The role of equilibrium volume and magnetism on the stability of iron phases at high pressures.

The present study provides new insights into the pressure dependence of magnetism by tracking the hybridization between crystal orbitals for pressures up to 600 GPa in the known hcp, bcc and fcc iron. The Birch-Murnaghan equation of state parameters are; bcc: V0 = 11.759 A(3)/atom, K0 = 177.72 GPa; hcp: V0 = 10.525 A(3)/atom, K0 = 295.16 GPa; and fcc: V0 = 10.682 A(3)/atom, K0 = 274.57 GPa. These parameters compare favorably with previous studies. Consistent with previous studies we find that the close-packed hcp and fcc phases are non-magnetic at pressures above 50 GPa and 60 GPa, respectively. The principal features of magnetism in iron are predicted to be invariant, at least up to ∼6% overextension of the equilibrium volume. Our results predict that magnetism for overextended fcc iron disappears via an intermediate spin state. This feature suggests that overextended lattices can be used to stabilize particular magnetic states. The analysis of the orbital hybridization shows that the magnetic bcc structure at high pressures is stabilized by splitting the majority and minority spin bands. The bcc phase is found to be magnetic at least up to 600 GPa; however, magnetism is insufficient to stabilize the bcc phase itself, at least at low temperatures. Finally, the analysis of the orbital contributions to the total energy provides evidence that non-magnetic hcp and fcc phases are likely more stable than bcc at core earth pressures.

Density functional theory calculations of XPS binding energy shift for nitrogen-containing graphene-like structures.

Our results validate the use of independent DFT predicted BE shifts for defect identification and constraining ambient pressure XPS observations for Me-Nx moieties in pyrolyzed carbon based ORR electrocatalysts. This supports the understanding of such catalysts as vacancy-and-substitution defects in a graphene-like matrix.

Combination of chemical suppression techniques for dual suppression of fat and silicone at diffusion-weighted MR imaging in women with breast implants.

OBJECTIVES: Silicone breast prostheses prove technically challenging when performing diffusion-weighted MR imaging in the breasts. We describe a combined fat and chemical suppression scheme to achieve dual suppression of fat and silicone, thereby improving the quality of diffusion-weighted images in women with breast implants. METHODS: MR imaging was performed at 3.0 and 1.5 T in women with silicone breast implants using short-tau inversion recovery (STIR) fat-suppressed echo-planar (EPI) diffusion-weighted MR imaging (DWI) on its own and combined with the slice-select gradient-reversal (SSGR) technique. Imaging was performed using dedicated breast imaging coils. RESULTS: Complete suppression of the fat and silicone signal was possible at 3.0 T using EPI DWI with STIR and SSGR, evaluated with dedicated breast coils. However, a residual silicone signal was still perceptible at 1.5 T using this combined approach. Nevertheless, a further reduction in silicone signal at 1.5 T could be achieved by employing thinner slice partitions and the addition of the chemical-selective fat-suppression (CHESS) technique. CONCLUSIONS: DWI using combined STIR and SSGR chemical suppression techniques is feasible to eliminate or reduce silicone signal from prosthetic breast implants. KEY POINTS: Breast magnetic resonance imaging (MRI) is frequently needed following breast implants. Unsuppressed signal from silicone creates artefacts on diffusion-weighted MR sequences. Dual fat/chemical suppression can eliminate signal from fat and silicone. STIR with slice selective gradient reversal can suppress fat and silicone signal.

Lithium hydroxide dihydrate: a new type of icy material at elevated pressure.

We show that, in addition to the known monohydrate, LiOH forms a dihydrate at elevated pressure. The dihydrate involves a large number of H-bonds establishing chains along the <001> direction. In addition, the energy surface exhibits a saddle point for proton locations along certain O interatomic distances, a feature characteristic for superprotonic conductors. However, MD simulations indicate that LiOH · 2H(2)O is not a superprotonic conductor and suggest the relevant interpolyhedral O-O distances being too large to allow for proton transfer between neighboring Li-coordinated polyhedra at least on the time scale of the MD-simulations.

Distribution of extracellular matrix components in normal and degenerated canine tricuspid valve leaflets.

