Comparison of radiopaque dye materials for localization of pulmonary nodules before video-assisted thoracic surgery

Abstract

Background:
Although a mixture of pigments and radiopaque materials was reported to be useful material for lung nodule localization, the optimal combination has not been well investigated. The purpose of this study is to evaluate the characteristics of various combinations of pigments and radiopaque materials for localization of pulmonary nodules prior to video-assisted thoracic surgery (VATS).

Methods:
We compared stability, viscosity, and visibility of 6 radiopaque dye materials of (I) mixture of indigo carmine and lipiodol; (II) mixture of indigo carmine, lipiodol, and lidocaine gel; (III) mixture of indocyanine green in water solution (w-ICG) and lipiodol; (IV) mixture of w-ICG, lipiodol, and lidocaine gel; (V) ICG in contrast medium solution (cm-ICG); and (VI) mixture of cm-ICG and lidocaine gel. Stability was evaluated by observing changes in the mixtures in the test tube with time visually and radiographically. Viscosities were measured by rotational viscometer. Materials were injected into an expanded pig-lung phantom, and area on CT and visibility on thoracoscopy camera were evaluated.

Results:
Separation could be seen 15 min after preparation in (I) and (III), and 1 h after preparation in (II), both visually and radiographically. In (IV), separation could be seen on the photographs but not on the X-ray images from 3 h after preparation. (V) and (VI) showed no changes within the 2-day observation period. The viscosities of the materials were (I) 0.2±0.1, (II) 2.9±0.1, (III) 0.2±0.1, (IV) 2.6±0.1, (V) 0.2±0.1, and (VI) 1.2±0.1 dPa·s. The area on CT showed very strong negative correlation with viscosity (r=-0.97). The injection point of each material was easily detected on thoracoscopy camera.

Conclusions:
Radiopaque dye materials appear useful for localizing pulmonary nodules before VATS; their diffusion in the lung parenchyma can be suppressed by using materials of high viscosity.

Full text

© Journal of Thoracic Disease. All rights reserved. J Thorac Dis 2020;12(5):2070-2076 | http://dx.doi.org/10.21037/jtd-19-4057
Introduction
Video-assisted thoracic surgery (VATS) is increasingly being
performed for partial lobectomy for pulmonary nodules
because it is less invasive than thoracotomy and offers the
possibility of therapeutic diagnosis (1,2). However, because
small or ground-grass opacity nodules are difcult to detect
on thoracoscopy, localization is required prior to VATS (3,4).
Several percutaneous localization techniques have been
reported, including hook-wire insertion (5-7), radionuclide
Original Article
Comparison of radiopaque dye materials for localization of
pulmonary nodules before video-assisted thoracic surgery
Takaaki Hasegawa1, Hiroaki Kuroda2, Shohei Chatani1, Yuichiro Furuya1, Yozo Sato1, Hiroaki Iwamasa1,
Tsubasa Asai1, Hideki Yashiro3, Shigeru Matsushima1, Yoshitaka Inaba1
1Department of Diagnostic and Interventional Radiology, 2Department of Thoracic Surgery, Aichi Cancer Center, Nagoya, Aichi, Japan;
3Department of Diagnostic Radiology, Hiratsuka City Hospital, Hiratsuka, Japan
Contributions: (I) Conception and design: T Hasegawa, H Kuroda, H Yashiro; (II) Administrative support: H Kuroda, S Matsushima, Y Inaba; (III)
Provision of study materials or patients: T Hasegawa, H Kuroda, Y Sato; (IV) Collection and assembly of data: T Hasegawa, H Kuroda, S Chatani,
Y Furuya, H Iwamasa, T Asai; (V) Data analysis and interpretation: T Hasegawa, S Chatani, Y Sato; (VI) Manuscript writing: All authors; (VII) Final
approval of manuscript: All authors.
Correspondence to: Takaaki Hasegawa, MD. Department of Diagnostic and Interventional Radiology, Aichi Cancer Center Hospital, 1-1 Kanokoden,
Chikusa-ku, Nagoya, Aichi 464-8681, Japan. Email: t-hasegawa@aichi-cc.jp.
Background: Although a mixture of pigments and radiopaque materials was reported to be useful material
for lung nodule localization, the optimal combination has not been well investigated. The purpose of this
study is to evaluate the characteristics of various combinations of pigments and radiopaque materials for
localization of pulmonary nodules prior to video-assisted thoracic surgery (VATS).
Methods: We compared stability, viscosity, and visibility of 6 radiopaque dye materials of (I) mixture of
indigo carmine and lipiodol; (II) mixture of indigo carmine, lipiodol, and lidocaine gel; (III) mixture of
indocyanine green in water solution (w-ICG) and lipiodol; (IV) mixture of w-ICG, lipiodol, and lidocaine
gel; (V) ICG in contrast medium solution (cm-ICG); and (VI) mixture of cm-ICG and lidocaine gel. Stability
was evaluated by observing changes in the mixtures in the test tube with time visually and radiographically.
Viscosities were measured by rotational viscometer. Materials were injected into an expanded pig-lung
phantom, and area on CT and visibility on thoracoscopy camera were evaluated.
Results: Separation could be seen 15 min after preparation in (I) and (III), and 1 h after preparation in (II),
both visually and radiographically. In (IV), separation could be seen on the photographs but not on the X-ray
images from 3 h after preparation. (V) and (VI) showed no changes within the 2-day observation period.
The viscosities of the materials were (I) 0.2±0.1, (II) 2.9±0.1, (III) 0.2±0.1, (IV) 2.6±0.1, (V) 0.2±0.1, and
(VI) 1.2±0.1 dPa·s. The area on CT showed very strong negative correlation with viscosity (r=−0.97). The
injection point of each material was easily detected on thoracoscopy camera.
Conclusions: Radiopaque dye materials appear useful for localizing pulmonary nodules before VATS;
their diffusion in the lung parenchyma can be suppressed by using materials of high viscosity.
Keywords: Thoracic surgery; video-assisted; pulmonary nodule; coloring agents; contrast media
Submitted Dec 17, 2019. Accepted for publication Mar 27, 2020.
doi: 10.21037/jtd-19-4057
View this article at: http://dx.doi.org/10.21037/jtd-19-4057
2076

