Polypoid lesions of airways: early experience with computer-assisted detection by using virtual bronchoscopy and surface curvature

A comparison of computer-assisted detection (CAD) programs for the identification of colorectal polyps: performance and sensitivity analysis, current limitations and practical tips for radiologists

AIM

To directly compare the accuracy and speed of analysis of two commercially available computer-assisted detection (CAD) programs in detecting colorectal polyps.

MATERIALS AND METHOD

In this retrospective single-centre study, patients who had colorectal polyps identified on computed tomography colonography (CTC) and subsequent lower gastrointestinal endoscopy, were analysed using two commercially available CAD programs (CAD1 and CAD2). Results were compared against endoscopy to ascertain sensitivity and positive predictive value (PPV) for colorectal polyps. Time taken for CAD analysis was also calculated.

RESULTS

CAD1 demonstrated a sensitivity of 89.8%, PPV of 17.6% and mean analysis time of 125.8 seconds. CAD2 demonstrated a sensitivity of 75.5%, PPV of 44.0% and mean analysis time of 84.6 seconds.

CONCLUSION

The sensitivity and PPV for colorectal polyps and CAD analysis times can vary widely between current commercially available CAD programs. There is still room for improvement. Generally, there is a trade-off between sensitivity and PPV, and so further developments should aim to optimise both. Information on these factors should be made routinely available, so that an informed choice on their use can be made. This information could also potentially influence the radiologist's use of CAD results.

Virtual and fiber-optic bronchoscopy in patients with indication for tracheobronchial evaluation

OBJECTIVE

The aim of this study was to compare the results of virtual bronchoscopy (VB) images in defining tracheobronchial pathologies with those of fiber-optic bronchoscopy (FOB) in patients with clinical indication for bronchoscopy.

METHODS

Twenty-two patients with bronchoscopy indication were evaluated with FOB and VB. The VB results were evaluated blindly, independent of the FOB results.

RESULTS

In 19 of the 22 patients, tracheobronchial abnormalities were present on FOB, whereas 3 patients had normal findings on FOB. In 17 of 19 patients, VB demonstrated the FOB diagnosis of tracheobronchial abnormality. While FOB detected 11 endoluminal lesions, VB detected 6. While FOB detected 20 obstructive lesions, VB detected 26. In evaluating external compression, FOB detected 2 lesions and VB detected 15.

CONCLUSIONS

VB is a non-invasive, uncomplicated, and reproducible examination method in patients with an indication for thorax examination. Virtual bronchoscopy could find a clinically broader field of application in the future.

Massive-training support vector regression and Gaussian process for false-positive reduction in computer-aided detection of polyps in CT colonography

PURPOSE

A massive-training artificial neural network (MTANN) has been developed for the reduction of false positives (FPs) in computer-aided detection (CADe) of polyps in CT colonography (CTC). A major limitation of the MTANN is the long training time. To address this issue, the authors investigated the feasibility of two state-of-the-art regression models, namely, support vector regression (SVR) and Gaussian process regression (GPR) models, in the massive-training framework and developed massive-training SVR (MTSVR) and massive-training GPR (MTGPR) for the reduction of FPs in CADe of polyps.

