Sergio Lo Meo

Induction motor faults diagnostic via artificial neural network (ANN)

The paper deals with the analysis of an artificial neural network (ANN) approach suitable for online faults detection of induction machines. The aim of this paper is to develop an alternative with respect to traditional fault detector techniques that overcomes the limitations of present technology. After an analytical discussion about theoretical principles and relations used for the diagnosis of electrical machines failures, a simple ANN algorithm is presented and tested. The results prove the feasibility of to tool arranged by means of artificial neural network for a fast and accurate detection of stator faults in induction machines. Furthermore a good accuracy of the results have been achieved notwithstanding the great simplicity of the algorithm with respect to a complete model arranged by a space vector analysis.<<ETX>>

Continuous DoI determination by gaussian modelling of linear and non-linear scintillation light distributions

The Depth of Interaction (DoI) detection is crucial in many medical imaging applications such as small ring PET and high resolution SPECT. In this work we investigate the possibility to discriminate the DoI using continuous crystals. A LaBr3(Ce) crystal has been used in the detection system for its intrinsic high light yield, that especially at low energies (e.g. 140 keV) reduces considerably the statistical uncertainties increasing the DoI discrimination power. The innovative suggestion of this work is the use of spectrometric observables to discriminate events on top and bottom of the crystal, under the hypothesis that scintillation light distributions can be parameterized by a gaussian model. The spread of the light cone (σ) is proportional to the DoI simply by geometrical considerations, but under the gaussian hypothesis relations between the spectrometric variables (maximum high I and integral of the distribution N) and the DoI become a straightforward consequence. Two methods are proposed and discussed: a linear treatment of the light distribution and a non linear (quadratic) manipulation of it. The expected correlations between the spectrometric variables (N and I), according to the gaussian model, are checked using a specific Monte Carlo simulation of the experimental apparatus. Those are then compared with experimental data obtained irradiating the LaBr3:Ce crystal with a Tc99m collimated source. A close agreement between experimental data and MC is verified. Finally, a preliminary test on experimental data has been performed irradiating the crystal with a Co57 source, in order to investigate the strong dependence of the non linear manipulation of the light distribution to the DoI.

Evaluation of Scattering in Cone-Beam Breast Computed Tomography: A Monte Carlo and Experimental Phantom Study

In this paper Monte Carlo simulations were performed for X-ray irradiations of breast phantoms of various sizes such as PMMA cylinders of different diameters and a hemi-ellipsoidal PMMA phantom. The aim was the evaluation of the 2D distribution of primary and scattered photons and Scatter-to-Primary Ratio (SPR) in projection images in cone-beam breast Computed Tomography (CT). Irradiation geometry and technique factors reproduce the experimental conditions used for validation measurements with a prototype CT breast scanner. Simulations were performed with GEANT4 software. We varied the phantom diameter and shape, the X-ray tube voltage and added filtration. Magnification was 1.31. SPR increases from 0.4 (at 8 cm cylinder diameter) up to 1.5 (14 cm cylinder diameter) at the centre of the phantom. In the same phantom, SPR has lower values toward the bases of the cylinder than at its centre. The scatter component increases by adopting a 50 kVp or higher tube voltages, up to 80 kVp, and by increasing the added filtration. Simulated and measured lateral profiles across a 14 cm cylinder diameter in projection images show a relative deviation of 4%. Simulations show a different distribution of scatter and SPR in a 14 cm diameter cylinder and 14 cm hemi-ellipsoidal phantom, so questioning the use of simple cylindrical geometries when simulating the attenuation of the pendant breast for scatter correction procedures. The strength and the non-uniformity of the SPR inside the cylindrical phantom decrease as the size of the air gap between object and detector increases.

