DOI:10.2214/AJR.07.3411
AJR 2008; 191:W112-W119
© American Roentgen Ray Society
Low-Dose MDCT for Surveillance of Patients with Severe Homogeneous Emphysema After Bronchoscopic Airway Bypass
Aleksandar Grgic1,2,
Heinrike Wilkens3,
Reinhard Kubale4,
Andreas Gröschel3,
Arno Buecker2 and
Gerhard W. Sybrecht3
1 Department of Nuclear Medicine, Universitätsklinikum des Saarlandes,
Kirrbergerstr. 1, 66421 Homburg, Saarland, Germany.
2 Department of Diagnostic and Interventional Radiology, University Hospital
Saarland, Homburg, Saarland, Germany.
3 Department of Internal Medicine V, University Hospital Saarland, Homburg,
Saarland, Germany.
4 Institute of Radiology and Nuclear Medicine, Pirmasens, Germany.
Received November 12, 2007;
accepted after revision April 4, 2008.
Address correspondence to A. Grgic
(aleksandar.grgic{at}gmx.de).
WEB
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Abstract
OBJECTIVE. The purpose of this study was to evaluate the usefulness
of low-dose MDCT for radiologic monitoring of patients who have undergone
placement of bronchial stents for airway bypass.
SUBJECTS AND METHODS. In a prospective study, seven patients
underwent MDCT according to a low-dose protocol (40 mAs, 120 kVp) before and
after stent placement. The positions of the stents in the segmental bronchi
were analyzed and compared with the bronchoscopic findings, which were
reference standard. Patency versus lack of patency of stents was classified
with five levels of confidence, and a definitive diagnosis was assigned to
each stent. Prediction of stent dislodgment, follow-up findings, and
complications occurring during the observation period were recorded. Consensus
reading was performed by two radiologists. Statistical analysis was conducted
by receiver operating characteristic analysis or four-field table.
RESULTS. Seven patients underwent implantation of 37 stents (mean, 5
± 2 [SD] stents per patient; range, 2–8 stents). The area under
the curve for differentiating patent from occluded stents was 0.995 with
resulting sensitivity and specificity of 86.5% and 98.1%. The correct
diagnosis of patency was established with MDCT for all but one stent
(sensitivity, 94.7%; specificity, 100%). Sensitivity and specificity for
prediction of dislodgment were 80% and 91%. Five stents were not identified
during inspection bronchoscopy but were found in a regular position at MDCT.
Three instances of minor bleeding and one of pneumothorax resolved
spontaneously. The mean effective dose of the scan was 1.3 ± 0.6
mSv.
CONCLUSION. Low-dose MDCT is feasible for radiologic monitoring
after airway bypass procedure.
Keywords: airway bypass procedure • bronchoscopic lung volume reduction • chronic obstructive pulmonary disease • COPD • low-dose CT • lung • pulmonary emphysema
Introduction
Despite medical and surgical treatment, pulmonary emphysema is associated
with high morbidity and mortality
[1,
2]. It is characterized by
irreversible destruction of lung parenchyma distal to the terminal
bronchioles. The destruction of lung parenchyma occurs concomitantly with
marked enhancement of collateral ventilation. Collateral ventilation may be
essential for redistribution of airflow beyond obstructed terminal airways
[3]. Development and
reinforcement of passages between the lung parenchyma and the lateral chest
wall (i.e., bypassing the obstructed small airways) should allow trapped gas
to leave the lung, may alleviate hyperinflation, and may improve respiratory
mechanics [4]. Because
management can be difficult
[5], bronchial fenestration has
been proposed for ventilation of emphysematous air spaces into the main
airways [6].
