[Protocol optimization of three-dimensional spiral CT of craniofacial bones]. / Protokolloptimierung zur 3D-CT des Gesichtsschädels.

PURPOSE: To identify and optimize parameters determining the diagnostic quality of three-dimensional surface models derived from craniofacial spiral CT. MATERIALS AND METHODS: Three dry bone skull specimens were scanned with 1-slice, 4-slice, and 16-slice spiral CT. A total of 60 surface models were calculated with variation of several parameters of the CT scan and calculation of the primary data set and SSD reformations. Two observers evaluated the quality of the resulting models independently using a structured questionnaire. RESULTS: Slice thickness was the only independent factor that influenced image quality. The quality of the 1-slice CT models was poor in all cases. The 4-slice CT models were rated as superior, but also showed relevant impairments. In contrast, the 16-slice CT models provided improved quality with only minor shortcomings. CONCLUSION: Actual clinical applications of three-dimensional models for surgical planning or guidance require high quality of the underlying CT data sets. The slice thickness should not exceed 1 mm. CT examination should be performed using a 4-slice system, or preferably a 16-slice system with a dedicated post-processing protocol.

[Imaging of paranasal sinuses today]. / Bildgebung der Nasennebenhöhlen (NNH) in der heutigen Zeit.

CT is accepted as the gold standard for pathological-anatomical evaluation of paranasal sinus disease, CT is especially considered an obligatory part of planning surgical procedures. Indications for paranasal sinus CT include trauma, malignant disease, and chronic sinusitis, which accounts for the major part of examinations. Due to the benign character of the disease and the relatively moderate age of the patients involved, the radiation dose of paranasal sinus CT plays an important role. The use of a low-dose spiral CT technique and the reformation of coronal images out of the axial CT data instead of an additional direct coronal scan allow the effective dose of paranasal sinus CT to be reduced to the order of a chest radiogram. MRI is the preferred imaging modality in malignant disease or complications of inflammatory sinus disease that extend beyond the limits of the paranasal sinuses. The clinical value of other imaging modalities, including plain film radiography, ultrasound, or scintigraphy, is limited to special indications.

[Laser-based quality assurance for robot-assisted milling at the base of the skull]. / Laserbasierte Qualitätssicherung für die robotergestützte Fräsabtragung an der Schädelbasis.

BACKGROUND: Implanting active hearing devices in the lateral base of the skull requires high-precision, secure fixation of the electromagnetic transducer and long-life anchorage using osteosynthetic fixation plates referred to as mountain brackets. Nonlinear distortion in the acoustic signal path and consecutive implant loosening can only be avoided by exact osseous milling to create the necessary cavity bed while avoiding excessive milling. Robot technology is ideal for high-precision milling. However, safety measures are necessary in order to prevent errors from occurring during the reduction process. Ideally, a robot should be guided by a navigation system. However, robotic systems so far available do not yet have an integrated global navigation system. MATERIALS AND METHODS: We used an animal model under laboratory conditions to examine the extent to which the semiautomatic ROBIN assistant system developed could be expected to increase osseous milling accuracy before implanting active electronic hearing devices into the recipient tissue in the cranium. An existing prototype system for robot-assisted skull base surgery was equipped with laser sensors for geometric measurement of the operation site. The three-dimensional measurement data was compared with CT simulation data before, during, and after the robot-assisted operation. The experiments were conducted on test objects as well as on animal models. RESULTS: Under ideal conditions, the operation site could be measured at a spatial resolution of better than 0.02 mm in each dimension. However, reflections and impurities in the operation site from bleeding and rinsing fluids did have a considerable effect on data collection, necessitating specialised registering procedures. Using an error-tolerant procedure specifically developed, the effective registering error could be kept under 0.3 mm. After milling, the resulting shape matched the intended form at an accuracy level of 0.8 mm. CONCLUSION: The results show that robot systems can reach the accuracy required for reliable microsurgery on the cranial base. High-resolution laser-based geometric measurement of the operation site enables head registration without additional artificial landmarks. During the navigated operation, the procedure can be used to ensure that the resulting cavity matches the intended shape as determined in the preoperative planning phase. This will enable quantitative analysis of, and improvement in the quality of robot-assisted surgery in the future.

