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Biomedical subjects

M Wong

Publications and source records attributed to M Wong.

408 records · Page 23Linked to original sources
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The propagation of relativistic heavy ions in multielement beam lines.

We describe calculations of the energy loss, range, stopping power, multiple scattering, and other related properties of a high-energy heavy-ion beam at any one of a set of beam line elements. A beam line element (e.g., any beam modification, detection, or control device) is characterized by its thickness, areal density, aperture, and function. The loss of multiply scattered particles to any finite-aperture detector is calculated in the small-angle approximation, and the position of the Bragg peak, as given by particles stopping in the second of two ionization chambers used for Bragg curve measurements, is estimated. A general purpose computer program, PROPAGATE, has been written to allow addition, deletion, and modification of the beam line elements used in the calculation and to provide a convenient means of repeating such calculations for arbitrary beam lines. Calculations and experimental measurements are compared and found to be in satisfactory agreement.

Computers↗
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The multiple Coulomb scattering of very heavy charged particles.

An experiment was performed at the Lawrence Berkeley Laboratory BEVALAC to measure the multiple Coulomb scattering of 650-MeV/A uranium nuclei in 0.19 radiation lengths of a Cu target. Differential distributions in the projected multiple scattering angle were measured in the vertical and horizontal planes using silicon position-sensitive detectors to determine particle trajectories before and after target scattering. The results were compared with the multiple Coulomb scattering theories of Fermi and Molière, and with a modification of the Fermi theory, using a Monte Carlo simulation. These theories were in excellent agreement with experiment at the 2 sigma level. The best quantitative agreement is obtained with the Gaussian distribution predicted by the modified Fermi theory.

Computer Simulation↗
PubMedDate not supplied

Diastolic spectrum of left-ventricular hypertrophy: the impact of etiology and coronary artery disease on Doppler transmitral velocity.

UNLABELLED: Diastolic filling of hypertrophied left ventricles has frequently been observed by Doppler methods. We hypothesized that filling characteristics in hypertrophy vary with etiology and concurrent ischemia. For patients with hypertrophy, the left-ventricular ejection fraction was > 0.47 +/- 0.16, end-diastolic pressure was > 15 +/- 2 mm Hg, end-diastolic volume index was < 96 +/- 12 ml/m2 and left-ventricular mass index was 127 +/- 7 g/m2. Peak E (early) and peak A (late) diastolic velocities and E-wave deceleration time, respectively, were as follows (significant unless otherwise indicated): normal subjects (NS), 79 +/- 9 and 82 +/- 19 cm/s, and 151 +/- 7 ms; cardiomyopathic hypertrophy, 63 +/- 16, 83 +/- 15 (NS) and 193 +/- 63, aortic stenosis without coronary disease, 110 +/- 10, 128 +/- 12 and 158 +/- 22 (NS); aortic stenosis with coronary disease, 57 +/- 12, 86 +/- 26 (NS) and 187 +/- 39; hypertension without coronary disease, 107 +/- 9, 128 +/- 9 and 143 +/- 22 (NS); hypertension with coronary disease, 58 +/- 12, 84 +/- 26 (NS) and 189 +/- 29. CONCLUSIONS: Hypertrophied left ventricles filled with two diastolic Doppler patterns: a relaxation abnormality with low peak E and delayed deceleration in hypertrophic cardiomyopathy, and a compliance abnormality with tall peak E and normal deceleration in pressure overload hypertrophy. When coronary artery disease occurred with pressure overload hypertrophy, impaired relaxation was the dominant pattern. Therefore, in addition to the known physiologic influences on diastolic filling, the etiology and presence of coronary artery disease modulate the configuration of transmitral velocities into hypertrophied ventricles.

Aortic Valve Stenosis↗
PubMedDate not supplied

Connective tissue proteinases and inhibitors in abdominal aortic aneurysms. Involvement of the vasa vasorum in the pathogenesis of aortic aneurysms.

