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Peng Qu

Publications and source records attributed to Peng Qu.

15 recordsLinked to original sources
PubMed2006

Potential advantage of higher-order modes of birdcage coil for parallel imaging.

The potential advantages of the higher-order resonant modes of a low-pass birdcage coil for parallel imaging are investigated using FDTD simulations in a spherical phantom. Better parallel imaging performance can be achieved in axial planes than in sagittal planes. If more modes are employed, the average g-factor (gmean) and maximum g-factor (gmax) will be improved for a specific acceleration factor (R). G-factor performance at 3 T (gmean=1.79, gmax=3.55) and 7 T (gmean=1.60, gmax=2.45) can be achieved even with an acceleration factor as high as four when all six order modes of 12-rung low-pass birdcage coil are incorporated for imaging on a mid-axial plane. For a specific number of channels, the optimum combination of corresponding modes can be obtained for different acceleration factors. Based on the g-factor and SNR performance, the total degenerate multi-mode birdcage coil with six order resonant modes has better homogeneous coverage and SENSE performance than the 8-element phased array coil, although requiring fewer channels. In addition, the dielectric effects at high field can improve the parallel imaging performance.

Journal Article↗
PubMed2006

Design of an inductively decoupled microstrip array at 9.4 T.

By independent control of the phases and amplitudes of its elements, the microstrip transmission-line array can mitigate sample-induced RF non-uniformities, and has been widely used as the transceiver in parallel imaging applications. One major challenge in implementing the microstrip array is the reduction of mutual coupling among individual elements. The low-input impedance preamplifier is commonly used for the decoupling purpose. However, it is impractical in the transceiver array design. Although interconnecting capacitors can be utilized to reduce the mutual coupling, they only efficiently work for the neighbor elements. In addition, this approach is impractical at fields higher than 300 MHz, in which the required decoupling capacitance is commonly less than 0.5 pF. We propose a novel decoupling approach by using decoupling inductors in this study. Due to the fact that the decoupling inductance is independent of the resonant frequency, the microstrip arrays can be well decoupled at ultra-high fields. To verify the proposed approach, an eight-channel microstrip array is fabricated and tested at 9.4 T. For this prototype, couplings between elements are significantly reduced by using the interconnecting inductors. The phantom experiment shows that the inductively decoupled microstrip array has good parallel imaging performance.

Equipment Design↗
PubMed2006

Electric potential induced dissociation of hybridized DNA with hairpin motif immobilized on silicon surface.

DNA probes were immobilized on silicon surfaces through ester condensation between the -COOH group on the surface and the terminal -OH group in the oligonucleotide, and the surface density of DNA probes against the concentration of immobilization solution was measured by radioactive labeling. The dissociation of DNA duplex on the surface by an electric potential was studied with the scanning potential hairpin denaturation/dissociation (SPHD). The influence of the stem length in the hairpin probe on the SPHD curve was systematically investigated. It was found that the capability of discrimination on single nucleotide polymorphism (SNP) by a hairpin probe was related to the free energy of formation of the secondary structure in the probe (DeltaG(ss)). In our system, when DeltaG(ss) was around -3 kcal/mol, an optimal recognition of SNP was reached and the SPHD curve was sigmoid. In contrast, the equivalent SPHD curve from a linear probe was exponential-decay alike with a poor discrimination of SNP. The concentration dependent experiments showed good linearity between the melting potential and logarithm of target concentration in the range of 1 x 10(-9) to 5 x 10(-7) M.

DNA Probes↗
PubMed2006

Discrepancy-based adaptive regularization for GRAPPA reconstruction.

PURPOSE: To develop a novel regularization method for GRAPPA by which the regularization parameters can be optimally and adaptively chosen. MATERIALS AND METHODS: In the fit procedures in GRAPPA, the discrepancy principle, which chooses the regularization parameter based on a priori information about the noise level in the autocalibrating signals (ACS), is used with the truncated singular value decomposition (TSVD) regularization and the Tikhonov regularization, and its performance is compared with the singular value (SV) threshold method and the L-curve method, respectively by axial and sagittal head imaging experiments. RESULTS: In both axial and sagittal reconstructions, normal GRAPPA reconstruction results exhibit a relatively high level of noise. With discrepancy-based choices of parameters, regularization can improve the signal-to-noise ratio (SNR) with only a very modest increase in aliasing artifacts. The L-curve method in all of the reconstructions leads to overregularization, which causes severe residual aliasing artifacts. The 10% SV threshold method yields good overall image quality in the axial case, but in the sagittal case it also leads to an obvious increase in aliasing artifacts. CONCLUSION: Neither a fixed SV threshold nor the L-curve are robust means of choosing the appropriate parameters in GRAPPA reconstruction. However, with the discrepancy-based parameter-choice strategy, adaptively regularized GRAPPA can be used to automatically choose nearly optimal parameters for reconstruction and achieve an excellent compromise between SNR and artifacts.

