Limitations of stimulated echo acquisition mode (STEAM) techniques in cardiac applications.

Stimulated echoes are widely used for imaging functional tissue parameters such as diffusion coefficient, perfusion, and flow rates. They are potentially interesting for the assessment of various cardiac functions. However, severe limitations of the stimulated echo acquisition mode occur, which are related to the special dynamic properties of the beating heart and flowing blood. To the well-known signal decay due to longitudinal relaxation and through-plane motion between the preparation and the read-out period of the stimulated echoes, additional signal loss is often observed. As the prepared magnetization is fixed with respect to the tissue, this signal loss is caused by the tissue deformation during the cardiac cycle, which leads to a modification of the modulation frequency of the magnetization. These effects are theoretically derived and corroborated by phantom and in vivo experiments.

Stimulated-echo acquisition mode (STEAM) MRI for black-blood delayed hyperenhanced myocardial imaging.

PURPOSE: To develop a breathhold method for black-blood viability imaging of the heart that may facilitate identifying the endocardial border. MATERIALS AND METHODS: Three stimulated-echo acquisition mode (STEAM) images were obtained almost simultaneously during the same acquisition using three different demodulation values. Two of the three images were used to construct a black-blood image of the heart. The third image was a T(1)-weighted viability image that enabled detection of hyperintense infarcted myocardium after contrast agent administration. The three STEAM images were combined into one composite black-blood viability image of the heart. The composite STEAM images were compared to conventional inversion-recovery (IR) delayed hyperenhanced (DHE) images in nine human subjects studied on a 3T MRI scanner. RESULTS: STEAM images showed black-blood characteristics and a significant improvement in the blood-infarct signal-difference to noise ratio (SDNR) when compared to the IR-DHE images (34 +/- 4.1 vs. 10 +/- 2.9, mean +/- standard deviation (SD), P < 0.002). There was sufficient myocardium-infarct SDNR in the STEAM images to accurately delineate infarcted regions. The extracted infarcts demonstrated good agreement with the IR-DHE images. CONCLUSION: The STEAM black-blood property allows for better delineation of the blood-infarct border, which would enhance the fast and accurate measurement of infarct size.

Performance of an ICU ventilator and two turbin-based ventilators dedicated to non invasive ventilation (NIV) in simulated high inspiratory effort and rate: a NIV-bench-study.

INTRODUCTION. The role of turbine-based NIV ventilators (TBV) versus ICU ventilators with NIV mode activated (ICUV) to deliver NIV in case of severe respiratory failure remains debated. OBJECTIVES. To compare the response time and pressurization capacity of TBV and ICUV during simulated NIV with normal and increased respiratory demand, in condition of normal and obstructive respiratory mechanics. METHODS. In a two-chamber lung model, a ventilator simulated normal (P0.1 = 2 mbar, respiratory rate RR = 15/min) or increased (P0.1 = 6 mbar, RR = 25/min) respiratory demand. NIV was simulated by connecting the lung model (compliance 100 ml/mbar; resistance 5 or 20 l/mbar) to a dummy head equipped with a naso-buccal mask. Connections allowed intentional leaks (29 ± 5 % of insufflated volume). Ventilators to test: Servo-i (Maquet), V60 and Vision (Philips Respironics) were connected via a standard circuit to the mask. Applied pressure support levels (PSL) were 7 mbar for normal and 14 mbar for increased demand. Airway pressure and flow were measured in the ventilator circuit and in the simulated airway. Ventilator performance was assessed by determining trigger delay (Td, ms), pressure time product at 300 ms (PTP300, mbar s) and inspiratory tidal volume (VT, ml) and compared by three-way ANOVA for the effect of inspiratory effort, resistance and the ventilator. Differences between ventilators for each condition were tested by oneway ANOVA and contrast (JMP 8.0.1, p\0.05). RESULTS. Inspiratory demand and resistance had a significant effect throughout all comparisons. Ventilator data figure in Table 1 (normal demand) and 2 (increased demand): (a) different from Servo-i, (b) different from V60.CONCLUSION. In this NIV bench study, with leaks, trigger delay was shorter for TBV with normal respiratory demand. By contrast, it was shorter for ICUV when respiratory demand was high. ICUV afforded better pressurization (PTP 300) with increased demand and PSL, particularly with increased resistance. TBV provided a higher inspiratory VT (i.e., downstream from the leaks) with normal demand, and a significantly (although minimally) lower VT with increased demand and PSL.

