Correlation of objective image quality and working length measurements in different CBCT machines: An ex vivo study.

To investigate potential correlations between objective CBCT image parameters and accuracy in endodontic working length determination ex vivo. Contrast-to-noise ratio (CNR) and spatial resolution (SR) as fundamental objective image parameters were examined using specific phantoms in seven different CBCT machines. Seven experienced observers were instructed and calibrated. The order of the CBCTs was randomized for each observer and observation. To assess intra-operator reproducibility, the procedure was repeated within six weeks with a randomized order of CBCT images. Multivariate analysis (MANOVA) did not reveal any influence of the combined image quality factors CNR and SR on measurement accuracy. Inter-operator reproducibility as assessed between the two observations was poor, with a mean intra-class correlation (ICC) of 0.48 (95%-CI  0.38, 0.59) for observation No. 1. and 0.40 (95%-CI 0.30, 0.51) for observation No. 2. Intra-operator reproducibility pooled over all observers between both observations was only moderate, with a mean ICC of 0.58 (95%-CI 0.52 to 0.64). Within the limitations of the study, objective image quality measures and exposure parameters seem not to have a significant influence on accuracy in determining endodontic root canal lengths in CBCT scans. The main factor of variance is the observer.

Cone-beam computed tomography and its applications in dental and maxillofacial radiology.

Cone-beam computed tomography (CBCT) was first used in dental and maxillofacial radiology (DMFR) at the end of the 1990s. Since then, it has been successfully established as the standard three-dimensional radiographic imaging technique in DMFR, with a wide variety of applications in this field. This manuscript briefly reviews the background information on the technology and summarises available data on effective dose and dose optimisation. In addition, typical clinical applications and indications of the technique in DMFR are presented.

Detection accuracy of maxillary sinus floor septa in panoramic radiographs using CBCT as gold standard: a multi-observer receiver operating characteristic (ROC) study.

OBJECTIVES: To investigate diagnostic accuracy of panoramic radiography in detecting maxillary sinus floor septa by means of a multi-observer receiver operating characteristic (ROC) analysis and a standardized protocol for reporting (STARD protocol; Clin Chem 49(1):1-6, 2003). MATERIAL AND METHODS: From our database, 25 cone beam computed tomographies (CBCTs) were selected with one maxillary sinus floor septum (height ≥ 2.5 mm). For the same patient, a recent panoramic radiograph (PAN) had to be available in the database. As controls, 28 CBCTs plus corresponding PANs without evidence of a sinus septum were selected. Using the CBCTs as ground truth, 17 observers from our dental school on a five-point confidence scale rated both sinuses in all 53 PANs with respect to presence/absence of a sinus septum. Areas beneath ROC curves (Az-values), sensitivity/specificity (SNT/SPF), positive/negative predictive values (PPV, NPV), and positive/negative likelihood ratios (LR+, LR-) were computed for each observer and pooled over all observers. Inter-rater reproducibility was assessed by means of the intraclass coefficient (ICC) using a two-way random effects model. RESULTS: A pooled Az-value of 0.839 was observed (SNT 84.6%, SPF 73.5%). PPV ranged between 0.492 and 0.824 (median 0.627) and NPV between 0.838 and 0.976 (median 0.917). A median LR+ of 3.567 was computed (LR- median 0.193). Inter-rater reliability revealed an ICC of 0.55 (95% confidence interval 0.48 to 0.62). CONCLUSIONS: Our results indicate that PAN is a moderately accurate method for sinus elevation planning for the purpose of septum detection. Ruling out a septum by PAN seems to work more accurately than ruling in. CLINICAL RELEVANCE: For the purpose of maxillary sinus floor septa detection, panoramic radiography can be relatively safely advocated, particularly for judgment of a septum-free sinus.

Spatial resolution in CBCT machines for dental/maxillofacial applications-what do we know today?

Spatial resolution is one of the most important parameters objectively defining image quality, particularly in dental imaging, where fine details often have to be depicted. Here, we review the current status on assessment parameters for spatial resolution and on published data regarding spatial resolution in CBCT images. The current concepts of visual [line-pair (lp) measurements] and automated [modulation transfer function (MTF)] assessment of spatial resolution in CBCT images are summarized and reviewed. Published measurement data on spatial resolution in CBCT are evaluated and analysed. Effective (i.e. actual) spatial resolution available in CBCT images is being influenced by the two-dimensional detector, the three-dimensional reconstruction process, patient movement during the scan and various other parameters. In the literature, the values range between 0.6 and 2.8 lp mm(-1) (visual assessment; median, 1.7 lp mm(-1)) vs MTF (range, 0.5-2.3 cycles per mm; median, 2.1 lp mm(-1)). Spatial resolution of CBCT images is approximately one order of magnitude lower than that of intraoral radiographs. Considering movement, scatter effects and other influences in real-world scans of living patients, a realistic spatial resolution of just above 1 lp mm(-1) could be expected.

