A review of the technical and clinical aspects of virtual endoscopy

The Accuracy of Different Modalities Used for Preoperative Primary Tumour Localisation in Operated Colorectal Cancer Patients

Aim Colonoscopy and computed tomography (CT) scans of the abdomen and pelvis are routine pre-operative assessment tools in colorectal cancer (CRC) patients. There have been some discrepancies regarding the location of cancer when seen by colonoscopy versus CT scan. The purpose of this study was to compare the accuracy of a colonoscopy with a computed tomography (CT) scan of the abdomen and pelvis with contrast, which is done routinely before surgery to localise the exact site of the tumour within the large bowel, whilst comparing both to the operative, gross and histopathology findings of the exact location. Methods A retrospective study was carried out on 165 colorectal cancer patients operated on between January 1, 2010, and December 31, 2014, using electronic hospital records that were reviewed anonymously, comparing the location of cancer within the large bowels as was found on colonoscopy and CT scan of the abdomen and pelvis with contrast, comparing both to post-operative histopathology specimen or intra-operative assessment in cases where no resection of the primary tumour was performed. Results CT and colonoscopy were both accurate in diagnosing 70.5% of cases that had done both investigations pre-operatively. The best results were obtained when the cancer was located in the caecum as confirmed post-operatively; the combined accuracy rate was 100%. CT was accurate, whilst colonoscopy was not in eight (6.2%) cases (all are rectal or sigmoid cancers), and colonoscopy was accurate and CT was not in 12 cases, 10 of them were rectal and two were ascending colonic. Colonoscopy was not performed in 36 (21%) cases for a variety of reasons, including large bowel obstruction or perforation on presentation. In 32 of these cases, CT scan managed to accurately predict the location of cancer (mostly rectal and caecal), and CT scan was inaccurate in 20.6% of cases (34 out of 165), whilst colonoscopy was inaccurate in 13.9% of cases (18 out of 129). Conclusion Colonoscopy is more accurate in localising colorectal cancers than CT scan of the abdomen and pelvis with contrast. CT scan diagnoses regional and distant spread of colorectal cancers such as nodal status, invasion of neighbouring organs and/or peritoneum and the presence of liver metastases, whilst colonoscopy is limited to intraluminal diagnosis but can be both a diagnostic and therapeutic tool, with higher accuracy, in general, in localising colorectal cancers. Both CT scan and colonoscopy were equal in appendicular, caecal, splenic flexure and descending colon cancer localisation accuracy.

Colorectal cancer, screening and primary care: A mini literature review

Colorectal cancer (CRC) is a common health problem, representing the third most commonly diagnosed cancer worldwide and causing a significant burden in terms of morbidity and mortality, with annual deaths estimated at 700000. The western way of life, that is being rapidly adopted in many regions of the world, is a well discussed risk factor for CRC and could be targeted in terms of primary prevention. Furthermore, the relatively slow development of this cancer permits drastic reduction of incidence and mortality through secondary prevention. These facts underlie primary care physicians (PCPs) being assigned a key role in health strategies that enhance prevention and prompt diagnosis. Herein, we review the main topics of CRC in the current literature, in order to better understand its pathogenesis, risk and protective factors, as well as screening techniques. Furthermore, we discuss preventive and screening policies to combat CRC and the crucial role served by PCPs in their successful implementation. Relevant articles were identified through electronic searches of MEDLINE and through manual searches of reference lists.

Virtual endoscopy of laryngeal carcinoma: Is it useful?

OBJECTIVE: To compare virtual endoscopy (VE) with flexible endoscopy in patients with cancer of the larynx.

STUDY DESIGN AND SETTINGS: This prospective study includes 24 patients with proven cancer of the larynx. Patients underwent spiral CT according to our standard protocol for upper airway imaging. This same set of axial scans was transferred to a dedicated workstation to obtain VE images. Results of VE were compared with the findings of flexible endoscopy.

