Ivan Buliev

Estimation of the heart respiratory motion with applications for cone beam computed tomography imaging: a simulation study

Computed tomography (CT) reconstruction methods assume imaging of static objects; object movement during projection data acquisition causes tomogram artifacts. The continuously moving heart, therefore, represents a complicated imaging case. The associated problems due to the heart beating can be overcome either by using very short projection acquisition times, during which the heart may be considered static, or by ECG-gated acquisition. In the latter case, however, the acquisition of a large number of projections may not be completed in a single breath hold, thus heart displacement occurs as an additional problem. This problem has been addressed by applying heart motion models in various respiratory motion compensation algorithms. Our paper focuses on cone beam computed tomography (CBCT), performed in conjunction with isocentric, fluoroscopic equipment, and continuous ECG and respiratory monitoring. Such equipment is used primarily for in-theater three-dimensional (3-D) imaging and benefits particularly from the recent developments in flat panel detector technologies. The objectives of this paper are: (i) to develop a model for the motion of the heart due to respiration during the respiratory cycle; (ii) to apply this model to the tomographic reconstruction algorithm, in order to account for heart movement due to respiration in the reconstruction; and (iii) to initially evaluate this method by means of simulation studies. Based on simulation studies, we were able to demonstrate that heart displacement due to respiration can be estimated from the same projection data, required for a CBCT reconstruction. Our paper includes semiautomatic segmentation of the heart on the X-ray projections and reconstruction of a convex 3-D-heart object that performs the same motion as the heart during respiration, and use of this information into the CBCT reconstruction algorithm. The results reveal significant image quality improvements in cardiac image reconstruction.

Robust identification and localization of intramedullary nail holes for distal locking using CBCT: a simulation study.

Closed intramedullary nailing is a common technique for treatment of femur and tibia fractures. The most challenging step in this procedure is the precise placement of the lateral screws that stabilize the fragmented bone. The present work concerns the development and the evaluation of a method to accurately identify in the 3D space the axes of the nail hole canals. A limited number of projection images are acquired around the leg with the help of a C-arm. On two of them, the locking hole entries are interactively selected and a rough localization of the hole axes is performed. Perpendicularly to one of them, cone-beam computed tomography (CBCT) reconstructions are produced. The accurate identification and localization of the hole axes are done by an identification of the centers of the nail holes on the tomograms and a further 3D linear regression through principal component analysis (PCA). Various feature-based approaches (RANSAC, least-square fitting, Hough transform) have been compared for best matching the contours and the centers of the holes on the tomograms. The robustness of the suggested method was investigated using simulations. Programming is done in Matlab and C++. Results obtained on synthetic data confirm very good localization accuracy - mean translational error of 0.14 mm (std=0.08 mm) and mean angular error of 0.84° (std=0.35°) at no radiation excess. Successful localization can be further used to guide a surgeon or a robot for correct drilling the bone along the nail openings.

ECG signal recording, processing and transmission using a mobile phone

Telemedicine is being rapidly developed. In isolated places, i.e. islands, mountains or ships, where access to medical services is time-consuming or infeasible, it can prove life-saving. Powerful programming languages such as C++ and Java#8482; are supported by the modern mobile phones, which gives a possibility for easy developing of useful telemedicine applications. In this paper we present an approach for distant simultaneous monitoring of several ECG signals. The individual channel signals are packed through modulation into a complex sound signal, which is further recorded by a mobile phone. The phone is interfaced to the measuring device through a modified hands-free accessory. JAVA applications allow storing the signals in multimedia files and their transmitting to a second mobile phone via MMS or other means. A real-time ECG monitoring is also possible. The feasibility of the signal processing algorithms is confirmed through simulations in MATLAB.

In-line phase-contrast breast tomosynthesis: a phantom feasibility study at a synchrotron radiation facility.

