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Biomedical subjects

A Wu

Publications and source records attributed to A Wu.

At least 127 records · Page 7Linked to original sources
PubMed1993

Seed strength determination for eye plaque therapy.

Standardized radioactive plaques have been used in the irradiation of intraocular tumors. These plaques have defined slots to accommodate 125I seeds and hence produce predictable isodose distributions. The seed strength has to be adjusted to deliver 100 Gy to the prescription point, which varies with the tumor size. The purpose of this work is to develop lookup tables that relate the seed strength to different prescription distances. Dose rates were determined for a set of standardized eye plaques. Using these dose rates and the source strength decaying expression, the seed strengths were determined as a function of distance along a line through the plaque. Two seed-strength tables were created based on four-day and five-day treatment times delivering a 100 Gy to the prescription distance.

Brachytherapy↗
PubMed1993

Limited proteolysis of (1,3)-beta-glucan (callose) synthase from Beta vulgaris L: topology of protease-sensitive sites and polypeptide identification using Pronase E.

Plasma membrane (PM) vesicles of defined sidedness were obtained from Beta vulgaris L. and subjected to limited proteolysis to investigate the topology and subunit composition of UDP-glucose: (1,3)-beta-glucan (callose) synthase (CalS). Latency experiments demonstrated that protease-sensitive sites on the CalS complex are located primarily at the cytoplasmic face of the PM, with little or no CalS inactivation occurring as the result of proteolysis at the apoplastic face. In the PM-bound form, CalS activity was resistant to inactivation by Pronase E, however at least four polypeptides previously implicated as possible CalS components (92, 83, 57 and 43 kDa) were extensively hydrolyzed. Polypeptides of 31, 29 and 27 kDa resisted Pronase E hydrolysis and were also enriched in CalS fractions purified by glycerol gradient centrifugation and product entrapment. In contrast to PM-bound CalS, purified CalS was rapidly hydrolyzed by Pronase E, indicating that most Pronase E-sensitive sites are deeply embedded within the PM. This study provides direct biochemical evidence that hydrophobic integral membrane proteins oriented primarily towards the cytoplasmic face of the PM are important for callose biosynthesis in Beta. Furthermore, these results form the basis of a biochemically derived working model largely consistent with morphologically derived models proposed for intramembrane PM-bound, microfibril-synthesizing complexes in higher plants.

Carbohydrate Sequence↗
PubMed1993

A clinical and laboratory study to compare the addition of 0.2 mg of morphine, 0.2 mg of epinephrine, or their combination to hyperbaric bupivacaine for spinal anesthesia in cesarean section.

The aim of this prospective, randomized, double-blind study was to compare the effects of adding either preservative-free morphine, 0.2 mg (n = 20), epinephrine, 0.2 mg (n = 21), or a combination of both (n = 29) to hyperbaric bupivacaine in parturients having elective cesarean sections during spinal anesthesia. Ten additional patients receiving spinal bupivacaine alone were studied as the Control Group. High-pressure liquid chromatography with a sensitivity of 20 micrograms/mL was used to measure serum bupivacaine in all subjects. The results showed that the spread and regression of the sensory and motor blocks were similar among the study groups. However, the intraoperative analgesia was superior in patients receiving bupivacaine combined with morphine and epinephrine, whereas there was no difference between those given an addition of either morphine or epinephrine. Postoperative analgesia was the shortest and opioid requirement in the first 24 h the most with epinephrine alone. No respiratory depression occurred. The neonatal condition was excellent in all groups. Serum concentrations of bupivacaine at 10 min, at delivery (25 +/- 1.4 min), and at 60 min after the intrathecal injection were similar among the groups including the Control Group. The concentrations of bupivacaine in umbilical arterial and venous sera were less than the sensitivity level of the analytical method. We conclude that the addition of 0.2 mg of morphine plus 0.2 mg of epinephrine to hyperbaric bupivacaine improves the intra- and postoperative analgesia without an added risk. This improvement is not due to vasoconstriction and a reduction in the absorption of bupivacaine from the subarachnoid space.

Adult↗
PubMed1992

More RIpH.

Explore the source record for details and available documents.

Chemical Phenomena↗
PubMed1992

Radiosurgery and brain tolerance: an analysis of neurodiagnostic imaging changes after gamma knife radiosurgery for arteriovenous malformations.

