Computer-assisted simulations in orthodontic diagnosis and the application of a new cone beam X-ray computed tomography

Comparative analysis of traditional radiographs and cone-beam computed tomography volumetric images in the diagnosis and treatment planning of maxillary impacted canines

INTRODUCTION

In this prospective study, we compared differences in the diagnosis and treatment planning of impacted maxillary canines between 2 imaging modalities.

METHODS

Twenty-five consecutive impacted maxillary canines were identified from the pool of patients seeking orthodontic treatment. The first set of radiographs consisted of traditional 2-dimensional (2D) images including panoramic, occlusal, and 2 periapical radiographs. The second set comprised prints of 3-dimensional (3D) volumetric dentition images obtained from a cone-beam computed tomography (CBCT) scan. Seven faculty member completed a questionnaire for every impacted canine and diagnostic radiographic modality (2D and 3D).

RESULTS

The data show that the judges produced different decisions regarding localization depending on the x-ray method. There were 21% disagreement (or discordance) in the perceived mesiodistal cusp tip position and 16% difference in the perceived labiopalatal position. In the perception of root resorption of adjacent teeth, there was 36% lack of congruence. Twenty-seven percent of the teeth that were planned to be left, recovered, or extracted with the 2D radiographs had different treatment plans when the judges viewed the 3D CBCT images (McNemar test, chi-square, 4.45; P = 0.035). The clinicians' confidence of the accuracy of diagnosis and treatment plan was statistically higher for CBCT images (P <0.001).

CONCLUSIONS

These results showed that 2D and 3D images of impacted maxillary canines can produce different diagnoses and treatment plans.

Comparison of actual surgical outcomes and 3-dimensional surgical simulations

PURPOSE

The advent of imaging software programs has proved to be useful for diagnosis, treatment planning, and outcome measurement, but precision of 3-dimensional (3D) surgical simulation still needs to be tested. This study was conducted to determine whether the virtual surgery performed on 3D models constructed from cone-beam computed tomography (CBCT) can correctly simulate the actual surgical outcome and to validate the ability of this emerging technology to recreate the orthognathic surgery hard tissue movements in 3 translational and 3 rotational planes of space.

MATERIALS AND METHODS

Construction of pre- and postsurgery 3D models from CBCTs of 14 patients who had combined maxillary advancement and mandibular setback surgery and 6 patients who had 1-piece maxillary advancement surgery was performed. The postsurgery and virtually simulated surgery 3D models were registered at the cranial base to quantify differences between simulated and actual surgery models. Hotelling t tests were used to assess the differences between simulated and actual surgical outcomes.

RESULTS

For all anatomic regions of interest, there was no statistically significant difference between the simulated and the actual surgical models. The right lateral ramus was the only region that showed a statistically significant, but small difference when comparing 2- and 1-jaw surgeries.

CONCLUSIONS

Virtual surgical methods were reliably reproduced. Oral surgery residents could benefit from virtual surgical training. Computer simulation has the potential to increase predictability in the operating room.

Four curious cases of cone-beam computed tomography

Cone-beam computed tomography (CBCT) has become popular, and its many inherent advantages are indisputable. Nevertheless, CBCT is prescribed cautiously because the radiation dosage is higher than that of conventional radiography. When and to what extent should CBCT be prescribed for orthodontic patients? The purpose of this article is to present 4 curious cases in which a considerable discrepancy was found between the conventional panoramic radiograph and the CBCT view. Is it time to spare patients an unnecessary conventional panoramic radiograph and shift to CBCT for all patients?

Transverse, vertical, and anteroposterior changes from bone-anchored maxillary expansion vs traditional rapid maxillary expansion: a randomized clinical trial

INTRODUCTION

The purpose of this study was to compare the transverse, vertical, and anteroposterior skeletal and dental changes in adolescents receiving expansion treatment with tooth-borne and bone-anchored expanders. Immediate and long-term changes were measured on cone-beam computed tomography (CBCT) images.

METHODS

Sixty-two patients needing maxillary expansion were randomly allocated to 1 of 3 groups: traditional hyrax tooth-borne expander, bone-anchored expander, and control. CBCT images were taken at baseline, immediately after expansion, after removal of the appliance (6 months), and just before fixed bonding (12 months). Repeated measures multivariate analysis of variance (MANOVA) was applied to the distances and angles measured to determine the statistical significance in the immediate and long time periods. Bonferroni post-hoc tests were used to identify significant differences between the treatment groups.

