Analytical calculation of volumes-of-intersection for iterative, fully 3-D PET reconstruction

Use of iterative algorithms to reconstruct three-dimensional (3-D) positron emission tomography (PET) data requires the computation of the system probability matrix. The pure geometrical contribution can easily be approximated by the length-of-intersection (LOI) between lines-of-response (LOR) and individual voxels. However, more accurate geometrical projectors are desirable. Therefore, we have developed a fast method for the analytical calculation of the 3-D shape and volume of volumes-of-intersection (VOI). This method provides an alternative robust projector with a uniformly continuous sampling of the image space. The enhanced calculation effort is facilitated by using several speedup techniques. Exploiting intrinsic symmetry relations and the sparseness of the system matrix allows to create an efficiently compressed matrix which can be precomputed and completely stored in memory. In addition, a new voxel addressing scheme has been implemented. This scheme avoids time-consuming symmetry transformations of voxel addresses by using an octant-wise symmetrically ordered field of voxels. The above methods have been applied for a fully 3-D, iterative reconstruction of 3-D sinograms recorded with a Siemens/CTI ECAT HR+ PET scanner. A comparison of the performance of the reconstruction using LOI weighting and VOI weighting is presented

Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA

Deep-inelastic positron-proton interactions at low values of Bjorken-x down to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons are studied with the H1 experiment at HERA. The inclusive cross section for pi^0 mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward pi^0 meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Comment: 27 pages, 8 figures and 3 table

Differential (2+1) Jet Event Rates and Determination of alpha_s in Deep Inelastic Scattering at HERA

Events with a (2+1) jet topology in deep-inelastic scattering at HERA are studied in the kinematic range 200 < Q^2< 10,000 GeV^2. The rate of (2+1) jet events has been determined with the modified JADE jet algorithm as a function of the jet resolution parameter and is compared with the predictions of Monte Carlo models. In addition, the event rate is corrected for both hadronization and detector effects and is compared with next-to-leading order QCD calculations. A value of the strong coupling constant of alpha_s(M_Z^2)= 0.118+- 0.002 (stat.)^(+0.007)_(-0.008) (syst.)^(+0.007)_(-0.006) (theory) is extracted. The systematic error includes uncertainties in the calorimeter energy calibration, in the description of the data by current Monte Carlo models, and in the knowledge of the parton densities. The theoretical error is dominated by the renormalization scale ambiguity.Comment: 25 pages, 6 figures, 3 tables, submitted to Eur. Phys.

Multi-Jet Event Rates in Deep Inelastic Scattering and Determination of the Strong Coupling Constant

Jet event rates in deep inelastic ep scattering at HERA are investigated applying the modified JADE jet algorithm. The analysis uses data taken with the H1 detector in 1994 and 1995. The data are corrected for detector and hadronization effects and then compared with perturbative QCD predictions using next-to-leading order calculations. The strong coupling constant alpha_S(M_Z^2) is determined evaluating the jet event rates. Values of alpha_S(Q^2) are extracted in four different bins of the negative squared momentum transfer~\qq in the range from 40 GeV2 to 4000 GeV2. A combined fit of the renormalization group equation to these several alpha_S(Q^2) values results in alpha_S(M_Z^2) = 0.117+-0.003(stat)+0.009-0.013(syst)+0.006(jet algorithm).Comment: 17 pages, 4 figures, 3 tables, this version to appear in Eur. Phys. J.; it replaces first posted hep-ex/9807019 which had incorrect figure 4

Multiplicity Structure of the Hadronic Final State in Diffractive Deep-Inelastic Scattering at HERA

The multiplicity structure of the hadronic system X produced in deep-inelastic processes at HERA of the type ep -> eXY, where Y is a hadronic system with mass M_Y< 1.6 GeV and where the squared momentum transfer at the pY vertex, t, is limited to |t|<1 GeV^2, is studied as a function of the invariant mass M_X of the system X. Results are presented on multiplicity distributions and multiplicity moments, rapidity spectra and forward-backward correlations in the centre-of-mass system of X. The data are compared to results in e+e- annihilation, fixed-target lepton-nucleon collisions, hadro-produced diffractive final states and to non-diffractive hadron-hadron collisions. The comparison suggests a production mechanism of virtual photon dissociation which involves a mixture of partonic states and a significant gluon content. The data are well described by a model, based on a QCD-Regge analysis of the diffractive structure function, which assumes a large hard gluonic component of the colourless exchange at low Q^2. A model with soft colour interactions is also successful.Comment: 22 pages, 4 figures, submitted to Eur. Phys. J., error in first submission - omitted bibliograph

