Biomedical subjects

Richard L Webber

Publications and source records attributed to Richard L Webber.

5 recordsLinked to original sources

PubMed2003

Effect of iterative restoration on the detection of artificially induced vertical radicular fractures by Tuned Aperture Computed Tomography.

OBJECTIVE: The purpose of this study was to evaluate the effect of the number of iterative restorations (IR) on the diagnostic accuracy of Tuned Aperture Computed Tomography images (TACT) for detection of induced vertical/oblique root fractures in mandibular teeth. STUDY DESIGN: Fractures were induced in 28 single-rooted, endodontically treated cadaver mandibular teeth while another 26 such teeth served as controls. TACT slices reconstructed by using 9 arbitrary projections (angular disparity of 9 degrees -20 degrees) were iteratively restored 1, 2, and 3 times. Eight observers scored their diagnoses by using a confidence rating scale. Ground truth was available from direct examination with transillumination, following extraction. RESULTS: Mean areas under the representative ROC curves for the 3 operations were 0.96 (3 IRs), 0.87 (2 IRs), and 0.86 (1 IRs). Analysis of variance demonstrated significant differences between 3 and 1 to 2 IRs (P <.01), as well as between observers (P <.01). CONCLUSION: Diagnostic accuracy of TACT for vertical/oblique root fracture detection improved after 3 IRs.

Analysis of Variance↗

PubMed2003

Application of TACT to the evaluation of total joint arthroplasty.

Three-dimensional imaging may be valuable in the evaluation of total joint arthroplasty. The partial-volume effect and streak artifacts from the metallic components of these devices limit the applicability of computed tomography (CT) to this application. Tuned-aperture computed tomography (TACT) is a tomographic approach that has been successfully used in other medical applications. In TACT, the acquisition geometry is inferred from the localization of fiducial markers in a series of projection images. The flexibility and robustness of TACT, as well as the fact that through an appropriate choice of reconstruction algorithms it can suppress streak artifacts, potentially makes it an appropriate approach for evaluating total joint arthroplasty. A simple computer-simulated model of a total knee replacement (TKR) was generated and used to evaluate the accuracy and artifacts associated with three-dimensional (3-D) renderings produced using TACT. A knee specimen from a cadaver that had received a TKR was used to investigate further the potential of TACT for this application. In both tests, TACT provided high-quality 3-D representations of the object. Both simple back-projection and minimum pixel back-projection were used to reconstruct the data. Minimum pixel back-projection provided high-contrast images that appeared to be relatively free of tomosynthetic artifacts. In summary, the potential of TACT in the evaluation of total joint arthroplasty was demonstrated. Future investigations will study TACT's ability to quantify the spatial relationship between the metallic components of these devices as well as TACT's ability to identify bony changes of diagnostic consequence.

Algorithms↗

PubMed2002

Comparison of conventional and TACT (Tuned Aperture Computed Tomography) digital subtraction radiography in detection of pericrestal bone-gain.

Tuned Aperture Computed Tomography or TACT is a relatively new technique that transforms correlated two-dimensional images into a three-dimensional display. Associating TACT with digital subtraction radiography (TACT-DSR) may enhance its use in the detection of diseases. This study aims to assess observer performance in the task of detecting simulated bone-gain in periodontal defects, comparing conventional and TACT DSR. Buccal, lingual and proximal pericrestal bony defects in a human dry skull were imaged with and without increments of crushed-bone and wax mixtures using standardized vertical bitewing projections, acquired with an intraoral digital receptor in a tomographic X-ray machine. One hundred and twenty pairs of baseline and follow-up images were obtained for each imaging modality. Post-acquisition processing including image-registration, density-correction and subtraction operation were applied to both transmission images and TACT-slices. Eight calibrated observers evaluated the presence or absence of pericrestal bone-gain using a 5-point confidence scale. Details about the location of periodontal defects and the amount of bone-gain for each subtracted image were recorded and used in the statistical analysis. Observer performance and study design factors were analyzed by means of receiver operating characteristic (ROC) curve analysis and ANOVA. Mean values of areas under ROC curves for bone-gain detection performance were 0.82 for conventional DSR and 0.90 for TACT-DSR. TACT-DSR provided statistically superior detection performance of simulated periodontal bone-gain over conventional DSR for tooth-obscured defects (p = 0.001) and for the smallest bone mass (p = 0.024). The findings support TACT-DSR's potential to provide greater sensitivity and technique flexibility in detecting periodontal bone-gain than standard DSR.

Alveolar Bone Loss↗

PubMed2002

Evaluation of tuned-aperture computed tomography in the detection of simulated periodontal defects.

OBJECTIVE: The objective of this study was to compare the diagnostic efficacy of tuned-aperture computed tomography (TACT) and conventional film for the detection of simulated periodontal defects. STUDY DESIGN: Periodontal defects were created in 15 premolar-molar interproximal sites selected from 8 cadaver jaw segments. Ten observers viewed 45 image pairs (baseline and follow up) in 4 TACT modalities and film to assess the presence of defect. The TACT modalities were 1st and 2nd generation prototype systems (TACT-1 and TACT-2) with circular (C) and random (R) distribution patterns of source projection (TACT-1C, TACT-1R, TACT-2C, TACT-2R). Observer performance and related factors were analyzed by using receiver operating characteristic and analysis of variance. RESULTS: Mean A(z) values were 0.64 for film, 0.74 for TACT-1C, 0.82 for TACT-1R, 0.64 for TACT-2C, and 0.69 for TACT-2R. TACT-1R was significantly better than film (P < .001), TACT-2C (P < .001) and TACT-2R (P = .007). CONCLUSION: TACT-1R provided the best diagnostic performance in the detection of simulated periodontal defects among the 5 modalities compared in this study.

Algorithms↗

PubMed2002

Angular disparity in ETACT scintimammography.

Emission tuned aperture computed tomography (ETACT) has been previously shown to have the potential for the detection of small tumors (<1 cm) in scintimammography. However, the optimal approach to the application of ETACT in the clinic has yet to be determined. Therefore, we sought to determine the effect of the angular disparity between the ETACT projections on image quality through the use of a computer simulation. A small, spherical tumor of variable size (5, 7.5 or 10 mm) was placed at the center of a hemispherical breast (15 cm diameter). The tumor to nontumor ratio was either 5:1 or 10:1. The detector was modeled to be a gamma camera fitted with a 4-mm-diam pinhole collimator. The pinhole-to-detector and the pinhole-to-tumor distances were 25 and 15 cm, respectively. A ray tracing technique was used to generate three sets of projections (10 degrees, 15 degrees, and 20 degrees, angular disparity). These data were blurred to a resolution consistent with the 4 mm pinhole. The TACT reconstruction method was used to reconstruct these three image sets. The tumor contrast and the axial spatial resolution was measured. Smaller angular disparity led to an improvement in image contrast but at a cost of degraded axial spatial resolution. The improvement in contrast is due to a slight improvement in the in-plane spatial resolution. Since improved contrast should lead to better tumor detectability, smaller angular disparity should be used. However, the difference in contrast between 10 degrees and 15 degrees was very slight and therefore a reasonable clinical choice for angular disparity is 15 degrees.

Breast↗