RESULTS

Immediately after expansion, the subjects in the tooth-borne expander group had significantly more expansion at the crown level of the maxillary first premolars (P = 0.003). Dental crown expansion was greater than apical expansion and skeletal expansion with both appliances. The control group showed little change (growth) over the 6-month interval. At 12 months, no group had a statistically significant difference in angle changes, suggesting symmetric expansion. Both treatment groups had significant long-term expansion at the level of the maxillary first molar crown and root apex, first premolar crown and root, alveolus in the first molar and premolar regions, and central incisor root. Tooth-borne expansion resulted in significantly more long-term expansion at the maxillary premolar crown and root than did bone-borne expansion.

CONCLUSIONS

Both expanders showed similar results. The greatest changes were seen in the transverse dimension; changes in the vertical and anteroposterior dimensions were negligible. Dental expansion was also greater than skeletal expansion.

Morphologic quantification of the maxilla and the mandible with cone-beam computed tomography

INTRODUCTION

The purpose of this pilot study was to use cone-beam computed tomography (CBCT) to determine the volumes of the maxilla and the mandible in subjects with skeletal Class I, Class II, and Class III malocclusions. Hypothesis 1 was that the volume (size) of a skeletal Class II maxilla is larger than those of Class I and Class III. Hypothesis 2 was that the volume of a skeletal Class III mandible is larger than those of Class I and Class II.

METHODS

Thirty women patients were classified into 3 groups according to their skeletal pattern: skeletal Class I (0 degrees < or =ANB <6 degrees ), Class II (ANB > or =6 degrees ) and Class III (ANB <0 degrees ). The volumes of the maxilla and the mandible were measured with CBCT. CB MercuRay (Hitachi Medico, Tokyo, Japan) and CB works software (CyberMed, Seoul, Korea) were used to process the images.

RESULTS

There was a trend that skeletal Class III subjects might have significantly greater mandibular volume compared with Class II subjects (P = 0.089). The ratios of maxilla-to-mandible volumes between the skeletal Class II and Class III groups were significantly different (P = 0.005). Differences were observed in the ratios of maxillary and mandibular volumes across the 3 groups.

CONCLUSIONS

Hypotheses 1 and 2 were rejected; there was no trend for Class III subjects to have larger mandibles (P = 0.089) compared with Class II subjects. The ratio of the maxilla and mandible volumes in skeletal Class III subjects was significantly larger (P = 0.005) compared with Class II subjects.

Surgical orthodontic treatment for a patient with advanced periodontal disease: evaluation with electromyography and 3-dimensional cone-beam computed tomography

We report here the case of a woman with Class III malocclusion and advanced periodontal disease who was treated with surgical orthodontic correction. Functional recovery after orthodontic treatment is often monitored by serial electromyography of the masticatory muscles, whereas 3-dimensional cone-beam computed tomography can provide detailed structural information about, for example, periodontal bone defects. However, it is unclear whether the information obtained via these methods is sufficient to determine the treatment goal. It might be useful to address this issue for patients with advanced periodontal disease because of much variability between patients in the determination of treatment goals. We used detailed information obtained by 3-dimensional cone-beam computed tomography to identify periodontal bone defects and set appropriate treatment goals for inclination of the incisors and mandibular surgery. Results for this patient included stable occlusion and improved facial esthetics. This case report illustrates the benefits of establishing treatment goals acceptable to the patient, based on precise 3-dimensional assessment of dentoalveolar bone, and by using masticatory muscle activity to monitor the stability of occlusion.

Evaluation of the human airway using cone-beam computerized tomography

OBJECTIVE

The goal of this project was to define and measure human airway space with radiographic volumetric 3-dimensional imaging and digital reconstruction of the pharynx using cone-beam computerized tomography.

STUDY DESIGN

This was a randomized retrospective study. Ten patient scans were selected randomly from a pool of 196 subjects seeking dental treatment at the University of California, San Francisco. Digital Imaging and Communications in Medicine-format volume images were captured using a low-radiation rapid-scanning cone-beam computerized tomography system (Hitachi MercuRay).

RESULTS

Detailed progressive rostrocaudal cross-sectional area histograms indicated that 8 of the 10 subjects demonstrated a region of maximum constriction near the oropharynx level. The most restricted cross-sectional area varied from 90 mm(2) to 360 mm(2).

CONCLUSIONS

The maximum constriction of the airway in 10 subjects quietly breathing for 10 seconds indicated variation in the level of the pharynx and the extent of the rostrocaudal zone of restriction.

Absorbed and effective doses from cone beam volumetric imaging for implant planning

OBJECTIVES

Volumetric CT using a cone beam has been developed by several manufacturers for dentomaxillofacial imaging. The purpose of this study was to measure doses for implant planning with cone beam volumetric imaging (CBVI) in comparison with conventional multidetector CT (MDCT).

