Biomedical subjects

H L Liu

Publications and source records attributed to H L Liu.

At least 37 records · Page 2Linked to original sources

PubMed2001

Perfusion-weighted imaging of interictal hypoperfusion in temporal lobe epilepsy using FAIR-HASTE: comparison with H(2)(15)O PET measurements.

To detect perfusion abnormalities in areas of high magnetic susceptibility in the brain, an arterial spin-labeling MRI technique utilizing flow-sensitive alternating inversion recovery (FAIR) and half-Fourier single shot turbo spin-echo (HASTE) for spin preparation and image acquisition, respectively, was developed. It was initially tested in a functional study involving visual stimulation, and was able to detect significant activation with an increase (approximately 70%) in relative cerebral blood flow. Subsequently, it was applied in a clinical situation in eight patients with temporal lobe epilepsy (TLE). The perfusion-weighted images obtained showed no susceptibility artifacts even in the region of the inferior temporal lobe and were able to detect interictal hypoperfusion in TLE. The results were compared with those derived from H(2)(15)O PET perfusion imaging in each patient. A statistically significant correlation (r = 0.75, P < 0.05) was found between results acquired from these two modalities. Magn Reson Med 45:431-435, 2001.

Artifacts↗

PubMed2001

The neural system underlying Chinese logograph reading.

Written Chinese as logographic script differs notably from alphabets such as English in visual form, orthography, phonology, and semantics. Thus, research on the Chinese language is important to advance our understanding of the universality and particularity of the organization of language systems in the brain. In this study, we examine the neural systems associated with logographic reading using functional magnetic resonance imaging. Two experimental tasks were devised, one based on semantic decision and the other on homophone decision. Compared to the fixation baseline, peak activations resulting from semantic as well as homophony decisions were localized in the left middle frontal gyrus (BA 9). Left inferior frontal cortex also mediated Chinese processing. In addition, more right hemisphere cortical regions (i.e., BAs 47/45, 7, 40/39, and the right visual system) were involved in reading Chinese relative to reading English. This is attributed to the square shape of the logograph which requires an elaborated analysis of the spatial information and locations of various strokes comprising the logographic character. We suggest that the left middle frontal area (BA 9) coordinates and integrates the intensive visuospatial analysis demanded by logographs' square configuration and the semantic (or phonological) analysis required by the present experimental tasks. Our study has implicated brain regions common to both logographic and alphabetic languages as well as brain regions specialized in processing logographs.

Adult↗

PubMed2001

Extreme metabolic alkalosis treated with normal bicarbonate hemodialysis.

Metabolic alkalosis (MA), defined as a primary increment in plasma bicarbonate concentration, is a common complication in hospitalized patients and is associated with high morbidity and mortality in severe cases. One of the major routes of compensation for MA (ie, the secretion of an alkaline urine) is lost in renal failure patients. We report three cases involving four episodes of extreme MA with an arterial pH value greater than 7.60, serum bicarbonate concentration greater than 55 mmol/L, and stupor or seizure. Profound vomiting or massive gastric drainage combined with concurrent oliguric renal failure was the underlying mechanism for severe MA. Hydration and normal central venous pressure failed to improve the MA. The extreme MA was reversed quickly and safely by conventional hemodialysis with normal bicarbonate dialysate of 25 to 28 mmol/L. To our knowledge, this is the first reported successful use of normal bicarbonate dialysate in the treatment of severe MA. We also found that either H(2) blockers or proton-pump inhibitors have a prophylactic effect on the formation of MA.

Adult↗

PubMed2001

Cholinergic neurons expressing neuromedin K receptor (NK3) in the basal forebrain of the rat: a double immunofluorescence study.

