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Biomedical subjects

E C Wong

Publications and source records attributed to E C Wong.

At least 19 recordsLinked to original sources
PubMed1996

Diffusion weighted fMRI at 1.5 T.

Functional magnetic resonance imaging (fMRI) is capable of detecting task-induced blood oxygenation changes using susceptibility sensitive pulse sequences such as gradient-recalled echo-planar imaging (EPI). The local signal increases seen in the time course are believed to be due to an increase in oxygen delivery that is incommensurate with oxygen demands. To help isolate the sources of functional signal changes, the authors have incorporated various forms of diffusion weighting into EPI pulse sequences to characterize the apparent mobility of the functionally modulated protons. Results suggest that the majority of the functional signal at 1.5 T arises from protons that have apparent diffusion coefficients that are approximately four or five times higher than that of brain tissue. This implies that significant functional signal sources are either protons within the vascular space or protons from the perivascular space that is occupied by cerebrospinal fluid.

Adult↗
PubMed1995

High-resolution magnetic resonance imaging evaluation of blood-retinal barrier integrity following transscleral diode laser treatment.

OBJECTIVE: To compare the effects of contact transscleral diode laser treatment and retinal cryotherapy on blood-retinal barrier integrity with the use of high-resolution magnetic resonance imaging techniques with constant infusion of gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA). METHODS: Transscleral diode laser photocoagulation and retinal cryotherapy were used to treat equivalent areas of the inferior retinal periphery of pigmented rabbits. Magnetic resonance imaging time-course studies with measurement of signal enhancements due to Gd-DTPA leakage were conducted 2 and 15 days following treatment. RESULTS: Two days following treatment, cryotherapy-treated eyes exhibited a mean (+/- SD) effective Gd-DTPA permeability coefficient of 4.6 +/- 0.8 x 10(-6) cm/s; in comparison, diode laser-treated eyes exhibited 1.6 x 1.4 x 10(-6) cm/s effective permeability. Significant decreases in the effective permeability were also noted 15 days after treatment in both groups. CONCLUSIONS: Transscleral contact probe diode laser photocoagulation induces less disruption of the blood-retinal barrier than does conventional cryotherapy. In addition, the continuous infusion method of Gd-DTPA delivery is a reliable and easily interpretable alternative to the commonly used bolus injection approach.

Animals↗
PubMed1995

Optimized isotropic diffusion weighting.

The authors introduce several sets of time-efficient gradient waveforms for applying isotropic diffusion weighting in NMR experiments. This creates signal attenuation that depends on the trace of the diffusion tensor and is therefore rotationally invariant. Numerical methods for the calculation of such gradient sets are outlined, and results are shown for isotropic and anisotropic gradient hardware and first order flow moment nulled diffusion weighting gradients. Preliminary experimental results from the human brain validate this new technique.

Algorithms↗
PubMed1995

A time encoding method for single-shot imaging.

A new 2D single-shot imaging technique is introduced that uses only one dimension of Fourier encoding. The second dimension is encoded in time, rather than using phase encoding. The data is acquired in the form of a closely spaced echo train with each echo produced from a different physical line in the object. A 1D Fourier transform is applied to each echo for image reconstruction. Because only the desired lines are excited, there can be no aliasing in the time encoding direction even when the object is much larger than the field of view. This technique is also very insensitive to motion, as motion-related artifacts do not propagate in the time encoding direction.

Acrylic Resins↗
PubMed1994

Functional magnetic resonance imaging of human auditory cortex.

Magnetic resonance imaging methods recently demonstrated regional cerebral signal changes in response to limb movement and visual stimulation, attributed to blood flow enhancement. We studied 5 normal subjects scanned while listening to auditory stimuli including nonspeech noise, meaningless speech sounds, single words, and narrative text. Imaged regions included the lateral aspects of both hemispheres. Signal changes in the superior temporal gyrus and superior temporal sulcus were observed bilaterally in all subjects. Speech stimuli were associated with significantly more widespread signal changes than was the noise stimulus, while no consistent differences were observed between responses to different speech stimuli. Considerable intersubject variability in the topography of signal changes was observed. These observations confirm the utility of magnetic resonance imaging in the study of human brain structure-function relationships and emphasize the role of the superior temporal gyrus in perception of acoustic-phonetic features of speech, rather than processing of semantic features.

