Thoracic Imaging 2003 - Society of Thoracic Radiology

THURSDAY
268
threshold values for surface rendering techniques have been
described by Summers as –500. While these thresholds are effective
in the main and lobar bronchi, artifacts can occur in the
smaller airways, and may also result in a overestimation of
stenoses. Faster reconstruction times have made volume rendered
techniques more accessible are are used increasingy at our
institution.
As we have seen with more recent literature in virtual
colonscopy, an original fascination with the technology has given
way to a more realistic assessment of VBs particular capabilities
and weaknesses. One of the greatest strengths of virtual bronchoscopy
is the added benefits inherent in CT imaging. Unlike
fiberoptic bronchoscopy, the data used in the generation of the
virtual bronchoscope is not limited to the lumen: CT bronchosocpy
has the ability to accurate depict extraluminal anatomy
not available to the bronchoscopist Integration of this intraluminal
and extraluminal data will be discussed later. Many of the
imaging limitations of virtual bronchoscopy have been well
defined by Summers, but often describe the markedly limited
ability of the virtual bronchoscope to depict mucosal abnormalities.
The unavoidable integration of cardiac and respiratory
motion into the virtual bronchoscope introduces subtle error into
the depiction of VB data and therefore limits the ability to evaluate
the mucosal and submucosal pathology.
A number of papers have been written comparing the diagnostic
value of virtual bronchoscopy with standard CT images as
well as fiberoptic bronchoscopy. One of the values of virtual
endoscopy in the airways is the evaluation of the upper airways.
In a paper by Burke, Vinings and others using FreeFlight software,,
evaluation of airway obstruction was evaluated using virtual
bronchosocpy. This study included 30 patients with upper
airway disease ranging from airway stenosis, laryngtracheomalacia,
tumors and webs. There was excellent agreement
betweenVB and FOB is the evaluation of airway stenoses. The
differences in ratios of stenoses/lumen was within 10% for VB
vs upper airway endoscopy. The evaluation of dynamic airway
collapse was much less reliable with virtual endoscopy, but there
was clearly established a role for virtual endoscopy in airway
stenoses.
Several papers have been written defining the role of virtual
bronchoscopy in patients with airway stenoses secondary to bronchogenic
carcinoma. In the paper by Liewald et al, 30 patients
with bronchogenic carcinoma were studied. While central
lesions were well identified by virtual bronchosocpy, stenosis
secondary to smaller lobar lesions were not accurately identified.
In a paper by Rapp Bernhardt , a number of visualization thecniques
were compared, includeing axial, MPR, MinIp and virtual
bronchoscopy Virtual bronchosocopy evaluation of stenoses
showed the lowest interobserver variability. There was no significant
difference between virtual and fiberoptic bronchoscopy in
the estimation of stenoses, though there tended to be some overestimation
of stensos, felt to be due to thresholding limitationsof
stenoses in virtual bronchoscopy Mucosal abnormalies were not
well evaluated with virtual bronchscopy. Other work has looked
at the success of bronchial stenoses in a lung transplant population.
In this paper, stenoses at the anastomosis was evaluated by
axial and virtual bronchosocpy. Stenoses at the anastomotic sites
were better visualized by virtual bronchoscopy than axial CT,
though this was not statistically significant. Surface irregularties
due to infection were equally visualized with virtal and fibeeroptic
bronchoscopy.
There is an increasing literature on the use of virtual
bronchscopy in improving the diagnostic accuracy of fiberoptic
bronchoscopy. In a paper by McAdams, the virtual bronchoscopy
was reviewed by the pulmonologist for evaluation of
lymph node node biopsy, and was preferred to the axial CT slices.
There was a slight improvement in diagnostic yield compared to
standard axial images when VB images were reviewed. In a
paper by Hopper, a technique of lymph node highlight was
described. Mediastinal lymph nodes were manually segmented
and highlighted and iintegrated into the surface rendered virtual
bronchocopy. By the use of varying the transparency of the
bronchial wall, the involved lymph node could be chosen before
the procedure. While there was no significant difference in the
diagnostic sampling of subcarinal lymph nodes, these techniques
improved diagnostic yield significantly for hilar and pretracheal
lymph nodes.
We have used virtual endoscopy in the chest to also evaluate
the esophagus and aorta. Virtual endoscopy has been used extensively
by our thoracic surgeons to preoperatively assess the aorta.
Evaluation of atherosclerotic disease, endoscopic evaluation of
dissections, aneurysms and stenoses have helped the presurgical
planing of pulmonary thromboendarterectomy. It has been used
in the coronary arteries, and pulmonary arteries for evaluation of
stenoses and embolic disease. As our techniques improve, virtual
endoscopic techniques will only improve, as will their clinical
applications.
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Haponik E, Acquino S, Vining D, Virtual Bronchoscopy Clinics in
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Burke A, Vining DJ, McGuirt W, et al Evaluation of airway
Obstruction Using Virtual Bronchoscopy. Laryngosocope;110
23-29 2000
McAdams N, Palmer s, Erasmus JJ et al. Bronchial Anastomotic
Complications in Lung Transplant Recipients:Virtual
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Hopper K, Lucas TAS, Gleeson K, et al. Transbronchial Biopsy
with Virtual CT Bronchoscopy and Nodal Highlighting.
Radiology 2001;221:531-536.
Seeman M, Claussen C, Hybrid 3D Visualiztion of the chest and
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.Rapp-Bernhardt U. Welte T, Doerhing W, et al Diagnostic potential
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