Biomedical subjects

I L Kwee

Publications and source records attributed to I L Kwee.

At least 19 recordsLinked to original sources

PubMed2001

1H magnetic resonance spectroscopic imaging of permanent focal cerebral ischemia in rat: longitudinal metabolic changes in ischemic core and rim.

The purpose of this study was to determine whether regional differences in metabolites can be seen chronologically in permanent focal cerebral ischemia using 1H magnetic resonance spectroscopic imaging (MRSI), and whether these changes reflect pathological outcome. Regional variation in metabolites after permanent focal ischemia were investigated longitudinally in rats using 1H MRSI for a total of 7 days and then compared to histopathological findings. Four hours after the induction of ischemia, N-acetyl-L-aspartate (NAA) levels in the lateral caudo-putamen and the somatosensory cortex, core ischemic regions, decreased 22 and 40%, respectively. This reduction in NAA was coupled with a marked rise in lactate. In the medial caudo-putamen, the ischemic rim, however, NAA was preserved in spite of a marked increase in lactate. By 24 h post ischemia, the levels of NAA in medial caudo-putamen (ischemic rim in caudate) also decreased significantly. However NAA in cingulated cortex (ischemic rim in cortex) decreased more gradually between 24 and 48 h. This regional difference can reflect the severity of metabolic derangement in the acute stage. After 96 h following ischemia, the levels of all metabolites detected by 1H MRSI had decreased and the levels of NAA decline reflected the severity of histopathological damage. In conclusion, the regional metabolic differences could be assessed by 1H MRSI chronologically, and the depth of NAA decline reflected histopathological changes in the chronic stage.

Animals↗

PubMed2001

Brain strategies for reading in the second language are determined by the first language.

Brain activation associated with reading was investigated in ten normal Japanese volunteers (five highly literate in both Japanese and English) and ten American native English speakers (five highly literate in both English and Japanese) in order to determine the neuroanatomic substrates employed in reading the first language (L1), and to determine the effect of L1 on the neurosubstrates involved in reading the second language (L2). The study was performed using blood oxygenation level dependent (BOLD) contrast functional magnetic resonance imaging (fMRI) on a high-field (3.0T) system specifically optimized for fMRI. The activation patterns in Japanese subjects reading Japanese (L1) were substantially different from the patterns obtained in American subjects reading English text (L1). The activation patterns reading L2 were virtually identical to the patterns seen when reading L1 in both Japanese and English natives highly literate in both language systems. The results demonstrated that the neuroanatomical substrates underlying the cognitive processing of reading are differentially determined based on the language system. The study further indicates that the cognitive processes for reading in the second language involve the same cortical structures employed for the first language, supporting the hypothesis that the second language represents the cognitive extension of the first language.

Adult↗

PubMed2001

Planum temporale: where spoken and written language meet.

Functional magnetic resonance imaging studies on spoken versus written language processing were performed in 20 right-handed normal volunteers on a high-field (3.0-tesla) system. The areas activated in common by both auditory (listening) and visual (reading) language comprehension paradigms were mapped onto the planum temporale (20/20), primary auditory region (2/20), superior temporal sulcus area (2/20) and planum parietale (3/20). The study indicates that the planum temporale represents a common traffic area for cortical processing which needs to access the system of language comprehension. The destruction of this area can result in comprehension deficits in both spoken and written language, i.e. a classical case of Wernicke's aphasia.

Adolescent↗

PubMed2000

Independent component-cross correlation-sequential epoch (ICS) analysis of high field fMRI time series: direct visualization of dual representation of the primary motor cortex in human.

A new technique for functional magnetic resonance imaging (fMRI) time series analysis is presented. The technique referred to here as independent component-cross correlation-sequential epoch (ICS) analysis is a hybrid technique of two standard methodologies of biological signal analysis, namely, data driven methods, represented by independent component analysis, and hypothesis driven methods, represented by a general linear model. The technique successfully identified four functionally discrete areas within the primary sensorimotor cortex (SMI) in normal human subjects based on blood oxygenation level dependent (BOLD) contrast functional magnetic resonance imaging (fMRI) time series performed on a high field (3.0 T) system. Each of the four areas identified corresponded to the four physiological subdivisions of SMI, recognized in primates to be essential for voluntary hand motion, namely, 4 anterior (MI-4a) and 4 posterior (MI-4p) of the primary motor cortex, and 3a and the 'classical' (Brodmann areas 1, 2, and 3b) primary sensory cortex, respectively. ICS analysis appears to be a highly reliable and versatile technique for fMRI time series analysis.

