Volumetric (helical/spiral) CT (VCT) of the airways

Uncommon thoracic manifestations from extrapulmonary tumors: Computed tomography evaluation - Pictorial review

Although metastasis can occur at a variety of sites, pulmonary involvement is common in patients with cancer. Depending on the source and type of tumor, pulmonary metastases present with a wide range of radiologic appearances. Hematogenous dissemination through the pulmonary arteries to the pulmonary capillary network is the most common form of spread in pulmonary metastases. However, they may also reach the lung via lymphatic dissemination, secondary airway involvement, vessel tumor embolism, and direct chest invasion. In the evaluation of patients with known extrathoracic tumors, CT is the state-of-the-art imaging modality for detecting and characterize pulmonary metastases as well as to predict resectability. Although CT limitations are well known, knowledge of growth rates of various tumors and understanding the pattern of spread may be helpful clues in suggesting and even establish the specific diagnosis. The purpose of this pictorial review is to discuss the imaging appearances of different patterns of intrathoracic tumoral dissemination.

Diagnostic Value of Multidetector CT and Its Multiplanar Reformation, Volume Rendering and Virtual Bronchoscopy Postprocessing Techniques for Primary Trachea and Main Bronchus Tumors

Purpose

To evaluate the diagnostic value of multidetector CT (MDCT) and its multiplanar reformation (MPR), volume rendering (VR) and virtual bronchoscopy (VB) postprocessing techniques for primary trachea and main bronchus tumors.

Methods

Detection results of 31 primary trachea and main bronchus tumors with MDCT and its MPR, VR and VB postprocessing techniques, were analyzed retrospectively with regard to tumor locations, tumor morphologies, extramural invasions of tumors, longitudinal involvements of tumors, morphologies and extents of luminal stenoses, distances between main bronchus tumors and trachea carinae, and internal features of tumors. The detection results were compared with that of surgery and pathology.

Results

Detection results with MDCT and its MPR, VR and VB were consistent with that of surgery and pathology, included tumor locations (tracheae, n = 19; right main bronchi, n = 6; left main bronchi, n = 6), tumor morphologies (endoluminal nodes with narrow bases, n = 2; endoluminal nodes with wide bases, n = 13; both intraluminal and extraluminal masses, n = 16), extramural invasions of tumors (brokethrough only serous membrane, n = 1; 4.0 mm—56.0 mm, n = 14; no clear border with right atelectasis, n = 1), longitudinal involvements of tumors (3.0 mm, n = 1; 5.0 mm—68.0 mm, n = 29; whole right main bronchus wall and trachea carina, n = 1), morphologies of luminal stenoses (irregular, n = 26; circular, n = 3; eccentric, n = 1; conical, n = 1) and extents (mild, n = 5; moderate, n = 7; severe, n = 19), distances between main bronchus tumors and trachea carinae (16.0 mm, n = 1; invaded trachea carina, n = 1; >20.0 mm, n = 10), and internal features of tumors (fairly homogeneous densities with rather obvious enhancements, n = 26; homogeneous density with obvious enhancement, n = 1; homogeneous density without obvious enhancement, n = 1; not enough homogeneous density with obvious enhancement, n = 1; punctate calcification with obvious enhancement, n = 1; low density without obvious enhancement, n = 1).

Conclusion

MDCT and its MPR, VR and VB images have respective advantages and disadvantages. Their combination could complement to each other to accurately detect locations, natures (benignancy, malignancy or low malignancy), and quantities (extramural invasions, longitudinal involvements, extents of luminal stenoses, distances between main bronchus tumors and trachea carinae) of primary trachea and main bronchus tumors with crucial information for surgical treatment, are highly useful diagnostic methods for primary trachea and main bronchus tumors.

Multiplanar and two-dimensional imaging of central airway stenting with multidetector computed tomography

Background

Multidetector computed tomography (MDCT) provides guidance for primary screening of the central airways. The aim of our study was assessing the contribution of multidetector computed tomography- two dimensional reconstruction in the management of patients with tracheobronchial stenosis prior to the procedure and during a short follow up period of 3 months after the endobronchial treatment.

