Estimation of Nasal Airway Cross-sectional Area From Endoscopy Using Depth Maps: A Proof-of-Concept Study

OBJECTIVE

Endoscopy is routinely used to diagnose obstructive airway diseases. Currently, endoscopy is only a visualization technique and does not allow quantification of airspace cross-sectional areas (CSAs). This pilot study tested the hypothesis that CSAs can be accurately estimated from depth maps created from virtual endoscopy videos.

STUDY DESIGN

Cross-sectional.

SETTING

Academic tertiary medical center.

METHODS

Virtual endoscopy and depth map videos of the nasal cavity were digitally created based on anatomically accurate three-dimensional (3D) models built from computed tomography scans of 30 subjects. A software tool was developed to outline the airway perimeter and estimate the airspace CSA from the depth maps. Two otolaryngologists used the software tool to estimate the nasopharynx CSA and the nasal valve minimal CSA (mCSA) in the left and right nasal cavities. Model validation statistics were performed.

RESULTS

Nasopharynx CSA had a median percent error of 3.7% to 4.6% when compared to the true values measured in the 3D models. Nasal valve mCSA had a median percent error of 22.7% to 33.6% relative to the true values. Raters successfully used the software tool to identify subjects with nasal valve stenosis (ie, mCSA < 0.20 cm2 ) with a sensitivity of 83.3%, specificity ≥ 90.7%, and classification accuracy ≥ 90.0%. Interrater and intrarater agreements were high.

CONCLUSION

This study demonstrates that airway CSAs in 3D models can be accurately estimated from depth maps. The development of artificial intelligence algorithms to compute depth maps may soon allow the quantification of airspace CSAs from clinical endoscopies.

[Application of virtual endoscopy in the diagnosis of adenoid hypertrophy and the morphologic classification of adenoid]

Objective:To discuss the application of virtual endoscopy in the diagnosis of adenoid hypertrophy and the morphologic classification of adenoid. Methods:The clinical data of 97 children with adenoid hypertrophy admitted to Department of Otorhinolaryngology Head and Neck Surgery, Shenzhen University General Hospital from July 2022 to December 2022 were collected. The virtual endoscopic reconstruction of the nasopharynx was performed by cone beam computed tomography. The results of virtual endoscopic adenoid size measurement were compared with the results of nasopharyngeal CT median sagittal position and nasopharyngeal endoscopy. Virtual endoscopic classification of adenoid based on the size of the adenoids and their relationship with the torus tubarius. Results:The t-test results of the size of adenoids measured by virtual endoscopy and nasopharyngeal CT were t=1.699 and P=0.093, and the results of intra-group correlation coefficient（ICC） analysis were ICC=0.921 and P<0.01. The proportion of adenoids measured by virtual endoscopy and nasopharyngeal CT was highly consistent. The t-test results of the size of adenoids measured virtual endoscopy and nasopharyngeal endoscopy were t=1.543 and P=0.15, and the results of intra-group correlation coefficient（ICC） analysis were ICC=0.900 and P<0.01. The proportion of adenoids measured by virtual endoscopy and nasopharyngeal endoscopy was highly consistent. Among the 97 children, the morphological classification results of adenoids were 48 cases of overall hypertrophy type, 47 cases of central bulge type, and 2 cases of flat thickening type. Conclusion:The diagnosis of adenoid hypertrophy by virtual endoscopy has high accuracy, which not only avoids the invasive operation of traditional nasopharyngeal endoscopy, but also can observe the adenoid condition and its relationship with the torus tubarius from multiple angles. And, the morphological classification of adenoids using virtual endoscopy has guiding significance for perioperative preparation.

Computed tomography virtual oesophagography for the grading of oesophageal varices in cirrhotic liver disease patients with upper gastrointestinal endoscopic examination as the gold standard: a diagnostic validation study

Purpose

Virtual endoscopy is a postprocessing method using three-dimensional computed tomography (CT), which produces views of the inner surfaces of the human body like those produced by fibreoptic endoscopy. To evaluate and categorise patients who require medical or endoscopic band ligation to prevent oesophageal variceal bleed, a less invasive, less expensive, better tolerated, and more sensitive modality is required, as well as to reduce the use of invasive procedures in the follow-up of patients who do not require endoscopic variceal band ligation.

Material and methods

A cross-sectional study was conducted in the Department of Radiodiagnosis in association with the Department of Gastroenterology. The study was conducted over a period of 18 months from July 2020 to January 2022. The sample size was calculated as 62 patients. Patients were recruited on the basis of inclusion and exclusion criteria after giving informed consent. CT virtual endoscopy was performed through a dedicated protocol. Classification of variceal grading was done independently by a radiologist and endoscopist who were blinded to each other's findings.

Results

The diagnostic performance of oesophageal varices detection by CT virtual oesophagography was good, with sensitivity: 86%, specificity: 90%, PPV: 98%, NPV: 56%, and diagnostic accuracy: 87%. There was substantial agreement between the 2 methods, and this agreement was statistically significant (Cohen's k = 0.616, p ≤ 0.001).

