Actual Scans Research Articles

The Effect of Electroencephalography Leads on Image Quality in Cerebral Perfusion SPECT and 18F-FDG PET/CT.

Cerebral perfusion SPECT and 18F-FDG PET/CT are commonly performed diagnostic procedures for patients with epilepsy. Individuals undergoing these tests are often inpatients with electroencephalography leads. We have routinely removed these leads because of concern that they would lead to imaging artifacts. The leads would then be replaced at the conclusion of the scan. The goal of our study was to determine whether the electroencephalography leads actually do cause artifacts that can lead to erroneous scan interpretation or make the scan uninterpretable. Methods: 18F-FDG PET/CT and 99mTc-pertechnetate SPECT were performed on a 2-dimensional brain phantom. The phantom was scanned with standard leads, CT/MR-compatible leads, and no leads. The quality of the images was ranked by 3 experienced nuclear medicine physicians, who then determined whether they could differentiate each of the scans from a scan in which it was known that no leads were present. Results: No differences could be detected between scans obtained without leads and scans obtained with either set of leads. The standard electroencephalography leads did create artifacts in the CT portion of the PET/CT images, whereas the CT/MR-compatible leads did not. Conclusion: This phantom study suggests that electroencephalography leads, whether standard or CT/MR-compatible, do not need to be removed for SPECT or PET procedures. Further study evaluating the effect on actual patient scans would be of value to support this conclusion.

A new method for CT dose estimation by determining patient water equivalent diameter from localizer radiographs: Geometric transformation and calibration methods using readily available phantoms.

Water equivalent diameter (Dw) reflects patient's attenuation and is a sound descriptor of patient size, and is used to determine size-specific dose estimator from a CT examination. Calculating Dw from CT localizer radiographs makes it possible to utilize Dw before actual scans and minimizes truncation errors due to limited reconstructed fields of view. One obstacle preventing the user community from implementing this useful tool is the necessity to calibrate localizer pixel values so as to represent water equivalent attenuation. We report a practical method to ease this calibration process. Dw is calculated from water equivalent area (Aw) which is deduced from the average localizer pixel value (LPV) of the line(s) in the localizer radiograph that correspond(s) to the axial image. The calibration process is conducted to establish the relationship between Aw and LPV. Localizer and axial images were acquired from phantoms of different total attenuation. We developed a program that automates the geometrical association between axial images and localizer lines and manages the measurements of Dw and average pixel values. We tested the calibration method on three CT scanners: a GE CT750HD, a Siemens Definition AS, and a Toshiba Acquilion Prime80, for both posterior-anterior (PA) and lateral (LAT) localizer directions (for all CTs) and with different localizer filters (for the Toshiba CT). The computer program was able to correctly perform the geometrical association between corresponding axial images and localizer lines. Linear relationships between Aw and LPV were observed (with R2 all greater than 0.998) on all tested conditions, regardless of the direction and image filters used on the localizer radiographs. When comparing LAT and PA directions with the same image filter and for the same scanner, the slope values were close (maximum difference of 0.02mm), and the intercept values showed larger deviations (maximum difference of 2.8mm). Water equivalent diameter estimation on phantoms and patients demonstrated high accuracy of the calibration: percentage difference between Dw from axial images and localizers was below 2%. With five clinical chest examinations and five abdominal-pelvic examinations of varying patient sizes, the maximum percentage difference was approximately 5%. Our study showed that Aw and LPV are highly correlated, providing enough evidence to allow for the Dw determination once the experimental calibration process is established.

The art of mapping IoT devices in networks

Improperly secured Internet of Things (IoT) devices have been commandeered by bot herders and other malicious attackers. Organisations need a way to identify and track these IoT devices, which are often brought in unofficially by users. But network administrators face a number of challenges in tracking IoT devices across their organisation. Improperly secured Internet of Things (IoT) devices have been exploited by bot herders and other malicious attackers. So organisations need a way to identify and track these devices. Pranshu Bajpai, Aditya Sood and Richard J Enbody look at the difficulty of defining identifying characteristics of IoT devices due to their immensely diverse nature. They offer a model to identify IoT devices in networks using a variety of scanning techniques and they discuss the pros and cons of discovery techniques, presenting results from actual scans.

