Biomedical subjects

T Q Li

Publications and source records attributed to T Q Li.

At least 19 recordsLinked to original sources

PubMed2006

Effects of pH, organic acids, and inorganic ions on lead desorption from soils.

The desorption characteristics of lead in two variable charge soils (one developed from Arenaceous rock (RAR) and the other derived from Quaternary red earths (REQ)) were studied, and the effects of pH value, organic acid, and competitive ions were examined. Desorption of Pb(2+) decreased from nearly 100.0 to 20.0% within pH 1.0-4.0 in both soils, and then the decrease diminished at pH > 4.0. Organic ligands at relatively low concentrations (< or =10(-3) mol L(-1)) slightly inhibited Pb(2+) desorption, but enhanced Pb(2+) desorption at higher concentrations. In this study, citric acid or acetic acid at higher concentrations (>10(-3) mol L(-1)) had the greatest improvement of Pb(2+) desorption, followed by malic acid; and the smallest was oxalic acid. Desorption of the adsorbed Pb(2+) increased greatly with increasing concentrations of added Cu(2+) or Zn(2+). Applied Cu(2+) increased Pb(2+) desorption more than Zn(2+) at the same loading.

Acetic Acid↗

PubMed2004

Assessment of hepatic iron content using magnetic resonance imaging.

Numerous studies over the past decade have shown that magnetic resonance imaging (MRI) has great potential for detecting and quantifying the distribution of iron in the body. With MRI, tissue iron is indirectly identified by the paramagnetic effects of iron on the shortening of water proton MR relaxation times. However, these effects are complex and involve a number of factors, such as tissue hydration, distribution of iron and water within the tissue, and the amount of iron loading within the iron storage molecules. A coherent understanding of how these factors influence the MRI signal is still lacking. The dependence on experimental conditions, such as magnet field strength, pulse sequences, and data acquisition parameters, further complicates iron quantification with MRI. To date, there is no generally accepted MRI approach available for clinical application. In this review, we first explain the basic MR relaxation mechanisms underlying the detection of iron with MRI. We then review the literature on empirical MRI studies of hepatic iron. Finally, we summarize the critical issues that need to be addressed to develop MRI techniques for non-invasive iron detection in the body.

Humans↗

PubMed2004

Adsorption-desorption characteristics of lead in variable charge soils.

Adsorption desorption processes of Pb at contaminated levels in two variable charge soils were investigated. The red soil (RAR) developed on the Arenaceous rock (clayey, mixed siliceous thermic typic Dystrochrept) adsorbed more Pb2+ than the red soil (REQ) derived from the Quaternary red earths (clayey, kaolinitic thermic plinthite Aquult). The maximum adsorption values (Xm) that were obtained from the simple Langmuir model were 52.6 mmol Pb2+ kg(-1) soil and 29.9 mmol Pb2+ kg(-1) soil, respectively, for the RAR and REQ. Adsorption of Pb2+ decreased soil pH by 1.10 unit for the RAR soil and 1.21 unit for the REQ soil at the highest loading. The adsorption equilibrium pH of RAR was higher than that of REQ at the same Pb2+ concentration. The distribution coefficient (Kd) of Pb in the soils decreased exponentially with increasing Pb2+ loading. Most of the adsorbed Pb2+ in the soils was not desorbed in the 0.01 mol L(-1) NaNO3 solution. After five successive extractions with NaNO3, only 0-11% of the total adsorbed Pb2+ in the RAR soil was desorbed and the corresponding value of the REQ soil was 0-19%, indicating that the RAR soil had a greater affinity for Pb2+ than the REQ soil at the same Pb2+ loading. Different mechanisms might be involved in Pb2+ adsorption/desorption at different levels of Pb2+ loading and between the two soils.

Adsorption↗

PubMed2001

Current awareness in NMR in biomedicine.

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of NMR in biomedicine. Each bibliography is divided into 9 sections: 1 Books, Reviews ' Symposia; 2 General; 3 Technology; 4 Brain and Nerves; 5 Neuropathology; 6 Cancer; 7 Cardiac, Vascular and Respiratory Systems; 8 Liver, Kidney and Other Organs; 9 Muscle and Orthopaedic. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.

Animals↗

PubMed2001

A comparative fMRI study: T2-weighted imaging versus R2 mapping.

Functional magnetic resonance imaging experiments were performed in human motor cortex at 1.5 T by sampling two successive gradient recalled echo images in a single shot. Several aspects of brain mapping methods based on T2*-weighted imaging and R2* mapping were quantitatively compared. These include the detected activation volume, functional contrast (FC), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Studies based on the R2* mapping method have the following potential advantages: maximum functional contrast, less dependent on TE; and reduced inflow effects. R2* mapping produced the highest functional contrast, but not the largest activation volume due to the reduced signal-to-noise ratio and inflow effects. The sensitivity for activation detection is significantly correlated with the contrast-to-noise ratio, which is determined by both the SNR and FC.

