3D Cone-beam Computed Tomography Research Articles

POSSIBILITIES OF MODERN X-RAY EXAMINATION METHODS FOR DIAGNOSTICS OF HIDDEN DENTAL CARIES OF APPROXIMAL LOCALIZATION

Introduction: In case of hidden carious cavities development on the approximal teeth surfaces, the clinical diagnostics of this process is difficult. Then, the diagnostics of carious lesion is not possible without carrying out X-ray examination. The aim of the study was a comparative analysis of the effectiveness of clinical and X-ray diagnostics for hidden caries of approximal teeth surfaces. Materials and methods: Condition of 2 963 teeth of 115 people aged from 19 to 55 was analysed. Additionally, a digital panoramic 2D diagnostics (Planmeca ProSensor, Finland) and Cone Beam Computed Tomography 3D Diagnostics (Morita, Japan) were used for clinical examination of patients. Results: In both variants of diagnostics, the number of caries defects in the upper jaw was higher than in the lower one, and the frequency of caries lesion of various teeth groups had the following sequence in descending order: molar teeth, premolar teeth, incisor teeth and canine teeth. Hidden carious cavities of average depth and deep were detected with almost the same frequency in both variants of the study, which by 1.9 - 2.0 times respectively exceeded the frequency of superficial carious cavities detection (p = 0.0001). According to the results of clinical studies, hidden superficial carious cavities occurred in single cases and X-ray examination improved their diagnostics by 9.6 times (p = 0.0000). Conclusions: X-ray examination allows increasing the effectiveness of diagnostics of hidden carious cavities of approximal localization by 1.2 times on the whole (p <0,05). In such cases orthopantomography (OPG) has reasonably sufficient diagnostic capabilities. Definitely, 3D Cone Beam Computed Tomography (CBCT) has much more diagnostic capabilities, but its use can not be justified for the diagnostics of caries only.

Entrance skin dose of the thyroid gland area following exposure with different protocols of two panoramic and cone-beam computed tomography devices

Background: Cone-beam computed tomography (CBCT) has gained considerable use, while radiation burden remains an important concern. Aims: This study aimed at determining the entrance skin dose of the thyroid gland area through exposure with the normal, soft, and hard modes of Vatech (Pax-i) panoramic device as well as different field of views (FOVs) of Vatech (Pax-i 3D) CBCT system. Materials and Methods: Dose measurements were performed on a head-and-neck phantom by an ion chamber dosimeter. Panoramic imaging was done in three normal, soft, and hard modes, each entailing woman, man, and child options. CBCT examinations were performed with various FOVs, each having normal, soft, and hard modes as well as woman, man, and child choices. Doses obtained from different protocols of the two imaging modalities were compared by paired t-test. Results: All FOVs in CBCT resulted in greater radiation dose than panoramic in each of the normal, soft, and hard exposure modes (P

Thickness of Buccal and Lingual Alveolar Bone Plates according to the Position of Impacted Mandibular Third Molars on Cone-Beam Computed Tomography Scans.

Objectives:This study sought to assess the thickness of buccal and lingual alveolar bone plates according to the position of impacted mandibular third molars on cone-beam computed tomography (CBCT) scans.Materials and Methods:Eighty-four CBCT scans of impacted mandibular third molars were evaluated in this retrospective study. All images had been obtained by ProMax 3D CBCT system with the exposure settings of 78 kVp, 12 mA, 16 s time, 0.2 mm voxel size and 10 × 9 cm field of view. The impaction angle of teeth and the thickness of buccal and lingual cortical plates were determined on images by drawing lines in the anterior, middle, posterior, superior, central and inferior regions. Thickness of bone plates was analyzed according to the position of impacted molars relative to the buccal and lingual plates using the Student t-test and relative to the second molars using one-way ANOVA and Tukey’s test.Results:In the buccolingual direction, the buccal plate thickness was maximum in lingual position followed by central position, and minimum in buccal position of the teeth. The lingual plate thickness was minimum in horizontal and distoangular positions and maximum in the mesioangular position of impacted teeth.Conclusion:Risk of lingual plate preformation is higher in surgical removal of impacted third molars with distoangular and horizontal positions. Thus, further attention must be paid by the surgeons to such cases.

