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Biomedical subjects

C T Chen

Publications and source records attributed to C T Chen.

At least 145 records · Page 8Linked to original sources
PubMed1994

Electrical burns associated with head injuries.

Although electrical burns account for a small portion of all thermal injuries, their treatment becomes more complex when associated with injuries of other organs. From July 1987 through December 1991, 8 of 249 burned patients sustained electrical burns associated with head injuries. The mean total body surface area burned was 19% (range, 2%-45%). Computed tomographic (CT) scans of the brain revealed that six patients with moderate to severe head injuries had intracranial hemorrhage including three cases of intracerebral hematoma and another three cases of epidural hematoma. Half of these patients underwent surgical intervention for removal of intracranial hematomas and a compound depressed fracture segments of the skull, and the others were treated conservatively. All the patients progressively recovered consciousness with Glasgow Coma Scale scores of 14 or more and minimal neurologic sequelae. The combination of early detection and prompt removal of life-threatening intracranial hematomas with aggressive support of electrical victims who appear dead would minimize the morbidity and mortality in patients with electrical burns and head injuries.

Adolescent↗
PubMed1994

Insulating DNA directs ubiquitous transcription of the Drosophila melanogaster alpha 1-tubulin gene.

We identify DNA regions that are necessary for the ubiquitous expression of the Drosophila melanogaster alpha 1-tubulin (alpha 1t) gene. In vitro transcription showed that two upstream regions, tubulin element 1 (TE1 [29 bp]) and tubulin element 2 (TE2 [68 bp]), and a downstream region activate transcription. Germ line transformation demonstrated that these three regions are sufficient to direct the alpha 1t core promoter to begin transcribing at the stage of cellular blastoderm formation and to continue thereafter at high levels in all tissues and developmental stages. Remarkably, mutation of any one of these regions results in high sensitivity to chromosomal position effects, producing different but reproducible tissue-specific patterns of expression in each transformed line. None of these regions behaves as an enhancer in a conventional germ line transformation test. These observations show that these three regions, two of which bind the GAGA transcription factor, act ubiquitously to insulate from position effects and to activate transcription. The results also provide vectors for ubiquitous expression of gene products and for examining silencer activities.

Animals↗
PubMed1994

A case report of triple nostrils.

A rare case of supernumerary nostril is reported. The surplus nostril was located above and lateral to the right normal nostril and ended blindly. Fistulorhinoplasty was performed and the result was good.

Humans↗
PubMed1993

Soft x-ray magnetic circular dichroism: a probe for studying paramagnetic bioinorganic systems.

Soft x-ray magnetic circular dichroism was used to study a paramagnetic bioinogranic system. We measured the Fe L edges of Pyrococcus furiosus rubredoxin, using circularly polarized synchrotron radiation, a split-coil super-conducting magnet, low sample temperatures, and fluorescence detection. The observed dichroism effect is strong (30%) and in general agreement with the calculation. The method is element- and oxidation state-specific, and the data can be interpreted by established theoretical procedures. Soft x-ray magnetic circular dichroism demonstrates enormous potential as a probe for studying paramagnetic systems in biology, chemistry, and material science.

Bacteria↗
PubMed1993

Edema-inducing activity of a lethal protein with phospholipase A1 activity isolated from the black-bellied hornet (Vespa basalis) venom.

The lethal protein of the hornet (Vespa basalis) venom is a phospholipase A1 toxin (mol. wt approximately 32,000) with a potent hemolytic activity. Subplantar injection of the toxin caused a dose-dependent swelling in the rat hind paw. Its potency was higher than those of phospholipases A2 and cardiotoxin from cobra venoms. Hind-paw edema induced by the toxin was inhibited by antiserotonin drugs (cyproheptadine and methysergide), indomethacin and betamethasone. Antihistamine (chlorpheniramine) showed a relatively weak inhibition. Intradermal injection of the toxin into back skin of the rat also induced local edema which was inhibited by chlorpheniramine and methysergide. Rats pretreated with multiple doses of compound 48/80 showed a moderate decrease in the histamine and serotonin content of rat skin, and a slight decrease in paw edema induced by the toxin, while a single dose of reserpine markedly diminished the toxin-induced edema in association with depletion of serotonin in rat skin. The edema-inhibitory action of amine-depleting agents appeared to correlate with their potencies to deplete serotonin in the skin. It is suggested that serotonin, prostaglandin E2, and to a lesser extent of histamine are involved in producing the local effect of the toxin. However, serotonin released by the toxin appears to be the major factor mediating the toxin-induced edema in the rat.

Animals↗
PubMed1993

Correction for photon attenuation in SPECT: analytical framework, average attenuation factors, and a new hybrid approach.