Augmented Reality Presentation of Anatomical Variations

IntroductionRecognition of anatomical variations is critical for proper diagnosis and management. Although the literature provides detailed descriptions and images, structures and mechanisms are still often difficult to conceptualize. Augmented reality (AR) is a novel visualization tool that could enable effective understanding of variations. Here we use AR to present aberrant right subclavian arteries (ARSA), and assess its usefulness within the context of anatomy education within the medical school curriculum.MethodsTwo ARSA's were identified during routine dissections and quantitative characterization was performed. A plastinated heart was created and subjected to photogrammetry. Utilizing quantitative features of dissected specimens, ARSA was modeled and viewed within 3D space. An animation of its embryological mechanism was also created. The goal of this study was to assess the usefulness of this animation and AR for learning ARSA. First year medical students (N=125) participated in the online activity (including pre‐ and post‐tests) utilizing text, images and a 3D SketchFab (www.sketchfab.com) model to learn ARSA, and either text or narrated animation for its embryological mechanism. Students then completed a quiz and perception survey based on traditional resources alone or after visualization of the ARSA hologram as well. Comparisons were analyzed using paired sample t‐tests with p <.05 as the level of statistical significance.ResultsGroups performed similarly on the typical structures quiz (86.67% and 85.13%) and ARSA pre‐test (51.67% and 52.92%). Post‐test scores improved overall, and although the group with animation scored better, difference was not statistically significant (82.2%, compared to 76.7% (text), (NS)). Students found the SketchFab model to be helpful for learning ARSA, rating it as 4.4/5 (1: Not helpful; 5: Very helpful). For the embryological mechanism, 90% found the narrated animation more helpful than text. Regarding AR, both groups scored similarly, 76.3% (no AR) and 83.2% (with AR) (NS). Students viewed AR favorably, rating its helpfulness as 4.3/5 and ranked resources for learning ARSA from most to least helpful as follows (most common): 1) AR tool, 2) QuickTime, 3) SketchFab model, 4) Text, (p<0.01).ConclusionAugmented reality, alongside traditional resources, is a promising tool that could facilitate better understanding and retention of anatomical variations. In the classroom, AR could also be used for teaching complex anatomy concepts. In clinical practice it may be useful for patient education and could also serve as a more time‐efficient and cost‐effective way to plan complex surgical cases compared to current 3D printing of models. Work is being directed at developing 3D AR models from actual medical scans (of ARSA and complex pediatric surgical cases) and at developing tools to further assess usefulness of AR.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Analysis of 3D Scan Measurement Distribution with Application to a Multi-Beam Lidar on a Rotating Platform.

Multi-beam lidar (MBL) rangefinders are becoming increasingly compact, light, and accessible 3D sensors, but they offer limited vertical resolution and field of view. The addition of a degree-of-freedom to build a rotating multi-beam lidar (RMBL) has the potential to become a common solution for affordable rapid full-3D high resolution scans. However, the overlapping of multiple-beams caused by rotation yields scanning patterns that are more complex than in rotating single beam lidar (RSBL). In this paper, we propose a simulation-based methodology to analyze 3D scanning patterns which is applied to investigate the scan measurement distribution produced by the RMBL configuration. With this purpose, novel contributions include: (i) the adaption of a recent spherical reformulation of Ripley’s K function to assess 3D sensor data distribution on a hollow sphere simulation; (ii) a comparison, both qualitative and quantitative, between scan patterns produced by an ideal RMBL based on a Velodyne VLP-16 (Puck) and those of other 3D scan alternatives (i.e., rotating 2D lidar and MBL); and (iii) a new RMBL implementation consisting of a portable tilting platform for VLP-16 scanners, which is presented as a case study for measurement distribution analysis as well as for the discussion of actual scans from representative environments. Results indicate that despite the particular sampling patterns given by a RMBL, its homogeneity even improves that of an equivalent RSBL.