Algorithms↗
PubMed2005

Convergence behavior of iterative SENSE reconstruction with non-Cartesian trajectories.

In non-Cartesian SENSE reconstruction based on the conjugate gradient (CG) iteration method, the iteration very often exhibits a "semi-convergence" behavior, which can be characterized as initial convergence toward the exact solution and later divergence. This phenomenon causes difficulties in automatic implementation of this reconstruction strategy. In this study, the convergence behavior of the iterative SENSE reconstruction is analyzed based on the mathematical principle of the CG method. It is revealed that the semi-convergence behavior is caused by the ill-conditioning of the underlying generalized encoding matrix (GEM) and the intrinsic regularization effect of CG iteration. From the perspective of regularization, each iteration vector is a regularized solution and the number of iterations plays the role of the regularization parameter. Therefore, the iteration count controls the compromise between the SNR and the residual aliasing artifact. Based on this theory, suggestions with respect to the stopping rule for well-behaved reconstructions are provided. Simulated radial imaging and in vivo spiral imaging are performed to demonstrate the theoretical analysis on the semi-convergence phenomenon and the stopping criterion. The dependence of convergence behavior on the undersampling rate and the noise level in samples is also qualitatively investigated.

Algorithms↗
PubMed2005

Tailored utilization of acquired k-space points for GRAPPA reconstruction.

The generalized auto-calibrating partially parallel acquisition (GRAPPA) is an auto-calibrating parallel imaging technique which incorporates multiple blocks of data to derive the missing signals. In the original GRAPPA reconstruction algorithm only the data points in phase encoding direction are incorporated to reconstruct missing points in k-space. It has been recognized that this scheme can be extended so that data points in readout direction are also utilized and the points are selected based on a k-space locality criterion. In this study, an automatic subset selection strategy is proposed which can provide a tailored selection of source points for reconstruction. This novel approach extracts a subset of signal points corresponding to the most linearly independent base vectors in the coefficient matrix of fit, effectively preventing incorporating redundant signals which only bring noise into reconstruction with little contribution to the exactness of fit. Also, subset selection in this way has a regularization effect since the vectors corresponding to the smallest singular values are eliminated and consequently the condition of the reconstruction is improved. Phantom and in vivo MRI experiments demonstrate that this subset selection strategy can effectively improve SNR and reduce residual artifacts for GRAPPA reconstruction.

Algorithms↗
PubMed2005

Expression of CCL21 and 5'-Nase on pancreatic lymphatics in nonobese diabetic mice.

OBJECTIVES: To obtain better insight into the modulation of lymphatic endothelial cells during the autoimmune process, alterations of the structures and histochemical features in the pancreatic lymphatics were studied in nonobese diabetic (NOD) mice. METHODS: The expression of secondary lymphoid tissue chemokine (SLC/CCL21) and 5'-nucleotidase (5'-Nase) on pancreatic lymphatics was examined by histochemistry and immunoblot in NOD mice. RESULTS: As insulitis developed, the increased expression of CCL21 and podoplanin on pancreatic lymphatics was consistent with the increased number of cytoplasmic protrusions and vesicles, whereas 5'-Nase activity of lymphatics seemed to become decreased. The expression of CCL21 protein also showed an age-dependent increase in NOD pancreas, even though it was undetectable in normal controls. During the period of severe infiltration, reaction products of CCL21 and podoplanin were detected in the nucleus and cytoplasm of lymphatic endothelial cells. Dendritic cells and T lymphocytes frequently penetrated through the slender walls of lymphatics and adhered to the lymphatic luminal surfaces, precipitating with few 5'-Nase particles. In contrast to wild-type NOD mice, complete Freund adjuvant administration reduced CCL21 expression in NOD pancreas, suppressing the entry of activated dendritic cells into lymphatics. CONCLUSIONS: These findings suggest that CCL21 and 5'-Nase may be involved in the interaction between infiltrating cells and lymphatic vessels to induce the functional changes of lymphatic endothelial cells during insulitic and diabetic development.

5'-Nucleotidase↗
PubMed2005

[The effect of TLR4/NF-kappaB activation and LOX-1 on monocyte adhesion to endothelium].