METHODS

The authors applied SVR and GPR as volume-processing techniques in the distinction of polyps from FP detections in a CTC CADe scheme. Unlike artificial neural networks (ANNs), both SVR and GPR are memory-based methods that store a part of or the entire training data for testing. Therefore, their training is generally fast and they are able to improve the efficiency of the massive-training methodology. Rooted in a maximum margin property, SVR offers excellent generalization ability and robustness to outliers. On the other hand, GPR approaches nonlinear regression from a Bayesian perspective, which produces both the optimal estimated function and the covariance associated with the estimation. Therefore, both SVR and GPR, as the state-of-the-art nonlinear regression models, are able to offer a performance comparable or potentially superior to that of ANN, with highly efficient training. Both MTSVR and MTGPR were trained directly with voxel values from CTC images. A 3D scoring method based on a 3D Gaussian weighting function was applied to the outputs of MTSVR and MTGPR for distinction between polyps and nonpolyps. To test the performance of the proposed models, the authors compared them to the original MTANN in the distinction between actual polyps and various types of FPs in terms of training time reduction and FP reduction performance. The authors' CTC database consisted of 240 CTC data sets obtained from 120 patients in the supine and prone positions. The training set consisted of 27 patients, 10 of which had 10 polyps. The authors selected 10 nonpolyps (i.e., FP sources) from the training set. These ten polyps and ten nonpolyps were used for training the proposed models. The testing set consisted of 93 patients, including 19 polyps in 7 patients and 86 negative patients with 474 FPs produced by an original CADe scheme.

RESULTS

With the MTSVR, the training time was reduced by a factor of 190, while a FP reduction performance [by-polyp sensitivity of 94.7% (18/19) with 2.5 (230/93) FPs/patient] comparable to that of the original MTANN [the same sensitivity with 2.6 (244/93) FPs/patient] was achieved. The classification performance in terms of the area under the receiver-operating-characteristic curve value of the MTGPR (0.82) was statistically significantly higher than that of the original MTANN (0.77), with a two-sided p-value of 0.03. The MTGPR yielded a 94.7% (18/19) by-polyp sensitivity at a FP rate of 2.5 (235/93) per patient and reduced the training time by a factor of 1.3.

CONCLUSIONS

Both MTSVR and MTGPR improve the efficiency of the training in the massive-training framework while maintaining a comparable performance.

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.

Detection and segmentation of colonic polyps on implicit isosurfaces by second principal curvature flow

Today's computer aided detection systems for computed tomography colonography (CTC) enable automated detection and segmentation of colorectal polyps. We present a paradigm shift by proposing a method that measures the amount of protrudedness of a candidate object in a scale adaptive fashion. One of the main results is that the performance of the candidate detection depends only on one parameter, the amount of protrusion. Additionally the method yields correct polyp segmentation without the need of an additional segmentation step. The supervised pattern recognition involves a clear distinction between size related features and features related to shape or intensity. A Mahalanobis transformation of the latter facilitates ranking of the objects using a logistic classifier. We evaluate two implementations of the method on 84 patients with a total of 57 polyps larger than or equal to 6 mm. We obtained a performance of 95% sensitivity at four false positives per scan for polyps larger than or equal to 6 mm.

Computer-aided detection of polyps in CT colonography using logistic regression

We present a computer-aided detection (CAD) system for computed tomography colonography that orders the polyps according to clinical relevance. The CAD system consists of two steps: candidate detection and supervised classification. The characteristics of the detection step lead to specific choices for the classification system. The candidates are ordered by a linear logistic classifier (logistic regression) based on only three features: the protrusion of the colon wall, the mean internal intensity, and a feature to discard detections on the rectal enema tube. This classifier can cope with a small number of polyps available for training, a large imbalance between polyps and non-polyp candidates, a truncated feature space, unbalanced and unknown misclassification costs, and an exponential distribution with respect to candidate size in feature space. Our CAD system was evaluated with data sets from four different medical centers. For polyps larger than or equal to 6 mm we achieved sensitivities of respectively 95%, 85%, 85%, and 100% with 5, 4, 5, and 6 false positives per scan over 86, 48, 141, and 32 patients. A cross-center evaluation in which the system is trained and tested with data from different sources showed that the trained CAD system generalizes to data from different medical centers and with different patient preparations. This is essential to application in large-scale screening for colorectal polyps.

MDCT of the airways: technique and normal results

The new generation of multidetector CT (MDCT) has revolutionized noninvasive imaging of proximal and distal airways. Exquisite anatomic details of the airway lumen and airway wall on axial CT images benefit in routine practice from postprocessing tools in adequate orientation. This method ensures an excellent assessment of the morphology and location of any pathology. It may be combined with use of very low dose CT. Airway lumen and airway wall areas may be quantitatively assessed on MDCT images by using specific techniques that are reproducible and accurate.

