3D virtual endoscopy of the upper airway: optimization of the scan parameters in a cadaver phantom and clinical assessment

3D Virtual Pancreatography

We present 3D virtual pancreatography (VP), a novel visualization procedure and application for non-invasive diagnosis and classification of pancreatic lesions, the precursors of pancreatic cancer. Currently, non-invasive screening of patients is performed through visual inspection of 2D axis-aligned CT images, though the relevant features are often not clearly visible nor automatically detected. VP is an end-to-end visual diagnosis system that includes: A machine learning based automatic segmentation of the pancreatic gland and the lesions, a semi-automatic approach to extract the primary pancreatic duct, a machine learning based automatic classification of lesions into four prominent types, and specialized 3D and 2D exploratory visualizations of the pancreas, lesions and surrounding anatomy. We combine volume rendering with pancreas- and lesion-centric visualizations and measurements for effective diagnosis. We designed VP through close collaboration and feedback from expert radiologists, and evaluated it on multiple real-world CT datasets with various pancreatic lesions and case studies examined by the expert radiologists.

Current approaches to the diagnosis of vascular erectile dysfunction

Vascular erectile dysfunction (ED) is closely related to cardiovascular events, and early diagnosis of vascular ED may be helpful to predict the occurrence of cardiovascular events and improve prognosis. At present, there are many approaches to diagnose ED, but each method has its advantages and limitations. This study retrospectively reviewed all available literature focusing on the diagnosis of vascular ED through a systematic PubMed and EMBASE search. According to the different application scenarios, the main methods for the diagnosis of vascular ED are divided into four categories. Intra-cavernous injection of vasoactive drugs is the earliest method used in the diagnosis of vascular ED and is a basic test. For the diagnosis of arterial ED, color duplex Doppler ultrasound, selective penile angiography, magnetic resonance imaging, and computed tomography are more commonly used. While for the diagnosis of venous ED, shear wave elastography, dynamic infusion cavernosometry and cavernosography are more accurate. Endo-peripheral arterial tonometry (PAT) has also been used to detect vascular endothelial function. Although various existing examinations are widely used for the evaluation of vascular ED, they still have some shortcomings, such as invasiveness, contingency, high false positive (negative) rate. New methods of long-term dynamic detection are needed.

Role of virtual bronchoscopy in the evaluation of bronchial lesions

BACKGROUND

Virtual bronchoscopy (VB) is a type of 3-dimensional reconstruction in which the observation point is placed within the airway to produce an endoscopiclike view.

AIM

To evaluate the diagnostic role of VB in the diagnosis of tracheobronchial lesions, as compared to fiberoptic bronchoscopy (FOB).

SUBJECTS

Fifty patients with tracheobronchial lesions were enrolled (30 patients with bronchogenic carcinomas and 20 patients with tracheobronchial inflammatory lesions).

METHODS

The patients were examined using VB and FOB. Virtual bronchoscopic studies were calculated and reconstructed from cross-sectional images obtained from spiral computed tomographic examination of the chest.

RESULTS

Virtual bronchoscopy provided an excellent overview of the trachea, main stem, and lobar bronchi up to the fourth order. The data obtained by VB and FOB (signs of tumor infiltration including endobronchial mass, stenosis, obstruction, and external indentations) were comparable. However, FOB had the advantage of giving direct cues to color, vascularity, and motility. It also detected early tumor infiltration by picking up subtle mucosal changes. Alternatively, VB was superior in bypassing any obstruction and therefore provided an excellent view distal to the obstructive lesions or stenotic segments. Virtual bronchoscopy also defined the optimum pathway for passing instruments into lesions beyond the field of view.

CONCLUSIONS

Here, we compared the diagnostic capacities of both VB and FOB. The interventional and therapeutic ramifications of our findings await further investigations.

Utility of multidetector CT and virtual bronchoscopy in tracheobronchial obstruction in children

PURPOSE

The aim of this study was to evaluate the potential use of multidetector CT (MDCT) and virtual bronchoscopy (VB) in the evaluation of tracheobronchial patency in children with suspected bronchial obstruction and to compare its findings with fibreoptic/rigid bronchoscopy or surgery.