[CT-based assessment score after ventral spondylodesis for thoracolumbar spine fracture]. / CT-basierter Auswertungsscore nach ventraler Spondylodese bei thorakolumbalen Wirbelfrakturen.

BACKGROUND: Dorsoventral stabilization is a common procedure to treat thoracolumbar spine fractures. Especially in respect of the evaluation of alternative procedures to autogenous bone graft, a standardized evaluation score for ventral spondylodesis is necessary. PATIENTS AND METHODS: In a group of 44 patients a follow-up CT scan was evaluated with a standardized scoring system by four different independent evaluators (a trauma surgeon, an orthopedic surgeon, and two radiologists). The score is based on the morphologic classification of the region between graft and vertebral body. It allows a classification of the spondylodesis as sufficient, partial, and not sufficient. RESULTS: The statistical evaluation of the classification of the different evaluators shows very good interobserver agreement in monosegmental fusion and good agreement in bisegmental fusion. CONCLUSION: The demonstrated score is easy to handle, does not need special equipment for CT scans, and shows good interobserver agreement in the classification of spinal fusion after ventral spondylodesis for thoracolumbar spine fracture.

High-resolution magnetic resonance imaging of trabecular bone in the wrist at 3 tesla: initial results.

PURPOSE: To evaluate the feasibility of high-resolution magnetic resonance imaging (MRI) of trabecular bone of the wrist at 3 Tesla (3T) in vivo and to assess the potential benefit of the increased resolution for clinical assessment of structural changes in spongy bone. MATERIAL AND METHODS: High-resolution MRI of the wrist was performed with a whole-body 3T MR scanner using a dedicated circularly polarized transmit-receive wrist-coil. Two 3D-FISP sequences with a spatial resolution of 300 x 300 x 300 microm3 in a measuring time of TA = 7:51 min, and 200 x 200 x 200 microm3 in TA = 9:33 min were applied. Seven young healthy volunteers and three elderly subjects with suspected osteoporosis were examined. The signal-to-noise ratio (SNR) in the optimized setup at 3T was compared to measurements at 1.5T. RESULTS: The images at 3T allow microscopic analysis of the bone structure at an isotropic spatial resolution of 200 microm in examination times of <10 min. Differences in the structure of the spongy bone between normal and markedly osteoporotic subjects are well depicted. The SNR at 3T was found up to 16 times higher than at 1.5T applying unchanged imaging parameters. CONCLUSION: The proposed high-resolution MRI technique offers high potential in the diagnosis and follow-up of diseases with impaired bone structure of hand and/or wrist in clinical applications.

[Simplified production of multimedia based radiological learning objects using the flash format]. / Vereinfachte Herstellung multimedialer radiologischer Lernobjekte mit dem Flash-Format.

PURPOSE: Evaluation of the applicability of the Flash Format for the production of radiological learning objects used in an e-learning environment. MATERIAL AND METHODS: Five exemplary learning objects with different didactic purposes referring to radiological diagnostics are presented. They have been intended for the use within the multimedia, internet-based e-learning environment LaMedica. Interactive learning objects were composed using the Flash 5.0 software (Macromedia, San Francisco, USA) on the basis of digital CT and MR images, digitized conventional radiographs and different graphical elements prepared as TIFF files or in a vector graphics format. RESULTS: After a short phase of initial skill adaptation training, a radiologist author was soon able to create independently all learning objects. The import of different types of images and graphical elements was carried out without complications. Despite manifold design options, handling of the program is easy due to clear arrangement and structure, thus enabling the creation of simple as well as complex learning objects that provided a high degree of attractiveness and interaction. Data volume and bandwidth demand for online use was significantly reduced by the Flash Format compression without a substantial loss of visual quality. CONCLUSION: The universally compatible Flash Format offers an opportunity for the simple production of radiological learning objects that fulfill all relevant needs of modern internet based e-learning environments, such as interactivity, employment of multimedia and convertibility.

[Clinical implication of parameter-optimized 3D-FISP MR angiography (MRA) in children with aortic coarctation: comparison with catheter angiography]. / Stellenwert einer parameteroptimierten 3D-FISP-MR-Angiographie bei Kindern mit Aortenisthmusstenose im Vergleich zur Katheterangiographie.

