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Biomedical subjects

L F Miller

Publications and source records attributed to L F Miller.

At least 19 recordsLinked to original sources
PubMed2005

Comparison of treatment planning dose calculations with measurements and Monte Carlo calculations in a RANDO phantom.

Solid tumours are often treated with external beams of photons generated by Bremsstrahlung radiation. These beams are shaped and filtered to optimise the dose to specific regions defined by the treatment plans, which may involve irradiations from multiple angles. It is important that doses to healthy tissue do not exceed tolerance doses and that the dose to the tumour is maximised. To accomplish these objectives, commercially available 3-D treatment planning software is used to calculate doses to healthy tissue and to the tumour. It is generally believed that these commercial software packages calculate doses through the patient to within a few per cent. In order to examine this claim, dose calculations obtained from ADAC software for external beam treatment to the pelvic region of a RANDO phantom are compared with 37 thermoluminescence dosemeters placed into several slices of a RANDO phantom. The phantom was irradiated to obtain a prescription dose of 180 cGy at the tumour location. Data from homogeneous regions agree within several per cent with results obtained from ADAC software, whereas this comparison is less favourable in regions of heterogeneity. Results from Monte Carlo calculations in a homogeneous phantom are comparable to results from ADAC treatment planning software.

Computer Simulation↗
PubMed2005

Shielding for a cyclotron used for medical isotope production in China.

Monte Carlo and discrete ordinate calculations have been performed to determine the doses at several locations in a positron emission tomography (PET) facility in China, where the radiation source is a cyclotron that is used for the production of the isotopes necessary for PET scans. The energy-dependent neutron source term is obtained by calculations using the ALICE code, and is interpolated for input to Monte Carlo and discrete ordinate calculations. The building that houses the cyclotron has a labyrinth of walls to minimise dose to operators and to other occupants of the building. Unbiased Monte Carlo calculations did not converge after more than one week of CPU time, whereas direction biasing alone resulted in convergence in several days. A study of several biasing techniques indicated that about a factor of 3 in computational efficiency is obtained using evaluated biasing methods. The use of adjoint fluxes for biasing Monte Carlo calculations can improve computational efficiencies by one or two orders of magnitude for some problems.

China↗
PubMed2005

The microdosimetry of boron neutron capture therapy in a randomised ellipsoidal cell geometry.

Two reactions deliver the majority of local dose in boron neutron capture therapy. The ionised particles (protons, alpha particles and lithium nuclei) produced in the two reactions, 10B(n,alpha,gamma)7Li and 14N(n,p)14O, have short ranges that are less than -14 microm (which is on the order of the diameter of a typical human cell). The ionised particles are heavy and are in the 2+ charge state in the case of the boron reactions. These heavy 2+ ions will do significant damage to molecules near their tracks. Thus, the distribution of nitrogen and, in particular, of boron determines the spatial characteristics of the radiation field. Since the distribution of nitrogen is nearly homogeneous in the brain and is not easily altered for the purpose of radiotherapy, the spatial variation in the radiation dose is due mainly to the spatial distribution of boron. This implies that the spatial distribution of boron determines the microscopic energy deposition and therefore the spatial characteristics of the microscopic dose. The microscopic dose from the (n,alpha) and (n,p) reactions has been examined in detail and, as averred, the proton dose is relatively homogeneous except for statistical variability. The statistical variability in essence adds a false spatial variability that would not be seen if a large number of histories were performed. Since the majority of spatial variability occurs in the boron distribution, the (n,p) reaction can be suppressed to better understand the spatial distribution effects on the microscopic dose. Programs have been written in FORTRAN using Monte Carlo techniques to model ellipsoidal cells that are either randomly sized and located in the region of interest or are arranged in a face centred cubic array and are identical except for the location of the nuclei, which may be random. It is shown that closely packed prolate ellipsoidal cells with a large eccentricity in one dimension will receive a larger nuclear dose than cells that are more sparsely packed. This demonstrates that the boron content of a cell and its nucleus can have a significant impact upon the dose to neighbouring cells. The local boron distribution in a region of interest can be shown to affect the macrodosimetric dose, with possible implications for clinical outcomes.

