Ultrathin Laser Scanning Bronchoscope and Guidance System for the Peripheral Lung
*Eric J. Seibel Ph.D, Timothy D. Soper B.S., Richard S. Johnston M.S., Robb W. Glenny M.D.
*University of Washington, Seattle, WA, USA → eseibel@hitl.washington.edu
Ultrathin Laser + Scanning-Fiber Bronchoscope
Disease diagnosis by endoscopy is exceedingly difficult when the region of interest is located within a small, complex structure in the body. Often, the physical
size of the endoscope and the degree of bending required to navigate through tortuous geometries prevent the clinician from maneuvering to the desired location
in vivo. As a result, several diagnostic procedures must be performed blindly or with the aid of fluoroscopy which carries with it a significant financial and time
expense. We have constructed an ultrathin scanning fiber endoscope capable of imaging regions of the body that were previously inaccessible. This device uses
a piezo actuator to spirally scan a single-mode fiber to direct multi-wavelength laser illumination to the image plane. The distal tip of the scanning fiber endoscope
measures 1.6 mm in diameter and the highly flexible shaft is 1.3 mm in diameter. The scope has a 20:1 zoom capability to a maximum of >60º field of view (FOV)
with 5 to 30 micron resolution. The goals for the ultrathin flexible bronchoscope are reaching areas of the peripheral lung and providing the earliest diagnosis of
cancer to below the 8th degree of bifurcation, where flexible bronchoscopy is limited. In addition, laser-induced autofluorescence using violet laser diodes (405
nm) will be integrated with the reflectance imaging and using this diagnostic technique to guide FNA and brush biopsy. (See references 1 & 2 for additional info.)
Future Guided Bronchoscopy in the Peripheral Lung
Current bronchoscopes are only capable of reaching the airway branches within the first 5 generations. Given the high incidence of nodular masses detected on computed
tomography (CT) scans, a large percentage of these nodules are beyond the bronchoscope’s reach and must be biopsied blindly using forceps, fine needle, brush, or by
transthoracic needle biopsy which is significantly more invasive. Our ultrathin endoscope will allow physicians to travel further into the lung periphery where smaller cancer
nodules can be visualized earlier with high-resolution CT. While current bronchoscopes can physically navigate through 5 generations of airways totaling to 25 or 32
separate airways, our endoscope will be able to access at least the 8th generation airways, totaling 28 or 256 individual branches. Because of the large number of
passageways and the added structural complexity that exists beyond 5th generation airways, a guidance system is currently under development to assist the bronchoscopist
by directing them to a predetermined region of interest using a graphical interface that displays the position of the endoscope tip on a virtual lung model. The tip of the
endoscope is tracked in 6 degrees of freedom using an electromagnetic tracking system (microBIRD, Ascension Technology Corp., see reference 3).
Creating a Virtual Lung Model
The CT scan permits clinicians to view and identify anomalous masses in the peripheral lung, but also provides a detailed
picture of the patient’s anatomy. From this it is possible to extract a comprehensive map of the airway system leading from the
trachea down to the nodule. Image processing techniques (ref) are applied to the digital CT scan data to segment the airways
from the surrounding anatomy. Depicted ________ are front and side projection images of a binary volume of segmented
airways on a sample subject. From this binary volume of data, a surface model is generated using previously developed
software (ITK) to provide a realistic virtual rendering of the airways as they would appear to a clinician during bronchoscopy.
1.6 mm
Flexible shaft and collection fibers
Rigid microscanner tube
and lens system
Device Design
The single mode fiber is actuated by a piezo tube scanner at resonance. The fiber is
scanned in a spiral pattern starting from the center. The image plane is directly
illuminated by a diffraction limited gaussian beam. The FOV is adjusted by setting
the voltage on the piezo scanner corresponding to the desired angle of deflection of
the fiber. The single fiber carries ultraviolet and visible light from multiple lasers.
Encapsulated Distal Tip
Zoom Imaging
The distal tip encasing the single mode fiber, piezo
actuator, lenses and multiple light collection fibers
A test target is scanned and imaged
using a PC workstation using Labview
(National Instruments) and images are
displayed at 5 Hz. Reducing the actuator
voltage (<15 V) allows for zooming of
20x magnification to 5 micron resolution.
7.8 micron bar and space pattern
Electromagnetic Tracking System
5.5 micron bar and space pattern
The microBIRD tracking system includes an RF transmitter, a PCI board, two
signal pre-amplifiers, and two position sensors. The transmitter generates a
magnetic field within three orthogonal planes. As a result of magnetic induction,
current is generated from three orthogonal coils in the sensor. From this, the
precise location and orientation of the sensor can be deduced in terms of x,y,z,
azimuth, elevation and roll. Ascension Technology now produces two miniature
sensors measuring 1.8 mm and 1.3 mm in diameter.
Imaging a Dried Sheep Lung
Guided Bronchoscopy
The ultrathin laser scanning bronchoscope was inserted into a dried sheep lung and redmonochrome images of 500 lines of resolution were acquired as shown. An illustrative
full-color (RGB) image is shown when blue & green laser sources are combined into the
singlemode optical fiber, vibrated and spiraled at 250 circles, and RGB light is projected
using a commercial endoscope lens (Pentax) while backscattered RGB light is detected
simultaneously with three avalanche photodiodes (Hamamatsu).
After integrating a tracking system with a fully defined 3D map of the airways a virtual
interface is needed to assist the bronchoscopist in navigating a number of tortuous
paths to the desired region in the peripheral lung. At the outset of the procedure, the
virtual model must be registered to the 3D space in which both the patient and
tracking system subside. This ensures that both the endoscopic views obtained
from the device and the virtual view generated from the tracking system and surface
model are appropriately aligned. Depicted to the right is a screen shot from the userinterface that displays both endoscopic and virtual views simultaneously. An external
view of the virtual model is overlayed in the top-left corner with a color indicator to
represent the current position of the endoscope’s distal tip. Color-coded lines are
also presented to direct the clinician down the appropriate airway and to document
the “navigation history” of the procedure by virtually labeling which paths have been
explored and which have not.
Presented at 11th World Conference on Lung Cancer, Barcelona, Spain, 6 July 2005
References
1. Seibel EJ, Smithwick QY, Unique features of optical scanning, single fiber endoscopy, Lasers Surg Med. 2002;30(3):177-83.
2. Johnston RS, Seibel EJ, 1.6 mm diameter scanning fiber endoscope, OSA Frontiers in Optics 2005, Tucson, AZ (accepted).
3. MicroBIRD, Ascension Technology Corp. (Burlington, VT): www.ascension-tech.com/products/microbird.php
Financial Support: NIH/NCI R21/R33 Grant # CA110184/CA094303 and the PENTAX Corporation, Tokyo, Japan