Cone beam CT: a current overview of devices.

The purpose of this study was to review and compare the properties of all the available cone beam CT (CBCT) devices offered on the market, while focusing especially on Europe. In this study, we included all the different commonly used CBCT devices currently available on the European market. Information about the properties of each device was obtained from the manufacturers' official available data, which was later confirmed by their representatives in cases where it was necessary. The main features of a total of 47 CBCT devices that are currently marketed by 20 companies were presented, compared and discussed in this study. All these CBCT devices differ in specific properties according to the companies that produce them. The summarized technical data from a large number of CBCT devices currently on the market offer a wide range of imaging possibilities in the oral and maxillofacial region.

The "puffed cheek method" to evaluate mucosal thickness: case series.

OBJECTIVES: Mucosal thickness should be considered in implant treatment planning. Needle probing to measure mucosal thickness is invasive and therefore not used in routine diagnosis. The "puffed cheek" method is an established technique to visualize the vestibule in computed tomography (CT). As CT assesses bone availability, a simultaneous mucosal thickness measurement would be useful. The aim of this study was to evaluate the reliability of mucosal thickness measurement in CT with distended cheeks. MATERIALS AND METHODS: Buccal maxillary mucosa thickness was evaluated at four measurement sites in the incisor and molar area of 11 patients. Each site was evaluated via CT with cheek distension and needle probing. Measurement area was identified with the aid of a thermoplastic splint to localize the exact position by a gutta-percha marker point. The comparison between the two methods was performed by Bland-Altman diagram. RESULTS: The mean clinical thickness was 1.17 mm (±0.31) compared to 1.11 mm (±0.31) in CT evaluation. The mean difference between the two methods was 0.07 mm (±0.40; CI-0.14;0.12, P = 0.88, Krippendorff α = 0.38). According to Bland-Altman diagram the mucosal thickness may diverge by up to 0.9 mm from the radiologic thickness. CONCLUSIONS: The two measurement methods may not be interchangeably used. As additional information to three-dimensional bone analyses, CT may be performed as a pre-operative soft tissue analysis at most implant sites with distended cheeks. Nevertheless, this method yields less valid and reliable results than the gold standard.

Root canal system in the mesiobuccal root of the maxillary first molar: an in vitro comparison study of computed tomography and histology.

OBJECTIVES: The purpose of this study was to investigate a new diagnostic approach to the examination of the canal configuration of the mesiobuccal root of the maxillary first molar. MATERIALS AND METHODS: High-resolution computed tomography (CT) was compared with histology in vitro. There were 152 teeth investigated and classified according to Weine and Vertucci. RESULTS: CT describes the exact canal configuration, verifying information identical to histology, and thus serving as the "gold standard" in vitro. With regard to canal position, 9 (5.92%) of the teeth examined were Vertucci type 1, 48 (31.58%) were Vertucci type 2, 91 (59.87%) were Vertucci type 4, 1 (0.66%) was Vertucci type 5, 1 (0.66%) was Vertucci type 6. Of the 152 teeth examined, 3 (1.97%) could not be classified using Weine, 2 (1.31%) could not be classified according to either Weine or Vertucci, and no Vertucci types 3, 7 or 8 were identified. CONCLUSIONS: CT offers complete information on the number and configuration of root canals. As the root canal configuration of the adult does not change rapidly, CT investigations can be used for multiple subsequent treatments.

MRI of the cartilage.

With the introduction of fat-suppressed gradient-echo and fast spin-echo (FSE) sequences in clinical routine MR visualization of the hyaline articular cartilage is routinely possible in the larger joints. While 3D gradient-echo with fat suppression allows exact depiction of the thickness and surface of cartilage, FSE outlines the normal and abnormal internal structures of the hyaline cartilage; therefore, both sequences seem to be necessary in a standard MRI protocol for cartilage visualization. In diagnostically ambiguous cases, in which important therapeutic decisions are required, direct MR arthrography is the established imaging standard as an add-on procedure. Despite the social impact and prevalence, until recent years there was a paucity of knowledge about the pathogenesis of cartilage damage. With the introduction of high-resolution MRI with powerful surface coils and fat-suppression techniques, visualization of the articular cartilage is now routinely possible in many joints. After a short summary of the anatomy and physiology of the hyaline cartilage, the different MR imaging methods are discussed and recommended standards are suggested.