Conclusions

Based on our findings, we conclude that the current study has the potential to change the way chronic liver disease is managed, as well as generate similar medical research endeavours. A multicentric study with a large number of patients is needed to improve the experience with this modality.

The Transantral Endoscopic Approach: A Portal for Masses of the Inferior Orbit-Improving Surgeons' Experience Through Virtual Endoscopy and Augmented Reality

In the past years, endoscopic techniques have raised an increasing interest to perform minimally invasive accesses to the orbit, resulting in excellent clinical outcomes with inferior morbidities and complication rates. Among endoscopic approaches, the transantral endoscopic approach allows us to create a portal to the orbital floor, representing the most straightforward access to lesions located in the inferior orbital space. However, if endoscopic surgery provides enhanced magnified vision of the anatomy in a bloodless field, then it has several impairments compared with classic open surgery, owing to restricted operative spaces. Virtual surgical planning and anatomical computer-generated models have proved to be of great importance to plan endoscopic surgical approaches, and their role can be widened with the integration of surgical navigation, virtual endoscopy simulation, and augmented reality (AR). This study focuses on the strict conjugation between the technologies that allow the virtualization of surgery in an entirely digital environment, which can be transferred to the patient using intraoperative navigation or to a printed model using AR for pre-surgical analysis. Therefore, the interaction between different software packages and platforms offers a highly predictive preview of the surgical scenario, contributing to increasing orientation, awareness, and effectiveness of maneuvers performed under endoscopic guidance, which can be checked at any time using surgical navigation. In this paper, the authors explore the transantral approach for the excision of masses of the inferior orbital compartment through modern technology. The authors apply this technique for masses located in the inferior orbit and share their clinical results, describing why technological innovation, and, in particular, computer planning, virtual endoscopy, navigation, and AR can contribute to empowering minimally invasive orbital surgery, at the same time offering a valuable and indispensable tool for pre-surgical analysis and training.

Rectal dose-sparing effect with bioabsorbable spacer placement in carbon ion radiotherapy for sacral chordoma: dosimetric comparison of a simulation study

It is difficult to treat patients with an inoperable sarcoma adjacent to the gastrointestinal (GI) tract using carbon ion radiotherapy (C-ion RT), owing to the possible development of serious GI toxicities. In such cases, spacer placement may be useful in physically separating the tumor and the GI tract. We aimed to evaluate the usefulness of spacer placement by conducting a simulation study of dosimetric comparison in a patient with sacral chordoma adjacent to the rectum treated with C-ion RT. The sacral chordoma was located in the third to fourth sacral spinal segments, in extensive contact with and compressing the rectum. Conventional C-ion RT was not indicated because the rectal dose would exceed the tolerance dose. Because we chose spacer placement surgery to physically separate the tumor and the rectum before C-ion RT, bioabsorbable spacer sheets were inserted by open surgery. After spacer placement, 67.2 Gy [relative biological effectiveness (RBE)] of C-ion RT was administered. The thickness of the spacer was stable at 13-14 mm during C-ion RT. Comparing the dose-volume histogram (DVH) parameters, Dmax for the rectum was reduced from 67 Gy (RBE) in the no spacer plan (simulation plan) to 45 Gy (RBE) in the spacer placement plan (actual plan) when a prescribed dose was administered to the tumor. Spacer placement was advantageous for irradiating the tumor and the rectum, demonstrated using the DVH parameter analysis.

Comparison of diagnostic accuracy of computed tomography virtual endoscopy and flexible fibre-optic laryngoscopy in the evaluation of neck anatomic structures and neoplasms

BACKGROUND AND PURPOSE

Computed tomography virtual endoscopy (CT-VE) is a non-invasive technique which allows visualisation of intraluminal surfaces by tridimensional reconstruction of air/soft tissues. The aim of this study was to compare the diagnostic accuracy of CT-VE and flexible fibre-optic laryngoscopy (FFL) in identifying normal neck anatomic structures and pharyngeal and laryngeal lesions.

METHODS

Forty-two patients with a history of neck cancer were assessed by two ENT surgeons using FFL and by one neuroradiologist using CT-VE in order to evaluate the visualisation of the epiglottis, vallecula, glossoepiglottic folds, pyriform sinuses, vocal cords and mass pathology. The visualisation of the structures in both modalities was assessed according to the following score: 0 = not visualised, 1 = partial visualisation, 2 = complete and clear visualisation. A weighted kappa coefficient was used to evaluate the inter-observer agreement. McNemar's test was performed to compare the two diagnostic tests.

RESULTS

The inter-observer agreement between FFL and CT-VE was fair in the assessment of the vocal cords (k = 0.341); moderate in the assessment of the glossoepiglottic folds (k = 0.418), epiglottis (k = 0.513) and pyriform sinuses (k = 0.477); and substantial in the assessment of the vallecula (k = 0.618) and the tumour (0.740). McNemar's test showed no significant difference between the two tests (p<0.05).

CONCLUSION

CT-VE is a non-invasive technique with a diagnostic accuracy comparable to FFL in terms of visualisation of anatomical structures and pharyngeal and laryngeal lesions.