Anisotropic thermal conductivity in uranium dioxide.

The thermal conductivity of uranium dioxide has been studied for over half a century, as uranium dioxide is the fuel used in a majority of operating nuclear reactors and thermal conductivity controls the conversion of heat produced by fission events to electricity. Because uranium dioxide is a cubic compound and thermal conductivity is a second-rank tensor, it has always been assumed to be isotropic. We report thermal conductivity measurements on oriented uranium dioxide single crystals that show anisotropy from 4 K to above 300 K. Our results indicate that phonon-spin scattering is important for understanding the general thermal conductivity behaviour, and also explains the anisotropy by coupling to the applied temperature gradient and breaking cubic symmetry.

Density of states features in some anomalous melting elements.

Valence band photoemission measurements have been made on crystalline and supercooled liquid gallium, and across the liquid and solid phases of bismuth and indium. Measurements are angle integrated and made using photon excitations of 21.21 and 40.81 eV. In all cases the Bloch states are destroyed upon melting and the free electron gas is constrained by a charge-neutral liquid. The spectra of indium show little change upon solidification, indicating a common electronic structure for crystalline and liquid phases. In contrast, the energy distribution curves for supercooled gallium and bismuth show large changes in the electronic structure from solid to liquid phases, giving rise to the formation of pseudogaps in the density of states at the Fermi energy, EF. Observations of this kind enable us to distinguish normal or anomalous melting from photoemission measurements.

Incommensurate antiferromagnetism in a pure spin system via cooperative organization of local and itinerant moments.

Materials with strong correlations are prone to spin and charge instabilities, driven by Coulomb, magnetic, and lattice interactions. In materials that have significant localized and itinerant spins, it is not obvious which will induce order. We combine electrical transport, X-ray magnetic diffraction, and photoemission studies with band structure calculations to characterize successive antiferromagnetic transitions in GdSi. GdSi has both sizable local moments and a partially nested Fermi surface, without confounding contributions from orbital effects. We identify a route to incommensurate order where neither type of moment dominates, but is rooted in cooperative feedback between them. The nested Fermi surface of the itinerant electrons induces strong interactions between local moments at the nesting vector, whereas the ordered local moments in turn provide the necessary coupling for a spin-density wave to form among the itinerant electrons. This mechanism echoes the cooperative interactions between electrons and ions in charge-density-wave materials, and should be germane across a spectrum of transition-metal and rare-earth intermetallic compounds.

Understanding the complex phase diagram of uranium: the role of electron-phonon coupling.

We report an experimental determination of the dispersion of the soft phonon mode along [100] in uranium as a function of pressure. The energies of these phonons increase rapidly, with conventional behavior found by 20 GPa, as predicted by recent theory. New calculations demonstrate the strong pressure (and momentum) dependence of the electron-phonon coupling, whereas the Fermi-surface nesting is surprisingly independent of pressure. This allows a full understanding of the complex phase diagram of uranium and the interplay between the charge-density wave and superconductivity.

Band structure of SnTe studied by photoemission spectroscopy.

We present an angle-resolved photoemission spectroscopy study of the electronic structure of SnTe and compare the experimental results to ab initio band structure calculations as well as a simplified tight-binding model of the p bands. Our study reveals the conjectured complex Fermi surface structure near the L points showing topological changes in the bands from disconnected pockets, to open tubes, and then to cuboids as the binding energy increases, resolving lingering issues about the electronic structure. The chemical potential at the crystal surface is found to be 0.5 eV below the gap, corresponding to a carrier density of p=1.14 × 10(21) cm(-3) or 7.2 × 10(-2) holes per unit cell. At a temperature below the cubic-rhombohedral structural transition a small shift in spectral energy of the valance band is found, in agreement with model predictions.

Pose determination of a cylindrical (dental) implant in three-dimensions from a single two-dimensional radiograph.

OBJECTIVES: The aim was to develop an analytical algorithm capable of determining localization and orientation of a cylindrical (dental) implant in three-dimensional (3D) space from a single radiographic projection. METHODS: An algorithm based on analytical geometry is introduced, exploiting the geometrical information inherent in the 2D radiographic shadow of an opaque cylindrical implant (RCC) and recovering the 3D co-ordinates of the RCC's main axis within a 3D Cartesian co-ordinate system. Prerequisites for the method are a known source-to-receptor distance at a known locus within the flat image receptor. RESULTS: Accuracy, assessed from a small feasibility experiment in atypical dental radiographic geometry, revealed mean absolute errors for the critical depth co-ordinate ranging between 0.5 mm and 5.39 mm. This translates to a relative depth error ranging from 0.19% to 2.12%. CONCLUSIONS: Experimental results indicate that the method introduced is capable of providing geometrical information important for a variety of applications. Accuracy has to be enhanced by means of automated image analysis and processing methods.

