Pre-surgery planning tool for estimation of resection volume to improve nasal breathing based on lattice Boltzmann fluid flow simulations.

PURPOSE: State-of-the-art medical examination techniques (e.g., rhinomanometry and endoscopy) do not always lead to satisfactory postoperative outcome. A fully automatized optimization tool based on patient computer tomography (CT) data to calculate local pressure gradient regions to reshape pathological nasal cavity geometry is proposed. METHODS: Five anonymous pre- and postoperative CT datasets with nasal septum deviations were used to simulate the airflow through the nasal cavity with lattice Boltzmann (LB) simulations. Pressure gradient regions were detected by a streamline analysis. After shape optimization, the volumetric difference between the two shapes of the nasal cavity yields the estimated resection volume. RESULTS: At LB rhinomanometry boundary conditions (bilateral flow rate of 600 ml/s), the preliminary study shows a critical pressure gradient of -1.1 Pa/mm as optimization criterion. The maximum coronal airflow ΔA  := cross-section ratio [Formula: see text] found close to the nostrils is 1.15. For the patients a pressure drop ratio ΔΠ  := (pre-surgery - virtual surgery)/(pre-surgery - post-surgery) between nostril and nasopharynx of 1.25, 1.72, -1.85, 0.79 and 1.02 is calculated. CONCLUSIONS: LB fluid mechanics optimization of the nasal cavity can yield results similar to surgery for air-flow cross section and pressure drop between nostril and nasopharynx. The optimization is numerically stable in all five cases of the presented study. A limitation of this study is that anatomical constraints (e.g. mucosa) have not been considered.

Nasal cavity airflow: Comparing laser doppler anemometry and computational fluid dynamic simulations.

Objective parameters to assess the physical flow conditions of breathing are scarce and decisions for surgery, e.g. nasal septum correction, mainly rely on subjective surgeon judgment. To define decision supporting parameters, we compare laser Doppler anemometry (LDA) and numerical computational fluid dynamic simulations (CFD) of the airflow velocity vector fields in the nasal cavity, including lattice Boltzmann (LB) and finite volume methods (FVM). The simulations are based on an anonymous patient CT dataset with septal deviation. LDA measurements are preformed using a 3D printed model. Nasal airflow geometry is randomly deformed in order to approximate surgical changes. The root-mean-square velocity error near the nasal valve of laser Doppler anemometry and lattice Boltzmann simulations is 0.071. Changes in geometry similarly affect both measurement and simulation.

Custom implant design for large cranial defects.

PURPOSE: The aim of this work was to introduce a computer-aided design (CAD) tool that enables the design of large skull defect (>100 [Formula: see text]) implants. Functional and aesthetically correct custom implants are extremely important for patients with large cranial defects. For these cases, preoperative fabrication of implants is recommended to avoid problems of donor site morbidity, sufficiency of donor material and quality. Finally, crafting the correct shape is a non-trivial task increasingly complicated by defect size. METHODS: We present a CAD tool to design such implants for the neurocranium. A combination of geometric morphometrics and radial basis functions, namely thin-plate splines, allows semiautomatic implant generation. The method uses symmetry and the best fitting shape to estimate missing data directly within the radiologic volume data. In addition, this approach delivers correct implant fitting via a boundary fitting approach. RESULTS: This method generates a smooth implant surface, free of sharp edges that follows the main contours of the boundary, enabling accurate implant placement in the defect site intraoperatively. The present approach is evaluated and compared to existing methods. A mean error of 89.29 % (72.64-100 %) missing landmarks with an error less or equal to 1 mm was obtained. CONCLUSION: In conclusion, the results show that our CAD tool can generate patient-specific implants with high accuracy.

Medium-level laser in chronic tinnitus treatment.

The purpose of this study was to evaluate the effect of medium-level laser therapy in chronic tinnitus treatment. In a prospective double-blind placebo-controlled trial, either active laser (450 mW, 830 nm combined Ga-Al-As diode laser) or placebo irradiation was applied through the external acoustic meatus of the affected ear towards the cochlea. Fourty-eight patients with chronic tinnitus were studied. The main outcome was measured using the Goebel tinnitus questionnaire, visual analogue scales measuring the perceived loudness of tinnitus, the annoyance associated with tinnitus, and the degree of attention paid to tinnitus as well as psycho-acoustical matches of tinnitus pitch and loudness. The results did show only very moderate temporary improvement of tinnitus. Moreover, no statistically relevant differences between laser and placebo group could be found. We conclude that medium-level laser therapy cannot be regarded as an effective treatment of chronic tinnitus in our therapy regime considering the limited number of patients included in our study.