RESULTS: Quality of the examination was good in 96% of the patients. VE identified all exophytic lesions. Two small flat lesions could be observed as slightly enhanced plaques only on the axial scans. Subglottic extension was correctly demonstrated in all cases by associating VE to the axial scans.

CONCLUSION: VE shows high sensitivity in the identification of exophytic lesions of the larynx and can establish relationships between cancer and nearby structures. It can be performed in the presence of severe stenosis and does not require sedation and additional scanning. On the other hand, VE show limits in the identification of flat lesions and does not allow biopsies and functional imaging to be performed.

SIGNIFICANCE: VE is a useful tool for staging and presurgery treatment of cancer of the larynx.

Multi-detector computed tomography imaging of large airway pathology: A pictorial review

The tracheobronchial tree is a musculo-cartilagenous framework which acts as a conduit to aerate the lungs and consequently the entire body. A large spectrum of pathological conditions can involve the trachea and bronchial airways. These may be congenital anomalies, infections, post-intubation airway injuries, foreign body aspiration or neoplasms involving the airway. Appropriate management of airway disease requires an early and accurate diagnosis. In this pictorial essay review, we will comprehensively describe the various airway pathologies and their imaging findings by multi-detector computed tomography.

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.

An automatic method for colon segmentation in CT colonography

An automatic method for the segmentation of the colonic wall is proposed for abdominal computed tomography (CT) of the cleansed and air-inflated colon. This multistage approach uses an adaptive 3D region-growing algorithm, with a self-adjusting growing condition depending on local variations of the intensity at the air-tissue boundary. The method was evaluated using retrospectively collected CT scans based on visual segmentation of the colon by expert radiologists. This evaluation showed that the procedure identifies 97% of the colon segments, representing 99.8% of the colon surface, and accurately replicates the anatomical profile of the colonic wall. The parameter settings and performance of the method are relatively independent of the scanner and acquisition conditions. The method is intended for application to the computer-aided detection of polyps in CT colonography.

[CT colonography vs. barium enema for the preoperative study of colorectal cancer in patients with incomplete colonoscopy]

BACKGROUND AND OBJECTIVE

The complete preoperative evaluation of the colon is necessary in colorectal cancer owing to the frequency of synchronous tumors. The objective of this paper was to evaluate the utility of the computed tomography colonography (CTC) as opposed to barium enema (BEDC) when the colonoscopy was incomplete or impossible to perform.

PATIENTS AND METHOD

Group A: 50 patients with colorectal cancer with subsequent incomplete colonoscopy and BEDC. Group B: 40 patients with colorectal cancer with subsequent incomplete colonoscopy and CTC. As gold standard to match the tests, we carried out the pathological study of the surgical piece and the colonoscopy 3 months after surgery. In addition, we studied the degree of satisfaction, indirect effect and cost by test.

RESULTS

There were no synchronous tumors. For the detection of colonic polyps, we obtained for the CTC the following values: Sensitivity = 85.7%, Specificity = 96.1%, PPV = 92.3%, NPV = 92.6%, CPP = 21,97 and CPN =0,15. And for BEDC, the values were: Sensitivity = 23.5%, Specificity = 92.8%, PPV = 80%, NPV = 71.7%, CPP = 3.26 and CPN = 0.82 (p < 0.001). The degree of satisfaction was greater with CTC than with BEDC (p < 0.05). There were no differences as far as indirect effect was concerned. The cost of CTC was 33.18 Euros and it was 42.42 Euros for BEDC.

CONCLUSION

CTC is better than BEDC both to confirm the presence of polyps in colon and to rule out the absence of them in patients in whom a complete the study of the colon by colonoscopy has not been possible.