Reweighted Anisotropic Total Variation Minimization for Limited-Angle CT Reconstruction

Limited-angle problems encountered in computed tomography (CT) often necessitate image reconstruction using projection data from a particular angle range. To solve this severely ill-posed problem, prior information is utilized to constrain the problem. As a special case of compressed sensing, a total variation (TV) transform with an $l_{1}$ -norm image gradient is utilized in most cases, and manages to obtain very impressive reconstruction results. However, it is unfit for limited-angle problems owing to its isotropic property. This paper proposes a new iteratively reweighted anisotropic TV (ATV) method, in which a reweighted technique is incorporated into the idea of ATV. Our strategy successfully combines their merits and results in significantly improved performance. By using the reweighted technique, we are able to approximate the most direct measure of sparsity— $l_{0}$ -norm—better than $l_{1}$ -norm. As a result, the property of image sparsity can be utilized more efficiently. Because TV is isotropic, which prevents detection of blurred edges caused by missing angle ranges and may weaken edge-preserving ability along nonblurred directions, we consider the angle range of the data as additional prior information by assigning different weights to different directions; this allows the anisotropic property to be utilized. Therefore, the blurred directions can be prevented from affecting edge detection, and better reconstruction results can be achieved. To demonstrate the advantages of our method, we perform reconstruction using projection data from phantom CT scans and actual CT scans. We conducted comprehensive comparison between our method and many existing TV-based methods. Both qualitative and quantitative results are presented.

Systematic approaches for reviewing neuro-imaging scans in ophthalmology.

Neuroimaging is an important tool in ophthalmology, but many ophthalmologists are uncomfortable evaluating actual scans. Unfortunately, exclusive reliance on a radiologist's report can lead to diagnostic and management errors. We outline a methodology for equipping ophthalmologists with the skills necessary to read neuroimaging studies with respect to specific clinical questions.

Fast Fourier-based simulation of off-resonance artifacts in steady-state gradient echo MRI applied to metal object localization.

PurposeTo accelerate simulation of off‐resonance artifacts in steady‐state gradient echo MRI by using fast Fourier transforms and demonstrate its applicability to metal object localization.Theory and MethodsBy exploiting the repetitive nature of steady‐state pulse sequences it is possible to use fast Fourier transforms to calculate the MR signal. Based on this principle, a method for fast simulation of off‐resonance artifacts was designed. The method was validated against Bloch simulations and MRI scans. Its clinical relevance was demonstrated by employing it for template matching‐based metal object localization, as applied to a titanium cylinder, an oxidized zirconium knee implant, and gold fiducials.ResultsThe fast simulations were accurate compared with actual MRI scans of the objects. The differences between the fast simulations and Bloch simulations were minor, while the acceleration scaled linearly with the number of phase‐encoding lines. The object localization method accurately localized the various metal objects.ConclusionThe proposed simulation methodology provided accurate 3D simulations of off‐resonance artifacts with a lower computational complexity than Bloch simulations. The speed of the simulations opens up possibilities in image reconstructions involving off‐resonance phenomena that were previously infeasible due to computational limitations, as demonstrated for metal object localization. Magn Reson Med 78:2035–2041, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

On stochastic FEM based computational homogenization of magneto-active heterogeneous materials with random microstructure