Quantitative error analysis for computer assisted navigation: a feasibility study.

PURPOSE: The benefit of computer-assisted navigation depends on the registration process, at which patient features are correlated to some preoperative imagery. The operator-induced uncertainty in localizing patient features-the user localization error (ULE)-is unknown and most likely dominating the application accuracy. This initial feasibility study aims at providing first data for ULE with a research navigation system. METHODS: Active optical navigation was done in CT-images of a plastic skull, an anatomic specimen (both with implanted fiducials), and a volunteer with anatomical landmarks exclusively. Each object was registered ten times with 3, 5, 7, and 9 registration points. Measurements were taken at 10 (anatomic specimen and volunteer) and 11 targets (plastic skull). The active NDI Polaris system was used under ideal working conditions (tracking accuracy 0.23 mm root-mean-square, RMS; probe tip calibration was 0.18 mm RMS). Variances of tracking along the principal directions were measured as 0.18 mm(2), 0.32 mm(2), and 0.42 mm(2). ULE was calculated from predicted application accuracy with isotropic and anisotropic models and from experimental variances, respectively. RESULTS: The ULE was determined from the variances as 0.45 mm (plastic skull), 0.60 mm (anatomic specimen), and 4.96 mm (volunteer). The predicted application accuracy did not yield consistent values for the ULE. CONCLUSIONS: Quantitative data of application accuracy could be tested against prediction models with iso- and anisotropic noise models and revealed some discrepancies. This could potentially be due to the facts that navigation and one prediction model wrongly assume isotropic noise (tracking is anisotropic), while the anisotropic noise prediction model assumes an anisotropic registration strategy (registration is isotropic in typical navigation systems). The ULE data are presumably the first quantitative values for the precision of localizing anatomical landmarks and implanted fiducials. Submillimetric localization is possible for implanted screws; anatomic landmarks are not suitable for high-precision clinical navigation.

Optical and electromagnetic tracking for navigated surgery of the sinuses and frontal skull base.

BACKGROUND: New hardware and software algorithms in electromagnetic tracking for computer assisted surgery (CAS) have been developed. We aimed to compare electromagnetic tracking for navigated procedures in frontal skull base surgery to optical tracking. METHODS: Target registration error (TRE) was determined in 6 anatomic specimens in an experimental wet-lab. As targets, 6 titanium screws were evenly distributed over the surgical areas of interest from the frontal sinus to the clivus. Optical tracking and electromagnetic tracking was evaluated in identical software environment using a last generation commercially available navigation system. RESULTS: Submillimetric application accuracy could be achieved with both tracking modalities. Optical was more accurate than electromagnetic tracking and its reliability was better. Target position did not influence TRE, however TRE varied significantly from skull to skull. CONCLUSIONS: Although less accurate than optical tracking, electromagnetic tracking still offers excellent accuracy and reliability for anterior skull base surgery. Electromagnetic tracking is not dependent on direct line of sight between its hardware components and therefore easily integrated even in cluttered operating theatres.

[The learning curve of registration in navigated skull base surgery]. / Lernkurve bei der Registrierung navigierter Eingriffe an der Schädelbasis.

BACKGROUND: Computer aided surgery (CAS) is advantageous in challenging procedures in head and neck surgery. It is not clear, if the application of CAS has to be trained to achieve reliable results. The learning curve of the registration of the patient's coordinates to prior acquired radiologic imagery was investigated. MATERIAL AND METHODS: 4 residents performed pair-point registrations on 5 anatomic specimens in an experimental wet lab. The residents were in the same year of education and had no experience in CAS procedures. After each registration the application error was evaluated by determining the target registration error (TRE). Pair point matching by skin glued external fiducials was compared with pair point matching by internal anatomical landmarks. RESULTS: The application accuracy was improved by increasing numbers of performed registrations (p<0.001, trendtest of Page). An inverse trend of the learning curve could be observed, the median TRE values improved from 3.3 mm in the first registration to 1.6 mm after the fifth registration. In comparison e. g. an experienced CAS-user can achieve submillimetric TRE values under wet lab conditions. Pair point matching by anatomical landmarks resulted in worse application accuracy initially and the learning curve was steeper than with external fiducial markers. CONCLUSION: There is a training effect in CAS interventions. Pair point matching results in sufficient application accuracy after training only.

