Fig. 17.1
Electromagnetic location board placed at the cephalic end of the bronchoscopy table
A retractable microsensor probe is mounted on the tip of a flexible cable locatable guide (LG) (Fig. 17.2). This microsensor is the cardinal feature of the system. Once placed within the EM field, its position in x, y, and z axes as well as in motion (rotate, forward, and backward) is captured by the EMN system and displayed on the monitor in real time. These images are superimposed upon previously acquired CT images (Fig. 17.3).
Fig. 17.2
Edge locatable guide
Fig. 17.3
(Left) The position of locatable guide (LG) at the main carina in coronal view CT scan and (right) real-time superimposed bronchoscopic image of LG at the main carina
The Edge™ Catheter: Extended Working Channel (EWC)
Since the adult-size flexible bronchoscope cannot be advanced beyond the fourth- or fifth-generation bronchus, the iLogic® system provides extended working channel with the distal end angulated at different degrees to facilitate approaching the PPL (Edge™). The Edge™ catheter is a 130-cm-long, 1.9-mm-diameter flexible catheter, serving as a EWC for the FB. It is available with its distal end curved at 45°, 90°, or 180° angles. The distal tip of this catheter could be soft or hard and based on the bronchoscopist’s preference. These options are to facilitate navigation between the PPN and the adjacent bronchus, as judged by the bronchoscopist. The Edge navigation catheter can be steered to the PPN in 360° fashion. The proximal white steering knob has a socket for connecting a wire, which relays the information from the sensor to the main computer (Figs. 17.4 and 17.5).
Fig. 17.4
(Top) The Edge navigation catheter with sensor at the distal tip. (Bottom) Edge navigation catheter assembled with working channel of bronchoscope
Fig. 17.5
The main processor of the iLogic navigation system
Once the tip of the bronchoscope is wedged into the segmental bronchus of interest, the LG is advanced along with the EWC under the guidance provided by the navigation system. Upon reaching the desired target, the LG is withdrawn leaving the EWC in place. Endobronchial accessories (needle, brush, forceps) then are inserted through the EWC to sample the target. The GenCut biopsy device is the most recent biopsy tool in endobronchial lung navigation system. It is activated with aspiration to create shearing force and collect multiple tissue samples with a single pass. There was a single study in porcine lung model which reported the performance and safety of this catheter. The future study is required to establish the utility of this catheter in humans [18].
Computerized Tomography
To overlay the patient’s radiographic information on the patient’s anatomy in the electromagnetic field, a high-resolution spiral CT scan of the chest is performed (with or without the contrast) and reconstructed with a protocol specific to the scanner manufacturer. The recommended reconstruction protocols optimize CT images suitable for planning and navigation (Tables 17.1 and 17.2). DICOM (Digital Imaging and Communications in Medicine) images from a low-dose CT scan can be accepted and viewed in the planning module; however, the detail and quality of the images produced may not be suitable to enable the advanced features of the ENB system. The information is gathered in the DICOM format and placed either on a compact disk or directly downloaded on the system’s laptop from the picture archiving and communication system (PACS).
Table 17.1
Recommended CT scan and reconstruction parameters
Image resolution | 512 × 512 |
Overlap | 20–50% |
Field of view | At least 1 cm of trachea and entire lung volume |
Maximum images | 690 |
Table 17.2
The lists of the slide thickness and slice interval for a 50% and 20% overlap
Slice thickness (mm) | Minimum slice interval (mm) (at 50% overlap) | Maximum slice interval (mm)(at 20% overlap) |
|---|---|---|
1.0 | 0.5 | 0.8 |
1.25 | 0.625 | 1.0 |
1.5 | 0.75 | 1.2 |
2.0 | 1.00 | 1.6 |
2.5 | 1.25 | 2.0 |
3.0 | 1.50 | 2.4 |
4.0 | 2.00 | 3.2 |
5.0 | 2.50 | 4.0 |
Computer Interphase
The EMN system provides dedicated software for “planning” and “navigation procedure.” The CT chest images can be transferred from PACS into DICOM CD. The DICOM CD can be uploaded directly into the planning software. The planning software program provides images of the chest in coronal, sagittal, and axial fashion as well as a virtual bronchoscopic image and a three-dimensional representation of the patient’s tracheobronchial tree and pleura. These images are used to plan all aspects of the procedure. The main computer software and the monitor allow the bronchoscopist to view the reconstructed images of the patient’s anatomy together with superimposed graphic information depicting the position of the LG as well as position of the target lesion.
