K. Bliznakova

A three-dimensional breast software phantom for mammography simulation

This paper presents a methodology for three-dimensional (3D) computer modelling of the breast, using a combination of 3D geometrical primitives and voxel matrices that can be further subjected to simulated x-ray imaging, to produce synthetic mammograms. The breast phantom is a composite model of the breast and includes the breast surface, the duct system and terminal ductal lobular units. Coopers ligaments, the pectoral muscle, the 3D mammographic background and breast abnormalities. A second analytical x-ray matter interaction modelling module is used to generate synthetic images from monoenergetic fan beams. Mammographic images of various synthesized breast models differing in size, shape and composition were produced. A preliminary qualitative assessment performed by three radiologists and a quantitative evaluation study using fractal and grey-level histogram analysis were conducted. A comparative study of extracted features with published data has also been performed. The evaluation results indicated good correlation of characteristics between synthetic and actual radiographs. Applications foreseen are not only in the area of breast imaging experimentation but also in education and training.

Dual-energy mammography: simulation studies

This paper presents a mammography simulator and demonstrates its applicability in feasibility studies in dual-energy (DE) subtraction mammography. This mammography simulator is an evolution of a previously presented x-ray imaging simulation system, which has been extended with new functionalities that are specific for DE simulations. The new features include incident exposure and dose calculations, the implementation of a DE subtraction algorithm as well as amendments to the detector and source modelling. The system was then verified by simulating experiments and comparing their results against published data. The simulator was used to carry out a feasibility study of the applicability of DE techniques in mammography, and more precisely to examine whether this modality could result in better visualization and detection of microcalcifications. Investigations were carried out using a 3D breast software phantom of average thickness, monoenergetic and polyenergetic beam spectra and various detector configurations. Dual-shot techniques were simulated. Results showed the advantage of using monoenergetic in comparison with polyenergetic beams. Optimization studies with monochromatic sources were carried out to obtain the optimal low and high incident energies, based on the assessment of the figure of merit of the simulated microcalcifications in the subtracted images. The results of the simulation study with the optimal energies demonstrated that the use of the DE technique can improve visualization and increase detectability, allowing identification of microcalcifications of sizes as small as 200 microm. The quantitative results are also verified by means of a visual inspection of the synthetic images.

An integrated research tool for X-ray imaging simulation

This paper presents a software simulation package of the entire X-ray projection radiography process including beam generation, absorber structure and composition, irradiation set up, radiation transport through the absorbing medium, image formation and dose calculation. Phantoms are created as composite objects from geometrical or voxelized primitives and can be subjected to simulated irradiation process. The acquired projection images represent the two-dimensional spatial distribution of the energy absorbed in the detector and are formed at any geometry, taking into account energy spectrum, beam geometry and detector response. This software tool is the evolution of a previously presented system, with new functionalities, user interface and an expanded range of applications. This has been achieved mainly by the use of combinatorial geometry for phantom design and the implementation of a Monte Carlo code for the simulation of the radiation interaction at the absorber and the detector.

Evaluation of an improved algorithm for producing realistic 3D breast software phantoms: Application for mammography

PURPOSE This work presents an improved algorithm for the generation of 3D breast software phantoms and its evaluation for mammography. METHODS The improved methodology has evolved from a previously presented 3D noncompressed breast modeling method used for the creation of breast models of different size, shape, and composition. The breast phantom is composed of breast surface, duct system and terminal ductal lobular units, Coopers ligaments, lymphatic and blood vessel systems, pectoral muscle, skin, 3D mammographic background texture, and breast abnormalities. The key improvement is the development of a new algorithm for 3D mammographic texture generation. Simulated images of the enhanced 3D breast model without lesions were produced by simulating mammographic image acquisition and were evaluated subjectively and quantitatively. For evaluation purposes, a database with regions of interest taken from simulated and real mammograms was created. Four experienced radiologists participated in a visual subjective evaluation trial, as they judged the quality of the simulated mammograms, using the new algorithm compared to mammograms, obtained with the old modeling approach. In addition, extensive quantitative evaluation included power spectral analysis and calculation of fractal dimension, skewness, and kurtosis of simulated and real mammograms from the database. RESULTS The results from the subjective evaluation strongly suggest that the new methodology for mammographic breast texture creates improved breast models compared to the old approach. Calculated parameters on simulated images such as beta exponent deducted from the power law spectral analysis and fractal dimension are similar to those calculated on real mammograms. The results for the kurtosis and skewness are also in good coincidence with those calculated from clinical images. Comparison with similar calculations published in the literature showed good agreement in the majority of cases. CONCLUSIONS The improved methodology generated breast models with increased realism compared to the older model as shown in evaluations of simulated images by experienced radiologists. It is anticipated that the realism will be further improved using an advanced image simulator so that simulated images may be used in feasibility studies in mammography.

