Beam Computed Tomography Research Articles

Cone beam CT for QA of synthetic CT in MRI only for prostate patients.

PurposeMagnetic resonance imaging (MRI)‐only radiotherapy is performed without computed tomography (CT). A synthetic CT (sCT) is used for treatment planning. The aim of this study was to develop a clinically feasible quality assurance (QA) procedure for sCT using the kV‐cone beam CT (CBCT), in an MRI‐only workflow for prostate cancer patients.Material and methodThree criteria were addressed; stability in Hounsfield Units (HUs), deviations in HUs between the CT and CBCT, and validation of the QA procedure. For the two first criteria, weekly phantom measurements were performed. For the third criteria, sCT, CT, and CBCT for ten patients were used. Treatment plans were created based on the sCT (MriPlannerTM). CT and CBCT images were registered to the sCT. The treatment plan was copied to the CT and CBCT and recalculated. Dose–volume histogram (DVH) metrics were used to evaluate dosimetric differences between the sCT plan and the recalculated CT and CBCT plans. HU distributions in sCT, CT, and CBCT were compared. Well‐defined errors were introduced in the sCT for one patient to evaluate efficacy of the QA procedure.ResultsThe kV‐CBCT system was stable in HU over time (standard deviation <40 HU). Variation in HUs between CT and CBCT was <60 HU. The differences between sCT–CT and sCT–CBCT dose distributions were below or equal to 1.0%. The highest mean dose difference for the CT and CBCT dose distribution was 0.6%. No statistically significant difference was found between total mean dose deviations from recalculated CT and CBCT plans, except for femoral head. Comparing HU distributions, the CBCT appeared to be similar to the CT. All introduced errors were identified by the proposed QA procedure, except all tissue compartments assigned as water.ConclusionThe results in this study shows that CBCT can be used as a clinically feasible QA procedure for MRI‐only radiotherapy of prostate cancer patients.

Imaging modalities for temporomandibular joint disorders: an update.

The diagnosis and management of temporomandibular disorders (TMD) require both clinical and imaging examinations of the temporomandibular joint (TMJ). A variety of modalities can be used to image the TMJ, including magnetic resonance imaging (MRI), computed tomography (CT), cone beam CT, ultrasonography, conventional radiography. The present review outlines the indications of the most frequently used imaging techniques in TMD diagnosis.Because of the anatomic complexity of the TMJ, imaging can be difficult. Choosing the proper imaging technique is essential. Conventional radiography, nowadays, is of limited interest. The use of flat plane films for TMJ pathology is not sufficient, because this joint requires three dimensional imaging views. Osseous changes are better visualized with CT and cone beam CT. Cone beam CT provides high-resolution multiplanar reconstruction of the TMJ, with a low radiation dose, without superimposition of the bony structures. MRI is a noninvasive technique, considered to be the gold standard in imaging the soft tissue components of the TMJ. MRI is used to evaluate the articular disc in terms of location and morphology. Moreover, the early signs of TMD and the presence of joint effusion can be determined. High-resolution ultrasonography is a noninvasive, dynamic, inexpensive imaging technique, which can be useful in diagnosing TMJ disc displacements. The diagnostic value of high-resolution ultrasonography is strictly dependent on the examiner’s skills and on the equipment used.

Orthopaedic application of computed tomography metal artifact reduction

With the rapid increase of orthopedic metal implants, more and more computed tomography (CT) scans of such patients with metal implantation were conducted. However, CT metal artifact caused by these implants would interfer clinical diagnosis and treatment. In order to solve this problem, large amount of researches had been carried out to reduce the metal artifact in the aspect of engineers and doctors in recent years. In the view of engineers, methods mainly include: transformation of the type and the property of CT machine such as dual-energy CT (DECT) or cone beam CT (CBCT), instead of spiral CT. The methods of doctors mainly include: the transformation of CT scanning parameters, such as tube voltage, field of view (FOV), layer thickness; the CT post-processing software such as Orthopedics Metal Artifact Reduction (O-MAR) which was applied comprehensively in orthopedics in recent years. Domestic and international progress of relevant studies on metal artifact reduction technology will be demonstrated in both aspects of engineers and doctors. Final reference for reduction of metal artifact in orthopedic application will be provided based on the above methods. Key words: Metal implant; Computed tomography; Metal artifact; Orthopedics