In the current work we apply the stochastic version of the FEM to the homogenization of magneto-elastic heterogeneous materials with random microstructure. The main aim of this study is to capture accurately the discontinuities appearing at matrix-inclusion interfaces. We demonstrate and compare three different techniques proposed in the literature for the purely mechanical problem, i.e. global, local and enriched stochastic basis functions. Moreover, we demonstrate the implementation of the isoparametric concept in the enlarged physical-stochastic product space. The Gauss integration rule in this multidimensional space is discussed. In order to design a realistic stochastic Representative Volume Element we analyze actual scans obtained by electron microscopy and provide numerical studies of the micro particle distribution. The SFEM framework described in our previous work (Pivovarov and Steinmann in Comput Mech 57(1): 123---147, 2016) is extended to the case of the magneto-elastic materials. To this end, the magneto-elastic energy function is used, and the corresponding hyper-tensors of the magneto-elastic problem are introduced. In order to estimate the methods' accuracy we performed a set of simulations for elastic and magneto-elastic problems using three different SFEM modifications. All results are compared with "brute-force" Monte-Carlo simulations used as reference solution.

Radiation Dose and Image Quality Assessment of the Bolus Timing Method for CT Angiography

Background: Bolus timing monitoring scans used for computed tomography angiography (CTA) repetitively expose the same region of the body to radiation with a view to determining the appropriate threshold attenuation level of the contrast material (CM). Therefore, for an effective CT scan, it is necessary to minimize repetitive radiation exposures from bolus timing. Objectives: This study aims to effectively identify and reduce the radiation dose needed for repetitive monitoring scans utilized in CT involving the bolus timing method. Patients and Methods: To investigate the currently employed protocols and the number of monitoring scans in bolus timing CT studies, 983 patients (581 males and 402 females; mean age 62.7) were retrospectively analyzed from October 1, 2013 to March 31, 2014. To identify the appropriate kVp and mA change in the hounsfield unit (HU) and measure the contrast-to-noise ratio (CNR) and the signal-to-noise ratio (SNR) in the bolus timing method, a 2 mL syringe containing CM diluted with saline at a ratio of 1 to 300 was inserted into cavities of a CT dose index (CTDI) head phantom and scanned with a 64-section multi-detector row CT system. The dose variation was analyzed using results from the ionization chamber and CTDI. Results: This retrospective analysis of bolus-timing CT studies found that patients underwent an average of 4.5 to 5.4 monitoring scans. Furthermore, while the HU value of the mixed CM syringe in the central CTDI head phantom cavity was inversely proportional to mA, the decrease in the HU value became weaker at a value of 50 mA with 100 kVp and at 30 mA with 120 kVp. Here, the CNR (Pearson correlation r = 0.983, Kendall’s t = 0.978, P < 0.000) became slightly higher with an increase in mA at 100 kVp compared to 120 kVp, whereas the SNR (Pearson correlation r = 0.997, Kendall’s t = 1.0, P < 0.000) became similar to 100 kVp. Conclusion: It is recommended that minimum level of radiation (100 kVp, 50 mA; 120 kVp, 30 mA) at which the HU value at the trigger threshold is not significantly different from that of the actual helical scans should be used to minimize the radiation dose caused by repetitive monitoring scans in the bolus timing method.

Pulmonary Nodule Detection from X-ray CT Images Based on Region Shape Analysis and Appearance-based Clustering

In this paper, we propose a detection method of pulmonary nodules in X-ray computed tomography (CT) scans by use of three image filters and appearance-based k-means clustering. First, voxel values are suppressed in radial directions so as to eliminate extra regions in the volumes of interest (VOIs). Globular regions are enhanced by moment-of-inertia tensors where the voxel values in the VOIs are regarded as mass. Excessively enhanced voxels are reduced based on displacement between the VOI centers and the gravity points of the voxel values in the VOIs. Initial nodule candidates are determined by these filtering processings. False positives are reduced by, first, normalizing the directions of intensity distributions in the VOIs by rotating the VOIs based on the eigenvectors of the moment-of-inertia tensors, and then applying an appearance-based two-step k-means clustering technique to the rotated VOIs. The proposed method is applied to actual CT scans and experimental results are shown.

