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Biomedical subjects

Q Chen

Publications and source records attributed to Q Chen.

At least 127 records · Page 7Linked to original sources
PubMed2001

Effect of lung inflation on arterial spin labeling signal in MR perfusion imaging of human lung.

The effect of lung inflation on arterial spin-labeling signal in lung perfusion is investigated. Arterial spin-labeling schemes, called alternation of selective inversion pulse (ASI) and its hybrid (HASI), which uses blood water as an endogenous, freely diffusible tracer, were applied to magnetic resonance (MR) perfusion imaging of the lung. Perfusion-weighted images of the lung from nine healthy volunteers were obtained at different time delays. There was a significant signal difference in ASI images acquired at different respiratory phases. Greater signal enhancement has been observed when the volunteers performed breath holding on end expiration than on end inspiration. This is in agreement with the normal physiologic effect of lung inflation on the pressure-flow relationship of pulmonary vasculature. ASI and HASI perfusion-weighted images show similar lung features and image quality. Preliminary results from pulmonary embolism patients indicate that arterial spin labeling is sensitive for the detection of areas of perfusion deficit. J. Magn. Reson. Imaging 2001;13:954-959.

Adult↗
PubMed2001

MR ventilation-perfusion imaging of human lung using oxygen-enhanced and arterial spin labeling techniques.

Magnetic resonance ventilation-perfusion (V/Q) imaging has been demonstrated using oxygen and arterial spin labeling techniques. Inhaled oxygen is used as a paramagnetic contrast agent in ventilation imaging using a multiple inversion recovery (MIR) approach. Pulmonary perfusion imaging is conducted using a flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER) technique. A half Fourier single-short turbo spin echo (HASTE) sequence is used for data acquisition in both techniques. V/Q imaging was performed in ten of the twenty volunteers, while either ventilation or perfusion was imaged in the other ten. This V/Q imaging scheme is completely noninvasive, does not involve ionized radiation, and shows promising potential for clinical use in the diagnosis of lung diseases such as pulmonary embolism.

Adult↗
PubMed2001

Evaluation of regional pulmonary perfusion using ultrafast magnetic resonance imaging.

An ultrafast MR sequence was used to measure changes in signal intensity during the first pass of intravascular contrast through the pulmonary circulation. From this, mean transit time, relative blood volume, and relative blood flow were calculated. Data were collected in an isogravitational plane in six healthy subjects. A slight but significant gradient in transit time was present, with faster times at the lung apex. A significant decrease in blood volume, compared with the lung base, was also seen in the apex. Significant decreases in blood volume and blood flow, compared with central portions of the lung, were seen in the lung periphery. Six additional subjects were imaged along a gravitational plane. A significant gradient in transit time was seen, with faster transit in dependent regions of the lung. MRI is able to evaluate regional differences in pulmonary perfusion with high spatial and temporal resolution. Magn Reson Med 46:166-171, 2001.

Blood Volume↗
PubMed2001

Mitochondrial respiration as an early marker of viability in cardiac-arrested rat lungs.

BACKGROUND: To evaluate the possibility of using pulmonary mitochondrial respiratory functions as early markers of ischemic lung viability in non-heart-beating donors, we investigated the roles of the mitochondria in ischemia-reperfusion injury of cardiac-arrested rat lungs. MATERIALS AND METHODS: Male Lewis rats were exposed to various periods of postmortem warm ischemia (0, 1, and 2 h at 21 degrees C). After a pulmonary artery flush and cold preservation (1 h at 4 degrees C), the rat lungs were reperfused using an isolated rat lung model. Each experimental group consisted of three subgroups (n = 7 in each subgroup) to examine pulmonary functions and biochemical measurements. RESULTS: The pulmonary functions after reperfusion were exacerbated after a 1-h postmortem warm ischemia and worsened after a 2-h warm ischemia following cardiac arrest. The mitochondrial respiratory control ratios already significantly decreased after a 1-h warm ischemia compared with nonischemic rat lungs, at which time the value was almost equivalent to that after a 2-h ischemia. There were no significant changes in the state 3 and 4 respiration of the mitochondria, the pulmonary lactate levels, or the lipid peroxide levels in the lung tissues and mitochondria during the first 1-h period of warm ischemia. The adenine nucleotide levels significantly decreased with the prolongation of the period of warm ischemia, but did not seem to be practical, because their determination required a much longer time than that of the mitochondrial respiratory control ratio. CONCLUSION: These results suggested that the mitochondrial respiratory control ratio may be a useful early marker for lung viability after cardiac arrest.

