Automated hybrid TACT volume reconstructions.

OBJECTIVES: To design, implement in Java, and evaluate a method and means for the automated localization of artificial landmarks in optical images for tuned-aperture computed tomography (TACT) that allows the replacement of radiographic with optical landmarks. METHODS: Circular, colored, optical landmarks were designed to provide flexibility with regard to landmark constellation, imaging equipment, and lighting conditions. The landmark detection was based on Hough transforms (HT) for ellipses and lines. The HT for ellipses was extended to enable selective detection of bright ellipses on a dark background and vice versa, and the number of irrelevant votes in the accumulator arrays was reduced. An experiment was performed in vitro to test the automated landmark localization scheme, verify registration accuracy, and measure the required computation time. RESULTS: A visual evaluation of the tomographic slices that were produced using the new method revealed good registration accuracy. A comparison to tomographic slices similarly produced by means of conventional TACT showed identical results. The algorithm ran sufficiently fast on standard hardware to allow landmark localization in "real time" during successive image acquisition in clinical applications. CONCLUSIONS: The proposed method provides robust automated localization of landmarks in optical images. Using a hybrid imaging system, TACT can now be clinically applied without manual interaction of a human operator and without radiopaque landmarks, which might cover anatomic details of diagnostic interest.

Accuracy of tuned aperture computed tomography in the diagnosis of radicular fractures in non-restored maxillary anterior teeth--an in vitro study.

OBJECTIVES: This study compared the accuracy of three radiographic imaging modalities for the detection of artificially induced radicular fractures on maxillary anterior teeth. METHODS: Fractures were induced in 28 of 54 maxillary incisors in 15 cadaver specimens using a distally directed force. Radiographs evaluated included conventional two-dimensional direct digital radiographs (DDI), unprocessed Tuned Aperture Computed Tomography (TACT-U) and iteratively restored TACT (TACT-IR). Eight observers recorded their findings using a five-point confidence-rating scale. Receiver Operating Characteristic (ROC) analyses were done, followed by ANOVA to test for significant effects of observers, imaging modality and fracture location. Post hoc tests were carried out in instances where ANOVA indicated significance. RESULTS: The areas under the ROC-curves (A(z)) were, respectively: DDI: 0.53; TACT-U: 0.83 and TACT-IR: 0.97. TACT-IR and TACT-U performed significantly better than DDI (P < 0.001) with TACT-IR providing a higher detection accuracy than TACT-U (P < 0.033). A difference in detection accuracy was also noted based on fracture location (P < 0.001). Tukey's post hoc analyses revealed that fractures extending beyond the middle third of the root were more accurately detected. Inter-observer agreement was 0.68, and intra-examiner agreement, 0.87 (kappa analysis). CONCLUSIONS: TACT performed significantly better than direct digital images in detecting trauma-induced radicular fractures in unrestored, maxillary anterior teeth.

Virtual radiographs computed from TACT volume data as a gold standard for image registration prior to subtraction.

OBJECTIVE: To develop a three-dimensional (3D) model for quantitative analysis of image subtraction methods simulating clinical conditions and relevant to dental radiology. METHOD: A high-resolution volume representation of a formalin-preserved segment of a human maxilla was synthesized from a set of 51 digital radiographs equidistantly covering the entire sampling aperture by means of Tuned-Aperture Computed Tomography (TACT). Two-dimensional (2D) projection renderings of a 3D model were generated yielding arbitrary but well-known 2D projections with, and without, structured noise producing 'virtual radiographs'. RESULTS: Virtual radiographs were found to be similar to actual clinical images with respect to appearance, structure, and texture. Because the TACT reconstruction process allows all possible positions and orientations of source, specimen, and image plane to be simulated with negligible under sampling over a reasonable range of solid angles (sampling aperture), the resulting 3D model provided a rigorous method for establishing a truly objective gold standard (ground truth) for testing different registration techniques. CONCLUSIONS: TACT image registration can be assessed quantitatively by comparing actually observed vs theoretically professed parameters that presumably constrain the underlying projection geometries. Other attributes that vary from one method to the next, such as the use of nonlinear or region-specific techniques to facilitate registration, likewise, now can be rigorously measured by context-based methods such as quantitative determination of image similarity. Hence, a 3D model that renders idealized virtual radiographs from any desired projection geometry makes possible truly objective comparison of various digital subtraction techniques.

Hand-held three-dimensional dental X-ray system: technical description and preliminary results.