The virtual 3D bronchial tree made possible with the technology extends deep into the lung parenchyma and enables several automated features such as automatic registration, automated pathway planning, and airway sync. Further, the customized high-definition views offer the bronchoscopist multiple navigation perspectives to improve detection and diagnosis. A high-definition wide screen allows six viewports to be displayed simultaneously, including one video input, enabling the physician to evaluate positional data and optimize central and peripheral guidance within the lung (Fig. 17.6).
Fig. 17.6
Computer interphase: dedicated program on the laptop provides coronal, axial, and sagittal views of the chest along with virtual bronchoscopy
Procedure
The procedure of EMN is performed in the following steps:
Planning
Planning involves identifying the target, selecting anatomical landmarks, and identifying a virtual approach to the target using digital software provided by the system.
- (a)
Identification of the target:
Target(s) are identified by scrolling through the CT cross sections in axial, coronal, and sagittal axes. Once identified, the location of the target(s) is marked using a curser and highlighted. The dimensions of the target are also measured.
- (b)
Detecting anatomical landmarks:
A virtual bronchoscopy image extending to the fourth generation of tracheobronchial tree is required to enable automatic superimposition of the CT images on the patient’s body. If a 3D map is not available, anatomical landmarks (primary and secondary carinas) can be identified using the CT cross sections. Five or more easily recognizable endobronchial locations (landmarks) are selected for the purpose: more specifically main carina as well as two points in each lung, one in the upper lobe and one in its middle or lower lobe. These radiographic landmarks are matched with the actual anatomic landmarks of the patient during the bronchoscopic procedure either automatically or manually.
- (c)
Pathway planning:
If a 3D map is available, one or more automatic pathways to each target can be constructed to assist in navigation. The automatic pathway is constructed using the 3D map as a reference (Fig. 17.7). A review of the automatic pathway should be completed utilizing the CT cross sections and the 3D map. Additionally, a virtual navigation of the pathway can be performed using the pathway preview feature. The suggested pathway can be modified, can be extended with waypoints, or can be accepted for guidance as it is.
- (d)
Saving the plan and exiting:
When the procedure plan is complete, it is exported to a CD, to a removable disk (USB), or to a network storage location for transfer to the procedure system.
Fig. 17.7
Automatic pathway. Planning involves selecting the target (green) and the anatomical landmarks (purple)
Registration
The information gathered during the planning stage is uploaded into the system’s main computer using the external memory device. The electromagnetic censors are placed on the patient’s chest wall to accommodate for respiratory motion, coughing, and nominal patient movements. FB is performed in a usual fashion. The Edge catheter is inserted via the working channel of the scope.
During the automatic registration process (Fig. 17.8), the system records the location of the LG, while the bronchoscopist performs a bronchoscopic airway examination, creating a virtual cloud of navigation points that approximates the tracheobronchial tree. The system completes the registration process by matching the navigation cloud to the 3D map. The virtual bronchoscopy (VB) will appear during the bronchoscopic survey when the system has collected the minimal amount of data needed to match to the 3D tree. After completing the balanced survey, visual verification and image rotation for the registration is accepted, and the navigation phase of the procedure begins.
