To introduce a theoretical solution to a posteriori describe the pose of a cylindrical dental fixture as appearing on radiographs; to experimentally validate the method described. The pose of a conventional dental implant was described by a triplet of angles (phi-pitch, theta-roll, and psi-yaw) which was calculated throughout vector analysis. Radiographic- and simulated-image obtained with an algorithm were compared to test effectiveness, reproducibility, and accuracy of the method. The length of the dental implant as appearing on the simulated image was calculated by the trigonometric function and then compared with real length as it appeared on a two-dimensional radiograph. Twenty radiographs were analyzed for the present in silico and retrospective study. Among 40 fittings, 37 resulted as resolved with residuals ≤ 1 mm. Similar results were obtained for radiographic and simulated implants with absolute errors of − 1.1° ± 3.9° for phi; − 0.9° ± 4.1° for theta; 0° ± 1.1° for psi. The real and simulated length of the implants appeared to be heavily correlated. Linear dependence was verified by the results of the robust linear regression: 0.9757 (slope), + 0.1344 mm (intercept), and an adjusted coefficient of determination of 0.9054. The method allowed clinicians to calculate, a posteriori, a single real triplet of angles (phi, theta, psi) by analyzing a two-dimensional radiograph and to identify cases where standardization of repeated intraoral radiographies was not achieved. The a posteriori standardization of two-dimensional radiographs could allowed the clinicians to minimize the patient’s exposure to ionizing radiations for the measurement of marginal bone levels around dental implants.

/pdf/standardization-of-three-dimensional-pose-of-cylindrical-1wua9ygx5z.pdf

Standardization of three-dimensional pose of cylindrical implants from intraoral radiographs: a preliminary study

A reference-based radiographic “reference sphere method” (RSM) for accurate length measurements in (dental) projection radiographs for the assessment of tooth length in dry human mandible sections is evaluated. RSM determines the depth coordinates of reference spheres placed in the object plane from the elliptical distortion of their shadows. Two segments (one canine and one molar) of dry human mandibles were exposed 95 times at different angulations (0–40°) on a dental charge-coupled device receptor. Three steel spheres (diameters d
 1 = 2.00 mm, d
 2 = 3.00 mm) were attached roughly coplanar with the tooth’s main axis. Radiographs were assessed once by visual inspection plus manual landmark identification with a mouse-driven cursor. The results were compared to the true tooth length assessed after extraction and to a conventional method (C), i.e., the rule of proportion based on magnification of the sphere shadows. Mean relative length error was 2.28% (d
 1) and 0.46% (d
 2) for RSM and −13.58% (d
 1) and −9.90% (d
 2) for C. For both methods, length errors were significantly (p < 0.0001) correlated with the inclination relative to the receptor. RSM allows for complete a posteriori determination of the imaging geometry under the assumption of a known source-to-receptor distance. One specific application is foreshortening correction of objects coplanar with the reference spheres. Remaining errors are mainly due to incorrect landmark definition. In our setup, these were exaggerated by the visual/manual image-evaluation process. Automated image analysis has been shown for similar tasks to minimize these errors considerably.

Ex vivo radiographic tooth length measurements with the reference sphere method (RSM)

The aim of the study was to introduce a mathematical method to estimate the correct pose of a blade by evaluating the radiographic features obtained from a single two-dimensional image. Blade-form implant bed preparation was performed using the piezosurgery device, and placement was attained with the use of magnetic mallet. The pose determination of the blade was described by means of three consecutive rotations defined by three angles of orientation (triplet φ, θ and ψ). Retrospective analysis on periapical radiographs was performed. This method was used to compare implant (axial length along the marker, i.e. the implant structure) vs angular correction factor (a trigonometric function of the triplet). The accuracy of the method was tested by generating two-dimensional radiographic simulations of the blades, which were then compared with the images of the implants as appearing on the real radiographs. Two patients had to be excluded from further evaluation because the values of the estimated pose angles ...

Pose determination of a blade implant in three dimensions from a single two-dimensional radiograph.

