Relation of cardiac troponin I measurements at 24 and 48 hours to magnetic resonance-determined infarct size in patients with ST-elevation myocardial infarction.

Levels of circulating cardiac troponin I (cTnI) or T are correlated to extent of myocardial destruction after an acute myocardial infarction. Few studies analyzing this relation have employed a second-generation cTnI assay or cardiac magnetic resonance (CMR) as the imaging end point. In this post hoc study of the Efficacy of FX06 in the Prevention of Mycoardial Reperfusion Injury (F.I.R.E.) trial, we aimed at determining the correlation between single-point cTnI measurements and CMR-estimated infarct size at 5 to 7 days and 4 months after a first-time ST-elevation myocardial infarction (STEMI) and investigating whether cTnI might provide independent prognostic information regarding infarct size at 4 months even taking into account early infarct size. Two hundred twenty-seven patients with a first-time STEMI were included in F.I.R.E. All patients received primary percutaneous coronary intervention within 6 hours from onset of symptoms. cTnI was measured at 24 and 48 hours after admission. CMR was conducted within 1 week of the index event (5 to 7 days) and at 4 months. Pearson correlations (r) for infarct size and cTnI at 24 hours were r = 0.66 (5 days) and r = 0.63 (4 months) and those for cTnI at 48 hours were r = 0.67 (5 days) and r = 0.65 (4 months). In a multiple regression analysis for predicting infarct size at 4 months (n = 141), cTnI and infarct location retained an independent prognostic role even taking into account early infarct size. In conclusion, a single-point cTnI measurement taken early after a first-time STEMI is a useful marker for infarct size and might also supplement early CMR evaluation in prediction of infarct size at 4 months.

Is spinal stenosis assessment dependent on slice orientation? A magnetic resonance imaging study.

INTRODUCTION: Lumbar spinal stenosis (LSS) treatment is based primarily on the clinical criteria providing that imaging confirms radiological stenosis. The radiological measurement more commonly used is the dural sac cross-sectional area (DSCA). It has been recently shown that grading stenosis based on the morphology of the dural sac as seen on axial T2 MRI images, better reflects severity of stenosis than DSCA and is of prognostic value. This radiological prospective study investigates the variability of surface measurements and morphological grading of stenosis for varying degrees of angulation of the T2 axial images relative to the disc space as observed in clinical practice. MATERIALS AND METHODS: Lumbar spine TSE T2 three-dimensional (3D) MRI sequences were obtained from 32 consecutive patients presenting with either suspected spinal stenosis or low back pain. Axial reconstructions using the OsiriX software at 0°, 10°, 20° and 30° relative to the disc space orientation were obtained for a total of 97 levels. For each level, DSCA was digitally measured and stenosis was graded according to the 4-point (A-D) morphological grading by two observers. RESULTS: A good interobserver agreement was found in grade evaluation of stenosis (k = 0.71). DSCA varied significantly as the slice orientation increased from 0° to +10°, +20° and +30° at each level examined (P < 0.0001) (-15 to +32% at 10°, -24 to +143% at 20° and -29 to +231% at 30° of slice orientation). Stenosis definition based on the surface measurements changed in 39 out of the 97 levels studied, whereas the morphology grade was modified only in two levels (P < 0.01). DISCUSSION: The need to obtain continuous slices using the classical 2D MRI acquisition technique entails often at least a 10° slice inclination relative to one of the studied discs. Even at this low angulation, we found a significantly statistical difference between surface changes and morphological grading change. In clinical practice, given the above findings, it might therefore not be necessary to align the axial cuts to each individual disc level which could be more time-consuming than obtaining a single series of axial cuts perpendicular to the middle of the lumbar spine or to the most stenotic level. In conclusion, morphological grading seems to offer an alternative means of assessing severity of spinal stenosis that is little affected by image acquisition technique.

B1-insensitive T2 preparation for improved coronary magnetic resonance angiography at 3 T.