The major objective is to adopt, apply and test developed in-house algorithms for volumetric breast reconstructions from projection images, obtained in in-line phase-contrast mode. Four angular sets, each consisting of 17 projection images obtained from four physical phantoms, were acquired at beamline ID17, European Synchroton Radiation Facility, Grenoble, France. The tomosynthesis arc was  ±32°. The physical phantoms differed in complexity of texture and introduced features of interest. Three of the used phantoms were in-house developed, and made of epoxy resin, polymethyl-methacrylate and paraffin wax, while the fourth phantom was the CIRS BR3D. The projection images had a pixel size of 47 µm  ×  47 µm. Tomosynthesis images were reconstructed with standard shift-and-add (SAA) and filtered backprojection (FBP) algorithms. It was found that the edge enhancement observed in planar x-ray images is preserved in tomosynthesis images from both phantoms with homogeneous and highly heterogeneous backgrounds. In case of BR3D, it was found that features not visible in the planar case were well outlined in the tomosynthesis slices. In addition, the edge enhancement index calculated for features of interest was found to be much higher in tomosynthesis images reconstructed with FBP than in planar images and tomosynthesis images reconstructed with SAA. The comparison between images reconstructed by the two reconstruction algorithms shows an advantage for the FBP method in terms of better edge enhancement. Phase-contrast breast tomosynthesis realized in in-line mode benefits the detection of suspicious areas in mammography images by adding the edge enhancement effect to the reconstructed slices.

Modeling of small carbon fiber-reinforced polymers for X-ray imaging simulation

A methodology for generation of realistic three-dimensional software models of carbon fiber-reinforced polymer (CFRP) structures, dedicated for use in simulation studies of advanced X-ray imaging techniques for non-destructive testing (NDT), has been developed, implemented, and evaluated. Two CFRP models are presented in this paper, one built as a set of stacked layers that contain continuous carbon bundles and a second as a braided textile from woven carbon bundles. The following CFRP defects were modeled: porosity, missing carbon bundles, and non-carbon inclusions. X-ray projection images were generated using an in-house developed X-ray imaging simulator. The obtained preliminary visual and quantitative validation results showed an overall good correlation of characteristics between synthetic and experimental data radiographs and justify the use of this model for research in CFRP X-ray imaging. The application of the CFRP model is demonstrated in a feasibility study that aims to computationally evaluate the appropriateness of two advanced X-ray imaging techniques: cone-beam CT (CBCT) and tomosynthesis (limited arc tomography), as inspection techniques for NDT of CFRP parts. The simulation showed that in all cases the CBCT approach outperformed both conventional radiography and tomosynthesis in terms of defect characterization and visualization.

Evaluation of a breast software model for 2D and 3D X-ray imaging studies of the breast

INTRODUCTION In X-ray imaging, test objects reproducing breast anatomy characteristics are realized to optimize issues such as image processing or reconstruction, lesion detection performance, image quality and radiation induced detriment. Recently, a physical phantom with a structured background has been introduced for both 2D mammography and breast tomosynthesis. A software version of this phantom and a few related versions are now available and a comparison between these 3D software phantoms and the physical phantom will be presented. METHODS The software breast phantom simulates a semi-cylindrical container filled with spherical beads of different diameters. Four computational breast phantoms were generated with a dedicated software application and for two of these, physical phantoms are also available and they are used for the side by side comparison. Planar projections in mammography and tomosynthesis were simulated under identical incident air kerma conditions. Tomosynthesis slices were reconstructed with an in-house developed reconstruction software. In addition to a visual comparison, parameters like fractal dimension, power law exponent β and second order statistics (skewness, kurtosis) of planar projections and tomosynthesis reconstructed images were compared. RESULTS Visually, an excellent agreement between simulated and real planar and tomosynthesis images is observed. The comparison shows also an overall very good agreement between parameters evaluated from simulated and experimental images. CONCLUSION The computational breast phantoms showed a close match with their physical versions. The detailed mathematical analysis of the images confirms the agreement between real and simulated 2D mammography and tomosynthesis images. The software phantom is ready for optimization purpose and extrapolation of the phantom to other breast imaging techniques.