[A case report of Rosai-Dorfman disease with dyspnea]

Rosai-Dorfman disease, also known as sinus histiocytosis with massive lymphadenopathy, is a kind of very rare idiopathic disease. The most common feature is the excessive accumulation of Langerhans cells in lymph nodes, but it may also occur in other areas and lead to related organ damage. We report a case of a 60-year-old man with Rosai-Dorfman disease, which led to dyspnea. Surgery is the best treatment to relieve the patient's dyspnea in a short time. Rosai-Dorfman disease has trend to self-healing, but in the case of special location, surgery should be selected. Some similar mass recurred in the operative area and bilateral nasal cavity in half a year after operation. Now we reviewed the relevant literatures and summarized the experience of diagnosis and treatment in Rosai-Dorfman disease.

Detection of perilymphatic fistula in labyrinthine windows by virtual endoscopy and variation of reconstruction thresholds on CT scan

Background: Perilymphatic fistula (PLF) is a breach in a labyrinthine window. The opening might decrease the radiological density of the window.Aims/objectives: To evaluate the radiological density of the labyrinthine windows by virtual endoscopy on CT scan.Materials and methods: This prospective study included 47 adult patients with PLF and 98 control patients. Diagnosis of PLF was based on a composite radio clinical score and/or intra operative visualization of the fistula and/or resolution of the symptoms after surgery. On routine CT-scan, labyrinthine windows were examined by virtual endoscopy. The reconstruction threshold was gradually increased until a virtual opening appeared (opening threshold [OT]) and compared to the contralateral window (OT difference).Results: The OT difference was higher in patients than in controls (60.2 ± 10.36 (SEM), n = 47 versus 28.0 ± 2.29 Hounsfield units (HUs), n = 98, p < .01 unpaired t-test). A ROC analysis showed that at an OT difference of 31.5 UH had a sensitivity of 75% and a specificity of 75% for the PLF diagnosis.Conclusions: CT-scan virtual endoscopy and threshold variation provided high specificity and sensitivity in the PLF diagnosis.Significance: This post processing of radiological data appears to enhance the diagnostic value of CT scan.

Antegrade and retrograde CT urethrography with virtual urethroscopy in a dog with urethral narrowing after bilateral triple pelvic osteotomy

An 8-month-old, castrated male Golden Retriever was unable to urinate without catheterization after a single-session bilateral triple pelvic osteotomy. To determine the cause, a retrograde urethrography was performed, but the results were equivocal. Antegrade (voiding by abdominal compression with heavy material) and retrograde CT urethrography were performed with virtual urethroscopy and revealed that the urethral diameter was narrowed near the pubic bone remnants due to pelvic canal narrowing. After corrective surgery, the patient was able to urinate normally. A combination of antegrade and retrograde CT urethrography with virtual urethroscopy was helpful for guiding surgical decision-making in this patient.

Diagnostic Value of 128-slice Spiral CT Combined with Virtual Colonoscopy for Colorectal Cancer

The objective of this study was to evaluate the diagnostic value of 128-slice spiral CT combined with virtual colonoscopy in diagnosis of colorectal cancer. We retrospectively analyzed 45 patients of colorectal diseases who underwent definition AS+128-slice spiral CT combined with virtual colonoscopy after bowel preparation and gas injection to evaluate the clinical diagnostic value of this technology. All the patients received electronic colonoscopy and were confirmed by pathology. In total, colorectal cancer was confirmed in 42 cases and inflammation in 3 cases. Diagnostic results shows: there were 17 cases of lump, 10 cases of infiltration, 6 cases of ulcer, 9 cases of mixed type, 4 cases of liver metastases, and 36 cases of lymph node metastasis. There was no significant difference between 128-slice spiral CT combined with virtual colonoscopy and electronic colonoscopy in detection, localization and characterization of colorectal tumors. CT virtual endoscopy has great advantages in observing the invasion around the lesion and the presence or absence of metastasis in distant organs and lymph node metastasis. It is also possible to understand the shape of the lesion in the intestinal lumen and the length of the lesion involving the lumen of the intestine.

A pilot study of a cardiovascular virtual endoscopy system based on multi-detector computed tomography in diagnosing tetralogy of Fallot in pediatric patients

The present study aimed to investigate the capabilities of the cardiovascular virtual endoscopy (VE) system in diagnosing tetralogy of Fallot (TOF) and performing measurements. A total of 37 patients underwent two-dimensional echocardiography (2-DE) and multi-detector computed tomography (MDCT) examinations. The obtained MDCT images were applied to a cardiovascular VE system. Diagnostic time by VE was first studied and compared with MDCT. Subsequently, with surgical findings as the ground truth, the capabilities of VE, 2-DE and MDCT in diagnosing TOF and its complications were investigated. Additionally, measurements on aorta overriding ratio and diameters for the left pulmonary artery, right pulmonary artery and right ventricular outflow tract by 2-DE and VE were analyzed. Diagnostic time by VE was significantly shorter than MDCT (188±42 vs. 303±42 sec, respectively; P<0.0001). VE, MDCT and 2-DE demonstrated comparable diagnostic rates of TOF (35/37 vs. 34/37 vs. 32/37, respectively; P>0.05). Similar findings were demonstrated in diagnosing complications of the muscular ventricular septal defects, patent ductus arteriosus, vagus subclavian artery, right arch, double superior vena cava and pulmonary artery. Furthermore, in diagnosing the atrial septal defect, 2-DE outperformed MDCT and VE (accuracy, 100 vs. 81 vs. 73%, respectively; all P<0.05). In performing relevant measurements, VE outperformed MDCT and 2-DE, particularly in accessing aorta overriding ratios with no intra-operator difference (P=0.3770) and high consistency (r=0.916). In conclusion, cardiovascular VE was demonstrated to have acceptable accuracy in diagnosing TOF, and possess advantages in shortening the diagnostic time and in performing measurements.

