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| 3. |
- Bennati, Paolo, et al.
(författare)
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Preliminary study of a new gamma imager for on-line proton range monitoring during proton radiotherapy
- 2017
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Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- We designed and tested new concept imaging devices, based on a thin scintillating crystal, aimed at the online monitoring of the range of protons in tissue during proton radiotherapy. The proposed crystal can guarantee better spatial resolution and lower sensitivity with respect to a thicker one, at the cost of a coarser energy resolution. Two different samples of thin crystals were coupled to a position sensitive photo multiplier tube read out by 64 independent channels electronics. The detector was equipped with a knife-edge Lead collimator that defined a reasonable field of view of about 10 cm in the target. Geant4 Monte Carlo simulations were used to optimize the design of the experimental setup and assess the accuracy of the results. Experimental measurements were carried out at the Skandion Clinic, the recently opened proton beam facility in Uppsala, Sweden. PMMA and water phantoms studies were performed with a first prototype based on a round 6.0 mm thick Cry019 crystal and with a second detector based on a thinner 5 × 5 cm2, 2.0 mm thick LFS crystal. Phantoms were irradiated with mono-energetic proton beams whose energy was in the range between 110 and 160 MeV. According with the simulations and the experimental data, the detector based on LFS crystal seems able to identify the peak of prompt-gamma radiation and its results are in fair agreement with the expected shift of the proton range as a function of energy. The count rate remains one of the most critical limitations of our system, which was able to cope with only about 20% of the clinical dose rate. Nevertheless, we are confident that our study might provide the basis for developing a new full-functional system.
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| 6. |
- Colarieti-Tosti, M., et al.
(författare)
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Crystal field levels in lanthanide systems
- 2001
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Ingår i: Journal of Magnetism and Magnetic Materials. - 0304-8853 .- 1873-4766. ; 226-230:Part 1, s. 1027-1028
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Tidskriftsartikel (refereegranskat)abstract
- Crystalfieldlevels in lanthanide compounds have been calculated by first-principles theory, combining the strength of the standard model for rare earths in treating the localized 4f electrons and the power of Density Functional Theory in describing the, weakly correlated, delocalized, electrons. The stability of our calculations has been checked against changes of the constraints in the Full Potential-LMTO implementation. The assumption of weak 4f–4f inter-atomic interactions has also been checked by means of supercell calculations. Suggestions for the treatment of magnetic systems on a similar basis are given.
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| 7. |
- Colarieti-Tosti, Massimiliano, et al.
(författare)
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First-principles theory of intermediate-valence f-electron systems
- 2004
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 93:9, s. 096403-
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Tidskriftsartikel (refereegranskat)abstract
- We propose a first-principles based method for calculating the electronic structure and total energy of solids in an intermediate-valence configuration. The method takes into account correlation effects (d-f Coulomb interaction) and many-body renormalization of the effective hybridization parameter of the f system. As an example, the formation of a pressure-induced intermediate-valence state in Yb is considered and its electronic structure and equation of state are calculated and compared to experimental data. The agreement is found to be excellent for both properties, and we argue that the developed method, which applies to any element or compound, provides for the first time a quantitative theoretical treatment of intermediate-valence materials.
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| 8. |
- Dallera, C., et al.
(författare)
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Understanding mixed valent materials : Effects of dynamical core-hole screening in high-pressure x-ray spectroscopy
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:8, s. 081101-
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the electronic structure of Yb, a material whose valence is modified under pressure, are observed with remarkable detail in x-ray absorption and emission data measured between ambient conditions and 20 GPa. These changes are reproduced by a theory that essentially does not rely on experimental parameters, and includes dynamical core-hole screening. From the combined experimental and theoretical data we can firmly establish on a quantitative level how the valency of an intermediate valence material is modified by pressure. In metallic Yb it increases from 2 to 2.55 +/- 0.05 between 0 and 20 GPa.
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| 17. |
- Eckle, M, et al.