Detection of protrusions in curved folded surfaces applied to automated polyp detection in CT colonography

Over the past years many computer aided diagnosis (CAD) schemes have been presented for the detection of colonic polyps in CT Colonography. The vast majority of these methods (implicitly) model polyps as approximately spherical protrusions. Polyp shape and size varies greatly, however and is often far from spherical. We propose a shape and size invariant method to detect suspicious regions. The method works by locally deforming the colon surface until the second principal curvature is smaller than or equal to zero. The amount of deformation is a quantitative measure of the 'protrudeness'. The deformation field allows for the computation of various additional features to be used in supervised pattern recognition. It is shown how only a few features are needed to achieve 95% sensitivity at 10 false positives (FP) per dataset for polyps larger than 6 mm.

Improved Diagnosis and Navigation for CT Colonography

The goal of this research project is to develop a fast, accurate, and patient-friendly computer-aided diagnosis (CAD) component of CT colonography, that improves the robustness and accuracy of current colon wall segmentation and achieves earlier colorectal cancer diagnoses through an improved polyp detection method. Many advanced image processing techniques are applied to clearly outline the colon wall in the CT data set of human abdomen, and subtract the colon portion from the entire data set. After the subtraction, the detailed information and the surface curvature information on the colon wall is analyzed. The active contour model is assisted by presegmentation steps including mathematical morphology filtering, edge detection and other image processing techniques.

Tracheobronchial Anomalies and Stenoses: Detection with Low-Dose Multidetector CT with Virtual Tracheobronchoscopy—Comparison with Flexible Tracheobronchoscopy

PURPOSE

To prospectively assess the sensitivity and specificity of low-dose multidetector computed tomography (CT) with virtual tracheobronchoscopy (VT) for evaluation of suspected airway stenoses and/or abnormalities by using flexible tracheobronchoscopy (FT) as the reference standard.

MATERIALS AND METHODS

The study was approved by the local ethics committee; parental consent was obtained. Forty-five patients with clinically and/or radiographically suspected tracheobronchial stenosis and/or anomaly underwent FT and contrast material-enhanced single-phase multidetector CT with VT. CT was performed with an age- and weight-adjusted low-dose protocol: 120 or 80 kV; 120 or 60 mA; collimation, 1.5 or 0.75 mm; gantry rotation, 0.5 second. Mean effective dose was calculated for all examinations. Postprocessing was performed with surface rendering of VT images and multiplanar reformations. CT images were analyzed in consensus by two radiologists who were blinded to FT results. Statistical analysis was performed with 2 x 2 contingency tables; 95% confidence intervals (CIs) were calculated with the Blyth-Still-Casella procedure.

RESULTS

Mean patient age was 4.4 years (range, 2 months to 16 years; 53% male patients). Tracheobronchial narrowing and/or abnormality were depicted at FT in 38 of 45 patients. In 33 of 38 patients, multidetector CT with VT depicted a tracheobronchial narrowing and/or anomaly. In 10 of 38 patients, tracheobronchial stenosis was induced by vascular anomalies. Five patients with normal findings at multidetector CT with VT had tracheobronchomalacia with inspiratory airway stenosis at FT. Sensitivity and specificity of CT with VT were 86.8% (95% CI: 73.3%, 94.7%) and 85.7% (95% CI: 44.6%, 99.3%), respectively. Positive and negative predictive values were 97.1% (95% CI: 84.9%, 99.9%) and 54.5% (95% CI: 25.0%, 80.0%), respectively. Overall accuracy was 86.7% (95% CI: 74.3%, 94.0%). Mean effective dose was 1.1 mSv (range, 0.5-1.8 mSv).