METHODS

The two CBVI systems used were a 3D Accuitomo (J. Morita), including an image-intensifier type (II) and a flat-panel type (FPD), and a CB MercuRay (Hitachi). The 3D Accuitomo operated at 80 kV, 5 mA and 18 s. The CB MercuRay operated at 120 kV, 15 mA, 9.8 s. The MDCT used was a HiSpeed QX/i (GE), operated at 120 kV, 100 mA and 0.7 s, and its scan length was 77 mm for both jaws. Measurement of the absorbed tissue and organ doses was performed with an Alderson phantom, embedding the radiophotoluminescence glass dosemeter into the organs/tissues. The values obtained were converted into the absorbed dose. The effective dose as defined by the International Commission on Radiological Protection was then calculated.

RESULTS

The absorbed doses of the 3D Accuitomo of the organs in the primary beam ranged from 1-5 mGy, and were several to ten times lower than other doses. The effective dose of the 3D Accuitomo ranged from 18 muSv to 66 muSv, and was an order of magnitude smaller than the others. In conclusion, these results show that the dose in the 3D Accuitomo is lower than the CB MercuRay and much less than MDCT.

Detection of periodontal bone loss using digital intraoral and cone beam computed tomography images: an in vitro assessment of bony and/or infrabony defects

OBJECTIVES

To explore the diagnostic values of digital intraoral radiography and cone beam CT (CBCT) in the determination of periodontal bone loss, infrabony craters and furcation involvements.

METHODS

Accuracy assessment of the imaging modalities was conducted through bone level measurements, infrabony crater and furcation involvement classifications. For CBCT, images were obtained at 120 kV and 23.87 mAs, and observations were made on a 5.2 mm panoramic reconstruction view and on 0.4 mm thick cross-sectional slices. Intraoral radiographs of a size 2 charge-coupled device (CCD) sensor were obtained using the paralleling technique, at 60 kV (DC) and 0.28 mAs exposure. 71 human cadaver and dry skull bony defects were measured and evaluated by 3 observers. Comparison was made with the gold standard.

RESULTS

The mean error (gold standard deviation) of bone level measurements was 0.56 mm for intraoral radiography and 0.47 mm for the CBCT panoramic 5.2 mm reconstruction view. There were no significant differences (P = 0.165) between the two methods. However, on 0.4 mm thick cross-sections, the mean error was 0.29 mm and the Wilcoxon signed-rank test indicated a significant difference when compared with the CCD (P = 0.006). The detection of crater and furcation involvements failed in 29% and 44% for the CCD, respectively, in contrast to 100% detectability for both defects with CBCT.

CONCLUSIONS

CBCT on the panoramic 5.2 mm reconstruction view allowed comparable measurements of periodontal bone levels and defects as with intraoral radiography. CBCT with 0.4 mm thick cross-sections demonstrated values closer to the gold standard, indicating more accurate assessment of periodontal bone loss. Further research is needed to explore these results in vivo and to determine the use of CBCT in periodontal diagnosis.

Reproducibility of maxillofacial anatomic landmarks on 3-dimensional computed tomographic images determined with the 95% confidence ellipse method

OBJECTIVE

To assess the plotting reproducibility of landmarks on 3-dimensional computed tomography (3D-CT) images through use of the 95% confidence ellipse in order to propose sufficiently stable coordinate systems for 3D-CT measurements.

MATERIALS AND METHODS

Six dentists plotted 19 landmarks twice on 3D-CT images. Scatterplots and the 95% ellipses were produced 3-dimensionally, and the areas of the ellipses were calculated for evaluating the reproducibility of landmarks.

RESULTS

The plotting reproducibility of each landmark showed characteristic features. Among five landmarks (the sella [S], nasion [N], basion [Ba], orbitale [Or], and true porion [Po]) that are frequently used as reference points on cephalograms, Ba showed the smallest areas for all three coordinate axes, indicating high reproducibility. The coronoid process (CP) and the tooth-related landmarks showed relatively high reproducibility.

CONCLUSION

Sufficiently stable coordinate axes could be proposed for different treatments and studies.

Linear accuracy and reliability of cone beam CT derived 3-dimensional images constructed using an orthodontic volumetric rendering program

OBJECTIVE

To compare accuracy of linear measurements made on cone beam computed tomographic (CBCT) derived 3-dimensional (3D) surface rendered volumetric images to direct measurements made on human skulls.

MATERIALS AND METHODS

Twenty orthodontic linear measurements between anatomical landmarks on 23 human skulls were measured by observers using a digital caliper. The skulls were imaged with CBCT and Dolphin 3D (version 2.3) software used to generate 3D volumetric reconstructions (3DCBCT). The linear measurements between landmarks were computed by a single observer three times and compared to anatomic dimensions using Student's t-test (P < or = .05). The intraclass correlation coefficient (ICC) and absolute linear and percentage error were calculated.