A low-cost multimodal head-mounted display system for neuroendoscopic surgery

BACKGROUND

With rapid advances in technology, wearable devices as head-mounted display (HMD) have been adopted for various uses in medical science, ranging from simply aiding in fitness to assisting surgery. We aimed to investigate the feasibility and practicability of a low-cost multimodal HMD system in neuroendoscopic surgery.

METHODS

A multimodal HMD system, mainly consisted of a HMD with two built-in displays, an action camera, and a laptop computer displaying reconstructed medical images, was developed to assist neuroendoscopic surgery. With this intensively integrated system, the neurosurgeon could freely switch between endoscopic image, three-dimensional (3D) reconstructed virtual endoscopy images, and surrounding environment images. Using a leap motion controller, the neurosurgeon could adjust or rotate the 3D virtual endoscopic images at a distance to better understand the positional relation between lesions and normal tissues at will.

RESULTS

A total of 21 consecutive patients with ventricular system diseases underwent neuroendoscopic surgery with the aid of this system. All operations were accomplished successfully, and no system-related complications occurred. The HMD was comfortable to wear and easy to operate. Screen resolution of the HMD was high enough for the neurosurgeon to operate carefully. With the system, the neurosurgeon might get a better comprehension on lesions by freely switching among images of different modalities. The system had a steep learning curve, which meant a quick increment of skill with it. Compared with commercially available surgical assistant instruments, this system was relatively low-cost.

CONCLUSIONS

The multimodal HMD system is feasible, practical, helpful, and relatively cost efficient in neuroendoscopic surgery.

Enhancing airway assessment of patients with head and neck pathology using virtual endoscopy

Studies have demonstrated that poor assessment and planning contribute to airway complications and that current airway assessment strategies have a poor diagnostic accuracy in predicting difficult intubation in the general population. Patients with head and neck pathology are at higher risk for difficulties during airway management and are more likely to need emergency surgical access. Therefore, thorough assessment of this group of patients is mandatory. The addition of virtual endoscopy (VE) to clinical history and computerised tomography imaging has been shown to improve diagnostic accuracy for supraglottic, glottic and infraglottic lesions and has a positive influence in formulating a more cautious and thorough airway management strategy in this high-risk group of patients. This article reviews whether VE can enhance airway assessment in patients with head and neck pathology and help reduce airway complications.

Virtual Mapping of the Frontal Recess: Guiding Safe and Efficient Frontal Sinus Surgery

Objective To define relationships between the frontal sinus opening, ostia of other frontal recess cells, and endoscopic landmarks and to develop a clinically useful framework to guide frontal sinus surgery. Study Design Retrospective review. Setting Tertiary care academic referral center. Methods Adult patients with computed tomography (CT) without sinonasal pathology were included. Virtual endoscopy (using OsiriX) and corresponding CT reconstructions were used to identify all visible ostia in the frontal recess and characterize their positions in spaces between the uncinate/agger nasi (U), bulla ethmoidalis (EB), and middle turbinate (MT). Results Two hundred sides in 100 patients (median age 51 years, 62% female) were analyzed. The "center" of each map was defined as the intersection of spaces between U, EB, and MT. The frontal sinus opening was in the "center" in 53% of frontal recesses, lateral to this position in 29%, and anterior in 11%. When the frontal sinus opening was at the "center," anterior ostia drained frontal Kuhn T cells in 51% and intersinus septal cells in 23%. The skull base attachment of the apical strut of the uncinate process demarcated medial and lateral within the space between U and EB, with the opening to the frontal sinus medial in 68% and lateral in 31%. Left-right asymmetry in frontal sinus openings was noted in 46% of patients. Conclusion Combining preoperative imaging and knowledge of these anatomic relationships may facilitate more efficient frontal outflow tract identification and instrumentation. This represents the first and largest description of ostial configurations relative to endoscopic structural landmarks.

LEVEL OF EVIDENCE

4.

Ethmoidectomy combined with superior meatus enlargement increases olfactory airflow

OBJECTIVES

The relationship between a particular surgical technique in endoscopic sinus surgery (ESS) and airflow changes in the post-operative olfactory region has not been assessed. The present study aimed to compare olfactory airflow after ESS between conventional ethmoidectomy and ethmoidectomy with superior meatus enlargement, using virtual ESS and computational fluid dynamics (CFD) analysis.

STUDY DESIGN

Prospective computational study.

