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.

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.

Quality assurance in conformal radiotherapy: DYNARAD consensus report on practice guidelines.

BACKGROUND AND PURPOSE: Conformal radiotherapy has only recently been widely implemented. Although not all aspects have yet been adequately proven, it is generally recognized that maintaining a high degree of precision throughout the process is critical to the treatment outcome while the focus for quality assurance and quality improvement will need to concentrate more on human factors, procedures, communication, organization and training. A general consensus document on quality assurance guidelines for institutions that deliver conformal radiotherapy treatments to patients has been elaborated within the framework of the DYNARAD/BIOMED concerted action on conformal radiotherapy. The present paper aims to highlight those issues that were identified as of specific importance to conformal radiotherapy. The work reported here further details this guidance by direct correlation with the issues involved in the special case of conformal radiotherapy. METHODS: The DYNARAD document has been drafted in the form of a desktop guide comprising six sets of guidelines and is based on the ESTRO advisory report on 'Quality Assurance in Radiotherapy'. RESULTS AND CONCLUSIONS: The document has been endorsed by the DYNARAD group of institutions. As such it can form the basis for further discussions and enter into the subsequent phase of expanding its consensus basis.

A method for selective removal of out-of-plane structures in digital tomosynthesis.

The quality of the reconstructed images in Digital Tomosynthesis is often limited by the presence of artifacts due to blur from planes other than the fulcrum plane. A technique has been developed for the separation and subsequent removal of unrelated structures from the reconstructed plane. The method involves the reconstruction of the blur originating in user-selected "noisy" planes as it appears on the plane of interest. This is achieved by projecting the reconstructed images of the selected plane on the image formation plane for all viewing angles, and subsequently, synthesizing its blurred image on the plane of interest. There are no restrictions as to the identity of the planes to be removed. Reproduction of the noise is performed using the tomosynthesis algorithm itself, thus the technique can be modified to suit any reconstruction algorithm. The proposed technique was implemented on the Multiple Projection Algorithm and was experimentally evaluated using a radiotherapy simulator unit.

A multiple projection method for digital tomosynthesis.

A new method of optimized efficiency for the retrospective reconstruction of tomograms is presented. The method has been developed for use with isocentric fluoroscopic units and is capable of performing digital tomosynthesis of anatomical planes of user selected orientation and distance from the isocenter. Optimization of efficiency has been achieved by segmenting the reconstruction process into discrete transformations that are specific to groups of pixels, rather than performing pixel by pixel operations. These involve a number of projections of the acquired image matrices as well as parallel translations and summing. Application of this method has resulted in a significant reduction of computing time. The proposed algorithm has been experimentally tested on a radiotherapy simulator unit with the use of a phantom and the obtained results are reported and discussed.

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. Cooper's 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.

An anatomical filter for exposure equalization in mammography.

An anatomical filter has been designed, tested and subsequently used in clinical practice to equalize optical density over the entire mammographic image, thus eliminating the need for dual exposure whenever both the mammary gland and the peripheral structures of the breast must be clearly visualized. The use of the filter results in a reduction of the optical density, at the peripheral structures of the breast, with a simultaneous increase of the contrast, without causing deterioration of the mammary gland image. Improved visualization of the connective tissue, the skin, the nipple and the subcutaneous adipose tissue is achieved, as well as minimization of the radiation dose to the breast for patients with an indication of peripheral breast lesions.

A software data generator for radiographic imaging investigations.

A software data generation tool, intended to be used in radiographic applications, has been developed. The application integrates a phantom design module and an imaging simulator. Phantoms can be described as a set of either geometrical objects or voxels, or contours drawn on multiple tomographic slices. Radiographic projections of the phantoms are formed on the basis of a simulated irradiation process, with selectable imaging parameters. Comparison between actual projection images from a physical and a simulated phantom shows good correspondence. The application was used for digital tomosynthesis (DTS) investigations and has proven to be a useful tool in the study of tomographic noise. Further development is expected to expand the use of the application to more areas of radiological imaging research.

Three-dimensional localisation based on projectional and tomographic image correlation: an application for digital tomosynthesis.

Accurate three-dimensional tumor localisation in Radiotherapy, is critical to the treatment outcome, particularly when high dose gradients are present. A number of techniques have been proposed for the localisation of anatomical structures or markers. The present study proposes an approach to a concurrent maximisation of localisation accuracy and efficiency by correlation of tomographic and projectional images. The method introduces an element of direct verification and interactive optimisation of the process. Tomographic images are used for the identification of a point of interest. Its position is computed within the treatment co-ordinate system and verification of this position is achieved by obtaining the beam's eye view of the identified point on two projection radiographs. The key element of the approach is that all images used should be part of one single image data set. The implementation of this localisation method, as part of the functionality of a Digital Tomosynthesis prototype, has provided an integrated facility for localisation, of optimised accuracy and precision, while easy and efficient to use. The considerations are general and apply in principle to any imaging system that can augment tomographic images with projections.