Methods

This is a retrospective study with data collected from an electronic database and from the medical records. Patients evaluated with MDCT and who had undergone a stenting procedure were included. A Philips RSGDT 07605 model MDCT was used, and slice thickness, 3 mm; overlap, 1.5 mm; matrix, 512x512; mass, 90 and kV, 120 were evaluated. The diameters of the airways 10 mm proximal and 10 mm distal to the obstruction were measured and the stent diameter (D) was determined from the average between D upper and D lower.

Results

Fifty-six patients, 14 (25%) women and 42 (75%) men, mean age 55.3 ± 13.2 years (range: 16-79 years), were assessed by MDCT and then treated with placement of an endobronchial stent. A computed tomography review was made with 6 detector Philips RSGDT 07605 multidetector computed tomography device. Endobronchial therapy was provided for the patients with endoluminal lesions. Stents were placed into the area of stenosis in patients with external compression after dilatation and debulking procedures had been carried out. In one patient the migration of a stent was detected during the follow up period by using MDCT.

Conclusions

MDCT helps to define stent size, length and type in patients who are suitable for endobronchial stinting. This is a non-invasive, reliable method that helps decisions about optimal stent size and position, thus reducing complications.

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.

Multidetector computed tomography of pediatric large airway diseases: state-of-the-art

Advances in multidetector computed tomography (MDCT) technology have given rise to improvements in the noninvasive and comprehensive assessment of the large airways in pediatric patients. Superb two-dimensional and three-dimensional reconstruction MDCT images have revolutionized the display of large airways and enhanced the ability to diagnose large airway diseases in children. The 320-MDCT scanner, which provides combined detailed anatomic and dynamic functional information assessment of the large airways, is promising for the assessment of dynamic large airway disease such as tracheobronchomalacia. This article discusses imaging techniques and clinical applications of MDCT for assessing large airway diseases in pediatric patients.

Update on multidetector computed tomography imaging of the airways

Recent advances in multidetector computed tomography (MDCT) technology have transformed the imaging evaluation of the trachea and bronchi. Multiplanar 2-dimensional and 3-dimensional volume reconstruction techniques, including external rendering and virtual bronchoscopy, can be generated in mere minutes, thereby complementing conventional axial CT imaging in the depiction of various central airway disease processes including airway stenoses, central airway neoplasms, and congenital airway disorders. Paired inspiratory and dynamic expiratory MDCT imaging, along with newer cine CT imaging methods, have enhanced the assessment of tracheobronchomalacia in both adults and the pediatric population. In addition, MDCT imaging plays an essential complementary role to conventional bronchoscopy, facilitating planning and guidance of bronchoscopic interventions, and providing a noninvasive method for postprocedural surveillance.

Imaging-bronchoscopic correlations for interventional pulmonology

The improvements to patient care that can be achieved by combining advanced imaging techniques and bronchoscopy are considerable. In this regard, CT imaging often plays an indispensable role in both the selection of appropriate candidates tor therapy as well as the choice of optimal interventional techniques. However, it is apparent that alternate methods for evaluating the airways and lung including ultrasound and electromagnetic navigation will likely play an increasingly important diagnostic role, necessitating a thorough understanding of their advantages and limitations. Disease-specific applications for which imaging technologies, including CT and VB, are either currently routinely used or show the greatest promise are for suspected or diagnosed lung cancers, central and peripheral, and emphysema. It may be anticipated that with growing experience, the potential for additional indications of these remarkable technologies are likely to increase in the near future.

[Bronchial diseases: CT imaging features]

Multidetector row computed tomography (MDCT) is the imaging modality of reference for the diagnosis of bronchiectasis. MDCT may also detect a focal stenosis, a tumor or multiple morphologic abnormalities of the bronchial tree. It may orient the endoscopist towards the abnormal bronchi, and in all cases assess the extent of the bronchial lesions. The CT findings of bronchial abnormalities include anomalies of bronchial division and origin, bronchial stenosis, bronchial wall thickening, lumen dilatation, and mucoid impaction. The main CT features of bronchiectasis are increased bronchoarterial ratio, lack of bronchial tapering, and visibility of peripheral airways. Other bronchial abnormalities include excessive bronchial collapse at expiration, outpouchings and diverticula, dehiscence, fistulas, and calcifications.

