Interactive dynamic navigation for virtual endoscopy

3D CT-video fusion for image-guided bronchoscopy

Bronchoscopic biopsy of the central-chest lymph nodes is an important step for lung-cancer staging. Before bronchoscopy, the physician first visually assesses a patient's three-dimensional (3D) computed tomography (CT) chest scan to identify suspect lymph-node sites. Next, during bronchoscopy, the physician guides the bronchoscope to each desired lymph-node site. Unfortunately, the physician has no link between the 3D CT image data and the live video stream provided during bronchoscopy. Thus, the physician must essentially perform biopsy blindly, and the skill levels between different physicians differ greatly. We describe an approach that enables synergistic fusion between the 3D CT data and the bronchoscopic video. Both the integrated planning and guidance system and the internal CT-video registration and fusion methods are described. Phantom, animal, and human studies illustrate the efficacy of the methods.

System for the analysis and visualization of large 3D anatomical trees

Modern micro-CT and multi-detector helical CT scanners can produce high-resolution 3D digital images of various anatomical trees. The large size and complexity of these trees make it essentially impossible to define them interactively. Automatic approaches have been proposed for a few specific problems, but none of these approaches guarantee extracting geometrically accurate multi-generational tree structures. This paper proposes an interactive system for defining and visualizing large anatomical trees and for subsequent quantitative data mining. The system consists of a large number of tools for automatic image analysis, semi-automatic and interactive tree editing, and an assortment of visualization tools. Results are presented for a variety of 3D high-resolution images.

Macro-optical color assessment of the pulmonary airways with subsequent three-dimensional multidetector-x-ray-computed-tomography assisted display

Bronchial diseases alter the color and structural characteristics of the pulmonary mucosa through changes in blood flow, epithelial thickening, and abnormal cell growth. Current analysis of these subtle changes includes visual interpretation of the airway color and topography through bronchoscopy procedures, and quantitative multidetector-x-ray-computed-tomography (MDCT)-based structural analysis, each affording valuable insights to the health of the lungs. The fusion of the bronchoscopy and MDCT image data promises to provide a synergistic data set exhibiting both mucosal color and topography crucial to fostering an understanding of airway structure and function. A real-time airway color analysis imaging system is developed and utilized to perform pulmonary mucosal color assessment in healthy volunteers with subsequent comparative studies performed in example disease states. Our results indicate that macro-optical digital bronchoscopes with appropriate image analysis may have a significant impact on understanding bronchial diseases. To ensure the correct interpretation of scene content, which is critical in the assessment of airway topography, we are developing methods of extracting 3-D structure from 2-D bronchoscope images utilizing MDCT imaging techniques. The resulting 3-D true-color images of the pulmonary mucosa facilitate the combination of mucosal color and topography analysis as well as region of interest localization within the airway tree.

Automatic axis generation for virtual bronchoscopic assessment of major airway obstructions

Virtual bronchoscopy (VB) has emerged as a paradigm for more effective 3D CT image evaluation. Systematic evaluation of a 3D CT chest image using VB techniques, however, requires precomputed guidance data. This guidance data takes the form of central axes, or centerlines, through the major airways. We propose an axes-generation algorithm for VB assessment of 3D CT chest images. For a typical high-resolution 3D CT chest image, the algorithm produces a series of airway-tree axes, corresponding airway cross-sectional area measurements, and a segmented airway tree in a few minutes on a standard PC. Results for phantom and human airway-obstruction cases demonstrate the efficacy of the algorithm. Also, the algorithm is demonstrated in the context of VB-based 3D CT assessment.

The process and development of image-guided procedures

Medical imaging has been used primarily for diagnosis. In the past 15 years there has been an emergence of the use of images for the guidance of therapy. This process requires three-dimensional localization devices, the ability to register medical images to physical space, and the ability to display position and trajectory on those images. This paper examines the development and state of the art in those processes.