We provide a unified framework for the investigation of convergence properties of the iterative algorithms for photon attenuation correction in SPECT, including the iterative Chang method--a commonly used approach in which an average attenuation factor calculated over all projection angles is employed in a pointwise correction scheme. A new average attenuation factor calculated along the projection line is introduced, which can compensate exactly for the attenuation effect in the case of a uniform activity distribution. We propose a new hybrid approach in which we use this new average attenuation factor initially and then shift to the iterative Chang method in later iterations. This hybrid approach was evaluated in a simulation study by use of a computer-generated phantom with both non-uniform activity and non-uniform attenuation distributions. The results demonstrate that this hybrid approach improves the convergence speed of the iterative Chang method and produces reconstructed images of high quality.

Algorithms↗
PubMed1992

Nitrogen chemical structure in DNA and related molecules by X-ray absorption spectroscopy.

The electronic environment of nitrogen in nucleic acid bases, nucleotides, polynucleotides and DNA has been studied, for the first time using X-Ray Absorption Near-Edge Spectroscopy (XANES). Generally, the spectra of these complex molecules consist of low energy bands corresponding to 1s-->pi* transitions and high energy bands corresponding to 1s-->sigma* transition, as illustrated using several nitrogen model compounds. The 1s-->pi* transitions show particular sensitivity to the chemical environment of the nitrogen. Oxygen substitution on ring carbon atoms generally results in a significant blue shift of the lowest 1s-->pi* bands while halogen substitution results in a small blue shift. These observations illustrate the significance of the disturbance of the aromatic ring system produced by exocyclic carbonyl groups. Direct substitution on the nitrogen frequently results in significant spectral perturbations. Differences between the spectra of the polynucleotides and the sums of spectra of the individual nucleotides point to the effects of hydrogen-bonding in complementary double-helix structures. The XANES spectrum of a DNA sample with a known ratio of the polynucleotides is equivalent to the weighted sum of the spectra of individual polynucleotides, indicating that the difference in base stacking interactions produces negligible spectral effects. The variability of nitrogen K-edge spectra in these samples and in protein may be useful for chemically specific imaging using X-ray microscopes.

Animals↗
PubMed1992

Superresolved tomography by convex projections and detector motion.

If the spatial resolution of an image-acquisition system is limited by the size of its component detector elements, then scanning may be required for the signal to be fully sampled. In such cases interpolation methods are normally applied to reproduce a uniformly sampled signal from the set of observations. Alternatively, however, this step can be treated as a restoration problem, in which case the extra measurements made accessible by detector motion may contain sufficient information to superresolve the signal, i.e., to recover information beyond the limit normally associated with finite detector size. We describe the application of this concept to the problem of constructing the projection matrix from a set of noise-corrupted tomographic measurements made by a moving detector array. In particular we focus on the case encountered in many tomographic applications in which the spatial response functions are approximately stationary with object depth. The method of projections onto convex sets is used in conjunction with an underrelaxation scheme to recover the projection matrix, from which the image is reconstructed by the standard filtered backprojection algorithm. Simulation results demonstrate that this approach applied to data acquired by a wobbling positron emission tomography system can substantially enhance the quality of the reconstructed image, even in the presence of high levels of quantum noise. The projection-matrix recovery step can be performed in a matter of seconds; thus the benefits of signal recovery are gained without a significant sacrifice in computation time.

Image Processing, Computer-Assisted↗
PubMed1992

MIRD Pamphlet No. 14: a dynamic urinary bladder model for radiation dose calculations.

The constant-volume urinary bladder model in the standard MIRD phantom has recognized limitations. Various investigators have developed detailed models incorporating more physiologically realistic features such as expanding bladder contents and residual volume, and variable urinary input rate, initial volume and first void time. We have reviewed these published models and have developed a new model incorporating these factors. The model consists of a spherical source with variable volume to simulate the bladder contents and a wall represented by a spherical shell of constant volume. The wall thickness varies as the source expands or contracts. The model provides for variable urine entry rate (three different hydration states), initial bladder contents volume, residual volume and first void time. The voiding schedule includes an extended nighttime gap during which the urine entry rate is reduced to one-half the daytime rate. Radiation dose estimates have been calculated for the bladder wall surface (including photon and electron components) and at several depths in the wall (electron component) for [18F]FDG, 99mTc-DTPA, 99mTc-HEDP, [99mTc]pertechnetate 99mTc-RBCs, 99mTc-glucoheptonate, 99mTc-MAG3, [123I]/[124I]/[131I]OIH and sodium [131I]iodide(Nal). The initial bladder volume and first void time that provide the lowest radiation dose to the bladder wall are determined separately for each compound to give guidance for establishing dose reduction protocols.

Algorithms↗
PubMed1991

Bayesian image processing in magnetic resonance imaging.