CONCLUSION

Multidetector CT with VT with a low-dose protocol had high sensitivity and specificity for depiction of tracheobronchial narrowings and/or anomalies. However, tracheal narrowing due to tracheobronchomalacia was difficult to diagnose at single-phase multidetector CT with VT.

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.

Three-dimensional path planning for virtual bronchoscopy

Multidetector computed-tomography (MDCT) scanners provide large high-resolution three-dimensional (3-D) images of the chest. MDCT scanning, when used in tandem with bronchoscopy, provides a state-of-the-art approach for lung-cancer assessment. We have been building and validating a lung-cancer assessment system, which enables virtual-bronchoscopic 3-D MDCT image analysis and follow-on image-guided bronchoscopy. A suitable path planning method is needed, however, for using this system. We describe a rapid, robust method for computing a set of 3-D airway-tree paths from MDCT images. The method first defines the skeleton of a given segmented 3-D chest image and then performs a multistage refinement of the skeleton to arrive at a final tree structure. The tree consists of a series of paths and branch structural data, suitable for quantitative airway analysis and smooth virtual navigation. A comparison of the method to a previously devised path-planning approach, using a set of human MDCT images, illustrates the efficacy of the method. Results are also presented for human lung-cancer assessment and the guidance of bronchoscopy.

Effects of ECG Gating and Postprocessing Techniques on 3D MDCT of the Bronchial Tree

OBJECTIVE

Our goal was to determine the impact of ECG gating and different postprocessing techniques on 3D imaging of the bronchial tree. SUBJECTS AND METHODS. Retrospective ECG-gated MDCT and non-ECG-gated MDCT of the chest were performed in 25 patients. ECG-gated MDCT data were reconstructed mid diastole using a fixed interval of -400 msec in 25 patients and then additionally at -200, -300, and -500 msec in 10 of those patients. Shaded surface display and volume rendering of the bronchial tree combined with virtual bronchoscopy were performed using all data sets. The extent of bronchial tree visualization in shaded surface display-virtual bronchoscopy and volume rendering-virtual bronchoscopy and the presence of artifacts in volume-rendered images were scored by three blinded reviewers. The effective radiation doses of the ECG-gated and nongated acquisitions were compared.

RESULTS

The summary scores of all bronchial segments for gated shaded surface display-virtual bronchoscopy and gated volume rendering-virtual bronchoscopy did not differ significantly. The summary scores for nongated shaded surface display-virtual bronchoscopy and nongated volume rendering-virtual bronchoscopy were not significantly different. Non-gated acquisition yielded significantly better visualization of the bronchial tree for both post-processing techniques, regardless of the time interval used for reconstruction of the ECG-gated series. Artifact scores in volume-rendered images were significantly higher for ECG-gated MDCT compared with nongated MDCT. Effective radiation dose was significantly higher for the ECG-gated acquisition.

CONCLUSION

Given the advantage of volume rendering for representing the entire data set and given the lower radiation dose and better 3D image quality of nongated acquisition, volume rendering performed on nongated MDCT data is the method of choice for 3D visualization of the bronchial tree.

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.

Computed tomography gastrography with volume-rendering technique: correlation with double-contrast barium study and conventional gastroscopy

The volume-rendering technique uses computed tomography data to produce simulated images of conventional barium and endoscopic studies of the stomach. Various gastric lesions are detected on volume-rendered images, and submucosal tumors are easily differentiated from mucosal lesions by means of the overlying bridging fold. Lesions that are only manifested by a change of mucosal color (early gastric cancer type 2b) or a loss of mucosal detail (gastritis) are difficult to detect from volume-rendered images, however. In cases of gastric neoplasm and varix, both the extraluminal pathologies of the lesion and the relation between the intraluminal and extraluminal components can be evaluated simultaneously.

Feasibility of a Curvature-based Enhanced Display System for Detecting Cerebral Aneurysms in MR Angiography

PURPOSE

To assess the feasibility of a curvature-based enhanced display system for detecting cerebral aneurysms in MR angiography.

