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Biomedical subjects

H M Cheng

Publications and source records attributed to H M Cheng.

At least 91 records · Page 5Linked to original sources
PubMed1992

Magnetic resonance microscopy of rabbit eyes.

Magnetic resonance (MR) micro-imaging was performed on enucleated eyes from rabbits previously injected with perfluoropropane gas (C3F8), with or without the surgical creation of retinal detachment. Condensed vitreous, which exhibited shortened longitudinal relaxation time (T1), could be differentiated with proton-density and T1-weighted imaging. Gradient-echo imaging could in addition detect vitreo-retinal tractions. The detached retina itself was also seen. Further, proton-density but not T1-weighted imaging showed lens opacities appearing as high-intensity regions. MR microscopy is a convenient method for gross morphological examination of intact eyes.

Animals↗
PubMed1992

Shape of the myopic eye as seen with high-resolution magnetic resonance imaging.

We have obtained multislice magnetic resonance (MR) images of the eye and calculated ocular dimensions along the three cardinal axes: antero-posterior (A-P), equatorial, and vertical. We found no difference in the shape of hyperopic (average refractive error: +3.72 D) and emmetropic eyes, both of which had an equatorial diameter longer than the A-P and vertical diameters. Myopic eyes (average refractive error: -6.54 D) were larger than hyperopic eyes, and most had the same spheroelliptical shape as that of the emmetropic and hyperopic eyes. The results suggest that during myopic progression an overall enlargement or a radial volume expansion has occurred.

Adult↗
PubMed1992

Arginine induced insulin release in patients with newly onset non-insulin-dependent diabetes mellitus.

To examine the release of insulin in response to oral glucose, intravenous glucagon and intravenous arginine, we measured the levels of plasma glucose, immuno-reactive insulin (IRI) and C-peptide levels on fasting and following an oral glucose loading (OGTT), intravenous glucagon (GON) and arginine (ARG) infusion test in nine newly diagnosed non-insulin dependent diabetics. Their ages ranged from 38 to 65. The fasting plasma glucose and hemoglobin A1c levels were 240 +/- 14 mg/dl (Mean +/- SEM) and 10.7 +/- 0.54%, respectively. Mean values of the peak C-peptide/fasting C-peptide ratio and peak IRI/fasting IRI ratio were significantly increased, as compared with the basal level (P < 0.05), but not significantly different from those of the OGTT, GON and ARG test. In conclusion, the effect of arginine-induced insulin secretion in non-insulin dependent diabetes mellitus is as good as those of glucose or glucagon.

Adult↗
PubMed1992

Comparison between B-scan ultrasound and MRI in the detection of diabetic vitreous hemorrhage.

The efficacy of proton magnetic resonance imaging (MRI) was evaluated and compared with that of B-scan ultrasound in the detection and differentiation of diabetic vitreous hemorrhage. Although conventional spin-echo MRI could not locate vitreous hemorrhages, gradient-recalled-echo (GRE) MRI readily did so. The aberrant signals appeared to originate from the interfacing between hemorrhages and the vitreous, and possibly also from the paramagnetic effect of the ferrous ion. The information provided by boundary/susceptibility detection, unique to the GRE sequence, is useful in delineating the extent of vitreous hemorrhage and hemolysis. However, for the diagnosis and follow up of diabetic vitreous hemorrhages, MRI appears no more informative than B-scan ultrasonography.

Aged↗
PubMed1991

Analysis of diabetic cataractogenesis using chemical-shift nuclear magnetic resonance microscopy.

We here report the analysis of single rabbit lenses under high-glucose stress using four-dimensional 13C nuclear magnetic resonance (NMR) spectroscopy (three spatial and one chemical-shift). We have produced spatial maps of lenticular metabolites (glucose, sorbitol, and lactate) with submillimeter in-plane resolution. The production of sorbitol and its inhibition are also presented. This is the first study to report regional tissue metabolism. We expect further improvements in spatial resolution and acquisition times that will enable localized kinetic studies in intact tissues.