Adenine Nucleotides↗
PubMed2001

Presenilin binding protein is associated with neurofibrillary alterations in Alzheimer's disease and stimulates tau phosphorylation.

A novel presenilin binding protein, PBP, has recently been identified. PBP is localized to the particulate fraction of extracts of Alzheimer's disease brain but is found in the soluble fractions of brain from age matched normal controls. It is shown here that PBP is associated with neurofibrillary tangles in Alzheimer's disease brain. In addition, the expression of PBP increases the phosphorylation of tau in cultured cells. Therefore PBP may have a regulatory role in tau phosphorylation and in the genesis of neurofibrillary tangles.

Aged↗
PubMed2001

Division of modified Blalock-Taussig shunt at correction avoids distortion of the pulmonary artery.

BACKGROUND: Modified Blalock-Taussig (BT) shunt causing pulmonary artery distortion has been reported. This distortion may get worse after a corrective operation if the BT shunt is ligated, rather than divided. In this study we examined whether division of modified BT shunt at the time of corrective operation would allow pulmonary artery growth and avoid further distortion. METHODS: Fifteen patients who had modified BT shunts and subsequently had corrective operations performed by one surgeon between January 1980 to December 1990 were analyzed. The median time from the BT shunt to corrective operation was 46.3 months (range, 3 to 119 months). At the time of corrective procedure, the BT shunt was divided and metal clips were used to occlude and mark each end. At follow-up a chest roentgenogram was obtained and the distance between the two clips was measured. RESULTS: In all 15 patients measured sequentially the distances between the two clips increased steadily. CONCLUSIONS: Division of BT shunt at the time of corrective procedure reduces pulmonary artery distortion.

Angiography↗
PubMed2001

Quantitative analysis of three-dimensional-resolved fiber architecture in heterogeneous skeletal muscle tissue using nmr and optical imaging methods.

The determination of principal fiber directions in structurally heterogeneous biological tissue substantially contributes to an understanding of its mechanical function in vivo. In this study we have depicted structural heterogeneity through the model of the mammalian tongue, a tissue comprised of a network of highly interwoven fibers responsible for producing numerous variations of shape and position. In order to characterize the three-dimensional-resolved microscopic myoarchitecture of the intrinsic musculature of the tongue, we viewed its fiber orientation at microscopic and macroscopic length scales using NMR (diffusion tensor MRI) and optical (two-photon microscopy) imaging methods. Diffusion tensor imaging (DTI) of the excised core region of the porcine tongue resulted in an array of 3D diffusion tensors, in which the leading eigenvector corresponded to the principal fiber orientation at each location in the tissue. Excised axially oriented lingual core tissues (fresh or paraffin-embedded) were also imaged with a mode-locked Ti-Sapphire laser, (76 MHz repetition rate, 150 femtosecond pulse width), allowing for the visualization of individual myofibers at in situ orientation. Fiber orientation was assessed by computing the 3D autocorrelation of discrete image volumes, and deriving the minimal eigenvector of the center voxel Hessian matrix. DTI of the fibers, comprising the intrinsic core of the tongue, demonstrated directional heterogeneity, with two distinct populations of fibers oriented orthogonal to each other and in-plane to the axial perspective. Microscopic analysis defined this structural heterogeneity as discrete regions of in-plane parallel fibers, with an angular separation of ~80 degrees, thereby recapitulating the macroscopic angular relationship. This analysis, conceived at two different length scales, demonstrates that the lingual core is a spatially complex tissue, composed of repeating orthogonally oriented and in-plane fiber patches, which are capable of jointly producing hydrostatic elongation and displacement.

Algorithms↗
PubMed2001

Image reconstruction from electron and X-ray diffraction patterns using iterative algorithms: experiment and simulation.