A novel simulation algorithm for soft tissue compression.

This paper presents a novel general approach to simulation of soft tissue compression. A theoretical framework of the compression algorithm has been developed and implemented, based on the concept of a simple spring. The volume subjected to compression is divided into a number of “model elements”, each one consisting of 27 nodes. The nodes are connected with springs. The mechanical properties of the tissues are assumed to be linear and isotropic. The compressed volume remains constant due to the introduced concept of spring variable equilibrium lengths. Initial settings for compression simulation are introduced in order that the algorithm converges faster. The developed compression algorithm was used to model breast compression during a standard mammography examination. Specifically, the method was applied to a high-resolution three-dimensional software breast phantom, composed to have a medium glandularity and calcification abnormalities. The compression was set to 50%. Results showed that the abnormalities maintain their shape and dimensions during the compression, while the surrounding breast tissues undergo considerable deformation and displacement. A “decompression” algorithm was also applied to test the reversibility of the model.

Experimental validation of a radiographic simulation code using breast phantom for X-ray imaging

Computer models and simulations of X-ray imaging systems are becoming a very precious tool during the development and evaluation of new X-ray imaging techniques. To provide, however, a faithful simulation of a system, all components must be accurately modelled and tested, followed by verification through experimental measurements. This paper presents a validation study of the XRayImagingSimulator, an in-house developed X-ray imaging simulator, which is extensively used as a basic tool in carrying out complex breast imaging simulations. The approach followed compares results obtained via an experimental setup for breast phantom (CIRS 011A) imaging, using synchrotron radiation (SYRMEP beamline at ELETTRA), with those from its simulated setup under the same conditions. The study demonstrated a very good agreement between experimental and simulated images compared both in terms of subjective and objective criteria. The combination of the XRayImagingSimulator with our BreastSimulator provides a powerful tool for in silico testing of new X-ray breast imaging approaches.

Evaluation of digital breast tomosynthesis reconstruction algorithms using synchrotron radiation in standard geometry

PURPOSE In this article, the image quality of reconstructed volumes by four algorithms for digital tomosynthesis, applied in the case of breast, is investigated using synchrotron radiation. METHODS An angular data set of 21 images of a complex phantom with heterogeneous tissue-mimicking background was obtained using the SYRMEP beamline at ELETTRA Synchrotron Light Laboratory, Trieste, Italy. The irradiated part was reconstructed using the multiple projection algorithm (MPA) and the filtered backprojection with ramp followed by hamming windows (FBR-RH) and filtered backprojection with ramp (FBP-R). Additionally, an algorithm for reducing the noise in reconstructed planes based on noise mask subtraction from the planes of the originally reconstructed volume using MPA (MPA-NM) has been further developed. The reconstruction techniques were evaluated in terms of calculations and comparison of the contrast-to-noise ratio (CNR) and artifact spread function. RESULTS It was found that the MPA-NM resulted in higher CNR, comparable with the CNR of FBP-RH for high contrast details. Low contrast objects are well visualized and characterized by high CNR using the simple MPA and the MPA-NM. In addition, the image quality of the reconstructed features in terms of CNR and visual appearance as a function of the initial number of projection images and the reconstruction arc was carried out. Slices reconstructed with more input projection images result in less reconstruction artifacts and higher detail CNR, while those reconstructed from projection images acquired in reduced angular range causes pronounced streak artifacts. CONCLUSIONS Of the reconstruction algorithms implemented, the MPA-NM and MPA are a good choice for detecting low contrast objects, while the FBP-RH, FBP-R, and MPA-NM provide high CNR and well outlined edges in case of microcalcifications.

Integrated Software System for Improving Medical Equipment Management

The evolution of biomedical technology has led to an extraordinary use of medical devices in health care delivery. During the last decade, clinical engineering departments (CEDs) turned toward computerization and application of specific software systems for medical equipment management in order to improve their services and monitor outcomes. Recently, much emphasis has been given to patient safety. Through its Medical Device Directives, the European Union has required all member nations to use a vigilance system to prevent the reoccurrence of adverse events that could lead to injuries or death of patients or personnel as a result of equipment malfunction or improper use. The World Health Organization also has made this issue a high priority and has prepared a number of actions and recommendations. In the present workplace, a new integrated, Windows-oriented system is proposed, addressing all tasks of CEDs but also offering a global approach to their management needs, including vigilance. The system architecture is based on a star model, consisting of a central core module and peripheral units. Its development has been based on the integration of 3 software modules, each one addressing specific predefined tasks. The main features of this system include equipment acquisition and replacement management, inventory archiving and monitoring, follow up on scheduled maintenance, corrective maintenance, user training, data analysis, and reports. It also incorporates vigilance monitoring and information exchange for adverse events, together with a specific application for quality-control procedures. The system offers clinical engineers the ability to monitor and evaluate the quality and cost-effectiveness of the service provided by means of quality and cost indicators. Particular emphasis has been placed on the use of harmonized standards with regard to medical device nomenclature and classification. The systems practical applications have been demonstrated through a pilot evaluation trial.