Calcul de dose de radiothérapie à partir de tomographies coniques : état de l’art

In external beam radiotherapy, the dose planning is currently based on computed tomography (CT) images. A relation between Hounsfield numbers and electron densities (or mass densities) is necessary for dose calculation taking heterogeneities into account. In image-guided radiotherapy process, the cone beam CT is classically used for tissue visualization and registration. Cone beam CT for dose calculation is also attractive in dose reporting/monitoring perspectives and particularly in a context of dose-guided adaptive radiotherapy. The accuracy of cone beam CT-based dose calculation is limited by image characteristics such as quality, Hounsfield numbers consistency and restrictive sizes of volume acquisition. The analysis of the literature identifies three kinds of strategies for cone beam CT-based dose calculation: establishment of Hounsfield numbers versus densities curves, density override to regions of interest, and deformable registration between CT and cone beam CT images. Literature results show that discrepancies between the reference CT-based dose calculation and the cone beam CT-based dose calculation are often lower than 3%, regardless of the method. However, they can also reach 10% with unsuitable method. Even if the accuracy of the cone beam CT-based dose calculation is independent of the method, some strategies are promising but need improvements in the automating process for a routine implementation.

Development and tests of a 30 cm pencil-type ionization chamber for dosimetry in standard and clinical CT beams

The use of computed tomography (CT) for imaging procedures is growing due to advances in the CT equipment technology. To perform the dosimetry in CT beams, the most widely used instrument is the pencil type ionization chamber with a sensitive volume length of 100 mm; however, some studies have shown that this dosimeter has underestimated the dose values. Therefore, in this study an ionization chamber with sensitive volume length of 300 mm was developed at IPEN. The characterization of this chamber was performed, and the results were obtained within the international recommended limits. As an application, the developed ionization chamber was tested in clinical beams of two different hospitals.

ASSESSMENT OF RADIOMORPHOMETRIC INDICES ON DIGITAL PANORAMIC AND CONE BEAM COMPUTED TOMOGRAPHIC IMAGES IN OSTEOPOROTIC EGYPTIAN FEMALES.

15May 2017 ASSESSMENT OF RADIOMORPHOMETRIC INDICES ON DIGITAL PANORAMIC AND CONE BEAM COMPUTED TOMOGRAPHIC IMAGES IN OSTEOPOROTIC EGYPTIAN FEMALES. Sarah M. Kenawy , Dina M. El Beshlawy and Mushira M. Dahaba Assistant Lecturer, Oral and Maxillofacial Radiology Department, Faculty of Dentistry, Cairo University, Cairo, Egypt. Associate Professor, Oral and Maxillofacial Radiology Department, Faculty of Dentistry, Cairo University, Cairo, Egypt Professor, Oral and Maxillofacial Radiology Department, Faculty of Dentistry, Cairo University, Cairo, Egypt

Guided implant placement using the trephine drill non-sleeve and immediate provisional crown or bridge in the esthetic zone

The immediate restoration of dental implants has sh own revealed the clinical success rates compare with conventional multi-step protocol. However, the accuracy of guided dental implant placement using guided trephine drill and the restoration affect th e treatment success and more security. To provide t he professional tool improve the planning to choose th e implant size and position. The objectives of this study were to evaluate the accuracy and position of the digital surgical guide before and after implan t placement with the guided trephine drill. The digit al process chain work from Intra oral scan with denture will be performed. And then cone beam compu ter tomography (CBCT) with gutta-percha marker denture. The virtual prototyping precisions of 5 st ereolithographic surgical splints are validate a de sign before committing to making the rapid prototype wer e excellent. The satisfaction score compare with the conventional splint and provisional crown impro ve in term of time and esthetic outcome. The guided trephine drill can reduce the stage of bone augmentation. The mean measurement differences in accuracy between the computer-planned implant and t he before and after surgery for 6 implants guided placed were 1.18 mm for the apex (SD+/- 0.37), 0.35 mm for the mesial (SD+/-1.2) 0.35 mm (SD+/-1.5), f or the depth deviation. The results show a statistical ly significant difference of the implant placed bet ween the conventional and the virtually planed implant p ositions with the CAD/CAM-guided surgical template

