F. Casali

MicroCT Scan in paleobiology: application to the study of dental tissues

State of the art in paleoanthropological and paleoprimatological research foresees the use of advanced non-destructive investigative approaches. Microcomputed tomography (microCT) is a fundamental tool, since it offers the opportunity to get high quality morphological information with high spatial resolution. We carried out the set-up of an experimental microCT system able to examine paleobiological samples. The equipment can operate on small objects (size up to 3 cm) with a nominal spatial resolution of 30 μm, allowing their 3D volume reconstruction and morphometric analysis. This approach represents a forefront technique in paleobiological studies, successfully employed only in a limited number of advanced research centers. A specific program of microCT analysis has been planned on a sample of human and non-human fossil primate dentitions, in order to assess the specific nature of a number of tooth lesions (e.g. caries versus abrasion). This currently in progress experimental activity represents the first step for the set-up of a research center specifically devoted to the realization of advanced studies in the field of archaeo-paleobiology.

Chapter 2 X-ray and neutron digital radiography and computed tomography for cultural heritage

Abstract Methods of diagnosis based on digital radiography (DR) and computed tomography (CT), are more and more frequently used in the cultural heritage field. The application of these techniques can help restoration and conservation planners to understand historical construction techniques and to reveal poor restoration work and forgeries. As the size of objects of cultural interest varies greatly, from small fragments (for which high spatial resolution is needed) to large works of art (for which large detectors are necessary), it would not be appropriate to describe any one particular measuring device in detail. In this chapter, we will therefore provide an overview on Digital Radiography (DR) and Computed Tomography (CT) systems, underlining their range of applications. The chapter focuses mainly on X-ray radiation (with different kinds of sources) although neutron DR and CT are also mentioned, as neutron imaging should be considered complementary to X-ray imaging. Some DR and CT images, most of which were taken by researchers at the Department of Physics of the University of Bologna, are shown. This overview adopts a tutorial approach, as it is aimed at those with no specific knowledge of digital imaging. Three appendices have also been included (concerning Fourier transforms, modulation transfer function and DR and CT acquisition systems) for those readers who wish to acquire further skills in the field of digital imaging.

High-resolution 3D scaffold model for engineered tissue fabrication using a rapid prototyping technique.

Rapid prototyping, automatic image processing (computer-aided design (CAD)) and computer-aided manufacturing techniques are opening new and interesting prospects for medical devices and tissue engineering, especially for hard tissues such as bone. The development of a bone high-resolution scaffold prototype using these techniques is described. The results testify to the fidelity existing between microtomographic reconstruction and CAD. Furthermore, stereolithographic manufacturing of this scaffold, which possesses a high degree of similarity to the starting model as monitored by morphological evaluations (mean diameter 569±147 μm), represents a promising result for regenerative medicine applications.

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.

Digital radiography using an EBCCD-based imaging device

In the last few years, large efforts were devoted to the development of new intensified imaging systems to be applied mainly in medical radiographic devices for the reduction of the dose irradiated to the patient but also in high-energy physics for particle tracking or in astronomy for low-light imaging. Among a number of different image-intensifier systems, electron-bombarded charge coupled devices (EBCCD) present interesting characteristics providing the opportunity to be used also for special application such as X-ray imaging in industrial field. For this purpose, a prototype EBCCD image-intensifier tube suitable for X-ray digital radiography (DR) and computed tomography (CT) has been set up by the Physics Department of the University of Bologna (Italy) and Geosphaera Research Center of Moscow (Russia). Results concerning tests of EBCCD device and DR analysis of industrial components are presented and discussed.

An evaluation of the possible use of CdTe microdetectors for astrophysical, biomedical and industrial imaging

Abstract Various imaging techniques in fields as diverse as astrophysical research, biomedical diagnostics and industrial tomography are closely related to the development of γ-ray detectors with improved spectral and imaging performances. From this point of view, cadmium telluride solid state detectors are very promising due to their capability to operate at room temperature, their high stopping power and their possibility of miniaturization. The necessity to have contemporaneously good efficiency and high spatial resolution demands that these microdetectors are produced in a novel manner, where the polarization of the applied electric field is perpendicular to the direction of the incoming radiation. In this way, it is possible to achieve a good charge collection efficiency and hence a high energy resolution, together with a high absorption thickness while at the same time having a spatial resolution commensurate with the detector size of about 2×2 mm 2 . The results of measurements regarding the energy resolution of various sizes of μdetector, ranging from 2×2×2 mm 3 to 2.5×2.5×20 mm 3 , are presented and discussed.