PURPOSE: To implement parameter-optimized 3D-FISP MR angiography (MRA) with interleaved double-slab excitation and to compare the result with catheter angiography in children with aortic coarctation. MATERIALS AND METHODS: Eighteen children aged 2 - 15 years (mean 9.1 years) underwent MR imaging on a 1.5T body scanner (Magnetom Vision, Siemens, Germany). All patients had undergone correlative catheter angiography. T1-weighted turbo spin echo (TSE) images (TR 600 ms, TE 17 ms, flip 160 degrees, slice thickness 2 - 4 mm) were obtained in axial and parasagittal orientation, followed by an optimized 3D-FISP MR angiography in a sagittal plane (TR 12.5 ms, TE 5.5 ms, flip 22 degrees, matrix 256 x 256, slice thickness 1.25 mm). All children were sedated but on spontaneous breathing. Image quality was graded by two experienced reviewers using a 4-point scoring system. Source images and reformatted maximum intensity projections (MIP) were analyzed for blood-tissue contrast as well as size and focal stenoses of the aortic arch. RESULTS: Aortic coarctation was found in 13 of 18 patients, using the 3D-FISP MRA. A high correlation value (r = 0.96) was found compared to catheter angiography. Image quality was high in 94 % with well defined blood-tissue contrast in all cases. The sensitivity to flow and breathing motion was low. Examination time was about 15 minutes depending on volume of interest and heart rate. Diagnostic accuracy has shown improvement using a combined analysis of source and MIP images. The mentioned technique has provided an excellent display of thoracic vasculature. CONCLUSION: MR imaging represents an excellent tool for non-invasive examination of the cardiovascular system of children. The 3D-MRA allows the recording of a large 3D data set without the use of contrast agent and within an adequate measurement period, particularly in small infants unable to hold their breath. In addition, hemodynamic significance of aortic coarctation, the existence of collateral vessels and other congenital heart diseases can be described reliably by using this technique.

[Evaluation of different 16-row CT colonography protocols using a porcine model]. / Evaluation unterschiedlicher 16-Zeilen-CT-Colonographie-Protokolle am Schweinedarmmodell.

PURPOSE: To develop and to test an easily produced biological colon model with simulated polypoid lesions. Application of this phantom for the selection of an optimized scan protocol of 16-row CT colonography (CTC) for clinical use. METHODS AND MATERIAL: Six polypoid lesions (1 - 6 mm) were simulated with sutures on the inner face of a porcine colon segment (20 cm). After distending the colon segment with air, the phantom was placed in a water quench and CT scans were performed on a MDCT-scanner (Somatom Sensation 16, Siemens, Forchheim). At constant values for collimation (16x0.75 mm) and voltage (120 kV), 54 different combinations of mAs values (50, 75 and 100 mAs), pitch factors (1, 1.25 and 1.5) and slice thicknesses (0.75, 1.0, 1.5, 2.0, 3.0 and 5.0 mm) were tested systematically. The phantom was scanned in the longitudinal and transverse axis to simulate the different orientation of the colon in the abdomen. Axial slice images and virtual endoscopic views of all data sets were presented separately to 2 radiologists who independently determined number and size of detectable polyps. Dose exposure was measured with an Alderson phantom. RESULTS: The colon model offered a realistic imitation of a polyp-covered, human colon. The experimental set-up allowed a systematic evaluation of polyp detection related to lesion size, orientation of the colon and CTC parameters, with other influencing factors mostly excluded. Polyps were significantly better detected in the longitudinal than in the transverse orientation of the colon. For the detection of lesions of at least 3 mm, a low dose (50 mAs) 16-row CTC should be combined with a pitch of 1.5 and a maximum slice thickness of 3 mm. For the depiction of polyps smaller than 3 mm, slice thickness and pitch should amount to 1 mm and 1.0, respectively. Effective dose of this low dose protocol is 4.08 mSv. CONCLUSION: The porcine colon phantom represents a realistic and easily produced alternative to other colonography models. It allows a preselection of a CTC-protocol for subsequent clinical testings. If the high in vitro performance of the low-dose 16-row CTC-protocol is confirmed on a human collective, the use of 16-row technique would represent a big step for CTC toward a screening method.

[Registration using three-dimensional laser surface scanning for navigation in oral and craniomaxillofacial surgery]. / Registrierung mit dreidimensionaler Oberflächen-Laserscanner-Technik zur Navigation in der Mund-, Kiefer- und Gesichtschirurgie.