Limited-View Cone-Beam CT Reconstruction Based on an Adversarial Autoencoder Network With Joint Loss

Limiting scan views is an efficient way to reduce radiation doses in the cone-beam computed tomography (CBCT) examinations, which unfortunately degrades the reconstructed images. Some methods on the framework of the generative adversarial network (GAN) were developed to improve low-dose CT images after CT reconstruction from the limited-view projections. However, no GAN-based methods were devoted to restoring missing CBCT projections in the sinogram domain before CT reconstruction. To avoid the trade-off between radiation dose and image quality, we propose a limited-view CBCT reconstruction method in the sinogram domain, instead of the image domain. First, this method slices the 3D CBCT projections into multiple 2D pieces. Then, an adversarial autoencoder network is trained to estimate the missing parts of these 2D pieces. To improve the prediction, we apply a joint loss function, including reconstruction loss and adversarial loss to the network. When the new limited-view 3D CBCT projections are acquired, the proposed method uses the trained adversarial autoencoder network to generate the missing parts of the 2D pieces sliced from the current 3D CBCT projections. Then, stacking the completed 2D pieces in order yields full-view 3D CBCT projections. Finally, we reconstruct the CT images from the full-view 3D CBCT projections by using the Feldkamp, Davis, and Kress algorithm. The experiments validate that our method performs well in the prediction of unknown projections and CT reconstruction and are less vulnerable to the number of unknown projections than other methods.

1 Comparison of target coverage for two motion-encompassing methods for lung stereotactic body radiotherapy by using in-treatment 4D cone-beam CT

Introduction Recently, in-treatment 4D cone-beam CT (4D-CBCTin-treat) has been implemented in clinic allowing the acquisition of respiratory correlated CBCT projections concurrently with the beam delivery. With this imaging modality, the actual 4D target locations during treatment can be visualized at the end of each fraction. 4D-CBCTin-treat provides reliable information to evaluate actual target coverage during treatment and to verify planning target volume (PTV) adequacy for lung stereotactic body radiotherapy (SBRT). The purpose of this study was to compare in-treatment target coverage for two motion-encompassing PTV strategies: an internal target volume (ITV) based approach and the mid-ventilation (MidV) based approach. Methods Data from 27 lung cancer patients treated with a frameless SBRT technique using a volumetric modulated arc therapy (VMAT) were selected. For each patient, a 4D-CT was used for treatment planning. For the ITV-based approach, we applied the PTV setting currently used at our institute for lung SBRT: ITV was determined by contouring the target on 10 respiration phases and a generic 4 mm margin was then added to create the PTV. For the MidV-based approach, PTV was defined around the tumor closest to its time-weighted mean position (MidV CT phase) using the Van Herk margin recipe [1] . At each fraction, the target was localized using a 4D-CBCT on-line registration procedure and a 4D-CBCTin-treat was acquired during the VMAT delivery. The clinical target volume (CTV) was delineated in 10 respiration phases on all 4D-CBCTin-treat images reconstructed during the treatment course. We defined target coverage per treatment as the percentage of the CTV included within the PTV averaged over respiration phases and fractions. Results A total of 93 4D-CBCTin-treat were delineated. Mean target coverage per treatment was 98.6% (min: 93.4%) and 98.9% (min: 93.5%) for ITV and MidV approaches respectively. Mean PTV volume was 18.1 cc (min: 2.9 cc, max: 50.7 cc) and 18.6 cc (min: 5.4 cc, max: 49.9 cc) for ITV and MidV approaches respectively. Compared to the MidV, the ITV-based strategy using a 4 mm PTV margin resulted to a non-statistically significant difference neither for target coverage (p = 0.401) nor for PTV volume (p = 0.186). Conclusions With a fast VMAT delivery technique and a 4D image guidance protocol, a 4 mm PTV margin can be safely applied when using the ITV-based strategy for frameless lung SBRT. This ITV-based PTV setting provides equivalent irradiated volumes and tumor coverage than the MidV approach.

