18 research outputs found
Fock quantization of a Klein-Gordon field in the interior geometry of a nonrotating black hole
We study the canonical quantization of a scalar field in a Kantowski-Sachs
spacetime. For simplicity, we consider compactified spatial sections, since
this does not affect the ultraviolet behavior. A time-dependent canonical
transformation is performed prior to quantization. As in previously studied
cases, the purpose of this canonical transformation is to identify and extract
the background contribution to the field evolution which is obstructing a
unitary implementation of the field dynamics at the quantum level. This
splitting of the time dependence into a background piece and the part to be
seen as true quantum evolution is to a large extent determined by the unitarity
requirement itself. The quantization is performed in the usual setup of Fock
representations, demanding the preservation of the spatial symmetries. Under
the joint requirements of quantum unitary dynamics and compatibility with those
classical symmetries, the quantization is shown to be unique, in the sense that
any two representations with these properties are unitarily equivalent. This
confirms the validity of our conditions as criteria to discriminate among
possibly inequivalent quantum descriptions. The interest of this analysis goes
beyond cosmological applications since the interior of a nonrotating black hole
has a geometry of the Kantowski-Sachs type.Comment: 13 page
Safety, feasibility, and hemodynamic response of regadenoson for stress perfusion CMR
Owing to its pharmacodynamics and posology, the use of regadenoson for stress cardiac magnetic resonance (CMR) has
potential advantages over other vasodilators. We sought to evaluate the safety, hemodynamic response and diagnostic
performance of regadenoson stress-CMR in routine clinical practice. All regadenoson stress-CMR examinations performed
between May 2017 and July 2020 at our institution were retrospectively reviewed. A total of 698 studies were included
for the final analysis. A conventional stress/rest protocol was performed using a 1.5T MRI scanner (Magnetom Aera, Siemens Healthineers, Erlangen, Germany). Adverse events, clinical symptoms, and hemodynamic response were assessed.
Diagnostic accuracy of the test was evaluated in patients who underwent invasive coronary angiography. Nearly half of
patients (48.5%) remained asymptomatic. Most common clinical symptoms included dyspnea (137, 19.6%), chest pain
(116, 16.6%) and flushing (44, 6.3%). Two patients (0.28%) could not complete the examination due to severe hypotension or unbearable chest pain. Overall, an increase in heart rate (HR) response (36.2% [IQR: 22.5–50.9]) and a decrease
in systolic and diastolic blood pressure (BP) (median systolic BP response of -5% [IQR: -11.5-0.6]; median diastolic BP
response of -6.3 mmHg [IQR: -13.4-0]) was observed. Patients with symptoms induced by regadenoson showed higher
HR response (40.3%, IQR: 26.4–56.1 vs. 32.4%, IQR: 19-45.6, p<0.001), whereas a blunted HR response was observed
in diabetic (29.6%, IQR: 18.4–42 p<0.001), obese (31.7%, IQR: 20.7–46.2 p=0.005) and patients aged 70 years or
older (32.9%, IQR: 22.6–43.1 p<0.001). Overall, regadenoson stress-CMR showed 95.65% (IQ 91.49–99.81) sensitivity,
54.84% (IQ 35.71–73.97) specificity, 86.99% (IQ 82.74–94.68) positive predictive value, and 77.27% (IQ 57.49–97.06)
negative predictive value for detecting significant coronary stenosis as compared with invasive coronary angiography.
Regadenoson is a well-tolerated vasodilator that can be safely employed for stress perfusion CMR, with high diagnostic
performanc
Fock Quantization of a Klein–Gordon Field in the Interior Geometry of a Nonrotating Black Hole
We study the canonical quantization of a scalar field in Kantowski–Sachs spacetime. For simplicity, we consider compactified spatial sections, since this does not affect the ultraviolet behavior. A time-dependent canonical transformation is performed prior to quantization. As in previously studied cases, the purpose of this canonical transformation is to identify and extract the background contribution to the field evolution which is obstructing a unitary implementation of the field dynamics at the quantum level. This splitting of the time dependence into a background piece and the part to be seen as true quantum evolution is, to a large extent, determined by the unitarity requirement itself. The quantization is performed in the usual setup of Fock representations, demanding the preservation of the spatial symmetries. Under the joint requirements of quantum unitary dynamics and compatibility with those classical symmetries, the quantization is shown to be unique, in the sense that any two representations with these properties are unitarily equivalent. This confirms the validity of our conditions as criteria to discriminate among possibly inequivalent quantum descriptions. The interest of this analysis goes beyond cosmological applications since the interior of a nonrotating black hole has a geometry of the Kantowski–Sachs type
