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Towards quantitative perfusion MRI of the lung in COPD: The problem of short-term repeatability
(2018)
Purpose
4D perfusion magnetic resonance imaging (MRI) with intravenous injection of contrast agent allows for a radiation-free assessment of regional lung function. It is therefore a valuable method to monitor response to treatment in patients with chronic obstructive pulmonary disease (COPD). This study was designed to evaluate its potential for monitoring short-term response to hyperoxia in COPD patients.
Materials and methods
19 prospectively enrolled COPD patients (median age 66y) underwent paired dynamic contrast-enhanced 4D perfusion MRI within 35min, first breathing 100% oxygen (injection 1, O2) and then room air (injection 2, RA), which was repeated on two consecutive days (day 1 and 2). Post-processing software was employed to calculate mean transit time (MTT), pulmonary blood volume (PBV) and pulmonary blood flow (PBF), based on the indicator dilution theory, for the automatically segmented whole lung and 12 regions of equal volume.
Results
Comparing O2 with RA conditions, PBF and PBV were found to be significantly lower at O2, consistently on both days (p<10–8). Comparing day 2 to day 1, MTT was shorter by 0.59±0.63 s (p<10–8), PBF was higher by 22±80 ml/min/100ml (p<3·10–4), and PBV tended to be lower by 0.2±7.2 ml/100ml (p = 0.159) at both, RA and O2, conditions.
Conclusion
The second injection (RA) yielded higher PBF and PBV, which apparently contradicts the established hypothesis that hyperoxia increases lung perfusion. Quantification of 4D perfusion MRI by current software approaches may thus be limited by residual circulating contrast agent in the short-term and even the next day.
The development of crop varieties that are resistant to lodging is a top priority for breeding programmes. Herein, we characterize the rye mutant ´Stabilstroh’ (‘stable straw’) possessing an exceptional combination of high lodging resistance, tall posture and high biomass production. Nuclear magnetic resonance imaging displayed the 3-dimensional assembly of vascular bundles in stem. A higher number of vascular bundles and a higher degree of their incline were the features of lodging-resistant versus lodging-prone lines. Histology and electron microscopy revealed that stems are fortified by a higher proportion of sclerenchyma and thickened cell walls, as well as some epidermal invaginations. Biochemical analysis using Fourier-transform infrared spectroscopy and inductively coupled plasma-optical emission spectrometry further identified elevated levels of lignin, xylan, zinc and silicon as features associated with high lodging resistance. Combined effects of above features caused superior culm stability. A simplistic mathematical model showed how mechanical forces distribute within the stem under stress. Main traits of the lodging-resistant parental line were heritable and could be traced back to the genetic structure of the mutant. Evaluation of lodging-resistant wheat ‘Babax’ (‘Baviacora’) versus contrasting, lodging-prone, genotype ´Pastor´ agreed with above findings on rye. Our findings on mechanical stability and extraordinary culm properties may be important for breeders for the improvement of lodging resistance of tall posture cereal crops.
A search for heavy long-lived multicharged particles is performed using the ATLAS detector at the LHC. Data with an integrated luminosity of 36.1 fb(-1) collected in 2015 and 2016 from proton-proton collisions at root s = 13 TeV are examined. Particles producing anomalously high ionization, consistent with long-lived massive particles with electric charges from vertical bar q vertical bar = 2e to vertical bar q vertical bar = 7e, are searched for. No events are observed, and 95% confidence level cross-section upper limits are interpreted as lower mass limits for a Drell-Yan production model. Multicharged particles with masses between 50 and 980-1220 GeV (depending on their electric charge) are excluded.