2071Journal of Thoracic Disease, Vol 12, No 5 May 2020
© Journal of Thoracic Disease. All rights reserved. J Thorac Dis 2020;12(5):2070-2076 | http://dx.doi.org/10.21037/jtd-19-4057
injection (7,8), contrast medium (lipiodol or barium)
injection (9-11), and dye injection (12-17). However, these
each have advantages and disadvantages, and there is no
consensus regarding which technique is superior for lung
nodule localization.
Recent studies have reported the effectiveness of
lung nodule localization using a mixture of dye material
and contrast medium (18,19). The injection point of
the material can be detected on thoracoscopy by dye
pigmentation on the lung surface. In the event that
the pigmentation is unclear, the injection point can be
confirmed using intraoperative fluoroscopy because the
mixture is radiopaque. However, the optimal combination
of dye and contrast medium for this technique is unknown.
In addition, a previous study has reported the usefulness
of adding lidocaine gel to the mixture (19,20), but the
advantages of doing so have not been well investigated.
The aim of this study was to evaluate and compare the
characteristics of various combinations of pigments and
radiopaque materials and determine the most suitable type
of material for localization of pulmonary nodules prior to
VATS.
Methods
Samples
The following materials were used in the study: Indigo
carmine (Indigocarmine; Daiichi Sankyo Co. Ltd., Tokyo,
Japan), indocyanine green (ICG) (Diagnogreen; Daiichi
Sankyo Co. Ltd.), lipiodol (Lipiodol; Guerbet Japan K.K.,
Tokyo, Japan), nonionic iodine contrast medium (Iopamiron
300; Bayer Yakuhin, Ltd., Osaka, Japan) and lidocaine gel
(Xylocaine Jelly 2%; Aspen Japan K.K., Tokyo, Japan).
ICG was prepared as 1% by dissolving 25 mg of ICG with
2.5 mL distilled water (w-ICG) or with contrast medium
(cm-ICG).
We compared six radiopaque dye materials: (I) 1:1
mixture of indigo carmine and lipiodol; (II) 2:2:1 mixture
of indigo carmine, lipiodol, and lidocaine gel; (III) 1:1
mixture of w-ICG and lipiodol; (IV) 2:2:1 mixture of
w-ICG, lipiodol, and lidocaine gel; (V) cm-ICG; and (VI)
4:1 mixture of cm-ICG and lidocaine gel. Each mixture was
created using a three-way stopcock and two syringes.
Measurement of liquid characteristics
Stability was evaluated by observing changes in the mixtures
in the test tube with time. For each liquid material,
5 mL were added to a test tube, which was photographed
immediately and at 15 min, 30 min, 45 min, 1 h, 3 h, 12 h,
1 day, and 2 days after preparation. An X-ray image was
taken using a fluoroscopic apparatus (Infinix Celeve-I
INFX-8000C; Canon Medical Systems Corp., Otawara,
Japan) at the same timings as the photographs.
Viscosity was evaluated using a rotational viscometer
(Viscotester VT-06; RION Co. Ltd., Kokubunji, Japan).
During the experiments, the room temperature was
maintained at 25 ℃.
Visibility in the lung phantom
We compared the visibility of each liquid material after
its injection into a lung phantom. For each material, a
23-gauge needle (Terumo Cattelan Needle; Terumo Corp.,
Tokyo, Japan) was inserted 1 cm into a pig lung phantom
that had been expanded via an intubation tube under
CT fluoroscopic guidance (Aquilion LB; Canon Medical
Systems Corp., Otawara, Japan) and 0.5 mL of the material
was injected while withdrawing the needle until the material
reached to the lung surface. The CT image was obtained
immediately after injection. The area of the injected
material was measured on the slice showing the widest
extent.
The detectability of the injection point on the lung
surface was evaluated with normal thoracoscopic imaging
and near-infrared uorescence imaging (Image1 STM; Karl
Storz SE & Co. KG, Tuttlingen, Germany).
Statistical analysis
The viscosity of each material was measured five times,
and each material was injected five times into the pig
lung phantom. Data are expressed as the mean ± standard
deviation. The correlation between viscosity and area in the
pig lung phantom was calculated by correlation coefcients.
The correlation was dened as very weak, weak, moderate,
strong, and very strong when the correlation coefficient
value was 0≤r<0.2, 0.2≤r<0.4, 0.4≤r<0.7, 0.7≤r<0.9, and