The aim of the present study was to investigate the composition and distribution of various extracellular matrix (ECM) components in normal canine tricuspid valves (TVs) and in TVs affected by chronic valvular disease (CVD). The parietal (pTV) and septal (sTV) leaflets of the TVs from 27 dogs were investigated immunohistochemically for expression of collagen types I, III, IV and VI, elastin, laminin, fibronectin and heparan sulphate. Normal pTV consisted mainly of elastin and collagen VI in the atrialis, fibronectin in the thin spongiosa and mixed collagens in the fibrosa. The layered structure was less distinct in sTV, with numerous adipocytes and proteoglycans in the spongiosa and collagen III predominating in the fibrosa. The earliest stages of CVD affecting the pTV were recognized in the spongiosa and progression to advanced disease was characterized by nodular accumulation of proteoglycans within the free edge of the leaflet. These nodular lesions of the pTV contained more fibronectin, elastin and collagens I and VI than those affecting the sTV. These findings contrast with those reported in CVD affecting the mitral valve (MV) in which the early lesions affect the atrialis and advanced disease involves the entire leaflet. The pathogenesis of CVD in TV may involve initial alterations of the tricuspid annulus that lead to early lesions within the spongiosa, resulting in further shear stress and proteoglycan accumulation at the free edge of the pTV.

Expression of genes encoding matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in normal and diseased canine mitral valves.

The pathogenesis of canine chronic valvular disease (CVD) is not fully characterized. The present study investigates the expression of genes encoding matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in normal and diseased mitral valves (MVs). Samples from normal (n=15) or diseased (n=10) canine MVs were subject to real-time polymerase chain reaction (PCR) for quantification of mRNA encoding MMP-1, -2, -9 and -14 and TIMP-2, -3 and -4. In normal valves there was low expression of mRNA encoding MMP-2, -9 and -14 and TIMP-3. In the valves from dogs with CVD there was significantly increased transcription of mRNA encoding MMP-1 and -14 and TIMP-2, -3 and -4, but no elevation in mRNA encoding MMP-2 and -9. MMPs and TIMPs are therefore likely to be involved in extracellular matrix metabolism in normal canine MVs and there are significant alterations in the expression of genes encoding these molecules during CVD.

Image quality improvement of composed whole-spine MR images by applying a modified homomorphic filter--first results in cases of multiple myeloma.

To establish a modified homomorphic filter (BiFiC) for post-processing of composed MR images in clinical routine and to evaluate it in special regards to image quality and diagnostic safety. Twenty-three whole-spine examinations were post-processed with the filter. Qualitative image evaluation included documentation of lesions and their visualization at original and post-processed images. Variations of signal intensities were calculated pixel by pixel and visualized by color-coded maps. Quantitative data evaluation was conducted by region-by-region analysis with standardized regions of interests. The BiFiC filter could be implemented successfully on the scanner's software platform and used within clinical routine. Color-coded maps could demonstrate that the BiFiC filter improves the signal uniformity in all cases, including images with metallic artifacts caused by implants. The subjective image quality of the post-processed images was improved in 22 out of the 23 MR examinations; in one case it was rated as equal. All pathologies were visualized on post-processed images without the need of additional contrast adjustments. The implemented BiFiC filter significantly improves image signal homogeneity. The algorithm can consequently be integrated into clinical routine as an automatic image post-processing step.

Structural transition of PETN-I to ferroelastic orthorhombic phase PETN-III at elevated pressures.

Using powder x-ray diffraction and first-principles calculations, we provide evidence for a structural transition of PETN-I below 6 GPa to an orthorhombic phase of space group P2(1)2(1)2. The transition can be rationalized as shear-stress induced and ferroelastic, which involves a slight static displacement of the molecules that breaks the fourfold symmetry of PETN-I. Previously reported changes in the optical spectra reflect a lifting of the twofold degeneracy of modes in tetragonal PETN-I. The observed transition is expected to induce soft shear compliances along specific directions in PETN crystallites that may relate to the observed dependence of detonation pressure on crystal orientation.

Robust parametric modeling approach based on domain knowledge for computer aided detection of vertebrae column metastases in MRI.