Moderne Schläfenbeinbildgebung

This article describes the current significance of computed tomography (CT), magnetic resonance imaging (MRI), cone beam CT, digital subtraction angiography (DSA), and special X‑rays in the diagnostics of temporal bone diseases. The latter is obsolete for diagnostic intentions. Possibilities and limitations in terms of detection and/or depiction of the extent of inflammatory, traumatic, tumorous, and postoperative pathologies are discussed. Aconcrete question and conveyance of clinical findings influence the choice of the method to be applied in the individual case. Malformations of the middle ear can only be detected noninvasively by CT or cone beam CT. These are also the methods that may support the diagnosis of otosclerosis in clinically unclear cases. MRI is the method of choice for pathologies of the inner ear and internal auditory canal, including inner ear malformations. At present, only in few institutions is asuccessful visualization of endolymphatic hydrops in Menière's disease realized.

Performance of three pencil-type ionization chambers (10 cm) in computed tomography standard beams

The use of computed tomography (CT) has increased over the years, thus generating a concern about the doses received by patients undergoing this procedure. Therefore, it is necessary to perform routinely beam dosimetry with the use of a pencil-type ionization chamber. This detector is the most utilized in the procedures of quality control tests on this kind of equipment. The objective of this work was to perform some characterization tests in standard CT beams, as the saturation curve, polarity effect, ion collection efficiency and linearity of response, using three ionization chambers, one commercial and two developed at the IPEN.

A noble technique a using force-sensing resistor for immobilization-device quality assurance: A feasibility study

Many studies have reported that a patient can move even when an immobilization device is used. Researchers have developed an immobilization-device quality-assurance (QA) system that evaluates the validity of immobilization devices. The QA system consists of force-sensing-resistor (FSR) sensor units, an electric circuit, a signal conditioning device, and a control personal computer (PC) with in-house software. The QA system is designed to measure the force between an immobilization device and a patient’s skin by using the FSR sensor unit. This preliminary study aimed to evaluate the feasibility of using the QA system in radiation-exposure situations. When the FSR sensor unit was irradiated with a computed tomography (CT) beam and a treatment beam from a linear accelerator (LINAC), the stability of the output signal, the image artifact on the CT image, and changing the variation on the patient’s dose were tested. The results of this study demonstrate that this system is promising in that it performed within the error range (signal variation on CT beam < 0.30 kPa, root-mean-square error (RMSE) of the two CT images according to presence or absence of the FSR sensor unit < 15 HU, signal variation on the treatment beam < 0.15 kPa, and dose difference between the presence and the absence of the FSR sensor unit < 0.02%). Based on the obtained results, we will volunteer tests to investigate the clinical feasibility of the QA system.

A Proposed Method for Accurate 3D Analysis of Cochlear Implant Migration Using Fusion of Cone Beam CT.

The goal of this investigation was to compare fusion of sequential cone beam computerized tomography (CT) volumes to the gold standard (fiducial registration) in order to be able to analyze clinical cochlear implant (CI) migration with high accuracy in three dimensions. Paired cone beam CT volumes were performed on five human cadaver temporal bones and one human subject. These volumes were fused using 3D Slicer 4 and BRAINSFit software. Using a gold standard fiducial technique, the accuracy, robustness, and performance time of the fusion process were assessed. This proposed fusion protocol achieves a subvoxel median Euclidean distance of 0.05 mm in human cadaver temporal bones and 0.16 mm (mean) when applied to the described in vivo human synthetic data set in over 95% of all fusions. Performance times are <2 min. Here, a new and validated method based on existing techniques is described, which could be used to accurately quantify migration of CI electrodes.

