X-ray Cone-beam CT Research Articles

A new filter function for the image reconstruction of cone beam X-ray CT

A new filter function for the image reconstruction of cone beam X-ray CT

Data consistency-driven scatter kernel optimization for x-ray cone-beam CT

Accurate and efficient scatter correction is essential for acquisition of high-quality x-ray cone-beam CT (CBCT) images for various applications. This study was conducted to demonstrate the feasibility of using the data consistency condition (DCC) as a criterion for scatter kernel optimization in scatter deconvolution methods in CBCT. As in CBCT, data consistency in the mid-plane is primarily challenged by scatter, we utilized data consistency to confirm the degree of scatter correction and to steer the update in iterative kernel optimization. By means of the parallel-beam DCC via fan-parallel rebinning, we iteratively optimized the scatter kernel parameters, using a particle swarm optimization algorithm for its computational efficiency and excellent convergence. The proposed method was validated by a simulation study using the XCAT numerical phantom and also by experimental studies using the ACS head phantom and the pelvic part of the Rando phantom. The results showed that the proposed method can effectively improve the accuracy of deconvolution-based scatter correction. Quantitative assessments of image quality parameters such as contrast and structure similarity (SSIM) revealed that the optimally selected scatter kernel improves the contrast of scatter-free images by up to 99.5%, 94.4%, and 84.4%, and of the SSIM in an XCAT study, an ACS head phantom study, and a pelvis phantom study by up to 96.7%, 90.5%, and 87.8%, respectively. The proposed method can achieve accurate and efficient scatter correction from a single cone-beam scan without need of any auxiliary hardware or additional experimentation.

Comparison of Orthogonal Kilovolt X-Ray Plain Film and Cone Beam CT Matching Results in Setup Error Assessment and Correction for EB-PBI During Free Breathing

Comparison of Orthogonal Kilovolt X-Ray Plain Film and Cone Beam CT Matching Results in Setup Error Assessment and Correction for EB-PBI During Free Breathing

Comparison of orthogonal kilovolt X-ray images and cone-beam CT matching results in setup error assessment and correction for EB-PBI during free breathing

Objective To compare the differences in setup error (SE) assessment and correction between the orthogonal kilovolt X-ray images and CBCT in EB-PBI patients during free breathing.Methods Nineteen patients after breast conserving surgery EB-PBI were recruited.Interfraction SE was acquired using orthogonal kilovolt X-ray setup images and CBCT,after on-line setup correction,calculate the residual error and compare the SE,residual error and setup margin (SM) quantified for orthogonal kilovolt X-ray images and CBCT.Wilcoxon sign-rank test was used to evaluate the differences.Results The CBCT based SE (systematic error,∑) was smaller than the orthogonal kilovolt X-ray images based ∑ in AP direction (-1.2 mm vs 2.00 mm; P =0.005),and there was no statistically significant differences for three dimensional directions in random error (σ) (P =0.948,0.376,0.314).After on-line setup correction,CBCT decreases setup residual error than the orthogonal kilovolt X-ray imagesin AP direction (∑:-0.20 mm vs 0.50 mm,P =0.008 ; σ:0.45 mm vs 1.34 mm,P =0.002).And also the CBCT based SM was smaller than orthogonal kilovolt X-ray images based SM in AP direction (∑:-1.39 mm vs 5.57 mm,P =0.003 ;σ:0.00 mm vs 3.2 mm,P =0.003).Conclusions Compared with kilovolt X-ray images,CBCT underestimate the setup error in the AP direction,but decreases setup residual error significantly.An image-guided radiotherapy and setup error assessment using kilovolt X-ray images for EB-PBI plans was feasible. Key words: External beam partial breast irradiation; Tomography, X-ray computed, beam cone; Orthogonal kilovolt X-ray images; Setup error; Residual error

Comparison between neutron tomography and X-ray tomography: A study on polymer foams

This work aims at discussing the possibilities of high resolution neutron tomography, in comparison to conventional cone beam X-ray CT, based on the results on a set of polymeric foamed materials. The neutron experiments have been carried out at the V7/CONRAD-2 imaging instrument located at the BER-2 research reactor at HZB and compared to the images obtained in a X-ray CT system based on a microfocus tube and a flat panel detector. This type of materials has not been previously examined with neutron imaging. The enhanced neutron attenuation relative to the X-ray attenuation and the recent development of high-resolution neutron imaging detectors encouraged this investigation. The results point to a better signal-to-noise ratio of the X-rays in comparison with current neutron tomography – due to the rather low neutron flux. Nevertheless the contrast of polymeric materials in neutron imaging offers further possibilities for future developments in high resolution neutron tomography.