The hybrid input-output iterative algorithm, which solves the phase problem for scattering from non-periodic objects, is reviewed for application to X-ray and electron diffraction data. Desirable convex constraints, including the sign of the scattering potential for electrons, and compact support, are discussed. The cases of complex and real exit-face wavefunctions, strong and weak phase objects, various supports, and the use of coherent focussed radiation are reviewed. Reconstruction of general complex objects requires accurate knowledge of the support, which should consist of two holes or a triangle in an opaque mask. The support boundaries should be as sharp as possible. Strong phase objects without absorption can be recovered if the support consists of one hole, is accurately known and has sufficiently sharp boundaries. Real and weak phase objects with absorption can be recovered without accurate knowledge of the support area if the support boundaries are sufficiently sharp and the support consists of one or more holes. A sign constraint on the scattering potential is used to recover weak phase objects. The experimental realization of theoretically desirable support conditions is discussed. A two-stage method of finding the support for complex objects is proposed. Experimental results from applying the Gerchberg-Saxton-Fienup HiO-algorithm to coherent electron diffraction patterns are presented, using specially made e-beam lithographed support structures. Images with a resolution of about 5 nm are thus recovered from the intensities alone in coherent electron diffraction patterns from non-periodic objects. Limitations of the present experiments are identified and suggestions made for development of both X-ray and electron work.

Journal Article↗
PubMed2001

The NF-kappaB inhibitor diethyldithiocarbamate (DDTC) increases brain cell death in a transient middle cerebral artery occlusion model of ischemia.

A transient ischemic middle cerebral artery occlusion model of stroke was used to examine the role of the transcription factor NF-kappaB in cell death as measured by DNA fragmentation and infarction volume. The left middle cerebral artery was occluded for either 30 min or 2 h in rats. One set of animals was pretreated with diethyldithiocarbamate (DDTC), an inhibitor of NF-kappaB, 30 min prior to reperfusion. The animals were reperfused and allowed to survive for 2 or 7 days. DNA fragmentation was assayed by in situ end labeling in the stroke core and penumbral regions. Specific cortical and subcortical regions were measured using quantitative image analysis. DNA fragmentation was seen only on the ischemic side of the brains in all cases. Overall, the DDTC-treated groups showed significantly increased DNA fragmentation within the ischemic side compared to the saline control groups. DDTC treatment also caused an increase in stroke volume based on triphenyl tetrazolium chloride staining. Electrophoretic mobility shift assays showed NF-kappaB activation peaking 15 min following reperfusion and that this activation was blocked by the DDTC treatment. This study suggests that the use of NF-kappaB inhibitors to block cell death following stroke needs to be carefully examined because global inhibitors may not promote neuronal survival.

Animals↗
PubMed2001

Pulmonary ventilation: dynamic MRI with inhalation of molecular oxygen.

We have recently demonstrated a non-invasive technique to visualize pulmonary ventilation in humans with inhalation of molecular oxygen as a paramagnetic contrast agent. In the current study, T1 shortening of lung tissue by inhalation of oxygen was observed (P<0.001). The T1 values of lung tissue were also correlated with arterial blood oxygen pressure (PaO(2)) in a pig, resulting in excellent correlation (r(2)=0.997). Dynamic wash-in and wash-out MR ventilation images as well as dynamic wash-in wash-out signal intensity versus time curves were obtained. The mean wash-in decay constants were 26.8+/-10.5 s in the right lung, and 26.3+/-9.5 s in the left lung. The mean wash-out decay constants were 23.3+/-11.3 s in the right lung, and 20.8+/-10.5 s in the left lung. Dynamic assessment of pulmonary ventilation is feasible using oxygen-enhanced MR imaging, which could provide dynamic MR ventilation-perfusion imaging in combination with recently developed MR perfusion imaging technique, and thus a robust tool for the study of pulmonary physiology and pathophysiology.

Animals↗
PubMed2001

Oxygen-enhanced magnetic resonance ventilation imaging of lung.

The oxygen-enhanced magnetic resonance (MR) ventilation imaging is a new technique, and the full extent of its physiological significance has not been elucidated. This review article includes background on (1) respiratory physiology; (2) mechanism and optimization of oxygen-enhanced MR imaging technique; (3) recent applications in animal and human models; and (4) merits and demerits of the technique in comparison with hyperpolarized noble gas MR ventilation imaging. Application of oxygen-enhanced MR ventilation imaging to patients with pulmonary diseases has been very limited. However, we believe that further basic studies, as well as clinical applications of this new technique will define the real significance of oxygen-enhanced MR ventilation imaging in the future of pulmonary functional imaging and its usefulness for diagnostic radiology.