PATIENTS AND METHODS

A total of 43 children (15 girls, 28 boys) with clinically suspected bronchial obstruction underwent contrast enhanced MDCT, using an age- and weight- adjusted low dose protocol. Post-processing was performed and VB and multiplanar reformations (MPR) were obtained at the same sitting. Findings obtained at MDCT and VB were compared with fibreoptic/rigid bronchoscopy and surgery.

RESULTS

Obstructive pathology was found in 26 children, which included endoluminal foreign body, mucus plugs in 13 children, endobronchial tumour in three children and extrinsic compression (lymph node, aberrant Vessels, mediastinal cysts/tumours) of the tracheobronchial tree in 10 children. In 17 children, no obstructive lesion was identified. Excellent positive correlation was obtained, between MDCT-VB and bronchoscopy/surgery, however, in one child with endobronchial obstruction caused by tracheitis, low dose MDCT-VB was normal, but bronchoscopy revealed granularity and plaques.

CONCLUSION

MDCT-Virtual bronchoscopy is useful in evaluating bronchial stenosis and obstruction caused by both endoluminal pathology and external compression and has the advantage of looking beyond stenosis. Its main application lies in providing the exact location of suspected foreign body, prior to bronchoscopy. However, it fails to disclose exact nature of obstructing pathology.

Value of virtual tracheobronchoscopy and bronchography from 16-slice multidetector-row spiral computed tomography for assessment of suspected tracheobronchial stenosis in children

PURPOSE

To evaluate the value of dose-reduced 16-slice multidetector-row spiral computed tomography (16-MDCT) using virtual tracheobronchoscopy (VTB) and virtual bronchography (VBG) in children with suspected tracheobronchial stenosis.

MATERIALS AND METHODS

12 children (4 d to 3 years, body weight 1.2 kg to 13.5 kg) with stridor and suspected tracheobronchial stenosis were examined by contrast-enhanced low-dose 16-MDCT. Conventional axial slices, MPRs, VTB, and VBG were calculated. Image findings were correlated with the results of fiberoptic bronchoscopy (12 out of 12) as a gold standard and subsequent surgery (8 out of 12).

RESULTS

VTB and VBG demonstrated the fiberoptic bronchoscopically suspected tracheal stenosis in 11 of 12 children due to vascular compression because of the brachiocephalic trunk (6), a double aortic arch (2), a vascular compression of the left main bronchus (2), and a right aberrant subclavian artery (1). Eleven out of 12 stenoses were correctly depicted by conventional axial slices, MPRs, VTB, and VBG. Dose reduction was 79 to 85.8% compared to a standard adult chest CT.

CONCLUSION

Dose-reduced 16-MDCT with the use of VTB and VBG is effective for the evaluation of tracheobronchial stenosis in children and correlates well with fiberoptic bronchoscopy.

Multidetector CT of the central airways

Multidetector CT (MDCT) has revolutionized non-invasive imaging of the central airways. Compared to single-detector helical CT scans, MDCT results in higher spatial resolution, faster speed, greater anatomic coverage, and higher quality multiplanar reformation and 3-D reconstruction images. This article reviews recent advances in central airway imaging with MDCT. A special emphasis is placed upon the role of advanced reconstruction methods and functional imaging.

Virtual Bronchoscopy: Accuracy and Usefulness—An Overview

Multidetector CT generated virtual bronchoscopy (VB) represents one of the most recent developments in three-dimensional (3D) visualization techniques which allows a 3D evaluation of the airways down to the sixth- to seventh-generation. In comparison with real bronchoscopy, VB has some advantages: it is a non-invasive procedure that can visualize areas inaccessible to the flexible bronchoscope. Virtual bronchoscopy is able to evaluate bronchial stenosis and obstruction caused by both endoluminal pathology (tumor, mucus, foreign bodies) and external compression (anatomical structures, tumor, lymph nodes), can be helpful in the preoperative planning of stent placement and can be used to evaluate surgical sutures after lung transplantations, lobectomy or pneumectomy. In children, in some indications, VB can replace fiber optical bronchoscopy (FB) when this technique is considered too invasive. Finally, VB can also be used to evaluate anatomical malformations and bronchial variants. Virtual bronchoscopy is accurate but its accuracy is not 100% because false-positives and false-negatives occur. Virtual bronchoscopy contributes to a better understanding of tracheo-bronchial pathology. Fiber optical bronchoscopy will, without doubt, remain the golden standard but it can be expected that in the near future, the technique of VB will find a place in the daily routine.

