Biomedical subjects

Xiaoping Hu

Publications and source records attributed to Xiaoping Hu.

At least 37 records · Page 2Linked to original sources

PubMed2005

Differential activity in left inferior frontal gyrus for pseudowords and real words: an event-related fMRI study on auditory lexical decision.

After Newman and Twieg and others, we used a fast event-related functional magnetic resonance imaging (fMRI) design and contrasted the lexical processing of pseudowords and real words. Participants carried out an auditory lexical decision task on a list of randomly intermixed real and pseudo Chinese two-character (or two-syllable) words. The pseudowords were constructed by recombining constituent characters of the real words to control for sublexical code properties. Processing of pseudowords and real words activated a highly comparable network of brain regions, including bilateral inferior frontal gyrus, superior, middle temporal gyrus, calcarine and lingual gyrus, and left supramarginal gyrus. Mirroring a behavioral lexical effect, left inferior frontal gyrus (IFG) was significantly more activated for pseudowords than for real words. This result disconfirms a popular view that this area plays a role in grapheme-to-phoneme conversion, as such a conversion process was unnecessary in our task with auditory stimulus presentation. An alternative view was supported that attributes increased activity in left IFG for pseudowords to general processes in decision making, specifically in making positive versus negative responses. Activation in left supramarginal gyrus was of a much larger volume for real words than for pseudowords, suggesting a role of this region in the representation of phonological or semantic information for two-character Chinese words at the lexical level.

Acoustic Stimulation↗

PubMed2005

Tactile discrimination of grating orientation: fMRI activation patterns.

Grating orientation discrimination is employed widely to test tactile spatial acuity. We used functional magnetic resonance imaging (fMRI) to investigate the neural circuitry underlying performance of this task. Two studies were carried out. In the first study, an extensive set of parietal and frontal cortical areas was activated during covert task performance, relative to a rest baseline. The active regions included the postcentral sulcus bilaterally and foci in the left parietal operculum, left anterior intraparietal sulcus, and bilateral premotor and prefrontal cortex. The second study examined selective recruitment of cortical areas during discrimination of grating orientation (a task with a macrospatial component) compared to discrimination of grating spacing (a purely microspatial task). The foci activated on this contrast were in the left anterior intraparietal sulcus, right postcentral sulcus and gyrus, left parieto-occipital cortex, bilateral frontal eye fields, and bilateral ventral premotor cortex. These findings not only confirm and extend previous studies of the neural processing underlying grating orientation discrimination, but also demonstrate that a distributed network of putatively multisensory areas is involved.

Adolescent↗

PubMed2005

Evaluation of corpus callosum anisotropy in young adults with fetal alcohol syndrome according to diffusion tensor imaging.

BACKGROUND: Fetal alcohol syndrome (FAS) and associated disorders resulting from maternal alcohol use during gestation are among the most common developmental disorders. However, they are rarely diagnosed and not fully understood in terms of their behavioral and neurocognitive phenotype. Prenatal exposure leads to alterations in facial morphology, growth, and neurocognition. The nature and extent of teratogenic effects on the brain and the relationship between such effects and observed behaviors remain in debate because there are no established markers for the neurological effects of exposure. In this study, we examined the impact of prenatal alcohol exposure on white-matter integrity in the corpus callosum by using diffusion tensor imaging (DTI) and herein describe the relationship between such effects and observed physical and behavioral outcomes. METHODS: DTI was used to evaluate diffusion anisotropy in the genu and splenium of corpus callosum in 16 low-income, primarily African-American volunteers. Volunteers were recruited from a cohort of young adults who had received neuropsychological evaluations during adolescence. Nine had been prenatally exposed to alcohol and had characteristics of FAS, and seven were nonexposed controls. RESULTS: Significant difference in the means for diffusion fractional anisotropy (t = 2.26, df = 9, p <0.002) and apparent diffusion coefficient (t = 2.14, df = 14, p < 0.008) were observed in the corpus callosum of alcohol-exposed youth compared with nonexposed youth. No significant differences were found in intracranial volume between these groups. CONCLUSIONS: Our results illustrate that DTI can be used in evaluating the integrity of corpus callosum in alcohol-exposed individuals. If future studies support these findings, diffusion anisotropy, represented by fractional anisotropy, has the potential to be used as a clinical marker in the diagnosis of FAS.