We theoretically and experimentally investigate quantum features of an interacting light-matter system from a multidisciplinary perspective, combining approaches from semiconductor physics, quantum optics, and quantum-information science. To this end, we quantify the amount of quantum coherence that results from the quantum superposition of Fock states, constituting a measure of the resourcefulness of the produced state for modern quantum protocols. This notion of quantum coherence from quantum-information theory is distinct from other quantifiers of nonclassicality that have previously been applied to condensed-matter systems. As an archetypal example of a hybrid light-matter interface, we study a polariton condensate and implement a numerical model to predict its properties. Our simulation is confirmed by our proof-of-concept experiment in which we measure and analyze the phase-space distributions of the emitted light. Specifically, we drive a polariton microcavity across the condensation threshold and observe the transition from an incoherent thermal state to a coherent state in the emission, thus confirming the buildup of quantum coherence in the condensate itself.
The FR-I galaxy 3C 84, that is identified with the misaligned blazar NGC 1275, is well known as one of the very few radio galaxies emitting gamma-rays in the TeV range. Yet, the gamma-ray emission region cannot be pinpointed and the responsible mechanisms are still unclear. We calculate the optical absorption depth of high-energy photons in the broad-line region of 3C 84 depending on their energy and distance to the central black hole. Based on these calculations, a lower limit on the distance of the emission region from the central black hole can be derived. These lower limits are estimated for two broad-line region geometries (shell and ring) and two states of the source, the low state in 2016 October–December and a flare state in 2017 January. For the shell geometry, we can place the emission region outside the Ly α radius. For the ring geometry and the low flux activity, the minimal distance between the black hole, and the gamma-ray emission region is close to the Ly α radius. In the case of the flaring state (ring geometry), the results are not conclusive. Our results exclude the region near the central black hole as the origin of the gamma-rays detected by Fermi–LAT and Major Atmospheric Gamma-Ray Imaging Cherenkov. With these findings, we can constrain the theoretical models of acceleration mechanisms and compare the possible emission region to the source’s morphology resolved by radio images from the Very Long Baseline Array.
Gate-tuned anomalous Hall effect driven by Rashba splitting in intermixed LaAlO3/GdTiO3/SrTiO3
(2021)
The Anomalous Hall Effect (AHE) is an important quantity in determining the properties and understanding the behaviour of the two-dimensional electron system forming at the interface of SrTiO3-based oxide heterostructures. The occurrence of AHE is often interpreted as a signature of ferromagnetism, but it is becoming more and more clear that also paramagnets may contribute to AHE. We studied the influence of magnetic ions by measuring intermixed LaAlO3/GdTiO3/SrTiO3 at temperatures below 10 K. We find that, as function of gate voltage, the system undergoes a Lifshitz transition while at the same time an onset of AHE is observed. However, we do not observe clear signs of ferromagnetism. We argue the AHE to be due to the change in Rashba spin-orbit coupling at the Lifshitz transition and conclude that also paramagnetic moments which are easily polarizable at low temperatures and high magnetic fields lead to the presence of AHE, which needs to be taken into account when extracting carrier densities and mobilities.
This paper presents a measurement of forward-forward and forward-central dijet azimuthal angular correlations and conditional yields in proton-proton (pp) and proton-lead (p + Pb) collisions as a probe of the nuclear gluon density in regions where the fraction of the average momentum per nucleon carried by the parton entering the hard scattering is low. In these regions, gluon saturation can modify the rapidly increasing parton distribution function of the gluon. The analysis utilizes 25 pb(-1) of pp data and 360 mu b(-1) of p + Pb data, both at root S-NN = 5.02 TeV, collected in 2015 and 2016, respectively, with the ATLAS detector at the Large Hadron Collider. The measurement is performed in the center-of-mass frame of the nucleon-nucleon system in the rapidity range between -4.0 and 4.0 using the two highest transverse-momentum jets in each event, with the highest transverse-momentum jet restricted to the forward rapidity range. No significant broadening of azimuthal angular correlations is observed for forward-forward or forward-central dijets in p + Pb compared to pp collisions. For forward-forward jet pairs in the proton-going direction, the ratio of conditional yields in p + Pb collisions to those in pp collisions is suppressed by approximately 20%, with no significant dependence on the transverse momentum of the dijet system. No modification of conditional yields is observed for forward-central dijets.
