Evaluation of image reconstruction algorithms in cone-beam computed tomography technique

The aim of this study was to evaluate the accuracy of the results of cone beam computed tomography (CBCT) examinations, confirm the presence or absence of the second mesiobuccal (MB2) root canal in maxillary first and second molars, estimate the distance between the root canal orifices, observe the root types based on Vertucci classification system, and make comparisons between CBCT and periapical techniques in relation to the identification of the root canal form and the second root canal of the MB root. The CBCT and periapical radiographic data from the Department of Maxillofacial Radiology were used to select 156 individuals (78 females and 78 males) for the evaluation of the anatomy of maxillary first and second molars. The prevalence rate of the second root canal in the MB root in the maxillary first molars was 55.1%, with 44.1 and 63.3% in females and males respectively. The prevalence rate in maxillary second molars was 23.7%, with 15.7 and 30.2% in females and males respectively. In addition, the longest and shortest distances between the root canal orifices were 2.4 and 0.3 mm respectively, with a mean of 1.3 mm. There was a significant difference between the results of periapical and CBCT radiographic techniques in relation to the presence or absence of the second root canal in the MB roots of maxillary first and second molars (p < 0.01), with better results being provided by the CBCT technique. The results of CBCT images about the existence of the second root canal in the MB roots of maxillary first and second molars are more reliable, and we can use this technique in the finding of additional canals in the clinic. Keyword: Cone beam computed tomography, Dental radiography, Root canal therapy.

The purpose of this study was to investigate and compare microcalcification detectability using Digital Tomosynthesis (DTS), Dual Energy Mammography (DEM) and Cone Beam Computed Tomography (CBCT) with a flat-panel detector. A simulated 3D uncompressed breast approximating the medium sized breast, with 50% adipose and 50% glandular tissue was used. Microcalcifications were modeled as calcium carbonate spheres/ellipsoids with size in full range of 0.1 to 1mm. An amorphous-silicon CsI flatdetector, 2048 × 2048 mm2 at 0.1mm resolution was modeled. Images from the above phantom were simulated using three acquisition protocols for DTS, DEM and CBCT. For DTS, projections data were acquired for an acquisition arc from −200 to 200 with 20 sampling step, and the 3D reconstructed volume was obtained using a Multiple Projection Algorithm (MPA), with a 0.1 mm width between successive tomograms. In the DEM case, two synthetic projection images at 21 and 52 KeV respectively were simulated. A weighted subtraction of low and high — energy digital X-ray images was performed, allowing the removal of background morphology and enhancement of the obscured details. For the last method (CBCT), 181 projections acquired every 20 over a full circular scanning path were used for 3D breast volume reconstruction using the well-known FDK algorithm. The image quality of the reconstructed tomograms was visually assessed and quantified in terms of contrast to noise ratio (CNR), relative detail contrast (RC), as well as Artifacts Spread Function (ASF). The results show that microcalcifications with diameter equal or greater than 0.1mm can be detected, with the CBCT and DTS techniques. Superior quality is demonstrated by CBCT technique in comparison with DTS and DE by means of better microcalcification detection.Keywordsdual energy mammographytomosynthesiscone beam breast CT

Convergence rate calculation of simultaneous iterative reconstruction technique algorithm for diffuse optical tomography image reconstruction: A feasibility study

Background and objectives:Anatomy of the root canal system and determining the number and form of the canals are the most important steps for a successful root canal therapy without post-operative complications. The evidence supports the variability and complexity of maxillary molars. The aim of this study was to evaluate the prevalence of the additional mesiobuccal canals in the mesiobuccal roots, root canal configuration and root numbers of first and second permanent maxillary molars through the cone beam computed tomography (CBCT) technique. Methods:One hundred patients’ images taken of maxillary first and second molars bilaterally by cone beam computed tomography technique. Classification of first and second molar root canals was performed in accordance with Vertucci’s classifi- cation system. The patterns of anatomical variations in contralateral molars were classified according to the Zhang classification system. Results: The present study found that three roots were the most prevalent numbers of roots in the right and left, first and second molars, 96.0%, 75.0%, 97.0%, and 72.0%, respectively. In addition, the prevalence of additional mesiobuccal canals in both the right and left, first and second molars were 45.0%, 20.0%, 40.0%, and 27.0%, respectively. Conclusion: Tooth variant type I of Zheng et al classification and type I of Vertucci’s classification of the root canal system was the most prevalent type.