Acoustic Stimulation↗
PubMed1994

Echo-volume imaging.

Two single-shot volume imaging techniques are described. The first, single-echo echo-volume imaging, is essentially the echo-volume imaging (EVI) sequence suggested by Mansfield (J. Phys. C. 10, L55 (1977)). The second is a multi-spin-echo approach in which one plane of k-space is collected during each spin echo. In both techniques, phase encoding gradients are applied in the z direction, and three-dimensional k-space is filled by a raster pattern in Cartesian coordinates. Spatial saturation is used to avoid aliasing in the y direction, and a selctive pulse is applied to excite the desired slab of tissue and eliminate aliasing in z. The average echo-times, measured from the center of the 90 degrees pulse to the center of the acquisition k-space (kx = ky = kz = 0), were 45 and 104 ms for single echo and multi-echo methods, respectively. Images of the human brain using both sequences are shown.

Artifacts↗
PubMed1994

Spin-echo and gradient-echo EPI of human brain activation using BOLD contrast: a comparative study at 1.5 T.

In this study, Blood Oxygenation Level Dependent (BOLD) contrast in the detection of human brain activation was compared between spin-echo and gradient-echo echo-planar sequences at 1.5 T. Time course series of spin-echo and gradient-echo images containing the primary motor cortex were collected during rest (no finger movement) and activation (finger movement). Each time course series was collected using a different TE. Resting and active state signal intensities at each TE were measured in identical regions in the motor cortex. From these data, resting and active state R2 (1/T2) and R2* (1/T2*) values were obtained. Across four subjects, brain activation produced an average R2 change of -0.16 +/- 0.02/s (+/- SE), and an average R2* change of -0.55 +/- 0.08/s. The average delta R2*/delta R2 ratio was 3.52 +/- 0.56. The average gradient-echo/spin-echo ratio of activation-induced signal changes at the TE for maximal BOLD contrast for each sequence (TE approximately T2* and T2) was calculated to be 1.87 +/- 0.40.

Adult↗
PubMed1993

Processing strategies for time-course data sets in functional MRI of the human brain.

Image processing strategies for functional magnetic resonance imaging (FMRI) data sets acquired using a gradient-recalled echo-planar imaging sequence are considered. The analysis is carried out using the mathematics of vector spaces. Data sets consisting of N sequential images of the same slice of brain tissue are analyzed in the time-domain and also, after Fourier transformation, in the frequency domain. A technique for thresholding is introduced that uses the shape of the response in a pixel compared with the shape of a reference waveform as the decision criterion. A method is presented to eliminate drifts in data that arise from subject movement. The methods are applied to experimental FMRI data from the motor-cortex and compared with more conventional image-subtraction methods. Several finger motion paradigms are considered in the context of the various image processing strategies. The most effective method for image processing involves thresholding by shape as characterized by the correlation coefficient of the data with respect to a reference waveform followed by formation of a cross-correlation image. Emphasis is placed not only on image formation, but also on the use of signal processing techniques to characterize the temporal response of the brain to the paradigm.

Brain↗
PubMed1993

Leukocyte common antigen-related phosphatase (LRP) gene structure: conservation of the genomic organization of transmembrane protein tyrosine phosphatases.

The leukocyte common antigen-related protein tyrosine phosphatase (LRP) is a widely expressed transmembrane glycoprotein thought to be involved in cell growth and differentiation. Similar to most other transmembrane protein tyrosine phosphatases, LRP contains two tandem cytoplasmic phosphatase domains. To understand further the regulation and evolution of LRP, we have isolated and characterized mouse lambda genomic clones. Thirteen genomic clones could be divided into two non-overlapping clusters. The first cluster contained the transcription initiation site and the exon encoding most of the 5' untranslated region. The second cluster contained the remaining exons encoding the protein and the 3' untranslated region. The gene consists of 22 exons spanning over 75 kb. The distance between exon 1 and exon 2 is at least 25 kb. Characterization of the 5' ends of LRP mRNA by S1 nuclease protection identifies putative initiation start sites within a G/C-rich region. The upstream region does not contain a TATA box. Comparison of the LRP gene structure to the mammalian protein tyrosine phosphatase gene, CD45, shows striking similarities in size and genomic organization.