In airway bypass procedures, stents are introduced bronchoscopically by
establishment of fenestrations in the bronchial wall
[7]. In a study
[7] of 12 human lungs in which
an airway bypass procedure was performed after explantation, it was found that
the more passages made, the greater was the improvement in forced expiratory
volume in 1 second. Two studies
[8,
9] showed that airway bypass is
feasible and safe in animal experiments. In another study
[10], which involved 35
patients with severe emphysema, airway bypass reduced hyperinflation and
dyspnea. Improvement correlated with the degree of pretreatment
hyperinflation. A concern, how ever, is keeping stents patent, which can be
realized with topical application of antiproliferative or antiinflammatory
agents [8] or with use of
paclitaxel-eluting stents
[9].
In the clinical setting, frequent bronchoscopic procedures have been found
to prolong hospital stays. Therefore, follow-up bronchoscopy has been
eliminated in the evaluation of patients undergoing investigational airway
bypass [10]. It would be ideal
either to monitor patients noninvasively or to acquire reliable information
before bronchoscopy to minimize intervention time. The repetitive use of
standard-dose CT for follow-up of emphysema management is limited by the risk
of administration of a radiation dose of 8–12 mSv for each CT
examination [11]. Low-dose CT,
in which the radiation dose is six- to 10-fold less than in conventional CT
[12,
13], has been evaluated for
lung cancer screening and has substantial potential value for evaluation of
emphysema patients [14]. The
aim of this study was to evaluate the feasibility of thin-section low-dose
MDCT in the radiologic monitoring of patients after placement of bronchial
stents for airway bypass.
Subjects and Methods
Patients
The data collected in this study originated from a feasibility study of the
use of a drug-eluting stent system in patients with emphysema
(ClinicalTrials.gov,
NCT00207337). After ethical committee review and approval, written informed
consent was obtained from all patients. From November 2004 to October 2005,
seven patients were included prospectively and underwent airway bypass
procedures to manage severe emphysema. The inclusion and exclusion criteria
are shown in Table 1. The mean
age was 66 ± 7 (SD) years (range, 54–76 years). Despite optimal
medical therapy, all patients had severe dyspnea with a modified Medical
Research Council dyspnea score of 2.9 ± 0.45.
The patients had severe airway obstruction documented with serial lung
function tests showing a forced expiratory volume in 1 second of 0.61 ±
0.1 L (20.7% ± 4.6% of predicted value). All patients had severe
hyperinflation of the lungs with a total lung capacity of 7.57 ± 0.9 L
(135.7% ± 3.3% of predicted value), a residual volume of 265.4%
± 24.3% of predicted value, and a residual volume to total lung
capacity ratio of 73.41 ± 4.9. All subjects had been smokers. The
demographic and functional data are shown in
Table 2.
Airway Bypass Procedure
The airway bypass procedure has been described in detail
[10]. The procedure was
performed under general anesthesia with controlled mechanical ventilation. A
stent introduction system (Exhale System, Broncus Technologies) was used to
insert the stents through the working channel of a flexible bronchoscope in
the following manner: a Doppler probe was used to scan an appropriate site for
puncture and to avoid accidental puncture of the vessels; fenestration was
performed whereby the transbronchial dila tion needle, which is a
needle–dilation balloon catheter combination for passage establishment
and dilation, was introduced through the bronchial wall; after a channel was
made, the drug-eluting stent was introduced and deployed with an inflation
syringe. Efforts were made to place a minimum of two stents in each upper and
lower lobe. The middle lobe was not treated. After stent placement and
recovery from anesthesia, a routine chest radiograph was obtained. The patient
was sent to the hospital room the same day. IV antibiotics were administered
intraoperatively and for the first 24 hours after the procedure until
discharge from the hospital. At discharge, antibiotic administration was
changed to the oral route for 7 consecutive days.