OBJECTIVE: To design, fabricate, and perform preliminary in vitro testing of a portable, hand-held, three-dimensional (3D) dental X-ray system using options unique to Tuned-Aperture Computed Tomography (TACT). The design allows for task-specific positioning over an unlimited range of user-selected angles and incorporates an integrated laser guidance system to constrain the focal-object distance. METHODS: A prototype system was fabricated consisting of an extremely lightweight X-ray source cantilevered from an aluminum gunstock-type handle to which a transparent radiation scatter shield was attached. Aiming was facilitated by task-specific visual cues used in conjunction with a spherically shaped radiolucent alignment jig coupled to the tissues of interest. Proper range was assured by a laser-assisted guidance system. The image transducer was an extrinsically modified commercially available CMOS device. The irradiated patient was simulated by a DXTTR phantom. RESULTS: The prototype demonstrated automated display of radiographed intra-oral tissues in three dimensions from arbitrary projection geometries and simulated task-specific sequences. Uncontrolled movements between exposures produced no obvious degeneration of 3D image quality. The aiming system minimized technical errors from misangulation. All dental regions in the phantom were imaged without difficulty. Projected risk was observed to be within clinically acceptable limits. CONCLUSIONS: Task-specific 3D images can be generated from as few as three uncontrolled projections. Total exposures can be prorated to levels not greatly exceeding those required for conventional two-dimensional radiographs of comparable image quality. Predicted radiation risks lie well below existing guidelines for occupational exposure.

Implementation of a generalized TACT algorithm for arbitrary source-object distances.

OBJECTIVES: To implement, refine, and evaluate a generalized TACT reconstruction method that corrects for misregistration caused by uncontrolled variations in projective magnification, alleviates normalization artifacts at borders of backprojections, and exploits all available source information to minimize losses produced from projective truncations in three dimensions. METHODS: A new Java-based software application was designed and tested in vitro using clinically representive data derived from four titanium dental implants in a cadaver jaw segment. These implants were irradiated by an intra-oral X-ray machine from various angles and distances using a solid-state sensor producing 48 radiographs. Six radiopaque markers were attached to the segment facilitating inference of associated projection geometries from analyses of the distributions of their respective shadows as seen by the sensor. Three-dimensional (3D) images were produced using the new algorithm, and the results were compared with those obtained from existing code. RESULTS: Slices processed using the new program were corrected for magnification errors. The resulting 3D displays showed significantly reduced tomosynthetic blur relative to uncorrected counterparts. The new reconstructions also minimized known border artifacts and made use of all available information. These images demonstrated apparent details otherwise hidden or lost when comparably processed using the control algorithm. CONCLUSIONS: The new software reduces both misregistration and scaling artifacts in tomosynthetically reconstructed slices. Hence, these modifications are expected to increase diagnostic accuracy and facilitate the appropriate application of TACT to an enlarged set of diagnostic tasks as compared with earlier implementations of the method.

Evaluation of tuned aperture computed tomography (TACT) in the localization of simulated periodontal defects.

OBJECTIVES: To compare the diagnostic efficacy of tuned aperture computed tomography (TACT) with the application of the 'buccal object rule' (BOR) in the localization of simulated periodontal defects. METHODS: Thirty interproximal sites were selected in fifteen cadaver segments of maxillae and mandible. Artificial periodontal defects were created using round burs and 40% formic acid in the buccal, lingual or mid-buccolingual areas. Eight basis projections were obtained and TACT slices were reconstructed for each region of interest. Two of the basis images were used in application of BOR for localization of the defect. Eight observers scored the location of defects using TACT slices and the paired radiographs separately. Data were analysed using the kappa statistic and ANOVA. RESULTS: A mean weighted kappa of 0.14 for localization was obtained with both BOR and TACT. Using ANOVA, there was no significant difference between modality and observer. There was however, a significant difference (P=0.019) between different defect sizes. Both modalities performed better with larger defect sizes. TACT performed slightly better than BOR when the smaller lesions were included; however, with larger lesions, this trend was reversed. CONCLUSIONS: The results confirm the relationship between correlation distance (the resultant slice width) and object size in the application of TACT for localization. BOR remains a simple yet effective tool for localization. The clinical significance is not clear considering the low kappa scores obtained with both the modalities.

Tuned aperture computed tomography to evaluate osseous healing.