Influence of difference in cross-sectional dose profile in a CTDI phantom on X-ray CT dose estimation: a Monte Carlo study

The longitudinal dose profile in a computed tomography dose index (CTDI) phantom had been studied by many researchers. The cross-sectional dose profile in the CTDI phantom, however, has not been studied. It is also important to understand the cross-sectional dose profile in the CTDI phantom for dose estimation in X-ray CT. In this study, the cross-sectional dose profile in the CTDI phantom was calculated by use of a Monte Carlo (MC) simulation method. A helical or a 320-detector-row cone-beam X-ray CT scanner was simulated. The cross-sectional dose profile in the CTDI phantom from surface to surface through the center point was calculated by MC simulation. The shape of the calculation region was a cylinder of 1-mm-diameter. The length of the cylinder was 23, 100, or 300mm to represent various CT ionization chamber lengths. Detailed analyses of the energy depositions demonstrated that the cross-sectional dose profile was different in measurement methods and phantom sizes. In this study, we also focused on the validation of the weighting factor used in weighted CTDI (CTDI w ). As it stands now, the weighting factor used in CTDI w is (1/3, 2/3) for the (central, peripheral) axes. Our results showed that an equal weighting factor, which is (1/2, 1/2) for the (central, peripheral) axes, is more suitable to estimate the average cross-sectional dose when X-ray CT dose estimation is performed.

Breast density quantification with cone-beam CT: a post-mortem study

Forty post-mortem breasts were imaged with a flat-panel based cone-beam x-ray CT system at 50 kVp. The feasibility of breast density quantification has been investigated using standard histogram thresholding and an automatic segmentation method based on the fuzzy c-means algorithm (FCM). The breasts were chemically decomposed into water, lipid, and protein immediately after image acquisition was completed. The per cent fibroglandular volume (%FGV) from chemical analysis was used as the gold standard for breast density comparison. Both image-based segmentation techniques showed good precision in breast density quantification with high linear coefficients between the right and left breast of each pair. When comparing with the gold standard using %FGV from chemical analysis, Pearson's r-values were estimated to be 0.983 and 0.968 for the FCM clustering and the histogram thresholding techniques, respectively. The standard error of the estimate was also reduced from 3.92% to 2.45% by applying the automatic clustering technique. The results of the postmortem study suggested that breast tissue can be characterized in terms of water, lipid and protein contents with high accuracy by using chemical analysis, which offers a gold standard for breast density studies comparing different techniques. In the investigated image segmentation techniques, the FCM algorithm had high precision and accuracy in breast density quantification. In comparison to conventional histogram thresholding, it was more efficient and reduced inter-observer variation.

An accelerated RAMLA reconstruction algorithm for X-ray cone-beam CT

An accelerated RAMLA reconstruction algorithm for X-ray cone-beam CT

歯科用小照射野エックス線CT(3DX)用三次元データ構築ソフトウエアの開発

歯科用小照射野エックス線CT(3DX)用三次元データ構築ソフトウエアの開発

Development of 3-D Motion Display System to Assist Diagnostic Treatment of Occlusal Disorder (Contact State Analysis of Upper and Lower Teeth with Patient-Specific Hybrid Model)

Contact state of upper and lower teeth is very important for diagnostic treatment of occlusal disorders. This paper discusses a 3-D motion display system with a patient-specific hybrid model to analyze detailed contact state of upper and lower teeth. The hybrid model consists of maxillary and mandibular bone data with cone beam X-ray CT and precise teeth shape data with industrial X-ray CT. In terms of 3-D motion measurement, appropriate camera angles and frame rates are also discussed to improve the accuracy of the display system. With these improvements, this study achieves 0.1 mm accuracy which enables to evaluate the contact state of teeth. Several masticatory movements are analyzed with the new system and the analytical results provide detailed information of contact state during mastication of foods.