Automated Delineation of the Normal Urinary Bladder on Planning CT and Cone Beam CT

PurposeTo quantify the volumetric effect of delineation variability when using manual versus semiautomated tools to contour the normal bladder on planning computed tomography (CT) and cone beam CT. MethodsFollowing research ethics board approval, 10 prostate cancer patients were selected. For each patient, one pretreatment cone beam CT (CBCT) was randomly selected from the first treatment week and registered to the planning CT (planCT). Model-based auto adaptation was used to delineate the outer bladder (OB) surface for the planCT. That contour was then propagated and manually adapted onto the CBCT. A second observer delineated OB for the planCT and CBCT using typical manual methods. These delineation procedures were repeated four times on each image set, with observers blinded to the previous contours. Metrics of volumetric, geometric, and overlap concordance were used to compare the manual and automated OB contours. ResultsThe mean pairwise difference between the manual and model-based planCT volumes was 4 cm3 (2%), and the model-based contours exhibited approximately half the observer variation of the manual ones (3 cm3, 2%). The mean of pairwise differences between the manual and propagated CBCT volumes was 13 cm3 (8%), but the propagated contours exhibited approximately half the observer related volume variation (11 cm3, 6%). Small CBCT bladder volumes displayed larger observer variation with manual methods (r2, −0.640). Variability between the automated contours was significantly smaller than for the corresponding manual observations (P = .004 and .002, respectively). Metrics of three-dimensional overlap concordance indicated excellent agreement within and between the delineation methods. Automated CBCT contours were significantly smoother than the manual ones (surface sphericity index, 1.29 vs. 1.35; P = .03). ConclusionsVolumetric, geometric, and overlap metrics all indicated that planCT and CBCT automated OB contours fell within the range of manually delineated contours. The CBCT propagated contours were significantly smoother and associated with smaller intraobserver variability, compared with manual contours. Importantly, the findings from this research suggest that contour propagation may be more robust than manual delineation, especially in the presence of poor image quality.

Dimensional error of three-dimensional images generated by different software

The aim of this study was to evaluate the accuracy of three-dimensional (3D) reconstructions generated by different software, computed tomography (CT) scanners and slice thicknesses. Ten human dry mandibles were scanned by CT and cone beam CT (CBCT). Digital files were processed in different software systems and 3D reconstructions were performed. Linear measures were made and compared. The results showed significant differences in linear distances between the human dry mandibles and their 3D reconstructions. The relative error from CBCT images ranged from 3.10 to 4.82% and from 3.40 to 5.92% in CT images. It is important to consider that the performance of the software is not just related to the algorithm used, but mostly with its handling, that can facilitate or not the measurement by the operator. In conclusion, the discrepancies were not greater than 0.58 mm, so they should not affect the image quality.

A comprehensive evaluation of treatment accuracy, including end-to-end tests and clinical data, applied to intracranial stereotactic radiotherapy

Background and purposeA methodology is presented to quantify the uncertainty associated with linear accelerator-based frameless intracranial stereotactic radiotherapy (SRT) combining end-to-end phantom tests and clinical data. Methods and materialsThe following steps of the SRT chain were analysed: planning computed tomography (CT) and magnetic resonance (MR) scans registration, target volume delineation, CT and cone beam CT (CBCT) registration and intrafraction-patient displacement. The overall accuracy was established with an end-to-end test. The measured uncertainties were combined, deriving the total systematic (ΣT) and random (σT) error components, to estimate the GTV-PTV margin. ResultsThe uncertainty in the MR-CT registration was on average 0.40mm (averaged over AP, CC and LR directions). Rotational variations were smaller than 0.5° in all directions.Interobser variation in GTV delineation was on average 0.29mm.The uncertainty in the CBCT-CT registration was on average 0.15mm. Again, rotational variations were smaller than 0.5° in all directions.The systematic and random intrafraction displacement errors were on average 0.55mm and 0.45mm, respectively.The systematic and random positional errors from the end-to-end test were on average 0.49mm and 0.53mm, respectively.Combining these uncertainties resulted in an average ΣT=0.9mm and σT=0.7mm and an average GTV-PTV margin of 2.8mm. ConclusionThis comprehensive methodology including end-to-end tests enabled a GTV-PTV margin calculation considering all sources of uncertainties. This generic method can also be used for other treatment sites.

A rapid noninvasive characterization of CT x-ray sources.