MATERIALS AND METHODS

Nasal computed tomography images of four adult subjects were used to generate models of the nasal airway. The original preoperative model was digitally edited as virtual ESS by performing uncinectomy, ethmoidectomy, antrostomy, and frontal sinusotomy. The following two post-operative models were prepared: conventional ethmoidectomy with normal superior meatus (ESS model) and ethmoidectomy with superior meatus enlargement (ESS-SM model). The calculated three-dimensional nasal geometries were confirmed using virtual endoscopy to ensure that they corresponded to the post-operative anatomy observed in the clinical setting. Steady-state, laminar, inspiratory airflow was simulated, and the velocity, streamline, and mass flow rate in the olfactory region were compared among the preoperative and two postoperative models.

RESULTS

The mean velocity in the olfactory region, number of streamlines bound to the olfactory region, and mass flow rate were higher in the ESS-SM model than in the other models.

CONCLUSION

We successfully used an innovative approach involving virtual ESS, virtual endoscopy, and CFD to assess postoperative outcomes after ESS. It is hypothesized that the increased airflow to the olfactory fossa achieved with ESS-SM may lead to improved olfactory function; however, further studies are required.

LEVEL OF EVIDENCE

NA.

Digital 3D reconstructions using histological serial sections of lung tissue including the alveolar capillary network

Grothausmann R, Knudsen L, Ochs M, Mühlfeld C. Digital 3D reconstructions using histological serial sections of lung tissue including the alveolar capillary network. Am J Physiol Lung Cell Mol Physiol 312: L243-L257, 2017. First published December 2, 2016; doi:10.1152/ajplung.00326.2016-The alveolar capillary network (ACN) provides an enormously large surface area that is necessary for pulmonary gas exchange. Changes of the ACN during normal or pathological development or in pulmonary diseases are of great functional impact and warrant further analysis. Due to the complexity of the three-dimensional (3D) architecture of the ACN, 2D approaches are limited in providing a comprehensive impression of the characteristics of the normal ACN or the nature of its alterations. Stereological methods offer a quantitative way to assess the ACN in 3D in terms of capillary volume, surface area, or number but lack a 3D visualization to interpret the data. Hence, the necessity to visualize the ACN in 3D and to correlate this with data from the same set of data arises. Such an approach requires a large sample volume combined with a high resolution. Here, we present a technically simple and cost-efficient approach to create 3D representations of lung tissue ranging from bronchioles over alveolar ducts and alveoli up to the ACN from more than 1 mm sample extent to a resolution of less than 1 μm. The method is based on automated image acquisition of serially sectioned epoxy resin-embedded lung tissue fixed by vascular perfusion and subsequent automated digital reconstruction and analysis of the 3D data. This efficient method may help to better understand mechanisms of vascular development and pathology of the lung.

The paranasal sinuses: three-dimensional reconstruction, photo-realistic imaging, and virtual endoscopy

BACKGROUND

The purpose of the study was to create computer-aided design models of the paranasal sinuses (frontal, maxillary, and sphenoid) and to perform virtual endoscopy (VE) to them by using virtual reality modelling language technique.

MATERIALS AND METHODS

The visible human dataset was used as the input imaging data. The Surfdriver software package was applied on these images to reconstruct the paranasal sinuses as 3-dimensional (3D) computer-aided design models. These models were post-processed in Cinema 4D to perform the photorealistic imaging and VE of the paranasal sinuses.

RESULTS

The volumes of the maxillary sinuses were 24747.89 mm³ on the right and 29008.78 mm³ on the left. As for sphenoidal sinuses, an enormous variation was seen between the right and left cavities. The sphenoidal sinuses were 1995.90 mm3 on the right and 10228.93 mm³ on the left while the frontal sinuses were 20805.67 mm³ on the right and 18048.85 mm³ on the left. The largest sinus was left maxillary sinus by volume. Right frontal sinus was the largest sinus by surface area. It was calculated as 6002.73 mm². Our methodological outcomes proved that Surfdriver and Cinema 4D pair could be reliably used for 3D reconstructions, photo realistic imaging and creating 3D virtual environments from the serial sections of the anatomical structures.

CONCLUSIONS

This technique allows students, researchers, and surgeons to perform noninvasive visualisation, simulation, and precise quantitative measurements of internal structures of the body. It was developed as a complementary tool for endoscopic surgery. It could be especially preferable for the patients who could not tolerate flexible or rigid endoscopy.

Localized intraoperative virtual endoscopy (LIVE) for surgical guidance in 16 skull base patients

IMPORTANCE

Previous preclinical studies of localized intraoperative virtual endoscopy-image-guided surgery (LIVE-IGS) for skull base surgery suggest a potential clinical benefit.

OBJECTIVE

The first aim was to evaluate the registration accuracy of virtual endoscopy based on high-resolution magnetic resonance imaging under clinical conditions. The second aim was to implement and assess real-time proximity alerts for critical structures during skull base drilling.

DESIGN AND SETTING

Patients consecutively referred for sinus and skull base surgery were enrolled in this prospective case series.

PARTICIPANTS

Five patients were used to check registration accuracy and feasibility with the subsequent 11 patients being treated under LIVE-IGS conditions with presentation to the operating surgeon (phase 2).