Optimization of the composition of phantom materials for computed tomography.

Using available data for photon attenuation and tissue composition, a computer code was developed for the optimization of the composition of phantom materials for diagnostic radiology. The code allows selection of attenuation data in a photon energy range from 1 to 150 keV and the choice of a suitable weight function in the energy interval chosen. For applications in CT imaging a weight function is available reflecting the contribution of the x-ray spectrum to the CT-signal. Several phantom materials for CT were optimized (body fat, trabecular bone, an average bone composition for C4 vertebrae and water) by varying the mineral components in a polymer base in order to adjust x-ray attenuation properties. Measurements with the water equivalent material (PSPP1) showed good agreement of calculated and measured HU values (AHU = 7.3 +/- 5.3 at 80 kVp and 4.0 +/- 2.7 at 140 kVp) and little variation of HU for tube voltages from 80 to 140 kVp. The method provides a fast and flexible means for obtaining optimized phantom materials for a large variety of tissue compositions and energy ranges.

Temperature dependence of HU values for various water equivalent phantom materials.

The temperature dependence of water equivalent phantom materials used in radiotherapy and diagnostic imaging has been investigated. Samples of phantom materials based on epoxy resin, polyethylene, a polystyrene-polypropylene mixture and commercially available phantom materials (Solid Water, Gammex RMI and Plastic Water, Nuclear Associates) were scanned at temperatures from 15 to 40 degrees C and HU values determined. At a reference temperature of 20 degrees C materials optimized for CT applications give HU values close to zero while the commercial materials show an offset of 119.77 HU (Plastic Water) and 27.69 HU (Solid Water). Temperature dependence was lowest for epoxy-based materials (EPX-W: -0.23 HU degrees C(-1); Solid Water: -0.25 HU degrees C(-1)) and highest for a polyethylene-based material (X0: -0.72 HU degrees C(-1)). A material based on a mixture of polystyrene and polypropylene (PSPPI: -0.27 HU degrees C(-1)) is comparable to epoxy-based materials and water (-0.29 HU degrees C(-1)).

[Coxarthrosis]. / Koxarthrose.

Osteoarthritis of the hip joint is a very common disease. There is a minor prevalence of males. By etiology one can distinguish primary (idiopathic) from secondary osteoarthritis. Secondary are due to well-known etiologies as overweight, repetitive traumata, malposture, muscle- and tendon-imbalance etc. Osteoarthritis includes not only cartilage abnormalities, but also such of the subchondral-region, synovialis, synovial fluid and periarticular muscles. The cartilage shows in osteoarthritis typically edema and swelling, defects with tears, fibrillation, and "baldness" and (or) cartilagenous repair-islands and joint space narrowing as well, while subchondrally micro-edema, necrosis, ev. microfractures, "cysts", demineralisation followed by sclerosis, osteophyte-formation and deformity is seen. With conventional radiographs and CT joint space narrowing, subchondral cysts, sclerosis and osteophytes and deformities are well delineated, MRI however allows visualization of subtle bone marrow and cartilage abnormalities. Clinically, the diagnosis of pre-osteoarthritis becomes more and more important. This includes e.g. deformities and malpostures, labrum-pathologies and structural imbalances. There are three prognostic different types of hip-osteoarthritis depending on the migration of the head of the hip joint: the most common are the latero-cranial and the medio-caudal ones, while the central one is found very rarely. Basic imaging method are conventional radiographs, and CT, followed by MRI. The diagnosis of an "activated osteoarthritis" is made by bone-scintigraphy or MRI with i.v. application of contrast-media. The labrum- and cartilage diagnosis should be done with MRI or MR-arthrography. Functional computer-animated analysis will be of great diagnostic value in the near future. MRI indications are differences between clinical results and imaging, missing clinical improvement of an "activated" osteoarthritis under standard therapy, unclear joint-pain and before any arthroscopy.

Pathophysiology and imaging in inflammatory and blastomatous synovial diseases.

Variable pathologies are subsumed under the term "synovial disease", including common pathologies such as rheumatoid arthritis. While formerly radiologists had to rely on conventional radiographs and bone scintigraphy with their inherent problems in visualizing soft tissue, noninvasive imaging of the synovium has recently improved substantially with the technical development of MRI and (Doppler) ultrasound. These imaging modalities allow differentiation of characteristic pathologic features based on a profound knowledge of normal anatomy and pathophysiology.