Hindfoot alignment of adult acquired flatfoot deformity: A comparison of clinical assessment and weightbearing cone beam CT examinations

BackgroundClinical assessment of hindfoot alignment (HA) in adult acquired flatfoot deformity (AAFD) can be challenging and weightbearing (WB) cone beam CT (CBCT) may potentially better demonstrate this three-dimensional (3D) deformity. Therefore, we compared clinical and WB CBCT assessment of HA in patients with AAFD. MethodsIn this prospective study, we included 12 men and 8 women (mean age: 52.2, range: 20–88) with flexible AAFD. All subjects also underwent WB CBCT and clinical assessment of hindfoot alignment. Three fellowship-trained foot and ankle surgeons performed six hindfoot alignment measurements on the CT images. Intra- and Inter-observer reliabilities were calculated using intra-class correlation (ICC). Measurements were compared by paired T-tests, and p-values of less than 0.05 were considered significant. ResultsThe mean of clinically measured hindfoot valgus was 15.2 (95% confidence interval [CI]: 11.5–18.8) degrees. It was significantly different from the mean values of all WB CBCT measurements: Clinical Hindfoot Alignment Angle, 9.9 (CI: 8.9–11.1) degrees; Achilles tendon/Calcaneal Tuberosity Angle, 3.2 (CI: 1.3–5.0) degrees; Tibial axis/Calcaneal Tuberosity Angle, 6.1 (CI: 4.3–7.8) degrees; Tibial axis/Subtalar Joint Angle 7.0 (CI: 5.3–8.8) degrees, and Hindfoot Alignment Angle 22.8 (CI: 20.4–25.3) degrees. We found overall substantial to almost perfect intra- (ICC range: 0.87–0.97) and inter-observer agreements (ICC range: 0.51–0.88) for all WB CBCT measurements. ConclusionsUsing 3D WB CBCT can help characterize the valgus hindfoot alignment in patients with AAFD. We found the different CT measurements to be reliable and repeatable, and to significantly differ from the clinical evaluation of hindfoot valgus alignment.Level of evidence: Level II—prospective comparative study.

Three-dimensional reconstruction of the temporal bone: Comparison of in situ, CT, and CBCT measurements

ObjectiveTo evaluate the accuracy of three-dimensional (3D) Cone Beam Computed Tomography (CBCT) and Computed Tomography (CT) reconstructions of human temporal bones compared with in situ measurements. Material and methodsExperimental anatomical study of 10 human temporal bones. Wilcoxon's test was used to compare 8 distances on each temporal bone measured in situ and then on 3D CT and CBCT reconstructions. Six landmarks were used: external auditory canal (EAC), tip of the mastoid process, tip of the occiput, zygoma, a point situated 1cm above the tip of the mastoid process (T0) (open technique: lower limit of the mastoidectomy), head of stapes. ResultsNo significant difference was observed between the 3 measuring techniques for any of the distances studied (P>0.05). DiscussionThis study demonstrates the equivalence of CBCT and CT for temporal bone measurements. ConclusionCBCT is a new imaging modality providing 3D reconstructions of the temporal bone that are as reliable as those obtained by CT. As a result of better spatial resolution compared to CT, CBCT is associated with a significantly lower radiation dose. This technique constitutes a morphological progress, as CBCT is comparable to CT, allowing investigation of pathological ears with a lower radiation dose.

Blurring the lines for better visualisation

On-treatment imaging in radiotherapy has evolved over the last 60 years, bringing with it changes in the roles of radiographers, radiologists and oncologists. The ability to acquire and interpret high quality images (2D kilovoltage and megavoltage imaging and 3D CT and cone-beam CT) for radiotherapy planning and delivery requires therapy radiographers to have skills and knowledge that overlap with those of diagnostic radiographers. With the implementation of MRI-guided radiotherapy, treatment radiographers and clinical oncologists are exploring new territory, requiring truly collaborative working practices with their radiology partners. This short communication introduces the first images acquired using the hybrid MR Linac at our institution.