X-ray 3D computed tomography of bronze archaeological samples

X-ray cone-beam computed tomography (CT) is one of the most powerful non-destructive testing (NDT) technique for the whole 3D inspection of a sample. The development of suitable 2D detectors has permitted the set-up of very fast and efficient CT systems able to collect and reconstruct hundreds of tomographic slices in short time and with a more efficient use of the X-ray flux. At present, this technique is widely applied in industrial field but it can be employed successfully even in the analysis and restoration of archaeological samples. An experimental 3D CT system has been set up at the Physics Department of University of Bologna (Italy) for the investigation of small bronze objects. Preliminary tests have been carried out on an Etruscan fibula and results concerning radiographic inspection, slice tomographic analysis and 3D reconstruction of the object will be presented.

Evaluation of hydrogen content in metallic samples by neutron computed tomography

Neutron radiography is currently a well-known technique, which is employed for non-destructive testing in a number of industrial and environmental applications. Originally developed for reactor fuel examinations, it is now effective in detecting small amounts of corrosion and infiltrations of hydrogen or light materials within thick metallic structures due to the particular behaviour of total neutron cross sections. Nevertheless, improvements related to the development of tomographic systems, which allow far better imaging performances, have been achieved only in the last few years, as a consequence, primarily, of the production of large, charge coupled device (CCD) arrays. Nowadays, neutron computed tomography is the technique most suited for the study of the distribution of hydrogen within metallic matrices. In this field, a series of experimental tests were carried out employing a set of nickel samples containing a H/sub 2/O-D/sub 2/O solution in known percentages. It was possible, therefore, to obtain a calibration curve for the total neutron cross section vs. Gray level in the reconstructed image. >

An Innovative CCD-Based High-Resolution CT System for Analysis of Trabecular Bone Tissue

Synchrotron-based digital radiography and microtomography devices are powerful, nondestructive, high-resolution research tools. In this paper, we present a linear system with a pixel size of 22.5 mum and a field-of-view (FOV) 13 cm long and about 1 mm high. The system is composed of a linear converter GOS screen coupled to an intensified electron-bombarded CCD (EBCCD) camera, by means of a rectangular-to-linear fiber optic adapter. This optical guide is composed of seven bundles, each one transporting light in a coherent way to preserve spatial information. In this way, a high spatial resolution over an extended FOV is obtained. The detector works as an X-ray scanner by means of a high-precision translation mechanical device with 18 cm travel range. The total FOV obtained this way is 13 cm long and 18 cm high. The aim of this paper is to demonstrate the feasibility of this system to investigate a large area of a bone and to calculate the appropriate histomorphometric parameters. Here we present an investigation gained at ELETTRA synchrotron facility at Trieste, Italy. A monochromatic 34-keV beam has been used for imaging a human proximal femur, about 9 cm in width, with our system. The reconstructed images (13 cmtimes13 cm) were cross sections containing femoral head, femoral neck, and greater trochanter. The local variations in trabecular and cortical structure of the examined bone were clearly visible at a level not obtainable with medical CT scanners. The used spatial resolution allowed the visualization of thin trabeculae, which typically lie in a range of 100 mum or lower. The quality of the reconstructed cross-section images confirmed that the system presented is a novel tool for high resolution three-dimensional (3-D) imaging of bone structure, with a pixel size over a volume of interest not achievable with conventional microCT scanners

Timing response of CdTe detectors

Abstract Semiconductor CdTe detectors are gaining wide acceptance in many applications where X- and γ-ray measurements are necessary, such as in astrophysical research, medical imaging and industrial radiography. Good timing response is critical both in applications like positron emission tomography, where fast coincidence capabilities are required, and in single photon counting when a high counting rate is needed. The typical configuration employed, where the direction of the impinging radiation beam is parallel to the collecting electric field, has one well known drawback: an increase in active layer, necessary in order to reach a satisfactory absorption efficiency for the detection of high energy photons, leads to a longer transport path for the charge carriers generated. As a consequence, there is a degradation in energy resolution and a broadening in time response. In the present paper, measurements of the timing response for an unusual configuration of CdTe detectors are presented. In this configuration, which we call a PTF (planar transverse field) detector, the collecting electric field and hence the transport direction of carriers is transverse to the direction of the incoming photons and so detection thickness and transport length are independent. In this way the absorption layer can be increased without impairing the timing performance. The measurements described herein have been performed using a PTF detector having dimensions of 2.5 × 2.5 × 20 mm 3 , in order to have a good efficiency for annihilation γ-ray photons.