In order to analyze complications and the factors responsible for the development of serial imaging changes after stereotactic radiosurgery for intracranial arteriovenous malformations, we reviewed serial post-treatment magnetic resonance imaging scans in 72 patients. Median follow-up was 23 months (range 12 to 35 months). Twenty patients developed post-radiosurgical imaging changes consisting of new regions of increased T2 signal on magnetic resonance imaging in brain surrounding the arteriovenous malformation (two year actuarial incidence of 31%). Imaging changes were associated with headache or new neurological deficits in nine of these 20 (45%) and remained asymptomatic in 11 (55%). Symptoms developed in three of 13 patients with imaging changes in the cerebral cortex or cerebellum, in contrast to six of seven patients who had symptoms with imaging changes in the brainstem (p = .028). The onset of imaging changes varied from five to 18 months after radiosurgery (median, 12 months). Serial follow-up scans four to 25 months after the onset of imaging changes were available for review in 16 patients. Post-radiosurgical imaging changes completely resolved within 4 to 19 months in ten patients and have not yet completely resolved after 6 to 25 months in six patients. The projected actuarial rate for resolution of imaging changes was 88%, 19 months after onset; the median time for resolution was 14 months. Univariate analysis revealed that the development of imaging changes was significantly associated with treatment volume (p = .025), the risk predicted from the integrated logistic formula (p = .042), and the number of isocenters treated (p = .042). In multivariate analysis, volume was the only factor significantly associated with the development of imaging changes.

Adolescent↗
PubMed1992

High energy photon beam percent depth dose curves.

The percent depth dose of 8 MV and 18 MV photon beams were measured for various field sizes. The percent depth dose curves exhibited crossed over at selective depth in phantom. Hence, the percent depth dose increases at shallower depth, is independent at crossed over depth, and decreases at deeper depth with decreasing field size. This peculiar phenomenon, which cannot be explained using the primary and scattered radiation concept, should be noted.

Humans↗
PubMed1992

Determination of basal dose rates in Paris system of interstitial implants.

The isodose distributions are related to the source configurations in the Paris system of interstitial implants. In this system, the basal dose rates are determined at those points identified relative to the implant. Once these points have been located, the basal dose rates are merely the summation of the dose rate contributions from all the sources. By applying the symmetry properties of the implant, the number of basal dose rate computations and the number of dose rate summations are reduced. The reduction in both the number of computations and the number of summations has facilitated the determination of the average basal dose rate. After the average basal dose rate has been determined, the reference dose rate that is used clinically is calculated. Examples of determining the basal dose rates for a few interstitial implants are presented.

Brachytherapy↗
PubMed1992

Various wedge isodose angles for treatment planning.

Various wedge isodose angles or simply wedge angles smaller than the nominal wedge angle were created by combining the isodose distributions generated from a single physical wedge with the isodose distributions of the open field for the 8-MV photon beam. The particular wedge angle generated depends on the weights imposed on these isodose distributions. The relationship between these weights and the wedge angle were examined and found to be nonlinear. The difference between the wedge angles defined at 10 cm depth and those defined using the 50% isodose curve is less 6 degrees. The present data was fitted using two proposed empirical equations.

Humans↗
PubMed1992

Wedge filter effects on dosimetric parameters of a linear accelerator.

The open-field and wedged-field output factors as a function of field size for two linear accelerators were measured. Wedge factors were determined by taking the ratio of the outputs with and without the wedge filter. For one linear accelerator, the difference in the output factors between the wedged field and open field can be as large as 5%. The wedge factor for this linear accelerator also varies with the field size. On the other hand, the other linear accelerator shows smaller variation of output factors between wedge field and open field. The variation of wedge factor is less than 1% for a 60 degree wedge. In addition to modifying the isodose distributions, the wedge filter also changes the percent depth dose curves, the output factor, and the wedge factor. The degree of wedge effects on these dosimetric parameters is different for different linear accelerator.

Filtration↗
PubMed1992

The pharmacokinetics of prophylactic antibiotics in trauma.

