Matteo Bettuzzi

Experimental micro-CT system for x-ray NDT

This work describes the setup of an experimental system for microtomography developed in the framework of a collaboration between the Physics Department of the University of Bologna (Italy) and the Geosphaera Research Center of Moscow (Russia). The main goal of this inspection system is to carry out high-resolution analysis in vitro of biomedical samples as well as nondestructive testing (NDT) of industrial components. The detection system consists of a 30x15 mm2 rectangular fiberoptic taper (ratio 2:1) optically coupled to a cooled 12-bit CCD camera (1024x512 pixels). On the entrance window of the taper is deposited a thin layer of Gd2O2S:Tb phosphor which provides the X-light conversion. The image readout is carried out by means of a commercial frame grabber installed on a personal computer and specific software is used for data acquisition and control of the tomographic process. The object under investigation is arranged on a 3-degree micro-positioning system (x-y translation and rotation) and irradiated by an X-ray microfocus beam (up to 200 kVp). The sample can be positioned easily along the source-detector axis in order to obtain a large magnification of details of interest. The X-ray detector has been intensively tested in order to determine its performance in terms of MTF, NPS, and DQE. Moreover, preliminary tests have been carried out on several samples in order to evaluate the performance of the micro-CT system.

Relevance of head motion in dental cone-beam CT scanner images depending on patient positioning

ObjectivesThe aim of this study is to investigate the effect of head motion on the reconstruction image quality in relation to patient positioning in dental cone-beam computed tomography (CBCT) systems. This study should be intended as the first step to evaluate the effect of the head movements also in more stringent conditions.MethodsHead motion was monitored using an EasyTrack-500 system in three acquisition conditions: lying down, sitting and standing. Motion was simulated on a cylinder used to calculate the modulation transfer function in order to quantify the resolution loss associated with it.Results and discussionIn none of the three acquisition layouts, head motion could be avoided. As expected head rotation angles are found to be smaller in the lying down configuration than in the sitting and standing ones. In the latter there is a probability of 30% of cases with high excursion rotation angles which would have a clearly perceptible lower image quality.ConclusionPatient positioning during CBCT scanning can significantly influence occurrence of motion. This should be taken into account when very high image resolution is required in particular in patients that for age or clinical conditions may have difficulties in staying still.

X-ray 3D computed tomography of large objects: investigation of an ancient globe created by Vincenzo Coronelli

X-ray cone-beam Computed Tomography is a powerful tool for the non-destructive investigation of the inner structure of works of art. With regard to Cultural Heritage conservation, different kinds of objects have to be inspected in order to acquire significant information such as the manufacturing technique or the presence of defects and damages. The knowledge of these features is very useful for determining adequate maintenance and restoration procedures. The use of medical CT scanners gives good results only when the investigated objects have size and density similar to those of the human body, however this requirement is not always fulfilled in Cultural Heritage diagnostics. For this reason a system for Digital Radiography and Computed Tomography of large objects, especially works of art, has been recently developed by researchers of the Physics Department of the University of Bologna. The design of the system is very different from any commercial available CT machine. The system consists of a 200 kVp X-ray source, a detector and a motorized mechanical structure for moving the detector and the object in order to collect the required number of radiographic projections. The detector is made up of a 450x450 mm2 structured CsI(Tl) scintillating screen, optically coupled to a CCD camera. In this paper we will present the results of the tomographic investigation recently performed on an ancient globe, created by the famous cosmographer, cartographer and encyclopedist Vincenzo Coronelli.

X-Ray Computed Tomography Applied to Objects of Cultural Heritage: Porting and Testing the Filtered Back-Projection Reconstruction Algorithm on Low Power Systems-on-Chip

The embedded and high-performance computing (HPC) sectors, that in the past were completely separated, are now somehow converging under the pressure of two driving forces: the release of less power consuming server processors and the increased performance of the new low power Systems-on-Chip (SoCs) developed to meet the requirements of the demanding mobile market. This convergence allows the porting to low power embedded architectures of applications that were originally confined to traditional HPC systems. In this paper, we present our experience of porting the Filtered Back-projection Algorithm to a low power, low cost system-on-chip, the NVIDIA Tegra K1, which is based on a quad core ARM CPU and on a NVIDIA Kepler GPU. This Filtered Back-projection Algorithm is heavily used in 3D Tomography reconstruction software. The porting has been done exploiting various programming languages (i.e. OpenMP, CUDA) and multiple versions of the application have been developed to exploit both the SoC CPU and GPU. The performances have been measured in terms of 2D slices (of a 3D volume) reconstructed per time unit and per energy unit. The results obtained with all the developed versions are reported and compared with those obtained on a typical x86 HPC node accelerated with a recent NVIDIA GPU. The best performances are achieved combining the OpenMP version and the CUDA version of the algorithm. In particular, we discovered that only three Jetson TK1 boards, equipped with Giga Ethernet interconnections, allow to reconstruct as many images per time unit as a traditional server, using one order of magnitude less energy. The results of this work can be applied for instance to the construction of an energy-efficient computing system of a portable tomographic apparatus.

