1,721,167 research outputs found
Current studies and future perspectives of synchrotron radiation imaging trials in human patients
No full textThe coherent and monochromatic x-ray beams available at the synchrotron radiation (SR) laboratories are ideal tools for the development and the initial application of new imaging techniques. In the present paper the history of the clinical studies in k-edge subtraction imaging with SR is summarized, including coronary angiography and bronchography. The results of the recent trial in phase-contrast mammography at Elettra (Trieste, Italy) are discussed, in order to assess the clinical impact of the new imaging modality and the potential interest in its translation to clinical practice. The direct measurement of linear attenuation coefficient obtained during the SR mammography trial is also discussed. The new program of phase-contrast breast CT under development at Elettra is presented. Recently, 3D breast imaging (tomosynthesis and cone beam breast CT) has been introduced in clinical practice with significant improvement in diagnostic accuracy. The aim of this research is to study the contribution of the phase-contrast to the image quality of breast CT, is introduced. Increasing the image quality of the x-ray medical images at the level of the results obtained at the SR laboratories is highly desirable, hence the promising techniques for the translation of the phase-contrast imaging to the hospitals are briefly discussed
In vivo localized1H NMR spectroscopy: an experimental characterization of the PRESS technique
No full textImaging radiologico con sistemi a conteggio di fotoni
No full textI sistemi di imaging per radiologia diagnostica basati sul conteggio dei fotoni, anziché sull’integrazione del segnale, sono ancora poco diffusi ma hanno straordinarie potenzialità, sia per l’ottimo rapporto segnale su rumore che per il così detto “spectral imaging”, come dimostrato da alcuni studi pilota di recente pubblicazione. Infatti i nuovi detector a conteggio di fotoni con soglia multipla rendono possibile l’acquisizione di immagini relative a molteplici intervalli spettrali con una singola acquisizione da un comune spettro policromatico. In questo contributo faremo una breve storia delle applicazioni radiologiche dei detector a conteggio di fotoni, a partire dalle prime immagini di mammografia digitale con luce di sincrotrone, per soffermarci sui più recenti sviluppi di “spectral imaging” sia in imaging planare che tomografico
Quantitative 3D refractive index decrement reconstruction using single-distance phase-contrast tomography data
No full textX-ray propagation-based phase-contrast imaging is an attractive phase-sensitive imaging technique that has found applications in many research fields. Here, we report the investigations of a method which can quantitatively reconstruct in 3D the refractive index decrement of a quasi-homogeneous object using single-distance phase-contrast tomography data. The method extends the Born-type approximation phase-retrieval algorithm, which is based on the phase-attenuation duality (ε = δ/β, with constant ε) and suitable for homogeneous objects, to tomography and we study its application to quasi-homogeneous objects. The noise performance and the phase-attenuation duality influences of the method are
also investigated. In simulation, the method allows us to quantitatively reconstruct the 3D refractive index decrement for quasi-homogeneous and weakly absorbing samples and it performs well in the practical noise situation. Furthermore, it shows a substantial contrast increase and successfully distinguishes different materials in a quasi-homogeneous and weakly absorbing sample from experimental data, even with inappropriate ε value
Comparison of single distance phase retrieval algorithms by considering different object composition and the effect of statistical and structural noise
No full textPhase retrieval is a technique for extracting quantitative phase information from X-ray propagation-based phase-contrast tomography (PPCT). In this paper, the performance of different single distance phase retrieval algorithms will be investigated. The algorithms are herein called phase-attenuation duality Born Algorithm (PAD-BA), phase-attenuation duality Rytov Algorithm (PAD-RA), phase-attenuation duality Modified Bronnikov Algorithm (PAD-MBA), phase-attenuation duality Paganin algorithm (PAD-PA) and phase-attenuation duality Wu Algorithm (PAD-WA), respectively. They are all based on phase-attenuation duality property and on weak absorption of the sample and they employ only a single distance PPCT data. In this paper, they are investigated via simulated noise-free PPCT data considering the fulfillment of PAD property and weakly absorbing conditions, and with experimental PPCT data of a mixture sample containing absorbing and weakly absorbing materials, and of a polymer sample considering different degrees of statistical and structural noise. The simulation shows all algorithms can quantitatively reconstruct the 3D refractive index of a quasi-homogeneous weakly absorbing object from noise-free PPCT data. When the weakly absorbing condition is violated, the PAD-RA and PAD-PA/WA obtain better result than PAD-BA and PAD-MBA that are shown in both simulation and mixture sample results. When considering the statistical noise, the contrast-to-noise ratio values decreases as the photon number is reduced. The structural noise study shows that the result is progressively corrupted by ring-like artifacts with the increase of structural noise (i.e. phantom thickness). The PAD-RA and PAD-PA/WA gain better density resolution than the PAD-BA and PAD-MBA in both statistical and structural noise study
Dependence of the fractional anisotropy in cervical spine from the number of diffusion gradients, repeated acquisition and voxel size
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