This study evaluates a robust parametric modeling approach for computer-aided detection (CAD) of vertebrae column metastases in whole-body MRI. Our method involves constructing a model based on geometric primitives from purely anatomical knowledge of organ shapes and rough variability limits. The basic intensity range of primary 'simple' objects in our models is derived from expert knowledge of image formation and appearance for certain tissue types. We formulated the classification problem as a multiple instance learning problem for which a novel algorithm is designed based on Fisher's linear discriminant analysis. Evaluation of metastases detection algorithm is done on a separate test set as well as on the training set via leave-one-patient-out approach.

Effect of captivity and mineral supplementation on body composition and mineral status of mustached bats (Pteronotus parnellii rubiginosus).

We investigated the whole-body crude nutrient (fat, protein, ash) and mineral (Ca, P, Mg, Na, K) composition of mustached bats of three different groups: animals from the wild (n = 6), and animals from captivity on an unsupplemented feeding regime of mealworms (n = 7), and on a feeding regime in which the mealworms were kept on a mineral substrate prior to feeding (n = 6). It was shown that mealworms from the mineral substrate had higher Ca contents than mealworms from the conventional substrates. In an earlier study, differences in bone mineral density had been found between the groups. These differences, however, were not reflected in differences in whole-body composition. Captive animals showed a larger variation in body weight and fat content, indicating potential shortcomings of the dietary and husbandry regime.

Prostate biopsy in the supine position in a standard 1.5-T scanner under real time MR-imaging control using a MR-compatible endorectal biopsy device.

Thirty-seven consecutive patients with elevated PSA levels and negative tumor prostate biopsies underwent a MR-guided prostate biopsy in a 1.5-T scanner in the supine position. After localization of suspected tumor areas using an endorectal coil and two body-phased array coils, the biopsy device was positioned without any repositioning of the patient. The biopsy device consisted of a mount, a ball joint, a positioning stage and an insertion stage with a needle guide, which was filled with a MR-visible fluid to control positioning of the needle using a balanced steady-state free precession sequence (TrueFISP) and a high-resolution turbo spin echo (T2-TSE) sequence. Core biopsies were taken manually in the magnet. The biopsy needle could be correctly positioned in all cases. Suspected lesions with a diameter > or =10 mm could be successfully punctured. Four to nine (mean = 6) biopsies were taken per patient. In 14 patients, prostate cancer was confirmed at histology. Twenty-four biopsies positive for cancer were performed in 14 patients. A correct correlation was found between the site of biopsy and histology. MR-guided prostate biopsy can be effective in increasing primary positive tumor biopsy results in patients with a history of negative tumor TRUS-guided prostate biopsies.

Double echo steady state magnetic resonance imaging of knee articular cartilage at 3 Tesla: a pilot study for the Osteoarthritis Initiative.

BACKGROUND: Quantitative magnetic resonance imaging (qMRI) may provide valuable measures of cartilage morphology in osteoarthritis (OA) but has been confined to sequences with relatively long acquisition times at 1.5 Tesla (T). OBJECTIVE: To test the accuracy and precision of knee cartilage qMRI with a fast double echo, steady state (DESS) sequence with water excitation (we) at 3 T. METHODS: As a pilot study for the Osteoarthritis Initiative, test-retest MR images were acquired in the knees of 19 participants with no OA to moderate degrees of clinical OA. Two double oblique coronal fast low angle shot (FLASHwe) sequences (1.5 mm slice thickness) were acquired at 3 T, and two sagittal DESSwe sequences (0.7 mm slice thickness). Double oblique coronal multiplanar reformats (MPR) were performed (1.5 mm slice thickness) from the sagittal DESSwe. Knee joint cartilage plates were quantified unpaired in random order with blinding to subject identification. RESULTS: In the femorotibial joint, precision errors (root mean square coefficient of variation in % for unpaired analysis) for cartilage volume and thickness were 3.0-6.4% with coronal FLASHwe, 2.4-6.2% with coronal MPR DESSwe, and 2.3-8.2% with sagittal DESSwe. Correlation coefficients between DESSwe and FLASHwe ranged from r = 0.88 to 1.0. In the femoropatellar joint, precision errors (sagittal DESSwe) were 3.4-8.5%. CONCLUSIONS: DESSwe permits accurate and precise analysis of cartilage morphology in the femorotibial joint at 3 T. Further studies are needed to examine the accuracy of DESSwe in the femoropatellar joint and its ability to characterise sensitivity to longitudinal changes in cartilage morphology.

