Ultrasmall superparamagnetic particles of iron oxide (USPIO) MR imaging of infarcted myocardium in pigs

The purpose of this study is to assess the potential value of ultrasmall superparamagnetic iron oxide (USPIO) for the detection of acute myocardial infarction by magnetic resonance (MR) imaging. Spin-echo magnetic resonance imaging of the heart was performed before, immediately after, and approximately 35 and 90 min after 30 μmol Fe/kg of USPIO administration in seven pigs with surgically induced myocardial infarction. Gradient-echo sequences were used to identify contraction abnormalities at the site of infarction. Myocardial signal intensities were measured using region-of-interest analysis in normal and infarcted myocardium. In addition, liver and lung signal intensities were measured. Pathologic correlation was performed after sacrificing the animals. The infarct area was located with wall-motion analysis. The site of infarction was confirmed at pathologic examination. The signal-intensity ratio between infarcted and normal myocardium was not significantly changed after USPIO administration at equilibrium stages (immediately after injection p = 0.64, at 35 min p = 0.32, at 90 min p = 0.73). The signal intensity of the liver decreased significantly after contrast administration (p < 0.05). For the lung, the change in signal intensity after USPIO administration was not significant. This pig model is well suited to study wall motion abnormalities after induction of acute myocardial infarction. USPIO-enhanced magnetic resonance imaging does not improve the visualization of acute myocardial infarction at equilibrium stage.     

USPIO-Enhanced MR imaging of glycerol-induced acute renal failure in the rabbit

Enhanced-MR imaging in combination with ultrasmall superparamagnetic iron oxide (USPIO) was used in the glycerol-induced model of acute renal failure (ARF) in the rabbit to detect renal perfusion abnormalities. A control group (n = 5) and an ARF group (n = 5) were studied after intramuscular injection of glycerol (10 ml/kg) with T₂-weighted spin-echo sequence at 1.5 T and a 27 μmol/kg IV dose of iron. The signal intensity (SI) was quantified in the cortex, the outer medulla (OM), and the inner medulla (IM). In control rabbits, the maximum SI decrease after USPIO injection was in the OM (76% ± 3.6), as this is the region of maximal vascular density, then in the IM (73.4% ± 2.9). In the glycerol group, SI loss in the OM (61% ± 12.6) and the IM (45.2% ± 16.24) was significant less than in the control group (p < .05). Pathology results showed fibrinous thrombus in the efferent arterioles and congestive aspect of the vasa recta in the medulla. We argue that a reduced medullary concentration of USPIO in the renal failure group is indicative of medullary hypoperfusion.     

Magnetic resonance imaging dynamic contrast enhancement (DCE) characteristics of healed myocardial infarction differ from viable myocardium

Purpose

To determine whether healed myocardial infarction alters dynamic contrast-enhancement (DCE) curve shapes as well as late gadolinium-enhancement (LGE).

Materials and methods

Twenty patients with chronic myocardial infarction underwent MR imaging at 1.5 T with blood and myocardial T1 measurements before and after contrast administration for forty minutes. Viable and infarcted myocardial partition coefficients were calculated using multipoint slope methods for ten different DCE sampling intervals and windows. Partition coefficients and coefficients of determination were compared with paired statistical tests to assess the linearity of DCE curve shapes over the 40 min time period.

Results

Calculated partition coefficients did not vary significantly between methods (p = 0.325) for viable myocardium but did differ for infarcted myocardium (p < 0.001), indicating a difference in infarcted DCE. There was a significant difference between viable and infarcted myocardial partition coefficients estimates for all methods with the exception of methods that included measurements during the first 10 min after contrast agent administration.

Conclusion

Myocardial partition coefficients calculated from a slope calculation vary in healed myocardial infarction based on the selection of samples due to non-linear DCE curve shapes. Partition coefficient calculations are insensitive to data sampling effects in viable myocardium due to linear DCE curve shapes.     