Virtual laryngoscopy—preliminary experience

PURPOSE

Computed tomographic virtual laryngoscopy is a non-invasive radiological technique that allows visualisation of intra-luminal surfaces by three-dimensional reconstruction of air/soft tissue interfaces. It is particularly useful when the patient cannot tolerate clinical examination, when infection, neoplasm or congenital defects compromise the lumen and for assessment of the sub-glottic region. We have performed virtual laryngoscopy on patients referred because of upper airway symptoms, and compared the findings with those at conventional laryngoscopy.

MATERIALS AND METHODS

Axial scans were obtained using a Toshiba Xpress helical scanner. Virtual laryngoscopy was then performed on a workstation using Toshiba "Fly-thru" software and was completed within 5 min.

RESULTS

Pathology included vocal cord nodules, laryngeal cysts, Reinke's oedema, laryngeal neoplasms and leukoplakia.

CONCLUSIONS

Virtual laryngoscopy displays anatomical detail comparable to conventional endoscopy. Impassable obstructions are no hindrance and all viewing directions are possible. It is especially useful for providing views of the larynx from below.

Low-dose MDCT and virtual bronchoscopy in pediatric patients with foreign body aspiration

OBJECTIVE

The purpose of this study was to investigate the potential use of low-tube-current MDCT virtual bronchoscopy for the evaluation of children with suspected foreign body aspiration.

SUBJECTS AND METHODS

Low-tube-current MDCT was performed in 23 patients (10 girls, 13 boys) with a mean age of 3.3 years (9 months-13 years) with suspicion of foreign body aspiration. Chest radiographs were obtained before CT was performed. MDCT was performed using 25- to 50-mA tube currents. MDCT virtual bronchoscopy images were obtained. Neither sedation nor IV contrast medium was used during CT scanning. All patients underwent endoscopic evaluation within 24 hr after MDCT was performed. MDCT virtual bronchoscopy findings were retrospectively compared with the results of rigid bronchoscopy.

RESULTS

The mean tube current was 35 mA (range, 25-50 mA). Imaging quality was excellent in nine studies (39%), good in 12 studies (52%), and poor in two studies (9%). Motion artifacts were present on several slices in five examinations. In 15 patients, all foreign bodies detected by conventional bronchoscopy were also revealed on MDCT virtual bronchoscopy. The foreign body was in the right main bronchus in six patients, in the bronchus intermedius in one patient, and in the left main bronchus in eight patients. No discordance was found between the two techniques. MDCT revealed hyperaeration of the ipsilateral lung in five patients, atelectasis in five patients, infiltration in three patients, and infiltration and bronchiectasis in two patients; it showed infiltration in four patients and atelectasis in one of eight patients without a foreign body detected. There were no abnormal findings in three patients.

CONCLUSION

Evaluation of foreign body aspiration of the airway in children can be accomplished by using a low-tube-current MDCT protocol. It may be useful both in showing the exact location of a foreign body before bronchoscopy and in ruling out a foreign body in patients with a low level of suspicion and normal or nonspecific findings on chest radiography.

Hybrid segmentation and virtual bronchoscopy based on CT images

RATIONALE AND OBJECTIVES

Introduction of combination of the segmentation tool SegoMeTex and the virtual endoscopy system VIVENDI to perform virtual endoscopic inspections of the human lung. This virtual bronchoscopy system enables visualization of the tracheobronchial tree down to seventh generation. Furthermore, the modified virtual system visualizes hidden structures such as segmented vascular system or tumors.

MATERIALS AND METHODS

The segmentation is based on image data acquired by a multislice computed tomography scanner. SegoMeTex is used to segment the tracheobronchial tree by a hybrid system with minimal user action. Similarly, the complementary pulmonary arterial can be segmented, whereas additional structures such as tumors are marked manually. On this dataset, subsequently, data structures of the inner surface for virtual endoscopy are generated. Finally, the dataset can be explored by a virtual bronchoscopy procedure using the VIVENDI system.

RESULTS

The segmentation method was successfully tested on 22 patients. The hybrid segmentation system identified bronchi up to the sixth generation with a sensitivity of more than 58%, and a positive predictive value of more than 90%. After the segmentation, the datasets are explored interactively (>30 fps on a standard personal computer platform in real-time rendering) using the virtual endoscopy software. The exploration exposed a high-quality reconstruction, even of small structures throughout the dataset.