Optical projection tomography (OPT) is an advanced three-dimensional (3D) imaging technology, which uses the filtered backprojection (FBP) algorithm to recover the 3D volume with sufficient number of projections. As to in vivo imaging, it is urgent to reduce the number of projections because the acquisition time could be minimized. However, reconstructing from undersampled OPT data can lead to artifacts and the decline in image quality. The simultaneous iterative reconstruction technique (SIRT) is introduced to remove artifacts and improve the image quality. The image qualities reconstructed from FBP and SIRT separately are compared, and the structural similarity and peak signal-to-noise ratio are calculated. Through simulated phantoms and OPT data of in vivo zebrafish embryo, SIRT consistently outperforms FBP in terms of reduced artifacts and enhanced image contrast especially when the projection numbers are reduced. SIRT method can provide high-quality reconstruction with 50 or fewer projections, thereby significantly reducing the minimum acquisition time and light dose while maintaining reconstruction quality. Through optimization and GPU acceleration, the SIRT algorithm can converge faster so as to reduce the image processing time. To our knowledge, this is the first time one SIRT algorithm is used for reconstruction of sparse OPT data. The experimental results show that SIRT algorithm outperform FBP especially when the number of projections is reduced. In addition, SIRT performs better in the preservation of vascular signal, which is significant for the monitoring of angiogenesis.

Purpose:To present a cone beam computed tomography (CBCT) system, which uses a synchronized moving grid (SMOG) to reduce and correct scatter, an inter‐projection sensor fusion (IPSF) algorithm to estimate the missing information blocked by the grid, and a probability total variation (pTV) algorithm to reconstruct the CBCT image.Methods:A prototype SMOG‐equipped CBCT system was developed, and was used to acquire gridded projections with complimentary grid patterns in two neighboring projections. Scatter was reduced by the grid, and the remaining scatter was corrected by measuring it under the grid. An IPSF algorithm was used to estimate the missing information in a projection from data in its 2 neighboring projections. Feldkamp‐Davis‐Kress (FDK) algorithm was used to reconstruct the initial CBCT image using projections after IPSF processing for pTV. A probability map was generated depending on the confidence of estimation in IPSF for the regions of missing data and penumbra. pTV was finally used to reconstruct the CBCT image for a Catphan, and was compared to conventional CBCT image without using SMOG, images without using IPSF (SMOG + FDK and SMOG + mask‐TV), and image without using pTV (SMOG + IPSF + FDK).Results:The conventional CBCT without using SMOG shows apparent scatter‐induced cup artifacts. The approaches with SMOG but without IPSF show severe (SMOG + FDK) or additional (SMOG + TV) artifacts, possibly due to using projections of missing data. The 2 approaches with SMOG + IPSF removes the cup artifacts, and the pTV approach is superior than the FDK by substantially reducing the noise. Using the SMOG also reduces half of the imaging dose.Conclusion:The proposed technique is promising in improving CBCT image quality while reducing imaging dose.

To obtain useful knowledge and experience of CCERT under different excitation patterns, the image reconstruction performance of a 12-electrode CCERT sensor under five different excitation patterns (1-electrode excitation pattern, 2-electrode excitation pattern, 3-electrode excitation pattern, 4-electrode excitation pattern, and 5-electrode excitation pattern) are investigated and compared. A 12-electrode CCERT prototype, which can implement different excitation patterns, is developed to obtain the practical experiment data. Four typical image reconstruction algorithms (Linear Back Projection (LBP) algorithm, Landweber’s iteration algorithm, Algebraic Reconstruction Technique (ART) algorithm, and Simultaneous Iterative Reconstruction Technique (SIRT) algorithm) are introduced to investigate and compare the image reconstruction performance with the experimental data obtained from the CCERT prototype. Research results show that the 1-electrode excitation pattern and the 2-electrode excitation pattern have better global image reconstruction performance. These two excitation patterns are better choices, while the 3-electrode excitation pattern, the 4-electrode excitation pattern, and the 5-electrode excitation pattern are not recommended.