By using a double immunofluorescence method we have examined the distribution of cholinergic neurons expressing neuromedin K receptor (NK3) in the rat brain and spinal cord. The distribution of neuromedin K receptor-like immunoreactive neurons completely overlapped with that of choline acetyltransferase-positive neurons in certain regions of the basal forebrain, e.g. the medial septal nucleus, nucleus of the diagonal band of Broca, magnocellular preoptic nucleus and substantia innominata. Partially overlapping distributions of neuromedin K receptor-like immunoreactive and choline acetyltransferase-positive neurons were found in the basal nucleus of Meynert, globus pallidus, ventral pallidum of the forebrain, tegmental nuclei of the pons and dorsal motor nucleus of the vagus. Neurons showing both neuromedin K receptor-like and choline acetyltransferase immunoreactivities, however, were found predominantly in the medial septal nucleus, nucleus of the diagonal band of Broca and magnocellular preoptic nucleus of the basal forebrain: 66-80% of these choline acetyltransferase-positive neurons displayed neuromedin K receptor-like immunoreactivity. Neurons showing both neuromedin K receptor-like and choline acetyltransferase immunoreactivities were hardly detected in other aforementioned regions of the forebrain, brainstem and spinal cord. The present study has provided morphological evidence for direct physiological modulation or regulation of cholinergic neurons by tachykinins through the neuromedin K receptor in the basal forebrain of rats.

Animals↗

PubMed2001

Rate dependence of human visual cortical response due to brief stimulation: an event-related fMRI study.

The human brain response to a wide range of visual stimulus rates presented over a prolonged time period has been investigated by various neuroimaging techniques. However, to date, no imaging study has been performed to study the dynamic human brain response to various stimulus rates when presented in a short time. This report describes activation in the human brain due to brief visual stimulus presentation (1 s) for stimulus rates varying from 1 to 20 Hz using event-related functional MRI (fMRI). Our results show that the amplitude of the fMRI response increases with the stimulus frequency and plateaus at 6 Hz. This finding differs slightly from the results of previous blocked task paradigm experiments (with a longer time of stimulus presentation), in which the response peaks at approximately 8 Hz and then decreases. Our results are in close agreement with previously published psychophysical studies, suggesting that the fMRI signal in this experiment is indicative of cortical activity related to visual processing.

Evoked Potentials↗

PubMed2001

Cerebral hemodynamic response in Chinese (first) and English (second) language processing revealed by event-related functional MRI.

Comparative functional neuroimaging studies using the block design paradigm have previously demonstrated that there are no significant differences in the location of areas of cerebral activation when native Chinese speakers independently process single words or sentences in both the Chinese (first) and English (second) languages. While it has also been documented that significant domains of brain response include the inferior to middle left frontal lobe, the latency, amplitude and duration of the associated hemodynamic changes during isolated neural processing of Chinese and English languages still remain unknown. The aim of this study, therefore, was to examine the characteristics of the hemodynamic alterations in the above-mentioned regions with event-related functional MRI (ER-fMRI) when native Chinese speakers performed verb generation tasks in both the Chinese (first) and English (second) languages. Our results demonstrate the presence of a similar neural activity-induced hemodynamic response in the inferior to middle left frontal lobe during both tasks. Further, there were also no statistically significant differences among the variables that described the hemodynamic response curves. These findings strongly imply that the underlying neural mechanism for Chinese (first) and English (second) language processing may be similar in native Chinese speakers.

Adult↗

PubMed2001

Genetic parameters of reproductive traits in Brown Tsaiya ducks artificially inseminated with semen from Muscovy drakes.

A selection experiment on maximum duration of fertility of Brown Tsaiya ducks after artificial insemination (AI) with pooled Muscovy semen has been conducted since 1992. The Brown Tsaiya ducks were divided into two lines: a control line (T) with no selection and a selected line (S). The traits measured were the number of eggs set that were laid from Days 2 to 15 after one AI (NES), the number of fertile eggs at candling (NEF), the total number of dead embryos (NED), the maximum duration of fertility (MD), and the number of hatched mule ducklings (NEH). The selected trait was NEF. Six generations with a total of 2,127 females were measured. The variance components were estimated for each line in a multiple-trait animal model, using the restricted maximum likelihood (REML) methodology, which yields estimates free of bias caused by selection and inbreeding. Estimates of the heritability and genetic correlation from the two lines were very similar. Heritabilities in the S and T lines, respectively, were 0.14 and 0.10 for NES, 0.30 and 0.26 for NEF, 0.06 and 0.09 for NED, 0.28 and 0.21 for MD, and 0.18 and 0.19 for NEH. High and favorable genetic correlations existed between NEF and MD (0.96 and 0.92), between NEF and NEH (0.86 and 0.91), and between MD and NEH (0.90 and 0.82). The results suggested that selection for NEF could improve the maximum duration of fertility, but it could be useful to check the estimates of genetic parameters in a meat-type female duck.