Algorithms↗

PubMed1999

Perceptual processing of stereopsis in humans: high-field (3.0-tesla) functional MRI study.

Cortical activation associated with stereopsis was studied in eight right-handed neurosurgeons professionally trained in stereoscopic vision. The activation map associated with viewing three-dimensional images, as contrasted to viewing the corresponding two-dimensional images of identical contents (images of MR angiography), showed consistent activation in the cortex adjacent to the intraparietal sulcus. The study further demonstrated a dominant role of the right hemisphere in perceptual processing of stereopsis in humans.

Adult↗

PubMed1999

Clinical application of three-dimensional anisotropy contrast magnetic resonance axonography. Technical note.

The utility of three-dimensional anisotropy contrast (3DAC) magnetic resonance (MR) axonography, a method sensitive to neuronal fibers and their directionality, was investigated in the clinical setting using a 3-tesla MR imaging system based on a General Electric Signa platform. The study focused on healthy volunteers and patients with common structural central nervous system disorders, namely chronic infarction, brainstem cavernous hemangioma, supratentorial meningioma, and astrocytoma. Three orthogonal anisotropic diffusion-weighted images were first obtained. Three primary colors were each assigned to a diffusion-weighted image, respectively, and the images were subsequently combined into a single-color image in full-color spectrum (3DAC MR axonography image). Fiber-tract definition in the cerebral peduncle of the midbrain of healthy volunteers showed intersubject variation, with two general patterns recognized: dispersed (60% of cases) and compact (40% of cases). Pathological alterations in the fiber tracts were readily identified in cases involving wallerian degeneration of the pyramidal tract, as illustrated in the cases of chronic infarction. Displacement of major tracts, such as the medial lemniscus or corticospinal tract, as well as fiber directionality, was also easily recognized in cases of mass lesions. As an imaging method uniquely capable of providing information regarding axonal connectivity, 3DAC MR axonography appears to have promising potential for routine clinical application.

Astrocytoma↗

PubMed1998

'Musical brain' revealed by high-field (3 Tesla) functional MRI.

The cortical areas subserving music literacy were investigated using high-field (3 Tesla) functional magnetic resonance imaging (fMRI). The activation pattern associated specifically with music score reading was compared with that associated with reading text in a subject's primary and secondary language. While the areas of activation were predominantly identical for all three reading modalities, there were areas within the occipital cortex activated exclusively by music score reading. Grand analysis of the activation patterns of eight pianists unequivocally identified that the principal cortical area needed for music literacy is the cortex flanking the right transverse occipital sulcus (musical brain).

Adult↗

PubMed1998

High-field (3.0 T) functional MRI sequential epoch analysis: an example for motion control analysis.

The widely accepted method of blood oxygenation level dependent functional magnetic resonance imaging (BOLD-fMRI) is a subtractive approach of state related analysis based on pictorial statistics, analogous to its predecessor, H2O(15) positron emission tomography (H2O(15)-PET). Although BOLD-fMRI has been shown to have several definite advantages over H2O(15)-PET, it has also been found to be much more artifact prone. This is primarily due to pixel misalignment of raw image data. Furthermore, similar to H2O(15)-PET, conventional means for pictorial analysis in BOLD-fMRI tends to be limited by the relatively low specificity of the observed activation. To overcome this limitation, we investigated a technique for BOLD-fMRI, sequential epoch analysis (SEA), on a high-field (3.0 T) system. The method allows for experimental designs comparable to neurophysiological techniques in primates and enables determination of activation of a selected cerebral cortical region of interest corresponding to a specific task. Utilizing SEA, we successfully identified a specific area within the premotor cortex which is activated complementary to the contralateral hand motion. The findings have strong implications regarding the neurological substrate responsible for the well described clinical phenomenon of physiological mirror movements in infants. The current study validated SEA BOLD-fMRI on a high-field system as a complementary method in the pictorial analysis of conventional fMRI, effectively offsetting the inherent problems of the conventional method, principally pixel misalignment and the relatively low specificity of the observed activation.