Influence of disc degeneration on the development of disc prolapse

The present clinical-radiological study examines retrospectively the relation between lumbar disc prolapse and degenerations like chondrosis and spondylosis. Firstly the relation between disc prolapse and chondrosis was examined. 44 patients with disc prolapse and chondrosis in actual MRI scans in the same segment were recruited in our clinic. By regarding older MRI scans, we could find out which finding was first to occur. Concerning the second question, we followed patients with spondylosis to see if they could progress to a disc prolapse. In 67% of our cases with disc prolapse and chondrosis, a chondrosis was seen before the disc prolapse. More than a half had had a spondylosis and a chondrosis in the same segment before the herniation. Only 33% of our cases showed a prolapse before chondrosis. Concerning patients with disc prolapse and chondrosis in the same segment, chondrosis was seen before the herniation in most cases. Also patients with spondylosis progress to a herniation. A causal relation between both radiological findings is not possible. In a future study it must be analysed with statistical tests whether these results are generally valid.

PET attenuation correction using synthetic CT from ultrashort echo-time MR imaging.

Integrated PET/MR systems are becoming increasingly popular in clinical and research applications. Quantitative PET reconstruction requires correction for γ-photon attenuations using an attenuation coefficient map (μ map) that is a measure of the electron density. One challenge of PET/MR, in contrast to PET/CT, lies in the accurate computation of μ maps. Unlike CT, MR imaging measures physical properties not directly related to electron density. Previous approaches have computed the attenuation coefficients using a segmentation of MR images or using deformable registration of atlas CT images to the space of the subject MR images. In this work, we propose a patch-based method to generate whole-head μ maps from ultrashort echo-time (UTE) MR imaging sequences. UTE images are preferred to other MR sequences because of the increased signal from bone. To generate a synthetic CT image, we use patches from a reference dataset, which consists of dual-echo UTE images and a coregistered CT scan from the same subject. Matching of patches between the reference and target images allows corresponding patches from the reference CT scan to be combined via a Bayesian framework. No registration or segmentation is required. For evaluation, UTE, CT, and PET data acquired from 5 patients under an institutional review board-approved protocol were used. Another patient (with UTE and CT data only) was selected to be the reference to generate synthetic CT images for these 5 patients. PET reconstructions were attenuation-corrected using the original CT, our synthetic CT, Siemens Dixon-based μ maps, Siemens UTE-based μ maps, and deformable registration-based CT. Our synthetic CT-based PET reconstruction showed higher correlation (average ρ = 0.996, R(2) = 0.991) to the original CT-based PET, as compared with the segmentation- and registration-based methods. Synthetic CT-based reconstruction had minimal bias (regression slope, 0.990), as compared with the segmentation-based methods (regression slope, 0.905). A peak signal-to-noise ratio of 35.98 dB in the reconstructed PET activity was observed, compared with 29.767, 29.34, and 27.43 dB for the Siemens Dixon-, UTE-, and registration-based μ maps. A patch-matching approach to synthesize CT images from dual-echo UTE images leads to significantly improved accuracy of PET reconstruction as compared with actual CT scans. The PET reconstruction is improved over segmentation- (Dixon and Siemens UTE) and registration-based methods, even in subjects with pathologic findings.

SU‐F‐BRF‐14: Increasing the Accuracy of Dose Calculation On Cone‐Beam Imaging Using Deformable Image Registration in the Case of Prostate Translation