Semiempirical simulation of x‐ray detectors for imaging applications

PURPOSE The Monte Carlo (MC) simulation is widely used to design and test complex physical phenomena. This paper presents a simulator of x-ray detector for imaging applications by providing a simple component that can be embedded into a MC code and allowing developers to focus their attention on the primary goals without hanging in the quality of the final output image. METHODS A simplified semiempirical model of x-ray detector was developed and implemented starting from the definition of absorber material and developing scintillator and photoconductor screens and detectors. The validation was done by comparing a Hamamatsu C10900D digital flat panel with a simulation of the same detector using the presented model: MTF, nNPS, and NEQ. RESULTS The results of validation tests shown excellent agreement of the simulation with respect to the experimental data. The simulation was fast and efficient even in older computers (2004) and it was excellent in newer multicore computers (2010). CONCLUSIONS Comparisons between experimental data and simulations shown that the simulator is able to mimic the output of a real imaging system, and it can have many applications in fields such as industry, medical physics, and teaching.

Effective dynamic range measurement for a CCD in full-field industrial x-ray imaging applications

CCD cameras are widely used for different applications. Recently they are employed for imaging in industrial X-ray digital radiography or computed tomography inspections. Scientific grade CCD sensors are usually characterized for what concern defects (bad pixels), resolution capability, spectral sensitivity, dark current, pixel full well capacity and so on. In former times CCDs were mostly used in astronomy and dark current was one of the most important parameters to evaluate in this kind of applications because of the long exposure time needed to obtain a good image. Thus, most manufacturers still refer to noise of a CCD as the background (or dark current) noise. This might be in some cases misleading. When one wants to compute the effective dynamic range on the full scale of greylevels, in order to match with the correct number of bit required to quantize the information, and, most of all, to evaluate if the dynamics is adequate, a different analysis of noise is required. It is possible to find an experimental method to measure noise and to derive the effective intrinsic dynamic range of a CCD. A case study, carried out on a commercial CCD camera used in a prototype industrial CT system, is reported in this work and the experimental results are discussed.

Dosimetry of high intensity electron beams produced with dedicated accelerators in Intra-Operative Radiation Therapy (IORT)

The technique of High Dose Intra-Operative Radiation Therapy (HDR-IORT) consists in the delivery of irradiation immediately following the removal of a cancerous mass, where the same incision is used to direct the radiation to the tumour bed. Given its particular characteristics, IORT requires dose measurements that are different from those requested in external radiotherapy treatments. The main reason lies in the fact that in this case a single high dose must be delivered to a volume target whose extension and depths will be determined directly during the operation. Since the possibility of devising a treatment plan using a TPS (Treatment Planning System) is not available, it is necessary to know the physical and geometric characteristics of the beam. Defining the physical characteristics of the beam entails both measuring the delivered dose and defining (monitoring) procedures. In any case a much higher dose will be released than occurs with conventional external accelerators. The ionization chamber recommended by the standard protocols for radiotherapy cannot be used because of the ion recombination inside the gas. In this work we propose the use of a calorimetric phantom, the Dosiort, to measure the beam properties. We describe the main characteristics and some preliminary results of the Dosiort System, which is proposed within the framework of a research project of the INFN (Italian National Institute of Nuclear Physics). The set-up is a solid phantom of density approaching 1 g/cc with sensitive layers of scintillating fibres at fixed a position in a calorimetric configuration for the containment of electrons of energy 4-12 MeV. The prototype will be able to define the physical and geometrical characteristics of the electron beam (quality, isotropy, homogeneity, etc) and to measure the parameters needed to select the energy, the intensity and the Monitor Units (MU) for the exposition: Percentage Depth Dose; Beam profiles; Isodose curves; Values of dose for MU.