Inspection Bronchoscopy
The patients were scheduled to undergo inspection bronchoscopy with a
flexible video bronchoscope 1 month, 3 months, 6 months, and 1 year after the
procedure. All bronchoscopic proce dures were performed by two experienced
bron choscopists (both with more than 10 years of experience) working
together. Patency was evaluated in consensus by means of inspection, and
stents were rated patent, nonpatent, or not visible. Occluded stents were
defined as stents obstruct ed with granulation tissue or mucus. Both
bronchoscopists were blinded to the results of MDCT. Because the study
protocol was amended during the study period as a consequence of acute
exacerbations that occurred immediately after bronchoscopy, four of seven
patients underwent bronchoscopy and MDCT 1 month after the airway bypass
procedure. Three months after the procedure, one patient underwent
bronchoscopy but without MDCT correlation. Six months after the procedure, six
patients underwent inspection bronchoscopy; 1 year after the procedure two
patients underwent bronchoscopic follow-up. In summary, findings at 12
bronchoscopic examinations were directly comparable with the results of MDCT
in seven patients. Among the seven patients included in the study, two
patients had three MDCT–bronchoscopy correlations. Among the other five
patients, one patient had two correlations and four patients had one
correlation.
MDCT
All MDCT scans were obtained with a commercially available four-channel
MDCT scanner (MX 8000, Philips Healthcare). The scans were acquired during
full inspiration in the supine position in the caudocranial direction covering
the entire lung volume. No IV contrast medium was given. For all scans, 1-mm
collimation and a low-dose protocol with the following para meters was used:
120 kV, 40 mAs, 0.5-second rotation time, 4 x 1 mm collimation, pitch of
1.75, reconstruction of 1.25-mm-thick slices with reconstruction increment of
0.6 mm (overlapping images). For the reconstruction, a 512 x 512 matrix
and high-spatial-frequency reconstruction algorithm (bone algorithm) were
used. According to the study protocol, all scans had to be obtained within 2
months before the procedure (baseline scan) and during the first week and 1,
3, 6, and 12 months after the procedure (follow-up scans). A computer program
(CT-Expo, version 1.5 D) was used to calculate the effective dose for every
protocol with a thoracic length of 30 cm
[15].
Evaluation of MDCT Scans
All images were analyzed by two fully trained faculty radiologists working
together who had more than 8 years experience in interpreting chest CT scans.
Rare disagreements were resolved with a second look at the CT scans in all
cases. Both reviewers were aware of the diagnosis of emphysema but were
blinded to the results of broncho scopy and had no knowledge of the exact
location of or number of stents implanted. For characteriz ation of the
appearance of stents on MDCT, one unimplanted expanded stent was scanned
several times in different substances (sponge, plastic box, ball filled with
water) and positions (Fig. 1A,
1B,
1C,
1D).
Reviewers were required to assign a definite diagnosis to each stent. A
stent with a clearly open lumen with air content was considered patent. All
stents without a clearly open lumen were considered occluded. If bronchoscopic
findings confirmed the diagnosis in cases of nonpatent stent, the finding was
rated true-positive. If bronchoscopic findings confirmed the diagnosis of open
stent, the finding was rated true-negative. If bronchoscopy revealed a
nonpatent stent rather than a presumed patent stent, the finding was rated
false-negative. If bronchoscopy revealed a patent stent rather than a presumed
nonpatent stent, the finding was rated false-positive.
Prediction of Stent Dislodgment with Initial CT Results
The reviewers assessed the position of the stent in regard to the bronchial
wall at the first postprocedure MDCT examination to determine the probability
of stent dislodgment and expectoration. Stent dislodgment was determined on
the basis of subsequent imaging findings. If a stent was not perpendicular to
the bronchial wall (Fig. 2A,
2B) and was expectorated during
the follow-up period, the finding was rated true-positive. If a stent was
perpendicular to the bronchial wall and was not dislodged during the follow-up
period, the finding was rated true-negative. If a stent was not perpendicular
to the bronchial wall but was not dislodged during the follow-up period, the
finding was rated false-positive. If a stent was perpendicular to the
bronchial wall but was dislodged during the follow-up period, the finding was
rated false-negative.
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Fig. 2A —76-year-old woman with inappropriate positioning of stent.
Paraaxial multiplanar reformations in bone (A) and lung (B)
windows show inappropriate positioning of stent (arrow) in relation
to bronchial wall 1 week after stent implantation. At examination 1 month
after stent placement, stent was dislodged and expectorated (not shown).