CONCLUSION

Virtual bronchoscopy in combining with a highly sensitive segmentation is a valuable tool for the localization and measurement of stenosis for resection planning.

Assessment of VIE image quality using helical CT angiography: in vitro phantom study

The aim of this study is to quantify the effects of helical CT acquisitions parameters on the magnitude of three-dimensional stair-step artefacts, visualization of renal ostium and morphologies of suprarenal stents observed using virtual intravascular endoscopy. This was performed in a phantom of the human abdominal aorta with a stent graft in situ. Stair-step artefacts were quantified by measuring the standard deviation of signal intensity on surface shaded images and the influence of these artefacts on the visualization of arterial ostia and stent morphologies were assessed by three radiologists. The methodology may be used to optimise the CT system performance for helical CT angiography in aortic stent grafting.

State-of-the-Art Imaging of the Central Airways

Recent technological advances in CT imaging have revolutionized non-invasive imaging of the central airways. It is now possible to image the entire central airways in a few seconds and to create elegant three-dimensional reconstructions of the airways in a few minutes. The fast speed of CT scanning now allows for a dynamic assessment of the central airways, expanding the ability to non-invasively detect functional abnormalities such as tracheobronchomalacia. The purpose of this article is to familiarize clinicians with recent advances in airway imaging. A special emphasis is placed upon advanced CT reconstruction methods and their potential contributions to the evaluation of a variety of airway disorders.

Virtual bronchoscopy: comparison of different surface rendering models

The aim of this study was to compare different representation models of surface-rendered virtual bronchoscopy. 10 consecutive patients with inoperable primary lung tumors underwent thin-section spiral computed tomography. The structures of interest, the tracheobronchial system and anatomical and pathological thoracic structures were segmented using an interactive threshold interval volume-growing segmentation algorithm and visualized with the aid of a color-coded surface rendering method. For virtual bronchoscopy, the tracheobronchial system was visualized using a triangle-surface rendering model, a shaded-surface rendering model and a transparent shaded-surface rendering model. The triangle-surface rendering model allowed optimum detailed spatial representation of the dimensions of extraluminal anatomical and pathological mediastinal structures. As the lumen of the tracheobronchial system was less well defined, the rendering model was of limited use for depiction of the airway surface. The shaded-surface rendering model facilitated an optimum assessment of the airway surface, but the mediastinal structures could not be depicted. The transparent shaded-surface rendering model provides simultaneous adequate to optimum visualization and assessment of the intraluminal airway surface and the extraluminal mediastinal structures as well as a quantitative assessment of the spatial relationship between these structures. Fast data acquisition with a multi-slice detector spiral computed tomography scanner and the use of virtual bronchoscopy with the transparent shaded-surface rendering model obviate the need for time consuming detailed analysis and presentation of axial source images by providing improved the diagnostic imaging of endotracheal and endobronchial diseases and offering a useful alternative to fiberoptic bronchoscopy.

Multislice helical CT of the central airways

Multislice helical CT has revolutionized the non-invasive evaluation of the central airways with CT. The quick speed of image acquisition afforded by MSCT improves the quality of end-inspiration images and has expanded the ability to assess the airway during dynamic exhalation. Furthermore, the improved quality of multiplanar and three-dimensional images provided by MSCT has ushered in an exciting era of alternative methods of viewing CT data that are more visually accessible and often more anatomically meaningful. At present, the author routinely obtains multiplanar reformation and three-dimensional images for assessment of a variety of central airway abnormalities, including airway stenoses and webs, complex airway diseases, extrinsic airway compression, tracheobronchomalacia, and poststent placement. Further advances in CT technology, data processing, and image display, and increased clinical experience with advanced imaging reconstruction methods, will likely further expand the role of multiplanar and three-dimensional reconstruction images in the assessment of a wide variety of central airways disorders in the near future.

Recent advances in central airway imaging

The purpose of this article is to familiarize chest physicians with recent advances in airway imaging, with an emphasis on the emerging role of two-dimensional reformatted and three-dimensional CT reconstructed images in the assessment of central airway disorders.