Image quality evaluation of breast tomosynthesis with synchrotron radiation.

PURPOSE This study investigates the image quality of tomosynthesis slices obtained from several acquisition sets with synchrotron radiation using a breast phantom incorporating details that mimic various breast lesions, in a heterogeneous background. METHODS A complex Breast phantom (MAMMAX) with a heterogeneous background and thickness that corresponds to 4.5 cm compressed breast with an average composition of 50% adipose and 50% glandular tissue was assembled using two commercial phantoms. Projection images using acquisition arcs of 24°, 32°, 40°, 48°, and 56° at incident energy of 17 keV were obtained from the phantom with the synchrotron radiation for medical physics beamline at ELETTRA Synchrotron Light Laboratory. The total mean glandular dose was set equal to 2.5 mGy. Tomograms were reconstructed with simple multiple projection algorithm (MPA) and filtered MPA. In the latter case, a median filter, a sinc filter, and a combination of those two filters were applied on the experimental data prior to MPA reconstruction. Visual inspection, contrast to noise ratio, contrast, and artifact spread function were the figures of merit used in the evaluation of the visualisation and detection of low- and high-contrast breast features, as a function of the reconstruction algorithm and acquisition arc. To study the benefits of using monochromatic beams, single projection images at incident energies ranging from 14 to 27 keV were acquired with the same phantom and weighted to synthesize polychromatic images at a typical incident x-ray spectrum with W target. RESULTS Filters were optimised to reconstruct features with different attenuation characteristics and dimensions. In the case of 6 mm low-contrast details, improved visual appearance as well as higher contrast to noise ratio and contrast values were observed for the two filtered MPA algorithms that exploit the sinc filter. These features are better visualized at extended arc length, as the acquisition arc of 56° with 15 projection images demonstrates the highest image reconstruction quality. For microcalcifications, filtered MPA implemented with a combination of median and sinc filters indicates better feature appearance due to efficient suppression of background tissue. The image quality of these features is less sensitive to the acquisition arc. Calcifications with size ranging from 170 to 500 μm, like the ones presently studied, are well identified and visualized for all arcs used. The comparison of single projection images obtained under different beam conditions showed that the use of monochromatic beam can produce an image with higher contrast and contrast to noise ratio compared to an image corresponding to a polychromatic beam even when the latter is acquired with double incident exposure. CONCLUSIONS Filter optimization in respect to the type of feature characteristics is important before the reconstruction. The MPA combined with median and sinc filters results in improved reconstruction of microcalcifications and low-contrast features. The latter are better visualized at extended arc length, while microcalcifications are less sensitive to this acquisition parameter. Use of monochromatic beams may result in tomographic images with higher contrast acquired at lower incident exposures.

Simulation studies of field shaping in rotational radiation therapy.

This article presents simulation studies of field shaping in rotational radiation therapy by means of two categories of beam modifying devices: protectors and shapers. The protectors used are diminished copies of the organs at risk (OARs) and stay parallel to them during gantry rotation. Thus, each protector always keeps the corresponding OAR in its shadow, significantly reducing the irradiation. The shapers are used in order to obtain a more uniform dose distribution in the planning target volume (PTV) while preserving their initial orientation during gantry rotation. Thus, the use of beam modifying devices allows modulation of the beam intensity, to better fit irradiation requirements, at every gantry position. A software tool for calculations of geometrical position and dimensions of the beam modifying devices, using information about the shape, size, and position of the protected organ or area at risk as input, was developed. This tool was integrated into the in-house-developed Monte Carlo radiation therapy simulator (MCRTS), used to simulate the particle transport through the designed system. The verification of the software tool showed good agreement between experimental and simulation data, with discrepancies of less than 3%. Dose distributions in solid-geometry and voxel-based neck models were evaluated. Furthermore, the effectiveness of the shapers to modify the dose distribution outside the protected area was studied. Results demonstrated that the use of the shapers effectively improves dose uniformity. Studies using shapers of different materials were also carried out and resulted in similar dose distributions. The results of the simulation studies with a voxel-based model showed that rotational therapy with beam modifying devices offers adequate protection of the OAR and a uniform dose distribution outside the protected region.