OBJECTIVE: Recent studies have shown that Toll-like receptor 4 (TLR4), a mediator of for innate immune responses, is involved in the initiation and progression of atherosclerosis. TLR4 activation mediates the expression of chemokines and cytokines through activation of NF-kappaB. We investigated the expression of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), intercellular adhesion molecule-1 (CAM-1), E-selectin induced by TLR4/NF-kappaB in human umbilical vein endothelial cells (HUVECs), and their effects on adhesion of monocyte to HUVECs. METHODS: HUVECs were incubated with purified LPS for 24 h. TLR4, LOX-1, ICAM-1, E-selectin mRNA were measured by RT-PCR; the protein expression of TLR4, LOX-1 and activation of NF-kappaB were detected by Western blot; the adhesive percentage between HUVECs and monocytes was determined by direct counting. RESULTS: LPS (1 mg/L) not only enhanced expression of TLR4, activation of NF-kappaB and induction of LOX-1, ICAM-1, E-selectin expression, but also increased the percentage of monocyte adhesion to endothelium. Pretreatment of HUVECs with anti-LOX1, anti-ICAM-1 or anti E-selectin antibodies partly abolished the increase in monocyte adhesion to endothelium. NF-kappaB inhibitor CAPE suppressed LPS-induced these effects. CONCLUSION: TLR4/NF-kappaB plays an important role in monocyte-endothelium adhesion partly through upregulation of LOX-1, ICAM-1 and E-selection expression, which may provide a target for the treatment of atherosclerosis.

Cell Adhesion↗
PubMed2005

[Polarographic behavior and determination of glimepiride].

AIM: To establish a polarographic method of parallel catalytic hydrogen wave for determination of glimepiride. METHODS: The catalytic wave of glimepiride in the presence of K2S2O8 was used to improve the analytical sensitivity. The rapid determination of glimepiride was done by linear single sweep polarography. RESULTS: The catalytic hydrogen wave of glimepiride was measured at ca. -1.36 (vs SCE) in 0.09 mol x L(-1) Na2B4O7-KH2PO4 (pH 6.24 +/- 0.1) supporting electrolyte. When 1.0 x 10(-2) mol x L(-1) K2S2O8 was present, the current increased by 25 times, and the peak potentioal was unchanged, producing a more sensitive parallel catalytic hydrogen wave. The peak current of the parallel catalytic hydrogen wave was rectilinear to the glimepiride concentration in the range 1.0 x 10(-7) - 4.2 x 10(-5) mol x L(-1) (r = 0.9990, n = 9). The detection limit was 5.0 x 10(-8) mol x L(-1). CONCLUSION: The proposed method could be applied to the determination of glimepiride in pharmaceuticals without preliminary separation.

Catalysis↗
PubMed2004

Expression of VEGFR-3 and 5'-nase in regenerating lymphatic vessels of the cutaneous wound healing.

The vascular endothelial growth factor-C (VEGF-C), a specific lymphangiogenic growth factor, raises new questions and perspectives in studying lymphatic development and regeneration. Wound healing skins in mice were processed for 5'-nucleotidase (5'-Nase) and VEGFR-3 (the receptor of VEGF-C) histochemical staining to distinguish lymphatics from blood capillaries and to analyze lymphangiogenesis. In the wounds of 3-5 days after injury, anti-VEGFR-3 immunopositive signals unevenly appeared in 5'-Nase-positive lymphatic vessels in the subcutaneous tissue. A few small circular and irregular lymphatic-like structures with VEGFR-3 expression scattered in the dermal and subcutaneous tissues. Between days 7 and 15 of the wounds, numerous accumulated vasculatures were stained for 5'-Nase and PECAM-1, extending irregularly along the wound edge. Von Willebrand factor was expressed in the endothelial cells of blood vessels and lymphatics in the subcutaneous tissue. Ultrastructural changes of lymphatic vessels developed at different stages, from lymphatic-like structures to newly formed lymphatic vessels with an extremely thin and indented wall. Endothelial cells of the lymphatic vessel were eventually featured by typical intercellular junctions, which deposited with reaction products of VEGFR-3 and 5'-Nase-cerium but lacked VEGF-C expression. The present findings indicate that VEGF-C-induced lymphangiogenesis occurs from the subcutaneous to the dermis along the wound healing edge, especially in the dermal-subcutaneous transitional area, favorable to growth of regenerating lymphatic vessels.

5'-Nucleotidase↗
PubMed2004

Study on pancreatic lymphatics in nonobese diabetic mouse with prevention of insulitis and diabetes by adjuvant immunotherapy.