In the past several years, image processing techniques based on Bayesian models have received considerable attention. In our earlier work, we developed a novel Bayesian approach which was primarily aimed at the processing and reconstruction of images in positron emission tomography. In this paper, we describe how the technique has been adopted to process magnetic resonance images in order to reduce noise and artifacts, thereby improving image quality. In this framework, the image is assumed to be a statistical variable whose posterior probability density conditional on the observed image is modeled by the product of the likelihood function of the observed data with a prior density based our prior knowledge. A Gibbs random field incorporating local continuity information and with edge-detection capability is used as the prior model. Based on the formalism of the posterior density, we can compute an estimate of the image using an iterative technique. We have implemented this technique and applied it to phantom and clinical images. Our results indicate that the approach works reasonably well for reducing noise, enhancing edges, and removing ringing artifact.

Algorithms↗
PubMed1991

Radiation dose to the bladder wall from 2-[18F]fluoro-2-deoxy-D-glucose in adult humans.

Accurate determination of the radiation dose to the bladder wall from 2-[18F]fluoro-2-deoxy-D-glucose (2-[18F]FDG) is important because the bladder is the critical organ in radiotracer studies using 2-[18F]FDG. The radiation dose to the bladder wall from injected 2-[18F]FDG was estimated using both a dynamic bladder model and the conventional MIRD model. The dynamic model takes into account the excretion rate, the varying size of the bladder, the volume at injection, and an estimated bladder time activity curve. Our data from 302 adult subjects in a five-year period indicate that when the bladder is large at the time of injection, the dose to the bladder is greatly reduced. The absorbed dose of the bladder based on the dynamic model for an initial volume of 450 ml is 0.16 +/- 0.06 rad/mCi, while that for an initial volume of 200 ml is calculated to be 0.37 +/- 0.18 rad/mCi. The MIRD model estimates an average value of 0.35 +/- 0.16 rad/mCi for the 302 cases.

Adult↗
PubMed1990

Tonic suppression of baroreceptor reflex by endogenous neurotensin in the rat.

We evaluated the modulatory role of endogenous neurotensin (NT) in baroreceptor reflex (BRR) response in Sprague-Dawley rats anesthetized with pentobarbital sodium. Intracerebroventricular (i.c.v.) administration of NT (15 or 30 nmol) significantly reduced the sensitivity of the BRR response. Blocking the endogenous activity of the tridecapeptide with its specific antagonist, (D-Trp11)-NT (4 or 8 nmol) or antiserum against NT (1:20); or inhibiting the aminopeptidases with bestatin (200 nmol), on the other hand, promoted a potentiation of BRR response. When administered together with bestatin (200 nmol), the suppressive effect of NT (15 nmol) on the BRR response was further enhanced, as was the augmentative action of (D-Trp11)-NT (4 nmol). Upon microinjection into the bilateral nucleus tractus solitarius (NTS), NT (600 pmol) and (D-Trp11)-NT (150 pmol) respectively elicited a reduction and enhancement of the BRR response. These results suggest that neurons that contain NT may participate in central cardiovascular regulation by tonically suppressing the BRR, possibly via an action on the NTS where baroreceptor afferents terminate.

Animals↗
PubMed1990

Change in hexose distribution volume and fractional utilization of [18F]-2-deoxy-2-fluoro-D-glucose in brain during acute hypoglycemia in humans.

We used positron emission tomography (PET) to study the effects of mild hypoglycemia on cerebral glucose uptake and metabolism. Nine healthy men were studied under basal saline-infusion conditions, and during euglycemic and hypoglycemic clamp studies. Insulin was infused at the same rate (1 mU.kg-1.min-1) in both clamp studies. In euglycemic clamp studies, glucose was infused at a rate sufficient to maintain the basal plasma glucose concentration, whereas in hypoglycemic clamp studies, the glucose infusion rate was reduced to maintain the plasma glucose at 3.1 mM. Each study lasted 3 h and included a 30-min baseline period and a subsequent 150-min period in which insulin or glucose was administered. Blood samples for measurement of insulin, glucose, cortisol, growth hormone, and glucagon were obtained at 20- to 30-min intervals. A bolus injection of 5-10 mCi [18F]-2-deoxy-2-fluoro-D-glucose (2-DFG) was administered 120 min after initiation of the study, and plasma radioactivity and dynamic PET scans were obtained at frequent intervals for the remaining 40-60 min of the study. Cerebral regions of interest were defined, and concentrations of radioactivity were calculated and used in the three-compartment model of 2-DFG distribution described by Sokoloff. Glucose levels were similar during saline-infusion (4.9 +/- 0.1 mM) and euglycemic clamp (4.8 +/- 0.1 mM) studies, whereas the desired degree of mild hypoglycemia was achieved during the hypoglycemic clamp study (3.1 +/- 0.1 mM, P less than 0.05). The insulin level during saline infusion was 41 +/- 7 pM.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