Researchers sought to assess and improve the CEC image criteria for radiographic chest images. Diverse technique factors were used to obtain chest images of healthy volunteers. Image criteria were ...then used to help differentiate between the diverse images. Technique factors used in the project were selected so as to provide only slight differences in image quality. Data are reported for tests enacted using four different technique parameters, each with two settings used in contemporary clinical practice, including tube voltages of 102 and 114 kV, screen-film speeds of 160 and 320, maximum optical density in the parenchyma of 1.3 and 1.8, and both air gap and moving grid techniques for scatter reduction. Implications of the findings from this project are discussed.
Clinical and physical assessments of image quality are compared and the correlation between the two derived. Clinical assessment has been made by a group of expert radiologists who evaluated the ...fulfillment of the European Image Criteria for chest and lumbar spine radiography; yielding the so-called Image Criteria Score, ICS. Physical measures of image quality were calculated using a Monte Carlo model of the complete imaging system. This model includes a voxelised male anatomy and calculates contrast and signal-to-noise ratio of various anatomical details and a measure of useful dynamic range. Correlations between the ICS and the physical image quality measures were sought. Four lumbar spine and 16 chest imaging systems were evaluated and simulated with the model. The most useful physical quantities for chest radiography were the dynamic range and contrast of blood vessels in the retro-cardiac area. In lumbar spine, it was the signal-to-noise ratio of trabecular structures. The significant correlation is encouraging and shows that clinical image quality can be predicted provided the imaging conditions are well known and that relevant measures of physical image quality are used to assess the quality of the image.
Clinical and physical assessments of image quality are compared and the correlation between the two derived. Clinical assessment has been made by a group of expert radiologists who evaluated the ...fulfillment of the European Image Criteria for chest and lumbar spine radiography; yielding the so-called Image Criteria Score, ICS. Physical measures of image quality were calculated using a Monte Carlo model of the complete imaging system. This model includes a voxelised male anatomy and calculates contrast and signal-to-noise ratio of various anatomical details and a measure of useful dynamic range. Correlations between the ICS and the physical image quality measures were sought. Four lumbar spine and 16 chest imaging systems were evaluated and simulated with the model. The most useful physical quantities for chest radiography were the dynamic range and contrast of blood vessels in the retro-cardiac area. In lumbar spine, it was the signal-to-noise ratio of trabecular structures. The significant correlation is encouraging and shows that clinical image quality can be predicted provided the imaging conditions are well known and that relevant measures of physical image quality are used to assess the quality of the image
Clinical and physical assessments of image quality are compared and the correlation between the two derived. Clinical assessment has been made by a group of expert radiologists who evaluated the ...fulfillment of the European Image Criteria for chest and lumbar spine radiography; yielding the so-called Image Criteria Score, ICS. Physical measures of image quality were calculated using a Monte Carlo model of the complete imaging system. This model includes a voxelised male anatomy and calculates contrast and signal-to-noise ratio of various anatomical details and a measure of useful dynamic range. Correlations between the ICS and the physical image quality measures were sought. Four lumbar spine and 16 chest imaging systems were evaluated and simulated with the model. The most useful physical quantities for chest radiography were the dynamic range and contrast of blood vessels in the retro-cardiac area. In lumbar spine, it was the signal-to-noise ratio of trabecular structures. The significant correlation is encouraging and shows that clinical image quality can be predicted provided the imaging conditions are well known and that relevant measures of physical image quality are used to assess the quality of the image
We have investigated the unintentional
n
-type background doping in GaN(0001) layers grown on semi-insulating 4H-SiC(0001) substrate by plasma-assisted molecular beam epitaxy under Ga-rich conditions ...at growth temperatures from 780°C and 900°C. All layers exhibited very smooth surface morphology with monolayer steps as revealed by atomic force microscopy. Hall-effect measurements showed that the sample grown at 900°C had carrier concentration of 9.8 × 10
17
cm
−3
while the sample grown at 780°C had resistivity too high to obtain reliable measurements. Secondary-ion mass spectroscopy revealed O and Si concentrations of <10
17
cm
−3
in the sample grown at 900°C but >10
17
cm
−3
in the sample grown at 780°C. The trend for the atomic concentrations of O and Si, which are common donor impurities in GaN, was thus contrary to the trend of the carrier concentration. The full-width at half-maximum for x-ray rocking curves obtained across the GaN(0002) and GaN(10
1
¯
5) reflections for the sample grown at 900°C was 62 arcsec and 587 arcsec, respectively. The half-width increased with decreasing growth temperature. The atomic concentrations of O and Si are too low to account for the unintentional background doping levels. A possible explanation proposed in early reports for the background doping is N-vacancies.
We report on step‐flow growth of GaN(0001) on 4H‐SiC(0001) substrates by plasma‐assisted molecular beam epitaxy. The GaN layers were deposited directly on the substrate without using a buffer layer. ...A growth temperature of 900∘C and above resulted in an atomically flat surface morphology with locally straight steps indicating step‐flow growth. The step height was 0.21 nm corresponding to one‐half unit cell. The terrace width was 97 nm and the root‐mean‐square roughness was 0.06 nm. Samples grown below 900∘C exhibited a surface morphology consisting of spiraling terraces forming hexagonal hillocks. The full‐width at half‐maximum for X‐ray rocking‐curves recorded across the (0002) and (101‾5) reflections was as narrow as 62 and 587 arcsec, respectively. We show that the high growth temperature in conjunction with Ga adlayers on the growth front provides a path for achieving step‐flow growth of GaN by MBE.
