A novel platform for electromagnetic navigated ultrasound bronchoscopy (EBUS)

Abstract

Purpose: Endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) of mediastinal lymph nodes is essential for lung cancer staging and distinction between curative and palliative treatment. Precise sampling is crucial. Navigation and multimodal imaging may improve the efficiency of EBUS-TBNA. We demonstrate a novel EBUS-TBNA navigation system in a dedicated airway phantom.

Methods: Using a convex probe EBUS bronchoscope (CP-EBUS) with an integrated sensor for electromagnetic (EM) position tracking, we performed navigated CP-EBUS in a phantom. Preoperative computed tomography (CT) and real-time ultrasound (US) images were integrated into a navigation platform for EM navigated bronchoscopy. The coordinates of targets in CT and US volumes were registered in the navigation system, and the position deviation was calculated.

Results: The system visualized all tumor models and displayed their fused CT and US images in correct positions in the navigation system. Navigating the EBUS bronchoscope was fast and easy. Mean error observed between US and CT positions for 11 target lesions (37 measurements) was [Formula: see text] mm, maximum error was 5.9 mm.

Conclusion: The feasibility of our novel navigated CP-EBUS system was successfully demonstrated. An EBUS navigation system is needed to meet future requirements of precise mediastinal lymph node mapping, and provides new opportunities for procedure documentation in EBUS-TBNA.

Keywords: Convex probe endobronchial ultrasound (CP-EBUS); Electromagnetic navigation; Endobronchial ultrasound; Multimodal image fusion; Navigated EBUS; Navigated ultrasound bronchoscopy.

Figures

Fig. 1

Convex probe endobronchial ultrasound (CP-EBUS) guiding real-time transbronchial fine-needle aspiration of a mediastinal lymph node. The sampling needle is visualized sonographically inside the lymph node. Video bronchoscopy is displayed simultaneously (bottom left). The transbronchial needle system emerges from the bronchoscope’s working channel just proximal to the CP-EBUS probe (top right)

Fig. 2

Schematic workflow of navigated convex probe endobronchial ultrasound (CP-EBUS) in the diagnosis of mediastinal lymph node metastasis in a fictive lung cancer case. (1) Mediastinal lymph nodes suspect of metastasis are identified in preoperative 2D CT and/or PET–CT images (top left), defining the region of interest for CP-EBUS-guided sampling. If a primary lung tumor is also visible, bronchoscopic sampling of the tumor is also considered; (2) the CT images are preprocessed. The target for sampling (lymph node, tumor) is segmented, and the airway centerline is extracted (bottom left); (3) image-to-patient centerline-based registration is performed in the operation room in the first phase of EBUS (top right, EBUS figure by Terese Winslow, Bronchoscopy, NCI Visuals Online, National Cancer Institute); (4) the level of the target lesion is identified by combined video bronchoscopy and electromagnetic (EM) position tracking of the CP-EBUS bronchoscope (EM navigation, middle right), (5) 2D EBUS (middle right) is used for target confirmation and visualization when the region of interest is approached and will aid the physician in deciding an optimal site for transbronchial needle aspiration (TBNA) (EM navigated CP-EBUS, bottom right), (6) TBNA from the target lymph node can be performed (bottom right). A cytology smear will reveal whether metastatic lung cancer is present

Fig. 3

Prototype convex probe endobronchial ultrasound (CP-EBUS) bronchoscope with electromagnetic sensor integrated for position tracking

Fig. 4

OR setup and interface during navigated convex probe endobronchial ultrasound (CP-EBUS) of a phantom model

Fig. 5

Gelatin-based airway phantom used for endoscopy. The course and divisions of the phantom airways are indicated by a red line. All tumor models are assigned numbers according to their location in the phantom mediastinal space, and a letter indicating right (R) or left (L) side

Fig. 6

Transformation between the coordinate systems of the ultrasound image (US), the positions sensor on the bronchoscope (B), the reference sensor (R) on the phantom, and the computer tomography image of the phantom (CT)

Fig. 7

Imaging target is moved through the ultrasound (US) image plane. pR,pBiandpUSi describes the coordinate vectors of the image target relative to the sensor on the calibration arm, the sensor on the convex probe endobronchial ultrasound (CP-EBUS) bronchoscope and the US image plane. BTUS and RTBi are matrices describing the transformation from the US image plane to the sensor on the EBUS probe and from the sensor on the CP-EBUS probe to the sensor on the calibration arm

Fig. 8

An ultrasound image cutting through the imaging target (plastic sphere) during probe calibration. The location of the sphere center within that image was found by adjusting the position of a virtual circle of the same diameter as the sphere, until its circumference corresponded with the surface of the imaged sphere

Fig. 9

Graphical user interface (GUI) of navigation system during tracked convex probe endobronchial ultrasound (CP-EBUS) in a phantom. A model of the tip of the EBUS bronchoscope and the real-time ultrasound image are displayed. Tumor models are segmented from computed tomography (CT) (green). Axial, coronal, and sagittal views (right side). Yellow crosshairs top center position of ultrasound image. The 3D scene view direction of the patient/phantom is displayed in the top left corner

Fig. 10

Navigated convex probe endobronchial ultrasound (CP-EBUS) graphical user interface (GUI) example, with ongoing fine-needle puncture of a target lesion. The fine needle is not tracked, but can easily be visualized sonographically

Fig. 11

Manual shift correction to determine the position deviation between computed tomography (CT) and ultrasound (US) volumes. Reconstructed US volumes (gray) were moved manually to the corresponding surface model segmented from CT (red). The optimal alignment was then determined in 2D axial, coronal, and sagittal (ACS) planes. Top row ACS planes before manual correction. Bottom row ACS planes after manual correction

Fig. 12

Position of 3D data acquired during navigated convex probe endobronchial ultrasound (CP-EBUS) in a phantom model. Black line centerline of airways extracted from computed tomography (CT). Red circles center position of tumor model in CT. Blue crosses center position of tumor model in ultrasound (calculated as center position in CT + deviation found by manual alignment)