At 3 T, the effective wavelength of the RF field is comparable to the dimension of the human body, resulting in B1 standing wave effects and extra variations in phase. This effect is accompanied by an increase in B0 field inhomogeneity compared to 1.5 T. This combination results in nonuniform magnetization preparation by the composite MLEV weighted T2 preparation (T2 Prep) sequence used for coronary magnetic resonance angiography (MRA). A new adiabatic refocusing T2 Prep sequence is presented in which the magnetization is tipped into the transverse plane with a hard RF pulse and refocused using a pair of adiabatic fast-passage RF pulses. The isochromats are subsequently returned to the longitudinal axis using a hard RF pulse. Numerical simulations predict an excellent suppression of artifacts originating from B1 inhomogeneity while achieving good contrast enhancement between coronary arteries and surrounding tissue. This was confirmed by an in vivo study, in which coronary MR angiograms were obtained without a T2 Prep, with an MLEV weighted T2 Prep and the proposed adiabatic T2 Prep. Improved quantitative and qualitative coronary MRA image measurement was achieved using the adiabatic T2 Prep at 3 T.

In vivo measurement of glycine with short echo-time 1H MRS in human brain at 7 T.

OBJECT: To determine whether glycine can be measured at 7 T in human brain with (1)H magnetic resonance spectroscopy (MRS). MATERIALS AND METHODS: The glycine singlet is overlapped by the larger signal of myo-inositol. Density matrix simulations were performed to determine the TE at which the myo-inositol signal was reduced the most, following a single spin-echo excitation. (1)H MRS was performed on an actively shielded 7 T scanner, in five healthy volunteers. RESULTS: At the TE of 30 ms, the myo-inositol signal intensity was substantially reduced. Quantification using LCModel yielded a glycine-to-creatine ratio of 0.14 +/- 0.01, with a Cramer-Rao lower bound (CRLB) of 7 +/- 1%. Furthermore, quantification of metabolites other than glycine was possible as well, with a CRLB mostly below 10%. CONCLUSION: It is possible to detect glycine at 7 T in human brain, at the short TE of 30 ms with a single spin-echo excitation scheme.

Aortic blood pressure measured via EIT: investigation of different measurement settings.

Electrical impedance tomography (EIT) allows the measurement of intra-thoracic impedance changes related to cardiovascular activity. As a safe and low-cost imaging modality, EIT is an appealing candidate for non-invasive and continuous haemodynamic monitoring. EIT has recently been shown to allow the assessment of aortic blood pressure via the estimation of the aortic pulse arrival time (PAT). However, finding the aortic signal within EIT image sequences is a challenging task: the signal has a small amplitude and is difficult to locate due to the small size of the aorta and the inherent low spatial resolution of EIT. In order to most reliably detect the aortic signal, our objective was to understand the effect of EIT measurement settings (electrode belt placement, reconstruction algorithm). This paper investigates the influence of three transversal belt placements and two commonly-used difference reconstruction algorithms (Gauss-Newton and GREIT) on the measurement of aortic signals in view of aortic blood pressure estimation via EIT. A magnetic resonance imaging based three-dimensional finite element model of the haemodynamic bio-impedance properties of the human thorax was created. Two simulation experiments were performed with the aim to (1) evaluate the timing error in aortic PAT estimation and (2) quantify the strength of the aortic signal in each pixel of the EIT image sequences. Both experiments reveal better performance for images reconstructed with Gauss-Newton (with a noise figure of 0.5 or above) and a belt placement at the height of the heart or higher. According to the noise-free scenarios simulated, the uncertainty in the analysis of the aortic EIT signal is expected to induce blood pressure errors of at least ± 1.4 mmHg.

Direct noninvasive estimation of myocardial tricarboxylic acid cycle flux in vivo using hyperpolarized (13)C magnetic resonance.