Adolescent↗

PubMed2004

Cross-modal temporal order memory for auditory digits and visual locations: an fMRI study.

A function of working memory is to remember the temporal sequence of events, often occurring across different sensory modalities. To study the neural correlates of this function, we conducted an event-related functional magnetic resonance imaging (fMRI) experiment with a cross-modal memory task. Subjects were required to recall auditory digits and visual locations either in mixed order (cross-modality) or in separate order (within-modality). To identify the brain regions involved in the memory of cross-modal temporal order, we compared the blood oxygenation level-dependent (BOLD) response between the mixed and the separate order tasks. As a control, cortical areas sensitive to the memory load were mapped by comparing the 10-item condition with the 6-item condition in the separate order task. Results show that the bilateral prefrontal, right premotor, temporo-parietal junction (TPJ) and left superior parietal cortices had significantly more activation in the mixed task than in the separate task. Some of these areas were also sensitive to the memory load, whereas the right prefrontal cortex and TPJ were relatively more sensitive to the cross-modal order but not the memory load. Our study provides potential neural correlates for the episodic buffer, a key component of working memory as proposed previously [Baddeley. Trends Cogn Sci 2000;4:417-423].

Acoustic Stimulation↗

PubMed2004

Simultaneous acquisition of gradient-echo and asymmetric spin-echo for single-shot z-shim: Z-SAGA.

This article describes the Z-SAGA pulse sequence, a technique for recovering susceptibility losses in EPI images for neuroimaging applications. The pulse sequence is based on an asymmetric spin echo EPI sequence and acquires a gradient echo image and an asymmetric spin echo image in a single shot. For one of the images, a z-shim gradient pulse is applied to compensate for susceptibility-related field distortions. The two images are combined to form an image with reduced signal loss. This sequence is simple to implement and experimentally demonstrated to be effective for BOLD imaging.

Artifacts↗

PubMed2004

Enhancing measured diffusion anisotropy in gray matter by eliminating CSF contamination with FLAIR.

In this work, the effect of fluid-attenuated inversion recovery (FLAIR) on measured diffusion anisotropy was investigated in gray matter. DTI data were obtained with and without FLAIR in six normal volunteers. The application of FLAIR was experimentally demonstrated to lead to a consistent increase in fractional anisotropy (FA) in gray-matter regions, which was attributed to suppressed partial volume effects from CSF. In addition to these experimental results, Monte Carlo simulations were performed to ascertain the effect of noise on the measured FA under the experimental conditions of this study. The experimentally observed effect of noise was corroborated by the simulation, indicating that the increase in the measured FA was not due to a noise-related bias but to an actual increase in diffusion anisotropy. This enhanced measurement of diffusion anisotropy can be potentially used to differentiate directionally dependent structure and tracking fibers in gray matter.

Anisotropy↗

PubMed2004

Inherent insensitivity to RF inhomogeneity in FLASH imaging.

Radiofrequency (RF) field inhomogeneity is an unavoidable problem in MRI, and it becomes severe at high magnetic fields due to the dependence of B1 on the sample. It leads to nonuniformities in image intensity and contrast, causing difficulties in quantitative interpretation and image segmentation. In this work, it is observed that with the fast low-angle shot (FLASH) sequence, which is often used for anatomic imaging and morphometric studies, sensitivity to RF inhomogeneity can be substantially reduced when the same coil is used for both transmission and reception, and an appropriate nominal flip angle is employed. This observation can help us understand the signal behavior of FLASH in the presence of RF inhomogeneity, and provide a guide for selecting parameters in FLASH imaging.

Brain Mapping↗

PubMed2004

Advances in high-field magnetic resonance imaging.

Among advances in magnetic resonance imaging (MRI), the increase of the magnetic field strength is perhaps one of the most significant. The use of high magnetic fields for in vivo magnetic resonance is motivated by a number of considerations. Advantages are increases in signal-to-noise ratio, blood-oxygenation level-dependent contrast, and spectral resolution, while disadvantages include potential reduction of contrast in anatomic imaging owing to lengthening of T1 and effects of susceptibility of high fields. To address these challenges, technical advances have been made in various aspects of MRI, allowing high-field MRI to provide exquisite morphological and functional details in clinical and research settings. This review provides an overview of technical issues and applications of high-field MRI.

