Search results for "medical physics"
showing 10 items of 579 documents
Measurement of the Magnetic Moment of the One-Neutron Halo NucleusB11e
1999
The magnetic moment of ${}^{11}\mathrm{Be}$ ( ${T}_{1/2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}13.8\phantom{\rule{0ex}{0ex}}\mathrm{s}$) was measured by detecting nuclear magnetic resonance signals in a beryllium crystal lattice. The experimental technique applied to a ${}^{11}{\mathrm{Be}}^{+}$ ion beam from a laser ion source includes in-beam optical polarization, implantation into a metallic single crystal, and observation of rf resonances in the asymmetric angular distribution of the $\ensuremath{\beta}$ decay ( $\ensuremath{\beta}$-NMR). The nuclear magnetic moment $\ensuremath{\mu}{(}^{11}\mathrm{Be})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}1.6816(8…
Metodes grupēšanas procesu pētījumiem centrālajā redzes laukā un redzes lauka perifērijā
2018
Promocijas darbs uzrakstīts latviešu valodā uz 110 lapaspusēm. Tas satur 44 attēlus, 2 tabulas un 153 literatūras atsauces. Pētījumā tiek izvērtēta vizuālās informācijas grupēšanas un stimulu nozīmes ietekme uz informācijas apstrādes procesiem centrālajā redzes laukā un redzes lauka perifērijā. Acu kustību un psihofizikālo pētniecības metožu rezultāti norāda, ka vizuālās informācijas uztveres jutība uz nozīmi saturošiem stimuliem (bioloģiskā kustība vai burtu skenēšana) ir augstāka nekā uz nozīmi nesaturošiem stimuliem. Bioloģiskās kustības uztvere vizuālajā troksnī jeb figūras-fona nošķiršana precīzāk noris centrālajā redzes laukā ar tieš…
Study of the Planacon XP85012 photomultiplier characteristics for its use in a Cherenkov detector
2016
Main properties of the multi-anode microchannel plate photomultiplier to be used in a Cherenkov detector are discussed. The laboratory test results obtained using irradiation of the MCP-PMT photocathode by picosecond optical laser pulses with different intensities (from single photon regime to the PMT saturation conditions) are presented. peerReviewed
Magnetic Resonance Imaging and Computational Fluid Dynamics of High Frequency Oscillatory Ventilation (HFOV)
2011
In order to better understand the mechanisms of gas transport during High Frequency Oscillatory Ventilation (HFOV) Magnetic Resonance Imaging (MRI) with contrast gases and numerical flow simulations based on Computational Fluid Dynamics(CFD) methods are performed.
Incoherent optical correlator
1990
A nonconventional setup based on the Lau effect is employed for implementing a lensless incoherent correlator of 2-D signals with compact support.
Silicon as an Unconventional Detector in Positron Emission Tomography.
2012
Positron emission tomography (PET) is a widely used technique in medical imaging and in studying small animal models of human disease. In the conventional approach, the 511 keV annihilation photons emitted from a patient or small animal are detected by a ring of scintillators such as LYSO read out by arrays of photodetectors. Although this has been a successful in achieving ~5mm FWHM spatial resolution in human studies and ~1mm resolution in dedicated small animal instruments, there is interest in significantly improving these figures. Silicon, although its stopping power is modest for 511 keV photons, offers a number of potential advantages over more conventional approaches. Foremost is it…
The CALMA system: an artificial neural network method for detecting masses and microcalcifications in digitized mammograms
2004
The CALMA (Computer Assisted Library for MAmmography) project is a five years plan developed in a physics research frame in collaboration between INFN (Istituto Nazionale di Fisica Nucleare) and many Italian hospitals. At present a large database of digitized mammographic images (more than 6000) was collected and a software based on neural network algorithms for the search of suspicious breast lesions was developed. Two tools are available: a microcalcification clusters hunter, based on supervised and unsupervised feedforward neural network, and a massive lesions searcher, based on a hibrid approach. Both the algorithms analyzed preprocessed digitized images by high frequency filters. Clini…
Positron implantation profiles in layered samples
2009
The paper presents theoretical and experimental studies of the positron implantation profiles in layered samples. The Monte Carlo simulations performed using the GEANT4 toolkit reveal accumulation of positrons in the denser layer embedded between two less dense layers. That effect is significant not only for low energy positrons at slow monoenergetic positron beams but also for high energy positrons which are emitted from radioactive nuclei in conventional experiments. Measurements of the positron implantation profile into the samples which consist of silver and aluminium foils of different thickness show profile features which correspond well with those simulated by the GEANT4 toolkit for …
Spin-dipole nuclear matrix elements for double beta decays and astro-neutrinos
2014
Spin-dipole (SD) nuclear matrix elements (NMEs) M±(SD2) for unique first forbidden β±2−→0+ ground-state-to-ground-state transitions are studied by using effective microscopic two-nucleon interactions in realistic single-particle model spaces. The observed values of the NMEs Mexp±(SD2) are compared with the values of the single-quasiparticle NMEs Mqp±(SD2) without nucleon spin–isospin (στ) correlation and the QRPA NMEs MQRPA±(SD2) with the στ correlation. The observed SD matrix elements are found to be reduced by the factor k≈0.2 with respect to Mqp±(SD2) and by the factor kNM≈0.5 with respect to MQRPA±(SD2). We then infer that the SD NME is reduced considerably partly by the nucleon στ corr…
AX-PET: A novel PET concept with G-APD readout
2012
Abstract The AX-PET collaboration has developed a novel concept for high resolution PET imaging to overcome some of the performance limitations of classical PET cameras, in particular the compromise between spatial resolution and sensitivity introduced by the parallax error. The detector consists of an arrangement of long LYSO scintillating crystals axially oriented around the field of view together with arrays of wave length shifter strips orthogonal to the crystals. This matrix allows a precise 3D measurement of the photon interaction point. This is valid both for photoelectric absorption at 511 keV and for Compton scattering down to deposited energies of about 100 keV. Crystals and WLS s…