[Cardiovascular whole body MRI with parallel imaging]. / Kardiovaskuläre Ganzkörper-MRT mit paralleler Bildgebung.

PURPOSE: To create a whole-body cardiovascular MRI protocol with parallel imaging (iPAT). MATERIAL AND METHODS: Twenty two persons participated in the whole body scan. Due to iPAT high resolution imaging of the heart could be performed. 3D contrast enhanced MR angiography (3D-CE-MRA) took only 62 s to cover the whole body at a spatial resolution of less than 1.4x1.0x1.5mm(3). Scan time for HASTE lung imaging could be reduced by the factor of 2 while maintaining the signal to noise ratio (SNR). Image quality was rated by 2 radiologists blinded to each other. RESULTS: Mean scan time was 104 min on the standard system and less than 80 min on the new system. 75% of all MRA segments were rated good in terms of vessel conspicuity, more than 80% had no venous overlay. One case of distal occlusion of the anterior tibial artery and two cases of myocardial infarction were detected. CONCLUSION: Parallel imaging offers the possibility of fast whole body imaging. A combination of morphologic and functional imaging can be performed within less than 80 min.

Comparison of intracranial 3D-ToF-MRA with and without parallel acquisition techniques at 1.5T and 3.0T: preliminary results.

PURPOSE: To evaluate the performance of four 3D-ToF magnetic resonance angiography (MRA) sequences with and without integrated parallel acquisition techniques (iPAT) at 1.5T and 3.0T in imaging intracranial vessels. MATERIAL AND METHODS: Seven volunteers and 5 patients (4 aneurysms, 1 AVM) underwent 3D-ToF-MRA at 1.5T (Magnetom Sonata) and 3.0T (Magnetom Trio) with and without parallel acquisition techniques (iPAT) using similarly designed 8-channel phased-array head coils. Imaging time of the pulse sequences was set to 7.15 and 7.35 min, respectively. Images were analyzed quantitatively by calculating signal-to-noise (SNR) and contrast-to-noise (CNR) ratios of proximal M2 segments and qualitatively by using a 5-point scale. RESULTS: SNR and CNR were significantly higher for both 3D-ToF sequences at 3.0T compared with both pulse sequences at 1.5T. The highest SNR and CNR were obtained at 3.0T without iPAT. However, because of a higher spatial resolution (matrix 512 x 640) visualization of small vessel details was best at 3.0T with iPAT. CONCLUSION: Intracranial 3D-ToF-MRA at 3.0T offers superior image quality compared with 1.5T, particular in the delineation of smaller vessels. In contrast to 1.5T, implementation of iPAT at 3.0T is of additional benefit since the high SNR available at 3.0T allows for higher spatial resolution without prolongation of measurement time.

[Determining global heart function with real time TrueFISP in one respiratory cycle]. / Erfassung der globalen Herzfunktion mit Real-time-trueFISP in einer Atemphase.

Real-time multislice cine techniques lead to inaccurate results in ventricular volumes based on limited temporal resolution. The purpose of the study is to evaluate a real-time cine technique with parallel imaging algorithms in comparison to standard segmented techniques. Twelve patients underwent cardiac cine MRI using real-time multislice cine trueFISP. Temporal resolution was improved using parallel acquisition techniques (iPAT) and data acquisition was performed in a single breath-hold along the patients' short axis. Evaluation of EDV, ESV, EF and myocardial mass was performed and results compared to a standard segmented single-slice cine trueFISP. Combination of real-time cine trueFISP and iPAT provided a temporal resolution of 48 ms. Results of the multislice approach showed an excellent correlation to standard single-slice trueFISP for EDV (0.94, p <0.001), ESV (0.97, p <0.001) EF (0.99, p <0.001) and myocardial mass (0.93, p <0.001). No significant differences could be found. The use of parallel acquisition techniques (PAT) allow for a substantial improvement of temporal resolution in real-time cine MRI (<50 ms). Therefore these techniques enable an accurate and exact quantification of global ventricular function.

[Feasibilities and limitations of high field parallel MRI]. / Möglichkeiten und Grenzen der parallelen MRT im Hochfeld.