RESULTS

The ICC for 3DCBCT (0.975 +/- 0.016) was significantly less than for skull (0.996 +/- 0.007) measurements. Mean percentage measurement error for 3DCBCT (2.31% +/- 2.11%) was significantly higher than replicate skull measurements (0.63% +/- 0.51%). Statistical differences between 3DCBCT means and true dimensions were found for all of the midsagittal measurements except Na-A and six of the 12 bilateral measurements. The mean percentage difference between the mean skull and 3D-based linear measurements was -1.13% (SD +/- 1.47%). Ninety percent of mean differences were less than 2 mm, and 95% confidence intervals were all less than 2 mm except for Ba-ANS (3.32 mm) and Pog-Go(left) (2.42 mm).

CONCLUSIONS

While many linear measurements between cephalometric landmarks on 3D volumetric surface renderings obtained using Dolphin 3D software generated from CBCT datasets may be statistically significantly different from anatomic dimensions, most can be considered to be sufficiently clinically accurate for craniofacial analyses.

Cone-beam computed tomography for routine orthodontic treatment planning: a radiation dose evaluation

INTRODUCTION

Because of the advantages and possibilities of cone-beam computed tomography (CBCT), orthodontists use this method routinely for patient assessment. The aim of this study was to compare the radiation doses for conventional panoramic and cephalometric imaging with the doses for 2 different CBCT units and a multi-slice CT unit in orthodontic practice.

METHODS

The absorbed organ doses were measured by using an anthropomorphic phantom loaded with thermoluminescent dosimeters at 16 sites related to sensitive organs. The 4 devices (Sirona DS Plus [Sirona Dental Systems, Bernsheim, Germany], i-CAT [Imaging Sciences International, Hatfield, Pa], NewTom DVT 9000 [QR, Verona, Italy], and Somatom Sensation [Siemens Medical Solutions, Erlangen, Germany]) were used with standard protocols and, when possible, in the auto-exposure mode. Equivalent and effective doses were calculated. The calculation of the effective doses was based on the International Commission on Radiological Protection's 2005 recommendations.

RESULTS

The lowest organ dose (13.1 microSv) was received by the thyroid gland during conventional panoramic and lateral cephalometric imaging. The highest mean organ dose (15,837.2 microSv) was received by the neck skin from the multi-slice CT. The effective dose was also lower for the panoramic and lateral cephalometric device (10.4 microSv), and highest for the multi-slice CT (429.7 microSv).

CONCLUSIONS

From a radiation-protection point of view, conventional images still deliver the lowest doses to patients. When 3-dimensional imaging is required in orthodontic practice, a CBCT should be preferred over a CT image. Further studies are necessary to justify the routine use of CBCT in orthodontic treatment planning.

Comparison of cone beam computed tomography imaging with physical measures

OBJECTIVES

The goal of this study was to determine the accuracy of measuring linear distances between landmarks commonly used in orthodontic analysis on a human skull using two cone beam CT (CBCT) systems.

METHODS

Measurements of length were taken using volumetric data from two CBCT systems and were compared with physical measures using a calliper applied to one human adult skull. Landmarks were identified with chromium steel balls embedded at 32 cranial and 33 mandibular landmarks and the linear measures were taken with a digital calliper. The skull was then scanned with two different CBCT systems: the NewTom QR DVT 9000 (Aperio Inc, Sarasota, FL) and the Hitachi MercuRay (Hitachi Medico Technology, Tokyo, Japan). CT data including the landmark point data were threshold segmented using CyberMed's CB Works software (CB Works 1.0, CyberMed Inc., Seoul, Korea). The resulting segmentations were exported from CB Works as VRML (WRL) files to Amira software (Amira 3.1, Mercury Computer Systems GmbH, Berlin, Germany).

RESULTS

The error was small compared with the gold standard of the physical calliper measures for both the NewTom (0.07+/-0.41 mm) and CB MercuRay (0.00+/-0.22 mm) generated data. Absolute error to the gold standard was slightly positive, indicating minor compression relative to the calliper measurement. The error was slightly smaller in the CB MercuRay than in the NewTom, probably related to a broader greyscale range for describing beam attenuation in 12-bit vs 8-bit data.

CONCLUSIONS

The volumetric data rendered with both CBCT systems provided highly accurate data compared with the gold standard of physical measures directly from the skulls, with less than 1% relative error.