2072 Hasegawa et al. Comparison of radiopaque dye materials for lung nodule localization
© Journal of Thoracic Disease. All rights reserved. J Thorac Dis 2020;12(5):2070-2076 | http://dx.doi.org/10.21037/jtd-19-4057
B
E
H
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I
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G
0 min
45 min
12 hour
15 min
1 hour
1 day
3 hour
2 days
30 min
I
I
I
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I
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I
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III
III
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III
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V
V
V
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Figure 1 Photographs of each material (A) immediately, (B) 15 min, (C) 30 min, (D) 45 min, (E) 1 h, (F) 3 h, (G) 12 h, (H) 1 day, and (I)
2 days after preparation in the test tube. (I) and (III) showed separation from 15 minutes after preparation. (II) and (IV) showed separation
from 1 hour and 3 hours after preparation, respectively. (V) and (VI) showed no changes within the 2-day observation period.
0.9≤r<1.0, respectively. Statistical analyses were performed
using SPSS software (SPSS for Windows, version 24; IBM,
Armonk, NY, USA).
Results
Characteristics of the liquids
Photographs and X-ray images of the liquid materials
in test tubes are shown in Figures 1 and 2, respectively.
Separation could be seen 15 min after preparation in (I)
and (III), and 1 h after preparation in (II), both visually and
radiographically. In (IV), separation could be seen on the
photographs but not on the X-ray images from 3 h after
preparation. (V) and (VI) showed no changes within the
2-day observation period.
The viscosities of the liquid materials were 0.2±0.1 for (I),
2.9±0.1 for (II), 0.2±0.1 for (III), 2.6±0.1 for (IV), 0.2±0.1
for (V), and 1.2±0.1 dPa·s for (VI).
Visibility in the lung phantom
All materials were visible as areas of high attenuation on the
CT images of the lung phantom obtained after injection
of the liquid materials (Figure 3). The mean areas of the
materials in the CT slices that showed the widest areas
were 77.5±21.7 for (I), 41.8±3.4 for (II), 77.0±15.5 for (III),
45.5±3.5 for (IV), 75.9±14.0 for (V), and 54.1±10.5 mm2 for
(VI). There was very strong negative correlation between
viscosity and area in the pig phantom (r=−0.97, Figure 4)
The puncture point of each material could be detected
easily on the thoracoscopic image (Figure 5A). On near-
infrared fluorescence imaging, ICG fluorescence was
not detected at any injection point, even for materials
containing ICG (Figure 5B).
Discussion
The differences found among the radiopaque dye materials
evaluated in the present study may assist in selecting the
optimal material for localizing pulmonary nodules prior to
VATS.
The mixture of indigo carmine and lipiodol and the
mixture of w-ICG and lipiodol separated in the test tube
only 15 minutes after preparation. Although it is best to
perform preoperative localization immediately before
surgery because the dye becomes less detectable with