Adolescent↗

PubMed1996

Aldose reductase and sorbitol dehydrogenase activities in diabetic brain: in vivo kinetic studies using 19F 3-FDG NMR in rats.

The effects of diabetes mellitus on the kinetic constants of aldose reductase and sorbitol dehydrogenase in rat brain were investigated non-invasively in vivo using the 3-fluoro-3-deoxy-D-glucose (3-FDG) 19-fluorine (19F) nuclear magnetic resonance (NMR) method. While forward flux or both aldose reductase and sorbitol dehydrogenase (k1 and k2) were significantly increased, there was no corresponding increase in reverse flux (k3 and k4), and leakage of fructose (k5) was negligible. These findings indicate that the enzymatic kinetics of aldose reductase sorbitol (ARS) in diabetic brain undergo alteration favoring intracellular sorbitol and fructose accumulation, the frequently implicated biochemical basis of diabetic complications.

Aldehyde Reductase↗

PubMed1996

Computed tomography-negative acute thalamic hematoma.

A case of acute thalamic hematoma not detected by computed tomography (CT) but unequivocally diagnosed by magnetic resonance imaging (MRI) is presented. A 79-year-old woman presented with acute left hemiparesis. The results of CT obtained on admission as well as on the seventh hospital day were negative for a hematoma. By contrast, serial MRIs exhibited chronological changes in the relaxation properties characteristics of acute hematoma in the thalamus. The case illustrates that contrary to widespread practice, CT cannot absolutely be relied on for the detection of acute intracerebral hematoma.

Acute Disease↗

PubMed1995

Guanidinoethane sulfate is neuroprotective towards delayed CA1 neuronal death in gerbils.

The potential neuroprotective effects of guanidinoethane sulfate (GES) on delayed neuronal death of hippocampal CA1 neurons were investigated using a gerbil model of forebrain ischemia. Neuronal densities of CA1 neurons in the saline control group (255.1 +/- 11.7 cells/mm) and guanidinoethane sulfate pretreated control group (249.0 +/- 9.4 cells/mm) showed no significant differences. By contrast, in animals subjected to ischemia, CA1 neurons of the guanidinoethane sulfate pretreated group showed a significantly higher number of surviving neurons (61.1 +/- 55.11 cells/mm) compared to the saline group (17.75 +/- 12.73 cells/mm) (p < 0.05, t-test). The study indicated that although partial, guanidinoethane sulfate is neuroprotective towards gerbil hippocampal CA1 neurons against ischemic insult.

Animals↗

PubMed1995

Magnetic resonance axonography of the rat spinal cord: postmortem effects.

The recent development of magnetic resonance (MR) axonography, which uses three-dimensional anisotropy contrast (3DAC), a new algorithm for the treatment of an apparent diffusion tensor, has provided an unprecedented opportunity for visualizing the anatomical details of the spinal cord in live animals. In this study, the authors investigated the sensitivity of the 3DAC method in detecting pathological conditions by obtaining chronological MR axonography of the rat spinal cord immediately after induction of cardiac arrest. The results clearly demonstrated that 3DAC is highly sensitive to any perturbation of physiological conditions. Trichromatic coefficient analyses indicated postmortem changes observed pictorially are indeed due to loss of anisotropy. The study further indicated the presence of at least two independent factors responsible for observed physiological anisotropy. Considering its rather simple implementation process and high anatomical resolution as well as its sensitivity to pathological alteration, MR axonography based on the 3DAC method appears to be the ideal noninvasive imaging technique for assessment of the spinal cord in biomedicine.

Animals↗

PubMed1994

Magnetic resonance axonography of the rat spinal cord.

In spite of dramatic advancement in biomedical imaging technologies, non-invasive visualization of anatomic detail of the spinal cord has remained a major challenge. Here, a novel color-coded contrast method for magnetic resonance imaging (MRI) which provides superb resolution of the spinal cord in live animals, comparable to that of histological preparations, is described. The method, referred to here as three dimensional anisotropy (3DAC) contrast MRI, displays cross-sectional images in the full visible color spectrum, encoding directional information regarding intravoxel anisotropic water motion in space. Since neuronal fibers, especially axons, possess significantly higher intravoxel anisotropic water motion compared with other elements in the nervous system, 3DAC is highly sensitive to axonal direction and density. Axonography of the spinal cord of rats obtained using this technique showed anatomic detail at a resolution hitherto unobtainable in live animals.