A software platform for phase contrast x-ray breast imaging research

PURPOSE To present and validate a computer-based simulation platform dedicated for phase contrast x-ray breast imaging research. METHODS The software platform, developed at the Technical University of Varna on the basis of a previously validated x-ray imaging software simulator, comprises modules for object creation and for x-ray image formation. These modules were updated to take into account the refractive index for phase contrast imaging as well as implementation of the Fresnel-Kirchhoff diffraction theory of the propagating x-ray waves. Projection images are generated in an in-line acquisition geometry. To test and validate the platform, several phantoms differing in their complexity were constructed and imaged at 25 keV and 60 keV at the beamline ID17 of the European Synchrotron Radiation Facility. The software platform was used to design computational phantoms that mimic those used in the experimental study and to generate x-ray images in absorption and phase contrast modes. RESULTS The visual and quantitative results of the validation process showed an overall good correlation between simulated and experimental images and show the potential of this platform for research in phase contrast x-ray imaging of the breast. The application of the platform is demonstrated in a feasibility study for phase contrast images of complex inhomogeneous and anthropomorphic breast phantoms, compared to x-ray images generated in absorption mode. CONCLUSIONS The improved visibility of mammographic structures suggests further investigation and optimisation of phase contrast x-ray breast imaging, especially when abnormalities are present. The software platform can be exploited also for educational purposes.

Study of suitability of new materials for use with physical breast phantoms

Emerging X-ray breast imaging applications require the use of realistic physical three-dimensional phantoms are breast CT, phase-contrast mammography and the existing breast Tomosynthesis, dedicated to screen as early as possible and diagnose cancer in breast. However, manufacturing of such phantoms meets difficulties related to the current technology, suitable materials, manufacturing precision, format of the software models. This paper reports the preliminary results from simulation studies aiming to investigate mixtures prepared from epoxy resin and iodine powder in specific ratios as tissue substitutes for X-ray breast imaging. For each material, mass and linear attenuation coefficients were calculated for the X-ray energy range from 10 to 32 keV. Mixtures of epoxy resin and up to 1.8% iodine powder turn to be a suitable option for tissue substitutes. Selected materials were used in simulations of breast lesions with blurry edges.

Contrast Detail Phantoms for X-ray Phase-Contrast Mammography and Tomography

Primary goal of this study is to investigate the visibility of low-contrast details of different size on images obtained at conventional mammography unit, and at a monochromatic synchrotron radiation source, in absorption based and phase contrast imaging setups. For this purpose, three physical phantoms made of paraffin as a bulk material were used. They embedded various low contrast features. Single projection images were acquired with the GE Senographe mammography unit and at the beamline ID17, ESRF, Grenoble. Comparison of images showed that images obtained in a phase contrast mode have more visible details than the images acquired either in absorption mode at the synchrotron or at the conventional x-ray mammography unit. Analysis for i¾? and μ suggests that paraffin may be a suitable material for the manufacturing of tissue-mimicking phantoms dedicated to phase contrast applications. Results will be exploited in the development of a dedicated phantom for phase contrast imaging.

Comparison of algorithms for out-of-plane artifacts removal in digital tomosynthesis reconstructions

Digital tomosynthesis is a method of limited angle reconstruction of tomographic images produced at variable heights, on the basis of a set of angular projections taken in an arc around human anatomy. Reconstructed tomograms from unprocessed original projection images, however, are invariably affected by tomographic noise such as blurred images of objects lying outside the plane of interest and superimposed on the focused image of the fulcrum plane. The present work investigates the performance of two approaches for generation of tomograms with a reduced noise: a generalised post-processing method, based on constructing a noise mask from all planes in the reconstructed volume, and its subsequent subtraction from the in-focus plane and a filtered Multiple Projection Algorithm. The comparison between the two algorithms shows that the first method provides reconstructions with very good quality in case of high contrast features, especially for those embedded into a heterogeneous background.