Despite prophylactic antibiotic use in abdominal trauma patients, infection rates remain high. A previous study from our institution indicated that higher doses of prophylactic antibiotics in trauma patients could significantly reduce subsequent infection rates. To determine if this resulted from altered pharmacokinetic profiles, we performed individualized pharmacokinetic analysis of the prophylactic amikacin regimens given to 28 trauma patients undergoing laparotomy. Patients were prospectively randomized to receive a standard regimen of 11 mg/kg of amikacin every 12 hours or to have their regimens adjusted based upon pharmacokinetic analysis. Repeated pharmacokinetic analyses were performed daily for the three-day prophylactic regimen. There was a significant expansion in the apparent volume of distribution for amikacin that correlated with fluid resuscitation. This, along with increased elimination rates, helps to explain the failure to achieve adequate amikacin levels using standard regimens in trauma patients. Such underdosing may contribute to relatively high infection rates following major abdominal injury.

Abdominal Injuries↗
PubMed1992

Physics and dosimetry of the gamma knife.

Since 1968, the gamma knife has been one of the major radiosurgical devices. Although approximately 4300 patients worldwide had been treated with the gamma knife units through June 1990, gamma knife installments in the United States are still rather scarce compared to linear accelerators adapted for radiosurgery. This article describes the basic physical characteristics of the gamma knife, patient set-up procedures, the existing treatment-planning system, the measurements of dosimetry and physical parameters, dose delivery accuracy, and quality assurance procedures. It also includes a vision of future developments and improvements in these areas.

Brain Neoplasms↗
PubMed1992

Radiobiologic models for radiosurgery.

A series of initial radiobiologic investigations have been performed using three animal models. The baboon model proved to be a valuable technique to assess the in vivo radiobiologic response of single-fraction irradiation doses delivered to the primate brain stem. Multimodality neurodiagnostic testing, including CT, MR imaging, xenon-enhanced CT, evoked potential studies, and analysis of CSF myelin basic protein levels, all of which eventually were correlated with neuropathologic examination, enabled detection of lesions produced with high-dose (150 Gy) radiosurgery as early as 6 weeks. Within the first 6 months after radiosurgery, lower doses (20 Gy, 50 Gy) did not result in clinically or neurodiagnostically detectable lesions. The rat arteriovenous fistula model permits analysis of the delayed histopathologic effects of radiosurgery on an experimentally created fistula designed to mimic an AVM. The rat C6 glioma model is designed to evaluate the effect of radiosurgery in an infiltrative tumor that simulates a human malignant brain tumor. These studies are intended eventually to increase our knowledge about the safety and efficacy of radiosurgery in both the normal and tumor-implanted brains. We believe that such fundamental studies ultimately will improve our ability to reach the goals of radiosurgery: to destroy the target and spare the surrounding brain. Eventually, it may become feasible to achieve these goals by combining radiosurgical technique with both radiation sensitizers (for the treated volume) and brain protectors.

Animals↗
PubMed1991

Complementary DNA sequencing: expressed sequence tags and human genome project.

Automated partial DNA sequencing was conducted on more than 600 randomly selected human brain complementary DNA (cDNA) clones to generate expressed sequence tags (ESTs). ESTs have applications in the discovery of new human genes, mapping of the human genome, and identification of coding regions in genomic sequences. Of the sequences generated, 337 represent new genes, including 48 with significant similarity to genes from other organisms, such as a yeast RNA polymerase II subunit; Drosophila kinesin, Notch, and Enhancer of split; and a murine tyrosine kinase receptor. Forty-six ESTs were mapped to chromosomes after amplification by the polymerase chain reaction. This fast approach to cDNA characterization will facilitate the tagging of most human genes in a few years at a fraction of the cost of complete genomic sequencing, provide new genetic markers, and serve as a resource in diverse biological research fields.

Amino Acid Sequence↗
PubMed1991

Interstitial IR-192 implants of the oral cavity: the planning and construction of volume implants.

The success of radioactive implant therapy for head and neck carcinomas depends critically on careful planning and execution of the implant procedure. In this paper we discuss our experience with oral tongue and floor of mouth implants, and some innovations introduced to facilitate these procedures. Implants were carried out using standard angiocatheters modified with magnetic caps at the open end and terminated with Teflon spacers and lead shot at the closed end. The importance of accurate source placement and careful determination of the target dose rate is discussed with numerical examples. Differential hot-loading of sources is clearly indicated in cases of extension of the lesion to the dorsal or lateral tongue surface. For dorsal surface extension the use of Teflon spacers at the closed ends of the catheters helps to ensure adequate coverage of the target volume with the higher dose region enclosing the demonstrable tumor. All 10 patients implanted with this technique are controlled without recurrence at a median follow-up of 38 months. The two complications observed appeared to be associated with excessive hot-loading of edge plane sources.

Brachytherapy↗