Evaluation of the linearity characteristic of the cone-beam CT fixed on the Varian 23EX linear accelerator

Objective To investigate the CT number linearity of the cone-beam CT (CBCT) images at the different spatial locations in the scanning area.Methods The CatphanS04 phantom at the different locations are scanned repeatcdly using the CBCT on the Varian 23EX linear accelerator.The phantom is located the isocenter point,eccentric 3 cm,eccentric 6 cm,and different points on the z-axis successively on the accelerator.The scanned mode is the standard head mode.The reconstructive thickness is 2.5 cm.The different densities inserts of CTP404 module on the different locations are measured via Eclips treatment planning system (TPS) and computed by Matlab 7.0 and the CT linear fitting are then processed.In order to understand better the linear distribution along with the value of CT in the spatial distribution the results are compared with the fan-beam CT.Results Phantom studies show that:CBCT has good linearity performance not only under the standard header (body) of the scanning conditions,but also on such locations including the cross-sectional,the sagittal,the coronal plane and the eccentric position ( R2 ＞ 0.953 ).Bowtie filtration device does not change the CT finearity but changes the value of CT.Conclusions The linearity of X-ray CBCT on the Varian linear accelerator is favorable.CBCT will be used in the TPS dose calculation via further correction of the CT value. Key words: Tomography, X-ray computed, cone-beam; Linear fitting; Catphan504 phantom

Relationship between x‐ray illumination field size and flat field intensity and its impacts on x‐ray imaging

X-ray cone-beam CT (CBCT) is being increasingly used for various clinical applications, while its performance is still hindered by image artifacts. This work investigates a new source of reconstruction error, which is often overlooked in the current CBCT imaging. The authors find that the x-ray flat field intensity (I(0)) varies significantly as the illumination volume size changes at different collimator settings. A wrong I(0) value leads to inaccurate CT numbers of reconstructed images as well as wrong scatter measurements in the CBCT research. The authors argue that the finite size of x-ray focal spot together with the detector glare effect cause the I(0) variation at different illumination sizes. Although the focal spot of commercial x-ray tubes typically has a nominal size of less than 1 mm, the off-focal-spot radiation covers an area of several millimeters on the tungsten target. Due to the large magnification factor from the field collimator to the detector, the penumbra effects of the collimator blades result in different I(0) values for different illumination field sizes. Detector glare further increases the variation, since one pencil beam of incident x-ray is scattered into an area of several centimeters on the detector. In this paper, the authors study these two effects by measuring the focal spot distribution with a pinhole assembly and the detector point spread function (PSF) with an edge-spread function method. The authors then derive a formula to estimate the I(0) value for different illumination field sizes, using the measured focal spot distribution and the detector PSF. Phantom studies are carried out to investigate the accuracy of scatter measurements and CT images with and without considering the I(0) variation effects. On our tabletop system with a Varian Paxscan 4030CB flat-panel detector and a Varian RAD-94 x-ray tube as used on a clinical CBCT system, the focal spot distribution has a measured full-width-at-half-maximum (FWHM) of around 0.4 mm, while non-negligible off-focal-spot radiation is observed at a distance of over 2 mm from the center. The measured detector PSF has an FWHM of 0.510 mm, with a shape close to Gaussian. From these two distributions, the author calculate the estimated I(0) values at different collimator settings. The I(0) variation mainly comes from the focal spot effect. The estimation matches well with the measurements at different collimator widths in both horizontal and vertical directions, with an average error of less than 3%. Our method improves the accuracy of conventional scatter measurements, where the scatter is measured as the difference between fan-beam and cone-beam projections. On a uniform water cylinder phantom, more accurate I(0) suppresses the unfaithful high-frequency signals at the object boundaries of the measured scatter, and the SPR estimation error is reduced from 0.158 to 0.014. The proposed I(0) estimation also reduces the reconstruction error from about 20 HU on the Catphan©600 phantom in the selected regions of interest to less than 4 HU. The I(0) variation is identified as one additional error source in x-ray imaging. By measuring the focal-spot distribution and detector PSF, the authors propose an accurate method of estimating the I(0) value for different illumination field sizes. The method obtains more accurate scatter measurements and therefore facilitates scatter correction algorithm designs. As correction methods for other CBCT artifacts become more successful, our research is significant in further improving the CBCT imaging accuracy.