This paper presents the electron and photon energy calibration obtained with the ATLAS detector using about 36 fb(-1) of LHC proton-proton collision data recorded at root s = 13 TeV in 2015 and 2016. The different calibration steps applied to the data and the optimization of the reconstruction of electron and photon energies are discussed. The absolute energy scale is set using a large sample of Z boson decays into electron-positron pairs. The systematic uncertainty in the energy scale calibration varies between 0.03% to 0.2% in most of the detector acceptance for electrons with transverse momentum close to 45 GeV. For electrons with transverse momentum of 10 GeV the typical uncertainty is 0.3% to 0.8% and it varies between 0.25% and 1% for photons with transverse momentum around 60 GeV. Validations of the energy calibration with J/psi -> e(+)e(-) decays and radiative Z boson decays are also presented.
Quantitative nuclear magnetic resonance imaging (MRI) shifts more and more into the focus of clinical research. Especially determination of relaxation times without/and with contrast agents becomes the foundation of tissue characterization, e.g. in cardiac MRI for myocardial fibrosis. Techniques which assess longitudinal relaxation times rely on repetitive application of readout modules, which are interrupted by free relaxation periods, e.g. the Modified Look-Locker Inversion Recovery = MOLLI sequence. These discontinuous sequences reveal an apparent relaxation time, and, by techniques extrapolated from continuous readout sequences, a putative real T1 is determined. What is missing is a rigorous analysis of the dependence of the apparent relaxation time on its real partner, readout sequence parameters and biological parameters as heart rate. This is provided in this paper for the discontinuous balanced steady state free precession (bSSFP) and spoiled gradient echo readouts. It turns out that the apparent longitudinal relaxation rate is the time average of the relaxation rates during the readout module, and free relaxation period. Knowing the heart rate our results vice versa allow to determine the real T1 from its measured apparent partner.
Contrast and non-contrast MRI based characterization of myocardium by T1-mapping will be of paramount importance to obtain biomarkers, e.g. fibrosis, which determines the risk of heart failure patients.
T1-mapping by the standard post-processing of the modified look-locker inversion recovery (MOLLI) lacks of accuracy when trying to reduce its duration, which on the other hand, is highly desirable in patients with heart failure. The recently suggested inversion group fitting (IGF) technique, which considers more parameters for fitting, has a superior accuracy for long T1 times despite a shorter duration. However, for short T1 values, the standard method has a superior precision. A conditional fitting routine is proposed which ideally takes advantage of both algorithms.
Materials and methods
All measurements were performed on a 1.5 T clinical scanner (ACHIEVA, Philips Healthcare, The Netherlands) using a MOLLI 5(n)3(n)3 prototype with n(heart beats) being a variable waiting time between inversion experiments. Phantom experiments covered a broad range of T1 times, waiting times and heart rates. A saturation recovery experiment served as a gold standard for T1 measurement. All data were analyzed with the standard MOLLI, the IGF fit and the conditional fitting routine and the obtained T1 values were compared with the gold standard. In vivo measurements were performed in a healthy volunteer and a total of 34 patients with normal findings, dilative cardiomyopathy and amyloidosis.
Results
Theoretical analysis and phantom experiments provided a threshold value for an apparent IGF
determining processing with IGF post processing for values above, or switching to the standard technique for values below. This was validated in phantoms and patients measurements. A reduction of the waiting time to 1 instead of 3 heart beats between the inversion experiments showed reliable results. The acquisition time was reduced from 17 to 13 heart beats. The in vivo measurements showed ECV values between 25% (18–33%; SD 0.03) in the healthy, 30% (22–40%; SD 0.04) in patients with DCM and 45% (30–60%; SD 0.9) in patients with amyloidosis.
Conclusion
The adopted post-processing algorithm determines long T1 values with high accuracy and short T1 values while maintaining a high precision. Based on reduction of waiting time, and independence of heart rate, it shortens breath hold duration and allows fast T1-mapping, which is frequently a prerequisite in patients with cardiac diseases.