METHODS

MR angiography studies of 18 patients (eight male and 10 female, average age 65.7, age range 50 to 75 years old) with 23 known aneurysms were evaluated with a curvature-based display system. The two curvature features-the volumetric shape index and curvedness values-were calculated at each voxel. These were displayed independently on a workstation, overlaid on volume-rendered images. Two neuroradiologists evaluated the images for visibility and diagnosis of the cerebral aneurysms. The diagnostic results were compared with the original reports.

RESULTS

The calculation time for each curvature index was 30 to 40 s for 120 to 140 slices of original MR angiography data. Shape index images emphasized smooth and round aneurysms more than aneurysms with irregular surfaces. Curvedness images revealed aneurysms well when the aneurysms had diameters that differed from those of the surrounding vessels. The computer-assisted-detection method detected 24 aneurysms, three of which were not pointed out in the initial report.

CONCLUSION

Our results show that the curvature-based display system we have developed is feasible and that it may help to detect small aneurysms that are prone to be overlooked in routine readings.

Three-dimensional navigator for retroperitoneal laparoscopic nephrectomy using multidetector row computerized tomography

PURPOSE

We evaluated the efficacy of a 3-dimensional (D) navigator for retroperitoneal laparoscopic nephrectomy.

MATERIALS AND METHODS

A total of 21 patients with malignant localized renal (16) or ureteral (5) neoplasms underwent multi-detector row computerized tomography. The 3-D navigator was created using volume rendering technique. These findings were compared with videos obtained during laparoscopy.

RESULTS

The 3-D navigator depicted all renal arteries (100% sensitivity) and 24 of the 25 renal veins (96% sensitivity). Hilar anatomy, including the tumor, major vessels and adrenal gland, and their relationships were visualized as in laparoscopic views.

CONCLUSIONS

The 3-D navigator has a potentially important role in retroperitoneal laparoscopic nephrectomy. It is able to guide surgeons and aid in avoiding operative risks and possible complications.

Innovative molecular and imaging approaches for the detection of lung cancer and its precursor lesions

Current approaches for the therapy of lung cancer, the majority of which being advanced cancers, have failed to impact on long term survival. The key to improvement lies in the combination of early diagnosis and the introduction of novel targeted therapies. In this article we review some of the innovative approaches, both imaging and molecular, that are currently under investigation for early detection. Because lung cancers may arise in the central or peripheral compartments of the lung, newer approaches must target tumours arising in both of these compartments. Specimens available for analysis include sputa and blood. Detection of genetic changes in peripheral blood is a promising avenue being explored by several groups. Molecular techniques discussed include gene mutations, detection of nuclear riboprotein, methylation related silencing of genes and malignancy associated changes. Newer imaging technologies include autofluorescence bronchoscopy, virtual bronchoscopy, optical coherent tomography and confocal microscopy. Although the impact of these new technologies on survival has not been determined, they offer a wide range of exciting new approaches. In time they may completely revamp the present highly conservative and unsuccessful approaches to early diagnosis.

Technical innovation of cardiac multirow detector CT using multisector reconstruction

Multisector reconstruction is a newly developed algorithm for multirow detector CT in cardiac study. Using volume data sets obtained by ECG-gated scanning, we can reconstruct cardiac images at any desired phase of the cardiac cycle retrospectively. In retro-processing multiplanar and three-dimensional images, thin-slice images with overlapping increment have a great advantage due to increasing z-axis resolution. In this article, we present principles of the algorithm, a phantom study, clinical applications and perspectives for the 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.

CT virtual bronchoscopy of the central airways in patients with Wegener's granulomatosis

OBJECTIVES

To compare CT virtual bronchoscopy (VB) to CT alone and to conventional bronchoscopy for evaluation of central airway stenoses in patients with Wegener's granulomatosis.