Characterization of olive oil by carbon isotope analysis of individual fatty acids: Implications for authentication

The fatty acids of olive oils of distinct quality grade from the most important European Union (EU) producer countries were chemically and isotopically characterized. The analytical approach utilized combined capillary column gas chromatography-mass spectrometry (GC/MS) and the novel technique of compound-specific isotope analysis (CSIA) through gas chromatography coupled to a stable isotope ratio mass spectrometer (IRMS) via a combustion (C) interface (GC/C/IRMS). This approach provides further insights into the control of the purity and geographical origin of oils sold as cold-pressed extra virgin olive oil with certified origin appellation. The results indicate that substantial enrichment in heavy carbon isotope (C-13) of the bulk oil and of individual fatty acids are related to (1) a thermally induced degradation due to deodorization or steam washing of the olive oils and (2) the potential blend with refined olive oil or other vegetable oils. The interpretation of the data is based on principal component analysis of the fatty acids concentrations and isotopic data (delta(13)C(oil), delta(13)C(16:0), delta(13)C(18:1)) and on the delta(13)C(16:0) vs delta(13)C(18:1) covariations. The differences in the delta(13)C values of palmitic and oleic acids are discussed in terms of biosynthesis of these acids in the plant tissue and admixture of distinct oils.

Clinical studies with a vascular vasopressin antagonist.

The effect of circulating arginine vasopressin (AVP) on blood pressure, heart rate, and skin blood flow was assessed in normotensive subjects, mild hypertensive patients, and patients with congestive heart failure, utilizing the specific antagonist of AVP at the vascular receptor level, d(CH2)5Tyr(Me)AVP (5 micrograms/kg i.v.). The renin system of the normal volunteers treated with the AVP antagonist was either intact or acutely blocked with the angiotensin converting-enzyme inhibitor captopril (25 mg p.o.). In some volunteers, the cardiovascular effect of AVP released by Finnish sauna or cigarette smoking was studied. In patients with congestive heart failure, hemodynamic measurements (pressures and cardiac output) were obtained invasively. Acute blockade of AVP vascular receptors produced no cardiovascular effect unless plasma AVP levels were markedly elevated. In our experience, abnormally high circulating AVP appears to be responsible for the decrease in skin blood flow induced by cigarette smoking and to some extent for the maintenance of vascular tone in the rare patients with particularly severe congestive heart failure.

Combined functional and viability cardiac MR imaging in a single breathhold

The combination of cardiac viability and functional information enhances the identification of different heart tissues in the setting of ischemic heart disease. A method has recently been proposed for obtaining black-blood delayed-enhancement (DE) viability images using the stimulated-echo acquisition mode (STEAM) MRI pulse sequence in a single short breathhold. The method was validated against conventional inversion-recovery (IR) DE images for identifying regions of myocardial infarction (MI). The method was based on the acquisition of three consecutive images of the same anatomical slice. One image has T(1)-weighted contrast in which infarction appears bright. The two other images are used to construct an anatomical image of the heart, which is combined with the first image to produce a black-blood viability image. However, using appropriate modulation and demodulation frequencies, the latter two images bear useful information about myocardial deformation that results in a cardiac strain-encoding (SENC) functional image. In this work, a method is proposed for obtaining three consecutive SENC images in a single acquisition that can be combined to produce a composite image of the heart, which shows both functional and viability information. The proposed technique reduces scan time by one-half, compared with separate acquisitions of functional and viability images, and alleviates misregistration problems caused by separate breathholds.

Correction of through-plane deformation artifacts in stimulated echo acquisition mode cardiac imaging.

Attempts to use a stimulated echo acquisition mode (STEAM) in cardiac imaging are impeded by imaging artifacts that result in signal attenuation and nulling of the cardiac tissue. In this work, we present a method to reduce this artifact by acquiring two sets of stimulated echo images with two different demodulations. The resulting two images are combined to recover the signal loss and weighted to compensate for possible deformation-dependent intensity variation. Numerical simulations were used to validate the theory. Also, the proposed correction method was applied to in vivo imaging of normal volunteers (n = 6) and animal models with induced infarction (n = 3). The results show the ability of the method to recover the lost myocardial signal and generate artifact-free black-blood cardiac images.