2073Journal of Thoracic Disease, Vol 12, No 5 May 2020
© Journal of Thoracic Disease. All rights reserved. J Thorac Dis 2020;12(5):2070-2076 | http://dx.doi.org/10.21037/jtd-19-4057
B
E
H
C
F
I
A
D
G
0 min
45 min
12 hour
15 min
1 hour
1 day
3 hour
2 days
30 min
I
I
I
I
I
I
I
I
I
III
III
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III
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III
III
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V
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V
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II
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II
II
II
IV
IV
IV
IV
IV
IV
IV
IV
IV
VI
VI
VI
VI
VI
VI
VI
VI
VI
Figure 2 X-ray images of each material (A) immediately, (B) 15 min, (C) 30 min, (D) 45 min, (E) 1 h, (F) 3 h, (G) 12 h, (H) 1 day, and (I)
2 days after preparation in the test tube. (I) and (III) showed separation from 15 minutes after preparation. (II) showed separation from
1 hour after preparation. (IV), (V), and (VI) showed no changes within the 2-day observation period.
time (19), the timing of the localization procedure can be
delayed by the availability of the CT and surgery rooms.
Sometimes, the procedure must be performed several days
before surgery. Thus, stability is an important quality for
the material used to localize pulmonary nodules. Recently
Seol et al. reported that the proportion of indigo carmine,
lipiodol, and lidocaine gel of 5:5:2 was most stabilized (20).
We also experimented with not exactly the same but similar
proportion of 2:2:1 and showed good stability. Thus,
these proportions seem to be ideal to create mixture for
preoperative marking.
The pig phantom experiment showed very strong
negative correlation between viscosity and area. In other
words, by using highly viscous materials, diffusion is
suppressed and localization is more likely to be successful.
In addition, high viscosity may act to prevent the flow of
IIII V
II
IV
VI
0 0.5 1 1.5 2 2.5 3 3.5
Viscosity
r=–0.97
(mm2)
I
II
III
V
IV
VI
90
80
70
60
50
40
30
20
10
0
(P)
CT area size
Figure 3 CT image of the pig lung phantom after injection of each
radiopaque dye material. All materials were visualized as areas of
high attenuation. Figure 4 Graph showing the relation between viscosity and
area on CT after injection in the pig lung phantom. Very strong
negative correlation was detected (r=–0.97).