The aim of this study is to generate spatially varying half value layers (HVLs) that can be used to construct virtual equivalent source models of computed tomography (CT) x-ray sources for use in Monte Carlo CT dose computations. To measure the spatially varying HVLs, the authors combined a cylindrical HVL measurement technique with the characterization of bowtie filter relative attenuation (COBRA) geometry. An apparatus given the name "HVL Jig" was fabricated to accurately position a real-time dosimeter off-isocenter while surrounded by concentric cylindrical aluminum filters (CAFs). In this geometry, each projection of the rotating x-ray tube is filtered by an identical amount of high-purity (type 1100 H-14) aluminum while the stationary radiation dose probe records an air kerma rate versus time waveform. The CAFs were progressively nested to acquire exposure data at increasing filtrations to calculate the HVL. Using this dose waveform and known setup geometry, each timestamp was related to its corresponding fan angle. Data were acquired using axial CT protocols (i.e., rotating tube and stationary patient table) at energies of 80, 100, and 120 kVp on a single CT scanner. These measurements were validated against the more laborious conventional step-and-shoot approach (stationary x-ray tube). At each energy, HVL data points from the COBRA-cylinder technique were fit to a trendline and compared with the conventional approach. The average relative difference in HVL between the two techniques was 1.3%. There was a systematic overestimation in HVL due to scatter contamination. The described method is a novel, rapid, accurate, and noninvasive approach that allows one to acquire the spatially varying fluence and HVL data using a single experimental setup in a minimum of three scans. These measurements can be used to characterize the CT beam in terms of the angle-dependent fluence and energy spectra along the bowtie filter direction, which can serve as input for accurate CT dose computations.

An investigation into factors affecting the precision of CT radiation dose profile width measurements using radiochromic films.

To investigate the impact of x-ray beam energy, exposure intensity, and flat-bed scanner uniformity and spatial resolution on the precision of computed tomography (CT) beam width measurements using Gafchromic XR-QA2 film and an off-the-shelf document scanner. Small strips of Gafchromic film were placed at isocenter in a CT scanner and exposed at various x-ray beam energies (80-140 kVp), exposure levels (50-400 mA s), and nominal beam widths (1.25, 5, and 10 mm). The films were scanned in reflection mode on a Ricoh MP3501 flat-bed document scanner using several spatial resolution settings (100 to 400 dpi) and at different locations on the scanner bed. Reflection measurements were captured in digital image files and radiation dose profiles generated by converting the image pixel values to air kerma through film calibration. Beam widths were characterized by full width at half maximum (FWHM) and full width at tenth maximum (FWTM) of dose profiles. Dependences of these parameters on the above factors were quantified in percentage change from the baselines. The uncertainties in both FWHM and FWTM caused by varying beam energy, exposure level, and scanner uniformity were all within 4.5% and 7.6%, respectively. Increasing scanner spatial resolution significantly increased the uncertainty in both FWHM and FWTM, with FWTM affected by almost 8 times more than FWHM (48.7% vs 6.5%). When uncalibrated dose profiles were used, FWHM and FWTM were over-estimated by 11.6% and 7.6%, respectively. Narrower beam width appeared more sensitive to the film calibration than the wider ones (R(2) = 0.68 and 0.85 for FWHM and FWTM, respectively). The global and maximum local background variations of the document scanner were 1.2%. The intrinsic film nonuniformity for an unexposed film was 0.3%. Measurement of CT beam widths using Gafchromic XR-QA2 films is robust against x-ray energy, exposure level, and scanner uniformity. With proper film calibration and scanner resolution setting, it can provide adequate precision for meeting ACR and manufacturer's tolerances for the measurement of CT dose profiles.

Rapid prototyping modelling in oral and maxillofacial surgery: A two year retrospective study.

Background The use of rapid prototyping (RP) models in medicine to construct bony models is increasing. Material and Methods The aim of the study was to evaluate retrospectively the indication for the use of RP models in oral and maxillofacial surgery at Helsinki University Central Hospital during 2009-2010. Also, the used computed tomography (CT) examination – multislice CT (MSCT) or cone beam CT (CBCT) - method was evaluated. Results In total 114 RP models were fabricated for 102 patients. The mean age of the patients at the time of the production of the model was 50.4 years. The indications for the modelling included malignant lesions (29%), secondary reconstruction (25%), prosthodontic treatment (22%), orthognathic surgery or asymmetry (13%), benign lesions (8%), and TMJ disorders (4%). MSCT examination was used in 92 and CBCT examination in 22 cases. Most of the models (75%) were conventional hard tissue models. Models with colored tumour or other structure(s) of interest were ordered in 24%. Two out of the 114 models were soft tissue models. Conclusions The main benefit of the models was in treatment planning and in connection with the production of pre-bent plates or custom made implants. The RP models both facilitate and improve treatment planning and intraoperative efficiency. Key words:Rapid prototyping, radiology, computed tomography, cone beam computed tomography.