BACKGROUND: The heart relies on continuous energy production and imbalances herein impair cardiac function directly. The tricarboxylic acid (TCA) cycle is the primary means of energy generation in the healthy myocardium, but direct noninvasive quantification of metabolic fluxes is challenging due to the low concentration of most metabolites. Hyperpolarized (13)C magnetic resonance spectroscopy (MRS) provides the opportunity to measure cellular metabolism in real time in vivo. The aim of this work was to noninvasively measure myocardial TCA cycle flux (VTCA) in vivo within a single minute. METHODS AND RESULTS: Hyperpolarized [1-(13)C]acetate was administered at different concentrations in healthy rats. (13)C incorporation into [1-(13)C]acetylcarnitine and the TCA cycle intermediate [5-(13)C]citrate was dynamically detected in vivo with a time resolution of 3s. Different kinetic models were established and evaluated to determine the metabolic fluxes by simultaneously fitting the evolution of the (13)C labeling in acetate, acetylcarnitine, and citrate. VTCA was estimated to be 6.7±1.7μmol·g(-1)·min(-1) (dry weight), and was best estimated with a model using only the labeling in citrate and acetylcarnitine, independent of the precursor. The TCA cycle rate was not linear with the citrate-to-acetate metabolite ratio, and could thus not be quantified using a ratiometric approach. The (13)C signal evolution of citrate, i.e. citrate formation was independent of the amount of injected acetate, while the (13)C signal evolution of acetylcarnitine revealed a dose dependency with the injected acetate. The (13)C labeling of citrate did not correlate to that of acetylcarnitine, leading to the hypothesis that acetylcarnitine formation is not an indication of mitochondrial TCA cycle activity in the heart. CONCLUSIONS: Hyperpolarized [1-(13)C]acetate is a metabolic probe independent of pyruvate dehydrogenase (PDH) activity. It allows the direct estimation of VTCA in vivo, which was shown to be neither dependent on the administered acetate dose nor on the (13)C labeling of acetylcarnitine. Dynamic (13)C MRS coupled to the injection of hyperpolarized [1-(13)C]acetate can enable the measurement of metabolic changes during impaired heart function.

Rotational assessment of distal femur and its relevance in total knee arthroplasty: analysis by magnetic resonance imaging

AbstractObjective:To define the distal femur rotation pattern in a Brazilian population, correlating such pattern with the one suggested by the arthroplasty instruments, and analyzing the variability of each anatomic parameter.Materials and Methods:A series of 101 magnetic resonance imaging studies were evaluated in the period between April and June 2012. The epidemiological data collection was performed with the aid of the institution's computed imaging system, and the sample included 52 male and 49 female patients. The measurements were made in the axial plane, with subsequent correlation and triangulation with the other plans. The posterior condylar line was used as a reference for angle measurements. Subsequently, the anatomical and surgical transepicondylar axes and the anteroposterior trochlear line were specified. The angles between the reference line and the studied lines were calculated with the aid of the institution's software.Results:The mean angle between the anatomical transepicondylar axis and the posterior condylar line was found to be 6.89°, ranging from 0.25° to 12°. For the surgical transepicondylar axis, the mean value was 2.89°, ranging from –2.23° (internal rotation) to 7.86°, and for the axis perpendicular to the anteroposterior trochlear line, the mean value was 4.77°, ranging from –2.09° to 12.2°.Conclusion:The anatomical transepicondylar angle showed mean values corresponding to the measurement observed in the Caucasian population. The utilized instruments are appropriate, but no anatomical parameter proved to be steady enough to be used in isolation.

Magnetic Resonance Experiments with Atomic Hydrogen

In this thesis three experiments with atomic hydrogen (H) at low temperatures T<1 K are presented. Experiments were carried out with two- (2D) and three-dimensional (3D) H gas, and with H atoms trapped in solid H2 matrix. The main focus of this work is on interatomic interactions, which have certain specific features in these three systems considered. A common feature is the very high density of atomic hydrogen, the systems are close to quantum degeneracy. Short range interactions in collisions between atoms are important in gaseous H. The system of H in H₂ differ dramatically because atoms remain fixed in the H₂ lattice and properties are governed by long-range interactions with the solid matrix and with H atoms. The main tools in our studies were the methods of magnetic resonance, with electron spin resonance (ESR) at 128 GHz being used as the principal detection method. For the first time in experiments with H in high magnetic fields and at low temperatures we combined ESR and NMR to perform electron-nuclear double resonance (ENDOR) as well as coherent two-photon spectroscopy. This allowed to distinguish between different types of interactions in the magnetic resonance spectra. Experiments with 2D H gas utilized the thermal compression method in homogeneous magnetic field, developed in our laboratory. In this work methods were developed for direct studies of 3D H at high density, and for creating high density samples of H in H₂. We measured magnetic resonance line shifts due to collisions in the 2D and 3D H gases. First we observed that the cold collision shift in 2D H gas composed of atoms in a single hyperfine state is much smaller than predicted by the mean-field theory. This motivated us to carry out similar experiments with 3D H. In 3D H the cold collision shift was found to be an order of magnitude smaller for atoms in a single hyperfine state than that for a mixture of atoms in two different hyperfine states. The collisional shifts were found to be in fair agreement with the theory, which takes into account symmetrization of the wave functions of the colliding atoms. The origin of the small shift in the 2D H composed of single hyperfine state atoms is not yet understood. The measurement of the shift in 3D H provides experimental determination for the difference of the scattering lengths of ground state atoms. The experiment with H atoms captured in H2 matrix at temperatures below 1 K originated from our work with H gas. We found out that samples of H in H2 were formed during recombination of gas phase H, enabling sample preparation at temperatures below 0.5 K. Alternatively, we created the samples by electron impact dissociation of H₂ molecules in situ in the solid. By the latter method we reached highest densities of H atoms reported so far, 3.5(5)x10¹⁹ cm^-3. The H atoms were found to be stable for weeks at temperatures below 0.5 K. The observation of dipolar interaction effects provides a verification for the density measurement. Our results point to two different sites for H atoms in H2 lattice. The steady-state nuclear polarizations of the atoms were found to be non-thermal. The possibility for further increase of the impurity H density is considered. At higher densities and lower temperatures it might be possible to observe phenomena related to quantum degeneracy in solid.