DESIGN

Prospective observer study, in which 18 thin-section helical CT scans of the trachea and bronchi of 11 patients with Wegener's granulomatosis were obtained. VB was performed using surface rendering and was evaluated by one bronchoscopist and one radiologist in a blinded fashion. Bronchoscopic correlation within an average of 1.8 days of CT was available.

MEASUREMENTS AND RESULTS

VB displayed 188 of 198 bronchi (95%). Thirty-two of 40 stenoses (80%) were detected by VB by at least one of two physicians (double reading), and 22 of 40 stenoses (55%) were detected by a third physician reading only the CT.

CONCLUSIONS

VB depicts bronchi to the segmental level and detects the majority of central airway stenoses in patients with Wegener's granulomatosis. A team approach is useful to attain optimal clinical benefit from VB for these patients.

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.

Ultrasound virtual endoscopic imaging

Volume data acquisition, three dimensional (3D) imaging, and multiplanar reformatting have become widely used for computed tomography (CT) and magnetic resonance imaging (MRI). As an extension of this technology, virtual endoscopic visualization of hollow organs has become a reality that is now finding its way into clinical CT practice. The same methods of computer processing as are used for CT and MRI can be applied to an ultrasound (US) volume image data set with the same potential output; namely, 3D, multiplanar, and virtual endoscopic images. The use of this image processing technology for US applications has lagged behind the CT and MRI applications, but considerable progress in applying these methods to US has occurred in recent years. As a result, US virtual endoscopic imaging now can be performed on a clinical basis by using standard US instruments and commercially available computer software. The use of newer US imaging methods, such as tissue harmonic and power Doppler imaging, has enhanced the potential for US virtual endoscopy. This article reviews the technology of US virtual endoscopy. In addition, our preliminary experience of using this method for abdominal and vascular diagnosis is described. Finally, we speculate on technical improvements and potential applications that are likely in the future.

Automated polyp detector for CT colonography: feasibility study

An abdominal computed tomographic scan was modified by inserting 10 simulated colonic polyps with use of methods that closely mimic the attenuation, noise, and polyp-colon wall interface of naturally occurring polyps. A shape-based polyp detector successfully located six of the 10 polyps. When settings that enhanced the edge profile of polyps were chosen, eight of 10 polyps were detected. There were no false-positive detections. Shape analysis is technically feasible and is a promising approach to automated polyp detection.

Distortion reduction for fast soft straightening of the colon

RATIONALE AND OBJECTIVES

The purpose of this study was to suppress the geometric distortion associated with soft straightening of the colon by moderately adjusting curved cross sections, which is equivalent to appropriately modifying the underlying electrical field.

MATERIALS AND METHODS

A computational mechanism to reduce the geometric distortion associated with soft straightening was developed. Because the cause of distortion is uneven sampling of the colon wall with curved cross sections, the curved cross sections formed according to a numerically simulated electrical field were redistributed in the distortion reduction process. This mechanism can be directly incorporated into a previously published fast soft-straightening algorithm. Simulations were performed to evaluate the effectiveness of the mechanism, and a phantom colon with digitally implanted, spherical polyps was straightened and rendered to visually display the efficacy of the mechanism.

RESULTS

The distortion reduction mechanism was advantageous regarding shape preservation of polyps and alleviated distortion substantially. The mechanism occupied only a small portion of the total processing time.

CONCLUSION

The distortion reduction mechanism can effectively reduce the geometric distortion associated with soft straightening at little computational cost and has potential for use with computed tomographic colonography.

Virtual CT cystoscopy: color mapping of bladder wall thickness

RATIONALE AND OBJECTIVES

To improve the conspicuity of bladder tumors in a virtual environment, we developed an algorithm for color mapping the thickness of the bladder wall. The purpose of this study was to demonstrate the feasibility of this algorithm as a component of virtual CT cystoscopy.