[Automatic registration of patients with A-mode ultrasound for computer-assisted surgery. Laboratory proof of concept]. / Automatische Registration des Patienten mit A-Mode-Ultraschall für computerunterstützte Chirurgie. Funktionsnachweis im Labor.

BACKGROUND: The main source of error in 3D navigation is the patient-to-image registration process. Anatomical landmarks or adhesive markers perform sub-optimally. Bone-anchored invasive markers significantly change the clinical workflow of navigated ENT surgery, are invasive and cause patient discomfort. In order to minimize registration errors and to further streamline the clinical use of intraoperative 3D navigation we demonstrate that A-mode ultrasound allows an accurate 3D surface profile of the os occipitale to be created which can be reliably registered on preoperative patient CT data. METHODS: The transducer is mechanically positioned with sub-millimeter accuracy on the patient's occiput. From the sound echos a 3D surface is generated and registered to the preoperative CT images with the iterative closest point (ICP) algorithm. The evaluation of our setup was performed on three anatomic specimens and one bony skull. RESULTS: The ultrasound echoes from the occiput allowed the creation of an adequate 3D surface which could be registered to a segmentation of the CT image with an accuracy greater than 1.5 mm. The experiments were evaluated by an intuitive representation of the spatial deviation between CT and ultrasound data as a color-coded map. CONCLUSION: The approach to scan the posterior skull with A-mode ultrasound enables automatic intraoperative registration and can be integrated into the intraoperative setup.

High-resolution X-ray tomography of the human inner ear: synchrotron radiation-based study of nerve fibre bundles, membranes and ganglion cells.

The combination of osmium tetroxide staining and high-resolution tomographic imaging using monochromatic X rays allows visualizing cellular structures of the human inner ear, that is, the organ of Corti, the stria vascularis and further soft tissues of the membranous labyrinth, in three-dimensional space with isotropic micrometre resolution. This approach permits to follow the course of nerve fibre bundles in a major part of the specimen and reveals the detailed three-dimensional arrangement of individual ganglion cells with distinct nuclei by means of X-ray tomography for the first time. The non-destructive neuron cell counting in a selected volume of 125 microm x 800 microm x 600 microm = 0.06 mm(3) gives rise to the estimate that 2000 ganglion cells are present along 1 mm organ of Corti.

[Computer-assisted intraoperative navigation at the anterior skull base]. / Computerassistierte intraoperative navigation an der vorderen schädelbasis.

Intraoperative 3D-navigation at the anterior skull base has become a very valuable tool in the last years. For a successful use the clinical pathways need a slight adaptation only to provide the radiologic imagery to the system. Established algorithms and standardized protocols have proven 3D-navigation systems as a valuable clinical tool, when used in conjunction with appropriate intraoperative quality assurance. Ease-of-use and reliable intraoperative quality assurance is an active area of research that, combined with adequate strategies for referencing the patient to preoperative high-resolution radiologic data, will make 3D-navigation at the lateral skull base a successful clinical tool as well.

[3-D navigation in the petrous bone with submillimeter accuracy]. / Submillimetrische 3D-Navigation im Felsenbein. Eine Laboruntersuchung.