Imaging-bronchoscopic correlations for interventional pulmonology

The development and rapid advancement of both bronchoscopic, CT and ultrasound imaging technology has had considerable impact on the management of a wide variety of pulmonary diseases. The synergy between these newer imaging modalities and advanced interventional endoscopic procedures has led to a revolution in diagnostic and therapeutic options in patients with both central and peripheral airway disease. Given the broad clinical implications of these technological advances, only the most important areas of interventional pulmonology in which imaging has had a major impact will be selectively reviewed to highlight fundamental principles.

Tumors in the tracheobronchial tree: CT and FDG PET features

A variety of tumors, including primary malignant tumors, secondary malignant tumors, and benign tumors, can occur in the tracheobronchial tree. Primary malignant tumors commonly originate from the surface epithelium or the salivary glands, whereas most benign tumors arise from the mesenchymal tissue. At computed tomography (CT), primary malignant tumors manifest as a polypoid lesion, a focal sessile lesion, eccentric narrowing of the airway lumen, or circumferential wall thickening. At fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET), most squamous cell carcinomas show high uptake, whereas adenoid cystic carcinoma and mucoepidermoid carcinoma show variable uptake depending on the grade of differentiation. High-grade malignancies tend to show high and homogeneous uptake. Carcinoid tumors commonly show intense enhancement at contrast material-enhanced CT, which can be helpful in making the diagnosis, and usually have lower uptake at FDG PET than would be expected for a malignant tumor. Secondary malignant tumors occur as a result of either hematogenous metastasis or direct invasion by a malignancy from an adjacent structure. Their CT manifestations are similar to those of primary malignant tumors, with uptake at FDG PET depending primarily on the metabolic activity and degree of differentiation of the primary tumor. Among the benign tumors, hamartoma and lipoma can show characteristic CT findings such as "popcorn" calcification or internal fat. However, CT findings in most benign tumors are nonspecific. At FDG PET, benign tumors usually show little or no uptake and can be differentiated from malignant tumors. Knowledge of the characteristic CT and FDG PET findings of tracheobronchial tumors can aid in diagnosis and treatment planning.

Bronchial anatomy of left lung: a study of multi-detector row CT

Familiarity with prevailing pattern and variations in the bronchial tree is not only essential for the anatomist to explain bronchial variation in bronchial specimens, but also useful for guiding bronchoscopy and instructing pulmonary segmental resection. The purpose of this study was designed to demonstrate various branching patterns of left lung with 3D images, with special attention given to identify the major types at transverse thin-section CT. Two hundred and sixteen patients with routine thorax scans were enrolled. The images of bronchial tree, virtual bronchoscopy were reconstructed using post-processing technique of multi-detector row CT. We attempted to classify the segmental bronchi by interpreting the post-processing images, and identified them in transverse thin-section CT. Our results showed that the segmental bronchial ramifications of the left superior lobe were classified into three types mainly, i.e., common stem of apical and posterior segmental bronchi (64%, 138/216); trifurcation (23%, 50/216); common stem of apical and anterior segmental bronchi (10%, 22/216), and they could be identified at two typical sections of transverse thin-section CT. There were two major types in left basal segmental bronchi, i.e., bifurcation (75%, 163/216), trifurcation (18%, 39/216), and they could also be identified at two typical sections of transverse thin-section CT. In conclusion, our study have offered simplified branching patterns of bronchi and demonstrated various unusual bronchial branching patterns perfectly with 3D images, and have also revealed how to identify the main branching patterns in transverse thin-section CT.

[Volume CT: recent advances in acquired abnormalities of the trachea]

OBJECTIVES

To show the recent improvements in CT imaging of the trachea due to the introduction of multidetector computed tomography (MDCT).