Quantification of osseous healing is a challenging task, requiring expensive advanced imaging modalities. To improve diagnostic osseous imaging, we undertook this prospective study to explore the potential of Tuned Aperture Computed Tomography. Eighty defects in 20 rabbit mandibles, randomly carrying an osteoblast suspension or a polymer matrix or a combination thereof or no treatment, were imaged at 3, 6, 9, and 12 weeks post-surgery. TACT slices, iteratively restored TACT, and conventional digital radiographs were evaluated. Mean-gray-value distribution within regions of interest was correlated with histomorphometric data. Lesions treated with osteoblast/polymer-matrix delivery systems demonstrated the highest mean gray-value, while the diagnostic efficacy of TACT-IR was significantly better than that of other imaging modalities (p < 0.001). Thus, TACT is an accurate imaging modality for non-destructive quantification of osseous dynamics.

Fractal dimension analysis of weight-bearing bones of rats during skeletal unloading.

Fractal analysis was used to quantify changes in trabecular bone induced through the use of a rat tail-suspension model to simulate microgravity-induced osteopenia. Fractal dimensions were estimated from digitized radiographs obtained from tail-suspended and ambulatory rats. Fifty 4-month-old male Sprague-Dawley rats were divided into groups of 24 ambulatory (control) and 26 suspended (test) animals. Rats of both groups were killed after periods of 1, 4, and 8 weeks. Femurs and tibiae were removed and radiographed with standard intraoral films and digitized using a flatbed scanner. Square regions of interest were cropped at proximal, middle, and distal areas of each bone. Fractal dimensions were estimated from slopes of regression lines fitted to circularly averaged plots of log power vs. log spatial frequency. The results showed that the computed fractal dimensions were significantly greater for images of trabecular bones from tail-suspended groups than for ambulatory groups (p < 0.01) at 1 week. Periods between 1 and 4 weeks likewise yielded significantly different estimates (p < 0.05), consistent with an increase in bone loss. In the tibiae, the proximal regions of the suspended group produced significantly greater fractal dimensions than other regions (p < 0.05), which suggests they were more susceptible to unloading. The data are consistent with other studies demonstrating osteopenia in microgravity environments and the regional response to skeletal unloading. Thus, fractal analysis could be a useful technique to evaluate the structural changes of bone.

Fractal analyses of osseous healing using tuned aperture computed tomography images.

The aim of this study was to evaluate osseous healing in mandibular defects using fractal analyses on conventional radiographs and tuned aperture computed tomography (TACT; OrthoTACT, Instrumentarium Imaging, Helsinki, Finland) images. Eighty test sites on the inferior margins of rabbit mandibles were subject to lesion induction and treated with one of the following: no treatment (controls); osteoblasts only; polymer matrix only; or osteoblast-polymer matrix (OPM) combination. Images were acquired using conventional radiography and TACT, including unprocessed TACT (TACT-U) and iteratively restored TACT (TACT-IR). Healing was followed up over time and images acquired at 3, 6, 9, and 12 weeks post-surgery. Fractal dimension (FD) was computed within regions of interest in the defects using the TACT workbench. Results were analyzed for effects produced by imaging modality, treatment modality, time after surgery and lesion location. Histomorphometric data were available to assess ground truth. Significant differences (p < 0.0001) were noted based on imaging modality with TACT-IR recording the highest mean fractal dimension (MFD), followed by TACT-U and conventional images, in that order. Sites treated with OPM recorded the highest MFDs among all treatment modalities (p < 0.0001). The highest MFD based on time was recorded at 3 weeks and differed significantly with 12 weeks (p < 0.035). Correlation of FD with results of histomorphometric data was high (r = 0.79; p < 0.001). The FD computed on TACT-IR showed the highest correlation with histomorphometric data, thus establishing the fact TACT is a more efficient and accurate imaging modality for quantification of osseous changes within healing bony defects.

Emission tuned-aperture computed tomography: a novel approach to scintimammography.