Purpose:Artifacts can reduce the quality of dose re‐calculations on CBCT scans during a treatment. The aim of this project is to correct the CBCT images in order to allow for more accurate and exact dose calculations in the case of a translation of the tumor in prostate cancer.Methods:Our approach is to develop strategies based on deformable image registration algorithms using the elastix software (Klein et al., 2010) to register the treatment planning CT on a daily CBCT scan taken during treatment. Sets of images are provided by a 3D deformable phantom and comprise two CT and two CBCT scans: one of both with the reference anatomy and the others with known deformations (i.e. translations of the prostate). The reference CT is registered onto the deformed CBCT and the deformed CT serves as the control for dose calculation accuracy. The planned treatment used for the evaluation of dose calculation is a 2‐Gy fraction prescribed at the location of the reference prostate and assigned to 7 rectangular fields.Results:For a realistic 0.5‐cm translation of the prostate, the relative dose discrepancy between the CBCT and the CT control scan at the prostate's centroid is 8.9 ± 0.8 % while dose discrepancy between the registered CT and the control scan lessens to −2.4 ± 0.8 %. For a 2‐cm translation, clinical indices like the V90 and the D100 are more accurate by 0.7 ± 0.3 % and 8.0 ± 0.5 cGy respectively when using registered CT than when using CBCT for dose calculation.Conclusion:The results show that this strategy gives doses in agreement within a few percents with those from calculations on actual CT scans. In the future, various deformations of the phantom anatomy will allow a thorough characterization of the registration strategies needed for more complex anatomies.

Feasibility of Merging Sacroiliac Fusion Computed Tomography Preoperative Planning to Original Computed Tomography Scans

Background: Spinal merging has been done with preoperative CT scans merged with fluoroscopic imaging. However, preoperative and intraoperative CT scans have not been merged for the purposes of transferring a plan. If spine surgeons can create the optimal surgical pathway before surgery and then merge the pre-planned pathway onto the real patient CT scan in the operating room, the result will be efficiency and better time management for the spine surgeon. Our objective was to analyze the feasibility of merging computed tomography (CT) preplanned with sacroiliac fusion iliosacral screw trajectories with the original CT scans. Methods: Twenty-seven patients were identified from the institutional Faculty Group Practice who had undergone CT scans in the pelvic region. The pelvic CT scans were transferred to Medtronic's StealthStation ® , which allowed for analysis in coronal, sagittal, and axial sections. Three trajectories were mapped out, representing three working pathways for fixation. The position of the trajectories was localized by measuring their distance from anatomic landmarks. The CT scan with the planned trajectories was merged with the original CT scan. The same measurements made pre-merge were performed post-merge to check for the accuracy of the merging process. Results: Post-merge measurements were nearly identical to pre-merge measurements, with a maximum difference of ± 0.1 mm. No significant differences existed between pre-merge and post-merge measurements for any of the trajectories Conclusion: The merging of preplanned trajectory CT scans with intraoperative CT scans is a highly accurate technique. Clinical relevance: If this technique can be replicated by merging actual pre-operative CT scans with actual intra- operative scans, it could save time and expense. This would benefit the patient because time under anesthesia would be reduced.

WE‐C‐103‐04: The Optimization of CT Protocols Using Plots of CTDIvol and of Max and Min MA Versus Patient Size for Actual Clinical Scans Using Automatic Exposure Control (AEC)

Purpose: To determine the usefulness of the knowledge of CTDIvol and mA variations as a function of patient size for optimizing scan parameters in CT imaging using AEC. Methods: Data was collected from actual patient scans for a number of different CT protocols such as standard chest, body, head, vascular imaging, and pediatric body. A GE LightSpeed VCT scanner was used in Smart mA mode in which the user can select the Noise Index, and the maximum and minimum mA allowed during mA modulation. For each different protocol the CTDIvol, minimum mA, maximum mA and patient size where determined for at least 40 patients, along with information on when the mA had reached its specified minimum or maximum value. Plots were made of the CTDIvol versus patient size and of the maximum and minimum mA versus patient size. Results: Initial results demonstrated a significant variation in CTDIvol over the range of adult patient sizes of more than a factor of ten for abdominal imaging. The observation that clinical scans frequently reached the minimum allowed mA indicated that reduction of the rotation time and lowering of the minimum mA parameter would allow lower patient dose and better operation of the AEC system. These results also led us to create separate protocols for small, medium, and large patients, each with a different optimized Noise Index, kV, rotation time, and mA range. These were created in consultation with our radiologists in determining the lowest dose that would provide a clinically acceptable image after the AEC was deemed to be operating optimally. Conclusion: The above analysis can provide significant help in improving CT protocols and lowering patient dose. The plots of CTDIvol versus patient size also helped to educate radiologists in the dose variations to be expected for a range of patient sizes. Equipment grant from GE healthcare.