MATERIAL AND METHODS

MDCT technology, which was introduced in the early 00's, allows acquiring the entire airways within few seconds while using low dose parameters thanks to the natural high contrast of the airways.

RESULTS

Volume acquisition with isotropic voxels offers an excellent anatomical resolution in all directions, improving the quality of multiplanar reformations and 3D reconstructions, including virtual bronchoscopy. Therefore, the ability of CT for detecting and localizing tracheal abnormalities are improved, which is useful for planning endoscopy or open surgery, or assess their results. Dynamic acquisition during expiration is the last refinement permitted by MDCT, which is of value to detect tracheomalacia.

CONCLUSIONS

MDCT is a non-invasive technique to image the trachea. Its applications are numerous, such as depiction of anatomical or functional abnormalities, evaluation of local extent of the disease, planning and assessing open surgery or interventional endoscopy.

Tumoral and non-tumoral trachea stenoses: evaluation with three-dimensional CT and virtual bronchoscopy

BACKGROUND

We evaluated the ability of 3D-CT and virtual bronchoscopy to estimate trachea stenosis in comparison to conventional axial CT and fiberoptic bronchoscopy, with a view to assist thoracic surgeons in depicting the anatomical characteristics of tracheal strictures.

METHODS

Spiral CT was performed in 16 patients with suspected tracheal stenoses and in 5 normal subjects. Tracheal stenoses due to an endoluminal neoplasm were detected in 13 patients, whilst post-intubation tracheal stricture was observed in the other 3 patients. Multiplanar reformatting (MPR), volume rendering techniques (VRT) and virtual endoscopy (VE) for trachea evaluation were applied and findings were compared to axial CT and fiberoptic bronchoscopy. The accuracy of the procedure in describing the localization and degree of stenosis was tested by two radiologists in a blinded controlled trial.

RESULTS

The imaging modalities tested showed the same stenoses as the ones detected by flexible bronchoscopy and achieved accurate and non-invasive morphological characterization of the strictures, as well as additional information about the extraluminal extent of the disease. No statistically significant difference was observed between the bronchoscopic findings and the results of axial CT estimations (P = 1.0). No statistically significant differences were observed between bronchoscopic findings and the MPR, VRT and VE image evaluations (P = 0.705, 0.414 and 0.414 respectively).

CONCLUSION

CT and computed generated images may provide a high fidelity, noninvasive and reproducible evaluation of the trachea compared to bronchoscopy. They may play a role in assessment of airway patency distal to high-grade stenoses, and represent a reliable alternative method for patients not amenable to conventional 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.

Thoracic CT Performance and Interpretation in the Multi-Detector Era

Multi-detector CT (MDCT), in particular isotropic or nearly isotropic MDCT, changes the way in which imagers perform and interpret studies of the thorax. The speed of data acquisition enables new clinical applications of MDCT in the areas of angiography and dynamic perfusion. Cardiac gating software is available, and CT studies of the heart and coronary arteries are now feasible. This review, however, focuses on the impact of MDCT on the routine practice of thoracic imaging, rather than on newer specific MDCT applications. The topics of scan performance and interpretation are related, and MDCT changes each of these areas when compared with the era of axial CT.

Is virtual bronchoscopy useful for physicians practising in a district general hospital?

BACKGROUND

Virtual bronchoscopy software is now available to district general hospitals (DGHs). There is limited information on the clinical utility of virtual bronchoscopy and whether it offers any additional information over conventional axial computed tomography in the setting of a busy DGH chest unit.

METHODS

Virtual bronchoscopy and computed tomography findings were compared in all patients who had a virtual bronchoscopy study over a 12 month period.

RESULTS

Eighteen consecutive patients had virtual bronchoscopy for a specific clinical indication over the study period. Additional information was conveyed by virtual bronchoscopy in five patients (in four patients the airways distal to an obstruction were better visualised thereby influencing decisions about airway stenting and in one patient the virtual bronchoscopy study showed an endobronchial lesion missed on computed tomography). In nine patients who were unfit for fibreoptic bronchoscopy (FOB) the radiologist was more confident in excluding an obstructive airway lesion. The main indication for performing a virtual bronchoscopy study was to rule out an obstructive airway lesion in patients who were unfit for FOB (n = 11).

