Enhancement Of Peak Intensity Research Articles

Renal cortical perfusion in rabbits: visualization with color amplitude imaging and an experimental microbubble-based US contrast agent.

To evaluate an experimental microbubble-based ultrasound (US) contrast agent (Imagent US, formulation AF0150) in the kidney to help identify focal perfusion abnormalities. Six incremental doses (0.007-0.2 mL/kg) of contrast material were injected intravenously in six New Zealand rabbits (3.1-3.5 kg), with experimental focal renal ischemia in five kidneys. Unenhanced and contrast material-enhanced color amplitude and gray-scale images of the kidney were analyzed for changes in mean pixel intensity. Kidneys were harvested and examined pathologically. On contrast-enhanced color amplitude images, mean pixel intensity increased significantly in cortex and medulla at every dose level (P < .0005) (with doses as low as 0.007 mL/kg), and differences were significant in cortical peak intensity and duration of enhancement with incremental increases in dose (P < .006). On contrast-enhanced gray-scale images, renal cortical enhancement reached statistical significance only at the highest dose (0.2 mL/kg). Duration of gray-scale tissue enhancement was not dose related. Color mean pixel intensity markedly increased in areas of normally perfused kidney (P = .002) but remained essentially unchanged in ischemic areas (P = .34). Color Doppler and gray-scale images enhanced with this microbubble-based US contrast agent depict renal cortical perfusion clearly in rabbits.

Optical and structural properties of spontaneously formed long-range compositional modulation in (111)A and (111)B AlGaAs

We have studied the spontaneously formed long-range Al-rich and Ga-rich AlxGa1−xAs/AlyGa1−yAs superlattices in both (111)A and (111)B AlGaAs during epitaxial growth. The spontaneously formed compositional modulation has been investigated by cross-sectional transmission electron microscopy in AlxGa1−xAs (x=0.3–0.4) grown on (111)A and (111)B GaAs substrates at 600–700 °C. In contrast, similar superstructures are not observed in layers simultaneously grown on (100) substrates. The observed structural compositional modulation is closely related to the large peak energy redshift and peak intensity enhancement in 15 K photoluminescence (PL) of samples grown on both (111)A and (111)B orientations to those on (100). The respective redshifts of PL peak energy for (111)A and (111)B Al0.27Ga0.73As to that of (100) are 137 and 45 meV, while the PL integrated intensity enhancement to (100) amounts to 200 and 2000 times, respectively. The effect of compositional modulation is reduced with the increasing growth temperatures as shown in the considerably less compositionally modulated (111)A and (111)B Al0.40Ga0.60As grown at 700 °C.

Lasing behavior in a liquid spherical dye laser containing highly scattering nanoparticles

With the addition of scattering nanoparticles to dye-doped spherical droplets, lasing has been observed with well-defined thresholds in input-output data. One-order or more magnitude enhancement of peak intensity from droplet emission has been obtained with certain (optimum) additive scattering particles compared with nonadditive scattering particles (neat dye-doped droplets). Characteristics of input-output intensities, emission spectra (with wavelength shifts), and spectral linewidths are reported experimentally, depending on additive quantities of scattering nanoparticles.

Spontaneously formed long-range Al-rich and Ga-rich AlxGa1−xAs/AlyGa1−yAs superlattice and optical properties enhancement in (111)A AlGaAs

Spontaneously formed long-range Al-rich and Ga-rich AlxGa1−xAs/AlyGa1−yAs superlattice in (111)A was demonstrated. This was observed by cross-sectional transmission electron microscopy (TEM) in 0.75 μm Al0.30Ga0.70As grown on (111)A GaAs substrates at 640 °C. In contrast, none of the above superstructure was observed by TEM on a side-by-side grown (100) oriented substrate. 15 K photoluminescence (PL) showed a 31 meV redshift and six times peak intensity enhancement in layers grown on (111)A substrates to that on (100). A reduced long-range compositional modulation can be achieved by growth at higher temperatures and is shown in the finer and moderately modulating (111)A Al0.40Ga0.60As grown at 700 °C. A 15 K PL linewidth of 17 meV was achieved in 700 °C grown (111)A A0.40Ga0.60As that is the narrowest reported linewidth for (111)A AlGaAs.