(författare)
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Electronic structure of UCx films prepared by sputter co-deposition
- 2004
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 334:1, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- Thin layers of UCx (x = 0-12) have been prepared by sputter co-deposition of uranium and carbon in an Ar atmosphere. The films were investigated in-situ by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively). Special interest was put on the evolution of the electronic structure with the composition of the films, as deduced from the U-4f, C-1s and valence region spectra. With increasing carbon content, three types of carbon species were detected according to C-1s core level line, at 282, 282.6 and 284.5 eV binding energy (BE). They are attributed to the UC, UC2 and graphite phases, respectively. The U-4f core levels do not change strongly with increasing carbon content, showing well-itinerant U-5f electrons. Similarly, valence region spectra show three types of carbon species for different UCx films, which are differentiated by their C-2p signals. A strong hybridisation between C-2p and U-5f states is detected in UC, while the C-2p signal in UC2 appears only weakly hybridised, and for higher carbon contents a pi band characteristic of graphite appears.
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| 18. |
- Eriksson, Olle, et al.
(författare)
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Many-body projector orbitals for electronic structure theory of strongly correlated electrons
- 2005
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Ingår i: INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY. - : Wiley. - 0020-7608 .- 1097-461X. ; 105:2, s. 160-
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Tidskriftsartikel (refereegranskat)abstract
- We describe a technique to evaluate projector functions to be used, e.g., in self-interaction corrected versions of the Kohn-Sham equation (or in the LSDA+U method). The projector functions reproduce by construction the expectation values of spin and orbital moments (or any other property one is interested in) for the atomic many-body state. We therefore refer to these projector functions as many-body projector orbitals (MBPO). We describe how, once these projector states have been calculated, one can use them in any electronic structure method for a solid or molecule, to calculate ground-state properties of materials with strongly correlated states.
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| 19. |
- Larsson, David, et al.
(författare)
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An ex-vivo setup for characterization of atherosclerotic plaque using shear wave elastography and micro-computed tomography
- 2016
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - : IEEE conference proceedings. - 9781467398978
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Konferensbidrag (refereegranskat)abstract
- Quantification of the mechanical properties of atherosclerotic plaque has shown to be important in assessing carotid artery plaque vulnerability. For such, shear wave elastography (SWE) has been applied on both in-vitro and in-vivo setups. The aim of this study was to build an ex-vivo setup for combined evaluation of plaque characteristics using SWE and micro-computed tomography (μCT). As a proof-of-concept of the constructed experimental setup, a single human carotid plaque specimen was extracted during carotid endarterectomy. The plaque was imaged in the μCT system, and subsequently imaged using SWE. For the SWE measurement, group and phase velocity was extracted from the obtained in-phase/quadrature data, with its spatial distribution being compared to anatomical features visible in the μCT images. The results indicated wave velocity changes at boundaries identified in the μCT, with group velocity data slightly increasing when entering a calcified nodule. Additionally, μCT images seemed to provide good contrast between several plaque constituens using the defined imaging settings. Overall, the study represents a proof-of-concept for detailed ex-vivo plaque analysis using combined SWE and μCT, with obtained wave speed and shear modulus values falling within observed values for atherosclerotic plaque tissue. With an experimental setup defined, future studies on carotid plaque behaviour both in SWE and μCT is enabled, where a large-scale plaque study could be performed to investigate the ability of SWE to differentiate between different plaque types.
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| 20. |
- Liu, HP, et al.
(författare)
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On the structural polymorphism of CePt2Sn2: experiment and theory
- 2000
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Ingår i: JOURNAL OF ALLOYS AND COMPOUNDS. - : ELSEVIER SCIENCE SA. - 0925-8388. ; 306:1-2, s. 30-39
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Tidskriftsartikel (refereegranskat)abstract
- Samples of the heavy fermion compound CePt2Sn2 with varying compositions have been synthesised and examined from room temperature up to the melting point. Two crystallographic structures of the intermetallic alloy CePt2Sn2 were observed and they were syst
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| 22. |
- Marlevi, David, et al.