CONCLUSION

Virtual bronchoscopy is feasible and useful in the management of a few selected patients in a DGH chest unit. Virtual bronchoscopy may convey additional information over computed tomography when the distal airways need to be visualised and for discrete endoluminal lesions.

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.

3-D imaging with MDCT

Without doubt, the greatest challenge of multidetector-row CT is dealing with 'data explosion'. For our carotid/intracranial CT angiograms, we routinely have 375 images to review (300 mm coverage reconstructed every 0.8 mm); for aortic studies we have 450-500 images ( approximately 600 mm coverage reconstructed every 1.3 mm); and for a study of the lower extremity inflow and run-off, we may generate 900-1000 transverse reconstructions. While we could reconstruct fewer images for these data, experience with single-detector row CT scanners indicates that longitudinal resolution and disease detection is improved when at least 50% overlap of cross-sections is generated [Radiology 200 (1996) 312]. If we are to optimize our clinical protocols and take full advantage of these CT scanners, we will need to change the way that we interpret, transfer, and store CT data. Film is no longer a viable option. Workstation based review of transverse reconstructions for interpretation is a necessity, but the workstations must improve to provide efficient access to these data, and we must have a way of providing our clinicians with images that can be transported to clinics and the operating room. Alternative visualization and analysis using volumetric tools, including 3-D visualization must evolve from luxury to necessity. We cannot rest on historical precedent to interpret these near isotropically sampled volumetric data using transverse reconstructions alone [Radiology 173 (1989) 527]. Although the tools for volumetric analysis on 3-D workstations have evolved over recent years, they have probably not yet evolved to a level that routine interpretation can be performed as efficiently and accurately as transverse section review. Both hardware and software developments must occur. While current computer workstations and visualization software are certainly adequate for assessing these MDCT data volumetrically, the process is very time consuming. What follows are a description of current workstation capabilities and a brief discussion of where development needs to go to facilitate the complete integration of volumetric analysis into the interpretive process of CT data.

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.

Hepatic segments II and III mimicking a lung mass: diagnosis of a normal variant using reformatted multiplanar CT images

We describe a patient misinterpreted to have a lung mass on CT owing to extension of hepatic segments II and III between the diaphragm and spleen. This report underscores the importance of being aware of this normal anatomic variant and the utility of two-dimensional multiplanar reformation in interpretation of abnormalities in the region of the thoracoabdominal junction.

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.

Administration of a CT division

A computed tomography (CT) division can be viewed as a business subsidiary of a larger corporation-the radiology department. While a large amount of radiologic literature has been devoted to specific CT techniques and applications, there has been less of a focus on the operational structure required to achieve quality and efficiency in a CT division. This report includes discussion of the managerial structure, equipment purchases, continuing education, protocols, billing, and quality assurance measures that can be used to administer a CT division.

Multi-detector row CT of thoracic disease with emphasis on 3D volume rendering and CT angiography

Multi-detector row computed tomography (CT) with three-dimensional (3D) volume rendering provides a unique perspective on thoracic anatomy and disease. Multi-detector row CT allows shorter acquisition times, greater coverage, and superior image resolution. Three-dimensional volume rendering now permits real-time, interactive modification of relative pixel attenuation in an infinite number of planes and projections. In vascular imaging, this technique provides image quality that equals or surpasses that of conventional angiography. Its use has expanded to aid in diagnosis and surgical planning, often obviating conventional or digital angiography and reducing costs. It is reliable in depicting clot and the pulmonary vasculature and may also be used to evaluate thoracic venous anomalies (eg, pulmonary arteriovenous malformations) and to plan therapy. Airway imaging with multi-detector row CT with 3D volume rendering is particularly useful in the planning and follow-up of stent placement. In diffuse lung disease, this technique can increase nodule detection and help differentiate between small nodules and vessels. It is also helpful in imaging the musculoskeletal system and the thoracic cage. Multi-detector row CT with 3D volume rendering has enhanced the conventional roles of thoracic CT and challenged the supremacy of other imaging modalities. It will likely play a leading role in future radiologic research and practice.