The evolving role of CT colonography

Colorectal cancer (CRC) screening is widely recommended as part of standard preventive care. All average risk persons over the age of 50 y are eligible. Various authorities have advocated fecal occult blood testing, flexible sigmoidoscopy, barium enema and colonoscopy at varying intervals as acceptable screening options. Despite the array of choices, CRC screening lags in frequency behind other cancer screening maneuvers like mammography or Pap smear. Of late, there is growing interest in CT colonography (CTC) as another screening option. CTC, or virtual colonoscopy, may represent an attractive, non-invasive method of CRC screening that provides images akin to traditional colonoscopy. Improvements in CTC performance, especially when coupled with declining costs, suggest that CTC's role in average risk screening will increase in the future. This review summarizes available data about the efficacy of CTC in average and high risk screening populations. Current indications as well as limitations to this technology are discussed, as are practical issues like the cost-effectiveness of CTC for widespread use.

Colonografía tomográfica computarizada: aplicaciones, ventajas e inconvenientes

INTRODUCTION

Complete preoperative study of the colon is required in the management of colorectal cancer, due to the frequent association of primary colonic neoplasms with colonic adenomas (28%) and/or synchronous carcinomas (5%) of the colon. We present a series of patients who underwent computed tomographic colonography, the indications for this procedure, and the results.

PATIENTS AND METHODS

We performed a descriptive prospective study. Between May 2003 and August 2004, 50 computed tomographic colonographies were performed in 50 patients with suspected stenosing colorectal cancer and incomplete conventional colonoscopy.

RESULTS

Fifty computed tomographic colonographies were performed. The findings were as follows: three were normal (6%), and in the remainder, one was a false positive for a suspected neoplastic pelvic mass (3.125%) and two were false positives (11.7%) for colonic polyps. Fifty percent of the findings (n = 32) were related to peritoneal metastases and colonic neoplasms. There were 12 technical complications [lack of cleaning of the colon (5), lack of distension (2), little air insufflation (5)]. Patient complications included vegetative manifestations in one (vomiting) and rectal bleeding in another. The overall complication rate was 27.4% (23.4% corresponded to technical complications and the remaining 4% were patient-related). There was no mortality related to the procedure.

CONCLUSION

Because computed tomographic colonography is safe, effective and well tolerated by the patient, it should be considered as a technical alternative in the study of stenosing neoplasms of the proximal colon with incomplete colonoscopy. In addition, it allows other associated findings, both intra- and extracolonic, to be obtained and improves the diagnostic and therapeutic management of the patient.

Clinical usefulness of 3-dimensional computed tomography laryngography in laryngeal and hypopharyngeal cancer

This study was designed to evaluate the clinical usefulness of 3-dimensional computed tomography (CT) laryngography for the determination of subglottic extension in laryngeal cancer and for the involvement of the pyriform sinus apex in hypopharyngeal cancer. Twenty-one patients with laryngeal cancer and 19 patients with hypopharyngeal cancer underwent spiral CT during quiet breathing, /E/ phonation, Valsalva's maneuver, and modified Valsalva's maneuver. Three-dimensional volume rendering with CT data was performed on a workstation. Three-dimensional CT laryngography was compared to laryngoscopy, axial CT, endoscopy, and/or histopathologic findings. Three-dimensional CT laryngography was useful for showing subglottic extension in laryngeal cancer and involvement of pyriform sinus apex in hypopharyngeal cancer. Three-dimensional CT laryngography with quiet breathing was most informative for the determination of subglottic extension, whereas 3-dimensional CT laryngography with modified Valsalva's maneuver was most informative for the diagnosis of pyriform sinus apex involvement. In patients with vocal cord palsy, the contour of the vocal cord was the same during all 4 maneuvers. Three-dimensional CT laryngography during quiet breathing, /E/ phonation, Valsalva's maneuver, and modified Valsalva's maneuver may be useful in assessing laryngeal and hypopharyngeal cancers. This technique may provide important information not provided by conventional CT images.