Fig. 17.8
Automatic registration
In a small percentage of procedures, the CT images will not support generation of a 3D tree. In this case, manual registration will be required. The radiological landmarks (registration points) selected on the virtual bronchoscopy images in planning are identified in vivo and touched with the tip of the LG to register their location in the system’s main computer to establish radiographic-anatomic alignment. Registration of all the above information into the computer software automatically synthesized a navigation scheme to approach the lesion with precision. Accuracy of the navigation depends upon this radiographic-anatomic alignment also referred as “average fiducial target registration error” (AFTRE), which defines registration quality. The AFTRE can be improved or corrected by repositioning the misplaced landmarks or by eliminating that with a greatest deviation. The registration error of 5 mm or less can be considered acceptable.
Real-Time Navigation
Following a successful registration, the scope with the LG in place is advanced toward the segmental bronchus of interest. The navigation screen consists of six different viewports. The configuration of viewports is customizable with 11 different viewports available. Each viewport provides information that is meaningful at different points in the navigation procedure. The targets and pathways defined during planning will be available for selection during navigation. Once a target and pathway have been selected, the available views are used to guide the LG to the target.
The following are the viewports available to aid navigation (Figs. 17.9 and 17.10):
Planar CT axial, coronal, and sagittal image (three views). The views show the selected target and, optionally, the selected pathway and waypoints.
Static 3D map. A view of the 3D map showing the selected target, pathway, waypoints, and real-time location of the LG tip.
Dynamic 3D map. A view of the 3D map showing the selected target, pathway, waypoints, and real-time location of the LG tip. The 3D map is automatically rotated, panned, and zoomed during navigation.
Tip view. A graphical representation of the steering wheel on the LG handle. This view shows the direction to rotate the steering wheel to turn the LG toward the selected navigation object (target, pathway, or waypoint).
3D CT. A planar projection of the CT volume located directly in front of the LG tip.
Video bronchoscope. Live display of the video input feed, typically used to show the bronchoscope video.
Virtual bronchoscopy. A live display of the virtual bronchoscopy showing the real-time location of the LG tip. The selected pathway, waypoints, and 3D map centerlines can be overlaid on the view.
Local view. A planar CT image located at and aligned with the LG tip. The view shows the selected target, pathway, waypoints, and 3D map branches.
Alignment view. A view of target alignment with the LG tip.
MIP (maximum intensity projection). A pseudo-three-dimensional projection of the CT volume below the LG tip. MIP shows high-intensity structures, such as blood vessels and lesions.
Fig. 17.9
Peripheral navigation view
Fig. 17.10
Target alignment view
Navigation guidance to the target is primarily given through the selected pathway. The pathway is displayed in the 3D map, local view, virtual bronchoscopy, and CT cross sections. The objective during navigation is to steer and advance the LG along the pathway.
In addition to pathway guidance, steering directions are provided to specific navigation objects using the tip view. Navigation objects include targets, the automatic pathway, and waypoints and are represented by spheres in all views.
The lesion is represented as a green sphere on all of the system viewports. As the LG gets closer to the lesion, the green dot continues to get larger in a relative fashion. The screen also shows the distance between the LG and the targeted lesion in millimeters (mm). Once the LG reaches the desired target location, the EWC is fixed at the proximal end of the biopsy channel of the bronchoscope by a special locking mechanism and the LG is withdrawn. Fluoroscopy can be performed to view the LG in the desired location before its removal. A rEBUS probe can also be inserted for additional location confirmation. Bronchoscopic accessories such as biopsy forceps, transbronchial aspiration needle, and endobronchial brush can be inserted via the EWC to obtain a tissue specimen.
SPiNView®
The SPiNView system uses an Always-On Tip Tracked technology. The sensor tracking is built into the biopsy instruments allowing for real-time navigation of the biopsy tools.
There are two additional features of the SPiNView system: (1) it incorporates a transthoracic needle system to biopsy lesions similar to CT-guided transthoracic needle aspiration (TTNA), and (2) the SPiNView offers the 4D respiration technology that monitors patient respiration during the procedure. Respiratory motion can be a problem during TBBx because an average motion of pulmonary lesions has shown to be approximately 17.6 mm. With this much respiratory motion, it may affect the diagnostic yield of EMN-guided TBBX or any other lung biopsy procedures [19].