Animals↗

PubMed2001

Optimization of power deposition and a heating strategy for external ultrasound thermal therapy.

The purpose of this paper is to examine the thermal dose distribution, to configure the optimal absorbed power deposition, and to design an appropriate heating strategy for ultrasound thermal therapy. This work employs simulation programs, which are based on the transient bio-heat transfer equation and an ideal absorbed power deposition or an ideal temperature elevation within a cube of tissue, to study the optimal absorbed power deposition. Meanwhile, a simplified model of a scanned ultrasound transducer power deposition (a cone with convergent/divergent shape) is used to investigate the heating strategy for a large tumor with a sequence of heating pulses. The distribution of thermal dose equivalence defined by Sapareto and Dewey is used to evaluate the heating result for a set of given parameters. The parameters considered are the absorbed power density, heating duration, temperature elevation, blood perfusion, and the size of heating cube. The results demonstrate that the peak temperature is the key factor determining the thermal dose for this short-duration heating. Heat conduction has a very strong influence on the responses of temperature and thermal dose for a small heating cube and the boundary portion of a large heating cube. Hence, for obtaining the same therapeutic result, a higher power density is required for these two conditions to compensate the great temperature difference between the heating cube and the surrounding tissue. The influence of blood perfusion on the thermal dose is negligible on the boundary portion of the heating cube, while in the central portion it may become a crucial factor as a lower power density is used in this portion to save the delivered energy. When using external ultrasound heating method to treat a large tumor, the size of heating unit, the sequence of heating pulses, and the cooling-time interval between the consecutive heating pulses are the important factors to be determined to have an appropriate treatment within a reasonable overall treatment time.

Hot Temperature↗

PubMed2001

[Isolation, purification and renaturation of recombinant-DNA-derived porcine somatotropin].

Large scale abstraction and isolation of bacterially synthesized, recombinant-DNA-derived, porcine growth hormone (r-pST) is described. The r-pGH is found in genetic engineering E. coli as the form of inclusion bodies. Pellet fraction which were mainly inclusion bodies, after cell breakage and centrifugation, were collected. Cell envelope components, such as protein, lipid, endotoxin and nucleic acids are selectively removed from the pellet fraction by an EDTA/lysozyme/deoxycholate extraction. Inclusion bodies were dissolved using 6 mol/L guanidine/HCl and air oxidation is then carried out in the presence of the guanidine/HCl. The Guanidine/HCl protein mixture were diluted by renaturation solution. Guanidine/HCl were removed by dialysis and then correctly refolded, oxidized r-pGH were obtained. Injection experiment of hypophysectomized rats proved r-pST with high native bioactivity was obtained.

Animals↗

PubMed2001

[Preparation, characterization and evaluation of cellulose tris (3,5-dimethylphencarbamate) chiral stationary phase].

With the deposition of cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) on aminopropylated silica gel (mean particle size, 5 microns; pore size, 13 nm; surface area, 110 m2/g) by using two different methods (evaporation and precipitation), two chiral stationary phases (CSP1 and CSP2) characterized by elemental analysis and scanning electron micrography were obtained. They were also evaluated by using seven racemic compounds with n-hexane/ethanol(95/5, V/V) and n-hexane/2-propanol (90/10, V/V) as mobile phases. The results showed that the chiral stationary phase CSP1 obtained by the evaporation method had better efficiency and chiral resolution ability than CSP2 by the precipitation method.