Peak Intensity Enhancement and Pulse Compression of a Picosecond Laser Pulse by Frequency Doubling with a Predelay

Theoretical investigation of frequency doubling of a short-duration, high-intensity laser pulse in a potassium dihydrogen phosphate (KDP) crystal is given. The coupled nonlinear equations for the parametric process, including the third-order nonlinear susceptibility, have been solved. By applying a time delay between the extraordinary and ordinary waves for the fundamental pulse in type-II phase matching, the group velocity mismatch and the nonlinear phase shift can be made to compensate each other, resulting in peak intensity enhancement and pulse width compression. The optimum conditions for the incident intensity, the crystal thickness and the predelay time have been derived. It is shown that intensity conversion efficiency of 440% accompanied by pulse width reduction from 1 ps fundamental pulse to 100 fs second-harmonic pulse is achieved for incident intensity of 50 GW/cm2.

Evaluation of regional myocardial perfusion in areas of old myocardial infarction after revascularization by means of intraoperative myocardial contrast echocardiography

Because myocardial revascularization to areas of old myocardial infarction brings about functional recovery to some extent to myocytes in those areas, the assessment of regional myocardial perfusion on those areas after myocardial revascularization may allow myocardial viability to be estimated. Using intraoperative myocardial contrast echocardiography by direct injection of 2 ml sonicated 5% human albumin into saphenous vein grafts, we assessed regional myocardial perfusion in 16 revascularized areas of old myocardial infarction. We estimated the myocardial viability of areas with respect to myocardial perfusion, and we compared these results to both the improvement of regional wall motion after myocardial revascularization (increase in segmental wall thickening during systole) and relative thallium 201 activity obtained by quantitative analysis of preoperative exercise myocardial thallium 201 distribution on delayed images. The background-subtracted peak peak intensity of myocardial enhancement and the ratio of endocardial to epicardial intensity were determined in each revascularized area. An inverse correlation existed between peak intensity (18 +/- 7) and the endocardial/epicardial ratio (0.88 +/- 0.17) (r = -0.63, p < 0.01). A good correlation was found between peak intensity and both the percent increase in segmental wall thickening (r = 0.73, p < 0.005) and the relative thallium 201 activity (r = 0.81, p < 0.005). These results suggested that regional myocardial perfusion after myocardial revascularization in areas of old myocardial infarction distributed better to the epicardial halves than to the endocardial halves, and that the peak intensity could be related to myocardial viability.

Spontaneous formation of Al rich and Ga rich AlxGa1−xAs/AlyGa1−yAs superlattice and strong enhancement of optical properties

Long range composition ordering and spontaneous formation of Al rich and Ga rich AlxGa1−xAs/AlyGa1−yAs superlattice were demonstrated. This was observed by cross-sectional transmission electron microscopy (TEM) in a 280 Å Al0.4GaAs quantum well laser diode heterostructure with Al0.7GaAs barriers grown on (111)B GaAs substrates. On the contrary, none of above superstructure was observed by TEM on a side-by-side grown (100) oriented substrate. More evidence is shown in the (111)B Al0.7GaAs barriers which were disordered due to a high growth temperature and did not show any superstructure. 10 K photoluminescence was shown with 32 meV redshift and a 12-times peak intensity enhancement in (111)B orientation.

Does Cardiac Function Modify Left Heart Opacification with Transpulmonary Echo Contrast Agents?