Effect of Different CT Scanner Types and Beam Collimations on Measurements of Three-Dimensional Volume and Hounsfield Units of Artificial Calculus Phantom

The objective of this study was to evaluate the differences and reproducibility of Hounsfield unit (HU) value and volume measurements on different computed tomography (CT) scanner types and different collimations by using a gelatin phantom. The phantom consisting of five synthetic simulated calculus spanning diameters from 3.0 mm to 12.0 mm with 100 HU was scanned using a two-channel multi-detector row CT (MDCT) scanner, a fourchannel MDCT scanner, and two 64-channel MDCT scanners. For all different scanner types, the thinnest possible collimation and the second thinnest collimation was used. The HU values and volumes of the synthetic simulated calculus were independently measured three times with minimum intervals of 2 weeks and by three experienced veterinary radiologists. ANOVA and Scheffe test for the multiple comparison were performed for statistical comparison of the HU values and volumes of the synthetic simulated calculus according to different CT scanner types and different collimations. The reproducibility of the HU value and volume measurements was determined by calculating Cohen’s k. The reproducibility of HU value and volume measurements was very good. HU value varied between different CT scanner types, among different beam collimations. However, there was not statistically significant difference. The percent error (PE) decreased as the collimation thickness decreased, but the decrease was statistically insignificant. In addition, no statistically significant difference in the PEs of the different CT scanner types was found. It can be concluded that the CT scanner type insignificantly affects HU value and the volumetric measurement, but that a thinner collimation tends to be more useful for accurate volumetric measurement.

Monte Carlo simulations in multi-detector CT (MDCT) for two PET/CT scanner models using MASH and FASH adult phantoms

The combination of positron emission tomography (PET) and computed tomography (CT) has been extensively used in oncology for diagnosis and staging of tumors, radiotherapy planning and follow-up of patients with cancer, as well as in cardiology and neurology. This study determines by the Monte Carlo method the internal organ dose deposition for computational phantoms created by multidetector CT (MDCT) beams of two PET/CT devices operating with different parameters. The different MDCT beam parameters were largely related to the total filtration that provides a beam energetic change inside the gantry. This parameter was determined experimentally with the Accu-Gold Radcal measurement system. The experimental values of the total filtration were included in the simulations of two MCNPX code scenarios. The absorbed organ doses obtained in MASH and FASH phantoms indicate that bowtie filter geometry and the energy of the X-ray beam have significant influence on the results, although this influence can be compensated by adjusting other variables such as the tube current–time product (mAs) and pitch during PET/CT procedures.

A Monte Carlo study of the energy spectra and transmission characteristics of scattered radiation from x-ray computed tomography

Existing data used to calculate the barrier transmission of scattered radiation from computed tomography (CT) are based on primary beam CT energy spectra. This study uses the EGSnrc Monte Carlo system and Epp user code to determine the energy spectra of CT scatter from four different primary CT beams passing through an ICRP 110 male reference phantom. Each scatter spectrum was used as a broad-beam x-ray source in transmission simulations through seventeen thicknesses of lead (0.00–3.50 mm). A fit of transmission data to lead thickness was performed to obtain α, β and γ parameters for each spectrum. The mean energy of the scatter spectra were up to 12.3 keV lower than that of the primary spectrum. For 120 kVp scatter beams the transmission through lead was at least 50% less than predicted by existing data for thicknesses of 1.5 mm and greater; at least 30% less transmission was seen for 140 kVp scatter beams. This work has shown that the mean energy and half-value layer of CT scatter spectra are lower than those of the corresponding primary beam. The transmission of CT scatter radiation through lead is lower than that calculated with currently available data. Using the data from this work will result in less lead shielding being required for CT scanner installations.