Influence of respiratory motion on image quality of 4D-CBCT

Objective To investigate the relationship between the image quality of 4D cone beam CT (4D-CBCT) and the characteristic parameters of respiratory motion. Methods Catphan 500 was fixed on the Mapcheck XY/4D table by a fixation device. The control platform was utilized to simulate the static and 19 motion states. A synergy accelerator was adopted to perform 4D-CBCT scan of the image quality detection module under different motion states. By analyzing the geometric accuracy, spatial resolution, low-contrast visibility, CT value uniformity and motion position accuracy of the images of the 10 phases of the reconstructed images, the relationship among the image quality of 4D-CBCT, motion direction, amplitude and cycle was analyzed. Results 4D-CBCT images could not be properly reconstructed in the static state or only in the left-right (LR) direction. The image quality was significantly worse than that in the SI direction. The contrast-to-noise ratio (CNR) was decreased as the motion cycle was increased. When the cycle was increased from 2 s to 6 s, the CNR was significantly declined from 3.33 to 1.72(P<0.01), whereas respiratory motion exerted no significant effect upon the geometric accuracy, spatial resolution and sagittal position. Conclusions The CNR, horizontal and vertical geometric accuracy and motion position accuracy of 4D-CBCT image quality are significantly affected by respiratory motion, whereas spatial resolution and sagittal geometric accuracy are not significantly influenced by respiratory motion.4D-CBCT requires the intervention of periodical motion in the SI direction. Excessively slow or absence of periodical motion can influence the image quality and even the images cannot be accurately reconstructed.4D-CBCT image reconstruction equally requires the intervention of periodical motion in the SI direction. The image quality is simultaneously affected by the amplitude and cycle of respiratory motion. For 4D-CBCT scan, the respiratory cycle of 0.75 cm are recommended. Key words: Image quality; Respiratory motion; Cone beam CT, four-dimensional

P275] Comparison of 3D surface scan system and conebeamct in daily patient positioning for breast radiotherapy

Purpose Portal imaging is performed before the radiotherapy treatment to ensure that the target volume and patient position are correct. Three-dimensional images are obtained and patient positioning can be done very precisely and accurately with ConeBeamCT. So patients are irradiated with extra radiation except for treatment with ConeBeamCT. In addition, the patient can be positioned with a laser-based surface scanning system Catalyst.The patient’s body is scanned with the optical laser system and the patient is positioned according to the scan results with Catalyst. In our study, the differences between the shift values obtained by ConeBeamCT and Catalyst surface scanning were compared. Methods IMRT or VMAT plans are prepared for 22 breast cancer patients in Monaco 5.11 treatment planning system. Two partial VMAT fields or six IMRT fields were used in the plans. 22 patients were positioned with a C-RAD laser-based surface scan in 389 fractions and then three-dimensional images were obtained with ConeBeamCT. Results ConeBeamCT images were evaluated with the XVI program. The average difference between the Catalyst and XVI shift values were found in the lateral direction X (cm): 0.24 ± 0.21, in the longitudinal direction Y (cm): 0.36 ± 0.29, in the vertical direction Z(cm): 0.23 ± 0.20. The maximum difference between Catalyst and XVI shift values were found in the lateral direction X (cm): 1.28, in the longitudinal direction Y (cm): 1.54, in the vertical direction Z (cm): 1.30. Conclusions In Breast CA Radiotherapy, target volume should be irradiated accurately for treatment success. Moreover, the right positioning of the patient has a very important role to success treatments. During this procedure, a laser-based surface scanning system can be used to reduce the radiation dose implemented to the patient for portal. Several fraction ConeBeamCT and Catalyst should be used simultaneously and if the difference is small, the number of ConeBeamCT should be reduced and the C-RAD surface scan system should be used, taking into account the entire treatment of the patient.

Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters

BACKGROUND CONTEXT Several studies have shown that the use of a combination of intraoperative CT images and navigation, significantly improves pedicle screw placement accuracy. A new concept of surgical navigation system using augmented reality (AR) with intraoperative 3D cone beam CT (CBCT) was developed specifically for spinal surgery. PURPOSE To evaluate accuracy, efficiency, and safety of an AR-based surgical navigation system for pedicle screw placement. STUDY DESIGN/SETTING Prospective study. PATIENT SAMPLE Twenty patients. OUTCOME MEASURES Pedicle screw placement accuracy, procedural time, patients and occupational radiation doses. METHODS Twenty patients (1:1 male:female, 30±19 years) eligible for spine surgery with pedicle screw placement (13 scoliosis deformity cases and 7 other surgical indications) were prospectively enrolled and treated using surgical navigation with AR (Philips Healthcare, Best, the Netherlands). A total of 253 screws were placed in the patients using AR. The navigation system consists of optical video cameras integrated in a ceiling-mounted C-arm in a hybrid operating room (OR). An intraoperative CBCT was acquired from the C-arm to plan an optimal path for screw placement. The screws were navigated thanks to the planned paths augmented to the reality scene shown by the video cameras. An additional CBCT was performed to evaluate the accuracy of screw placement by independent reviewers using the Gertzbein scale. Total navigation time for screw placement, patient radiation dose as well as occupational staff dose was measured. RESULTS In average 13±6 screws per patient were placed with navigation. The accuracy of pedicle screw placement was 94% yielding 15/253 screws rated as grade 2 (2–4 mm pedicle breach) from which 13 were lateral breaches. Thirteen of these grade 2 screws had a diameter larger than the pedicle isthmus size where they were placed. The average navigation time was 5.2±4.1 minutes with a median value of 4 minutes from making the bone entry burr-hole to the final screw placement. Navigation time corresponded to an average of 16.8% of the total procedure time. The average patient radiation dose was 31±13 Gy cm2 (median 32, range: 14–51) with an average of 4 CBCT scans per procedure. During intraoperative 3D acquisitions, the OR staff was behind a leaded shield in the corner of the OR and did not wear apron lead protection during surgery. The average cumulative occupational dose of all staff member in the OR was 0.8±1.1 µSv (median 0.3, range: 0.0–3.2). CONCLUSIONS Surgical navigation using AR with intraoperative CBCT demonstrated clinical accuracy as high as 94% of pedicle screw placement with no related clinical complications. The average required time of navigation per screw placement was as short as 5.2 minutes. The use of navigation was a short fraction of the total procedure time. The CBCT intraoperative imaging available on the AR-based navigation system demonstrated negligible cumulative staff dose.

OA189] 4D-CBCT streak reduction by simulated undersampling from 3D reconstruction

Purpose 4D-Cone Beam CT (4D-CBCT) scans used for image guided radiotherapy (IGRT) are usually undersampled and therefore affected by streaking artifacts. This study investigates a streak reduction method that simulates undersampling from a 3D reconstruction. Methods This study is based on small field of view (SFOV) 4D-CBCT and 4D-CT scans of 20 lung cancer patients subjected to curatively intended IGRT. The proposed method resembles elements of the McKinnon-Bates algorithm [IEEE Trans Biomed Eng., 28, 123, 1981]. CBCT projections were 3D reconstructed and re-projected onto the original gantry angles. Re-projections were reconstructed as 3D and as 4D by respiratory phase binning. Streaks produced due to undersampling were estimated by subtracting the 3D volume from the 4D volumes. Corrected 4D-CBCT was made by subtracting the estimated streaks from a standard 4D-CBCT image. Quantitative analyses were conducted on the expiration phase. Streak-reduction was measured as the ratio of summed gradients in corrected image to uncorrected image, with less than unity indicating improvement. Corrected and uncorrected CBCT images were mapped onto CT by image registration and for each CBCT image the average HU error between CT and CBCT was calculated. Results The total process took less than 5 min for a 10 phase reconstruction. Visual improvements were observed when applying streak correction for the 4D-CBCT images. The ratio of summed gradients also favored the corrected images (mean = 0.8, SD = 0.05) and no sign of overall degradation of HU values were observed, given that average HU error for corrected CBCT was lower for corrected CBCT (mean = 181, SD = 22.1) than for uncorrected CBCT (mean = 193, SD = 24.7). Conclusions The quality of SFOV 4D-CBCT images subjected to streak correction was found to be improved based on visual and quantitative validations. A GPU-based implementation could potentially reduce the computation process to less than a minute and thereby making it usable for on-line IGRT.