Dependence of left heart opacification on ventricular function was evaluated for the new transpulmonary echo enhancing agent (SH U 508-A). The contrast agent was injected intravenously in 5 patients with normal cardiac function (ejection fraction [EF] greater than 60% and echocardiographic left ventricular end-diastolic diameter [LVED] less than 56 mm) and in five patients with pathological ventricular function (EF less than 40%, LVED greater than 65 mm). A concentration of 400 mg/mL with dosages of 5, 9, and 16 mL was used in all patients. The visually assessed signal enhancement as well as the videodensitometrically determined peak intensity and duration of signal enhancement did not differ significantly between the two patient groups, while the transit times were markedly prolonged in patients with impaired ventricular function. No significant alteration was found for systemic blood pressure and heart rate. Side effects were transitory and dose related. The noninvasive nature of the procedure and the absence of hemodynamic effects make repeated studies of left ventricular performance with SH U 508-A in patients with varied hemodynamic status possible.

Assessment of regional and transmural myocardial perfusion by means of intraoperative myocardial contrast echocardiography during coronary artery bypass grafting

By using intraoperative myocardial contrast echocardiography, we assessed regional myocardial perfusion and transmural blood flow distribution immediately after myocardial revascularization. A total of 62 revascularized myocardial areas were studied in 31 patients undergoing coronary artery bypass grafting. The revascularized areas were divided into three different areas: S area, supplied by significantly stenosed coronary arteries (43 areas); C area, supplied by coronary collateral situation associated with totally occluded coronary arteries (12 areas); MI area, preexisting transmural myocardial infarction (7 areas). Myocardial contrast echocardiography was obtained by direct injection of 2 ml of sonicated 5% human albumin into the saphenous vein grafts at rest and during atrial pacing. Each area was divided into two layers of endocardial and epicardial halves, and myocardial enhancement of peak intensity was measured for each half and endocardial/epicardial gray level ratio was calculated: (1) The peak intensity of myocardial enhancement in S area and C area was significantly higher than that in MI area at rest as well as during pacing after myocardial revascularization. There was no significant difference in the peak intensity between S area and C area both at rest and during pacing. In S area the peak intensity significantly increased during pacing (p < 0.01), whereas it did not change in C area and MI area. (2) S area demonstrated no significant change in endocardial/epicardial intensity ratio during pacing. In contrast, the ratio in C area significantly decreased during pacing. (3) In S area with preoperative percent increase of segmental wall thickening lower than 25%, there was a significant correlation (r = 0.84, p < 0.001) between the peak intensity of myocardial enhancement and the postoperative changes of percent increase of segmental wall thickening in the revascularized areas. Thus, immediately after myocardial revascularization, intraoperative myocardial contrast echocardiography could provide a quantitative assessment of regional myocardial perfusion as well as blood flow distribution in the areas with myocardial infarction and with coronary collateral situation and in the areas supplied by stenosed coronary arteries.

Sensitivity enhancement in whole‐body natural abundance 13C spectroscopy using 13C/1H double‐resonance techniques at 4 tesla

In vivo 13C spectroscopy experiments were performed using a whole-body MR system at a static field of 4 T. The main goal of the investigations was to evaluate the sensitivity increase achievable by means of 13C/1H double-resonance techniques at 4 T. Spectra from subcutaneous fat as well as muscle glycogen from the lower leg were acquired using frequency selective proton decoupling and the polarization transfer method SINEPT. With respect to measurements on subcutaneous fat, polarization transfer turned out to be more efficient than selective decoupling. About a fourfold enhancement in spectral peak intensity for the C = C line doublet of the unsaturated fatty acid chain was obtained. Combining polarization transfer with decoupling yielded a factor of 6 in signal amplitude. In contrast to that, the signal enhancement observed in measurements on the glycogen C-1 resonance was only around twofold. The lower efficiency is explained by fast T2 relaxation of the proton transition. A T2 value of about 3 ms was derived from the experimental data. Acquisition times as low as 3 min were realized for normal level glycogen in human calf muscle, enabling a time resolution adequate for dynamic studies on muscle glycogen depletion. Aspects of RF power absorption in tissue and the generally higher efficiency make polarization transfer methods preferable to selective decoupling in whole-body 13C spectroscopy at 4 T.