Adult↗

PubMed2001

Diffusion tensor trace mapping in normal adult brain using single-shot EPI technique. A methodological study of the aging brain.

PURPOSE: To quantify age-related changes of the average diffusion coefficient value in normal adult brain using orientation-independent diffusion tensor trace mapping and to address the methodological influences on diffusion quantification. MATERIAL AND METHODS: Fifty-four normal subjects (aged 20-79 years) were studied on a 1.5-T whole-body MR medical unit using a diffusion-weighted single-shot echo-planar imaging technique. Orientation-independent diffusion tensor trace maps were constructed for each subject using diffusion-weighted MR measurements in four different directions using a tetrahedral gradient combination pattern. The global average (including cerebral spinal fluid) and the tissue average of diffusion coefficients in adult brains were determined by analyzing the diffusion coefficient distribution histogram for the entire brain. Methodological influences on the measured diffusion coefficient were also investigated by comparing the results obtained using different experimental settings. RESULTS: Both global and tissue averages of the diffusion coefficient are significantly correlated with age (p<0.03). The global average of the diffusion coefficient increases 3% per decade after the age of 40, whereas the increase in the tissue average of diffusion coefficient is about 1% per decade. Experimental settings for self-diffusion measurements, such as data acquisition methods and number of b-values, can slightly influence the statistical distribution histogram of the diffusion tensor trace and its average value. CONCLUSION: Increased average diffusion coefficient in adult brains with aging are consistent with findings regarding structural changes in the brain that have been associated with aging. The study also demonstrates that it is desirable to use the same experimental parameters for diffusion coefficient quantification when comparing between different subjects and groups of interest.

Adult↗

PubMed2001

[Appraisal and analysis of heat removing characteristic of liquid cooling garment using thermal manikin].

OBJECTIVE: To analyze the relation of the design parameters and appraise the heat removing characteristic of liquid cooling garment (LCG) using thermal manikin. METHOD: To appraise the design of LCG, the thermal manikin wearing LCG and heat insulation garment was put in the temperature cabin, then the inlet and outlet temperature of cooling liquid in the LCG were measured and the heat removed was calculated. RESULT: The relationship between the design parameters and heat removed, and also that between the design parameters and temperature ratio efficiency were found. And the heat removed was calculated. It provided a reasonable basis for appraisal of LCG. CONCLUSION: The design of the LCG for the EVA space suit was found to be reasonable. The flow rate regulation range was too narrow, and the change of heat removing capacity depended on the change of inlet temperature.

Body Temperature Regulation↗

PubMed2001

[A study on physical characteristics of porous plates for water sublimator].

Objective. To investigate the development method of porous plate, the key part of water sublimator, and its main physical characteristics. Method. Technical parameters of porous plates used in water sublimator were analyzed. On the basis of this, porous plates made of different materials were developed by making use of sintered powder technology. A tester for testing the physical characteristics of porous plate was designed. All around physical characteristic tests for porous plates were conducted. Result. Main factors affecting performance of porous plates were tested. These provided basis for performance test of sublimator, established porous plate criterion and optimized porous plate. Conclusion. Porous plates developed by making use of sintered powder technology could meet requirements of performance of water sublimator.

Life Support Systems↗

PubMed2000

Changes in baseline cerebral blood flow in humans do not influence regional cerebral blood flow response to photic stimulation.

The effect of changes in baseline regional cerebral blood flow (rCBF) values on the cerebral blood flow response during neuronal activation was studied with functional magnetic resonance imaging (fMRI). Using a breath-holding challenge as a hypercapnic stimulus, rCBF alterations during photic stimulation under normo- and hypercapnia were determined in nine volunteers. With breath-holding, baseline rCBF in areas corresponding to the visual cortex significantly increased from 54 +/- 5 ml/100 g/min to 85 +/- 9 ml/100 g/min (P < 0.001). Despite this significant change in baseline flow values, the rCBF increase during visual stimulation was very similar under normo- and hypercapnic conditions (28 +/- 8 ml/100 g/min versus 26 +/- 8 ml/100 g/min, respectively). This study supports the notion that within wide physiologic variations, task-induced cerebral blood flow changes are independent of baseline rCBF values.

Adult↗

PubMed2000

Image-based method for retrospective correction of physiological motion effects in fMRI: RETROICOR.