INTRODUCTION: Recent innovations in laser scanning technology provide a potentially useful tool for three-dimensional surface registration for image-guided surgery. The purpose of this study is to evaluate the clinical reliability of this technique in oral and maxillofacial surgical procedures using image-guided navigation. METHODS: In an experimental step, a stable anthropomorphic skull model with prelabeled markers was scanned and registered with laser surface scanning (z-touch, BrainLAB) and marker- based algorithms. The registration protocol was then repeated 25-times. Root mean square error (RMSE) and target difference values were compared for their suitability for this application. Twelve patients with different indications for oral and maxillofacial surgery were planned for image-guided surgery using a passive infrared surgical navigation system (VectorVision, BrainLAB). Preoperative computed tomography (CT) scans were carried out with newest 16-line multisclice CT-scanner (Siemens Somatom Sensation 16). The new markerless laser surface scanning technique was applied in all intraoperative patient registrations. Registration error was noted. The clinical application accuracy was determined for anatomical landmark localization deviation. RESULTS: In the experimental protocol a mean registration error (RMSE) or target difference of 1.3 (0.14) or 2.08 (0.49) mm for laser scanning and 0.38 (0.01) or 0.99 (0.15) mm for marker registration was found. The differences for RMSE and target localization were statistically significant (p < 0.005). Furthermore, a strong correlation between RMSE and target difference was found for laser scanning (r = 0.96) and marker registration (r = 0.95). During various clinical procedures involving oral and maxillofacial surgery, the overall error of the registration procedure determined as RMSE was 1.21 (0.34) mm. Intraoperatively, the mean clinical application accuracy was found to be 1.8 (0.5) mm. CONCLUSION: Three-dimensional laser surface scanning technique may be a interesting and useful approach to register the patient for image-guided procedures, particularly during oral and craniomaxillofacial surgery.

[Distinctive features of the os naviculare pseudarthrosis vs the os naviculare accessorius]. / Unterscheidungsmerkmale der Os-naviculare-Pseudarthrose gegenüber dem Os naviculare accessorius.

We report on two cases in which the differential diagnosis between an os tibiale externum (os naviculare accessorius) and a post-traumatic pseudarthrosis of the os naviculare was subject to discussion.Both patients had suffered an acute trauma in the region of the middle foot and showed identical clinical symptoms. Conventional X-ray did not allow a definite classification of the diagnosis either.However, this was possible in both cases by virtue of typical signs evidenced by computed tomography and magnetic resonance imaging.

Image-guided navigation for minimal invasive approaches in craniomaxillofacial surgery.

The use of minimally invasive procedures in maxillofacial surgery will require new technologies involving surgical navigation and techniques. The aim of our studies is to improve the efficacy of image-guided navigation in combination with endoscopically assisted techniques for minimally invasive craniomaxillofacial procedures. Prospective evaluation was made of all patients who underwent surgical procedures using image-guided navigation. The most common type of operations performed were endoscopically assisted interventions within the paranasal sinuses, fracture treatment, the resection of bone lesions and further miscellaneous interventions. Our experience to date suggest that image-data based techniques are eminently applicable, providing a feasible alternative to conventional surgical treatment.

[Feasibility of intraoperative diagnosis with a mobile computed tomography scanner]. / Möglichkeiten der intraoperativen Diagnostik mit einem fahrbaren Computertomographen.

AIMS: The possibility of performing intraoperative computed tomography may add to the safety and efficiency of some maxillofacial procedures. It would be preferable for intraoperative image data acquisition to be available to a surgeon on demand for immediate control of therapy results. METHODS: In a pilot study, the use of a mobile computed tomographic scanner (Philips Tomoscan M, Philips Medical Systems, Eindhoven, Netherlands) was evaluated in our unit. The scanner is equipped with wheels, draws power from wall outlets in combination with batteries, and has a translating gantry. RESULTS: Experience to date with six patients has confirmed the feasibility of intraoperative CT. All patients operated on were treated for craniofacial trauma. The CT images showed good spatial resolution. In all cases, visualization of the correct fragment position was excellent without causing significant delay of the operative procedure. CONCLUSIONS: Intraoperative computed tomography could be the new state-of-the-art method for direct control of treatment results in maxillofacial traumatology. Nevertheless, the high expenses for installation of such technical infrastructure has to be pointed out; therefore, the routine use of this technique might be questioned.