UNLABELLED: Emission tuned-aperture computed tomography (ETACT) is a new approach to acquiring and processing scintimammography data. A gamma camera with a pinhole collimator is used to acquire projections of the radionuclide distribution within the breast. Fiducial markers are used to reconstruct these projections into tomographic slices. Simulation and phantom experiments were performed to evaluate the potential of the ETACT method. METHODS: In the simulation study, a hemispheric object of 15 cm in diameter was constructed to model a breast. A ray-tracing technique was used to generate ideal projections. These were blurred and noise was added to create images that resemble scintigraphic images. Tumor size, pinhole size, and target-to-nontarget radioactivity ratios (TNTs) were varied. The simulated projections were reconstructed into slices, and contrast and contrast-to-noise ratios were calculated to evaluate the effect of pinhole size. These results were compared with a simulated planar acquisition of the same object. A preliminary phantom evaluation was performed using an 8-mm "tumor" with a 10:1 TNT to validate the simulation results. RESULTS: A 3-mm pinhole was shown by the simulation study to be the optimal size. The ETACT images consistently yielded higher contrast than simulated planar images. The phantom study validated the simulation results and showed the feasibility of ETACT in a simulated clinical environment. CONCLUSION: ETACT is shown to be useful for imaging tumors <1 cm in diameter. Because ETACT requires only a gamma camera with a pinhole collimator, it has the potential to be applied in any hospital in a simple, flexible, and practical manner.

Analysis of fractal dimensions of rat bones from film and digital images.

OBJECTIVES: (1) To compare the effect of two different intra-oral image receptors on estimates of fractal dimension; and (2) to determine the variations in fractal dimensions between the femur, tibia and humerus of the rat and between their proximal, middle and distal regions. METHODS: The left femur, tibia and humerus from 24 4-6-month-old Sprague-Dawley rats were radiographed using intra-oral film and a charge-coupled device (CCD). Films were digitized at a pixel density comparable to the CCD using a flat-bed scanner. Square regions of interest were selected from proximal, middle, and distal regions of each bone. Fractal dimensions were estimated from the slope of regression lines fitted to plots of log power against log spatial frequency. RESULTS: The fractal dimensions estimates from digitized films were significantly greater than those produced from the CCD (P=0.0008). Estimated fractal dimensions of three types of bone were not significantly different (P=0.0544); however, the three regions of bones were significantly different (P=0.0239). The fractal dimensions estimated from radiographs of the proximal and distal regions of the bones were lower than comparable estimates obtained from the middle region. CONCLUSIONS: Different types of image receptors significantly affect estimates of fractal dimension. There was no difference in the fractal dimensions of the different bones but the three regions differed significantly.

Detection of simulated periodontal bone gain by digital subtraction radiography with tuned-aperture computed tomography. The effect of angular disparity.

OBJECTIVES: To investigate the influence of angular disparity on observer detection of simulated bone gain in digital subtraction radiography using tuned-aperture computed tomography (TACT). MATERIALS AND METHODS: Simulated periodontal defects were created in interproximal and buccal or lingual (tooth-obscured) areas of the premolar and molar regions of a dry human skull. Radiographs were obtained before and after known weights of amorphous bone were added to the defects to simulate bone gain. The skull was positioned in a multidirectional tomographic unit to achieve reproducibility. A series of nine basis images were acquired with a CMOS intra-oral receptor and repeated using angular disparities of 10 degrees, 20 degrees, and 30 degrees. Stacks of TACT slices generated from the basis images were paired for image-registration, histogram-equalization and subtraction using TACT Workbench. Eight calibrated observers randomly assessed the presence or absence of bone gain using a 5-point confidence scale. ROC curves were generated and A(z) values were analysed using ANOVA. RESULTS: There were significant differences in the performance of the observers (P=0.034), defect location (P=0.005), amount of bone gain (P<0.001), angular disparity (P=0.003) and angular disparity x defect location interaction (P=0.019). Mean A(z) values in detecting bone gain were 0.90, 0.85, 0.79 for angular disparities of 10 degrees, 20 degrees, and 30 degrees respectively. CONCLUSIONS: Smaller angular disparity provided better detection of bone gain with TACT-subtraction using nine basis-projections. This effect of angular disparity was especially evident with tooth-obscured defects.

Evaluation of linear and nonlinear tomosynthetic reconstruction methods in digital mammography.