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Fig. 2B —76-year-old woman with inappropriate positioning of stent.
Paraaxial multiplanar reformations in bone (A) and lung (B)
windows show inappropriate positioning of stent (arrow) in relation
to bronchial wall 1 week after stent implantation. At examination 1 month
after stent placement, stent was dislodged and expectorated (not shown).
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Complications and Follow-Up
We evaluated all complications occurring during or after the airway bypass
procedure, including pneumothorax, bleeding, and infiltration. The frequency
with which stents escaped bron choscopic detection was assessed.
Statistical Analysis
For differentiation of patent from nonpatent stents, receiver operating
characteristic analysis was performed with five levels of confidence. Level 1
indicated a definitely patent stent (Figs.
3A and
3B); level 2, probably patent
stent not perpendicular to the bronchial wall but with clearly open lumen
(Figs. 4A and
4B); level 3, not sure, stent
not perpendicular to the bronchial wall without clearly open lumen or stent
not directed to the lung parenchyma and surrounded by lung vessels or bronchi
(Fig. 5A,
5B); level 4, probably
nonfunctioning stent partly occluded by granu la tion tissue (Figs.
4C and
4D); level 5, defini tely
nonfunctioning stent completely occluded by granulation tissue (Figs.
3C and
3D).
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Fig. 3A —55-year-old woman with level 1 and level 5 stents.
Parasagittal multiplanar reformations in bone (A) and lung (B)
windows show correctly positioned (level 1) stent (arrow) in relation
to bronchial wall with clearly open lumen.
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Fig. 3B —55-year-old woman with level 1 and level 5 stents.
Parasagittal multiplanar reformations in bone (A) and lung (B)
windows show correctly positioned (level 1) stent (arrow) in relation
to bronchial wall with clearly open lumen.
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Fig. 4A —63-year-old man with emphysema and level 2 and level 4
stents. Paraaxial multiplanar reformations in bone (A) and lung
(B) windows show stent (arrow) is not perpendicular to
bronchial wall but has unequivocally open lumen (level 2).
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Fig. 4B —63-year-old man with emphysema and level 2 and level 4
stents. Paraaxial multiplanar reformations in bone (A) and lung
(B) windows show stent (arrow) is not perpendicular to
bronchial wall but has unequivocally open lumen (level 2).
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Fig. 5A —65-year-old woman with emphysema and level 3 stent. Paraaxial
multiplanar reformations in bone (A) and lung (B) windows show
stent (arrow) not perpendicular to bronchial wall in right lower lobe
and not clearly directed to lung parenchyma.
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Fig. 5B —65-year-old woman with emphysema and level 3 stent. Paraaxial
multiplanar reformations in bone (A) and lung (B) windows show
stent (arrow) not perpendicular to bronchial wall in right lower lobe
and not clearly directed to lung parenchyma.
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Fig. 4C —63-year-old man with emphysema and level 2 and level 4
stents. Paraaxial multiplanar reformations in bone (C) and lung
(D) windows show probably nonfunctioning (level 4) stent
(arrow) in anterior aspect of anterior basal segmental bronchus of
right lower lobe without unequivocally open lumen. Granulation tissue was
confirmed at bronchoscopy. Stent (arrowhead) in posterior basal
segmental bronchus of right lower lobe has unequivocally open lumen (level
1).
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Fig. 4D —63-year-old man with emphysema and level 2 and level 4
stents. Paraaxial multiplanar reformations in bone (C) and lung
(D) windows show probably nonfunctioning (level 4) stent
(arrow) in anterior aspect of anterior basal segmental bronchus of
right lower lobe without unequivocally open lumen. Granulation tissue was
confirmed at bronchoscopy. Stent (arrowhead) in posterior basal
segmental bronchus of right lower lobe has unequivocally open lumen (level
1).