3D C-Arm cone beam CT for targeting the portal vein during TIPS: Initial clinical experience

PurposeTo evaluate the feasibility, safety and usefulness of 3D CBCT with a new injection protocol for targeting the portal vein during TIPS and to determine if it allows decreasing the duration of the procedure. Materials and methods3D CBCT was obtained during creation of TIPS in 15 patients (group 2). Portogram quality score was defined using a 5 points scale. The time required to achieve portal puncture was also recorded and results were compared retrospectively in 15 patients who underwent TIPS without 3D CBCT (group 1). ResultsThe mean time required to puncture the portal vein was shorter when CBCT was used: 15 min versus 24 min (p = 0.156). We recorded 3 failures requiring a second procedure in group 1. There were no complications and no failure in group 2. We recorded 93% of good portography and 80% of good 3D roadmaps. Conclusion3D CBCT coupled with this new injection protocol provided high rate of good quality portography allowing to bring positional and directional information to improve the needle pass efficiency and to decrease the duration of the procedure.

GPU based parallel acceleration for fast C-arm cone-beam CT reconstruction

BackgroundWith the introduction of Flat Panel Detector technology, cone-beam CT (CBCT) has become a novel image modality, and widely applied in clinical practices. C-arm mounted CBCT has shown extra suitability in image guided interventional surgeries. During practice, how to acquire high resolution and high quality 3D images with the real time requirement of clinical applications remain challenging.MethodsIn this paper, we propose a GPU based accelerated method for fast C-arm CBCT 3D image reconstructions. A filtered back projection method is optimized and implemented with GPU parallel acceleration technique. A distributed system is designed to make full use of the image acquisition consumption to hide the reconstruction delay to further improve system performance.ResultsWith the acceleration both in algorithm and system design, we show that our method significantly increases system efficiency. The optimized GPU accelerated FDK algorithm improves the reconstruction efficiency. The system performance is further enhanced with the proposed system design by 26% and reconstruction delay is accelerated by 2.1 times when 90 frames of projections are used. When the number of frames used increases to 120, the numbers are 39% and 3.3 times. We also show that when the projection acquisition consumption increases, the reconstruction acceleration rate increases significantly.

4D cone-beam computed tomography (CBCT) using a moving blocker for simultaneous radiation dose reduction and scatter correction

Four-dimensional (4D) x-ray cone-beam computed tomography (CBCT) is important for a precise radiation therapy for lung cancer. Due to the repeated use and 4D acquisition over a course of radiotherapy, the radiation dose becomes a concern. Meanwhile, the scatter contamination in CBCT deteriorates image quality for treatment tasks. In this work, we propose the use of a moving blocker (MB) during the 4D CBCT acquisition (‘4D MB’) and to combine motion-compensated reconstruction to address these two issues simultaneously. In 4D MB CBCT, the moving blocker reduces the x-ray flux passing through the patient and collects the scatter information in the blocked region at the same time. The scatter signal is estimated from the blocked region for correction. Even though the number of projection views and projection data in each view are not complete for conventional reconstruction, 4D reconstruction with a total-variation (TV) constraint and a motion-compensated temporal constraint can utilize both spatial gradient sparsity and temporal correlations among different phases to overcome the missing data problem. The feasibility simulation studies using the 4D NCAT phantom showed that 4D MB with motion-compensated reconstruction with 1/3 imaging dose reduction could produce satisfactory images and achieve 37% improvement on structural similarity (SSIM) index and 55% improvement on root mean square error (RMSE), compared to 4D reconstruction at the regular imaging dose without scatter correction. For the same 4D MB data, 4D reconstruction outperformed 3D TV reconstruction by 28% on SSIM and 34% on RMSE. A study of synthetic patient data also demonstrated the potential of 4D MB to reduce the radiation dose by 1/3 without compromising the image quality. This work paves the way for more comprehensive studies to investigate the dose reduction limit offered by this novel 4D MB method using physical phantom experiments and real patient data based on clinical relevant metrics.