Amino Acid Sequence↗
PubMed1993

In vivo determination of the anisotropic diffusion of water and the T1 and T2 times in the rabbit lens by high-resolution magnetic resonance imaging.

PURPOSE: Several magnetic resonance imaging (MRI) "tools" for ophthalmologic research have recently been developed in this laboratory, including improved gradient and radiofrequency coils and pulse sequences for high-resolution and diffusion imaging (100-microns resolution). METHODS: These tools have been applied to the in vivo measurement of the relaxation parameters (T1 and T2) and the water diffusion coefficients (Dx and Dy) in the rabbit eye lens, both normal and cataractous. Maps of these parameters in the lens have been computer generated. RESULTS: In the normal lens, water diffusion is highly anisotropic and tends to be parallel to the surface. In the trauma-induced cataractous lens, an increase in spin-spin relaxation times (T2) consistent with edema and alteration of diffusion patterns was observed in a study conducted 2 weeks postsurgery. A partial reversal was observed 6 weeks postsurgery. The histologic data on the enucleated lens at 6 weeks showed a loss of normal lens architecture. Images are shown that display other small structures of the anterior segment with great clarity. CONCLUSIONS: An extension of this work, now underway, is the study of the formation of various types of cataract in animal models. It is hypothesized that these methods can be extended to humans as a quantitative alternative for the assessment of cataracts.

Animals↗
PubMed1992

Time course EPI of human brain function during task activation.

Using gradient-echo echo-planar MRI, a local signal increase of 4.3 +/- 0.3% is observed in the human brain during task activation, suggesting a local decrease in blood deoxyhemoglobin concentration and an increase in blood oxygenation. Images highlighting areas of signal enhancement temporally correlated to the task are created.

Brain↗
PubMed1992

A double-blind comparison of nasal budesonide and oral astemizole for the treatment of perennial rhinitis.

Sixty-nine outpatients with symptomatic perennial rhinitis were recruited to this double-blind, parallel-group study to compare budesonide nasal spray with oral astemizole. Following a 1-week run-in on placebo, 67 patients achieved a mean daily total symptom score of at least 4 (scoring for each symptom was 0 = none, 1 = mild, 2 = moderate, 3 = severe), and were randomized to study treatments - 33 to budesonide, 100 micrograms in each nostril morning and evening, and 34 to astemizole, one 10-mg tablet each morning, for a period of 4 weeks. No antihistamine preparations other than eye drops and no corticosteroids were permitted during the active treatment period. Patients recorded symptoms of blocked nose, runny nose, sneezing, itchy nose, sore eyes or runny eyes in diary cards each evening before retiring. Diary card data showed that there was significantly greater improvement in blocked nose, runny nose and runny eyes during the first 2 weeks of budesonide treatment than during the same period on astemizole. A similar, although non-significant, trend was observed for sneezing and itchy nose, but there was no apparent difference in the reporting of sore eyes. After 4 weeks, blocked nose and runny nose remained significantly less troublesome in the budesonide group. Both treatments were well-tolerated and no major adverse effects were reported. Patient ratings for treatment efficacy were significantly higher for budesonide than astemizole at both 2 weeks and 4 weeks.

Administration, Topical↗
PubMed1991

Association of calmodulin with isolated nuclei from rat hepatocytes.

Calmodulin plays an important role in regulating cell proliferation and intranuclear processes (J. Biol. Chem. 265: 18595, 1990). Therefore we studied the association of 125I-calmodulin with highly purified rat hepatocyte nuclear preparations which were characterized by marker enzymes and electron microscopy. Steady-state association of 125I-calmodulin was reached within 5 minutes. Half-maximal binding was achieved at approximately 7.1 microM. This association was partially Ca(2+)-dependent, but was not influenced by ATP, GTP or wheat germ agglutinin. Ultrastructural autoradiography showed specific association of 125I-calmodulin with peripheral and non-peripheral heterochromatin, nuclear membranes, and nucleoli. Specific binding (ratio of the grain density of 125I-calmodulin to Na125I) was greatest in the regions of the nucleoli and non-peripheral heterochromatin. The data indicate that exogenous calmodulin can associate with specific nuclear components in an energy-independent and Ca(2+)-dependent manner.

Adenosine Triphosphate↗