The aim of this study is to determine the performance of a direct CR reader, named "FCR Velocity U Focused Phosphor (FP)". The system is based on a CsBr columnar structured crystal, and the system's read out is based on the "linescan technology" that employs a wide-view CCD. The system's physical performance was tested by means of a quantitative analysis, with calculation of the modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE). Image quality was assessed by performing a contrast-detail analysis. The results are compared with those obtained with the well known CR system Fuji FCR XG5000, and the new one Kodak DirectView CR 975. For all the measurements the standard radiation quality RQA-5 was used. The relationship between signal amplitude and entrance air kerma is logarithmic for all the systems and the response functions were used to linearize the images before the MTF (edge method) and NPS calculations. The contrast detail analysis has been achieved by using the well known CDRAD phantom and a customized software designed for automatic computation of the contrast-detail curves. The three systems present similar MTFs, whereas the Fuji Velocity U FP system, thanks to its greater efficiency, has a better behavior in terms of NNPS, especially at low frequencies. That allows the system based on columnar phosphor to provide a better DQE. CDRAD analysis basically confirms that the structured phosphor used in the Velocity system improves the visibility of some details. This is especially true for medium and large details.
Indirect-conversion FFDM systems usually present a lower spatial resolution, with respect to the direct-conversion one. This can put serious issues in mammography, since high resolution is required. Digital software has been developed for restoring the losses in spatial resolution caused by blurring in the scintillation phosphor. GE Senographe DS system gives users the possibility of using such restoration. Basically, a filtering can be performed on the acquired images, by activating the FineView software option. In this work we present a complete characterization of a clinical system, in terms of MTF, NPS, DQE, and contrast-detail analysis. Figures of merit have been calculated on images acquired with and without the FineView software. The effects of the restoration software are investigated, both on image quality parameters, and on contrast-detail visibility. The MTF of the FFDM system is improved when FineView is activated. On the other hand, NPS presents noticeably changes, especially at high frequencies. DQE is fairly independent from the exposure, when FineView filter is not activated, whereas it presents a clear spread over the exposures, when FineView is activated. CDMAM analysis does not show significant differences between images with or without the restoration filter. Besides, the Mo/Mo beam seems to provide slightly better results than the Rh/Rh one.
Contrast-detail analysis is one the most common way for the assessment of the performance of an imaging system. Usually, the reading of phantoms, such as CDMAM, is obtained by human observers. The main drawbacks of this practice is the presence of inter-observer variability and the great amount of time needed. However, software programs are available, for reading CDMAM images in an automatic way. In this paper we present a comparison of human and software reading of CDMAM images coming from three different FFDM clinical units. Images were acquired at different exposures in the same conditions for the three systems. Once software has completed the reading, the interpretation of the results is achieved on the same way used for the human case. CDCOM results are consistent with human analysis, if we consider figures such as COR and IQF. On the other hand, we find out some discrepancies along the CD curves obtained by human observers, with respect to those estimated by automated CDCOM analysis.
Computed Tomography (CT) is one of the principal non-invasive techniques for the investigation of the inner structure of works of art. The main advantage of using CT is that it provides high resolution 3D information of the analyzed object. CT of large objects can be hampered by the long time needed and by the difficulties regarding the experimental arrangements required. In this paper we present a CT study of an ancient large globe (diameter of about 2.2 m). We set-up an ad hoc system for the analysis of the globe in situ. The system consists of an X-ray tube, a detector made of a GOS scintillator and an EBCCD camera, the movement axes, a vertical moving axis for the tube, a horizontal-vertical axis for the detector, and a rotating platform for the globe. The investigation of the entire globe has required the acquisition of about 32000 planar images, for providing the 3D tomographic reconstruction. The analysis of the reconstructed volume has allowed to estimate the composition of the inner structure of the globe.