Animals↗

PubMed2004

Anatomy of a live invertebrate revealed by manganese-enhanced Magnetic Resonance Imaging.

Non-invasive imaging technologies such as Magnetic Resonance Imaging (MRI) are increasingly in demand by researchers in many biological disciplines. However, when imaging small animals such as invertebrates, not only is the use of high-field magnets necessary to gain satisfactory spatial resolution, but the achievement of adequate contrast between tissues also requires the identification of applicable imaging parameters by means of expensive and time-consuming procedures. Here we report that systemically administered manganese can act as an effective MRI contrast agent for quick and non-invasive imaging of the nervous system and other complex anatomical structures in a small aquatic animal. Due to the tendency of manganese ions to differentially accumulate in most soft tissues, higher overall signal intensity and strongly improved contrast between structures yield data well suited for digital post-processing into three-dimensional models. Within a few hours this technique can efficiently generate anatomical images that are not obtainable with conventional methods, thus demonstrating a new and exciting approach to invertebrate research.

Animals↗

PubMed2003

Spin-echo fMRI in humans using high spatial resolutions and high magnetic fields.

The Hahn spin-echo (HSE)-based BOLD effect at high magnetic fields is expected to provide functional images that originate exclusively from the microvasculature. The blood contribution that dominates HSE BOLD contrast at low magnetic fields (e.g., 1.5 T), and degrades specificity, is highly attenuated at high fields because the apparent T(2) of venous blood in an HSE experiment decreases quadratically with increasing magnetic field. In contrast, the HSE BOLD contrast is believed to arise from the microvasculature and increase supralinearly with the magnetic field strength. In this work we report the results of detailed and quantitative evaluations of HSE BOLD signal changes for functional imaging in the human visual cortex at 4 and 7 T. This study used high spatial resolution, afforded by the increased signal-to-noise ratio (SNR) of higher field strengths and surface coils, to avoid partial volume effects (PVEs), and demonstrated increased contrast-to-noise ratio (CNR) and spatial specificity at the higher field strengths. The HSE BOLD signal changes induced by visual stimulation were predominantly linearly dependent on the echo time (TE). They increased in magnitude almost quadratically in going from 4 to 7 T when the blood contribution was suppressed using Stejskal-Tanner gradients that suppress signals from the blood due to its inhomogeneous flow and higher diffusion constant relative to tissue. The HSE signal changes at 7 T were modeled accurately using a vascular volume of 1.5%, in agreement with the capillary volume of gray matter. Furthermore, high-resolution acquisitions indicate that CNR increased with voxel sizes < 1 mm(3) due to diminishing white matter or cerebrospinal fluid-space vs. gray matter PVEs. It was concluded that the high-field HSE functional MRI (fMRI) signals originated largely from the capillaries, and that the magnitude of the signal changes associated with brain function reached sufficiently high levels at 7 T to make it a useful approach for mapping on the millimeter to submillimeter spatial scale.

Adult↗

PubMed2003

Microvascular BOLD contribution at 4 and 7 T in the human brain: gradient-echo and spin-echo fMRI with suppression of blood effects.

The BOLD signal consists of an intravascular (IV) and an extravascular (EV) component from both small and large vessels. Their relative contributions are dependent on field strength, imaging technique, and echo time. The IV and EV contributions were investigated in the human visual cortex at 4 and 7 T using spin-echo and gradient-echo BOLD fMRI with and without suppression of blood effects. Spin-echo acquisition suppresses EV BOLD from large veins and reflects predominantly blood T(2) changes and EV BOLD signal from small blood vessels. At a short echo time (32 ms), diffusion gradient-based suppression of blood signals resulted in a 75% and 20% decrease in spin-echo BOLD changes at 4 T and 7 T, respectively. However, at echo times (55-65 ms) approximating tissue T(2) typically used for optimal BOLD contrast, these gradients had much smaller effects at both fields, consistent with the decreasing blood T(2) with increasing field strength. Gradient-echo BOLD percent changes, with relatively long echo times at both fields, were virtually unaffected by gradients that attenuated the blood contribution because the EV BOLD surrounding both large and small vessels dominated. These results suggest that spin-echo BOLD fMRI at 4 and 7 T, with TE approximating tissue T(2), significantly reduces nonspecific mapping signals from large vessels and significantly accentuates microvasculature contributions.