Head-and-neck organ doses from an episode of orthodontic care

INTRODUCTION

The high prevalence of orthodontic treatment in young people makes the associated radiation to the head and neck of potential public-health significance. In this study, we estimated secular changes (1963-2003) in age-specific organ doses associated with orthodontic care and collective organ doses in the United States in 1999.

METHODS

A survey of radiographic records at 1 university clinic was combined with published estimates to provide organ-specific radiation doses. Collective organ doses were estimated from the 1999 US Nationwide Evaluation of X-ray Trends and published orthodontic utilization surveys.

RESULTS

Before 1992, orthodontic care in a university setting was associated with mean doses of 7.0 milligrays (mGy) to the thyroid, 0.8 mGy to the red bone marrow, 2.7 mGy to the brain, 13.2 mGy to the salivary glands, and 5.1 mGy to the bone. After 1992, the doses decreased to 2.8 mGy to the thyroid, 0.3 mGy to the red bone marrow, 0.7 mGy to the brain, 6.2 mGy to the saliva glands, and 2.4 mGy to the bone. Around 1999, the collective doses associated with orthodontic care in the United States in patients less than 19 years of age were 400 Gy to the red bone marrow and 3800 Gy to the thyroid.

CONCLUSIONS

Orthodontic care, in part due to its high prevalence, potentially contributes significantly to the diagnostic radiation burden in those less than 19 years old in the United States.

Evaluation of cleft lip bony depression of piriform margin and nasal deformity with cone beam computed tomography: "retruded-like" appearance and anteroposterior position of the alar base

BACKGROUND

As the nasal platform, the piriform margin is considered the most important nasal structure. An insufficient bony structure has been suggested to be the major factor in secondary nasal deformities such as the "depressed alar base." It is unclear, however, how the piriform margin is depressed or how bony depression influences nasal shape.

METHODS

Using cone beam computed tomography, the anteroposterior positions of the cleft-side piriform margin and alar base were compared with those of the noncleft side in 52 postoperative unilateral cleft lip patients with no alveolar bone graft. Patients were divided based on cleft type into either the unilateral cleft lip, alveolus, and palate group or the unilateral cleft lip and alveolus group.

RESULTS

In all cases, the cleft-side piriform margin was depressed. The anteroposterior position of the alar base was related to the piriform depression in both groups. However, in contrast with bony depression, the cleft-side alar base was located more anteriorly than the non-cleft-side alar base in 35 of 52 patients.

CONCLUSIONS

The authors' study suggests that bony depression does not necessarily lead to postoperative alar depression. The postoperative cleft lip alar position can be maintained independently of the collapsed lesser segment of the maxilla. In addition, in many cleft lip newborns the cleft alar crease is hypoplastic, and the paranasal triangle is easily elevated by operative manipulation because of the muscular dysfunction. This shallowness leads to a "retruded" appearance. For improvement, preservation of the paranasal triangle and alar crease plasty are important.

Accuracy of cone-beam computed tomography imaging of the temporomandibular joint: comparisons with panoramic radiology and linear tomography

INTRODUCTION

Cone-beam computed tomography (CBCT) is increasingly being used as an imaging modality, particularly in the assessment of the temporomandibular joint (TMJ). A blinded observational cross-sectional in-vitro study was conducted to compare the diagnostic accuracy of observers viewing images made with CBCT, panoramic radiography, and linear tomography. The task was to detect cortical erosions affecting the mandibular condylar head.

METHODS

The sample consisted of 37 TMJ articulations from 30 skulls with either normal condylar morphology (n = 19) or erosion of the lateral pole (n = 18). The articulations were imaged by using corrected angle linear tomography (TOMO), normal (Pan-N) and TMJ-specific (Pan-TM) panoramic radiography, and CBCT. Digital images were obtained with photostimulable phosphor plates for all modalities except CBCT. The CBCT detector used an amorphous silicon flat-panel array combined with cesium iodide. Images and 10 rereads were presented to 10 observers on a flat-panel display at a pixel-to-monitor ratio of 1:1. CBCT multi-planar images were presented both statically (CBCT-S) and interactively (CBCT-I). The observers were permitted to scroll through axial (0.4 mm) and para-sagittal (1 mm) sections and then independently rate their confidence about the presence or absence of cortical erosion. Intraobserver reliability was determined by weighted kappa and diagnostic accuracy by the fitted area under the ROC curve. Means were compared by using ANOVA (P < or =.05).