Virtual endoscopy of the tracheo-bronchial system: sub-millimeter collimation with the 16-row multidetector scanner

The purpose of this study was to evaluate the scope of sub-millimeter collimation reconstruction parameters using 16-row computer tomography and ECG triggering on image quality in virtual bronchoscopy. Thirty-two patients (5 women, 27 men, mean age 66.6+/-1.4) who had been admitted for coronary artery bypass graft surgery underwent CT examination of the thorax (Sensation 16, Siemens, Inc., Forchheim, Germany). All patients were examined with 16x0.75-mm collimation. Image reconstruction was performed for two groups. In group A ( n=32), slice thickness of 1.5 mm and an overlap of 0.75 mm were used. In group B ( n=32), slice thickness of 0.75 mm and an overlap of 0.4 mm were applied. Retrospective ECG triggering was performed in all patients. The maximum order of recognizable bronchi was determined in each data set. In addition to assessing the maximum order of bronchial bifurcation, bronchial diameter was determined in truly perpendicular sections in each patient. For every segment proximal to a bifurcation, image quality was subjectively graded as poor (grade 1), moderate (grade 2) or good (grade 3). The observers were asked to identify the minimum cardiac movement ECG-triggered image sets assuming that they would be of better quality than the maximum cardiac movement ECG-triggered image sets. The Mann-Whitney U-test and the Fisher's Exact Test were used for statistical evaluation. In group A, a mean of 4.8+/-0.2 bifurcations was ascertained vs. 6.5+/-0.3 bifurcations in group B [ P<0.0003]. For bronchial diameters in group A, a mean of 7.5+/-0.4 mm was determined vs. 4.6+/-0.4 mm in group B [ P<0.0001]. In group B, two independent radiologists observed a significant shift to better image quality in all segments evaluated [ P<0.006 to P<0.000001]. Motion artifacts were judged as being significantly reduced by minimum cardiac movement ECG-triggering in group B [observer 1: P=0.0007 (20/32); observer 2: P=0.008 (18/32)], but not in group A [observer 1: P=0.286 (13/32); observer 2: P=0.123 (16/32)]. Sub-millimeter collimation and minimum cardiac movement ECG-triggered data acquisition allow deeper penetration into the tracheo-bronchial system allowing visualization of the bronchial surface down to diameters below 5 mm in certain cases up to the eighth bifurcation. Along with an enhanced visualization as such, better image quality is acquired in all segments evaluated. Trade off between better image quality, of doubtful diagnostic consequence, and much higher irradiation dose must be made.

Automated segmentation of colonic walls for computerized detection of polyps in CT colonography

PURPOSE

A new method for fully automated segmentation of the colonic walls in volumetric CT data was developed for limitation of the search space in computerized detection of polyps.

METHOD

For reliable segmentation, an anatomy-oriented approach was used, in which several anatomical structures are segmented in addition to the colon for utilization of their properties.

RESULTS

The segmentation method was validated by use of 14 data sets, consisting of cases positive for colonic polyps. We found that the segmented colonic walls included all of the polyps. A subjective rating of the results was performed based on several criteria for visualization of anatomic detail of the colonic wall and mucosal surface. Except for a few cases in which insufflation of the colon was insufficient, all of the results included >95% of the colonic walls.

CONCLUSION

This method for colonic wall segmentation is reliable and the segmentation results are applicable in both visualization of the colon and computer-aided diagnosis in the detection of polyps in CT colonography.

Spiral CT colonography: reader agreement and diagnostic performance with two- and three-dimensional image-display techniques

PURPOSE

To assess the diagnostic performance and reader agreement with two-dimensional (2D) and three-dimensional (3D) display techniques for detecting colorectal polyps with spiral computed tomographic (CT) colonography.

MATERIALS AND METHODS

A test set of 30 colonic segments was developed from spiral CT colonographic studies (12 with polyps and 18 without). The 12 segments with polyps contained 22 lesions (11 polyps <10 mm, 11 polyps or cancers >/=10 mm), with all findings verified with colonoscopy. Three specific 2D and 3D image-display techniques were tested. Three experienced abdominal radiologists independently analyzed each test case and were retested 6 weeks later.

