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Izdelava in preizkus večžične proporcionalne komore s katodo z integrirano zakasnilno linijo
Full text linkDevelopment of detectors for high resolution positron tomography
Full text linkV delu je predstavljen razvoj detektorjev za uporabo pri visokoločljivostni pozitronski tomografiji PET, positron emmision tomography). Pozitronska tomografija je dobro uveljavljena metoda tridimenzionalnega slikanja v nuklearni medicini za postavljanje diagnoze. Ker diagnoza temelji na opazovanju slik pridobljenih s slikanjem, je bistvena kvaliteta slike oz. ločljivost. Z motivacijo izboljšanja krajevne ločljivosti pri slikanju s pozitronsko tomografijo je nastal koncept PET sonde, ki znotraj omejenega vidnega polja izboljša prostorsko ločljivost obstoječega
pozitronskega tomografa. Srce PET sonde je krajevno ločljiv silicijev senzor. V delu je opisan razvoj in karakterizacija silicijevih detektorjev za uporabo pri PET sondi, ter karakterizacija in umeritev detektorskih blokov za uporabo pri napravi PET v kombinaciji s PET sondo. V okviru tega dela je bil razvit večplastni način zlaganja silicijevih senzorjev, ki omogoča večjo verjetnost
pri interakciji anihilacijskih fotonov energije 511 keV in kot tak obeta izboljšanje kvalitete slike
pri slikanju s pozitronsko tomografijo v kombinaciji s PET sondo.This work represents development of detectors for high resolution positron emission tomography
(PET), which is a very well established 3 dimensional imaging method in nuclear medicine
for disease diagnoses. Since the diagnoses is based on images taken, the quality or resolution is
most important. In search for better spatial resolution, PET probe concept has been developed,
that within a limited field of view improves spatial resolution of positron tomograph. The heart
of PET probe is a position sensitive silicon sensor. In this work the development and characterization
of silicon detectors for use in PET probe is described. In addition characterization and
calibration of block detectors for use in PET with the combination of PET probe is described.
In this regard multilayer stacking mode of silicon sensors has been developed in order to achieve
better interaction probability for 511 keV annihilation photons. As such this multilayer stacking
mode promises improvements in image quality of positron tomography in combination with PET
probe
Uporaba silicijevih fotopomnoževalk za zaznavanje fotonov Čerenkova pri pozitronski tomografji
No full textThe use of Cherenkov light in positron emission tomography (PET) has the potential
to improve the time-of-fight (TOF) resolution and reduce the cost of detectors.
Lead fuoride (PbF2) has emerged as a highly performing radiator material suitable
for TOF-PET application due to its excellent gamma stopping power and optical
properties. Previous studies using coincidences between a small number of crystals
have shown good performance in terms of coincidence time resolution (CTR). In
this work, the feasibility of Cherenkov TOF-PET is studied in detail, extending the
number of channels and optimizing the detectors for better performance. Simulations
were used to study different detector geometries and PbF2 crystal optical surface
treatments, up to a whole-body PbF2 TOF-PET scanner. The simulation data
showed that the quality of reconstructed images obtained when using different
Cherenkov TOF-PET scanner geometries is comparable to current state-of-theart
scintillator scanners. Experiments with different detector confgurations were
carried out to measure CTR and e ciency. The HRFlexTOT electronics enabled
measurements of coincidences between two Cherenkov TOF-PET modules placed
in a back-to-back confguration with up to 16 channels per module. Of particular
interest is a multi-layer detector geometry, which improves the TOF resolution and
reduces the parallax error without compromising the detection e ciency. With a
multi-layer detector geometry, the CTR of the simulated whole-body PbF2 TOFPET
scanner was 143 ps, out of which the fundamental limitation due to light
production and transportation was only 22 ps. Experimentally, such CTR value
could not yet be achieved due to the limited performance of silicon photomultiplier
photodetectors currently available. With further development of the photodetectors
and the readout electronics, Cherenkov TOF-PET could become a competitive
reality in PET.Uporaba svetlobe Čerenkova v pozitronski tomografiji (PET) omogoča izboljšanje
ločljivosti meritve časa preleta (TOF) in znižanje cene detektorjev. Svinčev fuorid
(PbF2) se je izkazal kot visoko zmogljiv sevalec Čerenkove svetlobe za uporabo v
TOF-PET, zahvaljujoč njegovim odličnim optičnim lastnostim in moči ustavljanja
žarkov gama. Pretekle študije z manjšim številom kristalov so potrdile, da je mogoče doseči odlično ločljivost meritve časa med koincidencami (CTR). V tem delu je
podrobno preučena praktičnost Čerenkove pozitronske tomografije z meritvijo časa
preleta (Čerenkova TOF-PET), s študijami, ki vključujejo večje število kanalov detektorja,
in z optimizacijo detektorjev za boljšo zmogljivost. S pomočjo simulacij
so bile raziskane različne geometrije detektorjev in površinske obdelave kristalov
PbF2, vse do celotne naprave za Čerenkovo TOF-PET. Rezultati simulacij kažejo,
da je kvaliteta slik, rekonstruiranih z različnimi geometrijami Čerenkov TOF-PET
skenerjev, primerljiva s kvaliteto ki jo omogočajo trenutno najboljše scintilatorske
naprave za TOF-PET. V eksperimentih z različnimi konfiguracijami detektorja sta
bili izmerjeni CTR in učinkovitost zaznavanja. Posebej zanimiva je večplastna geometrija
detektorja, ki omogoča izboljšanje časovne ločljivosti in zmanjšanje napake
zaradi paralakse brez zmanjšanja učinkovitosti zaznavanja. Z večplastnim detektorjem
je bila CTR simuliranega Čerenkov TOF-PET skenerja 143 ps, pri čemer
je fundamentalna omejitev zaradi nastajanja fotonov in njihovega potovanja skozi
kristal le 22 ps. Eksperimentalno tako dobre ločljivosti še ni mogoče doseči, zaradi
omejene zmogljivosti uporabljenih fotodetektorjev, silicijevih fotopomnoževalk.
Elektronika HRFlexTOT je omogočila meritve koincidenc med dvema moduloma za
Čerenkovo TOF-PET, s 16 kanali na modul. Z nadaljnjim razvojem fotodetektorjev
in elektronike bi Čerenkova TOF-PET lahko postala konkurenčna metoda za PET
Krajevno občutljivo zaznavanje posameznih fotonov z večanodno fotopomnoževalko z mikrokanalnimi ploščami
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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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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