Respiration effects and cardiac pulsatility can induce signal modulations in functional MR image time series that increase noise and degrade the statistical significance of activation signals. A simple image-based correction method is described that does not have the limitations of k-space methods that preclude high spatial frequency correction. Low-order Fourier series are fit to the image data based on time of each image acquisition relative to the phase of the cardiac and respiratory cycles, monitored using a photoplethysmograph and pneumatic belt, respectively. The RETROICOR method is demonstrated using resting-state experiments on three subjects and compared with the k-space method. The method is found to perform well for both respiration- and cardiac-induced noise without imposing spatial filtering on the correction. Magn Reson Med 44:162-167, 2000.

Artifacts↗

PubMed2000

Condition number as a measure of noise performance of diffusion tensor data acquisition schemes with MRI.

Diffusion tensor mapping with MRI can noninvasively track neural connectivity and has great potential for neural scientific research and clinical applications. For each diffusion tensor imaging (DTI) data acquisition scheme, the diffusion tensor is related to the measured apparent diffusion coefficients (ADC) by a transformation matrix. With theoretical analysis we demonstrate that the noise performance of a DTI scheme is dependent on the condition number of the transformation matrix. To test the theoretical framework, we compared the noise performances of different DTI schemes using Monte-Carlo computer simulations and experimental DTI measurements. Both the simulation and the experimental results confirmed that the noise performances of different DTI schemes are significantly correlated with the condition number of the associated transformation matrices. We therefore applied numerical algorithms to optimize a DTI scheme by minimizing the condition number, hence improving the robustness to experimental noise. In the determination of anisotropic diffusion tensors with different orientations, MRI data acquisitions using a single optimum b value based on the mean diffusivity can produce ADC maps with regional differences in noise level. This will give rise to rotational variances of eigenvalues and anisotropy when diffusion tensor mapping is performed using a DTI scheme with a limited number of diffusion-weighting gradient directions. To reduce this type of artifact, a DTI scheme with not only a small condition number but also a large number of evenly distributed diffusion-weighting gradients in 3D is preferable.

Algorithms↗

PubMed2000

Assessment of hemodynamic response during focal neural activity in human using bolus tracking, arterial spin labeling and BOLD techniques.

In this study, the hemodynamic response and changes in oxidative metabolism during functional activation were measured using three functional magnetic resonance imaging (fMRI) techniques: the blood oxygenation level-dependent (BOLD) technique, flow-sensitive alternating inversion recovery (FAIR), and bolus tracking (BT) of an MR contrast agent. With these three techniques we independently determined changes in BOLD signal, relative cerebral blood flow (rCBF), and cerebral blood volume (rCBV) associated with brain activation in eight healthy volunteers. In the motor cortex, the BOLD signal increased by 1.8 +/- 0.5%, rCBF by 36.3 +/- 8.2% (FAIR), and 35.1 +/- 8.6% (BT), and rCBV by 19.4 +/- 4.1% (BT) in response to simultaneous bilateral finger tapping. In the visual cortex, BOLD signal increased by 2.6 +/- 0.5%, rCBF by 38.5% +/- 7.6 (FAIR), and 36.9 +/- 8.8% (BT), and rCBV by 18.8 +/- 2.8% (BT) during flickering checkerboard stimulation. Comparing the experimentally measured rCBV with the calculated rCBV using Grubb's power-law relation, we conclude that the use of power-law relationship results in systematic underestimate of rCBV.

Adult↗

PubMed2000

Diffusion- and perfusion-weighted MRI in a patient with a prolonged reversible ischaemic neurological deficit.

We report acute and follow-up diffusion- and perfusion-weighted MRI (DWI, PWI) findings in a patient with a prolonged reversible ischaemic neurological deficit. PWI 12 h after the patient was last seen to be without symptoms revealed a large perfusion deficit in the left posterior MCA territory with a relatively inconspicuous and much smaller abnormality on DWI. Follow-up showed resolution of abnormalities on both DWI and PWI, and conventional MRI was normal, apart from a very slight abnormality, visible only on FLAIR images, at the centre of the initially DWI-positive region. These findings demonstrate the utility of PWI when be used in combination with DWI to investigate the pathophysiology of transient ischemic syndromes.

Aged↗

PubMed2000

Diffusion- and perfusion-weighted MRI: influence of severe carotid artery stenosis on the DWI/PWI mismatch in acute stroke.

BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) have been used increasingly in recent years to evaluate acute stroke in the emergency setting. In the present study, we compared DWI and PWI findings in acute stroke patients with and without severe extracranial internal carotid artery (ICA) disease. METHODS: Twenty-seven patients with nonlacunar ischemic stroke were selected for this analysis. DWI, PWI, and conventional MRI were performed in all patients within 24 hours of symptom onset and after 1 week. To exclude patients with partial or complete reperfusion, we included only patients with a PWI deficit larger than the DWI lesion. Severe ICA disease (>70% stenosis) was present unilaterally in 9 and bilaterally in 2 patients. Acute DWI lesion volume, the size of the acute PWI/DWI mismatch, and final infarct size (on T2-weighted images) were determined. RESULTS: The PWI/DWI mismatch was significantly larger in patients with severe ICA disease than in patients without extracranial carotid stenosis, both when time-to-peak and mean transit time maps (P<0.01) were used to calculate the mismatch. Quantitative analysis of the time-to-peak delay in the mismatch indicated that a relatively smaller fraction of the total mismatch was critically ischemic in patients with carotid stenosis than in those without. Average lesion volume increased less in the stenosis group (P=0.14), despite the larger PWI/DWI mismatch, and final infarct size was smaller in the stenosis group (P<0.05). In the 2 patients with bilateral ICA disease, variable hemodynamic involvement of the contralateral hemisphere was found in addition to the ipsilateral PWI deficit. CONCLUSIONS: In most acute stroke patients with severe ICA stenosis, a considerably smaller fraction of the total PWI/DWI mismatch is at risk than in patients without carotid disease.

Acute Disease↗

PubMed2000

[A heat transfer model for liquid cooling garment (LCG) and its analysis].

Objective. To establish the heat transfer model for liquid cooling garment (LCG) and, basing on this model, to find the relations between the design parameters and heat removing, as well as that between the design parameters and heat transfer efficiency. Method. Heat transfer process of the LCG was analyzed according to engineering facts. Result. The relations between the design parameters and heat removing, and also that between the design parameters and heat transfer efficiency were interelative and the optimal values of the parameters were essential to the design of LCG. Conclusion. The results might be useful in the design of LCG in extra vehicular activity (EVA) space suit.

Body Temperature Regulation↗

PubMed1999

Relationship between cerebral blood flow changes during visual stimulation and baseline flow levels investigated with functional MRI.

Using fMRI, the relationship between regional cerebral blood flow (rCBF) changes during visual stimulation and the prevailing baseline global and regional flow levels was evaluated in 22 volunteers. The absolute increase in rCBF was not correlated with baseline rCBF values (r = 0.01, p = 0.8); however, the percentage change in rCBF showed a negative correlation (r=-0.78, p<0.001). Both absolute and relative changes in rCBF were independent of baseline global CBF values. These results indicate that caution should be exercised when comparing relative flow changes during focal brain activation, especially in functional neuroimaging studies dealing with altered baseline flow values.

Adult↗

PubMed1999

An image registration strategy for multi-echo fMRI.

Functional magnetic resonance imaging (fMRI) based on multiple-echo T(2)* mapping has attracted much attention recently. The contrasts in the parametric T(2)* maps are usually too low to allow direct image registration. In this study, an image registration strategy has been proposed for single-shot multi-echo data sets acquired for dynamic T(2)* mapping. We performed image registration of the T(2)*-weighted images before the calculation of the T(2)* parameter maps using two different strategies. One is to perform separate image registration on each echo and the other is to use the same motion correction parameters extracted from the second echo for all the data. Both strategies increase the number of activated voxels and reduce the effective noise level. The results also indicate that, for a single-shot dual-echo image data set, it is slightly preferable to use the second echo for direct image registration and then apply the same motion correction parameters to the first echo images. J. Magn. Reson Imaging 1999;10:154-158.

Brain↗

PubMed1999

ADC mapping by means of a single-shot spiral MRI technique with application in acute cerebral ischemia.

Diffusion-weighted MRI based on single-shot echo planar imaging (EPI) has been established as a useful tool to study acute cerebral ischemia. However, EPI is prone to spatial distortion and ghosting artifacts. In this study, a pulse sequence for diffusion-weighted imaging (DWI) based on a single-shot spiral readout is presented. Using this technique, multislice apparent diffusion coefficient (ADC) mapping can be performed in an interleaved fashion with the same temporal resolution as EPI. Other advantages associated with ADC mapping by the single-shot spiral method include minimal ghosting artifacts, reduced spatial distortion, and capability to scan in arbitrary planes. This technique has been successfully tested in five normal volunteers and three stroke patients. It has been demonstrated that the single-shot spiral technique is capable of producing high quality DWI and ADC trace maps (128 x 128) in the axial, sagittal, and coronal planes, which facilitate clinical diagnosis.

Acute Disease↗