In medical magnetic resonance imaging (MRI) it is standard to use MR scanners with a field strength of 1.5 Tesla. Recently, an ongoing development to higher field strength can be observed and a new clinical standard at 3.0 Tesla seems to be established. High field MRI with its intrinsic higher signal to noise ratio (SNR) can enable new applications of MRI in medical diagnosis, or can serve to improve existing methods. It is important to note, that the use of high field MRI is not without its limitations. Besides the SNR, other unwanted effects increase with a higher field strength. Without correction, these high field problems cause a serious loss in image quality. An elegant way to address these problems is the use of parallel imaging. In many clinical applications, parallel MRI (pMRI) is part of the standard protocol, because pMRI can enhance virtually every MRI application, without necessarily affecting the contrast behavior of the underlying imaging sequence. In high field MRI, besides the speed advantage of pMRI, the positive influence on high field specific problems and therefore on the image quality will be of major importance.

The maximum attainable body size of herbivorous mammals: morphophysiological constraints on foregut, and adaptations of hindgut fermenters.

An oft-cited nutritional advantage of large body size is that larger animals have lower relative energy requirements and that, due to their increased gastrointestinal tract (GIT) capacity, they achieve longer ingesta passage rates, which allows them to use forage of lower quality. However, the fermentation of plant material cannot be optimized endlessly; there is a time when plant fibre is totally fermented, and another when energy losses due to methanogenic bacteria become punitive. Therefore, very large herbivores would need to evolve adaptations for a comparative acceleration of ingesta passage. To our knowledge, this phenomenon has not been emphasized in the literature to date. We propose that, among the extant herbivores, elephants, with their comparatively fast passage rate and low digestibility coefficients, are indicators of a trend that allowed even larger hindgut fermenting mammals to exist. The limited existing anatomical data on large hindgut fermenters suggests that both a relative shortening of the GIT, an increase in GIT diameter, and a reduced caecum might contribute to relatively faster ingesta passage; however, more anatomical data is needed to verify these hypotheses. The digestive physiology of large foregut fermenters presents a unique problem: ruminant-and nonruminant-forestomachs were designed to delay ingesta passage, and they limit food intake as a side effect. Therefore, with increasing body size and increasing absolute energy requirements, their relative capacity has to increase in order to compensate for this intake limitation. It seems that the foregut fermenting ungulates did not evolve species in which the intake-limiting effect of the foregut could be reduced, e.g. by special bypass structures, and hence this digestive model imposed an intrinsic body size limit. This limit will be lower the more the natural diet enhances the ingesta retention and hence the intake-limiting effect. Therefore, due to the mechanical characteristics of grass, grazing ruminants cannot become as big as the largest browsing ruminant. Ruminants are not absent from the very large body size classes because their digestive physiology offers no particular advantage, but because their digestive physiology itself intrinsically imposes a body size limit. We suggest that the decreasing ability for colonic water absorption in large grazing ruminants and the largest extant foregut fermenter, the hippopotamus, are an indication of this limit, and are the outcome of the competition of organs for the available space within the abdominal cavity. Our hypotheses are supported by the fossil record on extinct ruminant/tylopod species which did not, with the possible exception of the Sivatheriinae, surpass extant species in maximum body size. In contrast to foregut fermentation, the GIT design of hindgut fermenters allows adaptations for relative passage acceleration, which explains why very large extinct mammalian herbivores are thought to have been hindgut fermenters.

Resolution enhancement in lung 1H imaging using parallel imaging methods.

Resolution in (1)H lung imaging is limited mainly by the acquisition time. Today, half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences, with short echo time (TE) and short interecho spacing (T(inter)) have found increased use in lung imaging. In this study, a HASTE sequence was used in combination with a partially parallel acquisition (PPA) strategy to increase the spatial resolution in single-shot (1)H lung imaging. To investigate the benefits of using a combination of single-shot sequences and PPA, five healthy volunteers were examined. Compared to conventional imaging methods, substantially increased resolution is obtained using the PPA approach. Representative in vivo (1)H lung images acquired with a HASTE sequence in combination with the generalized autocalibrating partially parallel acquisition (GRAPPA) method, up to an acceleration factor of three, are presented.