The present study has investigated the relationship between pancreatic lymphatics, infiltrating cells, and insulitic development after a single injection of complete Freund's adjuvant (CFA) given at an early age in the nonobese diabetic (NOD) mice. No CFA-treated NOD mice developed hyperglycemia, whereas most CFA-untreated mice died of diabetes at the age of 20-30 weeks. In untreated NOD mice, the increased infiltration of dendritic cells (DCs) and T-lymphocytes into the pancreatic islets appeared to be consistent with the increased expression of the secondary lymphoid chemokine (CCL21) and CD(31) by the endothelial cell lining of inter- and intralobular lymphatics. As the infiltration became severe, the reaction products of CCL21 and CD(31) were distributed in the nucleus and cytoplasm of lymphatic endothelial cells (LECs), through which DCs and T-lymphocytes migrated frequently. Administration of CFA reduced the number of infiltrating DCs and T-lymphocytes, but did not affect macrophage infiltration. The peri-insulitis occurred in numerous islets of CFA-treated NOD mice without the appearance of the intraislet infiltration and islet-associated lymphoid-like tissues. Furthermore, significant suppression of CCL21 and CD(31) was demonstrated on the infiltrating cells to the islets and islet-associated lymphatics. The abluminal endothelial cell lining of lymphatic vessels exhibited weaker immunoreactivity of CCL21 and CD(31) in comparison with the luminal surfaces. The reaction product of 5'-nucleotidase (5'-Nase) was evenly deposited on LECs, which were the absence of open junctions, cytoplasmic protrusions, and vesicles. CFA treatment influenced the migratory processes of the infiltrating cell, which were closely related with structural changes of pancreatic lymphatics and inhibited insulitic development. These findings suggest that in CFA-treated NOD mice, the suppression of insulitis and prevention of diabetes are secondary to the functional modulation of pancreatic lymphatics and infiltrating cells.

5'-Nucleotidase↗
PubMed2004

[A novel catalysis kinetics fluorimetry system for the determination of eliminating ratio of Chinese traditional medicine for *OH].

Benzoic acid with weak fluorescence may react on *OH, and then products with intense fluorescence are made. Extractives of Chinese traditional medicine may eliminate *OH in solution, and reduce the amounts of the products. Then, the increased level of fluorescence of the products in solution will be lowered. Based on this principle, a novel catalysis kinetics fluorimetry system for the determination of eliminating ratio of Chinese traditional medicine for *OH was developed. When the concentration of traditional Chinese herbal drugs was 4.0 mg (dry weight) x mL(-1), the eliminating ratios of Viola yedoensis, Atrctylodes chinensis and Paeonia veitchii were 60.8%, 40.1% and 94.3%, respectively. The results obtained by this method are in good agreement with those obtained by spectrophotometry.

Benzoic Acid↗
PubMed2002

The relation between left ventricular geometric patterns and left ventricular midwall mechanics in hypertensive patients.

To evaluate the alteration of myocardial contractility in hypertensive patients with different left ventricular geometric patterns by the end-systolic stress-midwall fractional shortening relation. Echocardiography was applied to study the left ventricular geometry and cardiac function among 117 cases of essential hypertension, with 45 normal cases as control(s). Left ventricular mass index (LVMI) and relative wall thickness (RWT) were calculated using echocardiographic data. All patients were divided into four kinds of left ventricular geometry pattern based on LVMI and RWT. Patients of the eccentric hypertrophy group suffered the most serious damage of left ventricular systolic function. Myocardial contractility shown by end-systolic stress-midwall fractional shortening relation was significantly decreased in the concentric remodeling group, eccentric hypertrophy group and concentric hypertrophy group, and those with concentric hypertrophy showed the worst contractility. The degree of myocardial contractility damage was different in patients with different left ventricular geometric patterns. Geometric changes may have compensated for the reduction of myocardial contractility in some phases in order to maintain the normal pump function.

Echocardiography↗
PubMed2002

Relationship between cardiomyocyte cell death and cardiac function during hypertensive cardiac remodelling in Dahl rats.

The exact mechanisms responsible for the progression of heart failure remain unclear. We investigated the in vivo relationship between the incidence of apoptotic cell death and left ventricular function serially from the beginning of hypertension to decompensated heart failure in Dahl salt-sensitive rats. Dahl salt-resistant and Dahl salt-sensitive rats were fed on a high-salt diet from 6 weeks of age. Systolic blood pressure was recorded by the tail-cuff method every week. Cardiac function in vivo was evaluated by echocardiography and cardiac catheterization. Cardiomyocyte apoptosis was detected by the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) method. The gene expression of Bax, Bcl-2 and Bcl-xL was analysed by Northern blotting. The TUNEL method revealed that the incidence of cardiomyocyte apoptosis was significantly increased in the hearts of 18-week-old Dahl salt-sensitive rats (apoptotic index 1.3 +/- 0.1%). Northern blot analysis revealed that the Bcl-xL mRNA level increased gradually during the progression towards heart failure. In conclusion, these data suggest that cardiomyocyte apoptosis is a terminal event, and plays a role as an aggravating factor in the vicious cycle of heart failure.

Analysis of Variance↗