Compressed sensing for resolution enhancement of hyperpolarized 13C flyback 3D-MRSI

High polarization of nuclear spins in liquid state through dynamic nuclear polarization has enabled the direct monitoring of 13C metabolites in vivo at very high signal-to-noise, allowing for rapid assessment of tissue metabolism. The abundant SNR afforded by this hyperpolarization technique makes high-resolution 13C 3D-MRSI feasible. However, the number of phase encodes that can be fit into the short acquisition time for hyperpolarized imaging limits spatial coverage and resolution. To take advantage of the high SNR available from hyperpolarization, we have applied compressed sensing to achieve a factor of 2 enhancement in spatial resolution without increasing acquisition time or decreasing coverage. In this paper, the design and testing of compressed sensing suited for a flyback 13C 3D-MRSI sequence are presented. The key to this design was the undersampling of spectral k-space using a novel blipped scheme, thus taking advantage of the considerable sparsity in typical hyperpolarized 13C spectra. Phantom tests validated the accuracy of the compressed sensing approach and initial mouse experiments demonstrated in vivo feasibility.     

Multi-channel metabolic imaging, with SENSE reconstruction, of hyperpolarized [1-(13)C] pyruvate in a live rat at 3.0 tesla on a clinical MR scanner

We report metabolic images of (13)C, following injection of a bolus of hyperpolarized [1-(13)C] pyruvate in a live rat. The data were acquired on a clinical scanner, using custom coils for volume transmission and array reception. Proton blocking of all carbon resonators enabled proton anatomic imaging with the system body coil, to allow for registration of anatomic and metabolic images, for which good correlation was achieved, with some anatomic features (kidney and heart) clearly visible in a carbon image, without reference to the corresponding proton image. Parallel imaging with sensitivity encoding was used to increase the spatial resolution in the SI direction of the rat. The signal to noise ratio in was in some instances unexpectedly high in the parallel images; variability of the polarization among different trials, plus partial volume effects, are noted as a possible cause of this.     

A CP5 calculus for space-time fields

Compactified Minkowski space can be embedded in projective five-space CP⁵ (homogeneous coordinates Xⁱ, i = 0, …, 5) as a four dimensional quadric hypersurface given by $\text{Ω}{}_{\mathrm{ij}}\text{X}{}^{\mathrm{i}}\text{X}{}^{\mathrm{j}}\text{= 0.}$ Projective twistor space (homogeneous coordinates Z^α, α = 0, …, 3) arises via the Klein representation as the space of two-planes lying on this quadric. These two facts of projective geometry form the basis for the construction of a global space-time calculus which makes use of the coordinates Xⁱ?X^αβ(=-X^βα) to represent spinor and tensor fields in a manifestly conformally covariant form. This calculus can be regarded as a synthesis of work on conformal geometry by Veblen, Dirac, and others, with the theory of twistors developed by Penrose.We provide here a systematic review of the basic framework: the underlying projective geometry; the calculus of tensor fields; the characterization of spinors as twistor-valued fields ψ^α(X) which satisfy a geometrical condition ($\text{ψ}{}^{\mathrm{\alpha }}\text{X}{}_{\mathrm{\alpha \beta }}\text{= 0 on Ω}$ ); and the introduction of the conformally invariant Laplacian operator $\text{?}{}^2\text{= Ω}{}^{\mathrm{ij}}\text{?}{}^2\text{/?}\text{X}{}^{\mathrm{i}}\text{?}\text{X}{}^{\mathrm{j}}$. In addition a number of subsidiary topics are discussed which illustrate the general scheme, including: the breaking of conformal symmetry to Poincaré symmetry; a derivation of the zero rest mass equations for all helicities; and a new and manifestly conformally covariant form of the twistor contour integral formulae for massless fields.     

Skew scattering of electrons in a spin glass

The field and temperature dependences of the extraordinary Hall effect in alloys of the $\text{Au}$Fe system have been measured for the first time over a range that encompasses the spin glass regime. We are able to show how the data reflect the competition between the spin glass ordering interactions and the disruptive effects of temperature and applied magnetic field.     

Plant delta(15)N associated with arbuscular mycorrhization, drought and nitrogen deficiency

It has long been evident that plant (15)N chiefly reflects the processes which fractionate (15)N/(14)N rather than the (15)N of plant N source(s). It has emerged recently that one of the most important fractionating processes contributing to the whole plant (15)N is the presence/absence, type or species of mycorrhiza, especially when interacting with nutrient deficiency. Ecto- and ericoid mycorrhizas are frequently associated with (15)N-depleted foliar (15)N, commonly as low as -12 per thousand. As shown by the present study, plants having no mycorrhiza, or those infected with various species of arbuscular mycorrhiza (AM)-forming fungi, interact with varying concentrations of soil nitrogen [N] and moisture to enrich plant (15)N by as much as 3.5 per thousand. Hence the lack of a mycorrhiza, or variation in the species of AM-forming fungal associations, can account for about 25% of the usually reported variations of foliar (15)N found in field situations and do so by (15)N enrichment rather than depletion. Copyright 1999 John Wiley & Sons, Ltd.     

Low field Hall effect in potassium

The anisotropic electron relaxation time in K caused by the freezing out of Umklapp processes on certain areas of the Fermi surface is predicted to give a temperature-dependent component to the low-field Hall effect at low temperatures. A previous attempt to demonstrate this component was defeated by the unsuitability of the existing data which contain an overwhelming high-field contribution in the temperature range of interest. To provide more suitable data, we have measured the Hall effect of polycrystalline K as the conditions tend towards the low-field limit. It is shown how the results can be qualitatively interpreted in terms of a competition between this predicted Umklapp component and the high-field tendencies inherent in the galvano-magnetic effect.     

Age-related waning of in vitro Interferon-γ levels against r32kDaBCG in BCG vaccinated children

Background  

Mycobacterium bovis BCG vaccine has displayed inconsistent efficacy in different trials conducted in various geographical regions. Nevertheless, it significantly reduces the risk of severe childhood tuberculosis and continues to be used to prevent tuberculosis in many countries. Many studies revealed that efficacy of vaccine wanes with age. Most of the studies were based on in vivo and in vitro responses to tuberculin. With the advent of newer tests such as in vitro interferon-γ assays and identification of potent immunogenic mycobacterial proteins there is a need to corroborate the observations. This study aims at ascertaining the need for a booster at a later age as indicated by in vitro release of IFN-γ while evaluating Ag85A as an antigen.