Brain↗

PubMed2003

The evaluation of preprocessing choices in single-subject BOLD fMRI using NPAIRS performance metrics.

This work proposes an alternative to simulation-based receiver operating characteristic (ROC) analysis for assessment of fMRI data analysis methodologies. Specifically, we apply the rapidly developing nonparametric prediction, activation, influence, and reproducibility resampling (NPAIRS) framework to obtain cross-validation-based model performance estimates of prediction accuracy and global reproducibility for various degrees of model complexity. We rely on the concept of an analysis chain meta-model in which all parameters of the preprocessing steps along with the final statistical model are treated as estimated model parameters. Our ROC analog, then, consists of plotting prediction vs. reproducibility results as curves of model complexity for competing meta-models. Two theoretical underpinnings are crucial to utilizing this new validation technique. First, we explore the relationship between global signal-to-noise and our reproducibility estimates as derived previously. Second, we submit our model complexity curves in the prediction versus reproducibility space as reflecting classic bias-variance tradeoffs. Among the particular analysis chains considered, we found little impact in performance metrics with alignment, some benefit with temporal detrending, and greatest improvement with spatial smoothing.

Adult↗

PubMed2003

A functional MRI study of high-level cognition. II. The game of GO.

GO is a board game thought to be different from chess in many aspects, most significantly in that GO emphasizes global strategy more than local battle, a property very difficult for computer programs to emulate. To investigate the neural basis of GO, functional magnetic resonance imaging (fMRI) was used to measure brain activities of subjects engaged in playing GO. Enhanced activations were observed in many cortical areas, such as dorsal prefrontal, parietal, occipital, posterior temporal, and primary somatosensory and motor areas. Quantitative analysis indicated a modest degree of stronger activation in right parietal area than in left. This type of right hemisphere lateralization differs from the modest left hemisphere lateralization observed during chess playing.

Brain Mapping↗

PubMed2003

A functional MRI study of high-level cognition. I. The game of chess.

Chess is a game that involves many aspects of high level cognition and requires sophisticated problem solving skills. However, there is little understanding of the neural basis of chess cognition. This study employed functional magnetic resonance imaging (fMRI) to identify cortical areas that are active during the analysis of chess positions compared with a spatial task with matched visual stimuli. Bilateral activation was revealed in the superior frontal lobes, the parietal lobes, and occipital lobes. Some small areas of activation were observed unilaterally in the left hemisphere. The left hemisphere showed more activation than the right. Results are discussed in relation to a similar brain imaging study on the game Go.

Adult↗

PubMed2003

Spatial dependence of the nonlinear BOLD response at short stimulus duration.

Most functional magnetic resonance imaging studies use linear models to predict the measured response by convolution of an impulse response with the stimulus profile. Using very short visual presentation times (<2 s), deviation from the linear model in the measured BOLD data from the human brain was found for the response integral, amplitude, and width. In this study, high temporal and spatial resolution were used to quantify nonlinear effects and investigate the spatial dependence. Data at 4 Tesla showed at short stimulus duration a nonlinearity, i.e., deviation from a linear model, with an index up to 400%, whereas data at 7 Tesla exhibited a nonlinearity index up to 40%. The effect was more pronounced for response amplitude than for response area. A reduced width and sharpening of responses at shorter stimulus duration was also found. A voxel-based analysis of 7 Tesla data with 1.2 x 1.2 x 2 mm(3) resolution revealed a correlation between response onset and nonlinearity index. This suggests that the nonlinearity effects are a tissue-specific phenomenon and are likely to be more localized to the site of neuronal activity. The observed magnetic field dependence and the demonstrated nonlinearity in the response width support the hypothesis that the source of the nonlinearity at short stimulus duration has a considerable hemodynamic contribution. The nonlinearity was modeled as a "switch"-type initial hemodynamic response onset. Understanding these nonlinearities in the BOLD response is important for design and the analysis of rapid event-related fMRI experiments with brief stimulus presentations.

Brain Mapping↗

PubMed2003

A base-line survey on birth defects in Gansu province, West China.