Diffusion- and T2-weighted MRI of closed-head injury in rats: A time course study and correlation with histology

Diffusion- and T₂-weighted MRI were used to evaluate changes in brain water characteristics following closed-head injury in rats. Images were collected within the first 2 h and at 24 h and 7 days following the traumatic event and then compared with histology. The ratios between the apparent diffusion coefficients (ADCs) of the traumatized tissues and normal brain tissues were significantly different from unity and were found to be 0.79 ± 0.25 (p < 0.01), 0.49 ± 0.33 (p < 0.0002), and 3.47 ± 1.36 (p < 10⁻⁶) at 1–2 h, 24 h, and 1 week after the trauma, respectively. In severe trauma, areas of hyperintensity which were not apparent on the T₂-weighted images could be detected on the diffusion-weighted images within 1–2 h after the trauma. At 24 h following the traumatic event, large areas of hyperintensity are observed in both types of images. One week following the trauma, the ADCs of the traumatized tissues (1.84 ± 0.69 × 10⁻⁵ cm²/s) are much larger than those of normal brain (0.57 ± 0.19 × 10⁻⁵ cm²/s) and approach the value of free water. At 7 days, the areas of hyperintensity in the T₂-weighted images seem to underestimate the injured areas found by histology. At this time point a good correlation is obtained between the areas of hypointensity observed on the diffusion-weighted images and the infarct areas obtained by histology (r = 0.88).     

Imaging Perfusion Deficits in Ischemic Heart Disease with Susceptibility-Enhanced T2-Weighted MRI: Preliminary Human Studies

Aim: This feasibility study explores relative myocardial perfusion characterization with an investigational T₂/T₂1 contrast agent. Methods: Dysprosium-DTPA bis (methylamide) was administered peripherally in six patients with thallium defects. Rest and stress multi-section, gated, T₂-weighted images were acquired with a 1.5 T echo-planar imager. Change in transverse relaxation rate was calculated in four segments for each subject. Results: Magnetic resonance (MR) identified five of five instances of ischemia or infarction, at a dose of agent (0.25 mmol/kg) that was comparable to that currently used with clinically approved gadolinium agents. Injection at twice this dose resulted in saturation of the signal change, and the one ischemic segment corresponding to the higher dose was not identified by MR. MR was negative in two segments which, on final diagnosis, were determined to manifest thallium attenuation artifact. Conclusion: MR perfusion imaging with high susceptibility agents has the potential to characterize myocardial perfusion deficits.     

Simultaneous measurements of diffusion and transverse relaxation in exercising skeletal muscle

The aim of this study was to compare proton T₂ and apparent diffusion coefficient (ADC) variations induced by exercise in skeletal muscle, to provide some more information on the source of their variations. T₂ and ADC were measured in the forearm flexor digitorum muscles in 12 healthy volunteers at rest and after an exercise, using a sequence allowing simultaneous measurements of both parameters. At rest, T₂ was 30.6 ± 1.8 ms (mean ± 1 SD) and ADC was 1.82 ± 0.11 × 10⁻⁹ m²/s. With exercise, T₂ varied by +28 ± 12% (p < .001 vs. rest) and ADC varied by +12 ± 3% (p < .001). The recovery of T₂ after exercise was faster than that of ADC, with half-times of 7 ± 2 min and of 15 ± 8 min (p < .01), respectively. It is concluded that both T₂ and ADC increase with exercise. However, the mechanisms of variation of T₂ and ADC with exercise are probably different, T₂ mostly reflecting changes in water content and ADC reflecting temperature variations.     

Influence of the hepatobiliary contrast agent mangafodipir trisodium (Mn-DPDP) on the imaging properties of abdominal organs

To assess the influence of Mangafodipir Trisodium on the imaging properties of abdominal organs when using T₁-weighted gradient-echo (GE) and T₂-weighted turbo spin-echo (TSE) sequences, thirty patients with focal lesions in the liver were examined at a field strength of 1.5 T before and after intravenous administration of Mangafodipir Trisodium (dose: 5 μmol/kg of body weight).Administration of Mangafodipir Trisodium led to a significant increase in the signal intensity of the liver tissue (p < 0.001), the spleen (p < 0.01), the pancreas (p < 0.001), and the kidneys (p < 0.001) in the T₁-weighted GE sequence, while there was no relevant enhancement in fatty tissue and the musculature. In the T₂-weighted turbo spin-echo sequence, there was no relevant change in the signal following administration of a contrast agent. The contrast-to-noise ratio (C/N) between the lesions and the liver tissue increased significantly in the post-contrast T₁-weighted GE sequence (p < 0.001), while there was no change in the contrast-to-noise ratio in the post-contrast T₂-weighted turbo spin-echo sequence. The contrast-to-noise ratio of the plain T₂-weighted TSE sequence was significantly higher than that in the post-contrast T₁-weighted GE sequence (p < 0.001). Although Mangafodipir Trisodium was primarily developed as a hepatobiliary contrast agent for demonstration and differentiation of liver lesions, it also affects the signal levels in the pancreas, spleen, and kidneys in the T₁-weighted image. Awareness of this effect on the extrahepatic tissue makes it easier to interpret pathological findings in magnetic resonance imaging (MRI) of the abdomen.     