RESULTS

The results of readings 1 and 2 were similar for all image-display techniques among the readers. Pooled segment results were sensitivity of 89%-92% and specificity of 72%-83%. Pooled polyp size results for sensitivity and positive predictive value were 77%-86% and 74%-86% (all polyps, n = 22), 91%-100% and 85%-100% (polyps or cancers >10 mm, n = 11), and 61%-73% and 61%-80% (polyps 5-9 mm, n = 11), respectively. Overall intraobserver agreement was good for the three display techniques (kappa, 0.60-1.00); however, interobserver agreement for 2D multiplanar reformation was lower (kappa, 0.53-0.80).

CONCLUSION

Among experienced abdominal radiologists, similar diagnostic performance in polyp detection was found among 2D multiplanar reformation and 3D display techniques, although individual cases showed improved characterization with 3D display techniques. Evaluation of reader agreement demonstrated good intraobserver agreement, with variable interobserver agreement.

Computed tomographic colonography and conventional colonoscopy for colon diseases: a prospective, blinded study

OBJECTIVES

Computed tomographic (CT) colonography or virtual colonoscopy is a new diagnostic method for the colon and rectum, developed on the basis of spiral computed axial tomography and employing virtual reality technology. The aim of this study was to determine the sensitivity, specificity, and diagnostic accuracy of CT colonography compared with colonoscopy in a prospective, blinded study in one single institution in Italy.

METHODS

Ninety-nine patients randomly selected among those attending the open-access endoscopy unit for diagnostic colonoscopy underwent colonoscopy and spiral CT. The images obtained were transmitted to generate the virtual colonoscopy pictures. A supervisor compared the results with the findings of conventional colonoscopy.

RESULTS

CT colonography diagnosed seven of eight tumors, one being missed because the patient had been inadequately prepared. In 28 patients, CT colonography identified 26 polyps of 45 (57.8% sensitivity, 92.6% specificity, 86.7% positive predictive value), regardless of their size. The sensitivity in detecting colonic polyps was 31.8% (7/22) in the first 25 cases and 91.6% (11/12) in the last 20 patients. CT colonography missed one flat adenoma, some angioectasias and colonic lesions because of portal hypertension in one patient, Crohn's disease ulcers in two patients, and ulcerative colitis lesions in three.

CONCLUSIONS

CT colonography shows poor sensitivity for identifying colonic polyps and does not always detect neoplastic lesions. Flat lesions are impossible to see by this method.

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.

Medical volume exploration: gaining insights virtually

Since modern imaging modalities deliver huge amounts of data, which cannot be assessed easily, the visualization techniques are utilized to emphasize the structures of interest. To compare them, the different visualization techniques (maximum intensity projection, multiplanar reformations, shaded surface display and volume rendering) are regressed to a common ground whereby their strengths and weaknesses can be revealed. Additionally, medical image analysis can detect anatomical objects in volumetric data sets and provides their descriptions for further use. Usually, segmentation plays a crucial roll in that process. There are many segmentation methods which can be categorized in boundary-based and content-based ones. The extraction of anatomical objects also allows their quantification. Image analysis and visualization do not squeeze more information out of a data volume, but they provide different ways to look at it. As in real life, this alone may enlarge the insight.

Real-time interactive virtual endoscopy of the tracheo-bronchial system: influence of CT imaging protocols and observer ability

OBJECTIVE

To evaluate the influence of different spiral CT examination protocols suitable for clinical use on image quality and to assess the observer dependence in interactive real-time virtual bronchoscopy.

METHODS AND PATIENTS

Real-time perspective volume rendering of the airways in twenty normal patients based on four different spiral CT examination protocols was evaluated by four observers in regard to the order of depictable bronchi.

RESULTS

Best results were obtained using an examination protocol with a small beam collimation and a maximum pitch. Depending on the observer's ability to control the fly path and the orientation of the bronchi with respect to the slice plane up to sixth order bronchi could be depicted. Inter-observer variability was up to two branching orders.