Animals↗
PubMed1991

GdDTPA-enhanced magnetic resonance imaging of the aqueous flow in the rabbit eye.

Magnetic resonance imaging with gadolinium-diethylenetriaminepentaacetic acid complex (GdDTPA) as the contrast agent was used to image the aqueous chamber of the eye. This method, in addition to providing spatial information, permits quantitative study of the aqueous flow. GdDTPA solution was applied either topically or intravenously, entering the anterior chamber via different pathways. The wash-in and wash-out of GdDTPA follow a two-compartment model which enables determination of the aqueous flow rate by multiplying the aqueous chamber volume by the wash-out rate constant. Rabbit eyes showed a flow rate of 1.5-2 microliters/min which was retarded by the systemic administration of acetazolamide (Diamox).

Acetazolamide↗
PubMed1991

Measurement of water movement in the rabbit eye in vivo using H2(17)O.

Topically applied (eyedrop) H2(17)O (10% enrichment) was used in magnetic resonance studies to quantify intraocular water dispersion in vivo. The rate of H2(17)O removed from the aqueous chamber is in the order of 0.1 ml/min/ml of tissue. Similar results are obtained with either proton imaging or 17O spectroscopy. Parallel experiments of direct injection of H2(17)O into the aqueous chamber supported the topical data. Proton MR imaging of H2(17)O dissipation from the aqueous chamber with clinical imagers, coupled with eyedrop application, suggests clinical possibilities.

Animals↗
PubMed1991

Water movement in the rabbit eye.

The intraocular distribution of topically applied D2O was quantified using deuterium nuclear magnetic resonance (NMR) spectroscopy. D2O appeared in all tissues with the highest concentration in the aqueous humor (1.2 M); however, it rapidly dissipated from the eye. Surface coil NMR spectroscopy on D2O-treated eyes in vivo showed that the flow pattern was best described by a single exponential decay plus a constant. This suggests that the D2O flow consisted of a flow component representing vascular circulation (with a flow rate constant of 0.101 min-1), and a reservoir-like component. Topical D2O in conjunction with the surface-coil NMR technique can be used to examine the movement of water in the anterior segment of the living eye.

Animals↗
PubMed1991

The effect of insulin and aldose reductase inhibition on the phosphate metabolism of streptozotocin-diabetic rat lens.

Sorbitol-3-phosphate (S3P) and fructose-3-phosphate (F3P) are novel phosphorus compounds recently discovered and identified in the crystalline lens as well as other tissues. These phosphates increased with diabetes progression in streptozotocin-diabetic rat lenses. Treatment of these rats with an orally administered aldose reductase inhibitor eliminated S3P and intramuscularly injected insulin obliterated F3P. These results indicate that enzymes catalyzing S3P and F3P formation co-activate with aldose reductase activation and hyperglycemia, respectively.

Aldehyde Reductase↗
PubMed1991

Analysis of concurrent glucose consumption by the hexose monophosphate shunt, glycolysis, and the polyol pathway in the crystalline lens.

A method based on 13C-NMR spectroscopy is described, in which the metabolism of [13C2]glucose was assessed in intact rat lenses. By analysing the ratio of 13C3/(13C2 + 13C3) lactate, a quantitative measurement of the hexose monophosphate shunt (HMPS) activity could be derived. Similarly, measurements of the time-dependent increase of lactate and sorbitol permitted the determination of the activity of the Embden-Meyerhof pathway and the polyol pathway, respectively. This method offers significant advantages over other biochemical and spectroscopic methods and allows for the first time a direct correlation between the activities of the polyol pathway and the HMPS.

Animals↗
PubMed1991

Soft filamentous woven polyester arterial prosthesis from China.