Analysis of errors in medical rapid prototyping models

Rapid prototyping (RP) is a relatively new technology that produces physical models by selectively solidifying UV-sensitive liquid resin using a laser beam. The technology has gained a great amount of attention, particularly in oral and maxillofacial surgery. An important issue in RP applications in this field is how to obtain RP models of the required accuracy. We investigated errors generated during the production of medical RP models, and identified the factors that caused dimensional errors in each production phase. The errors were mainly due to the volume-averaging effect, threshold value, and difficulty in the exact replication of landmark locations. We made 16 linear measurements on a dry skull, a replicated three-dimensional (3-D) visual (STL) model, and an RP model. The results showed that the absolute mean deviation between the original dry skull and the RP model over the 16 linear measurements was 0.62 +/- 0.35 mm (0.56 +/- 0.39%), which is smaller than values reported in previous studies. A major emphasis is placed on the dumb-bell effect. Classifying measurements as internal and external measurements, we observed that the effect of an inadequate threshold value differs with the type of measurement.

Virtual tools for imaging of the thorax

Helical computed tomography (HCT) allows for volume acquisition of the entire thorax during a single apnoea. Combination of HCT acquisition with synchronous vascular enhancement gives rise to HCT angiography (HCTA). In the last decade, HCT and HCTA have revolutionized the diagnosis of thoracic diseases, modifying many diagnostic algorithms. Because HCT provides for a true volume acquisition free of respiratory misregistration, three-dimensional (3D) rendering techniques can be applied to HCT acquisitions. As these 3D rendering techniques present the HCT information in a different format to the conventional transaxial CT slices, they can be summarized as virtual tools. The purpose of this review is to give the readers the most important technical aspects of virtual tools, to report their application to the thorax, to answer clinical and scientific questions, and to stress their importance for patient management, clinical decision making, and research.

Hybrid 3D visualization of the chest and virtual endoscopy of the tracheobronchial system: possibilities and limitations of clinical application

OBJECTIVE

A hybrid rendering method which combines a color-coded surface rendering method and a volume rendering method is described, which enables virtual endoscopic examinations using different representation models.

MATERIALS AND METHODS

14 patients with malignancies of the lung and mediastinum (n=11) and lung transplantation (n=3) underwent thin-section spiral computed tomography. The tracheobronchial system and anatomical and pathological features of the chest were segmented using an interactive threshold interval volume-growing segmentation algorithm and visualized with a color-coded surface rendering method. The structures of interest were then superimposed on a volume rendering of the other thoracic structures. For the virtual endoscopy of the tracheobronchial system, a shaded-surface model without color coding, a transparent color-coded shaded-surface model and a triangle-surface model were tested and compared.

RESULTS

The hybrid rendering technique exploit the advantages of both rendering methods, provides an excellent overview of the tracheobronchial system and allows a clear depiction of the complex spatial relationships of anatomical and pathological features. Virtual bronchoscopy with a transparent color-coded shaded-surface model allows both a simultaneous visualization of an airway, an airway lesion and mediastinal structures and a quantitative assessment of the spatial relationship between these structures, thus improving confidence in the diagnosis of endotracheal and endobronchial diseases.

CONCLUSIONS

Hybrid rendering and virtual endoscopy obviate the need for time consuming detailed analysis and presentation of axial source images. Virtual bronchoscopy with a transparent color-coded shaded-surface model offers a practical alternative to fiberoptic bronchoscopy and is particularly promising for patients in whom fiberoptic bronchoscopy is not feasible, contraindicated or refused. Furthermore, it can be used as a complementary procedure to fiberoptic bronchoscopy in evaluating airway stenosis and guiding bronchoscopic biopsy, surgical intervention and palliative therapy and is likely to be increasingly accepted as a screening method for people with suspected endobronchial malignancy and as control examination in the aftercare of patients with malignant diseases.

Virtual endoscopy

Virtual endoscopy is a technique in which three-dimensional viewing of hollow structures is conducted through the utilization of high-resolution imaging and unique computer processing methods. The basic components of this technique and its applications for urology and other clinical disciplines are reviewed.