RATIONALE AND OBJECTIVES: The purpose of this study was to comparatively evaluate digital planar mammography and both linear and nonlinear tomosynthetic reconstruction methods. MATERIALS AND METHODS: A "disk" (ie, target) identification study was conducted to compare planar and reconstruction methods. Projective data using a composite phantom with circular disks were acquired in both planar and tomographic modes by using a full-field, digital mammographic system. Two-dimensional projections were reconstructed with both linear (ie, backprojection) and nonlinear (ie, maximization and minimization) tuned-aperture computed tomographic (TACT) methods to produce three-dimensional data sets. Four board-certified radiologists and one 4th-year radiology resident participated as observers. All images were compared by these observers in terms of the number of disks identified. RESULTS: Significant differences (P < .05, Bonferroni adjusted) were observed between all reconstruction and planar methods. No significant difference, however, was observed between the planar methods, and only a marginally significant difference (P < .054, Bonferroni adjusted) was observed between TACT-backprojection and TACT-minimization. CONCLUSION: A combination of linear and nonlinear reconstruction schemes may have potential implications in terms of enhancing image visualization to provide radiologists with valuable diagnostic information.

Detection of artificially induced vertical radicular fractures using tuned aperture computed tomography.

This study compared the accuracy of three imaging modalities for the detection of artificially induced vertical root fractures (VRF) on teeth in cadaver mandibles. Fifty-four single-rooted, endodontically treated mandibular teeth being prepared to carry posts were evaluated using direct digital radiography (DDI) with a Schick sensor, unprocessed Tuned Aperture Computed Tomography (TACT-U) images and iteratively restored TACT (TACT-IR) images. Twenty-eight of these teeth had been subjected to fracture induction using an apically driven force. Nine basis images were used for each TACT image generation. Eight observers used a five-point confidence rating scale to record the confidence with which they considered a fracture to be present or not. Sensitivity and specificity values were computed and receiver operating characteristic (ROC) curves were generated. The areas under the curves (Az) used as an indication of the diagnostic accuracy of the imaging system were as follows: DDI: 0.37; TACT-U: 0.77 and TACT-IR: 0.81. DDI was significantly inferior to the TACT modalities. Differences in detection efficacy based on observers and observation sessions were noted on ANOVA and post-hoc Tukey's tests. This study indicates that TACT is the imaging modality of choice for VRF in endodontically treated teeth.

Comparison of tomosynthesis methods used with digital mammography.

RATIONALE AND OBJECTIVES: The authors performed this study to investigate the potential applicability of tomosynthesis to digital mammography. Four methods of tomosynthesis-tuned aperture computed tomography (TACT)-backprojection, TACT-iterative restoration, iterative reconstruction with expectation maximization, and Bayesian smoothing-were compared to planar mammography and analyzed in terms of their contrast-detail characteristics. Specific comparisons between the tomosynthesis methods were not attempted in this study. MATERIALS AND METHODS: A full-field, amorphous, silicon-based, flat-panel digital mammographic system was used to obtain planar and tomosynthesis projection images. A composite tomosynthesis phantom with a centrally located contrast-detail insert was used as the object of interest. The total exposure for multiple views with tomosynthesis was always equal to or less than that for the planar technique. Algorithms were used to reconstruct the object from the acquired projections. RESULTS: Threshold contrast characteristics with all tomosynthesis reconstruction methods were significantly better than those with planar mammography, even when planar mammography was performed at more than twice the exposure level. Reduction of out-of-plane structural components was observed in all the tomosynthesis methods analyzed. CONCLUSION: The contrast-detail trends of all the tomosynthesis methods analyzed in this study were better than those of planar mammography. Further optimization of the algorithms could lead to better image reconstruction, which would improve visualization of valuable diagnostic information.

Comparative evaluation of Tuned Aperture Computed Tomography for the detection of mandibular fractures.

OBJECTIVES: To compare the diagnostic efficacy of Tuned Aperture Computed Tomography (TACT) with conventional imaging modalities for detection of fractures of the mandible. METHODS: Fractures were induced using blunt trauma in human defleshed mandibles. Conventional extra-oral and indirect digital images, unprocessed TACT images reconstructed from eight and 16 basis images (BI) and iteratively restored TACT images from eight and 16 BI were used for fracture evaluation. Twelve observers recorded their diagnoses using a five-point confidence rating scale. The data were analysed using ROC curve analysis. RESULTS: Significant differences were found (P < 0.0001) in the areas under the curve (Az): film, 0.6954; digital images 0.6169; TACT unprocessed images using 8 BI, 0.7420; TACT unprocessed images using 8 BI, 0.7667; TACT unprocessed images using 16 BI, 0.7730; TACT iteratively restored images using 16 BI, 0.8143. No observer-based differences were found. Fractures in the condylar and coronoid regions were more difficult to detect than those in the ramus and body of the mandible. CONCLUSIONS: Iteratively restored TACT images generated using 16 BI had a superior diagnostic performance to all the other imaging modalities. Studies are in order to evaluate its in vivo potential.