BACKGROUND: In order to evaluate the possible submillimeter application accuracy in computer-aided navigation in the petrous bone, we performed a set of approximately 3,000 measurements on a specially prepared anatomic specimen using the Zeiss STN intraoperative navigation system. This allowed direct measurements of relevant anatomic structures in and around the petrous bone which are usually not directly accessible. RESULTS: We found that the best results can be achieved by exploiting contemporary multislice CT-imaging with 0.5 mm slice thickness and by direct radiologic imaging of the petrous bone; additionally, an extrinsic marker structure, the VBH-referencing element, served as an extension of the applied surface markers for the "patient-to-image" referencing procedure. Interestingly, the additional use of a surface registration, as provided by the STN-navigation system, to potentially optimize the registration, did not improve the results. In the best case, i.e. with high-resolution CT-imaging, 0.5 mm slice spacing, the use of surface markers, and the extrinsic referencing structure applied, an absolute difference between the calculated and actual position of the probe was 0.42+/-0.69 mm. CONCLUSIONS: These results show that intraoperative 3-D navigation can be successfully transferred to a clinical application in the petrous bone or at the cerebellopontine angle with satisfactory accuracy in this highly sensitive anatomic region, even if only a restricted area of the patient can be used for the referencing procedure.

[Stereotactic telepresence in otorhinolaryngologic surgery]. / Stereotaktische Telepräsenz in der Hals-, Nasen- und Ohrenchirurgie.

BACKGROUND: Intraoperative three-dimensional (3D) navigation systems determine spatial positions and visualize them in radiological data sets. Usually, data from 3-D computed tomography (CT) are used. We have successfully implemented "augmented reality" in routine clinical practice by superimposing positional data and guiding and ancillary structures on the live endoscopic video of the operating site. Thus, optimal access paths and anatomical structures such as the a. carotis interna or the n. opticus can be displayed. METHODS AND RESULTS: With modern telecommunication, any two locations can be connected for intraoperative consultations with a remote expert, and 3D navigation is an ideal complement. We have successfully tested telephone, ISDN, Ethernet, and ATM technology intraoperatively and find that the ARTMA system provides well-developed technology. CONCLUSIONS: Stereotactic telepresence can provide essential aid in difficult surgical procedures, and the ARTMA Knowledge-Guided Surgery system will contribute further to the optimization of computer-assisted surgery.

A full 3D-navigation system in a suitcase.

OBJECTIVE: To reduce the impact of contemporary 3D-navigation systems on the environment of typical otorhinolaryngologic operating rooms, we demonstrate that a transfer of navigation software to modern high-power notebook computers is feasible and results in a practicable way to provide positional information to a surgeon intraoperatively. MATERIALS AND METHODS: The ARTMA Virtual Patient System has been implemented on a Macintosh PowerBook G3 and, in connection with the Polhemus FASTRAK digitizer, provides intraoperative positional information during endoscopic endonasal surgery. RESULTS: Satisfactory intraoperative navigation has been realized in two- and three-dimensional medical image data sets (i.e., X-ray, ultrasound images, CT, and MR) and live video. CONCLUSIONS: This proof-of-concept study demonstrates that acceptable ergonomics and excellent performance of the system can be achieved with contemporary high-end notebook computers.

Experience with various 3-dimensional navigation systems in head and neck surgery.

OBJECTIVE: To evaluate the benefits and difficulties encountered when using various 3-dimensional (3-D) navigation systems in head and neck procedures. DESIGN: Five different navigation systems were used for preoperative planning and intraoperative 3-D navigation in procedures at the paranasal sinuses, the frontal and lateral skull bases, and the petrous bone. INTERVENTION: Intraoperative 3-D localizing systems (position-sensitive mechanical arms, infrared cameras, etc) demand reliable patient fixation on the operating table. We achieved this by developing a noninvasive head holder. Other systems allow patient movements by using magnetic digitizing technology (ARTMA System) and sophisticated programming. RESULT: Having surpassed an initial learning curve, we now achieve an accuracy of 1 to 2 mm regularly. Especially in paranasal and frontal basal surgery, all navigation systems used provide valuable positioning information during surgery. In particular for revision or tumor surgery, decisive benefits resulted from use of these systems: shorter overall operation time; safer manipulation near delicate structures; and reliable identification of the skull base even in patients with bleeding, scarring, or missing anatomical landmarks. CONCLUSIONS: We performed approximately 250 operations with different systems and introduced navigation at the lateral skull base and the petrous bone with mechanical, optic, and magnetic digitizers. In these anatomical areas, navigation was used successfully; the technical challenge is greatest at the lateral skull base, however.

Head and neck tumors: fractionated frameless stereotactic interstitial brachytherapy-initial experience.