MR imaging of non-cancerous hepatic lesions in Long-Evans Cinnamon rats

We measured MR images of the liver of Long-Evans Cinnamon (LEC) rats with pathologic correlation and assessed the effectiveness of MR imaging (MRI) for diagnosis of noncancerous hepatic lesions. T₁- and T₂-weighted images of their livers were obtained, and the dynamic and delayed studies after intravenous gadolinium injection were also performed. Cholangiofibrosis showed low signal intensity on T₁-weighted images and high signal intensity on T₂-weighted images. The T₂ relaxation time of cholangiofibrosis was significantly prolonged (p < .01), and the signal intensity ratio of this lesion to muscle on T₁-weighted images was significantly lower than that of normal liver parenchyma to muscle (p < .01). The lesion was enhanced immediately after gadolinium injection and the enhancement was prolonged. Among three cases of peliosis hepatis identified, one showed heterogeneous intensities on both T₁- and T₂-weighted images and the other two showed similar intensity pattern to cholangiofibrosis. The characteristic MR appearance of cholangiofibrosis may be useful to distinguish it from hepatocellular carcinoma (HCC).     

On the decay of61Zn and60Zn using mass separated sources

The γ-ray spectrum of⁶¹Zn and⁶⁰Zn was studied with a 75 cm³ Ge(Li) detector using mass separated sources. For the half-lives we foundT _1/2(⁶¹Zn)=89.1 ± 0.2 sec andT _1/2(⁶⁰Zn)=2.33 ±0.05 min, together with the valuesT _1/2(⁶¹Cu)=3.26± 0.05 hr andT _1/2(⁶⁰Cu)=24.0 ± 0.3 min for the half-lives of the daughter activities.     

Search for direct single-photon production at large pT in photon-proton collisions at √s = 62.4 GeV

As part of a study of large p_T phenomena in photon-proton collisions at the CERN ISR, a search for direct single photon production has been performed. A statistical division of the data sample into the fraction consistent with single photon and the fraction due to multiphoton decays of neutral hadrons is accomplished by measuring the average conversion probability for the sample in a one radiation length thick converter. The fraction of the sample attributable to direct single photon production is 〈γ/all〉 = 0.074 ± 0.012 for 6 GeV/c < p_T 10 GeV/c, and 〈γ/all〉 = 0.26 ± 0.04 for p_T > 10 GeV/c, with an additional systematic uncertainty of ±0.05 for both values.     

Functional magnetic resonance imaging of human renal allografts during the post-transplant period: Preliminary observations

Graft dysfunction is a common occurrence during the first weeks following renal transplantation. The current study was designed to evaluate the potential of renal magnetic resonance (MR) perfusion imaging to differentiate acute allograft rejection (AAR) from acute tubular necrosis (ATN) during the post-transplant period. Twenty-three consecutive patients with clinically suspected ATN and/or AAR and eight consecutive control patients (asymptomatic, serum creatinine concentration < 1.5 mg/dL) underwent MR perfusion imaging of the renal allograft within 64 days after transplantation. Histopathology was obtained in all cases with clinical suspicion of ATN or AAR. Sixty sequential fast gradient-recalled-echo MR images were acquired in each patient after intravenous administration of gadolinium-DTPA (0.1 mmol/kg). Histopathology revealed 6 patients with pure AAR, 4 patients with a combination of AAR and ATN, 12 patients with ATN and 1 patient with normal findings. Kidney graft recipients with normal renal function showed a moderate increase in signal intensity (SI) of the renal cortex and medulla after administration of contrast agent followed by an immediate and short decrease in SI of the medulla (biphasic medullary enhancement pattern). The increase in cortical SI of patients with AAR was significantly smaller (61 ± 4% increase above baseline) than that measured in normal allografts (136 ± 9% increase above baseline) (p < 0.05) and patients with ATN (129 ± 3% increase above baseline) (p < .05). Patients with ATN had a slightly delayed and diminished cortical enhancement and an uniphasic and lesser medullary enhancement pattern compared to that observed in normal allografts (p < 0.05). A close correlation (r = 0.72) was found between serum creatinine concentration levels and changes in SI. Thus, MR imaging results and histopathology were in agreement in 22 of 23 patients (96%). MR perfusion imaging of renal allografts can be used to noninvasively differentiate ATN from AAR during the post-transplant period, and may also be helpful in cases where covert AAR is superimposing ATN during a phase of anuria. Patients with ATN can be separated from normals in the majority of cases as reflected by an uniphasic medullary enhancement pattern.     