Broadband excitation in the system identification of active magnetic bearing rotor systems

One of the targets of the climate and energy package of the European Union is to increase the energy efficiency in order to achieve a 20 percent reduction in primary energy use compared with the projected level by 2020. The energy efficiency can be improved for example by increasing the rotational speed of large electrical drives, because this enables the elimination of gearboxes leading to a compact design with lower losses. The rotational speeds of traditional bearings, such as roller bearings, are limited by mechanical friction. Active magnetic bearings (AMBs), on the other hand, allow very high rotational speeds. Consequently, their use in large medium- and high-speed machines has rapidly increased. An active magnetic bearing rotor system is an inherently unstable, nonlinear multiple-input, multiple-output system. Model-based controller design of AMBs requires an accurate system model. Finite element modeling (FEM) together with the experimental modal analysis provides a very accurate model for the rotor, and a linearized model of the magneticactuators has proven to work well in normal conditions. However, the overall system may suffer from unmodeled dynamics, such as dynamics of foundation or shrink fits. This dynamics can be modeled by system identification. System identification can also be used for on-line diagnostics. In this study, broadband excitation signals are adopted to the identification of an active magnetic bearing rotor system. The broadband excitation enables faster frequency response function measurements when compared with the widely used stepped sine and swept sine excitations. Different broadband excitations are reviewed, and the random phase multisine excitation is chosen for further study. The measurement times using the multisine excitation and the stepped sine excitation are compared. An excitation signal design with an analysis of the harmonics produced by the nonlinear system is presented. The suitability of different frequency response function estimators for an AMB rotor system are also compared. Additionally, analytical modeling of an AMB rotor system, obtaining a parametric model from the nonparametric frequency response functions, and model updating are discussed in brief, as they are key elements in the modeling for a control design. Theoretical methods are tested with a laboratory test rig. The results conclude that an appropriately designed random phase multisine excitation is suitable for the identification of AMB rotor systems.

Design of Instrument for Knee Joint Kinematics Measurement

This thesis describes the process of design and modeling of instrument for knee joint kinematics measurement that can work for both in-vivo and in-vitro subjects. It is designed to be compatible with imaging machine in a sagittal plane. Due to the invasiveness of the imaging machine, the instrument is designed to be able to function independently. The flexibility of this instrument allows to measure anthropometrically different subject. Among the sixth degree of freedom of a knee, three rotational and one translational degree of freedom can be measured for both type of subject. The translational, proximal-distal, motion is stimulated by external force directly applied along its axis. These angular and linear displacements are measured by magnetic sensors and high precision potentiometers respectively

Magnetic properties of multi-walled nanotubes on polysterene substrate

Nanotubes are one of the most perspective materials in modern nanotechologies. It makes present investigation very actual. In this work magnetic properties of multi-walled nanotubes on polystyrene substrate are investigated by using quantum magnetometer SQUID. Main purpose was to obtain magnetic field and temperature dependences of magnetization and to compare them to existing theoretical models of magnetism in carbon-bases structures. During data analysis a mathematical algorithm for obtained data filtration was developed because measurement with quantum magnetometer assume big missives of number data, which contain accidental errors. Nature of errors is drift of SQUID signal, errors of different parts of measurement station. Nanotube samples on polystyrene substrate were studied with help of atomic force microscope. On the surface traces of nanotube were found contours, which were oriented in horizontal plane. This feature was caused by rolling method for samples. Detailed comparison of obtained dependences with information of other researches on this topic allows to obtain some conclusions about nature of magnetism in the samples. It emphasizes importance and actuality of this scientific work.