Dental CT evaluation of mandibular first premolar root configurations and canal variations.

OBJECTIVES: Routine dental CT scans were used to describe mandibular first premolar root configurations and canal variations. STUDY DESIGN: One hundred twenty dental CT examinations were evaluated for mandibular first premolar root configurations and canal variations regarding shape of root and root canal, incidence of multiple canals, and level of bifurcation. RESULTS: A total of 17 teeth in 12 patients showed mesial invagination of the root of the mandibular first premolar. One root displayed 3 canals with 3 apical foramina. In 2 teeth, a single canal divided into 2 canals, but merged into 1 apical foramen. One root showing 2 root canals finally divided into 2 roots near the apex. Thirteen roots had 2 canals and 2 apical foramina. The distance from the cementoenamel junction to the level of bifurcation was between 4 and 13 mm (mean, 7.4 mm). CONCLUSION: The occurrence of incidentally found mandibular first premolar root variations should be an important component of dental CT reports.

[A simple method for estimating effective dose in dental CT. Conversion factors and calculation examples for a clinical low dose protocol]. / Eine einfache Methode zur Abschätzung der effektiven Dosis bei Dental-CT. Konversionsfaktoren und exemplarische Berechnung für ein klinisches Low-Dose-Protokoll.

PURPOSE: An easily applicable method to estimate effective dose including in its definition the high radiosensitivity of the salivary glands from dental computed tomography is presented. Effective doses were calculated for a markedly dose reduced dental CT protocol as well as for standard settings. Data are compared with effective doses from the literature obtained with other modalities frequently used in dental care. METHODS: Conversion factors based on the weighted Computed Tomography Dose Index were derived from published data to calculate effective dose values for various CT exposure settings. RESULTS: Conversion factors determined can be used for clinically used kVp settings and prefiltrations. With reduced tube current an effective dose for a CT examination of the maxilla of 22 microSv can be achieved, which compares to values typically obtained with panoramic radiography (26 microSv). A CT scan of the mandible, respectively, gives 123 microSv comparable to a full mouth survey with intraoral films (150 microSv). CONCLUSION: For standard CT scan protocols of the mandible, effective doses exceed 600 microSv. Hence, low dose protocols for dental CT should be considered whenever feasable, especially for paediatric patients. If hard tissue diagnoses is performed, the potential of dose reduction is significant despite the higher image noise levels as readability is still adequate.

Lingual vascular canals of the mandible: evaluation with dental CT.

PURPOSE: To evaluate whether dental computed tomography (CT) can depict the frequency, diameter, position, and direction of vessels entering the mandible through lingual bone canals. MATERIALS AND METHODS: Thirty-two consecutive patients underwent preimplantation CT of the lower jaw and examination for the presence, number, location, diameter, and direction of lingual canals entering the mandible. In addition, three cadaver mandibles were investigated with dental CT and subsequently dissected to confirm the CT findings. RESULTS: All patients demonstrated at least one lingual vascular canal, and 20 (63%) had multiple (two to five) canals. The typical lingual canal locations were the midline of the mandible and the premolar region. The mean diameter of the lingual canals was 0.7 mm +/- 0.3 (SD) (range, 0.4--1.5 mm) in the midline and 0.6 mm +/- 0.2 (range, 0.3--1.2 mm) in both premolar regions of the mandible. Examination results in the three cadaver mandibles confirmed the CT findings in those mandibles. CONCLUSION: Dental CT can depict the occurrence, position, and size of the lingual vascular canals of the mandible. Radiologists should be aware of this anatomic feature and its possible implications.

Detection of the mandibular canal via shaded surface display and multiplanar reconstruction of CT data.