Region-Specific Susceptibilities to Cuprizone-Induced Demyelination of C57BL/6 Mouse: In vivo T2WI and DTI Studies at 7.0T

The cuprizone (CPZ) mouse model of demyelination was recognized and used to explore multiple sclerosis (MS)-like brain lesions. In this study, we assessed CPZ-treated mice using T₂-weighted imaging and diffusion tensor imaging (DTI). C57BL/6 mice treated with 2 weeks of 0.2 % CPZ-containing diet (n = 10) and regular chow diet (n = 10) were scanned with a 7.0 T MRI scanner (Agilent, USA), respectively, using fast spin-echo and fast spin-echo DTI sequences. The normalized T₂ signal intensity (normalized to the cerebrospinal fluid) was calculated and fractional anisotropy (FA value), mean diffusivity, axial diffusivity and radial diffusivity were measured in the brain region of the cerebral cortex (CTX), caudate putamen (CP), hippocampus (HP) and thalamus (TH). Compared with controls, increased normalized T₂ signal intensities and reduced FA values (p < 0.05) were observed in the CTX, HP and CP (p < 0.01), but not in TH in cuprizone-fed mice. In the regions of reduced FA values, an increase in mean diffusivity (p < 0.05) and radial diffusivity (p < 0.05) was also found. Significant decreased axial diffusivity was only observed in CTX (p < 0.05). DTI is sensitive to detecting cuprizone-induced demyelination of C57BL/6 mice. This study suggests that CTX, HP and CP are more susceptible to cuprizone-induced demyelination than TH. Our results also indicate that the decrease of FA value may be more likely due to increased radial diffusivity.     

The relaxivity of Gd-EOB-DTPA and Gd-DTPA in liver and kidney of the Wistar rat

The NMR relaxivities of Gd-EOB-DTPA and Gd-DTPA were determined in the kidney and liver of intact male Wistar rats immediately following sacrifice and in vitro in solutions and gels, at 1.5 T using a clinical MR scanner. T₁ and T₂ values of tissue samples were derived from spin-echo image sequences. Tissue gadolinium concentrations were determined by radioassay of Gd¹⁵³. Gd-EOB-DTPA T₁ and T₂ relaxivities, R₁ and R₂ (s⁻¹ mmole⁻¹ kg), were found to be 10.7 ± 0.5 and 22.5 ± 3.2, respectively, for liver, 2.4 ± 0.2 and 12.1 ± 1.7 for kidney cortex, 2.7 ± 0.2 and 14.5 ± 1.9 for kidney outer medulla, 2.0 ± 0.2 and 11.4 ± 2.1 for kidney inner medulla. Gd-DTPA R₁ and R₂ were found to be 4.8 ± 0.4 and 14.5 ± 3.7 for liver, 1.2 ± 0.1 and 7.9 ± 0.8 for kidney cortex, 1.6 ± 0.1 and 10.2 ± 1.4 for kidney outer medulla, 1.3 ± 0.1 and 10.2 ± 1.2 for kidney inner medulla. Gd-EOB-DTPA and Gd-DTPA R₁ was increased in liver compared to agarose gels at 38°C (4.49 ± 0.03 and 3.47 ± 0.06), but reduced in kidney tissues. All R₂ were elevated compared to agarose gels at 38°C (5.72 ± 0.12 and 4.12 ± 0.03). Elevated R₂ and R₁ (expressed in terms of the concentration of gadolinium per kg of tissue) can be accounted for in part by the lower water content of tissues compared with gels or solutions, increased microviscosity and binding to macromolecules. In addition, susceptibility effects may give rise to further increases in R₂. By contract, the reduced R₁ observed in kidney may be the result of compartmentalization of the magnetopharmaceuticals. Statistically improved fits were obtained for T₁ recovery curves for liver in the presence of Gd-EOB-DTPA when a dual exponential model was used. Assuming in vitro values for the relaxivities of these artificial contrast agents will lead to inaccuracies when relating observed signal enhancement factors to tissue gadolinium concentration.     

