1,720,983 research outputs found
Risonanza Magnetica per Immagini
No full textSono descritti i principi fisici della risonanza magnetica con particolare riferimento alla risonanza magnetica per immagini. Il fenomeno fisico è descritto sia da un punto di vista classico sia da un punto di vista quantistico. Termina la trattazione una descrizione delle tecniche di ricostruzione dell'immagine di RM e una descrizione delle singole componenti di uno strumento per MRI
Fisica e tecnica delle apparecchiature biomediche
No full textIl volume fornisce un valido strumento a chi, studente di Fisica, ingegneria biomedica o professionista in ambito ospedaliero, di fronte a problemi riguardanti la fisica e la tecnica delle apparecchiature biomedicali e' costretto a consultare piu' testi non sempre afferenti alle stesse discipline.
Gli autori hanno limitato l'impiego dello strumento matematico allo stretto necessario, pur ponendo particolare attenzione alla trattazione dei principi su cui si basa il funzionamento delle apparecchiature per la produzione delle immagini a fini diagnostici.
Gli argomenti trattati affrontano l'interazione tra radiazione e materia, propedeutici alla comprensione delle apparecchiature per la tomografia computerizzata; i principi sui quali si fonda la risonanza magnetica nucleare e le applicazioni sui tomografi impiegati per le indagini diagnostiche; nell'ultimo capitolo, dedicato all'ecografia, le onde ultrasonore ed il loro comportamento all'interno del corpo umano
Portable EDXRF surface mapping of sulfate concentration on Michelangelo’s David
No full textThe study presented in this paper was carried out within a large international project founded in the context of the Michelangelo’s David’s 500th anniversary celebration. A group of experts analysed Michelangelo’s masterpiece with several techniques with the aim of helping restorers to choose the most suitable treatment for cleaning of the statue. The task of the present team was to map the possible presence of sulfur (as
sulfates) on the surface of the sculpture due to pollution effects. A portable energy-dispersive x-ray fluorescence (EDXRF) system was used. The EDXRF technique is not only non-destructive, sensitive and capable of simultaneous multi-elemental analysis but also, in its portable version, it allows the analysis of many areas before, during and after restoration. A large number of measurements were made to obtain an overall picture of the sulfur distribution on the sculpture and then further measurements were made at selected strategic points. After applying different removal procedures at each of these points, the measurements were repeated to obtain a quantitative evaluation of the effectiveness of each cleaning procedures. The results are presented and discussed
Rayleigh to Compton ratio with monochromatic radiation from an X-ray tube
No full textResults on the Rayleigh to Compton ratio (R/C) for elements and compounds with low atomic number (5 6 Z 6 12) are presented.
These materials are difficult to identify and characterize with other radiological techniques because of their very close linear attenuation coefficients. A transportable setup for R/C measurements was assembled and tested. This comprises an X-ray tube, in which the output radiation is partially ‘‘converted’’ to monochromatic radiation emitted by a secondary target. The experimental results are compared with theory, determined through coherent and incoherent scattering cross sections
Automatic Segmentation of Cerebral Glioma in DT-MR Images by 3D Texture Analysis
No full textTumor cells in cerebral glioma invade surrounding tissues preferentially along white matter tracts, spreading beyond the abnormal area seen on conventional MR images. Diffusion tensor imaging can reveal larger peritumoral abnormalities in gliomas that are not apparent on MRI. Our aim was to characterize pathological vs healthy tissue in DTI datasets by 3D statistical Texture Analysis, developing an automatic segmentation technique (CAD) for cerebral glioma, especially useful in a patient follow-up during chemotherapy, and for preoperative assessment of tumor extension. Fifteen patients with glioma (9 low-grade, 6 high-grade) were selected. 3T MR-DTI consisted of a single-shot EPI sequence (b=1000 s/mm2, 32 gradient directions). Fractional anisotropy (FA), mean diffusivity (MD), p and q maps, were obtained. Manual segmentation of pathological areas was performed on each map. 3D texture analysis was applied with a sliding window approach to the segmented ROIs and to the contralateral healthy tissue, in order to identify discriminating features from the intensity and the gradient histogram, and from the cooccurrence (COM) and the run length matrix (RLM). After determining (according to their Fisher-filter score) the best features for each map, the feature-space dimensionality was reduced by Principal Component Analysis, and a neural-network classifier was trained. Glioma segmentations, performed by tissue classification, were compared with the manual ones. Six patients were employed for training, nine for testing. Classifier sensitivity, specificity and ROC curves were calculated: preliminary results were obtained for the p map (AUC = 0.96, sensitivity and specificity equal to 90%, classification error 10.0%) and FA map (AUC = 0.98, sensitivity and specificity equal to 92.6%, classification error equal to 7.3%). Test images were automatically segmented by tissue classification; manual and automatic segmentations were compared, showing good concordance. Our preliminary results show that this approach could allow objective tumor identification and quantitative measurement, with good accuracy
Diffusion Tensor Magnetic Resonance Imaging: a Semi-Automated Algorithm to Identify Damaged Brain Areas from Fractional Anisotropy Maps
No full textAim of this study was to analyse diffusion tensor
imaging (DTI) datasets in order to identify damaged areas or
disorders of the brain in a semi-automatic way. For this
purpose, a software tool has been developed: it takes in input
the fractional anisotropy (FA) map of a (damaged) brain and,
after several steps involving the comparison between the two
brain hemispheres, it gives back, as output, a binary mask
with a ROI (Region of Interest) that shows the probably
damaged area. In the same way, starting from the MR image
without diffusion weighting (b0), we find another ROI that we
compare with the one previously detected from the FA map.
Then we overlay these ROIs onto both the FA map and the
image without diffusion weighting, trying to quantify how
well the ROIs cover the pathological tissue.
This procedure was repeated on a few patients (healthy and
pathological ones). The algorithm worked well, showing as a
preliminary result that FA maps allow a neater detection of
the pathological tissue if compared to MR images without
diffusion weighting
A CAD system for cerebral glioma based on texture features in DT-MR images
No full textTumor cells in cerebral glioma invade the surrounding tissues preferentially along white-matter tracts,
spreading beyond the abnormal area seen on conventional MR images. Diffusion Tensor Imaging can
reveal large peritumoral abnormalities in gliomas, which are not apparent on MRI.
Our aim was to characterize pathological vs. healthy tissue in DTI datasets by 3D statistical Texture
Analysis, developing an automatic segmentation technique (CAD, Computer Assisted Detection) for
cerebral glioma based on a supervised classifier (an artificial neural network). A Matlab GUI (Graphical
User Interface) was created to help the physician in the assisted diagnosis process and to optimize
interactivity with the segmentation system, especially for patient follow-up during chemotherapy, and
for preoperative assessment of tumor extension. Preliminary tissue classification results were obtained
for the p map (the calculated area under the ROC curve, AUC, was 0.96) and the FAmap (AUC1⁄40.98). Test
images were automatically segmented by tissue classification; manual and automatic segmentations
were compared, showing good concordance
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