Benzoin↗

PubMed2001

[The development of the multifunctional cephalostat and its applications in anesthesia].

The multifunctional cephalostat is able to hold the patients' head better and firmly at prone position after tracheal intubation under general anesthesia According to the size of patients head, the anesthetist can properly adjust the distance of the malor holder and the distance between the superciliary ridge and the lower jaw, and fix the two tempora to prevent the head swaying. So this instrument greatly facilitates the anesthesia managements.

Anesthesia, General↗

PubMed2000

Retinal dopaminergic neurons (A17) expressing neuromedin K receptor (NK(3)): a double immunocytochemical study in the rat.

By using a double immunofluorescence method we examined the distribution of dopaminergic neurons (A17) expressing neuromedin K receptor (NKR, NK(3)) in the rat retina. The distribution of NKR-like immunoreactive (-LI) neurons partially overlapped that of tyrosine hydroxylase (TH)-LI neurons in the inner retina of section and flat-mount preparation. Neurons showing both TH- and NKR-like immunoreactivities were found in the retina (A17): 100% of these TH-LI neurons displayed NKR-like immunoreactivity, and they constituted about 3.5% of total NKR-LI neurons. The majority of double-labeled neurons with TH- and NKR-like immunoreactivities were distributed in the proximal inner nuclear layer and the upper part of inner plexiform layer of the retina, and characterized with appearance of amacrine cells. The present study has provided morphological evidence for direct physiological modulation of dopaminergic neurons by tachykinins through NKR in the rat retina (A17).

Animals↗

PubMed2000

Noradrenergic neurons expressing substance P receptor (NK1) in the locus coeruleus complex: a double immunofluorescence study in the rat.

By using a double immunofluorescence method we examined the distribution of noradrenergic neurons expressing substance P receptor (NK1) or neuromedin K receptor (NK3) in the rat brainstem. The distribution of SPR-like immunoreactive (-LI) neurons completely overlapped that of tyrosine hydroxylase (TH)-LI neurons in the locus coeruleus (A6), ventrolateral and lateral reticular formation of pons (A5 and A7). Partially overlapping distribution of SPR- and TH-LI neurons were found in certain regions of the medulla oblongata (A1-A4). Neurons showing both SPR- and TH-like immunoreactivities, however, were only found in the locus coeruleus complex (A5-A7): 100% of these TH-LI neurons displayed SPR-like immunoreactivity. Neurons showing both NKR- and TH-like immunoreactivities were not detected in the aforementioned areas of brainstem. The present study has provided morphological evidence for direct physiological modulation of noradrenergic neurons by tachykinins through SPR in locus coeruleus complex (A5-A7).

Animals↗

PubMed2000

Detection of the brain response during a cognitive task using perfusion-based event-related functional MRI.

Event-related (ER) fMRI has evoked great interest due to the ability to depict the dynamic features of human brain function during various cognitive tasks. Thus far, all cognitive ER-fMRI studies have been based on blood oxygenation level-dependent (BOLD) contrast techniques. Compared with BOLD-based fMRI techniques, perfusion-based fMRI is able to localize the region of neuronal activity more accurately. This report demonstrates, for the first time, the detection of the brain response to a cognitive task using high temporal resolution perfusion-based ER-fMRI. An English verb generation task was used in this study. Results show that perfusion-based ER-fMRI accurately depicts the activation in Broca's area. Average changes in regional relative cerebral blood flow reached a maximum value of 30.7% at approximately 6.5 s after the start of stimulation and returned to 10% of the maximum value at approximately 12.8 s. Our results show that perfusion-based ER-fMRI is a useful tool for cognitive neuroscience studies, providing comparable temporal resolution and better localization of brain function than BOLD ER-fMRI.

Adult↗

PubMed2000

The temporal response of the brain after eating revealed by functional MRI.