4D registration and 4D verification of lung tumor position for stereotactic volumetric modulated arc therapy using respiratory-correlated cone-beam CT

We propose a clinical workflow of stereotactic volumetric modulated arc therapy (VMAT) for a lung tumor from planning to tumor position verification using 4D planning computed tomography (CT) and 4D cone-beam CT (CBCT). A 4D CT scanner, an Anzai belt and a BodyFix were employed to obtain 10-phase respiratory-correlated CT data for a lung patient under constrained breathing conditions. A planning target volume (PTV) was defined by adding a 5-mm margin to an internal target volume created from 10 clinical target volumes, each of which was delineated on each of the 10-phase planning CT data. A single-arc VMAT plan was created with a D95 prescription dose of 50 Gy in four fractions on the maximum exhalation phase CT images. The PTV contours were exported to a kilovoltage CBCT X-ray Volume Imaging (XVI) equipped with a linear accelerator (linac). Immediately before treatment, 10-phase 4D CBCT images were reconstructed leading to animated lung tumor imaging. Initial bone matching was performed between frame-averaged 4D planning CT and frame-averaged 4D CBCT datasets. Subsequently, the imported PTV contours and the animated moving tumor were simultaneously displayed on the XVI monitor, and a manual 4D registration was interactively performed on the monitor until the moving tumor was symmetrically positioned inside the PTV. A VMAT beam was delivered to the patient and during the delivery further 4D CBCT projection data were acquired to verify the tumor position. The entire process was repeated for each fraction. It was confirmed that the moving tumor was positioned inside the PTV during the VMAT delivery.

Iterative image reconstruction in helical cone-beam x-ray CT using a stored system matrix approach

We present a stored system matrix (SM) approach for iterative x-ray CT image reconstruction with helical cone-beam geometry. Because of the symmetry of a helical source trajectory, it is sufficient to calculate and store the SM entries for one transaxial slice only and for all source positions illuminating the slice. This is made possible by (1) selecting the reconstruction slice thickness to be an integer multiple of the source translation per projection view, and (2) discretizing the 3D reconstruction volume on a rotated stack of slices. Using the proposed method, the memory requirement for reconstructing a full field-of-view of clinical scanners is manageable on current computing platforms. The same storage principle can be generalized and applied to volume-of-interest (VOI) image reconstruction for helical cone-beam CT. In this case, the stored SM entries correspond to a partial- or full-ring region on one transaxial slice, and for all source positions illuminating the ring. The size and location of the ring depend on the size and the location of the VOI and the scan geometry. We demonstrate by both computer simulations and clinical patient data the speed and efficacy of iterative image reconstruction using the stored SM approach.

Abstract 5725: Accuracy of off-line bioluminescence imaging to localize targets in pre-clinical radiation research

