4 research outputs found
Cardiovascular magnetic resonance evaluation of aortic stenosis severity using single plane measurement of effective orifice area
<p>Abstract</p> <p>Background</p> <p>Transthoracic echocardiography (TTE) is the standard method for the evaluation of the severity of aortic stenosis (AS). Valve effective orifice area (EOA) measured by the continuity equation is one of the most frequently used stenotic indices. However, TTE measurement of aortic valve EOA is not feasible or not reliable in a significant proportion of patients. Cardiovascular magnetic resonance (CMR) has emerged as a non-invasive alternative to evaluate EOA using velocity measurements. The objectives of this study were: 1) to validate a new CMR method using jet shear layer detection (JSLD) based on acoustical source term (AST) concept to estimate the valve EOA; 2) to introduce a simplified JSLD method not requiring vorticity field derivation.</p> <p>Methods and results</p> <p>We performed an in vitro study where EOA was measured by CMR in 4 fixed stenoses (EOA = 0.48, 1.00, 1.38 and 2.11 cm<sup>2</sup>) under the same steady flow conditions (4-20 L/min). The in vivo study included eight (8) healthy subjects and 37 patients with mild to severe AS (0.72 cm<sup>2 </sup>†EOA †1.71 cm<sup>2</sup>). All subjects underwent TTE and CMR examinations. EOA was determinated by TTE with the use of continuity equation method (TTE<sub>CONT</sub>). For CMR estimation of EOA, we used 3 methods: 1) Continuity equation (CMR<sub>CONT</sub>); 2) Shear layer detection (CMR<sub>JSLD</sub>), which was computed from the velocity field of a single CMR velocity profile at the peak systolic phase; 3) Single plane velocity truncation (CMR<sub>SPVT</sub>), which is a simplified version of CMR<sub>JSLD </sub>method. There was a good agreement between the EOAs obtained in vitro by the different CMR methods and the EOA predicted from the potential flow theory. In the in vivo study, there was good correlation and concordance between the EOA measured by the TTE<sub>CONT </sub>method versus those measured by each of the CMR methods: CMR<sub>CONT </sub>(r = 0.88), CMR<sub>JSLD </sub>(r = 0.93) and CMR<sub>SPVT </sub>(r = 0.93). The intra- and inter- observer variability of EOA measurements was 5 ± 5% and 9 ± 5% for TTE<sub>CONT</sub>, 2 ± 1% and 7 ± 5% for CMR<sub>CONT</sub>, 7 ± 5% and 8 ± 7% for CMR<sub>JSLD</sub>, 1 ± 2% and 3 ± 2% for CMR<sub>SPVT</sub>. When repeating image acquisition, reproducibility of measurements was 10 ± 8% and 12 ± 5% for TTE<sub>CONT</sub>, 9 ± 9% and 8 ± 8% for CMR<sub>CONT</sub>, 6 ± 5% and 7 ± 4% for CMR<sub>JSLD </sub>and 3 ± 2% and 2 ± 2% for CMR<sub>SPVT</sub>.</p> <p>Conclusion</p> <p>There was an excellent agreement between the EOA estimated by the CMR<sub>JSLD </sub>or CMR<sub>SPVT </sub>methods and: 1) the theoretical EOA in vitro, and 2) the TTE<sub>CONT </sub>EOA in vivo. The CMR<sub>SPVT </sub>method was superior to the TTE and other CMR methods in terms of measurement variability. The novel CMR-based methods proposed in this study may be helpful to corroborate stenosis severity in patients for whom Doppler-echocardiography exam is inconclusive.</p
Skipper-CCD Sensors for the Oscura Experiment: Requirements and Preliminary Tests
Oscura is a proposed multi-kg skipper-CCD experiment designed for a dark
matter (DM) direct detection search that will reach unprecedented sensitivity
to sub-GeV DM-electron interactions with its 10 kg detector array. Oscura is
planning to operate at SNOLAB with 2070 m overburden, and aims to reach a
background goal of less than one event in each electron bin in the 2-10
electron ionization-signal region for the full 30 kg-year exposure, with a
radiation background rate of 0.01 dru. In order to achieve this goal, Oscura
must address each potential source of background events, including instrumental
backgrounds. In this work, we discuss the main instrumental background sources
and the strategy to control them, establishing a set of constraints on the
sensors' performance parameters. We present results from the tests of the first
fabricated Oscura prototype sensors, evaluate their performance in the context
of the established constraints and estimate the Oscura instrumental background
based on these results
Early Science with the Oscura Integration Test
Oscura is a planned light-dark matter search experiment using Skipper-CCDs
with a total active mass of 10 kg. As part of the detector development, the
collaboration plans to build the Oscura Integration Test (OIT), an engineering
test experiment with 10% of the Oscura's total mass. Here we discuss the early
science opportunities with the OIT to search for millicharged particles (mCPs)
using the NuMI beam at Fermilab. mCPs would be produced at low energies through
photon-mediated processes from decays of scalar, pseudoscalar, and vector
mesons, or direct Drell-Yan productions. Estimates show that the OIT would be a
world-leading probe for low-mass mCPs.Comment: 21 pages, 13 figure
Searching for millicharged particles with 1 kg of Skipper-CCDs using the NuMI beam at Fermilab
Abstract Oscura is a planned light-dark matter search experiment using Skipper-CCDs with a total active mass of 10 kg. As part of the detector development, the collaboration plans to build the Oscura Integration Test (OIT), an engineering test with 10% of the total mass. Here we discuss the early science opportunities with the OIT to search for millicharged particles (mCPs) using the NuMI beam at Fermilab. mCPs would be produced at low energies through photon-mediated processes from decays of scalar, pseudoscalar, and vector mesons, or direct Drell-Yan productions. Estimates show that the OIT would be a world-leading probe for mCPs in the âŒMeV mass range