After eating, the human brain senses a biochemical change and then signals satiation, but precisely when this occurs is unknown. Even for well-established physiological systems like glucose-insulin regulation, the timing of interaction between hormonal processes and neural events is inferred mostly from blood sampling. Recently, neuroimaging studies have provided in vivo information about the neuroanatomical correlates of the regulation of energy intake. Temporal orchestration of such systems, however, is crucial to the integration of neuronal and hormonal signals that control eating behaviour. The challenge of this functional magnetic resonance imaging study is to map not only where but also when the brain will respond after food ingestion. Here we use a temporal clustering analysis technique to demonstrate that eating-related neural activity peaks at two different times with distinct localization. Importantly, the differentiated responses are interacting with an internal signal, the plasma insulin. These results support the concept of temporal parcellation of brain activity, which reflects the different natures of stimuli and responses. Moreover, this study provides a neuroimaging basis for detecting dynamic processes without prior knowledge of their timing, such as the acute effects of medication and nutrition in the brain.

Adult↗

PubMed2000

Identification of selective estrogen receptor modulators by their gene expression fingerprints.

Clinical studies have shown that estrogen replacement therapy (ERT) reduces the incidence and severity of osteoporosis and cardiovascular disease in postmenopausal women. However, long term estrogen treatment also increases the risk of endometrial and breast cancer. The selective estrogen receptor (ER) modulators (SERMs) tamoxifen and raloxifene, cause antagonistic and agonistic responses when bound to the ER. Their predominantly antagonistic actions in the mammary gland form the rationale for their therapeutic utility in estrogen-responsive breast cancer, while their agonistic estrogen-like effects in bone and the cardiovascular system make them candidates for ERT regimens. Of these two SERMs, raloxifene is preferred because it has markedly less uterine-stimulatory activity than either estrogen or tamoxifen. To identify additional SERMs, a method to classify compounds based on differential gene expression modulation was developed. By analysis of 24 different combinations of genes and cells, a selected set of assays that permitted discrimination between estrogen, tamoxifen, raloxifene, and the pure ER antagonist ICI164384 was generated. This assay panel was employed to measure the activity of 38 compounds, and the gene expression fingerprints (GEFs) obtained for each compound were used to classify all compounds into eight groups. The compound's GEF predicted its uterine-stimulatory activity. One group of compounds was evaluated for activity in attenuating bone loss in ovariectomized rats. Most compounds with similar GEFs had similar in vivo activities, thereby suggesting that GEF-based screens could be useful in predicting a compound's in vivo pharmacological profile.

Animals↗

PubMed2000

Comparison of the temporal response in perfusion and BOLD-based event-related functional MRI.

Event-related functional MRI (ER-fMRI) based on both blood oxygen level-dependent (BOLD) contrast and perfusion contrast has been recently developed to study human brain activation due to brief stimulation. In this report, both BOLD- and perfusion-based ER-fMRI were directly compared using repeated single-trial, short visual stimulation (1 sec) in six human volunteers. The results show that the cerebral blood flow change reached a maximum approximately 1 sec earlier than the BOLD signal change (4.2 +/- 0.2 sec vs. 5.1 +/- 0.2 sec after the stimulation, P < 0.05). The full width at half maximum of the hemodynamic response measured by perfusion was not significantly different from that measured with BOLD (5.1 +/- 0.6 sec vs. 5.9 +/- 0.6 sec). A positive linear correlation was found between the maximum perfusion and maximum BOLD signal changes (r = 0. 77, P = 0.07).

Cerebrovascular Circulation↗

PubMed2000

A B(0) shift correction method based on edge RMS reduction for EPI fMRI.

Shifting of echoplanar images (EPI) in the phase-encoding direction during functional magnetic resonance imaging (fMRI) experiments can be observed due to B(0) drift. These shifts can cause artifacts in functional activation maps that can be corrected using a navigator echo (NE) technique, but the NE correction requires pulse sequence modifications not available on many clinical systems. A fast, postprocessing correction method based on edge root-mean-square error reduction (ERMSR) is introduced and shown to provide an equivalent correction. J. Magn. Reson. Imaging 2000;12:956-959.

Artifacts↗