Investigation of the velocity field in a full-scale model of a cerebral aneurysm

Due to improved and now widely used imaging methods in clinical surgery practise, detection of unruptured cerebral aneurysms becomes more and more frequent. For the selection and development of a low-risk and highly effective treatment option, the understanding of the involved hemodynamic mechanisms is of great importance. Computational Fluid Dynamics (CFD), in vivo angiographic imaging and in situ experimental investigations of flow behaviour are powerful tools which could deliver the needed information. Hence, the aim of this contribution is to experimentally characterise the flow in a full-scale phantom model of a realistic cerebral aneurysm. The acquired experimental data will then be used for a quantitative validation of companion numerical simulations. The experimental methodology relies on the large-field velocimetry technique PTV (Particle Tracking Velocimetry), processing high speed images of fluorescent tracer particles added to the flow of a blood-mimicking fluid.First, time-resolved planar PTV images were recorded at 4500 fps and processed by a complex, in-house algorithm. The resulting trajectories are used to identify Lagrangian flow structures, vortices and recirculation zones in two-dimensional measurement slices within the aneurysm sac. The instantaneous inlet velocity distribution, needed as boundary condition for the numerical simulations, has been measured with the same technique but using a higher frame rate of 20,000 fps in order to avoid ambiguous particle assignment. From this velocity distribution, the time-resolved volume flow rate has been also derived. In this manner, a direct comparison between numerical simulations and PTV measurements will be possible in the near future, opening the door for highly accurate computational predictions.     

Directly detected Mn MRI: Application to phantoms for human hyperpolarized C MRI development

In this work we demonstrate for the first time directly detected manganese-55 (⁵⁵Mn) magnetic resonance imaging (MRI) using a clinical 3 T MRI scanner designed for human hyperpolarized ¹³C clinical studies with no additional hardware modifications. Due to the similar frequency of the ⁵⁵Mn and ¹³C resonances, the use of aqueous permanganate for large, signal-dense, and cost-effective “¹³C” MRI phantoms was investigated, addressing the clear need for new phantoms for these studies. Due to 100% natural abundance, higher intrinsic sensitivity, and favorable relaxation properties, ⁵⁵Mn MRI of aqueous permanganate demonstrates dramatically increased sensitivity over typical ¹³C phantom MRI, at greatly reduced cost as compared with large ¹³C-enriched phantoms. A large sensitivity advantage (22-fold) was demonstrated. A cylindrical phantom (d = 8 cm) containing concentrated aqueous sodium permanganate (2.7 M) was scanned rapidly by ⁵⁵Mn MRI in a human head coil tuned for ¹³C, using a balanced steady state free precession acquisition. The requisite penetration of radiofrequency magnetic fields into concentrated permanganate was investigated by experiments and high frequency electromagnetic simulations, and found to be sufficient for ⁵⁵Mn MRI with reasonably sized phantoms. A sub-second slice-selective acquisition yielded mean image signal-to-noise ratio of ~ 60 at 0.5 cm³ spatial resolution, distributed with minimum central signal ~ 40% of the maximum edge signal. We anticipate that permanganate phantoms will be very useful for testing HP ¹³C coils and methods designed for human studies.     

Guillain-Barré syndrome and anti-ganglioside antibodies: a clinician-scientist's journey

Guillain-Barré syndrome (GBS) is the most frequent cause of acute flaccid paralysis. Having seen my first GBS patient in 1989, I have since then dedicated my time in research towards understanding the pathogenesis of GBS. Along with several colleagues, we identified IgG autoantibodies against ganglioside GM1 in two patients with GBS subsequent to Campylobacter jejuni enteritis. We proceeded to demonstrate molecular mimicry between GM1 and bacterial lipo-oligosaccharide of C. jejuni isolated from a patient with GBS. Our group then established a disease model for GBS by sensitization with GM1 or GM1-like lipo-oligosaccharide. With this, a new paradigm that carbohydrate mimicry can cause autoimmune disorders was demonstrated, making GBS the first proof of molecular mimicry in autoimmune disease. Patients with Fisher syndrome, characterized by ophthalmoplegia and ataxia, can develop the disease after an infection by C. jejuni. We showed that the genetic polymorphism of C. jejuni sialyltransferase, an enzyme essential to the biosynthesis of ganglioside-like lipo-oligosaccharides determines whether patients develop GBS or Fisher syndrome. This introduces another paradigm that microbial genetic polymorphism can determine the clinical phenotype of human autoimmune diseases. Similarities between the clinical presentation of Fisher syndrome and Bickerstaff brainstem encephalitis have caused debate as to whether they are in fact the same disease. We demonstrated that IgG anti-GQ1b antibodies were common to both, suggesting that they are part of the same disease spectrum. We followed this work by clarifying the nosological relationship between the various clinical presentations within the anti-GQ1b antibody syndrome. In this review, I wanted to share my journey from being a clinician to a clinician-scientist in the hopes of inspiring younger clinicians to follow a similar path.(Communicated by Kunihiko SUZUKI, M.J.A.).     