An integrated system for the production of field shaping devices in radiotherapy.

A system has been developed in our department that simplifies the production processes of field shaping devices in radiotherapy, integrating an image grabbing and processing facility at a radiotherapy simulator and an automated block cutter. The data acquisition subsystem captures images, processes and corrects them for pincushion distortions, creates a composite radiograph, records user defined contours of blocks and exports data to the block cutter controller. A robotic subsystem drives and controls the polystyrene cutting unit. The system has been experimentally evaluated. Errors in contour definition were found to be less than 1 mm for a broad range of gantry angles and not exceeding 1.5 mm for those gantry orientations that present maximum magnetic field related image intensifier distortion, while the automated block cutter is capable of cutting out contours in polystyrene with an accuracy comparable to that of commercially available systems. The system is expected to contribute to the overall improvement of radiotherapy processes, particularly in low budget radiotherapy departments, introducing improvements in accuracy and efficiency at minimum costs.

A wavelet-based method for removal of out-of-plane structures in digital tomosynthesis.

Reconstructed images in digital tomosynthesis (DTS) are affected by artifacts due to blur from planes other than the fulcrum plane. A wavelet-based method has been developed for the discrimination and subsequent removal of unrelated structures from the reconstructed plane. The approach exploits both the specific pattern of noise in DTS and the spatial locality of the wavelet transformation. The technique was implemented on a DTS clinical protoype system. Experimental evaluation on angiographic types of images demonstrated excellent noise differentiation and elimination. The method is therefore particularly useful for certain medical imaging applications such as vascular DTS imaging.

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.

Q-Pro: a quality control management system for medical equipment.

Q-Pro is an application for quality control (QC) and inspection of medical equipment. The system has been designed on the basis of a broad requirements analysis, contributed by clinical engineers from several European countries and with a focus on current and forthcoming regulatory requirements concerning the quality control and risk management for medical equipment. Q-Pro comprises a generalized application, providing the necessary flexibility to accommodate the different degrees of difficulty and specialization in creating or customizing QC protocols, carrying out inspections and managing collected data. The system incorporates a tool library for QC protocol design, widely used multimedia as well as a local database for protocol and inventory data archiving. The paper presents a detailed account of the system context of use, design and functionality.

Improving user acceptance of health-care telematics.

Telehealth represents a new approach to health-care with the potential for improving accessibility and reducing costs. Over the years, technology has become increasingly interactive, cheaper and standardized. Despite this, the uptake of technology has been low. One of the main reasons is that the introduction of telematics in health-care requires more than technology and software--organizational and cultural change is required as well. A suggested approach is based on the principles of service quality and quality management, to produce a partnership between the users and the developers of new technologies. This will in turn make it possible to bring user-validated requirements into the design of the system and create feelings of ownership and motivation on the part of users, in order to prepare their environment for the change. The methodology has been effectively used in various projects of the Telematics Application Programme of the European Commission.

Education in biomedical engineering: experience from a European ERASMUS program.

Based on recent advances in biomedical research and the developments of new equipment and techniques, the field of Biomedical Engineering and Health Care Telematics are currently undergoing a rapid evolution characterized by an increasing degree of specialization. This, in turns, imposes new requirements in advanced education, while the changing scene at European level, introduces a major challenge for harmonization and standardization of education with a focus on meeting the emerging needs. At the same time information technologies provide new means and tools supporting the educational and training activities. An initiative for the development of a multinational advanced course in Biomedical Engineering, is implemented in the University of Patras with extended collaboration of European Universities, providing a unique case for achievement of excellency. In order to take full advantage of this potential, a Quality Assurance system has been designed and implemented over the past four years, aiming to provide the appropriate framework for mutual recognition amongst the participating institutions. Additionally, the implementation of new telematic tools is scheduled for the near future, in order to provide the Course with teleconference facilities and allow a much larger number of students to remotely attend the lectures.

Monte Carlo simulation of the radiographic imaging procedure for electronically designed phantoms.

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 and image formation. This software tool is an augmented version of a previously presented system with expanded range of application by the implementation of Monte Carlo approach for the simulation of the radiation interaction at the absorber and the detector. 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.

A protocol building software tool for medical device quality control tests.

Q-Pro is an application for Quality Control and Inspection of Medical Devices. General system requirements include friendly and comprehensive graphical environment and proper, quick, easy and intuitive user interface. Functions such as, a tool library for protocol design widely used multimedia, as well as, a support of a local database for protocol and inventory data archiving are provided by the system. In order to serve the different categories of users, involved in Quality Control procedures, the system has been split into three modules of different functionality and complexity, each of which can work as a stand-alone application. The implementation of protocols and use of the software functions, as well as, the user interface itself have been proved by the evaluators to be clear and intuitive. The software seems to adapt easily to different kinds of Quality Control procedures and objectives. Q-Pro effectively supports and enhances the processes to attain a highly tuned, professional, responsive and effective quality control and preventive maintenance procedures for biomedical equipment management.

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.