Middle ear imaging using virtual endoscopy and its application in patients with ossicular chain anomaly

Virtual endoscopy (VE) is a recently developed technique to provide a realistic surface rendering of various organs, which can be applied to the use of three-dimensional (3D) studies of several lesions. However, its advantages in otological disease have not been well investigated. In this study, we evaluated the application of VE in patients with ossicular chain anomalies. Virtual middle ear endoscopy was a time-saving method, however, we needed the appropriate technical procedures of algorithm and reconstruction spacing to generate accurate 3D images of ossicles. We obtained virtual surgical views of middle ear structures and related anomalies, and confirmed by intraoperative findings that these images were mostly compatible with the actual lesions of ossicles. VE allowed an identification of the anatomy of the ossicles and adjacent structures simultaneously. The elements of the stapedial crura were clearly visualized with VE images in 93.3% of normal ears. Pathological ossicular chain findings such as malleus or incus fixation, dislocation and disruption, except footplate fixation were investigated successfully. One possible procedure, using alterable CT value in the obtained VE images on the monitor, is proposed for further detection of fine lesions of the ossicles. These observations suggest that virtual middle ear simulations accurately represent major intraoperative findings. This technique may have an important role in preoperative planning, surgical training, and/or postoperative evaluation in otology.

Evaluating laryngotracheal stenosis in a canine model with virtual bronchoscopy

We performed a prospective masked animal study to determine whether virtual bronchoscopy, a noninvasive computed tomography technique, can accurately measure upper airway stenosis. Virtual bronchoscopy creates a 3-dimensional endoscopic image from spiral computed tomography data. Laryngotracheal stenosis was endoscopically induced in 18 dogs. The excised larynges were examined by endoscopy, virtual bronchoscopy, and macrodissection. Measurements were made of the anteroposterior (A-P) diameter, the left-right (L-R) diameter, the full length of stenosis in the sagittal plane, and the length of the tightest stenotic segment. Each measurement method was performed independently. All investigators were unaware of measurements made by others. The measurements obtained through virtual bronchoscopy and actual endoscopy were compared to those made at dissection by interclass correlation coefficients (ICCs). Endoscopy was better than virtual bronchoscopy in measuring the A-P diameter (ICC = .79, p < .0001; ICC = .42, p = .01). Both were equally effective in measuring the L-R diameter (ICC = .53, p = .0062; ICC = .52, p = .0064). The endoscopes could not assess the full length of the stenosis, whereas virtual bronchoscopy measured it fairly accurately (ICC = .72, p = .0001). Virtual bronchoscopy relatively accurately measured the length of the tightest stenotic segment (ICC = .68, p = .0002), whereas endoscopy produced measurements in only 11 of 18 larynges, and the measurements were less accurate (ICC = .45, p = .0068). Virtual bronchoscopy can provide good measurements of stenotic lesions in the airway. It is more accurate than actual endoscopy in determining the length of stenosis. It may therefore be useful as an adjunct imaging method in preoperative planning for reconstructive surgery.

Evaluation of airway obstruction using virtual endoscopy

OBJECTIVES

This study examines the use of virtual endoscopy (VE) in the evaluation of patients with upper airway obstruction. The utility of VE compared with actual endoscopy was investigated with respect to accuracy of diagnosis and reproduction of endoscopic images.

STUDY DESIGN

A random cohort of 30 patients with various causes of airway obstruction was examined.

METHODS

The computed tomography (CT) data were reconstructed using a proprietary VE software program, FreeFlight, blind to the actual endoscopic findings. The cause of obstruction was identified and compared with actual endoscopic findings. This included 21 patients with airway stenoses, 8 patients with laryngotracheomalacia, 3 tracheal tumors, 2 glottic webs, 5 patients with innominate artery compression, 2 tracheal granulomas, and 7 patients with impaired true vocal cord mobility.

RESULTS

Virtual endoscopic evaluation was accurate in assessing stenosis width and length of fixed airway lesions. Correlation of stenosis shape and contour between actual endoscopy and VE was excellent. The stenosis-to-lumen ratios were compared between VE and actual endoscopy and were found to be within 10% (SD = 8). However, virtual endoscopic evaluation could not illustrate one of the glottic webs, half of the cases of tracheomalacia, or any of the cases of impaired true vocal cord mobility.

CONCLUSIONS

Virtual endoscopy was not as sensitive as actual endoscopy in detecting the cause of airway obstruction that was based on dynamic movement. However, VE was excellent for the measurement and definition of fixed airway lesions.

Head and neck computed tomography virtual endoscopy: evaluation of a new imaging technique

OBJECTIVE

To evaluate a new radiographic imaging technique: computed tomography virtual endoscopy (CTVE) for head and neck tumors.