Unlike patients receiving implants or endodontic treatment, most orthodontic patients are children who are particularly sensitive to ionizing radiation. Cone-beam computed tomography (CBCT) carries risks and benefits in orthodontics. The principal risks and limitations include ionizing radiation, the presence of artifacts, higher cost, limited accessibility, and the need for additional training. However, this imaging modality has several recognized indications in orthodontics, such as the assessment of impacted and ectopic teeth, assessment of pharyngeal airway, assessment of mini-implant sites, evaluation of craniofacial abnormalities, evaluation of sinus anatomy or pathology, evaluation of root resorption, evaluation of the cortical bone plate, and orthognathic surgery planning and evaluation. CBCT is particularly justified when it brings a benefit to the patient or changes the outcome of the treatment when compared with conventional imaging techniques. Therefore, CBCT should be considered for clinical orthodontics for selected patients. Prescription of CBCT requires judicious and sound clinical judgment. The central question of this narrative review article is: when does CBCT add value to the practice of orthodontics? To answer this question, this article presents discussion on radiation dosage of CBCT and other imaging techniques used in orthodontics, limitations of CBCT in orthodontics, justifying the use of CBCT in orthodontics, and the benefits and evidence-based indications of CBCT in orthodontics. This review summarizes the central themes and topics in the literature regarding CBCT in orthodontics and presents ten orthodontic cases in which CBCT proved to be valuable.

The use of transmission electron tomography for three dimensional morphology analysis of nanostructured materials has grown significantly in recent years due to the improved robustness of automated image collection, alignment and reconstruction routines. Although the amount of published 3D electron tomography data has increased accordingly, in many cases the data is used purely for visualization purposes, due to the difficulty of making quantitative measurements from the as-reconstructed data. This is due to the traditionally difficult step of segmentation of the 3D image volume, which has been hindered due to noise, artifacts and lack of necessary image detail or sharpness. In this work the Simultaneous Iterative Reconstruction Technique (SIRT) is used to reconstruct High Angle Annular Dark Field-Scanning Transmission Electron Microscopy (HAADF-STEM) tomography data. The number of SIRT iterations is varied to optimize the reconstruction for segmentation. In particular, signal to noise ratio, signal to artifact ratio, and image blur are identified as parameters which each contribute to the suitability of the reconstruction for segmentation. The Expectation Maximization/ Maximization of Posterior Marginals image segmentation algorithm is applied to the SIRT reconstructions, and the resulting Average Intensity Projection (AIP) of the segmented image stack is compared to the raw tomography projection data.

Examples of extracting meaningful information from image projection data using tomographic reconstruction techniques can be found in many areas of science. Within the photochemical dynamics community, tomography allows for complete three-dimensional (3D) charged particle momentum distributions to be reconstructed following a photodissociation or photoionization event. This permits highly differential velocity- and angle-resolved measurements to be made simultaneously. However, the generalized tomographic reconstruction strategies typically adopted for use with photochemical imaging-based around the Fourier-slice theorem and filtered back-projection algorithms-are not optimized for these specific types of problems. Here, we discuss pre-existing alternative strategies-namely, the simultaneous iterative reconstruction technique and Hankel Transform Reconstruction (HTR)-and introduce them in the context of velocity-map imaging applications. We demonstrate the clear advantages they afford, and how they can perform considerably better than approaches commonly adopted at present. Most notably, with HTR we can set a bound on the minimum number of projections required to reliably reconstruct 3D photoproduct distributions. This bound is significantly lower than what is currently accepted and will help make tomographic imaging far more accessible and efficient for many experimentalists working in the field of photochemical dynamics.

Aim: This study primarily aimed to assess the accuracy of classically-advocated reference points for the measurement of transverse jaw-base and dental relationships using conventional Postero-Anterior Cephalometry (PAC) and Cone-Beam Computed Tomography (CBCT). Method: PAC and CBCT images were collected from 31 randomly selected orthodontic patients (12 males, 19 females), all of whom had a full permanent dentition. The transverse widths of the maxilla, mandible and the dentition were measured using reference points on both image modalities. Confidence intervals, intra-class coefficients and Bland Altman plots were used to assess the measurement differences derived from the two acquirement methods. Results: Measurements on PAC and CBCT images demonstrated statistically significant differences in the majority of the assessed variables. The interjugal (J-J) width was one of only two variables which did not demonstrate a statistically significant difference on image comparison. The mean differences of the antegonial width (Ag-Ag) (-4.44mm, 95% CI -5.38 to -3.51) represented the greatest difference between the imaging techniques. The application of these points to a transverse skeletal analysis (J-J/Ag-Ag ratio) revealed that five of the 31 subjects (16%) recorded ‘false positive’ readings according to the derived data. Conclusion: It is recommended that clinicians are cautious when interpreting and making decisions related to transverse dimensions derived from a PAC. The PAC has a higher tendency to falsely identify individuals who require maxillary expansion procedures based on conventional clinical criteria. The errors primarily associated with identifying structures which represent the width of the mandible are significant in both PAC and CBCT techniques and require further investigation. It is postulated that the confounding effects of overlying soft tissues have a significant impact on a clinician’s ability to identify relevant landmarks.