Level structure of170Er observed in the decay of the 2.76 min170Ho

TheΒ ^?-decay of the longer-lived¹⁷⁰Ho isomer produced through the¹⁷⁰Er(n, p)¹⁷⁰Ho reaction has been investigated by using a versastile detector and coincidence equipment. The half-life andΒ ^?-decay energy were determined to beT _1/2=2.76±0.05 min andQ _β =3.85±0.15 MeV, respectively. In addition to the ground state band and some higher energy levels, the proposed level scheme of¹⁷⁰Er contains 11 states between 1.0 and 1.6 MeV (6 new ones), which are connected mutually by previously unknown low-energy transitions. Spin and/or parity assignments based mainly on coincidence data and multipolarity determinations are suggested for most of these states. By using systematic considerations and the nuclear projection model calculations several bands withK≧2 can be assigned tentatively. As a side result the half-life of¹⁶⁹Ho was determined to be 4.7 ±0.2 min.     

Oxygen-induced MR signal changes in murine tumors

Breathing of 100% oxygen was used to challenge vascular autoregulation in 14 mice with either osteosarcomas (n = 6) or mammary carcinomas (n = 8). Reproducible and statistically significant signal intensity changes of –29 ± 6% to +35 ± 3% were observed on heavily T₂1-weighted images in the tumors during the oxygen challenge. No significant changes were observed in muscle. For the mammary carcinomas a higher percentage of tumor voxels showed significant signal-intensity decrease (31 ± 8%) compared to the percentage of voxels showing a signal-intensity increase (22 ± 3%). In contrast, for the osteosarcomas, a higher percentage of tumor voxels showed signal-intensity increase (52 ± 9%) compared to the percentage of voxels showing signal-intensity decrease (27 ± 9%). The regional distribution of these signal intensity changes did not correlate with the signal pattern on T₁-, T₂-,and T₂1-weighted and Gd-DTPA enhanced images acquired without breathing 100% oxygen. Most likely, the signal intensity changes represented the inability of the tumor’s neovascularization for autoregulation during the oxygen challenge, particularly in hypoxic regions. Although further investigation is needed, the findings that malignant tumor tissue showed signal intensity changes, whereas normal muscle tissue did not, suggests that this technique may prove useful in distinguishing benign from malignant tissue.     

Synthetic T2-weighted images of the lumbar spine derived from an accelerated T2 mapping sequence: Comparison to conventional T2w turbo spin echo

ObjectivesTo evaluate the diagnostic usefulness of synthetic T₂-weighted images of the lumbar spine derived from ten-fold undersampled k-space data using GRAPPATINI, a combination of a model-based approach for rapid T₂ and M₀ quantification (MARTINI) extended by generalized autocalibrating partial parallel acquistion (GRAPPA).Materials and methodsOverall, 58 individuals (26 female, mean age 23.3 ± 8.1 years) were examined at 3 Tesla with sagittal and axial T₂w turbo spin echo (TSE) sequences compared to synthetic T₂₋weighted contrasts derived at identical effective echo times and spatial resolutions. Two blinded readers graded disk degeneration and evaluated the lumbar intervertebral disks for present herniation or annular tear. One reader reassessed all studies after four weeks. Weighted kappa statistics were calculated to assess inter-rater and intra-rater agreement. Also, all studies were segmented manually by one reader to compute contrast ratios (CR) and contrast-to-noise ratios (CNR) of the nucleus pulposus and the annulus fibrosus.ResultsOverall, the CR_T2w was 4.45 ± 1.80 and CR_T2synth was 4.71 ± 2.14. Both correlated (rsp = 0.768;p < 0.001) and differed (0.26 ± 1.38;p = 0.002) significantly. The CNR_T2w was 1.73 ± 0.52 and CNR_T2synth was 1.63 ± 0.50. Both correlated (rsp = 0.875;p < 0.001) and differed (−0.10 ± 0.25;p < 0.001) significantly. The inter-rater agreement was substantial to almost perfect (κ = 0.808–0.925) with the intra-rater agreement also substantial to almost perfect (κ = 0.862–0.963). The area under the curve of the receiver operating characteristics assessing disk herniation or annular tear ranged from 0.787 to 0.892.ConclusionsThis study concludes that synthetic images derived by GRAPPATINI can be used for clinical routine assessment with inter-rater and intra-rater agreements comparable to conventional T₂w TSE.     

