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Biomedical subjects

S Tung

Publications and source records attributed to S Tung.

16 recordsLinked to original sources
PubMed2004

Vortex-lattice dynamics in rotating spinor Bose-Einstein condensates.

We observe interlaced square vortex lattices in rotating dilute-gas spinor Bose-Einstein condensates (BEC). After preparing a hexagonal vortex lattice in a one-component BEC in an internal atomic state |1, we coherently transfer a fraction of the superfluid to a different state |2. The subsequent evolution of this pseudo-spin-1/2 superfluid towards a state of offset square lattices involves an intriguing interplay of phase-separation and -mixing dynamics, both macroscopically and on the length scale of the vortex cores, and a stage of vortex turbulence. The stability of the square structure is proved by its response to applied shear perturbations. An interference technique shows the spatial offset between the two vortex lattices. Vortex cores in either component are filled by fluid of the other component, such that the spin-1/2 order parameter forms a Skyrmion lattice.

Journal Article↗
PubMed2001

Catheter ablation in patients with multiple and unstable ventricular tachycardias after myocardial infarction: short ablation lines guided by reentry circuit isthmuses and sinus rhythm mapping.

BACKGROUND: Extensive lines of radiofrequency (RF) lesions through infarct (MI) can ablate multiple and unstable ventricular tachycardias (VTs). Methods for guiding ablation that minimize unnecessary RF applications are needed. This study assesses the feasibility of guiding RF line placement by mapping to identify a reentry circuit isthmus. METHODS AND RESULTS: Catheter mapping and ablation were performed in 40 patients (MI location: inferior, 28; anterior, 7; and both, 5) with an electroanatomic mapping system to measure the infarct region and ablation lines. The initial line was placed in the MI region either through a circuit isthmus identified from entrainment mapping or a target identified from pace mapping. A total of 143 VTs (42 stable, 101 unstable) were induced. An isthmus was identified in 25 patients (63%; 5 with only stable VTs, 5 with only unstable VTs, and 15 with both VTs). Inducible VTs were abolished or modified in 100% of patients when the RF line included an isthmus compared with 53% when RF had to be guided by pace mapping (P=0.0002); those with an isthmus identified received shorter ablation lines (4.9+/-2.4 versus 7.4+/-4.3 cm total length, P=0.02). During follow-up, spontaneous VT decreased markedly regardless of whether an isthmus was identified. VT stability and number of morphologies did not influence outcome. CONCLUSIONS: A 4- to 5-cm line of RF lesions abolishes all inducible VTs in more than 50% of patients. Less ablation is required if a reentry circuit isthmus is identified even when multiple and unstable VTs are present.

Aged↗
PubMed2001

Epidemiological survey of oral submucous fibrosis and leukoplakia in aborigines of Taiwan.

A population-based survey was designed to investigate the prevalence of areca/betel quid chewing, oral submucous fibrosis and leukoplakia in a typical aboriginal community of southern Taiwan. Three hundred and twelve people 20 years of age or older were collected in the study. The prevalence of chewing areca/betel quid was 69.5%, with an average of 17.3 portions a day for an average 24.4 years. More women (78.7%) than men (60.6%) chewed areca/betel quid. The prevalences of oral submucous fibrosis and leukoplakia were 17.6% and 24.4%, respectively. It was found that the odds ratio for chewing areca/betel quid and having at least one of the above oral mucosal lesions was 8.21. Any additional smoking or drinking habits were not significant for having oral mucosal lesions. Although the areca/betel quid in Taiwan does not contain any tobacco, a significant association was still identified between areca/betel quid chewing and oral mucosal lesions.

Adult↗
PubMed2000

Sleep disturbances in clinic patients with functional bowel disorders.