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Fig. 3C —55-year-old woman with level 1 and level 5 stents. Curved
planar multiplanar reformations along upper lobe bronchus in bone (C)
and lung (D) windows show definitively occluded (level 5) stent
(arrow) completely surrounded by granulation tissue.
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Fig. 3D —55-year-old woman with level 1 and level 5 stents. Curved
planar multiplanar reformations along upper lobe bronchus in bone (C)
and lung (D) windows show definitively occluded (level 5) stent
(arrow) completely surrounded by granulation tissue.
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Area under the curve was calculated with logistic regression analysis. The
optimal cutoff value was defined as the value that maximized sensitivity and
specificity. The corresponding 95% CI was obtained for each sensitivity and
specificity at each level of confidence. Descriptive statistics were used to
analyze the intervals between stent introduction and CT and the intervals
between inspection bronchoscopy and CT. A four-field table was used to predict
stent dislodgment. All values are expressed as mean ± SD. All tests
were performed at the 5% level of statistical significance. SPSS software
(SPSS 11, SPSS) was used for statistical analysis.
Results
MDCT
Baseline scans were obtained a mean of 23.1 ± 25 days (range,
1–60 days) before the procedure. Follow-up scans were obtained 3
± 2 days (range, 1–7 days) and 28.5 ± 4 days (range,
23–35 days) after the procedure for all patients. Two patients underwent
additional follow-up MDCT 88.5 ± 6 days (range, 84–93 days) after
the procedure; five patients did not undergo MDCT in this period. Six patients
underwent MDCT 186.5 ± 23 days (range, 148–213 days) after the
procedure. One patient refused MDCT in the short period after she had
undergone coronary angiography for angina pectoris. Six patients underwent
MDCT 432.3 ± 17 days (range, 416–450 days) after the procedure.
Table 3 shows an overview of
stent distribution in every patient, and
Table 4 shows the corre lation
between MDCT and bronchoscopic findings. The mean calculated effective dose of
the scans was 1.3 ± 0.6 mSv (range, 1.2–1.9 mSv).
Follow-Up During First Week After Stent Introduction
A total of 37 stents were inserted in seven patients (mean, 5 ± 2
stents per patient) (Tables 3
and 4). One stent lost between
the procedure and the first MDCT examination after the procedure was not
visualized on MDCT. Another stent was found in the left main bronchus,
although this stent had been placed in the left lower lobe. The stent was
expectorated several hours after the procedure. One stent was lost in the lung
parenchyma during placement, and this malposition was confirmed on MDCT. Thus
a total of 36 stents were visualized on MDCT.
Follow-Up in First Month After Stent Introduction
At examination 1 month after the procedure, 32 (86%) of the 37 stents
originally implanted were in situ. The close correlation between the
bronchoscopic and MDCT findings in four patients showed that 20 of the
originally implanted 24 stents were in situ. One of these stents was located
in the lung parenchyma and was not functioning, and seven of 20 stents were
found occluded at bronchoscopic evaluation. Four stents were missed at
bronchoscopic evaluation.
Follow-Up 6 Months After Stent Introduction
Six months after the procedure, six patients underwent MDCT, and direct
correlation between MDCT and bronchoscopic findings was possible in these six
patients. Stents in two other patients had been dislodged. Eleven (48%) of the
23 stents seen at bronchoscopy were occluded. One of stents was missed during
bronchoscopy, and one was lost in the lung parenchyma.
Follow-Up 1 Year After Stent Introduction
Direct comparison between bronchoscopic and MDCT findings was available for
two patients (both with seven stents), and six patients underwent MDCT (Tables
3 and
4). Five additional stents were
dislodged; one stent was dislocated in the lung parenchyma. Bronchoscopic
evaluation showed that one stent was occluded.
Patency of Stents
The position and patency of the 45 stents seen at bronchoscopy were
correlated with the results of MDCT. According to bronchoscopic findings, 19
(42%) of the stents were occluded and 26 stents were patent. According to the
MDCT findings, 21 stents were classified level 1; four stents, level 2; six
stents, level 3; four stents, level 4; and 10 stents, level 5. In
differentiation of patent and nonpatent stents, the receiver operating
characteristic analysis (Fig.