2074 Hasegawa et al. Comparison of radiopaque dye materials for lung nodule localization
© Journal of Thoracic Disease. All rights reserved. J Thorac Dis 2020;12(5):2070-2076 | http://dx.doi.org/10.21037/jtd-19-4057
I
IIII
III V
VII
II IV
IV VI
VI
BA
Figure 5 Thoracoscopic images of the surface of the pig lung phantom after injection of each dye material. (A) The injection point of
each material is easily detected. (B) Near-infrared uorescence image shows no enhancement of injected materials containing ICG. ICG,
indocyanine green.
liquid materials into the vessels. Yoshida et al. reported an
instance of ow of the mixture of dye and contrast medium
into the vessels at the time of percutaneous lung nodule
localization (21). To the best of our knowledge, no studies
have reported ischemic complications following lung
nodule localization using liquid materials, but lipiodol
migration to the brain has been reported after trans-
arterial chemoembolization or lymphatic embolization
using lipiodol (22,23). Use of high viscosity materials might
prevent migration and ischemic complications.
In this study, the puncture point of each material in
the pig lung phantom could be detected easily. However,
as there was no blood flow or respiratory motion in the
phantom, the puncture and injection might have been
easier than in a clinical localization procedure. Moreover,
as we evaluated the appearance immediately after injection,
diffusion might not have advanced in this short time frame.
Indigo carmine and methylene blue are difcult to detect
on lungs with severe anthracosis, in which case they show
as black or dark color tones (12,14). ICG is reported to be
effective for lung surface marking in this condition because
of its green color (14-17). The color tones of the mixtures
of w-ICG and lipiodol (III) and of w-ICG, lipiodol, and
lidocaine gel (IV) were brighter than the other materials on
thoracoscopy after injection in the pig lung phantom. We
hypothesize that these mixtures might be effective also in
lungs with severe anthracosis. Further investigations should
include evaluation of the appearance of the surface markers
after injection in human lung.
Near-infrared fluorescence imaging could not detect
ICG fluorescence at the injection point in the materials
containing ICG. Anayama et al. reported the effectiveness
of near-infrared fluorescence imaging in percutaneous
localization using ICG (15). As ICG shows fluorescence
after binding with plasma proteins such as albumin or
lipoprotein (24), the fluorescence might not have shown
in our lung phantom because there was no blood or lymph
ow. The usefulness of near-infrared uorescence imaging
with materials containing ICG should also be evaluated in
future.
This study has several limitations. First, because we
used a pig lung phantom, we could not evaluate the effects
of blood or lymph flow, or respiratory movement. Vital
reactions were also unclear. As there are some metabolic
differences between humans and pigs, the materials might
show an altered appearance in human lung. Second, as
we did not observe the lung phantom within the thoracic
cavity, we could not evaluate the actual appearance on
VATS. Third, the examination was performed at room
temperature (25 ℃). The characteristics of the liquids might
have been different than at body temperature. Fourth, we
evaluated only the selected materials and mix proportions.
Our selection was based on costs, availability, and technical
simplicity; however, it is not impossible that there might be
more effective materials and mix proportions. Despite these
limitations, the present study revealed various characteristics
of radiopaque dye materials, which will be useful for
selecting the optimal materials for use in localization of
pulmonary nodules prior to VATS.
Acknowledgments
Funding: This work was supported by the Aichi Cancer
Research Foundation.
Footnote
Conicts of Interest: All authors have completed the ICMJE

2075Journal of Thoracic Disease, Vol 12, No 5 May 2020
© Journal of Thoracic Disease. All rights reserved. J Thorac Dis 2020;12(5):2070-2076 | http://dx.doi.org/10.21037/jtd-19-4057
uniform disclosure form (available at http://dx.doi.
org/10.21037/jtd-19-4057). TH reports grants from Aichi
Cancer Research Foundation, during the conduct of the
study. The other authors have no conflicts of interest to
declare.
Ethical Statement: The authors are accountable for all
aspects of the work in ensuring that questions related
to the accuracy or integrity of any part of the work are
appropriately investigated and resolved.
Open Access Statement: This is an Open Access article
distributed in accordance with the Creative Commons
Attribution-NonCommercial-NoDerivs 4.0 International
License (CC BY-NC-ND 4.0), which permits the non-
commercial replication and distribution of the article with
the strict proviso that no changes or edits are made and the
original work is properly cited (including links to both the
formal publication through the relevant DOI and the license).
See: https://creativecommons.org/licenses/by-nc-nd/4.0/.
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Cite this article as: Hasegawa T, Kuroda H, Chatani S, Furuya Y,
Sato Y, Iwamasa H, Asai T, Yashiro H, Matsushima S, Inaba Y.
Comparison of radiopaque dye materials for localization of
pulmonary nodules before video-assisted thoracic surgery. J
Thorac Dis 2020;12(5):2070-2076. doi: 10.21037/jtd-19-4057