Virtual Bronchoscopy Tutorial intro

VIRTUAL BRONCHOSCOPY INTRODUCTION

Prepared by Dr. K Dheda, Dr. I Mootoosamy and Dr. CM Roberts.

Click here to download a Word 98 version of this document.

Virtual Bronchoscopy (VB) is a 3 dimensional, computer-generated technique that produces endobronchial images from spiral CT data ( McAdams et al AJR 1998). A spiral CT scanner acquires continuous images of a patient’s body thus providing imaging data between actual slices displayed. Overlapping slices can be reconstructed from the raw data set & high quality 2D and 3D reconstructions can be created. Advances in computer technique have allowed automatic creation of a 3D tracheobronchial tree model from CT scan images of the chest. The viewer can then navigate through the inside of the tracheobronchial tree as if in a simulated or virtual bronchoscopy (VB).

CT scanning method used at Whipps Cross Hospital:

Thorax first scanned post 100mls iv contrast at 5mm collimation.

For VB chest then scanned at 2-3mm collimation with reconstruction interval of 1-1.5mm

Images transferred to workstation for VB reconstruction.

In one study of 13 patients:

VB — third order bronchi seen in 90% cf. 85% with axial CT.

76% segmental bronchi seen with VB — lingula & middle lobe most difficult.

(Summers et al Radiology 1996)

VB showed 95% of central airways stenoses seen on FOB in 29 patients (Feretti et al European Rad 1997). High-grade stenosis or occlusion by central tumour was seen equally well by VB and FOB in 30 patients (Liewald et al Thoracic Cardiovasc Surgery 1998).

Potential applications of VB:

Educational

Diagnostic - Patient selection for FOB

Pre-bronchoscopic planning

Appraisal of central airways

Guide to peripheral airways

Staging - Guide to TBNA

Pre op planning

Interventional- Tracheobronchial stent placement

Endoluminal DXT

Laser photo ablation

Cryotherapy

Non invasive f/u-......... Post transplant & post sleeve .......... .............Resection stenoses.

(Haponik et al Pul Perspect 1997)

A great advantage of VB over FOB is its ability to see beyond a stenosis while limitations of VB include:

Mucous can mimic endobronchial lesions.

Incapable of evaluating the mucosa of the airways

Cannot sample lesions

Unable to distinguish between endobronchial, submucosal & extrinsic compression but can see at the same time the adjacent mediastinum on the multiplanar reconstructions on the workstation screen.

Risks of Diagnostic FOB are relatively low but cannot be ignored.

Virtually 0% mortality

0.8% rate of milder complications.

FOB is also relatively uncomfortable for patient and some patients may refuse or poorly tolerate the procedure.

VB as aid to TBNA:

VB images derived from routine helical CT scans were useful in directing TBNA in a clinical setting.

VB may have been responsible in improving the clinical yield of TBNA using 22g needles from less than 50% to 88%

1)VB & FOB images corresponded, therefore node location and angle of approach better correlated than with axial CT.
2) Confidence increased & smaller nodes aspirated in more difficult locations.

(McAdams et al AJR 1998)

Preliminary conclusions concerning 19 VB at Whipps Cross over the last 12 months:

Useful to study central airways if FOB not possible.

Aid to study airways distal to obstruction.

Possible aid to stenting.

Problem solving together with MPR reformats.

Major stenoses seen on FOB also seen on VB.

There are two MS PowerPoint presentations which provide some examples of VB images /case histories of patients seen Whipps Cross Hospital.

To view them you nee to have PowerPoint installed in the machine you're using. They may take 3-5 mins each to download, MS PowerPoint should open automatically when you click on the link. These files can be rapidly saved once they have opened fully should you wish to view them off-line.

PowerPoint file one

PowerPoint file two

Virtual Bronchoscopy video clip

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