Investigation of surface self-diffusion of Ni atoms on the Ni(100) plane by means of work function measurements and Monte Carlo calculations

A novel method is presented to study migration of adsorbed metal atoms on a clean (hkl) surface of a metal substrate. The system used was Ni on Ni(100). We make use of the assumption that each single step of random walk motion of an individual adatom on the metal substrate refers to an activation energy ΔE_if (indices i and f giving the number of occupied nearest neighbour sites in the initial and final position respectively). Furthermore, we assume that the dipole moment p_v of an adatom is determined by the number v of occupied nearest neighbour sites. Via their dipole moments the adsorbed atoms induce a change of work function ΔΦ of the substrate metal, ΔΦ being related to the average dipole moment per unit area by the Helmholtz equation. To measure ΔΦ we use a pendulum device. At fixed low coverage θ the variation of ΔΦ with temperature T has been calculated numerically within the framework of a Monte Carlo simulation (MCS) model, using various activation energies ΔE_if and dipole moments p_v as input parameters. By fitting these data to the experimental curves we could derive the following dipole moments and activation energies: p₀ = 0.45 ± 0.05 D, p₁ = 0.36 ± 0.05 D, p₂ = 0.27 ± 0.05 D, p₃ = 0.18 ± 0.05 D, ΔE₀₀ 0.60 ± 0.02 eV, ΔE₁₀ = 0.70 ± 0.025 eV, ΔE₂₁ = 0.80 ± 0.05 eV, ΔE₂₀ = 0.90 ± 0.05 eV. We compare these results with those of other workers.     

Thermophysical study of structural phase transitions in Na<Subscript>0.95</Subscript>Li<Subscript>0.05</Subscript>NbO<Subscript>3</Subscript> solid solution

Temperature dependences of specific heat C_p(T) and coefficient of thermal expansion ;(T) for Na_0.95Li_0.05NbO₃ sodium-lithium niobate ceramic samples are investigated in the temperature range of 100–800 K. The C_p(T) and α(T) anomalies at T₃ = 310 ± 3 K, T₂ = 630 ± 8 K, and T₁ = 710 ± 10 K are observed, which correspond to the sequence of phase transitions N ? Q ? S(R) ? T2(S). The effect of heat treatment of the samples on the sequence of structural distortions was established. It is demonstrated that annealing of the samples at 603 K leads to splitting of the anomaly corresponding to the phase transition Q → R/S in two anomalies. After sample heating to 800 K, the only anomaly is observed in both the C_p(T) and ;(T) dependence. Possible mechanisms of the observed phenomena are discussed.     

Decay studies of131Ba

Bombarding a⁸⁵Rb target by 27 MeVα-particles the following half-lives of excited states in different nuclei have been determined by means of the generalized controid shift method: in⁸⁷Y,T _1/2(2827.1 keV)=0.75±0.10 ns,T _1/2(2675.9 keV)=0.25±0.10 ns,T _1/2(3595.3 keV)=0.5±0.2 ns andT _1/2(2986.9, 3094.4 keV)<0.1 ns; in⁸⁸Y,T _1/2(232.1 keV)=0.8±0.1 ns and in⁸⁵Rb,T _1/2(151.2 keV)=0.6±0.1 ns. In⁸⁷Y, the members of the doublet (vg ₉ ^2/?2 )₈₊ (πp_1/2) are identified. E2 transition rates 21/2⁺? 17/2⁺ in odd A≈ 90 nuclei are shown to represent essentially core transitions. Evidence for the existence of seniority-five configurations is found.     

Decay of the first excited state at 13.3 keV in73Ge

Singles and coincidence measurements of the 13.3 keV transition of⁷³Ge are reported. The total andK conversion coefficients of this gamma-ray and the half-life of this level have been determined. The results are: α _T =1095±55; α _K =312±30;T _1/2=2.98±0.05 μs.