We report a study to determine the incidence, types and rank order of congenital anomalies and related fetal and infant mortality in Gansu province in China to provide a base-line for an intervention project directed at reducing birth defects in Gansu. Forty-two communities in four counties of Gansu were randomly selected by cluster sampling, based on economic and geographical features of the province. All infants born between 1 January 2001 and 1 January 2002 (live and stillborn) were investigated in departments of gynaecology and obstetrics, in birth control centres and in facilities for women and children in county and community hospitals. The types of birth defect were classified by the diagnostic standardisation ICD-9. The overall incidence of birth defects in Gansu was 15.4/1000 births (102/6621): 6.7/1000 (44) neural tube defects, 4.7/1000 (31) low birthweight infants, 2/1000 (13) limb defects, 0.8/1000 (five) cleft lip and palate and 0.5/1000 (three) Down's syndrome. The infant mortality rate was 14.8/1000 (98), to which birth defects contributed 7.3/1000 (48). We conclude that the incidence of birth defects in Gansu is one of the highest in China, that birth defects are the leading cause of infant mortality and that neural tube defects cause most deaths.

China↗

PubMed2003

Mapping cortical areas associated with Chinese word processing using functional magnetic resonance imaging.

OBJECTIVES: To identify the cortical areas engaged during Chinese word processing using functional magnetic resonance imaging (fMRI) and to examine the reliability and reproducibility of fMRI for localization of functional areas in the human brain. METHODS: FMRI data were collected on 8 young, right-handed, native Chinese speakers during performance of Chinese synonym and homophone judgment tasks on two different clinical MRI systems (1.5 T GE Signa Horizon and 1.5 T Siemens Vision). A cross correlation analysis was used to statistically generate the activation map. RESULTS: Broca's area, Wernicke's area, bilateral extrastriate, and ventral temporal cortex were significantly activated during both the synonym and homophone activities. There was essentially no difference between results acquired on two different MRI systems. CONCLUSIONS: FMRI can be used for localizing cortical areas critical to Chinese language processing in the human brain. The results are reliable and well reproducible across different clinical MRI systems.

Adult↗

PubMed2003

Prevalence of birth defects and rubella infection in pregnant women in Gansu, west China. A survey.

OBJECTIVE: To determine the incidence, disease types, sequence of birth defects and prevalence of IgG and IgM in rubella infection in prepregnancy and pregnancy within 3 months in Gansu, People's Republic of China, and to determine a baseline of birth defects for an intervention project on birth defects in Gansu. STUDY DESIGN: Liveborn and stillborn infants from January 1, 2001, to January 1, 2002, and 518 prepregnant and 373 pregnant women in 3 months in 4 counties, including 42 communities selected random by stratification cluster sampling for a survey on the economic and geographic features in the province in October 2001 were investigated. Every infant born in the study period was surveyed. The types of birth defects were classed by standard diagnostic codes (ICD-9). Five-milliliter blood samples were obtained from every prepregnant and pregnant women. Rubella IgG and IgM were measured by enzyme-linked immunosorbent assay. RESULTS: The overall number of birth defects in Gansu was 102 (16.35%). The incidence of birth defects by sex was 62 males (18.55%) and 40 females (13.9%). The types of birth defects were neural tube defect, 44 cases (7.07%); limb defects, 13 (2.09%); cleft lip and palate, 5 (0.8%); and Down syndrome, 3 (0.48%). Low birth weight occurred in 31 cases (4.98%). The seasonal incidence birth defects was spring, 24 cases (23.52%); summer, 31 (30.39%); autumn, 26 (25.49%); and winter, 21 (20.59%). There were significant differences between 4 counties. The death rate from birth defects was 48 cases (47.06%). The positive rates of IgM and IgG of rubella infection of prepregnant women were, respectively, 5.02% and 83.78%; in pregnant women they were, respectively, 2.41% and 86.33%. The seropositive rate of rubella infection of prepregnancy was 88.80%; that of pregnancy was 88.74%. CONCLUSION: The rate of rubella infection in prepregnant and pregnant women within 3 months in Gansu was one of the highest in the People's Republic of China. The rate of birth defects in Gansu was one of much higher than in the People's Republic of China as a whole.

Adult↗