Background:Epidural blood patch (EBP) is a common method utilized to treat intracranial hypotension, and secondarily, to treat unintentional dural puncture. The authors propose an effective technique for correct epidural needle positioning during EBP using cone-beam computed tomography (CB-CT) images.Case Description:A 31-year-old female underwent an EBP. Following confirmation of the spinal level of the cerebrospinal fluid leakage, the ideal trajectory for the proposed EBP was assessed from the entry point on the skin to the spinolaminar line under CB-CT imaging. The epidural needle was then gently advanced along the appropriate trajectory. At the 10 mm mark, behind the spinolaminar line, the inner needle was removed. This allowed for slow advancement of the outer needle until its tip reached the epidural space, and its location was confirmed by the “loss of resistance to the saline technique.” Using biplane epidurography, the spread of dye within the epidural space for appropriate localization was confirmed. In this case study, the patient’s postural headache immediately improved.Conclusion:Using the CB-CT technique described, a patient successfully underwent EBP without complications.

OA158] Noise equivalent number of quanta (NEQ): A tool for choosing the optimal reconstruction algorithm in computed tomography (CT)

Background: An accurate working length plays a pivotal role for the success of treatment in endodontics. It involves a wide array of procedures. Aim: Use of digital radiovisiography (RVG), apex locator (EAL) and cone beam computed tomography technique (CBCT) to evaluate working length in primary teeth. Materials and Methods: This study included thirty extracted primary teeth having at least 2/3rd of root. Alginate was combined with 0.9% normal saline solution and teeth were inserted in it after access opening. Two qualified examiners recorded working length for all canals twice with RVG, EAL and CBCT. In control group, a Kerr- file from coronal reference to the apical foramen was used to visually determine the actual (AL) under stereomicroscope. Statistical analysis: Intraclass correlation coefficient (ICC) and Bland and Altman analysis were used to calculate the agreement on measurements of all methods using actual values of different methods. Results: Electronic working length measured with AL (0.0007) was statistically significant compared to RVG (1.9570) and CBCT (0.8440). Amongst all methods for determination of working length the ICC showed the highest reliability for EAL and least for RVG. Conclusion: In comparison to RVG and CBCT, the EALperformed the best for determining working length in primary teeth.

BackgroundRapid kV cone‐beam computed tomography (CBCT) scans are achievable in under 20 s on select linear accelerator systems to generate volumetric images in three dimensions (3D). Daily pre‐treatment four‐dimensional CBCT (4DCBCT) is recommended in image‐guided lung radiotherapy to mitigate the detrimental effects of respiratory motion on treatment quality.PurposeTo demonstrate the potential for thoracic 4DCBCT reconstruction using projection data that was simulated using a clinical rapid 3DCBCT acquisition protocol.MethodsWe simulated conventional (1320 projections over 4 min) and rapid (491 projections over 16.6 s) CBCT acquisitions using 4D computed tomography (CT) volumes of 14 lung cancer patients. Conventional acquisition data were reconstructed using the 4D Feldkamp‐Davis‐Kress (FDK) algorithm. Rapid acquisition data were reconstructed using 3DFDK, 4DFDK, and Motion‐Compensated FDK (MCFDK). Image quality was evaluated using Contrast‐to‐Noise Ratio (CNR), Tissue Interface Width (TIW), Root‐Mean‐Square Error (RMSE), and Structural SIMilarity (SSIM).ResultsThe conventional acquisition 4DFDK reconstructions had median phase averaged CNR, TIW, RMSE, and SSIM of 2.96, 8.02 mm, 83.5, and 0.54, respectively. The rapid acquisition 3DFDK reconstructions had median CNR, TIW, RMSE, and SSIM of 2.99, 13.6 mm, 112, and 0.44 respectively. The rapid acquisition MCFDK reconstructions had median phase averaged CNR, TIW, RMSE, and SSIM of 2.98, 10.2 mm, 103, and 0.46, respectively. Rapid acquisition 4DFDK reconstruction quality was insufficient for any practical use due to sparse angular projection sampling.ConclusionsResults suggest that 4D motion‐compensated reconstruction of rapid acquisition thoracic CBCT data are feasible with image quality approaching conventional acquisition CBCT data reconstructed using standard 4DFDK.