RESULTS

Intraobserver reliability was moderate (0.57 +/- 0.22; range, 0.34-0.78). Pan-N (0.72 +/- 0.15), CBCT-I (0.65 +/- 0.21), and CBCT-S (0.65 +/- 0.17) reliability was significantly greater than TOMO (0.44 +/- 0.25). The diagnostic accuracy of CBCT-I (0.95 +/- 0.05) and CBCT-S (0.77 +/- 0.17) was significantly greater than all other modalities (Pan-N [0.64 +/- 0.11], Pan-TM [0.55 +/- 0.11], TOMO [0.58 +/- 0.15]). CBCT-I was also more accurate than CBCT-S, and Pan-N was more accurate than Pan-TM and TOMO.

CONCLUSIONS

CBCT images provide superior reliability and greater accuracy than TOMO and TMJ panoramic projections in the detection of condylar cortical erosion.

Accuracy of linear measurements from imaging plate and lateral cephalometric images derived from cone-beam computed tomography

INTRODUCTION

As orthodontic practice moves toward 3-dimensional cephalometric analyses, a solution is required to ensure sustained availability of well-established projected treatment outcomes based on 2-dimensional analyses. This ex-vivo study was conducted to compare the accuracy of linear measurements made on photostimulable phosphor cephalograms with 3 methods for simulating lateral cephalograms with cone-beam computed tomography (CBCT).

METHODS

The linear distances between anatomical landmarks on dentate dry human skulls were measured by observers using digital calipers for S-N, Ba-N, M-N, ANS-N, ANS-PNS, Pog-Go, Go-M, Po-Or, and Go-Co. The skulls were imaged with CBCT with a single 360 degrees rotation, producing 306 basis images and achieving 0.4 mm isotrophic voxel resolution on volumetric reconstruction for making ray-sum reconstructed cephalograms. Two other cephalogram approaches were used with the CBCT system--a single transmission image generated as a scout image designed to check patient positioning before CBCT, and a single-frame lateral basis image. Conventional digital lateral cephalograms (LCs) were acquired with the photostimulable phosphor system. Images were imported into a cephalometric analysis program (Dolphin Imaging Cephalometric and Tracing Software, Chatsworth, Calif) to compute the included linear measurements. Analyses were repeated 3 times and statistically compared with measured anatomic truth with ANOVA (P < or =.05). The intraclass correlation coefficient was determined as an index of intra- and interobserver reliability.

RESULTS

The intraclass correlation coefficient for the LCs was significantly less than for the measured anatomic truth and for all CBCT-derived images. CBCT images either produced with individual frames or reconstructed from the volumetric data set were accurate for all measurements except Pog-Go and Go-M. CBCT scout images had the second highest accuracy for all measurements except Pog-Go, Go-M, and Go-Co. Conventional LCs had the least accuracy; they were accurate only for Po-Or and ANS-N.

CONCLUSIONS

CBCT-derived 2-dimensional LCs proved to be more accurate than LCs for most linear measurements calculated in the sagittal plane. No advantage was found over single-frame basis images in using ray-sum generated cephalograms from the CBCT volumetric data set.

Clinical indications for digital imaging in dento-alveolar trauma. Part 1: traumatic injuries

Traumatized teeth present a clinical challenge with regard to their diagnosis, treatment plan, and prognosis. Recent developments in imaging systems have enabled clinicians to visualize structural changes effectively. Computed tomography, magnetic resonance imaging and cone beam computed tomography are among the most commonly used systems for dental and maxillofacial surgery. The purpose of this review is to describe the advantages and disadvantages of each technique and the clinical application for dento-alveolar trauma. Three clinical cases are described to illustrate the potential use of the NewTom 3G for diagnosis and treatment plan of dento-alveolar traumatic injuries.

R, Raymundo MV, Raymundo DV, Ferreira SN. Tomografia computadorizada de feixe cônico (Cone beam): entendendo este novo método de diagnóstico por imagem com promissora aplicabilidade na Ortodontia

OBJETIVO: este artigo visa informar e atualizar o profissional da área odontológica a respeito da tomografia computadorizada, incluindo informações concernentes à aquisição de imagens, dose de radiação e interpretação do exame tomográfico, com distinção entre a tomografia computadorizada tradicional e a tomografia computadorizada de feixe cônico. Adicionalmente, as possibilidades de aplicação deste método de diagnóstico por imagem na Ortodontia são discutidas. CONCLUSÕES: resultado de avanços tecnológicos, da redução da exposição à radiação e da ótima qualidade da imagem, as expectativas apontam para uma utilização mais abrangente da tomografia computadorizada de feixe cônico na Odontologia e na Ortodontia. Com a definição de novos conhecimentos gerados pela visão tridimensional do crânio e da face, o futuro reserva a renovação de conceitos e paradigmas, assim como a redefinição de metas e planos terapêuticos ortodônticos.