INTERVENTION

Sixteen skull base patients were endoscopically operated on by using image-based navigation while LIVE-IGS was tested in a clinical setting.

MAIN OUTCOME AND MEASURES

Workload was quantitatively assessed using the validated National Aeronautics and Space Administration Task Load Index (NASA-TLX) questionnaire.

RESULTS

Real-time localization of the surgical drill was accurate to ~1 to 2 mm in all cases. The use of 3-mm proximity alert zones around the carotid arteries and optic nerve found regular clinical use, as the median minimum distance between the tracked drill and these structures was 1 mm (0.2-3.1 mm) and 0.6 mm (0.2-2.5 mm), respectively. No statistical differences were found in the NASA-TLX indicators for this experienced surgical cohort.

CONCLUSIONS AND RELEVANCE

Real-time proximity alerts with virtual endoscopic guidance was sufficiently accurate under clinical conditions. Further clinical evaluation is required to evaluate the potential surgical benefits, particularly for less experienced surgeons or for teaching purposes.

Detection of hypoplasia of bony cochlear nerve canal by the opening threshold of virtual endoscopy: a pilot study

BACKGROUND

Dimensions of the bony cochlear nerve canal (BCNC) have been proposed as a potential diagnostic standard for BCNC hypoplasia, but the standard remains inconsistent. Some studies have revealed that computed tomography virtual endoscopy (CTVE) with variation of reconstruction threshold is good at identifying labyrinthine fistulas or semi-circular canal dehiscence.

PURPOSE

To examine diagnostic accuracy of VE in the evaluation of BCNC hypoplasia on basis of opening threshold.

MATERIAL AND METHODS

Twenty ears diagnosed with BCNC hypoplasia were included in this study. One hundred ears served as controls. The opening thresholds were measured by two reviewers. Intraclass correlation coefficients (ICC) were reported. The width of BCNC was obtained on transverse CT images. Association between the width of BCNC and opening threshold was assessed by using Spearman correlation coefficients. ROC curves were applied to assess the best cut-off value of opening threshold.

RESULTS

The opening threshold of BCNC was significantly higher in diseased ears (926 ± 308 Hounsfield units [HU]) than that in control ears (287 ± 72 HU). Inter-observer agreement was very good. The mean width of BCNC for diseased ears and control ears were 0.83 ± 0.36 mm and 2.21 ± 0.35 mm, respectively. Significant negative linear correlation was found between opening thresholds and width of BCNC (Spearman coefficient, -0.768; P < 0.001). The area under the ROC curve was 0.981. The cut-off opening thresholds of 408 for differentiation between the two groups provided the best combination of sensitivity (85%) and specificity (94%).

CONCLUSION

The VE with opening threshold may be an effective optional tool for prediction of hypoplasia of BCNC.

Augmented real-time navigation with critical structure proximity alerts for endoscopic skull base surgery

OBJECTIVES/HYPOTHESIS

Image-guided surgery (IGS) systems are frequently utilized during cranial base surgery to aid in orientation and facilitate targeted surgery. We wished to assess the performance of our recently developed localized intraoperative virtual endoscopy (LIVE)-IGS prototype in a preclinical setting prior to deployment in the operating room. This system combines real-time ablative instrument tracking, critical structure proximity alerts, three-dimensional virtual endoscopic views, and intraoperative cone-beam computed tomographic image updates.

STUDY DESIGN

Randomized-controlled trial plus qualitative analysis.

METHODS

Skull base procedures were performed on 14 cadaver specimens by seven fellowship-trained skull base surgeons. Each subject performed two endoscopic transclival approaches; one with LIVE-IGS and one using a conventional IGS system in random order. National Aeronautics and Space Administration Task Load Index (NASA-TLX) scores were documented for each dissection, and a semistructured interview was recorded for qualitative assessment.

RESULTS

The NASA-TLX scores for mental demand, effort, and frustration were significantly reduced with the LIVE-IGS system in comparison to conventional navigation (P < .05). The system interface was judged to be intuitive and most useful when there was a combination of high spatial demand, reduced or absent surface landmarks, and proximity to critical structures. The development of auditory icons for proximity alerts during the trial better informed the surgeon while limiting distraction.

CONCLUSIONS

The LIVE-IGS system provided accurate, intuitive, and dynamic feedback to the operating surgeon. Further refinements to proximity alerts and visualization settings will enhance orientation while limiting distraction. The system is currently being deployed in a prospective clinical trial in skull base surgery.