The authors used a frameless stereotactic navigation system, the Vogele-Bale-Hohner head holder, and a targeting device to reproducibly position brachytherapy needles for fractionated interstitial brachytherapy in 12 patients with inoperable cancers of the head and neck. In all cases, deviations of the needle relative to the planned position were within 1-15 mm depending on the location of the tumor.

[Computer-aided 3D-navigation systems. Survey and location determination]. / Computerunterstützte 3D-navigationssysteme

3D-navigation systems have only recently been introduced into the surgical field. Since then they have gained increasing importance not only in ENT surgery but also in neurosurgery, orthopedic surgery, maxillo-facial surgery, radiology and radiotherapy. Following a brief historical introduction this article reviews existing navigation technologies, in terms of indication, practicability, accuracy, forensic and financial aspects. The selection of the navigation system is strongly influenced by the planned procedure (endoscopic, microscopic, open approach). According to our experience most of these systems provide useful support intraoperatively. The clinical application accuracy regularly lies in the range of 1-2 mm.

Computer-aided surgery in the petrous bone.

OBJECTIVE: We demonstrate that computer-assisted frameless stereotactic navigation with the ISG/ELEKTA Viewing Wand system in the petrous bone is routinely possible with sufficient application accuracy. METHODS: High-resolution computed tomography imaging is done with a dedicated structure attached to the mouthpiece of the Vogele-Bale-Hohner (VBH) head holder, an integral part of our intraoperative patient fixation. The patient image registration can be reliably performed before surgery in an unsterile environment with the registration structure of the mouthpiece. For intraoperative navigation either the position-sensitive articulated arm or the optical three-dimensional digitizer of the ISG/ELEKTA system is used. RESULTS: In the operations of the petrous bone performed so far, i.e., mastoidectomy, cholesteatoma surgery, and lateral skull base revision surgery, the clinical value of three-dimensional navigation was clearly demonstrated with an application accuracy, constant throughout surgery, mostly limited only by the resolution of the computed tomography.

Three-dimensional navigation in otorhinolaryngological surgery with the viewing wand.

We report our experiences with the ISG Viewing Wand intraoperative 3-dimensional navigation device in endonasal endoscopic procedures of the paranasal sinuses, anterior skull base, and petrous bone. In the last 12 months we have routinely used the wand in 90 patients for treatment of polyposis nasi, for biopsies and removal of tumors in the nasal cavity and at the frontal skull base, for endocrine ophthalmopathy, and in 1 case for cholesteatoma. We present our computed tomography, magnetic resonance imaging, and clinical protocols that allow a precise routine use of the Viewing Wand. In all cases, the system was extremely helpful for intraoperative localization and helped to optimize surgery.

[First experiences with computer-assisted frameless stereotactic interstitial brachytherapy (CASIB)]. / Erste Erfahrungen mit computerunterstützter stereotaktischer interstitieller Brachytherapie.

PURPOSE: To reach an optimal treatment result and to avoid damage to critical structures a homogeneous dose distribution in the tumor volume with a rapid decreasing dose to the surrounding structures is necessary. Fractionated interstitial brachytherapy of tumors in the ENT region employing needles depends on exact localization of the target volume during all fractions. Therefore reproducibility of positioning of the needle(s) plays an important role. MATERIAL AND METHODS: We used the ISG Viewing Wand system in combination with the Vogele-Bale-Hohner (VBH) head holder and a new targeting device. Point of entrance, pathway, and target point of the needle were planned and insertion of the needle simulated in advance. To date we have treated 7 patients with inoperable tumors in the ENT region. The actual position of the needle in the control CT was compared to the planned position. RESULTS: The accuracy of positioning of the needle depended on the location of the tumor. In a patient with a recurrent retroorbital adenocarcinoma the mean accuracy was 1 mm. Due to soft tissue displacement in the neck region and the resulting necessity to readjust the targeting device the needle was placed with a mean deviation of 15 mm between the planned and the actual position. CONCLUSIONS: Computer-assisted frameless stereotactic interstitial brachytherapy allows for precise, reproducible and preplanned insertion of hollow needles into target structures closely adherent to the surrounding tissue, thus avoiding damage of neighbouring structures. This technique is of great advantage in treating deeply seated tumors which are fixed to bony structures, especially at the skull base. Inaccuracy in the neck region caused by soft tissue shift requires improvement of the immobilization in this region.