Previous studies support a role of oxygen-free radicals in the development of congestive heart failure (CHF).
The aim of this study was to investigate whether lipid peroxidation is increased in CHF ...patients on modern pharmacological therapy and whether there is a positive correlation between plasma levels of markers of lipid peroxidation and severity of heart failure (HF). Plasma malondialdehyde (MDA) and isoprostanes are often used as markers of lipid peroxidation and oxidative stress.
We also studied whether long-term treatment with isosorbide-5-mononitrate (IS-5-MN) in combination with standard HF therapy affects P-MDA levels in patients with evidence of left ventricular (LV) dysfunction following acute myocardial infarction (AMI).
Ninety-two patients with clinical or echocardiographic evidence of LV-dysfunction following AMI were randomized to treatment with either IS-5-MN or placebo. In a subgroup of 83 patients with available plasma MDA, echocardiography, right-heart catherization, and plasma natriuretic peptides were evaluated. Control subjects were 80 healthy blood donors. A second study group consisted of 56 patients with CHF, evaluated with respect to LV function, brain natriuretic peptide and markers of oxidative stress (P-MDA and
8-isoprostane). The second control group comprised 50 healthy subjects.
Lipid peroxidation measured by P-MDA and 8-isoprostane was not increased in patients with LV dysfunction treated with standard HF therapy. No positive correlation was found to the severity of HF. Long-term IS-5-MN therapy did not influence P-MDA concentrations.
Although results from many experimental and clinical studies suggest that oxidative stress is increased in HF, this may not be true for patients treated with beta blockers and inhibitors of the renin–angiotensin system.
BACKGROUND:Several neurohumoral mechanisms involved in cardiovascular regulation are activated in the failing heart, but only limited information is available regarding the influence of long-term ...nitrate therapy.
MATERIALS AND METHODS:This was a double-blind, randomized comparison of isosorbide-5-mononitrate (IS-5-MN), 60 mg given orally, once daily for 11 months to patients (n = 47) with left ventricular (LV) dysfunction following acute myocardial infarction (AMI). Forty-five patients received placebo. All patients received ramipril.Plasma natriuretic peptides (atrial ANP and brain BNP natriuretic peptide), epinephrine, norepinephrine (NEPI), antidiuretic hormone, aldosterone (Aldo), renin activity (PRA), substance P, neuropeptide Y-like immunoreactivity, calcitonin gene-related peptide, and vasoactive intestinal peptide were measured at baseline and at the end of the treatment period. Clinical, echocardiographic, and hemodynamic data were also obtained.
RESULTS AND CONCLUSIONS:Chronic nitrate therapy does not significantly affect the neurohumoral status in patients with LV dysfunction after AMI, apart from a decrease in ANP. Some hormones are more closely associated with diastolic dysfunction/increased volume load (ANP and BNP) and others are more closely associated with systolic dysfunction (PRA, NEPI, Aldo). There is a temporal dissociation of these 2 groups of hormones 1 year post infarctionANP and BNP decrease, whereas NEPI and Aldo show a slight increase. BNP levels do not reflect all important pathophysiologic mechanisms in heart failure. Consequently, the use of other neurohormonal factors than BNP for monitoring of heart failure therapy should be explored.
Background Nitrates are often administrated with a variety of other pharmacologic agents in the management of chronic heart failure (CHF). However, limited information is available concerning the ...long-term effects in patients with evidence of left ventricular (LV) dysfunction after acute myocardial infarction (AMI) already treated with standard heart failure therapy.
Methods In a randomized, double-blind, placebo-controlled trial, we evaluated the effects of a 60 mg dose of isosorbide-5-mononitrate (IS-5-MN) given daily for 11 months to 47 patients with clinical or echocardiographic evidence of left ventricular dysfunction after acute myocardial infarction. Forty-five patients received a placebo.
Results Invasive hemodynamic measurements did not show any difference between the treatment regimens. Overall changes in echocardiographic measurements were not significantly different between IS-5-MN therapy and the placebo groups. However, in a prespecified subgroup with left ventricular ejection fraction ≤40% at baseline, IS-5-MN therapy resulted in a lesser increase of end-diastolic volume index than the placebo (
P = .047). IS-5-MN significantly reduced the serum concentration of atrial natriuretic peptide (mean 20.0 pmol/L, 95% CI 7.7-32.3,
P = .002), whereas the placebo did not (
P = .041 for the difference between the groups). The proportion of patients taking diuretics was significantly reduced in the IS-5-MN group, from 30 of 44 to 20 of 44 (
P = .02), but not with placebo, which remained at 27 of 43 (
P = 1.0, with
P = .048 for the difference between the regimens).
Conclusions Oral, long-term IS-5-MN therapy resulted in lower atrial natriuretic peptide levels and reduced the need for additional diuretics. Less LV dilatation was observed in patients with more severe LV dysfunction at baseline. (Am Heart J 2003;145:e1.)
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