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Biomedical subjects

Y-Q Song

Publications and source records attributed to Y-Q Song.

10 recordsLinked to original sources
PubMed2006

p21 gene polymorphisms in systemic lupus erythematosus.

OBJECTIVE: Cyclin-dependent kinase inhibitor 1A (p21) is a negative regulator in the cell cycle. Development of sex-linked lupus-like syndrome in p21-/- mice and reduced p21 gene expression in patients with systemic lupus erythematosus (SLE) compared with those in healthy controls suggested that p21 is a susceptibility gene of SLE. We investigated the same by a case-control association study. METHODS: Six single nucleotide polymorphisms, p21US G/A, p21DS C/A, p21-1022 G/A, p21C31 C/A, p21In2 G/C and p21UTR T/C, were genotyped in 516 SLE patients and 693 healthy controls. Association of genotypes and alleles with disease, disease phenotypes, haplotypes construction, linkage disequilibrium analysis and p21 mRNA expression were performed. RESULTS: We found a significant association of p21US A allele (OR = 0.23, 95% CI: 0.14-0.38, P < 0.001) and p21-1022 A allele (OR = 1.95, 95% CI: 1.37-2.78, P < 0.001) with SLE. We identified significant differences in the frequencies of haplotypes ht1-ACACCC, which contains p21US A allele, and ht2-GCACCC, which contains p21-1022 A allele, between SLE patients and controls (P < 0.0001). Besides, the p21US GA was associated with SLE patients suffering from arthritis (P = 0.003). We also observed differential p21 mRNA expressions among different genotypes of p21US and p21-1022 which were statistically significant. CONCLUSION: Our results suggested that the p21US A allele and p21-1022 A allele were both associated with the development of SLE, and the p21US A allele was associated with arthritis in SLE patients.

Adult↗
PubMed2006

Fast imaging with the MMME sequence.

The multiple-modulation-multiple-echo sequence, previously used for rapid measurement of diffusion, is extended to a method for single shot imaging. Removing the gradient switching requirement during the application of RF pulses by a constant frequency encoding gradient can shorten experiment time for ultrafast imaging. However, having the gradient on during the pulses gives rise to echo shape variations from off-resonance effects, which make the image reconstruction difficult. In this paper, we propose a simple method to deconvolve the echo shape variation from the true one-dimensional image. This method is extended to two-dimensional imaging by adding phase encoding gradients between echoes during the acquisition period to phase encode each echo separately. Slice selection is achieved by a frequency selective pulse at the beginning of the sequence. Imaging speed is mainly limited by the phase encoding gradients' switching times and echo overlap when echo spacing is very short. This technique can produce a single-shot image of sub-millimeter resolution in 5 ms.

Journal Article↗
PubMed2005

Time-of-flight flow imaging using NMR remote detection.

A time-of-flight imaging technique is introduced to visualize fluid flow and dispersion through porous media using NMR. As the fluid flows through a sample, the nuclear spin magnetization is modulated by rf pulses and magnetic field gradients to encode the spatial coordinates of the fluid. When the fluid leaves the sample, its magnetization is recorded by a second rf coil. This scheme not only facilitates a time-dependent imaging of fluid flow, it also allows a separate optimization of encoding and detection subsystems to enhance overall sensitivity. The technique is demonstrated by imaging gas flow through a porous rock.

Journal Article↗
PubMed2003

PS1 Alzheimer's disease family with spastic paraplegia: the search for a gene modifier.

PS1 mutations are associated with classic Alzheimer's disease (AD); however, some families develop AD and spastic paraplegia (SP) with brain pathology characterized by Abeta cotton wool plaques. The authors report a variant AD family with the E280Q PS1 mutation. The fact that the same PS1 mutation can be found in patients with either variant or classic AD argues in favor of the presence of a genetic modifier. The authors have excluded that this modifier effect originates from coding sequence variations in three SP genes or from a second mutation in the other AD genes.

Alternative Splicing↗
PubMed2003

A method for rapid characterization of diffusion.

This paper describes a method to determine molecular displacements as a function of time in just two scans: one reference scan using the Carr-Purcell-Meiboom-Gill (CPMG) sequence, a second scan using a modified CPMG sequence (KCPMG). Measurements on free diffusion in bulk fluids, and on restricted diffusion in porous rock samples are reported. This technique can also be used for rapid measurement of flow and chemical exchange.

Journal Article↗
PubMed2003

Correlation functions for inhomogeneous magnetic field in random media with application to a dense random pack of spheres.

In porous media subject to applied magnetic field, the internal field arises out of susceptibility contrast of the constituents. We have examined the spatial inhomogeneity of the internal fields in a random pack of spheres using numerical computation. We find that the pair-correlation function of the internal field (K2) is a close approximation to the structure factor of the material, thus K2 can be used to characterize pore geometry. The magnetic length scale LambdaM exhibited in K2 is shown to be related to the fluid transport in the medium.

Anisotropy↗
PubMed2002

T(1)--T(2) correlation spectra obtained using a fast two-dimensional Laplace inversion.

Spin relaxation is a sensitive probe of molecular structure and dynamics. Correlation of relaxation time constants, such as T(1) and T(2), conceptually similar to the conventional multidimensional spectroscopy, have been difficult to determine primarily due to the absense of an efficient multidimensional Laplace inversion program. We demonstrate the use of a novel computer algorithm for fast two-dimensional inverse Laplace transformation to obtain T(1)--T(2) correlation functions. The algorithm efficiently performs a least-squares fit on two-dimensional data with a nonnegativity constraint. We use a regularization method to find a balance between the residual fitting errors and the known noise amplitude, thus producing a result that is found to be stable in the presence of noise. This algorithm can be extended to include functional forms other than exponential kernels. We demonstrate the performance of the algorithm at different signal-to-noise ratios and with different T(1)--T(2) spectral characteristics using several brine-saturated rock samples.

Journal Article↗
PubMed2002

Categories of coherence pathways for the CPMG sequence.

The CPMG sequence has been extremely useful for efficient measurements of NMR signal, spin-spin relaxation, and diffusion, particularly in inhomogeneous magnetic fields, such as when samples are outside the magnet and RF coil. Due to the inaccuracy of the pulses and the off-resonance effects, the CPMG echoes have contributions from the Hahn echo as well as signals that are similar to stimulated echoes. The systematic understanding of the CPMG pulse sequence requires decomposing the magnetization dynamics into different coherence pathways. In this paper, we describe a method to classify the CPMG coherence pathways and illustrate the nature of these types of pathways. This classification shows that direct echo and stimulated echoes are the major contribution to the CPMG signal. It also provides a clear understanding of the effect of restricted diffusion in porous media.

Journal Article↗