Animals↗
PubMed2001

Effects of using consumer and expert ratings of an activities of daily living scale on predicting functional outcomes of postacute care.

To test the effects of using preference weights for activities of daily living (ADL) outcome measures derived from different sources, data from a large study of the outcomes of postacute care (PAC study) were analyzed using two different weightings for the ADL measures. Both were developed using the same magnitude estimation technique; one from a panel of long-term care experts (the expert rating system); the other from a group of elderly Medicare beneficiaries (the consumer rating system). Neither group was directly involved in the PAC study. Although ADL scores generated by both rating systems were highly correlated prior to hospitalization and at hospital discharge, the consumer and expert rating systems generated significantly different functional outcomes measured by the change of ADL scores with a few exceptions. Compared to the consumer rating system, the expert rating system generated a greater change in functional outcomes at each of three follow-up time points after hospital discharge. This study suggests that the choice of weights for ADL items is important.

Activities of Daily Living↗
PubMed2001

Gene therapy for hepatocellular carcinoma based on tumour-selective suicide gene expression using the alpha-fetoprotein (AFP) enhancer and a housekeeping gene promoter.

The aim of this study was to examine whether the human alpha-fetoprotein (AFP) enhancer could be used to induce hepatocellular carcinoma (HCC)-selective expression of the herpes simplex virus thymidine kinase (HSV-tk) gene which is under the control of the phosphoglycerate kinase (pgk) promotor. The human AFP enhancer was linked with the non-tissue-specific, human housekeeping pgk promoter in a retroviral vector. AFP-producing HCC cells infected with retroviruses carrying the HSV-tk gene under the control of the AFP enhancer/pgk promoter were much more susceptible to the prodrug, ganciclovir (GCV), than those infected with the same retroviruses without the AFP enhancer. Non-HCC cells infected with retroviruses carrying the HSV-tk gene under the control of the AFP enhancer/pgk promoter exhibited profoundly increased resistance to GCV compared with those infected with the same retroviruses without the AFP enhancer. Northern blot analysis revealed that the AFP enhancer caused enhanced HSV-tk expression in AFP-producing HCC cells and suppressed HSV-tk expression in non-HCC cells. Our results indicate that the AFP enhancer could give HCC selectivity to the pgk promoter, and that this novel strategy may be useful for HCC-selective cancer gene therapy.

Blotting, Northern↗
PubMed2001

Acute pulmonary thromboembolism complicating pneumonectomy: successful operative management.

Pulmonary thromboembolism after pneumonectomy carries high fatality. Here we present a case of acute embolism to the left pulmonary artery with thrombus in the right atrium and inferior vena cava following right pneumonectomy. Diagnosis was made clinically and radiologically before proceeding to emergency surgery. Thromboembolectomy was successfully performed on cardiopulmonary bypass and the patient was subsequently discharged home after uneventful recovery.

Cardiopulmonary Bypass↗
PubMed2001

Mitral valve replacement with mechanical prostheses in children: improved operative risk and survival.