New techniques for efficient sliding thin-slab volume visualization

High-resolution three-dimensional (3-D) volumetric images obtained by today's radiologic imaging scanners are rich in detailed diagnostic information. Despite the many visualization techniques available to assess such images, there remains information that is challenging to uncover, such as the location of small structures (e.g., mediastinal lymph nodes, narrowed-airway regions). Recently, sliding thin-slab (STS) visualization was proposed to improve the visualization of interior structures. These STS techniques sometimes depend on user opacity specifications or extra preprocessing, and other rendering approaches that use the general STS mechanism are conceivable. We introduce two techniques for STS volume visualization. The first, a depth (perspective) rendering process, produces an unobstructed, high-contrast 3-D view of the information within a thin volume of image data. Results are a function of relative planar locations. Thus, rendered views accurately depict the internal properties that were initially captured as position and intensity. The second method produces a gradient-like view of the intensity changes in a thin volume. Results can effectively detect the occurrence and location of dramatic tissue variations, often not visually recognized otherwise. Both STS techniques exploit the concept of temporal coherence to form sequences of consecutive slabs, using information from previously computed slabs. This permits efficient real-time computation on a general-purpose computer. Further, these techniques require no preprocessing, and results are not dependent on user knowledge. Results using 3-D computed tomography chest images show the computational efficiency and visual efficacy of the new STS techniques.

Clinical applications of 2D and 3D CT imaging of the airways--a review

Hardware and software evolution has broadened the possibilities of 2D and 3D reformatting of spiral CT and MR data set. In the study of the thorax, intrinsic benefits of volumetric CT scanning and better quality of reconstructed images offer us the possibility to apply additional rendering techniques to everyday clinical practice. Considering the large number and redundancy of possible post-processing imaging techniques that we can apply to raw CT sections data, it is necessary to precisely set a well-defined number of clinical applications of each of them, by careful evaluation of their benefits and possible pitfalls in each clinical setting. In diagnostic evaluation of pathological processes affecting the airways, a huge number of thin sections is necessary for detailed appraisal and has to be evaluated, and information must then be transferred to referring clinicians. By additional rendering it is possible to make image evaluation and data transfer easier, faster, and more effective. In the study of central airways, additional rendering can be of interest for precise evaluation of the length, morphology, and degree of stenoses. It may help in depicting exactly the locoregional extent of central tumours by better display of relations with bronchovascular interfaces and can increase CT/bronchoscopy sinergy. It may allow closer radiotherapy planning and better depiction of air collections, and, finally, it could ease panoramic evaluation of the results of dynamic or functional studies, that are made possible by increased speed of spiral scanning. When applied to the evaluation of peripheral airways, as a completion to conventional HRCT scans, High-Resolution Volumetric CT, by projection slabs applied to target areas of interest, can better depict the profusion and extension of affected bronchial segments in bronchiectasis, influence the choice of different approaches for tissue sampling by better evaluation of the relations of lung nodules with the airways, or help to detect otherwise overlooked slight pathological findings. In the exploration of the air-spaces of the head and neck, targeted multiplanar study can now be performed without additional scanning by retro-reconstructed sections from original transverse CT slices. Additional rendering can help in surgical planning, by simulation of surgical approaches, and allows better integration with functional paranasal sinuses endoscopic surgery, by endoscopic perspective rendering. Whichever application we perform, the clinical value of 2D and 3D rendering techniques lies in the possibility of overcoming perceptual difficulties and 'slice pollution', by easing more efficient data transfer without loss of information. 3D imaging should not be considered, in the large majority of cases, as a diagnostic tool: looking at reformatted images may increase diagnostic accuracy in only very few cases, but an increase in diagnostic confidence could be not negligible. The purpose of the radiologist skilled in post-processing techniques should be that of modifying patient management, by more confident diagnostic evaluation, in a small number of patients, and, in a larger number of cases, by simplifying communication with referring physicians and surgeons. We will display in detail possible clinical applications of the different 2D and 3D imaging techniques, in the study of the tracheobronchial tree, larynx, nasal cavities and paranasal sinuses by Helical CT, review relating bibliography, and briefly discuss pitfalls and perspectives of CT rendering techniques for each field.