Measurement of Leading Proton and Neutron Production in Deep Inelastic Scattering at HERA

Deep--inelastic scattering events with a leading baryon have been detected by the H1 experiment at HERA using a forward proton spectrometer and a forward neutron calorimeter. Semi--inclusive cross sections have been measured in the kinematic region 2 <= Q^2 <= 50 GeV^2, 6.10^-5 <= x <= 6.10^-3 and baryon p_T <= MeV, for events with a final state proton with energy 580 <= E' <= 740 GeV, or a neutron with energy E' >= 160 GeV. The measurements are used to test production models and factorization hypotheses. A Regge model of leading baryon production which consists of pion, pomeron and secondary reggeon exchanges gives an acceptable description of both semi-inclusive cross sections in the region 0.7 <= E'/E_p <= 0.9, where E_p is the proton beam energy. The leading neutron data are used to estimate for the first time the structure function of the pion at small Bjorken--x.Comment: 30 pages, 9 figures, 2 tables, submitted to Eur. Phys.

Massively parallelizable list-mode reconstruction using a Monte Carlo-based elliptical Gaussian model

Purpose: A fully three-dimensional (3D) massively parallelizable list-mode ordered-subsets expectation-maximization (LM-OSEM) reconstruction algorithm has been developed for high-resolution PET cameras. System response probabilities are calculated online from a set of parameters derived from Monte Carlo simulations. The shape of a system response for a given line of response (LOR) has been shown to be asymmetrical around the LOR. This work has been focused on the development of efficient region-search techniques to sample the system response probabilities, which are suitable for asymmetric kernel models, including elliptical Gaussian models that allow for high accuracy and high parallelization efficiency. The novel region-search scheme using variable kernel models is applied in the proposed PET reconstruction algorithm...This work was partially supported by Spain’s Ministry of Science and Innovation through CDTI’s CENIT program (AMIT project) and INNPACTO (PRECISION project), Instituto de Salud Carlos III (PI09/91058 and PI09/91065), and Project Nos. TEC2010-21619-C04-03 and TEC2011-28972- C02-02, Comunidad de Madrid (ARTEMIS S2009/DPI- 1802), and the European Regional Development Funds (FEDER). CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008–2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions, and finance by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund.Publicad

Erfahrungen von Studierenden mit wechselseitigen Untersuchungen im Klinischen Untersuchungskurs