Study of an appropriate reconstruction algorithm for an innovative electron beam imaging system for dosimetry in IORT (intra operative radiation therapy)

Intra operative radiation therapy (IORT) is a technique based on delivery of a high dose of ionising radiation to the cancer tissue, after tumour ablation, during surgery. The Novac7 is a new linear accelerator expressly conceived for IORT that supplies electron beams at several energy, with high dose rate. These peculiar characteristics give rise to some complications with classical dosimetric techniques. In the framework of a research contract between ENEA and the Physics Department of Bologna, Italy, an original digital system has been developed to study and visualise the Novac7 electron beam in real time. The system is conceived as a grid consisting of two bundles of scintillating optical fibres (SOP) over-crossing each other, optically coupled with two arrays of photodiodes as read-out system. The problem of image reconstruction can be expressed as follows: there are only two profiles, or data arrays, which correspond respectively to the light emitted along the fibres perpendicular to the X-axis for the X-profile, and along the fibres perpendicular to the Y-axis for the Y-profile. This problem is not dissimilar to the reconstruction problem in tomography where several projections should be composed to trace them back to the original image. Unfortunately, here we have only two profiles: we have two one-dimensional profiles and are seeking one bidimensional image that could produce them. We selected a known beam image acquired by another digital instrument, then we extracted from it the two profiles simulating the acquisition arrays. Subsequently, we tested several reconstruction algorithms on these profiles, comparing the reconstructed image with the original one. We started from the simple sum algorithm until to iterative algorithms, searching the best compromise between the computational complexity and an high precision. We found that the iterative method is the best solution: it respects the geometrical characteristics and the absolute intensity values of the original image. Moreover it can reconstruct the image in a time of less than one second, a very good result.

Dosimetry of High Intensity Electron Beams Produced by Dedicated Accelerators in Intra-Operative Radiation Therapy (IORT)

The technique of High Dose Intra-Operative Radiation Therapy (HDR-IORT) consists in the delivery of irradiation immediately following the removal of a cancerous mass, where the same incision is used to direct the radiation to the tumour bed. Given its particular characteristics, IORT requires dose measurements that are different from those requested in external radiotherapy treatments. The main reason lies in the fact that in this case a single high dose must be delivered to a target volume whose extension and depths will be determined directly during the operation. Since the possibility of devising a treatment plan using a TPS (Treatment Planning System) is not available, it is necessary to know the physical and geometric characteristics of the beam. Defining the physical characteristics of the beam entails both measuring the delivered dose and defining (monitoring) procedures. In any case a much higher dose will be released than occurs with conventional external accelerators. The ionization chamber recommended by the standard protocols for radiotherapy cannot be used because of the ion recombination inside the gas. In this work we propose the use of a calorimetric phantom, the Dosiort, to measure the beam properties. We describe the main characteristics and some preliminary results of the Dosiort System, which is proposed within the framework of a research project of the INFN (Italian National Institute of Nuclear Physics). The set-up is a solid phantom of density approaching 1 g/cm3 with sensitive layers of scintillating fibres at fixed a position in a calorimetric configuration for the containment of electrons of energy 4-12 MeV. The prototype will be able to define the physical and geometrical characteristics of the electron beam (energy, isotropy, homogeneity, etc) and to measure the parameters needed to select the energy, the intensity and the Monitor Units (MU) for the exposition: Percentage Depth Dose; Beam profiles; Isodose curves; Values of dose for MU.

A mobile computed tomography system for on-site cultural heritage analysis

In consequence of the increasing request of on-site analysis the availability of portable systems for imaging paintings and other works of art has become really an issue for cultural heritage investigation. In many cases, authorities do not allow to transport paintings and works of art outside museums because of their value. We thus developed and used successfully a transportable X-ray Computed Tomography (CT) system that the operators can transport in a regular van and then mount inside museums or conservation centers. The system is composed of spare components that have to be properly mounted and carefully aligned in order to perform the radiographic or tomographic analysis. The basic elements are a 200 kV X-ray tube and a 12×12 cm2 flat-panel detector. With this system, it is possible to scan painting and works of art up to 1.5 × 1.5 m2 of size thanks to three mechanical translation axes. In the tomographic mode, a rotating platform provides high-resolution rotation of the object carrying up to 50 kg in weight. The operators control all the components of the system with a remote connection computer at a safe distance. In the present work, we report details about the development of this transportable X-ray CT system, we describe how it operates and the technical solutions we used and we show examples of application to real case studies with their specificity.