The purpose of this study was to evaluate the sensitivity of conventional two-dimensional (2D) multisection images (multiplanar rendering, MPR) and registered three-dimensional (3D) shaded surface images (shaded surface display, SSD) of standard axial computed tomography (CT) data for detecting the mandibular canal (MC) in the lower jaw of 136 patients. The patients, who had different indications for mandibular CT, were examined using standard axial CT scanning. Two post-processing programs were used for 3D visualization of the data sets. The cross-sectional rendered images and the shaded surface 3D images were graded for detection of the MC, the presence of artefacts, overall quality and clinical relevance. A 3D display of the MC was achieved using the MPR technique in 100% with high image quality. The surface rendered display depicted the MC in 80%. Artefacts markedly degraded the 3D displays obtained using the surface rendering technique; thus, SSD is an inappropriate technique for imaging the entire MC without manual segmentation. MPR-CT improves the sensitivity of CT imaging in the detection of the MC with very little time needed for post-processing compared with the SSD method. This post-processing modality should, therefore, be considered for serial studies of patients undergoing dental CT. The sensitivity of the MPR method is even superior to the standard axial CT slices.

Computed tomographic diagnosis and localization of bone canals in the mandibular interforaminal region for prevention of bleeding complications during implant surgery.

In this study, computed tomograms (CTs) of 70 patients were examined for visible vascular canals in the mandible as well as for their localization, incidence, diameter, and content. All patients examined showed at least 1 lingual perforating bone canal in the mandible. Since such vascular canals are encountered regularly, routine CT examination is recommended prior to implant surgery to help avoid severe bleeding complications during the placement of implants in the interforaminal region.

In-vitro assessment of a registration protocol for image guided implant dentistry.

In this study a computer aided navigation technique for accurate positioning of oral implants was assessed. An optical tracking system with specially designed tools for monitoring the position of surgical instruments relative to the patient was used to register 5 partially or completely edentulous jaw models. Besides the accuracy of the tracking system, the precision of localizing a specific position on 3-dimensional preoperative imagery is governed by the registration algorithm which conveys the coordinate system of the preoperative computed tomography (CT) scan to the actual patient position. Two different point-to-point registration algorithms were compared for their suitability for this application. The accuracy was determined separately for the localization error of the position measurement hardware (fiducial localization error-FLE) and the error as reported by the registration algorithm (fiducial registration error-FRE). The overall error of the navigation procedure was determined as the localization error of additional landmarks (steel spheres, 0.5 mm diameter) after registration (target registration error-TRE). Images of the jaw models were obtained using a high resolution CT scan (1.5 mm slice thickness, 1 mm table feed, incremental scanning, 120 kV, 150 mAs, 512 x 512 matrix, FOV 120 mm). The accuracy of the position measurement probes was 0.69 +/- 0.15 mm (FLE). Using 3 implanted fiducial markers, FRE was 0.71 +/- 0.12 mm on average and 1.00 +/- 0.13 mm maximum. TRE was found to be 1.23 +/- 0.28 mm average and 1.87 +/- 0.47 mm maximum. Increasing the number of fiducial markers to a total of 5 did not significantly improve precision. Furthermore it was found that a registration algorithm based on solving an eigenvalue problem is the superior approach for point-to-point matching in terms of mathematical stability. The experimental results indicate that positioning accuracy of oral implants may benefit from computer aided intraoperative navigation. The accuracy achieved compares well to the resolution of the CT scan used. Further development of point-to-point/point-to-surface registration methods and tracking hardware has the potential to improve the precision of the method even further. Our system has potential to reduce the intraoperative risk of causing damage to critical anatomic structures, to minimize the efforts in prosthetic modelling, and to simplify the task of transferring preoperative planning data precisely to the operating room in general.

Local calibrated bone mineral density in the mandible presented using a color coding scheme.

Calibrated information on bone mineral density (BMD) may be used in dental implantology to measure "bone quality". It can be used to estimate the expected primary implant stability preoperatively and to guide the surgeon in selecting optimum implant types and operation techniques. Using a preoperative dental computed tomography (Dental-CT) scan, all of this information can be obtained without additional examinations and thus without additional X-ray exposure of the patient. In contrast to bone mineral determination in other body regions, local BMD values are important in the jaw bone. Therefore, a regimen where color-coded information on local bone mineralization is superimposed on Dental-CT images is proposed using the original CT volumes as well as reformatted views.

Alternative to the median region of the palate for placement of an orthodontic implant.