6) resulted in an area under the curve of 0.995 (95% CI,
0.982–1.008). The results were within the corresponding 95% CI. The
cutoff value that optimized sensitivity and specificity was level 3, meaning
that all stents characterized level 3 (stent not perpendicular to the
bronchial wall without clearly open lumen or stent not directed to the lung
parenchyma and surrounded by the lung vessels or bronchi), level 4 (probably
not functioning stent partly occluded by granulation tissue), and level 5
(definitely not functioning stent completely occluded by granulation tissue)
were considered not patent. At this level, sensitivity was 86.5% and
specificity was 98.1%.
For exact diagnosis of stent patency, MDCT correctly depicted all but one
stent (sensitivity, 94.7% [18 of 19]; specificity, 100% [26 of 26]). The
positive predictive value was 100% (18 of 18), and the negative predictive
value was 96.2% (26 of 27). The one stent not accurately depicted was
surrounded by pulmonary vessels and bronchi (Fig.
7A,
7B). On a perpatient basis,
the patency of the stents was accurately described in six of seven
patients.
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Fig. 7A —55-year-old woman with stent surrounded by vessels.
Paracoronal multiplanar reformations in bone (A) and lung (B)
windows show stent (arrowhead) positioned close to bronchi and
vessels. Although appropriately positioned in relation to bronchial wall,
stent is covered by lung tissue (confirmed at bronchoscopy) and therefore is
not functioning. Proximity to pulmonary vessels and bronchi can prompt
radiologist to diagnose nonfunctioning stent.
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Fig. 7B —55-year-old woman with stent surrounded by vessels.
Paracoronal multiplanar reformations in bone (A) and lung (B)
windows show stent (arrowhead) positioned close to bronchi and
vessels. Although appropriately positioned in relation to bronchial wall,
stent is covered by lung tissue (confirmed at bronchoscopy) and therefore is
not functioning. Proximity to pulmonary vessels and bronchi can prompt
radiologist to diagnose nonfunctioning stent.
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Prediction of Stent Dislodgment on Early Postprocedure CT
At MDCT in the first week after the procedure, both reviewers assessed the
position of the stent in regard to the bronchial wall. Although 37 stents had
been introduced, 34 stents were used for the final calculation. Two stents
were excluded because they were dislodged before MDCT, and a third stent was
located in the parenchyma. In prediction of stent dislodgment, there were
eight true-positive and two false-negative findings, resulting in a
sensitivity of 80% (eight of 10). There were two false-positive findings,
resulting in a specificity of 91% (22 of 24). The positive predictive value
was 80% (eight of 10), and the negative predictive value was 91% (22 of
24).
Complications After Airway Bypass Procedure
Three patients had minor bleeding due to incidental puncture of small
pulmonary vessels during the airway bypass procedure. CT showed ground-glass
opacity in the corresponding lung segments in all three cases. One small
left-sided pneumothorax resolved spontaneously. Among the five stents not
reassessed at bronchoscopy, two were located in the left upper lobe, two were
located in the right lower lobe, and one was located in the left lower
lobe.
Discussion
The results of this study show for the first time, to our knowledge, that
low-dose MDCT is suitable for noninvasive monitoring of airway bypass
procedure. With MDCT it is possible to differentiate patent and occluded
stents. In the definite classification of stent patency, MDCT had excellent
specificity and positive predictive value and good negative predictive value
and sensitivity. Even in prediction of dislodgment of stents, MDCT had good
specificity and negative predictive value. In terms of reidentification of
stents, MDCT was better than bronchoscopy.