(författare)
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Estimation of Cardiovascular Relative Pressure Using Virtual Work-Energy
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Many cardiovascular diseases lead to local increases in relative pressure, reflecting the higher costs of driving blood flow. The utility of this biomarker for stratifying the severity of disease has thus driven the development of methods to measure these relative pressures. While intravascular catheterisation remains the most direct measure, its invasiveness limits clinical application in many instances. Non-invasive Doppler ultrasound estimates have partially addressed this gap; however only provide relative pressure estimates for a range of constricted cardiovascular conditions. Here we introduce a non-invasive method that enables arbitrary interrogation of relative pressures throughout an imaged vascular structure, leveraging modern phase contrast magnetic resonance imaging, the virtual work-energy equations, and a virtual field to provide robust and accurate estimates. The versatility and accuracy of the method is verified in a set of complex patient-specific cardiovascular models, where relative pressures into previously inaccessible flow regions are assessed. The method is further validated within a cohort of congenital heart disease patients, providing a novel tool for probing relative pressures in-vivo.
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| 23. |
- Pani, R., et al.
(författare)
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Excellent pulse height uniformity response of a new LaBr3:Ce scintillation crystal for gamma ray imaging
- 2015
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 787, s. 46-50
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear Medicine SPECT imaging is taking on new challenges, regarding the improvement of quality and contrast of images. In order to reach this goal, energy resolution and Compton rejection capability have to be enhanced. For detectors based on scintillation crystal, the choice of a scintillator with high light yield is suitable; recently one of the major candidates is Lanthanum Tri-Bromide (LaBr3:Ce), with its high 63,000 ph/MeV light yield. Unfortunately, LaBr3:Ce suffers size limitations due to the actual growth techniques (maximum 3 in diameter) and has also elevated cost. For these reasons, great interest is shown on small field of view deleclors based on LaBr3:Ce, Lhough l for imaging of specific physiological process or organ. To improve energy resolution, continuous crystals are more appropriate instead than pixelaled ones. Since in a continuous crystal a decrease in position linearity, due Lo Lhe light reflections, is typically obtained at the edges, an absorbent treatment of surfaces is generally ulilized for SPECT applicalions. On Lhe other hand, light absorption causes a relevara degraclalion of local energy resolution and pulse height uniformily response, affecling local image confrasl. In this work an analysis on a new conlinuous LaBr3:Ce scinlillalion crystal with size proper lo a small field of view gamma imager but with reflective treatment of surfaces is presented. This leads up to outstanding overall and local energy resolution results and excellent pulse height uniformity response On the whole field of view. Furthermore, preliminary imaging results are satisfactory, compared to the ones from a scintillation crystal with absorbent edges.
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| 24. |
- Pani, R., et al.
(författare)
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Investigation of radiation detection properties of CRY-018 and CRY-019 scintillators for medical imaging
- 2016
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Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- During the last years the research for new scintillation crystals has been crucial for the improvement of imaging performance in nuclear medicine applications. Crytur company has recently released two new scintillators named CRY-018 and CRY-019 which are non hygroscopic, have short decay time and low refraction index. They represent the ideal candidates to substitute NaI:Tl and BGO crystals in future PET ad SPECT applications. The purpose of this work is to characterize this unknown crystals, look for possible applications in imaging for nuclear medicine. The results of this work were compared with the results obtained with a LaBr3:ce scintillation crystal. This particular crystal is used as a comparison benchmark because of its strong linear pulse height uniformity response and high energy resolution. Measurements have been performed with a high count rate which is typical for medical applications. Irradiation of the crystals have been performed in three different geometries and in a photon energy range suitable with SPECT and PET applications. The experimental results identify the CRY-018 as an Yttrium and Silicon mixture and the CRY-019 with as Lutetium and Silicon one. Moreover a light yield of about 45% of LaBr3 one, was obtained for both the CRY-018 and CRY-019. This is one of the higher light yield between most of the scintillation crystals usually used in nuclear medicine. Both crystals are characterized by a non-proportionality in the pulse height linearity response. Energy resolutions of 7.4% for CRY-018 and 8.4% for CRY-019 at 661 keV, have been measured. The intrinsic component of the energy resolution has been esteemed for all three scintillators. An intrinsic detection efficiency of about 45% at 122 keV for CRY-018 and 14% at 661 keV for CRY-019 has been measured. Compared with LaBr3:Ce efficiency, which is highly deteriorated by the coating required by the hygroscopicity, CRY-018 and CRY-019 are really interesting considering that these two samples are only 6 mm thick. Crytur's crystals seem to be suitable for nuclear medicine applications.
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