Medium power x-ray crystal optics for synchrotron radiation sources

Abstract We describe the performance of a water-cooled channel-cut X-ray monochromator which is able to sink 30 W of thermal power (with no discernable compromise in performance) from a high power synchrotron radiation source. In addition to enhanced peak intensity compared with a simple channel-cut monochromator, the long-term stability of the monochromator is also improved.

Coupled multiline CW HF lasers - Experimental performance

The experimental performance of two coupled arc-driven continuous wave HF chemical lasers employing unstable resonators has been measured. Mode-matched adjoint coupling of 20% was accomplished with a beamsplitter. Multiline interference fringes were obtained when the two laser output beams were overlapped in the near field. The mutual coherence of the two beams was inferred from measurement of the visibility of these fringes. Single-tine fringe visibility was measured as 98% +/—2% for each of the two strongest lines. These data suggest that the two outputs are nearly completely phase locked. This locking was found to be insensitive to perturbations in the lengths of the laser resonators. Mode-beating measurements also suggest complete phase locking, since the coupled system behaves tike a single laser cavity. The coherent combination of the two laser output beams was attempted by minimizing the optical path difference between these beams at an external measuring station. This was achieved by changing the external path length of one beam until maximum multiline visibility (97%) was obtained. Demonstration of the corresponding far-field peak intensity enhancement and reduction in spot size for the combined outputs was also accomplished.

NMR studies of pig gastric microsomal H+,K+-ATPase and phospholipid dynamics. Effects of ethanol perturbation.

The effects of ethanol on the gastric H+,K+-ATPase activity and the degree of mobility of various microsomal phospholipids were assessed using 31P and 1H NMR. This illuminated the role of lipid-protein association in the function of pig gastric microsomes. Treatment of gastric microsomes with 15% ethanol for 1 min at 37 degrees C inactivated the H+,K+-ATPase activity, which could largely be reconstituted by supplementation with phosphatidylcholine isolated from the gastric microsomes. Under similar conditions, the 1H NMR profile of the microsomal +N(CH3)3 choline moiety showed dramatic enhancement of peak intensity as well as a break point at 25 degrees C which was restored to the untreated control value after reconstitution. This break, together with the dramatic enhancement in the overall lipid profile, compared to the control and reconstituted microsomes, suggested a greater degree of freedom of movement of the microsomal lipids following ethanol perturbation. The data demonstrate the unique ability that a combined approach using 31P and 1H NMR holds as a noninvasive probe to study the structure-function relationship of biomembranes.

J-scaling in two-dimensional homonuclear correlated spectroscopy for enhancement of cross peak intensities

New pulse schemes have been proposed for enhancement of cross peak intensities in two-dimensional homonuclear correlated spectra. These rely on non-selective scaling up of spin-spin coupling constant values and refocusing of the multiplet components. Experimental spectra illustrating the application of the new pulse schemes are presented.

Structure effects in low energy K + ion scattering from single crystal surfaces

Potassium ions with low energies (250–1000 eV) were scattered from a W(110) surface. The angular and energy distributions of the scattered ions were studied with a 127° electrostatic analyzer. The structure of the energy distribution is strongly influenced by the geometrical arrangement of the surface atoms and reveals the occurrence of many different scattering mechanisms. They are all found to take place in the first and second atomic layers. Single, double and several different zig-zag collision processes give rise to reflection from the top layer. For specific combinations of polar and azimuthal angles a strong enhancement of certain peak intensities is observed. This is attributed to ions scattered in the second layer and focussed by the atomic configuration in the first layer. The experiments are simulated in the binary collision approximation with the computer program MARLOWE. The main features in the experimental energy distributions are successfully reproduced and the corresponding backscattering mechanisms are identified. These simulations confirm the two- and three-dimensional processes suggested by an elementary analysis of the experimental results.