A comparison of the effect of task-specific with fixed beam alignment in tuned-aperture computed tomography.

OBJECTIVES: To test the hypothesis that fixed beam alignment, representative of conventional, fixed-projection three-dimensional (3D) imaging systems, yields significantly lower detectability of approximal radiolucencies than does a task-specific strategy that 'opens the contacts'. METHODS: Eleven pairs of extracted teeth containing systematically varying numbers of induced approximal low-contrast defects were evaluated from 3D displays produced by means of tuned-aperture computed tomography (TACT) under controlled conditions. Each of the resulting tomographic presentations was displayed in two random sequences to seven trained clinicians. The task-specific (test) series was generated from eight different projections varying in vertical disparity but constrained to open the contacts. The fixed-aiming (control) series was generated from eight projections distributed uniformly on a circle. RESULTS: Accuracy of defect detection averaged 5%, significantly higher with task-specific aiming than with fixed alignment projection geometry (P = 0.02). All observers unequivocally preferred the displays produced from projections with open contacts; however, they demonstrated considerable variation in their approach to the task, including the time required to interpret the displays. CONCLUSIONS: The improvement in observer accuracy obtained from radiographs displayed in three dimensions results from an imaging strategy that selectively increases the signal-to-noise ratio in regions of interest.

A controlled evaluation of tuned-aperture computed tomography applied to digital spot mammography.

The purpose of this work was to compare the detection accuracy of 3-dimensional (3D) modalities of tuned-aperture computed tomography (TACT) with that of conventional 2-dimensional (2D) digital spot mammograms. A standardized mammographic phantom was placed beneath cadaveric breast tissues of varying densities. Five radiologists were asked to detect as many objects (specks, fibers, and low-contrast masses) as possible from 90 displays in a controlled and factorially balanced multivariate experiment. Radiographic exposure was varied systematically, and projections were averaged to ensure stochastic comparability. Scores were weighted to eliminate task-specific bias and were analyzed by multivariate analyses of variance. All display modalities based on the linear application of the 3D TACT reconstruction method yielded significantly higher detection scores for all tasks than did conventional 2D digital spot mammography, which served as the scientific control modality. This effect was found to be statistically significant (P < .001) in spite of significant variations between tissues (P < .001), observers (P < .001), and exposures (P < .01). TACT may be a promising alternative or enhancement to conventional 2D digital mammography for tasks well simulated by this experimental design.

A method for correcting for errors produced by variable magnification in three-dimensional tuned-aperture computed tomography.

OBJECTIVES: To develop and test a method for correcting tomosynthetic misregistration caused by variation in projective magnification. METHODS: A tooth from a monkey was radiographed from various angles and distances using a solid-state sensor to which a plastic spacer with a wire frame was attached. The position of the tooth was fixed relative to both the frame and the sensor. Information derived from the frame's shadow was used to produce a series of tomosynthetic slices using tuned-aperture computed tomography (TACT(R)). One series was corrected for magnification errors and the other was not. Corresponding slices from each series were compared. RESULTS: The corrected slice exhibited much less artifactual blur than its uncorrected counterpart. Linear traces through corresponding portions of these slice images demonstrated discrepancies in homologous dimensions attributable to systematic variations in projective magnification. CONCLUSIONS: Correcting for differences in projective magnification reduces both misregistration and scaling artifacts in tomosynthetically reconstructed volumes.

An in vivo comparison of diagnostic information obtained from tuned-aperture computed tomography and conventional dental radiographic imaging modalities.

OBJECTIVE: The purpose of this study was to compare diagnostic information obtained by means of 3-dimensional tuned-aperture computed tomography (TACT) and by means of conventional radiography of patients requiring surgery. STUDY DESIGN: TACT produced digital images that yielded a series of tomographic slices viewed interactively. Controls were conventional periapical and/or panoramic radiographs. Each of 4 independent dentists performed 2 tasks, one requiring an estimation of confidence in their clinical assessments of the patient and the other requiring an estimation of the resulting diagnostic potential for altering associated treatment options. Data were analyzed through use of the nonparametric Mann-Whitney U Wilcoxon rank sum W test. RESULTS: A statistically significant difference for both tasks was observed (2-sided; P<.001). CONCLUSIONS: TACT displays were more diagnostically informative and had more impact on potential treatment options than did conventional radiographs.