OBJECTIVE: Sleep deprivation can lower visceral perception thresholds and nonregenerative sleep has been implicated as an etiological factor in chronic hyperalgesia syndromes. The aims of our study were to quantify the self-reported prevalence and type of sleep disturbances in patients with different functional bowel disorders (FBD) and to determine if this prevalence is related to involvement of the upper or lower gastrointestinal (GI) tract, perceived disease severity, or psychological comorbidity. METHODS: We enrolled 505 new FBD patients from an academic referral center specializing in functional GI disorders and 247 community based healthy controls. All patients and controls were prospectively evaluated by validated bowel symptom and sleep questionnaires. A psychological profile was obtained by SCL-90R. RESULTS: We found that 68% of functional dyspepsia (FD), 71.2% of irritable bowel syndrome (IBS)+FD, 50.2% of IBS, and 55.1% of the normal subjects reported having sleep disturbances. Waking up repeatedly during the night and waking up in the morning feeling tired or not rested were the most commonly reported sleep patterns; 57.2% of the patients reported that their abdominal ache awakened them from sleep during the night. Self-reported sleep disturbance was directly related to the perceived intensity of GI symptoms. Self-reported sleep disturbances were equally common in both male (57%) and female (58.4%) FBD patients. There was no significant difference between the mean anxiety and depression scores between patients with and without sleep dysfunction. CONCLUSIONS: FD patients, but not IBS patients, reported sleep disturbances more frequently than healthy control subjects. Abdominal pain or discomfort that awaken FBD patients from sleep during the night were common, and thus a poor discriminating factor between organic and functional disorders.

Abdominal Pain↗
PubMed1999

Symptoms and visceral perception in patients with pain-predominant irritable bowel syndrome.

OBJECTIVE: Abdominal pain is thought to be a hallmark of the irritable bowel syndrome (IBS), although currently used symptom criteria do not differentiate between abdominal pain and discomfort. By focusing on viscerosensory symptoms, we sought to determine: 1) which type of symptoms are most commonly reported by IBS patients, and 2) whether patients who report pain as their most bothersome symptom differ in clinical, psychological, and physiological characteristics. METHODS: A total of 443 consecutive new patient referrals to a tertiary referral center for functional gastrointestinal disorders who met symptom criteria for IBS were given validated, psychometric, health status, and bowel symptom questionnaires containing specific questions regarding the patients' predominant viscerosensory gastrointestinal symptom. Of these patients, 155 (35%) also met criteria for functional dyspepsia. A representative subset of the total IBS patient population (n = 58) underwent evaluation of perceptual responses to controlled rectal distension before and after a noxious sigmoid conditioning stimulus. RESULTS: Viscerosensory symptoms clustered into four groups: 1) abdominal pain, 2) bloating-type discomfort, 3) sensation of incomplete rectal evacuation, and 4) extraabdominal (chest pain or pressure and nausea). A total of 66% of patients reported gas as one of their viscerosensory symptoms, whereas 60% reported abdominal pain as one of their symptoms. Only 29% rated abdominal pain as their most bothersome symptom, whereas bloating-type symptoms were listed by 60% as most bothersome. Although pain predominance did not correlate with the severity of gastrointestinal or psychological symptoms, there was a significant correlation with the development of rectal hypersensitivity in response to the sigmoid conditioning stimulus. CONCLUSIONS: In a tertiary referral population of IBS patients: 1) abdominal pain is reported by only one third of patients as their most bothersome viscerosensory symptoms; and 2) pain-predominance correlates with development of rectal hypersensitivity after a noxious sigmoid stimulus.

Abdominal Pain↗
PubMed1998

A pencil-beam photon dose algorithm for stereotactic radiosurgery using a miniature multileaf collimator.

A computer-controlled miniature multileaf collimator (MMLC) with 4 mm leaf width and a maximum field size of 6 cm X 6 cm has been designed as a tertiary beam-shaping device for linac-based stereotactic radiosurgery. The purpose of this study is to develop an accurate and efficient dose calculation model for use with the MMLC. A pencil-beam based algorithm using a sum of three Gaussian kernels was developed to model the off-axis ratio of MMLC fields. Because the kernel integration over a rectangular field can be solved in closed form, dose to any point from an arbitrary MMLC field can be calculated efficiently by summing dose contribution from a set of rectangular apertures and transmission blocks that model individual leaf openings or leaf transmissions. The model uses an effective rectangular field and equivalent square method for determination of depth dose and dose output. Results showed that the calculated percentage depth dose was within 1% and output factor was within 1.5% of measured data. The parameters of the pencil beam kernels were extracted by fitting measured off-axis profiles for a few field sizes at a few depths. The accuracy of the calculated off-axis ratio was tested by comparison with measured data for a number of MMLC fields. The algorithm was shown to be accurate to within 1.5% or 1 mm for off-axis ratios. The algorithm computes at a speed of 34,600 data points per second on a DEC Alpha server model 2000/433 (Digital Equipment Corp., Maynard, MA), which is about 15 times faster than a Clarkson-type summation method.