Tooth-borne anchorage may be one of the greatest limitations of modern orthodontic treatment, because teeth move in response to forces. Previous investigators have placed temporary implants in the median-sagittal palate in order to establish maximum anchorage. This area, however, may be characterized by relatively low vertical bone support. The aim of this study was therefore to find an alternative palatal implant site which offers a higher amount of bone support. This study comprised 22 patients wishing for maximum anchorage underwent presurgical diagnostic evaluation by means of low-dose dental CT. The measuring results regarding vertical bone volume and the position of the neighbouring tooth roots were used as the basis for further treatment. The statistical data analysis indicated an area suitable for implant placement in the group of patients examined. This area was located 6 to 9 mm posterior to the incisive foramen and 3 to 6 mm paramedian, under avoidance of the mid-palatal suture. The patients showed such a great range of variation in vertical bone volume that a preoperative diagnostic evaluation also seems to be recommendable when very short implants are used in order to avoid perforations of the lower nasal duct.

Atypical appearance of elastofibroma dorsi on MRI: case reports and review of the literature.

Three patients with histologically proven elastofibroma dorsi underwent MRI, using T1-weighted, T2-weighted, STIR (short inversion time inversion recovery), and contrast-enhanced SE sequences. All lesions typically displayed low signal intensity masses interspersed with areas of high signal intensity on T1- and T2-weighted SE images. Contrary to prior reports, two patients showed marked enhancement of the mass after administration of Gd-DTPA. Although the characteristic signal intensity on conventional T1- and T2-weighted images may lead to the early diagnosis of this rare tumor, radiologists should be aware that marked contrast enhancement may be representative in elastofibroma dorsi.

Osteometry of the mandible performed using dental MR imaging.

BACKGROUND AND PURPOSE: On cross-sectional and panoramic reformatted images from axial (dental) CT scans of the mandible it may be difficult to identify the inferior alveolar neurovascular bundle (IANB) in patients lacking a clear-cut bony delimitation of the mandibular canal. Dental MR images are comparable to dental CT scans, which directly show the IANB; however, measurements of length may not be reliable owing to susceptibility artifacts and field inhomogeneities in the oral cavity. Therefore, the accuracy of length measurements on dental MR images was compared with that on dental CT scans and direct osteometry. METHODS: Dental T1-weighted MR imaging using a high-resolution turbo gradient-echo sequence and dental CT were performed in six anatomic specimens. The axial scans were reformatted as panoramic and cross-sectional reconstructions on a workstation and characteristic cross sections were obtained from all mandibles. The longest axis in the bucco-lingual and apico-basal directions, the distances from the top of the mandibular canal to the top of the alveolar ridge and from the bottom of the mandibular canal to the base of the mandible, and the diameter of the bone cortex at the alveolar ridge were measured with direct osteometry on the cross sections and compared with measurements on corresponding MR and CT reformatted images. RESULTS: The correlation between direct osteometry and dental MR and CT was strong, except for the bone cortex diameter at the top of the alveolar ridge, where only a moderate correlation was found. Means of comparable length measurements were not significantly different among the three methods. CONCLUSION: The accuracy of length measurements in the jaw bones obtained using dental MR is comparable to that of dental CT and is not significantly different from direct osteometry. Thus, dental MR is a potential alternative to CT for dental imaging.

Assessment of the blood supply to the mental region for reduction of bleeding complications during implant surgery in the interforaminal region.

Several life-threatening complications caused by hemorrhage that can occur during the placement of dental implants in the mandibular interforaminal region have been described in the literature. The aim of this study was to assess the vascular supply to this region and delineate the relative contribution and importance of the sublingual artery versus the submental artery. Thirty-four human cadavers were dissected. Special attention was directed to the presence of a branch of the submental artery that perforates the mylohyoid muscle and thus participates in the blood supply to the floor of the mouth together with the sublingual artery. A sublingual artery was found in 71% of the specimens. A large branch of the submental artery perforating the mylohyoid muscle was found in 41% of the specimens. The point of perforation was located an average of 31 mm posterior to the menton. The high risk of injuring the vessels of the floor of the mouth can be explained by the close vicinity of these vessels to the mandibular lingual cortical plate. To prevent complications in cases of unclear anatomic identification of the fossa sublingualis, preoperative lingual probing or elevation of the periosteum of the lingual aspect of the mandible is necessary. An alternative diagnostic procedure is precise preoperative noninvasive imaging (eg, computed tomography).