Procedure
The procedure of SPiNView is performed in the following steps.
Planning
This phase is similar to iLogic system. The system uses inspiratory CT images of the patients’ airways to plan the route to the lesion. The target PPN is marked and the software then creates a 3D road map of targeted lesion. The SPiNView software uses an expiration CT scan to match patient’s respiration state. Then, the pathway is transferred and is uploaded for the navigation phase.
Navigation
vPads patient tracker is placed on the patient chest. It contains electromagnetic sensors which enable automatic registration and respiratory motion tracking. A SPiNView bronchoscopy catheter is available with steerability. The SPiNView system can automatically perform registration without bronchoscopist’s effort. During this phase, the electromagnetic generator tracks the Always-On Tip Tracked® instrument as it advances toward the lesion in the lung. The View Peripheral Catheter provides digital laser optics which has built-in electromagnetic sensors. It provides guidance throughout the procedure.
Biopsy
The targeted lesion is reached by a phantom catheter. The bronchoscopist performs biopsies of the lesion while the instrument is left in place. The tip tracked steerable working channels, tip tracked aspiration needles, and navigation guide wires enable ultrathin bronchoscopes to be navigated to the peripheral regions of the lung all with clear virtual visualization. The SPin FleX needle is made with nitinol, making it possible to turn 180° and get to difficult lesions in the lungs. The bronchoscopist always knows where the sensor is within the body while sampling. The confirmation by fluoroscopic image is optional.
Results of EMN-Guided TBBx
A number of studies have been published establishing effectiveness of the EMN in the diagnosis of peripheral lung lesions (Table 17.3).
Table 17.3
Diagnostic yield of EMN-aided FB
Reference | Technique | N | Size (mm) Range or mean | Diagnostic yield (%) | Prevalence of lung cancer | AFTRE (mm) (mean ± SD) or range | Procedure duration (min) (mean ± SD) or range | Fluoro | PNX % (n) |
|---|---|---|---|---|---|---|---|---|---|
Becker, 2005 [14] | EMN+fluoro | 29 | 12–106 | 69 | 83% | RE: 6.1 ± 1.7 | NT: 7.3 RT: 2 | + | 3.3 (1) |
Hautmann, 2005 [15] | EMN+fluoro | 16 | 22 ± 6 | Not given | No data | 4.2 | NT: +3.9 min | + | 0 |
Schwarz, 2006 [16] | EMN+fluoro | 13 | 15–50 | 69 | 92% | NE: 5.7 | TPT: 46 min | + | 0 |
Gildea, 2006 [17] | EMN+fluoro | 58 | PL: 22.8 LN: 28.1 | PL: 74% LN: 100% | 74% | RE: 6.6 ± 2.1 NE: 9 ± 5 | RT: 3 ± 2 NT: 7 ± 6 TPT: 51 ± 6 | + | 3.4 (2) |
Makris, 2007 [20] | EMN | 40 | 23.5 | 62.5 | 85% | RE: 4 ± 0.15 NE: 8.7 ± 0.8 | Not studied | − | 7.5 (3) |
Eberhardt, 2007 [21] | EMN | 89 | 24 | 67 | 76% | RE: 4.6 ± 1.8 NE: 9 ± 6 | RT: 3.2 ± 2.3 NT: 4.5 ± 3.4 TPT: 29.9 ± 6.5 | − | 2.2 (2) |
Wilson, 2007 [22] | EMN+fluoro+ROSE | 248 | PL: 2.1 LN: 1.8 | 70–86% | 57% | RE: 0.5 ± 0.02 | Not studied | + | 1.2 (3) |
Eberhardt, 2007 [24] | EMN+EBUS | 40 | 26 | 88
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