Interactive CT-video registration for the continuous guidance of bronchoscopy

Bronchoscopy is a major step in lung cancer staging. To perform bronchoscopy, the physician uses a procedure plan, derived from a patient's 3D computed-tomography (CT) chest scan, to navigate the bronchoscope through the lung airways. Unfortunately, physicians vary greatly in their ability to perform bronchoscopy. As a result, image-guided bronchoscopy systems, drawing upon the concept of CT-based virtual bronchoscopy (VB), have been proposed. These systems attempt to register the bronchoscope's live position within the chest to a CT-based virtual chest space. Recent methods, which register the bronchoscopic video to CT-based endoluminal airway renderings, show promise but do not enable continuous real-time guidance. We present a CT-video registration method inspired by computer-vision innovations in the fields of image alignment and image-based rendering. In particular, motivated by the Lucas-Kanade algorithm, we propose an inverse-compositional framework built around a gradient-based optimization procedure. We next propose an implementation of the framework suitable for image-guided bronchoscopy. Laboratory tests, involving both single frames and continuous video sequences, demonstrate the robustness and accuracy of the method. Benchmark timing tests indicate that the method can run continuously at 300 frames/s, well beyond the real-time bronchoscopic video rate of 30 frames/s. This compares extremely favorably to the ≥ 1 s/frame speeds of other methods and indicates the method's potential for real-time continuous registration. A human phantom study confirms the method's efficacy for real-time guidance in a controlled setting, and, hence, points the way toward the first interactive CT-video registration approach for image-guided bronchoscopy. Along this line, we demonstrate the method's efficacy in a complete guidance system by presenting a clinical study involving lung cancer patients.

Computer modeled multiportal approaches to the skull base

Skull base surgical approaches have evolved significantly to minimize collateral tissue damage and improve access to complex anatomic regions. Many endoscopic surgical portals have been described, and these can be combined in multiportal approaches that permit improved angles for visualization and instrumentation. To assist in the choice of entry portal and surgical pathway analysis, a three-dimensional computer model with virtual endoscopy was created. The model was evaluated on transnasal and transorbital approaches to access 11 specified sellar and parasellar target locations on 14 computed tomography (CT) scans. Data were collected on length of approach, angle between instruments, and approach angle with respect to anatomical planes. Optimal multiportal approach combinations were derived. The data demonstrated that the shortest, most direct pathway to many sellar and parasellar targets was through transorbital portals. Distances were reduced by 35% for certain target locations; combining transorbital and transnasal portals increased the angle between instruments 4-fold for many targets. The predicted values from the model were validated on four cadaver specimens. Computer modeling holds the potential to play an integral role in the design, analysis, and testing of new surgical approaches, as well as in the selection of optimal approach strategies for the unique pathology of individual patients.

The diagnostic contribution of CT volumetric rendering techniques in routine practice

Computed tomography (CT) volumetric rendering techniques such as maximum intensity projection (MIP), minimum intensity projection (MinIP), shaded surface display (SSD), volume rendering (VR), and virtual endoscopy (VE) provide added diagnostic capabilities. The diagnostic value of such reconstruction techniques is well documented in literature. These techniques permit the exploration of fine anatomical detail that would be difficult to evaluate using axial reconstructions alone. Although these techniques are now widely available, many radiologists are either unfamiliar with them or do not fully utilize their potential in daily clinical practice. This paper is intended to provide an overview of the most common CT volumetric rendering techniques and their practical use in everyday diagnostics.

CT virtual endoscopy and 3D stereoscopic visualisation in the evaluation of coronary stenting. Biomed Imaging Interv J. 2009;5:e22. [PMID: 21610990 DOI: 10.2349/biij.5.4.e22]

The aim of this case report is to present the additional value provided by CT virtual endoscopy and 3D stereoscopic visualisation when compared with 2D visualisations in the assessment of coronary stenting. A 64-year old patient was treated with left coronary stenting 8 years ago and recently followed up with multidetector row CT angiography. An in-stent restenosis of the left coronary artery was suspected based on 2D axial and multiplanar reformatted images. 3D virtual endoscopy was generated to demonstrate the smooth intraluminal surface of coronary artery wall, and there was no evidence of restenosis or intraluminal irregularity. Virtual fly-through of the coronary artery was produced to examine the entire length of the coronary artery with the aim of demonstrating the intraluminal changes following placement of the coronary stent. In addition, stereoscopic views were generated to show the relationship between coronary artery branches and the coronary stent. In comparison with traditional 2D visualisations, virtual endoscopy was useful for assessment of the intraluminal appearance of the coronary artery wall following coronary stent implantation, while stereoscopic visualisation improved observers’ understanding of the complex cardiac structures. Thus, both methods could be used as a complementary tool in cardiac imaging.

Computer-based System for the Virtual-Endoscopic Guidance of Bronchoscopy

The standard procedure for diagnosing lung cancer involves two stages: three-dimensional (3D) computed-tomography (CT) image assessment, followed by interventional bronchoscopy. In general, the physician has no link between the 3D CT image assessment results and the follow-on bronchoscopy. Thus, the physician essentially performs bronchoscopic biopsy of suspect cancer sites blindly. We have devised a computer-based system that greatly augments the physician's vision during bronchoscopy. The system uses techniques from computer graphics and computer vision to enable detailed 3D CT procedure planning and follow-on image-guided bronchoscopy. The procedure plan is directly linked to the bronchoscope procedure, through a live registration and fusion of the 3D CT data and bronchoscopic video. During a procedure, the system provides many visual tools, fused CT-video data, and quantitative distance measures; this gives the physician considerable visual feedback on how to maneuver the bronchoscope and where to insert the biopsy needle. Central to the system is a CT-video registration technique, based on normalized mutual information. Several sets of results verify the efficacy of the registration technique. In addition, we present a series of test results for the complete system for phantoms, animals, and human lung-cancer patients. The results indicate that not only is the variation in skill level between different physicians greatly reduced by the system over the standard procedure, but that biopsy effectiveness increases.

