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Biomedical subjects

W Chau

Publications and source records attributed to W Chau.

10 recordsLinked to original sources
PubMed2007

Magnetic resonance imaging: a reliable method for measuring pancreatic volume in Type 1 diabetes.

AIM: To validate magnetic resonance imaging (MRI) for monitoring pancreatic atrophy in Type 1 diabetes. METHODS: Twelve male patients with Type 1 diabetes of duration >or= 10 years (median age 28, range 19-32 years) and 12 healthy controls (median age 30, range 22-36 years) were invited for two abdominal MRI scans, 14 days apart. Four sequences were used: standard T1-weighted; standard T2-weighted; volumetric interpolated breath-hold examination (VIBE); and T1-weighted breath hold with fat suppression (T1BHFS). The pancreas was identified on coded images by one observer and volumes estimated by interpolation. RESULTS: Eleven patients and all controls were scanned twice. Visualization of the pancreas was best with VIBE and T1BHFS, allowing volume estimation from 47 and 46 scans, respectively. The pancreatic volume of patients estimated from these sequences were half those of controls (52.4 ml, +/- 17.1 ml, mean +/- sd) vs. (101 ml, +/- 19.5 ml, P < 0.001) and estimates showed little bias between visits; mean difference 1.1 ml (95% CI; -3.1 to 5.3 ml, P = 0.61) using VIBE and -2.6 ml (-5.8 to 0.6 ml, P = 0.03) using T1BHFS. Both sequences gave similar precision; the standard deviation of the differences in volume estimates between visits was 9.7 ml for VIBE and 7.3 ml for T1BHFS, although mean volumes estimated from T1BHFS were 4.9 ml lower (-8.2 to -1.7 ml, P = 0.005). CONCLUSIONS: Pancreatic volume can be measured reliably using MRI and shows a 48% reduction in long-standing Type 1 diabetes as compared with age-matched normal subjects. MRI should prove useful in determining the natural history of pancreatic atrophy in diabetes.

Adult↗
PubMed2004

MEG analysis of "theory of mind" in emotional vignettes comprehension.

OBJECTIVE: Several studies suggested that an impaired "theory of mind" might play a key role in psychiatric disorders, such as autism and schizophrenia. Medial frontal lobe lesions of the right frontal lobe were reported to impair this ability. The aim of our study was to locate areas of the brain associated with the process of "theory of mind" in normal subjects. METHODS: In order to index the activity of brain areas related to "theory of mind" reasoning in sixteen normal adults, we administered an emotional ("happy", "sad", "angry" and "neutral") vignettes comprehension task during magnetoencephalography (MEG) recordings and analyzed these data by using SAM (synthetic aperture magnetometry), SPM99 and the permutation method. Subjects were presented with eight different videotaped social situations (each emotion has two vignettes) and were asked to indicate which emotion they represented. RESULTS: Statistically significant activation in the comparison of "happy"-"sad" and "angry"-"sad" was observed in the bilateral medial prefrontal cortices in the alpha frequency band. There were no significant differences in comparisons of each type of emotional vignette to the neutral vignettes, "happy"-"angry" comparison, and male-female comparisons. There was no significant difference in other frequency bands. CONCLUSION: This result suggests that bilateral medial prefrontal cortex are involved in the comprehension of emotional states of others.

Adult↗
PubMed2004

Detection of power changes between conditions using split-half resampling of synthetic aperture magnetometry data.

Synthetic Aperture Magnetometry (SAM) measures changes in task-related power using pseudo-t values which are affected by changes in both signal and noise. Detecting significant signal power changes between two separate experimental conditions should not be done directly due to possible fluctuation in the noise as well as the response. This study proposes a method to estimate the noise within a single condition, which is then used to test the null hypothesis of no difference between the conditions. The noise estimation is based on a split-half resampling technique. For each resampling, the data of a given condition is divided into two halves. The difference of the pseudo-t volumes between the pair of the datasets is calculated. After multiple resamplings, the confidence limits of the differences within this single condition are computed for a given p-value so that one can test the null hypotheses that the second condition is within the same distribution as the first. The limits are calculated using a bootstrap technique to correct for any bias in the estimated threshold. Power changes between the two conditions are considered significantly different if the difference of the pseudo-t value is larger than expected within conditions. To demonstrate the effectiveness of the technique, the proposed method was applied to MEG responses to two distinct visual stimuli recorded from a single subject. Major differences of brain activity between the two conditions were found in the occipital region. These results were validated using four pairs of split-half datasets, generated from either the odd or even trials in each condition. The method of split-half resampling should therefore be useful for localizing significant differences in brain activity between conditions within individual subjects.

Brain Mapping↗
PubMed2004

Cortical oscillations modulated by congruent and incongruent audiovisual stimuli.

Congruent or incongruent grapheme-phoneme stimuli are easily perceived as one or two linguistic objects. The main objective of this study was to investigate the changes in cortical oscillations that reflect the processing of congruent and incongruent audiovisual stimuli. Graphemes were Japanese Hiragana characters for four different vowels (/a/, /o/, /u/, and /i/). They were presented simultaneously with their corresponding phonemes (congruent) or non-corresponding phonemes (incongruent) to native-speaking Japanese participants. Participants' reaction times to the congruent audiovisual stimuli were significantly faster by 57 ms as compared to reaction times to incongruent stimuli. We recorded the brain responses for each condition using a whole-head magnetoencephalograph (MEG). A novel approach to analysing MEG data, called synthetic aperture magnetometry (SAM), was used to identify event-related changes in cortical oscillations involved in audiovisual processing. The SAM contrast between congruent and incongruent responses revealed greater event-related desynchonization (8-16 Hz) bilaterally in the occipital lobes and greater event-related synchronization (4-8 Hz) in the left transverse temporal gyrus. Results from this study further support the concept of interactions between the auditory and visual sensory cortices in multi-sensory processing of audiovisual objects.

Acoustic Stimulation↗
PubMed2003

Neuroimaging evidence for cortical involvement in the preparation and in the act of swallowing.

This study employed whole head magnetoencephalography and synthetic aperture magnetometry to investigate the cortical topography of the preparation and the execution of volitional and reflexive water swallowing and of a simple tongue movement. Concerning movement execution, activation of the mid-lateral primary sensorimotor cortex was strongly lateralized to the left during volitional water swallowing, less strongly lateralized to the left during reflexive water swallowing, and not lateralized at all during tongue movement. In contrast, the preparation for both volitional water swallowing and tongue movement showed a bilateral activation of the primary sensorimotor cortex. No activation was seen prior to reflexive water swallowing. Activation of the left insula and frontal operculum was observed only during both the preparation and the execution of volitional water swallowing. These new findings suggest a left hemispheric dominance for the cortical control of swallowing in humans.

Adult↗