STUDY DESIGN

Twenty-one patients presenting with head and neck masses who underwent axial computed tomography (CT) scan with contrast were evaluated by CTVE. Comparisons were made with video-recorded images and operative records to evaluate the potential utility of this new imaging technique.

METHODS

Twenty-one patients with aerodigestive head and neck tumors were evaluated by CTVE. One patient had a nasal cylindrical cell papilloma; the remainder, squamous cell carcinomas distributed throughout the upper aerodigestive tract. Patients underwent complete head and neck examination, flexible laryngoscopy, axial CT with contrast, CTVE, and in most cases, operative endoscopy. Available clinical and radiographic evaluations were compared and correlated to CTVE findings.

RESULTS

CTVE accurately demonstrated abnormalities caused by intraluminal tumor, but where there was apposition of normal tissue against tumor, inaccurate depictions of surface contour occurred. Contour resolution was limited, and mucosal irregularity could not be defined. There was very good overall correlation between virtual images, flexible laryngoscopic findings, rigid endoscopy, and operative evaluation in cases where oncological resections were performed. CTVE appears to be most accurate in evaluation of subglottic and nasopharyngeal anatomy in our series of patients.

CONCLUSION

CTVE is a new radiographic technique that provides surface-contour details. The technique is undergoing rapid technical evolution, and although the image quality is limited in situations where there is apposition of tissue folds, there are a number of potential applications for this new imaging technique.

Virtual arthroscopy of the visible human female temporomandibular joint

PURPOSE

This study was designed to obtain views of the temporomandibular joint (TMJ) by means of computed arthroscopic simulation (virtual arthroscopy) using three-dimensional (3D) processing.

MATERIAL AND METHODS

Volume renderings of the TMJ from very thin cryosection slices of the Visible Human Female were taken off the Internet. Analyze(AVW) software (Biomedical Imaging Resource, Mayo Foundation, Rochester, MN) on a Silicon Graphics 02 workstation (Mountain View, CA) was then used to obtain 3D images and allow the navigation "fly-through" of the simulated joint.

RESULTS

Good virtual arthroscopic views of the upper and lower joint spaces of both TMJs were obtained by fly-through simulation from the lateral and endaural sides. It was possible to observe the presence of a partial defect in the articular disc and an osteophyte on the condyle. Virtual arthroscopy provided visualization of regions not accessible to real arthroscopy.

CONCLUSION

These results indicate that virtual arthroscopy will be a new technique to investigate the TMJ of the patient with TMJ disorders in the near future.

Virtual endoscopic environments in modern neurosurgical practice

Modern radiographic techniques have allowed the creation of high-definition planar images that can provide important anatomical as well as physiological data. Planar imaging sets can be reformatted into three-dimensional (3-D) data sets that can then be manipulated to demonstrate important anatomical or gross pathological features. Three-dimensional data sets have been used with success in modern image-guided or frameless stereotactic surgery. Another potential application is so-called "virtual endoscopy" or "scopeless endoscopy," in which a 3-D anatomical data set is reformatted into a volume-rendered image that can then be viewed. By reformatting images in this way, a "surgeon's-eye" view can be obtained, which can aid in presurgical planning and diagnosis. The use of virtual endoscopy has the potential to increase our understanding of the appropriate anatomy and the anatomical relationships most apparent during neurosurgical approaches. In so doing, virtual endoscopy may serve as an important means of planning for therapeutic interventions.

On the other hand, one must always be cognizant of the technical limitations of these studies regardless of the quality of the reconstructed images. Prospective, correlative, clinical studies in which the anatomical advantages of virtual-based endoscopy are evaluated in large cadaver or patient series must be performed. Until then, the only potential ways to compensate for errors that exist in the algorithms and reconstructions of 3-D endoscopic images are based on the surgeon's understanding of the clinical state of the patient and prior experience with the anatomy in the region of question.