GEANT4 simulation for modelling the optics of LaBr scintillation imagers

The excellent scintillation properties of the LaBr3:Ce crystals makes their use very attractive in a system of gamma imaging for Single Photon Emission Tomography (SPET) applications. In this work we use GEANT4 simulations, in order to better understand the intrinsic properties of a gamma camera based on LaBr3:Ce crystals, coupled to a Hamamatsu H8500 Multi Anodes Photomultiplier (MA-PMT). All electromagnetic process are simulated, together with the detection of the scintillation light distribution on the anodic plane of a MAPMT. The position linearity response, the spatial and energy resolutions are investigated. The values obtained by Monte Carlo show a good agreement with the experimental results.

New position arithmetic for scintillation camera based on floating weight system

Over the last thirty years we have been seeing impressive advances in photodetection technology and in scintillation crystal production and manufacturing. Researchers proposed an impressive variety of small FoV scintillation cameras or detector modules for SPET and PET. The original position arithmetic based on linear weight is still widely used although this logic generates a conflict between position linearity and spatial resolution. In this paper, we propose a method of position arithmetic based on floating weights, simply utilizing non linear amplification of anode charge. The method has been tested on a continuous LaBr3:Ce scintillation crystal 51×51 mm2 area and 4.0 mm thickness coupled to a Hamamatsu H8500 multi-anodes PMT. The charge collected on each anode was independently digitized, so to be free to apply to the charge distribution any different non linear transformation. In this way the charge around the peak is much more weighed then the remaining. As a result, we obtain a floating weighting matrix according to event interaction location. Comparing the data with the analogous ones from linear weights, it resulted a general improvement of more than 30% of position calibration slope and of spatial resolution values. Position linearity response and spatial resolution values resulted in good agreement with simulated ones. The best spatial resolution value was about 1.0 mm and position linearity resulted in close agreement with that of scintillation array.

Scatter Correction in Cone-Beam Breast Computed Tomography: Simulations and Experiments

In Cone-Beam Computed Tomography (CBCT) the X-ray scatter control and reduction is one of the major challenges because CBCT is less immune to scatter than fan-beam CT. In breast volume imaging, studies on Cone-Beam Breast Computed Tomography (CBBCT) have shown the necessity to implement an efficient scatter reduction technique for a successful implementation of a breast CT scan using cone-beam geometry. X-ray scatter reduces image contrast, increases image noise and introduces reconstruction artifacts. A method for scatter evaluation through Monte Carlo simulations is investigated, leading to a scatter correction procedure applied to measured projections via subtraction of the simulated scatter component. Simulations are compared with measurements performed with a CBBCT prototype scanner. This paper presents the evaluation of the method through phantom studies on a cylindrical and on a hemi-ellipsoidal PMMA test object of 120- or 140-mm diameter at its base, simulating the pendant breast. The results indicate that this correction method is effective to reduce and correct X-ray scatter, with no increase of noise in the CT images. The cupping artifact due to scatter was reduced by a factor 3 (from 23% to 7%) for the hemi-ellipsoidal phantom of 140-mm diameter. Correspondingly, the relative noise in the CT slices remains constant to about 3%; the figure of merit for evaluating the correction efficacy was 98% of the ideal case. We discuss the application of this procedure to model breasts characterized in terms of few parameters, as indicated by recent published results of breast anatomy characterization derived from CBBCT patient data, from which a possible parametric breast size model in terms of bra cup size can be set forth. The scatter correction could be applied to projections from patient scans obtained with a breast holder, on the basis of a pre-determined database of simulated scatter distributions corresponding to the breast holder size, shape and estimated volume glandular fraction, for given beam quality and scanner geometry.