Algorithms↗
PubMed1997

Verification of radiosurgery target point alignment with an electronic portal imaging device (EPID).

A procedure has been developed using an electronic portal imaging device (EPID) to verify that the center of a patient's lesion is aligned with the center of a treatment cone prior to treatment in a linac-based stereotactic radiosurgery procedure. The coordinates of the lesion center are set on the Brown-Roberts-Wells phantom base using a target simulator. A 3 mm tungsten ball, mounted on the target simulator, is used as the reference point for the planned isocenter. The target simulator is then attached to an adapter mounted on the linac couch, and an EPID image of the simulated target is acquired. The center of the circular-shaped radiation field is calculated from the centroid of the segmented EPID image, and the center of the tungsten ball is identified by an automated computer search algorithm. A summation filter is used to find the position of the lowest radiation intensity coincident with the center of the ball. The alignment error is defined as the difference between the center of the radiation field and the center of the ball. The accuracy of this method was tested and found to be within 0.2 mm. The advantage of the EPID-based procedure is that it can give quantitative offset values quickly for immediate readjustment. We have found that the method is also a convenient tool for testing room laser alignment and the accuracy of the treatment cones.

Algorithms↗
PubMed1995

Fetal cerebral ventricular atrium: difference in size according to sex.

PURPOSE: To determine whether the diameter of the fetal lateral ventricular atrium is larger in male than in female fetuses. MATERIALS AND METHODS: The atrial diameter in 219 fetuses retrospectively identified from a consecutive group of healthy newborns was measured without knowledge of the subject's sex. RESULTS: Atrial size demonstrated a near-normal distribution, with mean size for all subjects 6.1 mm +/- 1.3 (standard deviation). When separated by sex, the mean atrial diameter of 122 female fetuses was 5.8 mm +/- 1.3, and the mean atrial diameter of 97 male fetuses was 6.4 mm +/- 1.3. The difference in mean size is statistically significant (P < .005). CONCLUSION: Male fetuses have a slightly larger atrial size than female fetuses. This discovery has implications for defining the upper limit of normal for fetal ventricular atrial size.

Cerebral Ventricles↗
PubMed1994

Dosimetry of effective wedge fields produced by an internal wedge.

A procedure is described to calculate the monitor unit ratios required to produce effective wedge fields having a desired wedge angle by combining an internal 60 degrees wedge with an open field. Complementary procedures are derived and demonstrated for calculating the effective wedge dose distributions with wedge angles of 15 degrees, 30 degrees, and 45 degrees using the central axis depth dose data and off-axis ratios of the open field and the 60 degrees wedged field. Measurements at five points on and off the central axis within each field and measurements of the effective wedge factor demonstrated that the calculated wedge distributions were correctly delivered to within 2% in all cases.

Biophysical Phenomena↗
PubMed1992

Dosimetric evaluation of a two-dimensional, arc electron, pencil-beam algorithm in water and PMMA.