Virtual bronchoscopy

Three-dimensional endoluminal tracheobronchial simulations can be derived successfully from thoracic helical CT scans, and can reproduce the appearances of major endobronchial abnormalities confirmed during FB. The prospects of ever-faster CT scanners (capable of submillimeter resolution) merged with greater computer power make it likely that current versions of virtual bronchoscopy images will seem primitive in the future. Initial descriptive reports suggest great potential, but the startling visual appeal of these 3-D portrayals of a patient's airway and mediastinal anatomy and the prospects of exploring this information in real time do not establish its clinical role. Such virtual bronchoscopy findings are generally predictable on the basis of currently available axial CT images alone. The extent to which these 3-D endobronchial renderings improve the already high predictive values of CT requires critical study. In their patients with lung cancer Cicero et al observed that neither the staging nor diagnosis was modified substantially, but virtual bronchoscopy contributed to enhanced understanding of the pathology of the neoplastic process. Whether this added perspective translates to tangible benefits for patients is an intriguing possibility that has yet to be proved. The unique 3-D endobronchial view may offer particular advantages in some individuals and contribute to the patient's noninvasive evaluation. Because of the already high yield of conventional CT, diagnostic yield alone is not likely to be the sole best measure of this evolving technology. Accordingly, future multidisciplinary research investigations will also need to prospectively address nuances of decision-making and measure appropriate patient outcomes. In these efforts the active dialogue between chest clinician and radiologist will remain essential to defining and realizing the true potential of virtual bronchoscopy.

Virtual cisternoscopy of intracranial vessels: a novel visualization technique using virtual reality

This paper introduces a different visualization method which we call "virtual cisternoscopy" using 3D MRA data sets. Virtual cisternoscopy uses well known tools, such as perspective volume rendering (pVR), fly-through techniques, and interactive visualization and combines them to a new approach featuring motion to resolve spatial relationships of intracranial vessels and vascular malformations. With a dedicated flight protocol extraluminal topography of intracranial arteries was analyzed using pVR. For evaluation of difficult vascular malformations extraluminal views are necessary. Therefore, movies of pVR views were produced simulating virtual tracks of neurosurgical flexible endoscopes, by flying around the intracranial vessels and vascular malformations within the cisterns. Endoluminal views were acquired additionally for precise evaluation of cases with complex vessel topography. Two healthy volunteers and three patients were examined. Comparing MIP and pVR images relevant advantages of pVR were found, such as depth information, perspective, lighting, and color. In contrast to MIP and source images of the MRA data set, virtual cisternoscopy of an aneurysm of the left middle cerebral artery demonstrated clearly an early origin of an artery in the region of the aneurysm neck/sac. In this case only virtual cisternoscopy led to the correct therapeutical decision. In a newborn, the type of a vein of Galen aneurysmal malformation could only be evaluated reliably by means of virtual cisternoscopy. The third case of a patient with a clipped aneurysm was evaluated more easily with virtual cisternoscopy than with DSA. In conclusion, virtual cisternoscopy may improve the pretherapeutic visualization of intracranial vascular malformations.

Virtual endoscopy for planning and simulation of minimally invasive neurosurgery

OBJECTIVE

This article demonstrates the usefulness and the problems of present-state software for virtual endoscopy as a tool for the planning and simulation of minimally invasive neurosurgical procedures.

METHODS

The software Navigator (General Electric Medical Systems, Buc, France) was applied for virtual endoscopic visualization of three-dimensional magnetic resonance data sets of healthy volunteers and neurosurgical patients, using a clinical magnetic resonance scanner (1.5-T Signa Hispeed; General Electric Medical Systems). Classical approaches for minimally invasive procedures were simulated.

RESULTS

Virtual endoscopy provided impressive three-dimensional views of intracranial and intracerebral cavities, with visualization of many anatomic details of the brain's inner and outer surfaces. The method proved to be especially suited for the simulation and planning of operations of intraventricular lesions, for which the technical limitations of the present state of development of this method have fewer implications. However, the present state of technology, as described in this article, has two major shortcomings: 1) the blood vessels cannot be visualized together with the brain tissue and cranial nerves; and 2) different tissue compartments cannot be stained in their original coloring, which would facilitate their recognition and thus orientation in space by anatomic landmarks. Another important disadvantage at this stage is time consumption for many single working steps.

CONCLUSION

Virtual endoscopy is a promising tool for teaching and training in intracranial neuroanatomy as well as for planning and simulation of minimally invasive (e.g., endoscopic), mainly intraventricular, operations. Direct clinical application is, at this stage of development, limited by several technical shortcomings of visualization and quantification of distances and modeling of surfaces.