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Utilizzo delle sequenze IDEAL (Iterative DEcomposition of water and fat with echo asymmetry And Least-squares estimation) in pazienti con protesi ed ausili metallici.
No full textOBIETTIVI DIDATTICI:
Descrivere i principi fisici su cui si basa la sequenza IDEAL e paragonarne l’utilità rispetto alle tradizionali sequenze a soppressione del grasso nel ridurre gli artefatti magnetici in pazienti portatori di protesi metalliche.
INTRODUZIONE:
La Risonanza Magnetica (RM) gioca un ruolo vitale nell’imaging post-operatorio dei pazienti con protesi metalliche. Tuttavia, sia gli artefatti da suscettibilità magnetica che quelli da disomogeneità di campo pongono un serio problema nel valutare tali pazienti; inoltre, la saturazione incompleta del segnale del grasso rappresenta un ulteriore ostacolo. Per risolvere tali inconvenienti è stata introdotta una nuova sequenza di imaging RM detta IDEAL, che determina una separazione uniforme del tessuto adiposo e dell'acqua in una singola acquisizione a contrasti multipli.
DESCRIZIONE:
La sequenza IDEAL utilizza 3 echi indipendenti, ciascuno al massimo punto di eccitazione, per ottenere un elevato rapporto segnale-rumore. Infatti, selezionando le immagini in-fase e fuori-fase, in realtà non completamente in-fase e fuori-fase (echi asimmetrici), si raggiunge una corretta valutazione della quantità di grasso e di acqua in ciascun voxel, ottenendo così un’immagine meno rumorosa. Il risultato è quello di ottenere quattro immagini co-registrate che possono essere utilizzate in combinazione per aumentare la confidenza diagnostica:
- In fase
- Fuori fase
- Grasso
- Acqua
Anche nel caso di anatomie complesse o in presenza di impianti metallici, la sequenza IDEAL è in grado di produrre immagini affidabili della sola acqua, fornendo però anche informazioni importanti relative al tessuto adiposo.
La sequenza IDEAL ha dimostrato di essere particolarmente utile in queste situazioni diminuendo gli effetti da disomogeneità di campo magnetico e determinando una omogenea saturazione del segnale del grasso sino ai margini delle strutture metalliche, garantendo quindi un’ottima qualità delle immagini.
CONCLUSIONI:
La sequenza IDEAL determina una effettiva riduzione degli artefatti ferro-magnetici e incrementa la qualità delle immagini rispetto alle tradizionali sequenza a saturazione del segnale del grasso
Local structure of gallate proton conductors
No full textLanthanum barium gallate proton conductors are based on disconnected GaO4 groups. The insertion of hydroxyls in the LaBaGaO4 network proceeds through self-doping with Ba2+, consequent O2- vacancy formation to fulfill charge neutrality. With a structural investigation on self-doped LaBaGaO4 oxides using synchrotron XRD and EXAFS on the Ga K-edge, we find that: (a) the GaO4 tetrahedra retain their size throughout the whole series; (b) the GaO4 tetrahedra rotate as rigid bodies on hydration, leading to the formation of a network of shorter O-O configurations that are stabilized by hydrogen bonds; (c) contraction of the lattice occurs along the a unit cell axis, as a consequence of an overall structural rearrangement of the hydrated solid
Ruolo dell'elastonosonografia nella valutazione del tendine achille dopo infiltrazione con pappa piastrinica nostra esperienza .
No full textIndium doping of proton-conducting solid oxides
Full text linkSolid oxides protonic conductors are prepared by doping the pure matrix compounds with cationic
species. Barium cerate and barium zirconate are perovskite-like compounds, characterized by a
network of corner-sharing MeO6 octahedra (Me=Ce, Zr). Barium lies in the cavities between
octahedra. Insertion of trivalent species in the octahedral site involves the formation of charge-
compensating oxygen vacancies, that can be filled by hydroxyls coming from dissociative water
absorption. Then, proton delocalization among structural oxygens ensures conductivity. The most
effective conductors are obtained by yttrium doping that, on the other hand, enters only in limited
amounts in both BaZrO3 and BaCeO3, thus involving limited carrier concentration. Perovskites are
affected by different drawbacks: barium cerate compounds are very sensitive to the acidic
components present in the environment and in particular to CO2 that induces decomposition in
barium carbonate and cerium oxide; barium zirconate, notwithstanding a very high bulk
conductivity, is biased by high grain boundary resistivity.
A possible alternative to perovskite-like compounds is constituted by fergusonite-type lanthanum
niobate and lanthanum tantalate compounds, characterized by a tetrahedral coordination of Nb and
Ta. These oxides present a very high chemical stability but very low carrier concentration, usually
induced by Ca-doping the lanthanum site [1].
Among the different trivalent dopants, it was demonstrated by X-ray absorption spectroscopy that
indium is able to enter in any composition in the perovskite network, thus providing a very high
carrier concentration, even if with lower proton mobility. This property of indium was ascribed to
its electronic structure and in particular to the low Pearson hardness, allowing this cation to fit in a
hosting matrix with the least structural strain [2]. A preliminar attempt of exploiting indium for
enhancing the carrier concentration of lanthanum niobate was carried out. The solid state synthesis
involved amounts of the reactant simple oxides suitable to force indium doping of the niobium site.
X-ray diffraction do not show significant amounts of secondary oxide phases
Pigmented villonodular bursitis (PVNB) in the medial gastrocnemius bursa:report of an unusual case.
No full textINTRODUCTION:
Pigmented villonodular synovitis (PVNS) represents an uncommon benign proliferative disorder that may involve the synovium of the joint diffusely or focally, or that may occur extraarticularly in a bursa (pigmented villonodular bursitis [PVNB]) or tendon sheath (pigmented villonodular tenosynovitis [PVNTS]). The knee, followed by the hip, is the most common location for PVNS or PVNB, whereas PVNTS occurs most often in the hand and foot. It primarily involves young adults, the peak age being between the second and fourth decade of life and appears with non-specific symptoms which mimic other pathologies, including traumatic knee injuries, thus often delaying the correct diagnosis.
REPORT/DISCUSSION:
A 17 year old female presented with swelling and mild degree of pain in her left knee for three months. No history of trauma or any other significant illness was present. Routine laboratory investigations were normal. X-ray was normal. MRI of the knee was performed and it showed a joint effusion with non-specific synovial proliferation and two focal nodular formations at the insertion of medial head of gastrocnemius muscle in the medial gastrocnemius bursa. Those two nodular formations had low signal intensity on all pulse sequences and bloom artifacts on the FGRE-sequence. T1 weighted fat-saturated gadolinium enhanced MR image showed a low marginal contrast-enhancement of the two nodular formations, and high contrast-enhancement of the synovial proliferation. Biopsy from the two lobulated nodules revealed synovial nodules which contained haemosiderin pigment.
Imaging characteristics of PVNS and PVNB are almost the same: radiographically visible calcifications are rare; CT scans show the lesions as high attenuating because of the haemosiderin content; MRI findings are prominent low signal intensity (seen with T2-weighting) and "blooming" artifacts from the hemosiderin deposits (seen with gradient-echo sequences) that are nearly pathognomonic. In addition, MR imaging is optimal for evaluating lesion extent. This information is crucial to guide treatment and to achieve complete surgical resection
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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