The accuracy of dose calculations from a pencil-beam algorithm developed specifically for arc electron beam therapy was evaluated at 10 and 15 MeV. Mid-arc depth-doses were measured for 0 degrees and 90 degrees arcs using 12 and 15 cm radius cylindrical water phantoms. Calculated depth-doses for the 90 degrees arced beams in the build-up region were as much as 3% less than measured values; the maximum dose was similar in magnitude but at a greater depth; and the therapeutic depth, R80, was 2-4 mm deeper. Calculated values of output (dose per monitor unit) at the depth of the maximum calculated dose were compared with measured values; for arcs ranging from 0-90 degrees, 12 and 15 cm radius water phantoms, and collimator widths of 4, 5 and 6 cm, results showed differences as great as 7%. Isodose countours for a 90 degrees arc were also measured in a 15 cm radius PMMA phantom. At the depth of maximum dose the algorithm predicted doses in the penumbral regions, both with and without collimation, which agreed within a few per cent of measured values. The largest discrepancies were 5%, which occurred in the penumbral portion of the depth-dose fall-off region. Differences between measurement and calculation are not believed to be clinically significant and are believed to be primarily due to the fact that the algorithm models neither large-angle scattering nor the effects of range straggling on the pencil-beam dose distribution.

Algorithms↗
PubMed1990

Alterations in phospholipid N-methylation of cardiac subcellular membranes due to experimentally induced diabetes in rats.

Phosphatidylethanolamine N-methylation was examined in cardiac subcellular membranes after inducing chronic experimental diabetes in rats (65 mg streptozotocin/kg, i.v.). The incorporation of radiolabeled methyl groups from S-adenosyl-L-methionine in diabetic sarcolemma was significantly depressed at all three catalytic sites (I, II, and III) of the methyltransferase system. An increase in methyl group incorporation was evident at site I without any changes at sites II and III in diabetic sarcoplasmic reticulum and mitochondria. Similar changes were also seen for the individual N-methylated lipids (monomethyl-, dimethylphosphatidylethanolamine, and phosphatidylcholine) specifically formed at each catalytic site in all cardiac membranes from diabetic animals. These alterations in N-methylation were reversible by a 14-d insulin therapy to the diabetic animals. In the presence of 10 microM ATP and 0.1 microM Ca2+, N-methylation was maximally activated at site I in both control and diabetic sarcolemma and sarcoplasmic reticulum, but not in mitochondria. Incubation of cardiac membranes with of S-adenosyl-L-methionine showed that Ca2(+)-stimulated ATPase activities in both sarcolemma and sarcoplasmic reticulum were augmented; however, the activation of diabetic sarcolemma was lesser and that of diabetic sarcoplasmic reticulum was greater in comparison with the control preparations. These results identify alterations in phosphatidylethanolamine N-methylation in subcellular membranes from diabetic heart, and it is suggested that these defects may be crucial in the development of cardiac dysfunction in chronic diabetes.

Animals↗
PubMed1986

Multilobated B-cell lymphoma, a variant of centroblastic lymphoma. Report of four cases.

Four cases of multilobated B-cell lymphoma, one follicular and three diffuse, are described. Many of the lymphoma cells show marked lobulation of the nuclei, and possess multiple prominent nucleoli. There are admixed classical centrocytes, classical centroblasts, and cells with morphology intermediate between classical centroblasts and multilobated cells. Multilobated cells are also observed in small numbers in germinal centres of lymph nodes showing reactive follicular hyperplasia. We believe that the multilobated B-cell may represent one form of centroblast during transition between the centroblastic and centrocytic stages. Multilobated B-cell lymphoma may be its neoplastic counterpart in which the nuclear lobulation is further exaggerated.

Adult↗
PubMedDate not supplied

Verification data for electron beam dose algorithms.

The Collaborative Working Group (CWG) of the National Cancer Institute (NCI) electron beam treatment planning contract has performed a set of 14 experiments that measured dose distributions for 28 unique beam-phantom configurations that simulated various patient anatomic structures and beam geometries. Multiple dose distributions were measured with film or diode detectors for each configuration, resulting in 78, 2-D planar dose distributions and one, 1-D depth-dose distribution. Measurements were made for 9- and 20-MeV electron beams, using primarily 6 x 6- and 15 x 15-cm applicators at several SSDs. Dose distributions were measured for shaped fields, irregular surfaces, and inhomogeneities (1-D, 2-D, and 3-D), which were designed to simulate many clinical electron treatments. The data were corrected for asymmetries, and normalized in an absolute manner. This set of measured data can be used for verification of electron beam dose algorithms and is available to others for that purpose.

Algorithms↗