Woven polyester arterial prostheses have traditionally been known for their tight construction and smooth surface which has limited their healing capacity and resulted in poor attachment of their internal and external capsules. A new woven prototype has recently been developed in the Peoples' Republic of China. Among its unique features are its high physical porosity, softness and flexibility. This study undertook a series of in vitro tests to characterize its structure and physical properties in comparison with four commercial polyester grafts of North American origin. In addition, an animal trial was completed in which the new prototype was implanted as an infrarenal aortic substitute in 20 dogs for periods ranging from 4 h to 12 month. The in vitro tests confirmed a unique lightweight, highly porous, satin weave construction. Because of its high water permeability, preclotting was necessary before implantation. Once preclotted and installed, no significant blood loss was observed, and 19 of the 20 grafts remained patent at the sacrifice. Rapid full-width healing was achieved with tightly bound capsules, and more extensive tissue ingrowth was observed. Further work is needed to evaluate its long-term durability as an arterial substitute.

Animals↗
PubMed1991

Fate of water in the soft contact lens immediately after lens placement onto the cornea.

Soft contact lenses presoaked in D2O or H2(17)O were used to examine the movement of water immediately after their placement onto the eye. Two experiments were conducted: (1) the rate of D2O loss from these soft lenses was determined by assaying residual D2O with nuclear magnetic resonance spectroscopy; and (2) the movement of water into/inside the eye was followed by tracking the path of H2(17)O using magnetic resonance imaging. D2O dissipation occurred in two phases: an initial rapid washout (1.25 ml/h) followed by a slower phase (0.13 ml/h). The latter was eliminated by previous contact lens wear. The H2(17)O study showed that once water entered the anterior chamber, it rapidly exchanged with water in the ocular (predominantly iris) circulation (flow rate constant = 0.1/min). It appears that exogenous water, in this case water from the soft lens, ultimately interacts with the ocular circulation. This is one aspect of cornea-soft lens interaction previously unreported.

Animals↗
PubMed1991

Magnetic resonance imaging of the human eye in vivo.

Because of the broad range of T1 (longitudinal relaxation time), T2 (transverse relaxation time), and proton density of the component tissues in the eye, proton magnetic resonance imaging (MRI) can provide ocular images of high contrast. The use of surface coils further enhances the signal-to-noise (S/N) ratio and shortens the image acquisition time to 1 to 6 min. High-resolution MR images of the eye therefore can be acquired readily and routinely. At present, with conventional spin-echo imaging, the in-plane resolution of MR images can be as high as (but not limited to) 0.3 x 0.3 mm with a 3-mm slice thickness. MRI can be used to detect and differentiate ocular lesions and to determine the ocular shape and measure ocular dimensions such as tissue thickness, curvature, and volume.

Contrast Media↗
PubMed1991

Epstein-Barr virus nuclear antigen 1 linear epitopes that are reactive with immunoglobulin A (IgA) or IgG in sera from nasopharyngeal carcinoma patients or from healthy donors.

The entire amino acid sequence of the unique region of the EBNA 1 protein was synthesized as a set of 41 20-residue peptides with an overlap of 10 amino acids. The peptides were tested in the enzyme-linked immunosorbent assay for reactivity with immunoglobulin A (IgA) and IgG in sera from 50 patients with nasopharyngeal carcinoma (NPC) as compared with 36 serum samples from healthy Epstein-Barr virus (EBV)-seropositive donors and 5 serum samples from EBV-negative donors. The most immunoreactive peptide for both IgA and IgG binding was localized to the glycine-alanine repeat domain of the antigen. In the unique regions, 16 immunoreactive peptides were found. Of these, four were reactive with IgG but not IgA and three peptides were reactive with IgA but not IgG in NPC sera. In addition, several IgA and IgG epitopes on the carboxy-terminal region were specifically reactive with NPC sera, but unreactive with sera from healthy EBV-positive donors. The results suggest that EBV serology specific for individual epitopes may provide additional useful information not available by conventional serology with whole antigens or the EBNA complex.

Amino Acid Sequence↗
PubMed1991

Magnetic resonance imaging of intraocular tamponades.

The efficacy of proton magnetic resonance imaging in differentiating vitreous from C3F8 gas and silicone oil tamponades, and in detecting fresh hemorrhages and condensed vitreous was tested in rabbits in vivo. The results suggest that this imaging method could provide a useful alternative to ultrasonography, especially in eyes with opaque media.

Animals↗