Hintergrund: Die körperliche Untersuchung ist eine medizinische Kernkompetenz und von zentraler Bedeutung für die klinische Ausbildung von Studierenden. Die wechselseitige Untersuchung (Peer-to-Peer-Untersuchung, PPE) in Kleingruppen mit teilweisem Entkleiden ist eine bewährte didaktische Methode. Studien aus verschiedenen Bereichen deuten jedoch auf eine Beeinträchtigung der Lernprozesse durch PPE mit anschließenden Defiziten bei der körperlichen Untersuchung hin. In dieser Studie wurden die Studierenden nach ihrer Wahrnehmung von wechselseitiger Untersuchung und Präferenzen für die Kursentwicklung befragt. Methoden: In dieser webbasierten Querschnittsstudie wurden Medizinstudierende befragt, die vor 2 bis 4 Semestern den Untersuchungskurs absolviert hatten. Der Fragebogen befasste sich mit den soziodemografischen Merkmalen der Studierenden, ihren Erfahrungen mit wechselseitiger Untersuchung und ihren Präferenzen für die Verbesserung des Kursformats. Ein logistisches Regressionsmodell analysierte den Zusammenhang zwischen der Bereitschaft der Studierenden, an der wechselseitigen Untersuchung teilzunehmen, und den Präferenzen für eine Weiterentwicklung des Lernformats. Ergebnisse: Die Rücklaufquote betrug 39,5% (n=156), 73,4% waren weiblich. Die Mehrheit stimmte der wechselseitigen Untersuchung zu: untersucht zu werden ist eine wichtige Erfahrung für zukünftige Ärzte (96,5%, n=138), das wechselseitige Untersuchen ist eine geeignete Lehrmethode (89,5%, n=128), und sie fühlten sich während des Kurses zunehmend wohler (75,2%, n=107). Allerdings waren 13,3% (n=19) der Studierenden nicht bereit, sich untersuchen zu lassen. 31,5% (n=45) berichteten über ≥1 Lernbeeinträchtigungen durch wechselseitiges Untersuchen, und 12,2% (n=17) fühlten sich zur Teilnahme gezwungen. Die Studierenden wählten durchschnittlich 5,8 von 14 (SD 1,9) der Vorschläge zur Anpassung des Kursformats. Studierende, die nicht bereit waren, an der wechselseitigen Untersuchung von ≥1 Körperregionen teilzunehmen (23,8%, n=34), wünschten signifikant häufiger Kursmodifikationen: Training zuerst an Dummies (35,3% (n=50) vs. 12% (n=17), p=0,005) oder Schauspielpatienten (23,5% (n=34) vs. 5,6% (n=8), p=0,005), Raumtrennung durch Vorhänge (54,8% (n=78) vs. 17,9% (n=26), p&lt;0,001) und gleichgeschlechtliche Tutoren (24,2% (n=35) vs. 1,9% (n=3), p&lt;0,001). Zusammenfassung: Die meisten Studierenden bewerten die wechselseitige Untersuchung positiv, doch etwa 30% (n=43) gaben an, dass sie mit dem Format nicht zufrieden waren. Optionen zur Weiterentwicklung des Lehrformats wurden insbesondere von den Studierenden bevorzugt, die sich mit einer wechselseitigen Untersuchung eher unwohl fühlten.Experiences of students with reciprocal examinations in the clinical examination course Background: Physical examination is a core medical skill and central to the clinical education of students. Peer-to-peer examination (PPE) in small groups with partial undressing is a well established didactic method. However, studies from various fields suggest that PPE impairs learning with subsequent deficits in physical examination. In this study, students were asked about their perceptions of PPE and preferences for course development. Methods: This web-based cross-sectional study surveyed medical students who had completed the examination course 2–4 semesters ago. The questionnaire addressed students’ sociodemographic characteristics, their experiences with PPE, and their preferences for improving the course format. A logistic regression model analyzed the relationship between students’ willingness to participate in PPE and preferences for enhancing the learning format. Results: The response rate was 39.5% (n = 156); 73.4% were female. The majority agreed that PPE is an important experience for future physicians (96.5%, n = 138), PPE is an appropriate teaching method (89.5%, n = 128), and they felt increasingly comfortable during the course (75.2%, n = 107). However, 13.3% (n = 19) of students were unwilling to be examined, and 22.4% (n = 32) were unwilling to be examined on ≥ 1 body part. In addition, 31.5% (n = 45) reported ≥ 1 issue with learning using PPE, and 12.2% (n = 17) felt forced to participate. Students chose on average 5.8 of 14 (standard deviation 1.9) suggestions to adapt the course format. Students who were unwilling to participate in PPE of ≥ 1 body region (23.8%, n = 34) were significantly more likely to indicate course modifications: training first on dummies (35.3% vs. 12%, p = 0.005) or actors trained as standardized patients (23.5% vs. 5.6% , p = 0.005), room separation by curtains (54.8% vs. 17.9%, p &lt; 0.001), and same-sex tutors (24.2% vs. 1.9%, p &lt; 0.001). Conclusion: Most students rated PPE positively, but about 30% indicated that they were not satisfied with the format. Options to further develop the teaching format were particularly preferred by students who were more uncomfortable with peer-to-peer physical examinations

Structural chemistry of metal coordination complexes at high pressure

The application of pressures of up to about 10 GPa may induce significant geometric, configurational, conformational and packing changes in molecular solids. This review highlights and describes recent advances in high pressure studies of coordination complexes, many of which have been conducted at synchrotrons or other central facilities. The main focus is on the wide range of geometric changes which occur with pressure. In some cases these changes have associated physical effects, and the review describes materials exhibiting negative linear compressibility, spin cross-over phenomena, magnetism and molecular conduction, as well as detailing the exciting possibilities for future developments in this area of research