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.

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.

Data explosion: the challenge of multidetector-row CT

The development of multi detector-row CT has brought many exciting advancements to clinical CT scanning. While multi detector-row CT offers unparalleled speed of acquisition, spatial resolution, and anatomic coverage, a challenge presented by these advantages is the substantial increase on the number of reconstructed cross-sections that are rapidly created and in need of analysis. This manuscript discusses currently available alternative visualization tecvhniques for the assessment of volumetric data acquired with multi detector-row CT. Although the current capabilities of 3-D workstations offer many possibilities for alternative analysis of MCDT data, substantial improvements both in automated processing, processing speed and user interface will be necessary to realize the vision of replacing the primary analysis of transverse reconstruction's with alternative analyses. The direction that some of these future developments might take are discussed.

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.

Benign abnormalities and carcinoid tumors of the central airways: diagnostic impact of CT bronchography

OBJECTIVE

The purpose of this retrospective study was to determine the added diagnostic value, if any, of CT bronchography for the detection and characterization of benign abnormalities and typical carcinoid tumors of the central airways.

MATERIALS AND METHODS

We used bronchoscopy and helical CT to examine 238 bronchial sections in 28 patients with 32 bronchial abnormalities and in five patients with normal bronchoscopy results. Postprocessing consisted of CT bronchography based on surface rendering. Images were interpreted independently by two observers (a radiologist and a pneumonologist) who were not informed of the bronchoscopy results. After initial interpretation of axial CT scans, the observers analyzed the axial CT scans with CT bronchograms. Results were evaluated for gain in diagnostic accuracy and in confidence.

RESULTS

Mean sensitivity for detection of abnormal bronchial sections was 89% (range, 87-90%) for axial CT and 92% (range, 90-94%) for axial CT with CT bronchography (not significant). Mean specificity of both approaches exceeded 99%. A correct diagnosis of the nature of the bronchial abnormalities was proposed for 68% of the cases in which axial CT was used alone and in 76% in which both axial CT and CT bronchography were used (not significant). The addition of CT bronchography significantly increased the confidence of the pneumonologist in the diagnoses.

CONCLUSION

Axial CT remains the technique of choice to detect and characterize benign abnormalities of the airways. CT bronchography provides little diagnostic gain but increases the confidence of chest physicians in the interpretation of CT scans for the assessment of benign abnormalities and typical carcinoids of the central airways.

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.

Evaluation of tracheobronchial diseases: comparison of different imaging techniques

OBJECTIVE

To compare the clinical utility of the different imaging techniques used for the evaluation of tracheobronchial diseases.

MATERIALS AND METHODS

Forty-one patients with tracheobronchial diseases [tuberculosis (n = 18), bronchogenic carcinoma (n = 10), congenital abnormality (n = 3), post-operative stenosis (n = 2), and others (n = 8)] underwent chest radiography and spiral CT. Two sets of scan data were obtained: one from routine thick-section axial images and the other from thin-section axial images. Multiplanar reconstruction (MPR) and shaded surface display (SSD) images were obtained from thin-section data. Applying a 5-point scale, two observers compared chest radiography, routine CT, thin-section spiral CT, MPR and SSD imaging with regard to the detection, localization, extent, and characterization of a lesion, information on its relationship with adjacent structures, and overall information.

RESULTS

SSD images were the most informative with regard to the detection (3.95+/-0.31), localization (3.95+/-0.22) and extent of a lesion (3.85+/-0.42), and overall information (3.83+/-0.44), while thin-section spiral CT scans provided most information regarding its relationship with adjacent structures (3.56+/-0.50) and characterization of the lesion (3.51+/-0.61).

CONCLUSION

SSD images and thin-section spiral CT scans can provide valuable information for the evaluation of tracheobronchial disease.

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.