METHODS

Five subjects with a history of superficial transitional-cell carcinoma of the bladder underwent helical CT scanning after insufflation of the bladder with air. Source images were transformed into three-dimensional models, and the thickness of the bladder wall was demarcated by using a new computer algorithm and a fixed color scale. Results were compared with those obtained by conventional cystoscopy.

RESULTS

Three tumors, one site of benign wall thickening, and normal wall thickness were correctly identified by using axial source images and virtual cystoscopy with color mapping.

CONCLUSIONS

Color mapping of bladder wall thickness is feasible and demonstrates both normal and thickened urothelium. Its value in identification of small or sessile tumors will require further trials.

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.

Fast algorithm for soft straightening of the colon

RATIONALE AND OBJECTIVES

In this study, the authors developed a fast algorithm for soft straightening of the colon with computed tomographic data that greatly accelerates the unraveling process based on the interpolation of representative electric force lines.

MATERIALS AND METHODS

Each curved cross section of the colon is defined by electric force lines of a common origin on an electrically charged central path and is constructed by interpolating most of these force lines from a limited number of representative force lines that are traced directly. Both a synthetic colon phantom and a colon in a living patient were used to demonstrate the feasibility of the fast interpolation algorithm compared with direct implementation for soft straightening of the colon.

RESULTS

The interpolation-based soft-straightening algorithm ran approximately 40 times faster than the direct implementation of the electric field-based soft-straightening algorithm.

CONCLUSION

The fast algorithm for soft straightening of the colon has potential for use in computed tomographic colonography.

Diagnostic potential of virtual bronchoscopy: advantages in comparison with axial CT slices, MPR and mIP?

The aim of this study was to evaluate the diagnostic potential of virtual endoscopy (VE) and to compare it with axial CT slices, multiplanar reconstructions (MPR), minimal intensity projections (mIP), and bronchoscopy in patients diagnosed with bronchogenic carcinoma. Thirty patients underwent a spiral CT. Axial CT images were transferred to an Onyx workstation (Silicon Graphics, Sun Microsystems, Mountain View, Calif.) for performing virtual endoscopy. Accuracy for this procedure was tested by three radiologists on a monitor in comparison with axial CT slices, MPR, mIP, and bronchoscopy concerning the localization and degree of stenoses. Endoluminal tumors were identified by virtual bronchoscopy with no statistically significant difference of localization or grading of stenosis in comparison with bronchoscopy, axial CT slices, MPR and mIP. Axial CT slices, MPR, and mIP showed poorer results with over- or underestimation of stenoses compared with VE and bronchoscopy. Passing of stenoses was only possible with VE in 5 patients. Virtual endoscopy is a non-invasive method for identification of endoluminal tumors and is comparable to real bronchoscopy.

Straightening the colon with curved cross sections: an approach to CT colonography

RATIONALE AND OBJECTIVES

The purpose of this study was to straighten digitally and consistently the colon with curved cross sections and to compare the results with planar cross-section-based processing for computed tomographic (CT) colonography.

MATERIALS AND METHODS

In electric field-based straightening, curved cross sections are formed along electric force lines because of electric charges digitally distributed along the colon central path. Four straightening experiments were conducted on CT scans of a colonoscopy phantom. Representative images were studied for polyp detectability and feature distortion. Two further trials involved patient data to demonstrate the clinical feasibility of this method.

RESULTS

In colon straightening with planar sections, a polyp was counted multiple times in both phantom and patient studies where the polyps were in central path turns with substantial curvature. Furthermore, opposite the central path turns, the colon walls were undersampled with planar sections. Straightening with curved sections produced consistent mappings. Image distortion was present in straightening with curved sections, but the conspicuity of polyps was maintained. In the soft-straightening process, trilinear interpolation greatly suppressed the surface- or volume-rendering noise associated with nearest neighbor interpolation.

CONCLUSION

Straightening with curved sections outperforms straightening with planar sections in terms of polyp detectability. This approach eliminates the navigation difficulties of current CT colonography and may have clinical use.

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.