Comparison of magnetic resonance imaging colonography with conventional colonoscopy for the assessment of intestinal inflammation in patients with inflammatory bowel disease: a feasibility study

AIM

Magnetic resonance imaging (MRI) based colonography represents a new imaging tool which has mainly been investigated for polyp screening. To evaluate this approach for patients with inflammatory bowel disease (IBD), we compared MRI based colonography with conventional colonoscopy for assessing the presence and extent of colonic inflammation.

PATIENTS AND METHODS

In 22 consecutive patients with suspected or known IBD, MRI colonography was performed immediately before conventional colonoscopy. After bowel cleansing, a T1 positive contrast agent was applied rectally. In addition to T2 weighted sequences, T1 weighted two dimensional and three dimensional Flash acquisitions as well as volume rendered virtual endoscopy were performed. All images were evaluated with regard to typical MRI features of inflammation. The results were compared with colonoscopy findings.

RESULTS

Distension and image quality was assessed as good to fair in 97.4% of all colonic segments. Only four of 154 segments were considered non-diagnostic. With colonoscopy serving as the gold standard, the sensitivity for correctly identifying inflammation on a per segment analysis of the colon was 31.6% for Crohn's disease (CD) and 58.8% for ulcerative colitis (UC). In CD, in most cases mild inflammation was not diagnosed by MRI while in UC even severe inflammation was not always depicted by MRI. Virtual endoscopy did not add any relevant information.

CONCLUSION

MRI based colonography is not suitable for adequately assessing the extent of colonic inflammation in patients with IBD. Only severe colonic inflammation in patients with CD can be sufficiently visualised.

A new filtering algorithm for medical magnetic resonance and computer tomography images

Inner views of tubular structures based on computer tomography (CT) and magnetic resonance (MR) data sets may be created by virtual endoscopy. After a preliminary segmentation procedure for selecting the organ to be represented, the virtual endoscopy is a new postprocessing technique using surface or volume rendering of the data sets. In the case of surface rendering, the segmentation is based on a grey level thresholding technique. To avoid artifacts owing to the noise created in the imaging process, and to restore spurious resolution degradations, a robust Wiener filter was applied. This filter working in Fourier space approximates the noise spectrum by a simple function that is proportional to the square root of the signal amplitude. Thus, only points with tiny amplitudes consisting mostly of noise are suppressed. Further artifacts are avoided by the correct selection of the threshold range. Afterwards, the lumen and the inner walls of the tubular structures are well represented and allow one to distinguish between harmless fluctuations and medically significant structures.

Evaluating virtual endoscopy for clinical use

Virtual endoscopy is a term used to describe computer simulated endoscopy procedures derived from high resolution images of patient anatomy. By simulating the endoscopic examination, the patient is spared the discomfort and possible complications of an actual examination. The physician also has more flexibility in a virtual endoscopic examination of 3D patient data in comparison to a real endoscopic examination. Virtual endoscopy removes the physical and physiologic constraints of real endoscopy and can create views that are not possible in an actual endoscopic examination. This may enhance the performance of actual endoscopic examinations. Virtual endoscopy may also be used to perform "numerical biopsies"; anatomic measurements such as size, distance, shape, and density. Virtual endoscopy allows the physician to comprehensively explore the patient anatomy using an intuitive and interactive interface. There are currently two technical approaches to performing virtual endoscopy: perspective volume rendering and surface rendering of polygonal models. Perspective volume rendering uses traditional volumetric rendering algorithms to create visualizations directly from the volumetric dataset. Polygonal models require a preprocessing step to convert the segmented volume information into a polygonal surface that may be displayed at real time frame rates. Both paradigms have inherent strengths and weaknesses. We illustrate and compare the methods on actual patient data, including simulated endoscopic examinations of the airways, colon and esophagus. Preliminary results in virtual endoscopy show promise and will continue to be an area of active research leading to useful clinical applications.

Patient-specific anatomic models from three dimensional medical image data for clinical applications in surgery and endoscopy

Virtual surgery and endoscopy use computer-generated volume renderings and/or models created from 3D medical image scans (CT or MRI) of individual patients. The patient's anatomy, including organs and other internal structures of interest, are then traversed in a virtual "fly-through," giving nearly the same visual impression as if the corresponding real organ was being examined intraoperatively, or as if an actual video or fiberoptic endoscopic procedure was being performed. Such virtual examinations may provide capabilities and information not possible or available in physical examinations. The potential is to provide a noninvasive computer-aided treatment plan or diagnostic screening procedure to augment or replace conventional invasive procedures. With sophisticated image processing and computational analysis, it is possible to perform realistic and useful simulations of surgical and endoscopic procedures, including "virtual dissection and resection" and "virtual biopsy." Surgical margins can be accurately assessed and differential tissue diagnoses made based upon spectral or other information contained in the patient-specific images and models.