Feasibility of non-invasive pressure support ventilation in infants with respiratory failure after extubation: a pilot study.

OBJECTIVE: To evaluate the feasibility and effects of non-invasive pressure support ventilation (NIV) on the breathing pattern in infants developing respiratory failure after extubation. DESIGN: Prospective pilot clinical study; each patient served as their own control. SETTING: A nine-bed paediatric intensive care unit of a tertiary university hospital. PATIENTS: Six patients (median age 5 months, range 0.5-7 months; median weight 4.2 kg, range 3.8-5.1 kg) who developed respiratory failure after extubation. INTERVENTIONS: After a period of spontaneous breathing (SB), children who developed respiratory failure were treated with NIV. MEASUREMENTS AND RESULTS: Measurements included clinical dyspnoea score (DS), blood gases and oesophageal pressure recordings, which were analysed for respiratory rate (RR), oesophageal inspiratory pressure swing (dPes) and oesophageal pressure-time product (PTPes). All data were collected during both periods (SB and NIV). When comparing NIV with SB, DS was reduced by 44% (P < 0.001), RR by 32% (P < 0.001), dPes by 45% (P < 0.01) and PTPes by 57% (P < 0.001). A non-significant trend for decrease in PaCO(2) was observed. CONCLUSION: In these infants, non-invasive pressure support ventilation with turbine flow generator induced a reduction of breathing frequency, dPes and PTPes, indicating reduced load of the inspiratory muscles. NIV can be used with some benefits in infants with respiratory failure after extubation.

Geochemistry of the thermal springs and fumaroles of Basse-Terre Island, Guadeloupe, Lesser Antilles

The purpose of this work was to study jointly the volcanic-hydrothermal system of the high-risk volcano La Soufriere, in the southern part of Basse-Terre, and the geothermal area of Bouillante, on its western coast, to derive an all-embracing and coherent conceptual geochemical model that provides the necessary basis for adequate volcanic surveillance and further geothermal exploration. The active andesitic dome of La Soufriere has erupted eight times since 1660, most recently in 1976-1977. All these historic eruptions have been phreatic. High-salinity, Na-CI geothermal liquids circulate in the Bouillante geothermal reservoir, at temperatures close to 250 degrees C. These Na-CI solutions rise toward the surface, undergo boiling and mixing with groundwater and/or seawater, and feed most Na-CI thermal springs in the central Bouillante area. The Na-Cl thermal springs are surrounded by Na-HCO3 thermal springs and by the Na-Cl thermal spring of Anse a la Barque (a groundwater slightly mixed with seawater), which are all heated through conductive transfer. The two main fumarolic fields of La Soufriere area discharge vapors formed through boiling of hydrothermal aqueous solutions at temperatures of 190-215 degrees C below the ``Ty'' fault area and close to 260 degrees C below the dome summit. The boiling liquid producing the vapors of the Ty fault area has SD and delta(18)O values relatively similar to those of the Na-CI liquids of the Bouillante geothermal reservoir, whereas the liquid originating the vapors of the summit fumaroles is strongly enriched in O-18, due to input of magmatic fluids from below. This process is also responsible for the paucity of CH;I in the fumaroles. The thermal features around La Soufriere dome include: (a) Ca-SO4 springs, produced through absorption of hydrothermal vapors in shallow groundwaters; (b) conductively heated, Ca-Na-HCO3 springs; and (c) two Ca-Na-Cl springs produced through mixing of shallow Ca-SO4 waters and deep Na-Cl hydrothermal liquids. The geographical distribution of the different thermal features of La Soufriere area indicates the presence of: (a) a central zone dominated by the ascent of steam, which either discharges at the surface in the fumarolic fields or is absorbed in shallow groundwaters; and (b) an outer zone, where the shallow groundwaters are heated through conduction or addition of Na-Cl liquids coming from hydrothermal aquifer(s).

Selective resonance suppression 1H-[13C] NMR spectroscopy with asymmetric adiabatic RF pulses.