CONCLUSION

The performance of virtual bronchoscopy strongly depends on the applied CT examination protocol and the observers experience with perspective volume rendering. Both of which have to be taken into account when virtual bronchoscopy is compared with fiberoptic bronchoscopy.

Perspective volume rendered motion: gaining insights virtually

Since modern imaging modalities deliver huge amounts of data the visualization techniques utilized must emphasize the structures of interest. To compare them, the different visualization techniques are regressed to a common ground whereby their strengths and weaknesses can be revealed. Perspective, lighting, color and motion support the real world look and feel. Virtual 3D techniques allow the observer to move through 3D images of anatomy almost in real time. In virtual cisternoscopy this concept is applied to 3D data of the head to reveal a closer look at the cerebral vessels. The more realistic presentation of the 3D data allows for higher efficiency.

Interactive dynamic navigation for virtual endoscopy

Complex anatomical information can be obtained from a 3D radiologic image by navigating through it in a manner similar to an endoscopic examination. Real-time computation of 'virtual' endoscopic views, however, is needed to permit interactive navigation. We present a fast volume-rendering method for computing such views. Our method, motivated by the temporal-coherence concept, performs dynamic volume rendering at interactive frame rates. Results demonstrate the method's efficiency and accuracy. Also, our method constitutes part of a complete virtual-endoscopic system we have devised. This system is illustrated for 3D pulmonary analysis.

Display modes for CT colonography. Part II. Blinded comparison of axial CT and virtual endoscopic and panoramic endoscopic volume-rendered studies

PURPOSE

To determine the sensitivity of radiologist observers for detecting colonic polyps by using three different data review (display) modes for computed tomographic (CT) colonography, or "virtual colonoscopy."

MATERIALS AND METHODS

CT colonographic data in a patient with a normal colon were used as base data for insertion of digitally synthesized polyps. Forty such polyps (3.5, 5, 7, and 10 mm in diameter) were randomly inserted in four copies of the base data. Axial CT studies, volume-rendered virtual endoscopic movies, and studies from a three-dimensional mode termed "panoramic endoscopy" were reviewed blindly and independently by two radiologists.

RESULTS

Detection improved with increasing polyp size. Trends in sensitivity were dependent on whether all inserted lesions or only visible lesions were considered, because modes differed in how completely the colonic surface was depicted. For both reviewers and all polyps 7 mm or larger, panoramic endoscopy resulted in significantly greater sensitivity (90%) than did virtual endoscopy (68%, P = .014). For visible lesions only, the sensitivities were 85%, 81%, and 60% for one reader and 65%, 62%, and 28% for the other for virtual endoscopy, panoramic endoscopy, and axial CT, respectively. Three-dimensional displays were more sensitive than two-dimensional displays (P < .05).

CONCLUSION

The sensitivity of panoramic endoscopy is higher than that of virtual endoscopy, because the former displays more of the colonic surface. Higher sensitivities for three-dimensional displays may justify the additional computation and review time.

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.

Occlusive colon carcinoma: virtual colonoscopy in the preoperative evaluation of the proximal colon

PURPOSE

To evaluate the use of preoperative virtual colonoscopy to examine the proximal colon in patients with distal occlusive carcinomas, defined as cancers that cannot be traversed endoscopically.

MATERIALS AND METHODS

Twenty-nine patients with occlusive colorectal carcinomas underwent preoperative virtual colonoscopy with use of a standard protocol. Patients with acute bowel obstruction were excluded. Results of virtual colonoscopy were compared with the findings of preoperative colonoscopy, preoperative barium enema examination, intraoperative colon palpation, histopathologic outcome, and postoperative colonoscopy and barium enema examination, where possible.