Tomosynthesis implementation with adaptive online calibration on clinical C-arm systems.

Cone beam computed tomography (CBCT) systems offer physicians crucial 3D and 2D imaging capabilities during interventions. However, certain medical applications only require very specific information from the CBCTs (e.g., determination of the position of high-contrast objects). In diagnostics, tomosynthesis techniques can be used in these cases to minimize dose exposure. Therefore, integrating such techniques on CBCT systems could also be beneficial for interventions. In this paper, we investigate the performance of our implementation of circular tomosynthesis on a CBCT device. The tomosynthesis scan trajectory is realized with step-and-shoot on a clinical C-arm device. The online calibration algorithm uses conventionally acquired 3D CBCT of the scanned object as prior knowledge to correct the imaging geometries. The online calibration algorithm was compared to an offline calibration to test its performance. A ball bearing phantom was used to evaluate the reconstructions with respect to geometric distortions. The evaluation was done for three different scenarios to test the robustness of our tomosynthesis implementation against object deviations (e.g., pen) and different object positioning. The circular tomosynthesis was tested on a ball bearing and an anthropomorphic phantom. The results show that the calibration is robust against isocenter shifts and object deviations in the CBCT. All reconstructions used 100 projections and displayed limited angle artifacts. The accuracy of the positions and shapes of high-contrast objects were, however, determined precisely. (The maximal center position deviation is 0.31mm.) CONCLUSION: For medical procedures that primarily determine the precise position of high-contrast objects, circular tomosynthesis could offer an approach to reduce dose exposure.

Three-dimensional CBCT images registration method for TMJ based on reconstructed condyle and skull base.

A method was introduced for three-dimensional (3D) cone-beamCT (CBCT) images registration of temporomandibular joint (TMJ). This study aimed to provide quantitative and qualitative analysis of TMJ bone changes in two-dimensional (2D) and 3D and to provide the technique for computer-aided diagnosis of temporomandibular joint disorders inthe future. 10 TMJ samples of six patients were obtained from Peking University Hospital of Stomatology. Four of the six patients imaged bilateral TMJs and the other two patients only imaged unilateral TMJ. Each sample consisted of two images from the same TMJ taken at different times. First, condyle and skull base were segmented semi-automatically for 3D model reconstruction. Then the segmented condyle and skull base were registered separately. Registration process can be divided into two processes of rough registration and fine registration. Rough registration step was achieved by selecting corresponding points manually and initialized fine registration. Condyle and skull base were fine registered by minimizing mean square error of condyle (MSEcondyle) and skull base (MSEskull) respectively. Qualitative assessment of osseous component changes utilized 2D color-fused model and 3D surface-fused model and quantitative analyses the convergence of this method used the mean square error of the model (MSEmodel). Independent repeated experiments were carried out to test the stability of our 3D registration method. Sufficiently alignment was achieved. Osseous abnormality and morphology changes were displayed using fusion model. MSEmodelof condylar registration and skull base registration declined 51.80% and 64.58% compared with that before registration. Quantitative analysis verified the stability of the method. The proposed method completed 3D TMJ registration for different physiological structure. The result of this method was accurate, reproducible and not relied on the experience of operators.