Animals↗

PubMed1994

Brain maturation and high-energy phosphate diffusivity: alteration in cytosolic microenvironment and effective viscosity.

Maturational changes in intracellular brain phosphocreatine (PCr) transport were investigated using 31P-nuclear magnetic resonance diffusion spectroscopy. The diffusivities of PCr showed significant maturational facilitation in rat brain in vivo. Physicochemical analysis of the cytosol microenvironment as a multicomponent solution, where one of the components is a dilute polymer, indicated that the observed developmental facilitation of PCr diffusivity is likely to be due to a decline in the concentration of the free amino acid taurine. Changes in the concentrations of biopolymers (i.e., proteins or lipids) have only little effect, if any, on PCr diffusivity. PCr diffusivity values of rat brain measured in vivo showed excellent quantitative agreement with the predicted values estimated using a model for multicomponent diffusion. The study confirmed that the taurine/N-acetylaspartate exchange observed during postnatal development of rat brain plays a major, it not unique, role in maturational facilitation of intracellular high-energy phosphate transport.

Albumins↗

PubMed1993

31P localized spectroscopy of fetal brain in utero.

31-Phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopy of fetal brain in utero was obtained entirely noninvasively in rat utilizing image selected in vivo spectroscopy (ISIS). The results were in excellent agreement with the data obtained using the surface coil method in the late stage fetus, namely, high phosphomonoester (PME), low phosphocreatine (PCr), and high intracellular pH. Localized spectroscopy provides unprecedented opportunities for the investigation of fetal brain metabolism in utero.

Animals↗

PubMed1993

Noninvasive analysis of aldose reductase activities in rat testis: 3-FDG NMR spectroscopy and imaging.

Noninvasive investigation of aldose reductase activities in rat testis was performed using 3-fluoro-3-deoxy-D-glucose (3-FDG) and nuclear magnetic resonance (NMR) spectroscopy/imaging. Quantitative determination of testis aldose reductase activities, expressed as the sorbitol index, showed a value similar to that of brain. Sorbitol imaging demonstrated aldose reductase activities in testis to be confined primarily to the central region of this organ. The 3-FDG 19F NMR method appears to have clinical potential in the evaluation of testicular function, especially that of spermatogenesis, noninvasively.

Aldehyde Reductase↗

PubMed1993

Guanidinoethane sulfate: brain pH alkaline shifter.

A new category of agents, brain pH alkaline shifters, is described. Using the prototype agent, guanidinoethane sulfate (GES), the actual alkaline shift in pH was demonstrated in adult mice brain by 31-phosphorus (31P) nuclear magnetic resonance (NMR) in vivo spectroscopy. This alkaline shift was also shown to effectively reduce the extent of brain intracellular lactic acidosis brought about by anoxic insult. These findings support the notion that a pH alkaline shift may protect the brain against the deleterious effects of lactic acidosis. Since higher pH has been shown to significantly reduce beta-amyloid deposition, alkaline shifters may also have therapeutic potential in Alzheimer's disease.

Alkalies↗

PubMed1992

DNA sequence of the yeast transketolase gene.

Transketolase (EC 2.2.1.1) is the enzyme that, together with aldolase, forms a reversible link between the glycolytic and pentose phosphate pathways. We have cloned and sequenced the transketolase gene from yeast (Saccharomyces cerevisiae). This is the first transketolase gene of the pentose phosphate shunt to be sequenced from any source. The molecular mass of the proposed translated protein is 73,976 daltons, in good agreement with the observed molecular mass of about 75,000 daltons. The 5'-nontranslated region of the gene is similar to other yeast genes. There is no evidence of 5'-splice junctions or branch points in the sequence. The 3'-nontranslated region contains the polyadenylation signal (AATAAA), 80 base pairs downstream from the termination codon. A high degree of homology is found between yeast transketolase and dihydroxyacetone synthase (formaldehyde transketolase) from the yeast Hansenula polymorpha. The overall sequence identity between these two proteins is 37%, with four regions of much greater similarity. The regions from amino acid residues 98-131, 157-182, 410-433, and 474-489 have sequence identities of 74%, 66%, 83%, and 82%, respectively. One of these regions (157-182) includes a possible thiamin pyrophosphate (TPP) binding domain, and another (410-433) may contain the catalytic domain.

Aldehyde-Ketone Transferases↗