Surgical reduction of lung volume has been found effective in certain
subgroups of patients with severe emphysema. This procedure, however, is
associated with a perioperative mortality of 4–5% and lack of clinical
improvement in approximately 30% of patients. Therefore, there is great
interest in development of less invasive techniques
[16–18]
of endobronchial lung volume reduction with the aim of decreasing
procedure-related morbidity and mortality and increasing the potential for
reversibility in cases of lack of response. Several bronchoscopically placed
devices for endobronchial lung volume reduction are under investigation. The
criteria for selecting patients for the various devices and for measuring
improvement are being established
[18,
19]. In patients with
heterogeneous emphysema and predominantly upper zone disease, the results of
endobronchial valve placement are promising; it is not certain, however,
whether this technique is truly effective
[18].
Patients with homogeneous emphysema, who are not candidates for surgical
lung volume reduction [2] or
endobronchial valves, may benefit from an airway bypass procedure. Unlike
endobronchial valve procedures, the airway bypass technique entails use of
collateral ventilation to reduce hyperinflation, to improve expiratory flow,
and to improve breathing mechanics
[7]. A multicenter feasibility
study with paclitaxel-eluting stents showed significant reduction of
hyperinflation and dyspnea in patients with homogeneous distribution of
emphysema [10].
During the study of Cardoso et al.
[10], several patients had
prolonged hospital stays because of episodes of exacerbation after follow-up
bronchoscopy for evaluation of stent position and patency. The potential of
MDCT in location and differentiation of patent and nonpatent stents therefore
was evaluated to obviate bronchoscopy. Receiver operating characteristic
analysis revealed a sensitivity of 86.5% and specificity of 98.1%. In reviewer
confidence, MDCT had an optimal cutoff at a confidence level of 3.
Although five of the implanted stents were not found at bronchoscopy, all
five were considered in place at MDCT, which further confirmed the added value
of MDCT. Inspection bronchoscopy was performed with flexible bronchoscopy and
spontaneous ventilation, whereas stent placement had been performed under
general anesthesia to allow better inspection of the bronchial tree with
positive pressure ventilation, preventing airway collapse. With general
anesthesia and positive pressure ventilation, all stents probably would have
been depicted, but the procedure would have been substantially more invasive
for the patient and introduced the risk of general anesthesia. With newer
techniques, such as virtual bronchoscopy, the possibility that CT may yield
detailed roadmaps leading automatically to segmental bronchi is being explored
[20,
21].
Because all stents can be directly visualized with MDCT, it is possible to
determine the position of a stent in regard to the bronchial wall. We
evaluated the utility of MDCT in prediction of dislodgment of stents in
appropriate positions up to 1 week after the procedure. The specificity and
negative predictive value were high (both 91%), and the sensitivity and
positive predictive value were moderate (both 80%). This result probably
occurred because the patient group was rather small. An interesting finding
was that the two cases of false-positive results involved stents not
perpendicular to the bronchial wall that were not patent 6 months after the
procedure.
The complex relations among radiation exposure, diagnostic accuracy, and
image quality must be analyzed and optimized for adequate, clinically useful
diagnosis and for avoidance of loss of diagnostic information
[11]. Because repeating CT up
to five times in 1 year is ethically unacceptable, we chose low-dose scanning
to minimize the radiation dose. With the protocol described, it is possible to
reduce the mean effective dose to 20–32% of the dose used in routine
chest CT examinations [11]
without substantially compromising image quality and results.
In addition to location and patency of stents, low-dose MDCT should give
further insight into the mechanism of action of the airway bypass procedure in
severely compromised patients who have no further treatment options. To
explore the therapeutic potential of the stenting procedure, optimal placement
of stents could be confirmed with analysis of the location and functioning of
stents depicted on MDCT. The results of our study are the basis for future
investigations in a larger population.
The results of our study indicate that low-dose MDCT is feasible for
radiologic monitoring of airway bypass procedures, an investigational
treatment of patients with severe homogeneous emphysema and disabling symptoms
despite optimal conservative therapy. With low-dose MDCT it is possible to
differentiate patent and nonpatent stents and to predict dislodgment of
stents. Because of its excellent high resolution, low-dose MDCT can be used to
help pulmonologists determine the need for intervention.
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Abstract
Introduction