Recent studies have shown that increases in proteolytic activity are associated with abdominal aortic aneurysms (AAAs). We have studied samples of the dilated aortic wall, taken during corrective surgery for AAAs, in terms of the number, type, and tissue location of connective tissue proteinases and their inhibitors. Five distinct caseinolytic serine proteinases and six gelatinolytic metalloproteinases were resolved by molecular weight by use of sodium dodecyl sulfate-substrate gel electrophoresis. Isoforms of the Mr 92,000 neutrophil gelatinase were identified by immunoprecipitation of biosynthetically labeled organ culture media. About 50% of the total radiolabeled protein secreted by AAA organ cultures was identified as the Mr 30,000 glycoprotein, tissue inhibitor of metalloproteinase (TIMP), by immunoprecipitation. Both TIMP and gelatinase were localized to the vasa vasorum by immunoperoxidase staining. However, interstitial collagenase could not be detected by any method. These results suggest the involvement of the vasa vasorum in the maintenance and possibly the genesis of AAAs.

Aorta, Abdominal↗
PubMedDate not supplied

In-vivo NMR thermometry with liposomes containing 59Co complexes.

The ability to make localized temperature measurements in tissue during hyperthermia treatment of cancer is an essential factor in optimizing its efficacy. To this end we have developed and evaluated the complex tris(ethylenediamine) cobalt(III) trichloride as a temperature sensor by determining the temperature dependence of it 59Co nuclear magnetic resonance chemical shift. Encapsulating this complex within liposomes targets the agent to the reticuloendothelial system. Temperature changes of the order of 0.1 degrees C have been measured in vivo on rats, and the half-life of the complex within the body determined by plasma emission spectroscopy.

Animals↗
PubMedDate not supplied

Differential effects of embryonic immobilization on the development of fibrocartilaginous skeletal elements.

The importance of mechanical influences during skeletal development has been well established in both experimental studies and computer models. Under conditions of embryonic immobilization, it has been observed that the early stages of joint formation proceed normally (up to and including interzone formation), but the later stages of joint cavitation and maintenance are impaired, resulting in fusion of the cartilaginous elements across the presumptive joint line. Two structures in particular are noticeably absent from late-stage synovial joints in immobilized chick embryos: the menisci of the tibiofemoral joint and the plantar tarsal sesamoid of the tibiotarsal joint. Both of these fibrocartilaginous structures are known to serve mechanical functions in postnatal animals, helping to distribute loads within the joint and, in the case of sesamoid structures, to provide a mechanical advantage to muscles acting across the joint. We demonstrate in this study that embryonic immobilization differentially affects the developmental fate of these two distinct fibrocartilages. The absence of the plantar tarsal sesamoid in late-stage immobilized embryos is due to a failure in the initial formation of this structure. In contrast, the early stages of meniscus formation proceed normally. Without the normal mechanical stimuli of skeletal muscle contractions, however, the meniscus fails to mature and ultimately degenerates.

Animals↗
PubMedDate not supplied

Bias in maternal reports of smoking during pregnancy associated with fetal distress.

BACKGROUND: Studies examining the adverse effects of smoking during pregnancy commonly use maternal reports. We hypothesized that if an adverse event occurred during pregnancy, women may underreport smoking. This study looked for bias in maternal report of smoking if fetal distress occurs. METHODS: Data were collected prospectively from patients attending The MotheRisk Program who smoked during pregnancy, and were categorized by delivery outcome, maternal and neonatal characteristics, and the raw number of cigarettes smoked per day during pregnancy reported at clinic and at follow-up. The difference between these two values was compared. RESULTS: 95 women had uneventful deliveries and 25 had fetal distress. Women who reported fetal distress decreased their report of smoking after delivery compared to their original report during pregnancy, whereas women with an uneventful labour did not (p = 0.04). CONCLUSIONS: Our results suggest that if an adverse pregnancy outcome occurs, mothers may tend to underreport their cigarette consumption.

Adult↗
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China↗