Shadow Image Processing of X-Ray Screening System for Aviation Security

We sought to validate a new method to detect the degree of correlation between simulated and real tilted blade implants as they appear on a single two-dimensional radiograph. The angular correction factor (CF^) was defined as the coupling of two subsequent angle transformations, a set of five angular values describing the theoretical radiographic appearance of the blade implant: (1) three consecutive rotations about the axes of the blade ($$\varphi$$, θ, and ψ, standing for pitch, roll, and yaw, respectively) to represent the polarization directions; (2) a two-dimensional projection defined by two angles (λ and $$\phi$$, respectively, longitude and latitude) to represent the vector of the X-ray beam intersecting the detector plate. Data of patients who received fixed prostheses supported by blade-form implants were employed to calculate a dimensional correction factor (CF°), a specific length through the major axis. The simulation of a distorted radiograph of a blade positioned in space was compared with the real radiograph. Differences in the angular measurements served as an initial test to assess the effectiveness of the method. In the acquired sets of periapical radiographs, mean misalignments of + 3.58° in longitude and − 0.04° in latitude were registered. The following variations were detected during the accuracy testing: the absolute error was 0.1 ± 7.5° for angle $$\varphi$$; 2.4 ± 6.7° for angle θ; − 1.0 ± 3.7° for angle ψ; 4.5 ± 8.6° for angle λ; and 2.0 ± 9.3° for angle $$\phi$$. The linear dependence between CF° and CF^ was estimated by a robust linear regression: slope + 0.991, intercept + 0.007, and adjusted R2 0.992. This a posteriori analysis introduces the explicit trigonometric equations of the theoretical standard (CF^) used to describe the blade implant radiographic position and misalignment on two-dimensional radiographs.

A methodological approach to standardize and control the quality of the position and alignment of lamina implants on two-dimensional radiographs.

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 threedimensional 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 ¼ 1.5 mm, r2 ¼ 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 ¼ 2.5 mm) and 1.4 ^ 1.4 mm (weighted version, r ¼ 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 $ 2 two-dimensional views. Dentomaxillofacial Radiology (2005) 34, 205–211. doi: 10.1259/dmfr/56357032

https://www.staff.uni-mainz.de/schoemer/publications/DentRad05.pdf

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

Abstract Purpose The aim of this study was to evaluate interobserver agreement (IOA) on target volume definition for pancreatic cancer (PACA) within the Radiosurgery and Stereotactic Radiotherapy Working Group of the German Society of Radiation Oncology (DEGRO) and to identify the influence of imaging modalities on the definition of the target volumes. Methods Two cases of locally advanced PACA and one local recurrence were selected from a large SBRT database. Delineation was based on either a planning 4D CT with or without (w/wo) IV contrast, w/wo PET/CT, and w/wo diagnostic MRI. Novel compared to other studies, a combination of four metrics was used to integrate several aspects of target volume segmentation: the Dice coefficient (DSC), the Hausdorff distance (HD), the probabilistic distance (PBD), and the volumetric similarity (VS). Results For all three GTVs, the median DSC was 0.75 (range 0.17–0.95), the median HD 15 (range 3.22–67.11) mm, the median PBD 0.33 (range 0.06–4.86), and the median VS was 0.88 (range 0.31–1). For ITVs and PTVs the results were similar. When comparing the imaging modalities for delineation, the best agreement for the GTV was achieved using PET/CT, and for the ITV and PTV using 4D PET/CT, in treatment position with abdominal compression. Conclusion Overall, there was good GTV agreement (DSC). Combined metrics appeared to allow a more valid detection of interobserver variation. For SBRT, either 4D PET/CT or 3D PET/CT in treatment position with abdominal compression leads to better agreement and should be considered as a very useful imaging modality for the definition of treatment volumes in pancreatic SBRT. Contouring does not appear to be the weakest link in the treatment planning chain of SBRT for PACA. 

/pdf/interobserver-agreement-on-definition-of-the-target-volume-2phknbmu.pdf

Interobserver agreement on definition of the target volume in stereotactic radiotherapy for pancreatic adenocarcinoma using different imaging modalities.

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

Interobserver agreement on definition of the target volume in stereotactic radiotherapy for pancreatic adenocarcinoma using different imaging modalities.