Abstract Introduction Pre-clinical methods of delivering focal radiation to biological targets have made significant advances. Our group has developed the Small Animal Radiation Research Platform (SARRP), which is capable of using x-ray cone-beam CT (CBCT) to accurately guide delivery of conformal radiation. However, CBCT is deficient in localizing small orthotopic soft-tissue tumors. Bioluminescent imaging (BLI) is an affordable, accessible and sensitive ancillary method of detecting such tumors. In this study, we evaluate the setup accuracy of off-line BLI as a means to guide focal irradiation of small tumor volumes. Methods Athymic nude mice were used in accordance with institutional guidelines. Human pancreatic carcinoma cells (MiaPaCa-2) stably expressing luciferase were injected into a small glass bulb and sutured intra-abdominally to the tail of the pancreas in euthanized mice. Two methods of animal repositioning were employed during this process in which the animals were either unrestrained (n=6) or restrained (n=5). Two dimensional (2D) BLI and 3D bioluminescent tomography (BLT) were acquired of each supine mouse carcass. An ink-dot marked the “visual” centroid of the surface BL image. Carcasses were then transported to a SARRP for CBCT localization. Three methods of image guidance were applied. Using visual setup, the animal was positioned to align the ink-dot with the central axis of the SARRP. In the CBCT-aided setup, the pose of each carcass was adjusted to recapitulate its pose at the time of BLI. The 2D radial offset of the “true” bulb centroid in CBCT from the central axis of the SARRP was measured. In the 3D setup, the 3D contours of CBCT and BLT contours were registered and the 3D radial offset between the 2 centroids was calculated. Results Using the visual set up, single plane offsets of 2.2 mm +/- 1.2 mm and 2.5 mm +/- 1.5 mm were calculated between the isocenter of the vertical beam and the centroid of the bulb in unrestrained and restrained mice, respectively. After fusing the coronal 2D BL image to a corresponding coronal CBCT image, the central axis of the vertical beam was again aligned to the skin mark. The offset distances in a single plane were 2.2 mm +/- 1.2 mm and 2.4 mm +/- 1.1 mm in unrestrained and restrained mice, respectively. Finally, the offsets between the center of mass of the BL source and the CBCT glass bead after 3D fusion were 1.5 mm +/- 1 mm and 1.6 mm +/- 0.8 mm in unrestrained and restrained mice, respectively. Conclusion Restraining mice between modalities did not result in significant reduction of set up uncertainty. Similarly, use of 2D-BLI did not improve upon the visual set up method. The 3D-BLT fusion represents the best that can be achieved with off-line localization. An on-board approach with further improvement in BLT using prior information of anatomic and optical properties should be investigated to further improve localization uncertainty. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5725. doi:1538-7445.AM2012-5725

歯科用小照射野X線CT(Ortho-CT)用3次元画像表示プログラムの開発

歯科用小照射野X線CT(Ortho-CT)用3次元画像表示プログラムの開発

Erratum: "A general framework and review of scatter correction methods in x-ray cone beam CT. Part 1: Scatter Compensation Approaches" [Med. Phys. 38(7), 4296-4311 (2011)

Erratum: "A general framework and review of scatter correction methods in x-ray cone beam CT. Part 1: Scatter Compensation Approaches" [Med. Phys. 38(7), 4296-4311 (2011)

歯科用小照射野X線CT(Ortho-CT)の口腔外科領域への臨床応用

歯科用小照射野X線CT(Ortho-CT)の口腔外科領域への臨床応用

Data-Driven Problem Reduction for Image Reconstruction From Projections Using Gift Wrapping

A generic data-driven approach called focus of attention is presented that automatically segments first the projection data and then the image into object and background prior to reconstruction. This segmentation, which is based on the formation of convex hulls, subsequently allows the computational resources to be devoted to the object data while the background data is discarded from further consideration. Experimental results are presented for high-resolution reconstruction of a cone beam x-ray CT image of a laboratory mouse.

Evaluation of kV Cone-Beam CT Performance for Prostate IGRT

Cone-beam computed tomography (CBCT) is a new image-guided radiation therapy (IGRT) technique for patient alignment in radiotherapy. The CBCT x-ray volume imaging system from Elekta allows for a variety of alignment methods. The aim of this study is to assess the accuracy of soft-tissue-based automatic alignment as compared with manual alignment using intraprostatic fiducials. All patients were treated on an Elekta Synergy S linear accelerator with kilovoltage CBCT. All alignments were performed using the x-ray volume imaging system and associated software. Automatic alignment with gray-value-based registration and manual alignment to fiducial markers were performed. Transitional corrections along each axis as well as 3-dimensional vectors were compared with evaluate the accuracy of gray-value-based registration compared with fiducials. The distribution of the 3-dimensional vectors between gray-value and fiducial registrations demonstrated notable differences. The mean summed vector was 0.75 cm, with a standard deviation (SD) of 0.52 cm and range from 0.04 to 2.06 cm. There was minimal difference along the lateral direction, with a mean ± SD of -0.02 cm ± 0.13 cm. However, there were large discrepancies along the superior-inferior and anterior-posterior direction alignments, with mean ± SD values of -0.55 ± 0.48 cm and -0.31 ± 0.43 cm, respectively. CBCT with soft-tissue-based automatic corrections is not an accurate alignment compared with manual alignment to fiducial markers for prostate IGRT. We have concluded that a daily manual alignment to fiducials is one of the most reliable methods to maintain accuracy in prostate IGRT.