Evaluation of scattering in cone-beam breast computed tomography: A Monte Carlo and experimental phantom study

Monte Carlo simulations of X-ray irradiations of breast phantoms of various sizes as PMMA cylinders of different diameters and a hemi-ellipsoidal PMMA phantom were performed in order to evaluate the 2D distribution of primary and scattered photons and Scatter-to-Primary Ratio (SPR) in projection images in cone-beam breast CT. Irradiation geometry and technique factors were set so as to reproduce the experimental conditions used for validation measurements with a prototype CT breast scanner. In the simulations, performed with GEANT4 software, we varied the phantom diameter and shape, the X-ray tube voltage and added filtration. SPR increases from 0.4 (at 8 cm cylinder diameter) up to 1.5 (14 cm cylinder diameter) at the center of the phantom. In the same phantom, SPR has lower values toward the bases of the cylinder than at its center. The scatter fraction increases by adopting a 50 kVp or higher tube voltages, up to 80 kVp, and by increasing the added filtration. Simulated and measured lateral profiles across a 14 cm cylinder diameter in projection images show a relative deviation of 4%. Simulations show a different distribution of scatter in a 14 diameter cylinder and 14 cm hemi-ellipsoidal phantom, so preventing the use of simple cylindrical geometries when simulating the attenuation of the pendant breast for scatter correction procedures.

LaBr 3 (Ce) and NaI(Tl) performance comparison for single photon emission imaging

LaBr3(Ce) crystal showed excellent spectrometric properties mainly due to a very high light output and to an energy resolution slightly affected by the intrinsic factor. Furthermore, the properties of the radiation absorption are very similar to NaI(Tl) ones, hence it offers the potential to replace it in scintillation imaging detectors. Unfortunately, the cost of this crystal is high and it is also affected by a very high hygroscopicity and lower mechanical stability which may compromise its durability. In order to evaluate the real benefits of LaBr3(Ce), we propose an imaging comparison with a second sample of NaI(Tl) by coupling them to a Hamamatsu H8500C multi-anode PMT. The crystal was produced identical in shape by Saint Gobain. In addition a second high QE MA-PMT was also tested (H8500C-Mod8 series PMT). A Geant4 Monte Carlo simulation was also implemented, where the light transport inside the crystals was taken into account. Very close results were obtained for both crystals when coupled to the new high QE MA-PMT and (0.95±0.05) mm spatial resolution -SR resulted, in spite of simulation where SR of LaBr3(Ce) was expected to be 22% better than the NaI(Tl) one. This results seems to be related to an unexpected scintillation light background measured only in the LaBr3(Ce), which limits the advantages would occur due to its highest light yield. Saint-Gobain, the most important manufacturer of LaBr3(Ce) crystals, has established its own choices in the surface treatment so apparently limiting the intrinsic response of this crystal. In conclusion, these results revisit the use of continuous crystals for small-FoV gamma-camera applications with high spatial and energy resolution tanks to the improvement obtained with the new MA-PMT with high quantum efficiency.

Design and characterization of a dual modality (SPET-US) tomographic device

In the last few years, integrated dual-imaging systems have emerged as a new modality for cancer staging with the aim to offer both functional and anatomic information. At moment the prevalent dual modality devices are based on Computer Tomography and Positron Emission Tomography. In this sense, the scientific community is debating about the high effective dose to the patient, representing an indicator of the stochastic risk, especially from Computer Tomography examination. So, a new dual modality imager, based on a Ultrasound probe and a Single Photon Emission Tomography was made in order to combine functional information, from gamma camera with structural one, obtained from the Ultrasound equipment. The Ultrasound probe is the most diffuse anatomical examination device at zero-dose, using a cost-effective and reliable method with few restriction in use. The proposed Single Photon Emission Tomography detector is a compact gamma camera (10×10 cm2 active area), based on LaBr3:Ce scintillation crystal coupled to 4×4 array of Hamamatsu H8500C-MOD8 Multi Anode Photomultiplier, with high spatial and energy resolution performances, equipped with rotating slant-hole collimator. A calibration phantom, made of a Co57 point source inside a water filled box, was utilized to acquire 3D dual modality images. The detector has shown good performances in terms of spatial resolution and localization along z-axis of object of interest. This project was developed by several Italian Universities under an INFN collaboration.