Evaluation of the spatial resolution characteristics of a cone-beam breast CT scanner

The purpose of this study was to examine the spatial resolution of a prototype pendant-geometry cone-beam breast computed tomography (CT) system. Modulation transfer functions (MTFs) of the reconstructed image in the coronal (x and y) plane were computed as a function of the cone angle, the radial distance from the axis of rotation, the size of the reconstruction matrix, the back-projection filter used, and the number of projections acquired for the reconstruction. The results show that the cone angle and size of the reconstruction matrix have minimal impact on the MTF, while the MTF degraded radially from the axis of rotation (from 0.76 at 2.6 mm from axis of rotation down to 0.37 at 76.9 mm from axis of rotation at f=0.5 mm(-1)). The Ramp reconstruction filter increases the MTF near the axis of rotation relative to the Shepp-Logan filter, while an increase in the number of projections from 500 to 1000 increased the MTF near the periphery of the reconstructed image. The MTF in the z direction (anterior-posterior direction) was also evaluated. The z-direction MTF values tend to be higher when compared to the coronal MTF (0.85 at f =0.5 mm(-1)), and tend to be very constant throughout the coronal plane direction. The results suggest that an increase in the MTF for the prototype breast CT system is possible by optimizing various scanning and reconstruction parameters.

Three-dimensional cephalometry: Spiral multi-slice vs cone-beam computed tomography

Three-dimensional (3D) craniofacial imaging techniques are becoming increasingly popular and have opened new possibilities for orthodontic assessment, treatment, and follow-up. Recently, a new 3D cephalometric method based on spiral multi-slice (MS) computed tomography (CT) was developed and validated by our research group. This innovative 3D virtual approach is a bridge between conventional cephalometry and modern craniofacial imaging techniques and provides high-quality, accurate, and reliable quantitative 3D data. The aim of this article was to describe the advantages and the disadvantages of spiral MS-CT 3D cephalometry and to discuss the potential of cone-beam CT 3D cephalometry.

Accuracy of measurements of mandibular anatomy in cone beam computed tomography images

OBJECTIVES

Cone beam computed tomography (CBCT) images of ideally positioned and systematically mispositioned dry skulls were measured using two-dimensional and three-dimensional software measurement techniques. Image measurements were compared with caliper measurements of the skulls.

STUDY DESIGN

Cone beam computed tomography volumes of 28 skulls in ideal, shifted, and rotated positions were assessed by measuring distances between anatomic points and reference wires by using panoramic reconstructions (two-dimensional) and direct measurements from axial slices (three-dimensional). Differences between caliper measurements on skulls and software measurements in images were assessed with paired t tests and analysis of variance (ANOVA).

RESULTS

Accuracy of measurement was not significantly affected by alterations in skull position or measurement of right or left sides. For easily visualized orthodontic wires, measurement accuracy was expressed by average errors less than 1.2% for two-dimensional measurement techniques and less than 0.6% for three-dimensional measurement techniques. Anatomic measurements were significantly more variable regardless of measurement technique.

CONCLUSIONS

Both two-dimensional and three-dimensional techniques provide acceptably accurate measurement of mandibular anatomy. Cone beam computed tomography measurement was not significantly influenced by variation in skull orientation during image acquisition.

Development of imaging selection criteria and procedures should precede cephalometric assessment with cone-beam computed tomography

Cone-beam computed tomography (CBCT) systems for craniofacial imaging are now available from several manufacturers. CBCT potentially provides opportunities for 3-dimensional cephalometrics in orthodontic assessment of bony landmarks and air-bounded surfaces such as the facial skin. Two-dimensional cephalogram simulation could facilitate the transfer of growth projections from existing data sets as a starting point for use of a new 3-dimensional paradigm. Three methods are described to simulate conventional 2-dimensional cephalograms from CBCT images and volumetric data sets. However, certain precautions are required to assure that selection criteria and imaging parameters guarantee a radiation dose that is as low as reasonably achievable.

Plane orientation for standardization in 3-dimensional cephalometric analysis with computerized tomography imaging

INTRODUCTION

The purpose of this study was to propose certain landmarks and planes to standardize 3-dimensional image orientation.

METHODS

Cone-beam computerized tomographic images were obtained from 10 adolescent patients and analyzed with AMIRA software (AMIRA, Mercury Computer Systems, Berlin, Germany).

RESULTS

Four points (ELSA, right superior external auditory meatus, left superior external auditory meatus, and mid-dorsum foramen magnum) were located on each image. The axial-horizontal plane (x-y plane) was then determined by using both superior external auditory meatus and ELSA; the sagittal-vertical plane (z-y plane) was formed by ELSA and mid-dorsum foramen magnum perpendicular to the x-y plane.

CONCLUSIONS

All points had high intrareliability and were adequate for standardizing the orientation of 3-dimensional images.