OBJECTIVE: The purpose of this study was to assess the early and late outcome following mitral valve replacement (MVR) with mechanical prostheses in children. PATIENTS AND METHODS: Between 1981 and 2000, 44 consecutive children (mean age 6.8+/-4.7 years, 2 months--16 years) underwent mechanical MVR in Southampton. Twenty-three children were less than 5-years-old and nine were infants. Disease aetiology was congenital in 37, rheumatic in four, infective in two and Marfan's syndrome in one. Mitral regurgitation was present in 36 and mitral stenosis in eight. Concomitant procedures were performed in 13, including aortic valve replacement (AVR) in seven. Follow-up was complete (mean 6.4+/-4.8 years, 1 month--18.1 years). RESULTS: The overall operative mortality was 14% (six patients). Before and after 1990 operative mortality was 31 vs 3.6% (P=0.02). From 1990, operative mortality for infants was zero out of six, for children less than 5-years-old was one out of 16 (one death after emergency AVR and MVR) and for older children it was 0/12. Seven children experienced valve or anticoagulation treatment-related events and eight had a mitral valve re-operation. Ten-year freedom from thromboembolism, prosthetic valve infection, bleeding, paravalvular leak and a mitral valve re-operation was 92.8+/-5.2, 97.3+/-2.7, 97.7+/-2.3, 97.2+/-2.7 and 75+/-9.7%, respectively. Overall 10-year survival was 78+/-7% (four late deaths); for children under vs over 5 years it was 61+/-11 vs 95.2+/-4.6% (P=0.02), for atrio-ventricular septal defect (AVSD) vs other pathology 55+/-15 vs 89+/-6.1% (P=0.05) and for those operated before 1990 vs after 1990 it was 63+/-8.1 vs 86+/-8.2% (P=0.04). CONCLUSIONS: Mechanical MVR, in the current era, carries a low operative risk across the spectrum of paediatric age. Late survival is better for older children and those having no-AVSD pathology but it has improved substantially during the 1990s irrespective of age and disease aetiology.

Age Factors↗
PubMed2001

Is there still a place for open surgical valvotomy in the management of aortic stenosis in children? The view from Southampton.

OBJECTIVE: The most appropriate management of aortic stenosis (AS) in children remains controversial. The purpose of this study was to determine the outcome following open valvotomy for AS in children. METHODS: Ninety-seven consecutive, unselected, children (mean age 3.2 +/- 3.6 years, 1 day--15 years) underwent an open valvotomy for critical (n=36) or severe (n=61) AS between 1979 and 2000 in Southampton. Twenty-six were neonates (1--31 days), 27 were infants (1--12 months) and 44 were older children (1--15 years). Mean follow-up was 10 +/- 5.4 years, 1 month--21.9 years. RESULTS: Two neonates died early giving an overall operative mortality of 2.1% (7.7% for the neonates and 0% for infants and older children). The mean aortic gradient was reduced from 76 to 24.5 mmHg (P < 0.0001). Residual or recurrent AS occurred in 17 patients and severe aortic regurgitation in eight patients. Kaplan--Meier 10-year freedom from residual or recurrent AS was 83.1 +/- 4.7% and from severe aortic regurgitation was 95.3 +/- 2.7%. Twenty-five patients required an aortic re-operation or re-intervention, 18 of whom had an aortic valve replacement (AVR) (mean valve size 21.8 +/- 0.9 mm, range 21--25 mm). Ten-year freedom from any aortic re-operation or re-intervention was 78.4 +/- 5.2% and from AVR was 85.1 +/- 4.6%. There were ten late deaths. Overall 10-year survival, including hospital mortality, was 90.2 +/- 3.1% (69.7 +/- 9.7% for the neonates, 92 +/- 5.4% for the infants and 100% for older children, (P < 0.0001). Ten-year survival for children with isolated AS (n = 69) was 100% and for those with associated cardiovascular problems (n = 28) was 67.3 +/- 8.9% (P < 0.0001). All survivors are in New York Heart Association functional class I. CONCLUSIONS: Open valvotomy remains the gold standard in the management of AS in neonates, infants and older children. It is associated with low operative mortality and provides lengthy freedom from recurrent AS and regurgitation. Re-operations are common but if AVR is required, implantation of an adult-sized prosthesis is usually possible. There is a late death-hazard for those with severe associated lesions, but the survival prospects for the patients with isolated AS are excellent.

Adolescent↗
PubMed2001

Fourier-transform Raman and infrared spectroscopic analysis of dipyrrinones and mesobilirubins.

The Fourier-transform Raman (FT-Raman), infrared (FT-IR), and UV-visible absorption spectra of four dipyrrinones and two mesobilirubins have been investigated in the solid state and in CH2Cl2 solutions. A detailed spectral analysis, assignment and discussion of these spectra are presented. The bands at 1735-1738, 1691-1707 and 1359-1377 cm(-1) which were assigned to the stretching vibrations of the C-O-C and C-O-H and symmetric deformation of C-H bonds, respectively, can act as a marker to distinguish the compounds of this class. The striking differences between the spectra of the compounds suggest that mesobilirubin XIIIalpha is tending to adopt as ridge-tile conformation, rather than linear conformation.

Bilirubin↗