Electromagnetic based navigated bronchoscopy using preoperative CT images has reached the clinic during the last decade. One of the challenges is the “CT to patient anatomy alignment” of the CT images acquired days or even weeks ahead of bronchoscopy. An automatic registration method, without manual registration of anatomical landmarks, was developed, implemented, and evaluated in the current study.
The registration method aligns automatically the preoperative CT images to the patient's anatomy during the initial part of the bronchoscopy. The algorithm is a modified version of an iterative closest point algorithm, which in addition to the positions also utilizes the orientation of the bronchoscope and the running direction of the CT centerline. The method was evaluated both by model-based simulated bronchoscopies and by clinical data from six real bronchoscopies. In the clinical evaluation, an electromagnetic position sensor was placed temporarily in the working channel close to the tip of a conventional bronchoscope. Position data, which were acquired while the bronchoscope was moving inside the airways, were registered to the centerline extracted from the airways in the CT image.
A mean registration accuracy of 3.0 ± 1.4 mm was found when simulating bronchoscopies. In the clinical part of the study, the registration method was successfully applied to the data from all six patients. The positions of the bronchoscope tip aligned to the CT centerline with a mean distance range 4.7–6.5 mm.
The authors have developed and evaluated an automatic registration algorithm for electromagnetic navigated bronchoscopy. It functioned to its purpose and did not affect the workflow for the bronchoscopic investigation of the six patients included in the study.
This work was supported by Unimed Innovation Forskningsfond (Trondheim), the Ministry of Health and Care Services of Norway through the National Competence Centre for Ultrasound and Image-Guided Therapy (St. Olavs University Hospital, SINTEF and NTNU, Trondheim, Norway), project 196726/V50 eMIT (Enhanced minimally invasive therapy, FRIMED program), and Liaison Committee between the Central Norway Regional Health Authority (RHA) and the Norwegian University of Science and Technology (NTNU) (Samarbeidsorganet). The authors also wish to thank Randi Sailer, Department of Pulmonology at St. Olavs Hospital, for excellent assistance in the clinic to carry out the measurements during patient interventions. The authors declare that they have no conflict of interest in conducting the research.
II. MATERIALS AND METHODS
II.A. Registration method
II.B. Evaluation by simulation
II.C. Evaluation by clinical data
II.C.1. CT imaging
II.C.2. CT preprocessing
II.C.3. Bronchoscope tracking
II.C.5. Registration accuracy
III.A. Evaluation by simulation
III.B. Evaluation by clinical data
- Computed tomography
- Medical imaging
- Inductively coupled plasma
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