Knowledge-driven 3-D extraction of the masseter from MR data

In this paper, we propose a knowledge-driven highly automatic methodology for extracting the masseter from magnetic resonance (MR) data sets for clinical purposes. The masseter is a muscle of mastication which acts to raise the jaw and clench the teeth. In our initial work, we designed a process which allowed us to perform 2-D segmentation of the masseter on 2-D MR images. In the methodology proposed here, we make use of ground truth to first determine the index of the MR slice in which we will carry out 2-D segmentation of the masseter. Having obtained the 2-D segmentation, we will make use of it to determine the region of interest (ROI) of the masseter in the other MR slices belonging to the same data set. The upper and lower thresholds applied to these MR slices, for extraction of the masseter, are determined through the histogram of the 2-D segmented masseter. Visualization of the 3-D masseter is achieved via volume rendering. Our methodology has been applied to five MR data sets. Validation was done by comparing the segmentation results obtained by using our proposed methodology against manual contour tracings, obtaining an average accuracy of 83.5%

Proposed reference point for 3-dimensional cephalometric analysis with cone-beam computerized tomography

INTRODUCTION

The purpose of this article is to propose a reference landmark for use in 3-dimensional cephalometric analysis with 3-dimensional volumetric images.

METHODS

Cone-beam computerized tomographies were obtained from 10 adolescent patients. They were analyzed with AMIRA software (Mercury Computer Systems, Berlin, Germany).

RESULTS

The proposed reference point is located between both foramina spinosum.

CONCLUSION

This point has high intrareliability and is an adequate landmark for use as a reference in 3-dimensional cephalometric analysis.

Accuracy of linear temporomandibular joint measurements with cone beam computed tomography and digital cephalometric radiography

INTRODUCTION

Cone beam computed tomography (CBCT) is making headway into imaging for orthodontics. The purpose of this study was to define CBCT multi-planar reformatted projections for temporomandibular joint (TMJ) examination and compare the accuracy of linear measurements of the TMJ and related structures from these projections with similar measurements made with conventional cephalograms and with the anatomic truth.

METHODS

Linear dimensions between 11 anatomical sites were measured with a digital caliper to assess the anatomic truth for 25 dry human skulls. The skulls were imaged with iCAT (Xoran Technologies, Ann Arbor, Mich/Imaging Sciences International, Hatfield, Pa) CBCT, and cephalograms were made in all 3 orthogonal planes (lateral cephalometric [LC], posteroanterior [PA], and submentovertex [SMV]) acquired with photostimulable phosphor plates. Linear measurements were made on 7 custom CBCT reconstructions and the digital cephalograms. Modality means and the natural log of the standard deviations were compared post hoc against the actual dimensions by using analysis of variance with the Dunnett t test. Significance was set at P < .05.

RESULTS

All CBCT measurements were accurate; however, 3 of 5 LC measurements, 4 of 5 PA measurements, and 4 of 6 SMV measurements varied significantly from the truth. Intraobserver CBCT measurements were highly reliable compared with anatomic truth and significantly more reliable than measurements made from LC, PA, and SMV images.

CONCLUSIONS

Custom oblique multi-planar reformatted reconstructions with iCAT CBCT provide accurate and reliable linear measurements of mandibular and TMJ dimensions.

Evaluation of x-ray scatter properties in a dedicated cone-beam breast CT scanner

The magnitude of scatter contamination on a first-generation prototype breast computed tomography (CT) scanner was evaluated using the scatter-to-primary ratio (SPR) metric. The SPR was measured and characterized over a wide range of parameters relevant to breast CT imaging, including x-ray beam energy, breast diameter, breast composition, isocenter-to-detector distance, collimated slot thickness, and grid ratio. The results demonstrated that in the absence of scatter reduction techniques, the SPR levels for the average breast (e.g., 14 cm diameter 50/50 composition cylindrical phantom) are quite high (approximately 0.5 at the center of the phantom for 80 kVp in true cone-beam CT geometry), and increases as the diameter of the phantom is increased (to approximately 1.0 at the center of a 18 cm diameter 50/50 phantom). The x-ray beam energy and the phantom compositions had only minimal impact on the measured SPR. When an ideal bowtie filter was used, the SPRs at the central axis of the 14 and 18 cm cylindrical phantoms were reduced while the SPRs at the edge of the phantoms were increased. Lastly, collimation in the vertical direction had a significant impact on the SPRs at the central axis of the phantoms. These high SPR levels might lead to cupping artifacts and increased noise in the reconstructed CT images, and this suggests that efficient scatter rejection and/or correction techniques may be required to improve the quality and accuracy of cone beam CT images.