The use of hybrid stereolithographic models for the planning of complex craniofacial procedures.

Preoperative planning of orthognathic surgery is usually based on plaster cast models. Those are integrated in an articulator, simulating the movement of the jaws. We present a new procedure to combine the individual jaw anatomy by stereolithographical models with dental plaster casts, which are more accurately reproducing dental and bony anatomy. For image fusion the patient and the individual plaster casts are scanned by computed tomography, the occlusal planes being covered by a splint with radioopaque makers. After threshold segmentation of both, the plaster cast and the patients skull images are fused. The plaster cast volume is then subtracted from the patients upper and lower jaw, thus sparing out the place for later fusion of stereolithographic model and plaster cast.

Initial experience with intraoperative computed tomography in maxillofacial surgery.

With respect to the complex anatomy in the head and neck region, computed tomography has been established as a routine method for preoperative evaluation. Whereas in neurosurgery intraoperative tomographic image data acquisition (CT, MR) serves for control of therapeutic effects on a routine base, maxillofacial surgeons aren't accustomed to use the method in this way. Using a mobile Philips Tomoscan M scanner, we examined the clinical significance and especially the ergonomy of intraoperative CT scans in maxillofacial traumatology.

[Intraoperative computer tomography control within the scope of maxillofacial traumatology using a mobile scanner]. / Intraoperative computertomographische Kontrolle im Rahmen der maxillofazialen Traumatologie unter Verwendung eines fahrbaren Scanners.

Advances in intra-operative imaging and the development of new minimally invasive techniques are having an ever greater impact on modern surgery. Mobile CT scanners in the operating room is a new technique that permits image-guided surgery, and helps minimize postoperative complications. We report on our initial experience with intraoperative CT scanning during surgery on patients suffering lateral midface trauma. A mobile CT unit, the Tomoscan M (Philips, Utrecht, Netherlands) set up in the operating room, was evaluated in 6 patients with zygomatic bone fractures. The patients were placed on the CT scanner table, which is detachable from the gantry. The unit is powered by batteries charged from an ordinary ring mains supply via a conventional plug. The CT images obtained were of good quality in all cases. No technical problems were observed during surgery. Using repeat CT scans, the procedure also permits accurate intraoperative monitoring of the anatomical repositioning of the bone fragments, and accurate implantation. No intraoperative or early postoperative complications were observed. This new technical aid ensures highly accurate reduction of the bone fragments, and minimizes the need for reoperation. High-quality intraoperative imaging with surgical navigation increase surgical outcome, and expand the spectrum of minimally invasive surgery.

[Image processing in radiology]. / Bildverarbeitung in der Radiologie.

Medical imaging processing and analysis methods have significantly improved during recent years and are now being increasingly used in clinical applications. Preprocessing algorithms are used to influence image contrast and noise. Three-dimensional visualization techniques including volume rendering and virtual endoscopy are increasingly available to evaluate sectional imaging data sets. Registration techniques have been developed to merge different examination modalities. Structures of interest can be extracted from the image data sets by various segmentation methods. Segmented structures are used for automated quantification analysis as well as for three-dimensional therapy planning, simulation and intervention guidance, including medical modelling, virtual reality environments, surgical robots and navigation systems. These newly developed methods require specialized skills for the production and postprocessing of radiological imaging data as well as new definitions of the roles of the traditional specialties. The aim of this article is to give an overview of the state-of-the-art of medical imaging processing methods, practical implications for the radiologist's daily work and future aspects.

[Rational CT diagnosis before operations on the paranasal sinuses]. / Rationelle CT-Diagnostik vor Operationen an den Nasennebenhöhlen.

Movement or metal artefacts as well as the relatively high radiation exposure of both the axial and the coronal scan are disadvantages of computed tomography. A single spiral CT scan with a secondary reformation replacing the second CT scan might solve these problems. The goal of this project was to compare the diagnostic value of primary spiral CT scans of paranasal sinuses with secondary reformations. These were evaluated by ENT surgeons as well as radiologists. We performed axial and coronal spiral-CT's of paranasal sinuses in 80 patients. The secondary coronal and axial reformations were calculated with 2 mm image sections. Although a reduced resolution was observed in the secondary reformations, this did not compromise the detection of important anatomical features. Image deterioration due to artifacts was significantly reduced.