The effect of wavelet and discrete cosine transform compression of digital radiographs on the detection of subtle proximal caries. ROC analysis.

The study compared diagnostic performances of 2 different image compression methods: JPEG (discrete cosine transform; Joint Photographic Experts Group compression standard) versus JPEG2000 (discrete wavelet transform), both at a compression ratio of 12:1, from the original uncompressed TIFF radiograph with respect to the detection of non-cavitated carious lesions. Therefore, 100 approximal surfaces of 50 tooth pairs were evaluated on the radiographs by 10 experienced observers using a 5-point confidence scale. Observations were carried out on a standardized viewing monitor under subdued light conditions. The proportion of diseased surfaces was balanced to approximately 50% to avoid bias. True caries status was assessed by serial ground sectioning and microscopic evaluation. A non-parametric receiver operating characteristic analysis revealed non-significant differences between the 3 image modalities, as computed from the critical ratios z not exceeding +/-2 (JPEG/JPEG2000, z = -0.0339; TIFF/JPEG2000, z = 0.251;TIFF/JPEG, z = 0.914). The mean area beneath the curve was highest for TIFF (0.604) followed by JPEG2000 (0.593) and JPEG (0.591). Both intra-rater and inter-rater agreement were significantly higher for TIFF (kappa(intra) = 0.52; kappa(inter) = 0.40) and JPEG2000 images (kappa(intra) = 0.49; kappa(inter) = 0.38) than for JPEG images (kappa(intra) = 0.33; kappa(inter) = 0.35). Our results indicate that image compression with typical compression algorithms at rates yielding storage sizes of around 50 kB is sufficient even for the challenging task of radiographic detection of non-cavitated carious approximal lesions.

Combined experimental and theoretical investigation of the premartensitic transition in Ni2MnGa.

Ultraviolet-photoemission (UPS) measurements and supporting specific-heat, thermal-expansion, resistivity, and magnetic-moment measurements are reported for the magnetic shape-memory alloy Ni2MnGa over the temperature range 100T(PM) is due to the Ni d minority-spin electrons. Below T(M) this peak disappears, resulting in an enhanced density of states at energies around 0.8 eV. This enhancement reflects Ni d and Mn d electronic contributions to the majority-spin density of states.

Laser acceleration of quasi-monoenergetic MeV ion beams.

Acceleration of particles by intense laser-plasma interactions represents a rapidly evolving field of interest, as highlighted by the recent demonstration of laser-driven relativistic beams of monoenergetic electrons. Ultrahigh-intensity lasers can produce accelerating fields of 10 TV m(-1) (1 TV = 10(12) V), surpassing those in conventional accelerators by six orders of magnitude. Laser-driven ions with energies of several MeV per nucleon have also been produced. Such ion beams exhibit unprecedented characteristics--short pulse lengths, high currents and low transverse emittance--but their exponential energy spectra have almost 100% energy spread. This large energy spread, which is a consequence of the experimental conditions used to date, remains the biggest impediment to the wider use of this technology. Here we report the production of quasi-monoenergetic laser-driven C5+ ions with a vastly reduced energy spread of 17%. The ions have a mean energy of 3 MeV per nucleon (full-width at half-maximum approximately 0.5 MeV per nucleon) and a longitudinal emittance of less than 2 x 10(-6) eV s for pulse durations shorter than 1 ps. Such laser-driven, high-current, quasi-monoenergetic ion sources may enable significant advances in the development of compact MeV ion accelerators, new diagnostics, medical physics, inertial confinement fusion and fast ignition.

Software for automated application of a reference-based method for a posteriori determination of the effective radiographic imaging geometry.

OBJECTIVES: Presentation and validation of software developed for automated and accurate application of a reference-based algorithm (reference sphere method: RSM) inferring the effective imaging geometry from quantitative radiographic image analysis. METHODS: The software uses modern pattern recognition and computer vision algorithms adapted for the particular application of automated detection of the reference sphere shadows (ellipses) with subpixel accuracy. It applies the RSM algorithm to the shadows detected, thereby providing three-dimensional Cartesian coordinates of the spheres. If the three sphere centres do not lie on one line, they uniquely determine the imaging geometry. Accuracy of the computed coordinates is investigated in a set of 28 charge-coupled device (CCD)-based radiographs of two human mandible segments produced on an optical bench. Each specimen contained three reference spheres (two different radii r1=1.5 mm, r2=2.5 mm). True sphere coordinates were assessed with a manually operated calliper. Software accuracy was investigated for a weighted and unweighted algebraic ellipse-fitting algorithm. RESULTS: The critical depth- (z-) coordinates revealed mean absolute errors ranging between 1.1+/-0.7 mm (unweighted version; r=2.5 mm) and 1.4+/-1.4 mm (weighted version, r=2.5 mm), corresponding to mean relative errors between 5% and 6%. Outliers resulted from complete circular dense structure superimposition and one obviously deformed reference sphere. CONCLUSIONS: The software provides information fundamentally important for the image formation and geometric image registration, which is a crucial step for three-dimensional reconstruction from > or =2 two-dimensional views.