Despite obvious improvements in spectral resolution at high magnetic field, the detection of 13C labeling by 1H-[13C] NMR spectroscopy remains hampered by spectral overlap, such as in the spectral region of 1H resonances bound to C3 of glutamate (Glu) and glutamine (Gln), and C6 of N-acetylaspartate (NAA). The aim of this study was to develop, implement, and apply a novel 1H-[13C] NMR spectroscopic editing scheme, dubbed "selective Resonance suppression by Adiabatic Carbon Editing and Decoupling single-voxel STimulated Echo Acquisition Mode" (RACED-STEAM). The sequence is based on the application of two asymmetric narrow-transition-band adiabatic RF inversion pulses at the resonance frequency of the 13C coupled to the protons that need to be suppressed during the mixing time (TM) period, alternating the inversion band downfield and upfield from the 13C resonance on odd and even scans, respectively, thus suppressing the detection of 1H resonances bound to 13C within the transition band of the inversion pulse. The results demonstrate the efficient suppression of 1H resonances bound to C3 of Glu and Gln, and C4 of Glu, which allows the 1H resonances bound to C6 of NAA and C4 of Gln to be revealed. The measured time course of the resolved labeling into NAA C6 with the new scheme was consistent with the slow turnover of NAA.

Haemodynamic role of vasopressin released during Finnish sauna.

The effect of vasopressin released during Finnish sauna on blood pressure, heart rate and skin blood flow was investigated in 12 healthy volunteers. Exposure to the hot air decrease body weight by 0.6 to 1.25 kg (mean = 0.8 kg, P less than 0.001). One hour after the end of the sauna sessions, plasma vasopressin was higher (1.7 +/- 0.2 pg/ml, P less than 0.01 mean +/- SEM) than before the sauna (1.0 +/- 0.1 pg/ml). No simultaneous change in plasma osmolality, plasma renin activity, plasma norepinephrine, epinephrine, cortisol, aldosterone, beta-endorphin and metenkephalin levels was observed. Despite the slight sauna-induced elevation in circulating vasopressin, intravenous injection of the specific vascular vasopressin antagonist d(CH2)5Tyr(Me)AVP (5 micrograms/kg) 1 h after the sauna had no effect on blood pressure, heart rate or skin blood flow. These data suggest that vasopressin released into the circulation during a sauna session reaches concentrations which are not high enough to interfere directly with vascular tone.

Authentication of vegetable oils by bulk and molecular carbon isotope analyses with emphasis on olive oil and pumpkin seed oil

The authenticity of vegetable oils consumed in Slovenia and Croatia was investigated by carbon isotope analysis of the individual fatty acids by the use of gas chromatography-combustion-isotope ratio mass spectrometry (GC/C/IRMS), and through carbon isotope analysis of the bulk oil. The fatty acids from samples of olive, pumpkin, sunflower, maize, rape, soybean, and sesame oils were separated by alkaline hydrolysis and derivatized to methyl esters for chemical characterization by capillary gas chromatography/mass spectrometry (GC/MS) prior to isotopic analysis. Enrichment in heavy carbon isotope (C-13) of th, bulk oil and of the individual fatty acids are related to (1) a thermally induced degradation during processing (deodorization, steam washing, or bleaching), (2) hydrolytic rancidity (lipolysis) and oxidative rancidity of the vegetable oils during storage, and (3) the potential blend with refined oil or other vegetable oils. The impurity or admixture of different oils may be assessed from the delta C-13(16:0) VS. delta C-13(18:1) covariations. The fatty acid compositions of Slovenian and Croatian olive oils are compared with those from the most important Mediterranean producer countries (Spain, Italy, Greece, and France).

Soil diffuse degassing and thermal energy fluxes from the southern Lakki plain, Nisyros (Greece)

Two diffuse soil CO2 flux surveys from the southern Lakki plain show that CO2 is mainly released from the hydrothermal explosion craters. The correspondence between high CO2 fluxes and elevated soil temperatures suggests that a flux of hot hydrothermal fluids ascends towards the surface. Steam mostly condenses near the surface and the heat given off is conductively transferred to the atmosphere through the soil, accompanied by a large CO2 flux. Tt was calculated, that 68 t d(-1) of hydrothermal CO2 are released through the total surveyed area of similar to1.3 km(2) Admitting that a steam flux of 2200 t d(-1) accompanies this CO2 flux, the thermal energy released through steam condensation amounts to 58 MW.