Strong magnetic field pulse generator

High magnetic fields and extremely low temperatures are essential in the study of new semiconductor materials for example in the field of spintronics. Typical phenomenons that arise in such conditions are: Hall Effect, Anomalous Hall effect and Shubnikov de-Haas effect. In this thesis a device capable for such conditions was described. A strong magnetic field pulse generator situated in the laboratory of physics and the Lappeenranta University of Technology was studied. The device is introduced in three parts. First one is the pulsed field magnetic generator, which is responsible for generating the high magnetic field. Next one is the measurement systems, which are responsible for monitoring the sample and the system itself. The last part describes the cryostat system, which allows the extremely cold temperatures in the system.

Quantitative Magnetic Resonance Imaging of the Liver and Heart In Iron Overload

Systemic iron overload (IO) is considered a principal determinant in the clinical outcome of different forms of IO and in allogeneic hematopoietic stem cell transplantation (alloSCT). However, indirect markers for iron do not provide exact quantification of iron burden, and the evidence of iron-induced adverse effects in hematological diseases has not been established. Hepatic iron concentration (HIC) has been found to represent systemic IO, which can be quantified safely with magnetic resonance imaging (MRI), based on enhanced transverse relaxation. The iron measurement methods by MRI are evolving. The aims of this study were to implement and optimise the methodology of non-invasive iron measurement with MRI to assess the degree and the role of IO in the patients. An MRI-based HIC method (M-HIC) and a transverse relaxation rate (R2*) from M-HIC images were validated. Thereafter, a transverse relaxation rate (R2) from spin-echo imaging was calibrated for IO assessment. Two analysis methods, visual grading and rSI, for a rapid IO grading from in-phase and out-of-phase images were introduced. Additionally, clinical iron indicators were evaluated. The degree of hepatic and cardiac iron in our study patients and IO as a prognostic factor in patients undergoing alloSCT were explored. In vivo and in vitro validations indicated that M-HIC and R2* are both accurate in the quantification of liver iron. R2 was a reliable method for HIC quantification and covered a wider HIC range than M-HIC and R2*. The grading of IO was able to be performed rapidly with the visual grading and rSI methods. Transfusion load was more accurate than plasma ferritin in predicting transfusional IO. In patients with hematological disorders, the prevalence of hepatic IO was frequent, opposite to cardiac IO. Patients with myelodysplastic syndrome were found to be the most susceptible to IO. Pre-transplant IO predicted severe infections during the early post-transplant period, in contrast to the reduced risk of graft-versus-host disease. Iron-induced, poor transplantation results are most likely to be mediated by severe infections.

Electronic, magnetic and thermal properties of Pb₂₋x AxCrO₅ (A = K or La)

Lead chromium oxide is a photoconductive dielectric material tha t has great potential of being used as a room temperature photodetector. In this research, we made ceramic pellets of this compound as well as potassium doped compound Pb2-xKxCr05, where x=O, 0.05, 0.125. We also investigate the properties of the lanthanum doped sample whose chemical formula is Pb1.85Lao.15Cr05' The electronic, magnetic and thermal properties of these materials have been studied. Magnetization measurements of the Pb2Cr05 sample indicate a transition at about 310 K, while for the lanthanum doped sample the transition temperature is at about 295 K indicating a paramagnetic behavior. However, the potassium doped samples are showing the transition from paramagnetic state to diamagnetic state at different temperatures for different amounts of potassium atoms present in the sample. We have studied resistivity as a function of temperature in different gas environments from 300 K to 900 K. The resistivity measurement of the parent sample indicates a conducting to insulating transition at about 300 K and upon increasing the temperature further, above 450 K the sample becomes an ionic conductor. As temperature increases a decrease in resistance is observed in the lanthanum/potassium doped samples. Using Differential Scanning Calorimetry experiment an endothermic peak is observed for the Pb2Cr05 and lanthanum/potassium doped samples at about 285 K.