RESULTS

Virtual colonoscopy helped identify all 29 occlusive carcinomas and demonstrated two cancers and 24 polyps in the proximal colon. Both synchronous cancers were confirmed intraoperatively and resected. Postoperative conventional colonoscopy in 12 patients confirmed 16 polyps identified at virtual colonoscopy and demonstrated two subcentimeter polyps missed at virtual colonoscopy. Postoperative barium enema examination was performed in two patients and helped confirm two polyps identified at virtual colonoscopy. Virtual colonoscopy successfully demonstrated the proximal colon in 26 of 29 patients examined compared with preoperative barium enema examination, which failed to adequately demonstrate the proximal colon in any patient examined.

CONCLUSION

Virtual colonoscopy is a feasible and useful method for evaluating the entire colon before surgery in patients with occlusive carcinomas.

Colorectal neoplasm detection using virtual colonoscopy: a feasibility study

BACKGROUND

Virtual colonoscopy is a potentially powerful tool for non-invasive colorectal evaluation. In vitro studies have established its accuracy in simulated polyp detection but little data exist regarding its use in clinical practice.

AIMS

To evaluate the ability of virtual colonoscopy to detect colorectal cancers and polyps in patients with endoscopically proven colorectal neoplasms and to correlate the findings of virtual colonoscopy with those of conventional colonoscopy, surgery, and histopathology.

PATIENTS

Thirty eight patients with endoscopic findings suggestive of colorectal carcinoma.

METHODS

Virtual colonoscopy was performed using thin section helical computed tomography (CT) of the abdomen and pelvis after rectal insufflation of room air. Commercially available software was used to generate endoscopic "fly through" examinations of the colon from the CT data. Results were correlated with the findings of conventional colonoscopy and with the surgical and histopathological outcome in each case.

RESULTS

Thirty eight pathologically proven colorectal cancers and 23 adenomatous polyps were present. On virtual colonoscopy, all cancers and all polyps measuring greater than 6 mm in size were identified; there were two false positive reports of polyps. On conventional colonoscopy, there was one false positive report of a malignant sigmoid stricture; four subcentimetre polyps were overlooked. Virtual colonoscopy enabled visualisation of the entire colon in 35 patients; conventional colonoscopy was incomplete in 14 patients. Virtual colonoscopy correctly localised all 38 cancers, compared with 32 using conventional colonoscopy.

CONCLUSION

Virtual colonoscopy is a feasible method for evaluating the colon; it may have role in diagnosis of colorectal cancer and polyps.

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.

CT colonography with three-dimensional problem solving for detection of colonic polyps

OBJECTIVE

We performed CT colonography in patients referred for conventional colonoscopy, interpreted the axial images, and used commercially available software to reconstruct endoluminal perspective views to differentiate polyps from folds.

SUBJECTS AND METHODS

We prospectively examined 44 patients (27 men and 17 women; mean age, 58 years old) with CT colonography by interpreting the axial images and using three-dimensional rendering for problem solving only. The CT scans were interpreted by two radiologists who were unaware of patients' histories as revealed by colonoscopic findings. The findings on colonography were compared with those of conventional colonoscopy to determine sensitivity, specificity, time spent on interpretation, and confidence of interpretation.

RESULTS

Colonoscopy showed normal findings in 28 patients and 22 polyps in the remaining 16 patients. Six polyps were 8 mm or larger, three were 5-7 mm, and 13 were 5 mm or smaller. The findings of the two observers revealed an overall sensitivity of 50% and 38%, respectively, and a specificity of 93% and 86%, respectively. Sensitivity for polyps larger than 8 mm was 83% and specificity was 100% for both observers. The average amount of time spent on interpretation was 28 min 30 sec (range, 14-65 min). Both observers used the endoluminal view for differentiating folds from polyps in 23 (52%) of 44 patients, which had only minimal impact on interpretation time.

CONCLUSION

CT colonography can be performed and the images interpreted using currently available hardware and software by initially using the axial images to search for polyps of significant size. Endoluminal views should be used only when necessary to help distinguish normal folds from fixed raised lesions that are suggestive of polyps.

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.