm. The sensitivity and negative predictive
value of EMB for malignancy were 57 and 25%,
respectively.
Eberhardt and colleagues20 reported their expe-
rience with EMB in 89 subjects in whom they
reached a diagnostic yield of 67%, (independent
of lesion size). They had a CT-to-body divergenceof 4.6 1.8 mm (range, 1 to 31). There was no
occurrence of pneumothorax. The mean naviga-
tion error was 9 6 mm. These investigators
also found that size of the lesion was not
a determinant in diagnostic yield, and noted that
the time needed for the electromagnetic naviga-
tion method is around 30 minutes or less. This is
similar to the time for performing bronchoscopy
on patients with interstitial lung diseases and for
obtaining a transbronchial biopsy.
The same group21
compared the added value ofusing the US probe to verify and correct the posi-
tion of the sensor once it had reached the lesion,
as indicated by the software. By doing so, they
were able to correct the position of the sensor
and thereby improved their yield. They concluded
that combined EBUS and EMB enhance the diag-
nostic yield of flexible bronchoscopy in peripheral
lung lesions without compromising patient safety.
Specifically, combined EBUS/EMB had a signifi-
cantly higher diagnostic yield (88%) compared
with EBUS (69%) or EMB alone (59%; P5 .02),
with an overall pneumothorax rate of 6%.Several explanations were given by the users of
the EMB for the failure to reach near 100%
success, one being the absence of an airway
leading to the targeted nodule, another being the
Fig. 5. Registration step: during the bronchoscopy the carina and the major bronchial bifurcations are marked onthe VB images at the planning step in the same position using the sensor applied lightly on the carina mucosa.
Electromagnetic Navigation 71
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lesion extrinsic to an airway making adequate
tissue sampling difficult.
Wilson and Bartlett22 performed a larger EMB
retrospective consecutive study in a community
bronchoscopic unit using rapid on-site cytologic
evaluation (ROSE) on 248 patients referred for
diagnosis of peripheral lesions or mediastinallymph nodes (71). Pneumothorax was reported
in 1.2%, mainly because of the efforts to reach
a diagnosis, which occurred in 70%. Mean size of
targeted peripheral lung lesion (PLL) and lymph no-
des was 2.1 1.4 (SD) cm and 1.8 0.9 (SD) cm,
respectively. The mean follow-up period was 6
5 (SD) months. Fifty-one percent of PLLs were in
the upper lobes; EMB 1 ROSE success was
96% for PLL (34 samples per patient with
forceps and needle). Lymph nodes success
was 94.3% (56 samples with needle biopsy).
Overall diagnosis was made in 173 patients of
the 248 (70%). The investigators used fluoros-
copy to verify the location of the LG and biopsy
forceps.
Therapeutic uses of the EMB have also been
described in the literature. In year 2006, Harms
and colleagues23 applied EMB technology to ther-
apeutic objectives and described the successful
placement of a brachytherapy catheter after navi-
gation to a peripheral, unresectable lung cancer. A
second article showing the applicability of EMB in
therapeutics was published by Kupelian andcolleagues.24 They placed metallic markers for
radiation therapy for a small early-stage lung
cancer using the EMB system transbronchially.
They concluded that the markers placed using
this less invasive method remained stable within
the tumors throughout the treatment duration
without any incidence of pneumothorax as
compared with the 8 out of 15 in whom the trans-
thoracic route was used and who developed the
complication.
Anantham and colleagues
25
reported theirexperience with placement of 39 fiducial markers
in 9 patients. The success rate was 89% (8 of 9
patients). The mean number of fiducial markers
placed in each patient was 4.9 1 1.0 (range, 4
to 6). No migration was encountered in 90% of
the patients.
Weiser and colleagues26 published their experi-
ence in diagnosis and in placing fiducial markers in
and around the lesions to enable stereotactic
radiosurgery. They used ROSE and in case of
a negative result, they continued surgically for
additional biopsies. Krimsky and colleagues27
used the EMB system to tattoo the subpleural
area of the lung nodules after malignant diagnosis
and to perform a therapeutic video-assisted
thoracoscopic surgery.
Electromagnetic navigation bronchoscopy
using overlaid CT images is a safe procedure. It
improves the diagnostic yield of the flexible bron-
choscopy for peripheral lesions and also allows
sampling of the mediastinal lymph nodes. Also,
the system affords several other advantages: there
is no additional radiation, and it has a shortlearning curve. It can also be used for fiducial
marker placement for brachytherapy or stereo-
tactic radiosurgery. It plays a complementary
role to other modalities such as an ultrathin
bronchoscopy or an EBUS.
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