Phantom Maps from a Strong Homology Viewpoint

Let X and Y be connected nilpotent CW-complexes of finite type. In this paper we deal with another complete analysis of a set of phantom maps in terms of strong homology by using the derived functors. We also prove that the set of homotopy classes of maps is independent of the choice of both rational homotopy equivalent classes and completion genera.     

Does the Big Rip survive quantization?

It is known that certain quantum cosmological models present quantum behavior for large scale factors. Since quantization can suppress past singularities, it is natural to inquire whether quantum effects can prevent future singularities. To this end, a Friedmann–Robertson–Walker quantum cosmological model dominated by a phantom energy fluid is investigated. The classical model displays accelerated expansion ending in a Big Rip. The quantization is performed in three different ways, which turn out to lead to the same result, namely there is a possibility that quantum gravitational effects could not remove the Big Rip.     

Accuracy and stability of measuring GABA, glutamate, and glutamine by proton magnetic resonance spectroscopy: a phantom study at 4 Tesla

Proton magnetic resonance spectroscopy has the potential to provide valuable information about alterations in gamma-aminobutyric acid (GABA), glutamate (Glu), and glutamine (Gln) in psychiatric and neurological disorders. In order to use this technique effectively, it is important to establish the accuracy and reproducibility of the methodology. In this study, phantoms with known metabolite concentrations were used to compare the accuracy of 2D J-resolved MRS, single-echo 30 ms PRESS, and GABA-edited MEGA-PRESS for measuring all three aforementioned neurochemicals simultaneously. The phantoms included metabolite concentrations above and below the physiological range and scans were performed at baseline, 1 week, and 1 month time-points. For GABA measurement, MEGA-PRESS proved optimal with a measured-to-target correlation of R(2)=0.999, with J-resolved providing R(2)=0.973 for GABA. All three methods proved effective in measuring Glu with R(2)=0.987 (30 ms PRESS), R(2)=0.996 (J-resolved) and R(2)=0.910 (MEGA-PRESS). J-resolved and MEGA-PRESS yielded good results for Gln measures with respective R(2)=0.855 (J-resolved) and R(2)=0.815 (MEGA-PRESS). The 30 ms PRESS method proved ineffective in measuring GABA and Gln. When measurement stability at in vivo concentration was assessed as a function of varying spectral quality, J-resolved proved the most stable and immune to signal-to-noise and linewidth fluctuation compared to MEGA-PRESS and 30 ms PRESS.     

Prospective tissue-mimicking materials for use in NMR imaging phantoms

Water-based proteinaceous gels, which—with appropriate additives—are stable with time and possess a high melting point, have been used as base materials in ultrasonically tissue-mimicking materials. In the present work, versions of these gels having various concentrations of glycerol and graphite particles were studied regarding their NMR T₁ and T₂ dependencies at a proton Larmor frequency of 10.7 MHz. It has been found that T₁ depends primarily on the concentration of glycerol and T₂ depends primarily on the graphite particle concentration. Also, the ranges of T₁ and T₂ likely span those which exist for soft tissue parenchymae. Thus, these materials are good candidates for use as NMR tissue-mimicking materials. T₁ and T₂ also vary with gelatin concentration. The latter fact, together with the strong dependence of T₂ on graphite concentration, mean that effective contrast-resolution phantoms and anthropomorphic phantoms with stable T₁ and T₂ distributions can be produced.     

On the cosmological viability of the Hu-Sawicki type modified induced gravity

It has been shown recently that the normal branch of a DGP braneworld scenario self-accelerates if the induced gravity on the brane is modified in the spirit of f(R) modified gravity. Within this viewpoint, we investigate cosmological viability of the Hu-Sawicki type modified induced gravity. Firstly, we present a dynamical system analysis of a general f(R)-DGP model. We show that in the phase space of the model, there exist three standard critical points; one of which is a de Sitter point corresponding to accelerating phase of the universe expansion. The stability of this point depends on the effective equation of state parameter of the curvature fluid. If we consider the curvature fluid to be a canonical scalar field in the equivalent scalar-tensor theory, the mentioned de Sitter phase is unstable, otherwise it is an attractor, stable phase. We show that the effective equation of state parameter of the model realizes an effective phantom-like behavior. A cosmographic analysis shows that this model, which admits a stable de Sitter phase in its expansion history, is a cosmologically viable scenario.     

On Covers and Envelopes in Some Functor Categories

We study the existence of covers and envelopes by some special functors on the category of finitely presented modules. As an application, we characterize some important rings using these functors. We also investigate homological properties of some functors on the stable module category. The relationship between phantoms and Ext-phantoms is obtained. It is shown that every left R-module M has an Ext-phantom preenvelope f: M → N with coker(f) pure-projective. Finally, we prove that, as a torsionfree class of (mod-R, Ab), (mod-R, Ab) is generated by the FP-injective objects.     

Phantom Divide Crossing on Brane World

We study the RSII brane world corrected by the four-dimensional scalar curvature and five-dimensional Gauss-Bonnet curvature. The energy transfer between brane and bulk is also taken into account. Parameterizing the energy transfer, the resulting Friedmann equation on brane is solved at low energy. It is shown that phantom divide crossing may be achieved in the braneworld model with wide possibilities, embodying the combined effect of brane-bulk energy transfer, curvature corrections, and the fine-turning mechanics.