Caracterización de la miocarditis por COVID-19 mediante resonancia magnética cardiaca
Desde su primera descripción en diciembre de 2019 en la ciudad de Wuhan (Hubei, China), un nuevo tipo de coronavirus mutado, llamado coronavirus 2 del síndrome respiratorio agudo grave (SARS-CoV-2), ha infectado a más de 3,6 millones de personas y ha causado más de 257.000 muertos en todo el mundo (hasta el 5 de mayo de 2020). Preocupa cada vez más que la afección respiratoria aguda que tiene lugar en la enfermedad coronavírica de 2019 (COVID-19) tenga fuerte relación con el daño cardiovascular. Los pacientes con COVID-19 corren el riesgo de sufrir arritmias cardiacas, síndromes coronarios agudos, eventos relacionados con insuficiencia cardiaca y miocarditis fulminante. La lesión miocárdica puede ocurrir en distintas fases de la COVID-19 (p. ej., fases viral, pulmonar, inflamatoria y de recuperación), incluso tardíamente tras el inicio de los síntomas
Safety, feasibility, and hemodynamic response of regadenoson for stress perfusion CMR
Owing to its pharmacodynamics and posology, the use of regadenoson for stress cardiac magnetic resonance (CMR) has
potential advantages over other vasodilators. We sought to evaluate the safety, hemodynamic response and diagnostic
performance of regadenoson stress-CMR in routine clinical practice. All regadenoson stress-CMR examinations performed
between May 2017 and July 2020 at our institution were retrospectively reviewed. A total of 698 studies were included
for the final analysis. A conventional stress/rest protocol was performed using a 1.5T MRI scanner (Magnetom Aera, Siemens Healthineers, Erlangen, Germany). Adverse events, clinical symptoms, and hemodynamic response were assessed.
Diagnostic accuracy of the test was evaluated in patients who underwent invasive coronary angiography. Nearly half of
patients (48.5%) remained asymptomatic. Most common clinical symptoms included dyspnea (137, 19.6%), chest pain
(116, 16.6%) and flushing (44, 6.3%). Two patients (0.28%) could not complete the examination due to severe hypotension or unbearable chest pain. Overall, an increase in heart rate (HR) response (36.2% [IQR: 22.5–50.9]) and a decrease
in systolic and diastolic blood pressure (BP) (median systolic BP response of -5% [IQR: -11.5-0.6]; median diastolic BP
response of -6.3 mmHg [IQR: -13.4-0]) was observed. Patients with symptoms induced by regadenoson showed higher
HR response (40.3%, IQR: 26.4–56.1 vs. 32.4%, IQR: 19-45.6, p<0.001), whereas a blunted HR response was observed
in diabetic (29.6%, IQR: 18.4–42 p<0.001), obese (31.7%, IQR: 20.7–46.2 p=0.005) and patients aged 70 years or
older (32.9%, IQR: 22.6–43.1 p<0.001). Overall, regadenoson stress-CMR showed 95.65% (IQ 91.49–99.81) sensitivity,
54.84% (IQ 35.71–73.97) specificity, 86.99% (IQ 82.74–94.68) positive predictive value, and 77.27% (IQ 57.49–97.06)
negative predictive value for detecting significant coronary stenosis as compared with invasive coronary angiography.
Regadenoson is a well-tolerated vasodilator that can be safely employed for stress perfusion CMR, with high diagnostic
performanc
Long-term prognostic value of coronary CTA in orthotopic heart transplant recipients
OBJECTIVE. This study aimed to evaluate the long-term prognostic value of coronary
CTA (CCTA) in heart transplant recipients.
MATERIALS AND METHODS. The records of 114 patients who had undergone a
heart transplant (mean age, 61.7 ± 11.1 [SD] years; 83.3% men) and who underwent
CCTA for the surveillance of coronary allograft vasculopathy (CAV) from June 2007 to
December 2017 were retrospectively evaluated for the occurrence of major adverse
cardiovascular events (MACEs) (cardiac death, nonfatal myocardial infarction, unstable angina requiring hospitalization, coronary revascularization, cardiac arrhythmias,
stroke, and retransplant). Patients were classified according to the presence of nonobstructive CAV (lumen reduction < 50%) or obstructive disease (lumen reduction ≥ 50%)
and using a coronary segment involvement score (SIS). Differences in MACE rate between groups were compared.
RESULTS. Obstructive CAV was observed in 12 heart transplant recipients (10.5%).
During a mean follow-up of 67.5 ± 41.4 months the overall rates of MACE were 50% and
14.7% in patients with obstructive and nonobstructive CAV, respectively (p < .05), resulting in an odds ratio for MACE of 6 (95% CI, 1.7–21.2). Comparison of event-free survival
showed a hazard ratio (HR) of 5 (95% CI, 1.95–13; p =. 004) for patients with obstructive
disease. The presence of four or more stenotic coronary segments (SIS ≥ 4) was associated with a higher rate of events (HR, 3.46; 95% CI, 1.46–8.23).
CONCLUSION. In patients who have undergone a heart transplant, CCTA offers a significant long-term prognostic impact on the prediction of MACEs