[Root growth after wisdom tooth transposition. Case documentation with proposal for a radiologic method to quantify growth]. / Wurzelwachstum nach Weisheitszahntransposition. Falldokumentation mit Vorschlag einer radiologischen Methode zur Wachstumsquantifizierung.

OBJECTIVES: To introduce a method for assessment of root growth on panoramic radiographs exemplified by a case report on an autotransplanted lower third molar. MATERIAL AND METHODS: A lower left third molar (T) with incomplete root formation was transplanted for replacement of the lower left first molar in an 18-year-old woman. T was monitored clinically and, together with its neighboring lower second molar (37) with constant root length, also radiographically by means of two panoramic radiographs (OPGs) produced 12 days and 20 months postoperatively. A method for calculation of the root length as a multiple of the crown length is introduced, using accurately reproducible landmarks defining the coronal and apical endpoints of the examined tooth in all OPGs of the series. This method minimizes error due to different magnifications within the set of radiographs. RESULTS: Using the method introduced, the root length of the constant tooth 37 varied at 2.7% within the set of OPGs, whereas it revealed a 5.6% variation when the evaluation was based on direct measurement. Based on the described method, T revealed a postoperative root growth of approximately one-third of its final length and showed clinically no pathological findings during the observation period. CONCLUSIONS: Our results indicate that with the described method root growth assessment on panoramic radiographs is more accurate than with direct measurement.

Failure of Russell-Saunders coupling in the 5f states of plutonium.

Using high energy-electron energy loss spectroscopy, transmission electron microscopy, and synchrotron-radiation-based x-ray absorption spectroscopy, we provide the first experimental evidence that Russell-Saunders (LS) coupling fails for the 5f states of Pu. These results support the assumption that only the use of jj or intermediate coupling is appropriate for the 5f states of Pu. High energy-electron energy loss spectroscopy experiments were performed by use of a transmission electron microscope and are coupled with image and diffraction data; therefore, the measurements are completely phase specific.

A method to calculate angular disparities between object and receptor in "paralleling technique".

OBJECTIVE: To develop an image analysis method for calculation of angular disparities between an object, temporarily equipped with a reference system, and a radiographic receptor. MATERIALS AND METHODS: A mathematical method based on a reference system containing two metallic spheres is developed, allowing calculation of inclination between the inter-spherical axis and the digital image receptor using image features. Experimental evaluation was done in standardized projection geometry for two sphere sizes at four randomly chosen inclinations per size, with each radiograph assessed three times. Truth was assessed threefold from photographs obtained at each inclination. RESULTS: Mean standard deviation between single assessments was 2.6 degrees. Significant differences (P Maloney/Rastogy=0.00) were found between absolute values of truth and calculated values (mean: -0.9 degrees; range: -6.0 degrees; 3.6 degrees), indicating a significant lack of accuracy. CONCLUSIONS: Although so far not sufficiently accurate, the method yields information relevant for correction of distortion in intra-oral radiology.

Mathematical analysis of projection errors in "paralleling technique" with respect to implant geometry.

"Standardized" radiographs acquired in paralleling technique serve for monitoring of marginal bone levels around endosseous implants. Under clinical conditions, parallel adjustment of the film to the implant is beset with great difficulties. A mathematical model matching clinical conditions was developed to evaluate projection geometry within an interval of clinically relevant angulations (+/- 10 degrees from parallel position). Radiographs of two implants (Frialit 2, Friadent AG, Mannheim, Germany; Implant No. 1: 3.8 mm, length 10 mm; Implant No. 2: 6.5 mm, length 13 mm) were separately produced per angulation (2 degrees increments) at one focus-object distance (FO=322.9 mm). Implant images were repeatedly measured along their midline/vertical edge, local magnification (MF) was calculated and the values were compared to the computed ones. Projected dimensions of the implants were calculated for a second distance (232.3 mm). The experimentally acquired data were in agreement with the mathematical calculation. MF calculated for assessment along the vertical edge varied less (+/-1.94% from mean value) than along the midline (+/-2.74%), with a range of 1.037-1.068 (FO=322.9 mm) and 1.061-1.099 (FO=232.3 mm) for implant No.1, and 1.060-1.101 (FO=232.3 mm) and 1.037-1.069 (FO=322.9 mm) for Implant No. 2. Magnification revealed a mean variation of 4%. Radiographic evaluation of periimplant bone level should not exceed a precision of 0.5 mm, when parallelism between film and implant is not guaranteed and FO is less than 380 mm.