Hybrid regularization for MRI reconstruction with static field inhomogeneity correction

Rapid acquisition of magnetic resonance (MR) images via reconstruction from undersampled $k$-space data has the potential to greatly decrease MRI scan time on existing medical hardware. To this end, iterative image reconstruction based on the technique of compressed sensing has become the method choice for many researchers [1]. However, while conventional compressed sensing relies on random measurements from a discrete Fourier transform, actual MR scans often suffer from off-resonance effects and thus generate data by way of a non-Fourier operator [2]. Correcting for these effects requires that one employs more sophisticated image reconstruction methods and introduces computational bottlenecks that are not encountered in standard compressed sensing. In this work, we demonstrate how one may accelerate the convergence of algorithms for solving the image reconstruction problem, \begin{equation}\label{eq:caneq} (1)&nbsp; &nbsp &nbsp; &nbsp &nbsp; &nbsp &nbsp; &nbsp \underset{\rho}{argmin} J(\rho) subject to A \rho = s \end{equation} by opting for a regularization of the form: \begin{equation}\label{eq:hybrid} (2) &nbsp; &nbsp &nbsp; &nbsp &nbsp; &nbsp; &nbsp &nbsp;&nbsp; &nbsp &nbsp; &nbsp &nbsp &nbsp J(\rho) = | \nabla \rho| + \nu | F \rho | \end{equation}when $F$ is a tight frame and $A$ is only approximately a Fourier transform. In our experiments, reconstructing field-corrected MR images with the hybrid regularization of 2 provides a speedup of roughly one order of magnitude when compared with an approach based solely on total-variation and may produce higher quality images than an approach based solely on tight frames.

Soft Tissue Changes After Orthodontic Surgical Correction of Jaws Asymmetry Evaluated by Three-Dimensional Surface Laser Scanner

Aesthetic improvement is an essential goal of treatment of facial asymmetry, and it is often difficult to achieve. Reliable three-dimensional measurements are required to support outcome studies. In this study, 15 white adult subjects, 9 females and 6 males, with maxillomandibular asymmetry and malocclusion were studied. The patients were treated with orthodontics and different surgical procedures in single or multiple steps. All patients received double-jaw surgery, except 1 patient who underwent only maxillary osteotomy. Nine of the 15 patients received additional procedures (genioplasty and rhinoplasty) to achieve better symmetry. Posterior-anterior and lateral cephalometry and three-dimensional facial surface data were obtained before (T0) and 1 year (T1) after surgery. Scan data at T0 and T1 were pooled by electronic surface averaging to obtain the mean pretreatment and posttreatment facial model. A symmetric model was constructed by averaging the actual T0 scans and their mirrored models to obtain the virtual optimal symmetric face. Different linear and angular measurements were then calculated for comparison of the mean T0 and T1 models. The normalization of facial proportion and a high increase in symmetry were evident. Residual defects were documented in the postoperative symmetry of the chin. Treatment of facial asymmetry, combined with dental occlusion problems, is still a challenge for maxillofacial surgeons. Orthognathic surgery provides an important improvement of symmetry, but further refinements of technique are still required. Three-dimensional evaluation results in an effective method to support outcome studies on the surgical correction of complex facial deformities.