0553 Non-Surgical Osseous Remodeling and Myofunctional Therapy for Skeletal class III Malocclusion with Severe OSA

Obstructive Sleep Apnea (OSA), is a common sleep-disorder; causes of OSA vary, including decreased pharyngeal muscle tone, craniofacial obesity, and craniofacial deficiencies amongst others. Current treatments are continuous positive airway pressure therapy (CPAP), as well as MRA and MMA surgery. This study tests that if a non-surgical biomimetic oral appliance therapy (BOAT) DNA® System is used in combination with a sagittal expander and Myofunctional therapy for soft tissue remodeling and brain remapping; then AHI can be reduced in addition to oxygen desaturation. This study includes two class III adults: male A (45 years) with 65% oxygen desaturation and male B (45 years) with 78% oxygen desaturation. The cases were treated with FDA-cleared DNA Appliance© for osseous remodeling, and Myofunctional therapy for 6 months, followed by sagittal expansion. Before treatment the craniofacial region was imaged using 3D cone-beam CT scans. After 9 months of treatment, the apnea hypopnea index (AHI) was reassessed, without any appliance, by home sleep study (HST). The upper airway volume was reassessed with another 3D cone-beam CT scan and upper airway analysis. This process was repeated after the sagittal expander. For both cases, the mean AHI decreased from severe to mild, while the upper airway volume (from the posterior nasal spine to the epiglottis) increased by 15% and oxygen desaturation decreased. This preliminary study suggests that a decrease in AHI and oxygen desaturation may be associated with combined non-surgical osseous upper airway remodeling, a sagittal expander; and Myofunctional therapy, for soft tissue remodeling and brain pattern remapping, for skeletal class III with severe OSA in adults with craniofacial deficiencies. N/A.

Mandible and skull segmentation in cone beam computed tomography using super-voxels and graph clustering

Cone beam computed tomography (CBCT) is a medical imaging technique employed for diagnosis and treatment of patients with cranio-maxillofacial deformities. CBCT 3D reconstruction and segmentation of bones such as mandible or maxilla are essential procedures in surgical and orthodontic treatments. However, CBCT image processing may be impaired by features such as low contrast, inhomogeneity, noise and artifacts. Besides, values assigned to voxels are relative Hounsfield units unlike traditional computed tomography (CT). Such drawbacks render CBCT segmentation a difficult and time-consuming task, usually performed manually with tools designed for medical image processing. We present an interactive two-stage method for the segmentation of CBCT: (i) we first perform an automatic segmentation of bone structures with super-voxels, allowing a compact graph representation of the 3D data; (ii) next, a user-placed seed process guides a graph partitioning algorithm, splitting the extracted bones into mandible and skull. We have evaluated our segmentation method in three different scenarios and compared the results with ground truth data of the mandible and the skull. Results show that our method produces accurate segmentation and is robust to changes in parameters. We also compared our method with two similar segmentation strategy and showed that it produces more accurate segmentation. Finally, we evaluated our method for CT data of patients with deformed or missing bones and the segmentation was accurate for all data. The segmentation of a typical CBCT takes in average 5 min, which is faster than most techniques currently available.

A fast 4D cone beam CT reconstruction method based on the OSC-TV algorithm.

Four-dimensional cone beam computed tomography allows for temporally resolved imaging with useful applications in radiotherapy, but raises particular challenges in terms of image quality and computation time. The purpose of this work is to develop a fast and accurate 4D algorithm by adapting a GPU-accelerated ordered subsets convex algorithm (OSC), combined with the total variation minimization regularization technique (TV). Different initialization schemes were studied to adapt the OSC-TV algorithm to 4D reconstruction: each respiratory phase was initialized either with a 3D reconstruction or a blank image. Reconstruction algorithms were tested on a dynamic numerical phantom and on a clinical dataset. 4D iterations were implemented for a cluster of 8 GPUs. All developed methods allowed for an adequate visualization of the respiratory movement and compared favorably to the McKinnon-Bates and adaptive steepest descent projection onto convex sets algorithms, while the 4D reconstructions initialized from a prior 3D reconstruction led to better overall image quality. The most suitable adaptation of OSC-TV to 4D CBCT was found to be a combination of a prior FDK reconstruction and a 4D OSC-TV reconstruction with a reconstruction time of 4.5 minutes. This relatively short reconstruction time could facilitate a clinical use.