Synthetic CT: Simulating low dose single and dual energy protocols from a dual energy scan

The choice of CT protocol can greatly impact patient dose and image quality. Since acquiring multiple scans at different techniques on a given patient is undesirable, the ability to predict image quality changes starting from a high quality exam can be quite useful. While existing methods allow one to generate simulated images of lower exposure (mAs) from an acquired CT exam, the authors present and validate a new method called synthetic CT that can generate realistic images of a patient at arbitrary low dose protocols (kVp, mAs, and filtration) for both single and dual energy scans. The synthetic CT algorithm is derived by carefully ensuring that the expected signal and noise are accurate for the simulated protocol. The method relies on the observation that the material decomposition from a dual energy CT scan allows the transmission of an arbitrary spectrum to be predicted. It requires an initial dual energy scan of the patient to either synthesize raw projections of a single energy scan or synthesize the material decompositions of a dual energy scan. The initial dual energy scan contributes inherent noise to the synthesized projections that must be accounted for before adding more noise to simulate low dose protocols. Therefore, synthetic CT is subject to the constraint that the synthesized data have noise greater than the inherent noise. The authors experimentally validated the synthetic CT algorithm across a range of protocols using a dual energy scan of an acrylic phantom with solutions of different iodine concentrations. An initial 80/140 kVp dual energy scan of the phantom provided the material decomposition necessary to synthesize images at 100 kVp and at 120 kVp, across a range of mAs values. They compared these synthesized single energy scans of the phantom to actual scans at the same protocols. Furthermore, material decompositions of a 100/120 kVp dual energy scan are synthesized by adding correlated noise to the initial material decompositions. The aforementioned noise constraint also allows us to compute feasible mAs values that can be synthesized for each kVp. The single energy synthesized and actual reconstructed images exhibit identical signal and noise properties at 100 kVp and at 120 kVp, and across a range of mAs values. For example, the noise in both the synthesized and actual images at 100 kVp increases by 2 when the mAs is halved. The synthesized and actual material decompositions of a dual energy protocol show excellent agreement when the decomposition images are linearly weighted to form monoenergetic images at energies from 40 to 100 keV. For simulated single energy protocols with kVp between 80 and 140, the highest feasible mAs exceeds that of either initial scan. This work describes and validates the synthetic CT theory and algorithm by comparing its results to actual scans. Synthetic CT is a powerful new tool that allows users to realistically see how protocol selection affects CT images and enables radiologists to retrospectively identify the lowest dose protocol achievable that provides diagnostic quality images on real patients.

TH-E-211-01: The Ability of CTDIvol to Estimate Organ Doses from Typical Tube Current Modulated Abdomen/Pelvis CT Scans

Purpose: When tube current modulation (TCM) scanning is performed over multiple anatomic regions (e.g. abdomen/pelvis), typically only the average CTDIvol over all regions is reported. The purpose of this work was to compare simulated organ doses from tube current modulated scans with different CTDIvol values (including a region specific CTDIvol) and to investigate the feasibility of estimating organ doses using CTDIvol and patient size. Methods: Voxelized models with contoured abdominal organs(liver, spleen and kidneys) were created using 40 abdomen/pelvis scans with tube current modulation (Care Dose4D) acquired on a Siemens Sensation 64. Dose to these organs were estimated using Monte Carlo methods that simulate actual scans. Simulated organ doses were compared with three CTDIvol values: CTDIvol reported on the scanner (CTDIvol, Abd/Pel), CTDIvol based on average effective mAs of abdomen region of the scan (CTDIvol,Abd), and CTDIvol based on average effective mAs from images containing the organ (e.g. CTDIvol,Liver). Organ doses were normalized by each CTDIvol and the relationship between each of these ratios and patient perimeter was investigated. These results were also compared to organ doses normalized by CTDIvol for 32cm CTDI phantom for fixed tube current. Results: This study showed that CTDIvol based on the entire exam underestimates organ dose by up to 33%. This percentage increased to 43% and 38% for CTDIvol,Abd and CTDIvol,Liver, respectively. However, organ doses normalized by CTDIvol,Abd and CTDIvol, Liver showed a strong linear correlation with patient perimeter. Similar linear correlation was observed for fixed tube current results. Conclusions: When using TCM, the CTDIvol reported is over the entire scan which does not correlate well with actual patient dose. However, specific region‐CTDIvol‐normalized organ doses showed strong correlation with patient size and therefore can be used to estimate organ doses from a TCM scan using patient perimeter and region specific CTDIvol.