Animals↗
PubMed1999

Collecting information on disability in the 2000 Census: an example of interagency cooperation.

The United States Constitution requires that an enumeration (or census) of the population be conducted every 10 years to apportion seats in the House of Representatives. Census information is also used to allocate funds and to plan and manage programs. Census 2000 occurs on April 1, 2000, when one-sixth of all American households will be mailed the "long form," containing disability, demographic, economic, and housing questions. Although no short set of commonly accepted questions on disability existed, one was developed for Census 2000 by a collaborative, federal interagency work group on disability, convened by the Office of Management and Budget. The work group consisted of staff from the Social Security Administration (SSA), the Department of Health and Human Services, the U.S. Census Bureau, and other agencies. They reviewed questions initially proposed by the Census Bureau, developed an alternative proposal, tested both versions in the Census Bureau's cognitive questionnaire lab, and on the basis of testing, derived a consensus version for Census 2000. In many ways, the six questions now contained on Census 2000 are an improvement over previous efforts. Disability is ascertained for children as well as for adults, and information will be collected separately for several domains of disability (for example, sensory, mental, physical). The need for a brief set of disability measures goes beyond Census 2000. If such data were collected regularly on national surveys, critical policy and program concerns across agencies could be addressed because better information could be gathered on changes in disability prevalence and on the characteristics of persons with disabilities. Other similar efforts include the former Disability Evaluation Study, now known as the National Study of Health and Activity--a national sample survey on working-age disability to be conducted by SSA--and the President's Task Force on the Employment of Adults with Disabilities (Executive Order 13078).

Activities of Daily Living↗
PubMed1993

Effects of exogenous porcine somatotropin on the carcass composition, hormonal and metabolic profiles, lipogenic capacity, and binding of insulin to erythrocyte receptors of fast- versus slow-growing swine.

Twenty barrows were designated as fast-growing (FG) and their littermates designated as slow-growing (SG) based on birth, weaning, and 56-d weight. Half of each group received 70 micrograms of porcine somatotropin (pST)/kg BW daily beginning at 40 kg BW. At 60 and 105 kg BW, blood was collected every .5 h for 12 h beginning 1 h before pST injection, fat biopsies were taken for in vitro lipogenic activity, and insulin erythrocytes were isolated for receptor binding. Swine treated with pST had elevated ADG (.95 vs .88 kg/d; P < .1) and reduced days to slaughter (61 vs 67; P < .1). The pST-treated pigs had less average backfat (2.73 vs 3.96 cm; P < .01), larger longissimus muscle areas (32.3 vs 28.2 cm2; P < .05), and a higher percentage of muscle (56.3 vs 50.3%; P < .01) than control pigs. Exogenous pST increased protein (17.4 vs 13.2%; P < .05) and decreased fat (22.9 vs 37.1%; P < .05). The FG pigs had higher ADG (.98 vs .86 kg/d; P < .01) and required fewer days to slaughter (57 vs 71; P < .01) than SG pigs. Administration of pST increased (P < .01) average pST levels (1.7 vs 14.0 ng/mL) in FG and SG pigs at 60 kg BW. At 105 kg BW, pST was higher (P < .01) in pST-FG than in pST-SG swine (46.0 vs 19.3 ng/mL) but was not different between FG and SG control swine (1.9 vs 1.8 ng/mL). Administration of pST increased concentrations of IGF-I (510.0 vs 160.0 ng/mL) and nonesterified fatty acids (182 vs 109 muEq/L, P < .01) in FG and SG swine. Over sample periods and growth rates, pST reduced (P < .05) CO2 production and lipid synthesis (.345 and 1.85 vs .575 and 2.71 mumol of glucose incorporated.g-1.2 h-1). At 60 kg BW, FG swine had less (P < .01) CO2 production and lipid synthesis (.299 and 1.83 vs .921 and 3.61 mumol.g-1.2 h-1) than did SG swine. Exogenous pST increased (P < .05) binding to insulin erythrocyte receptors (7.25 vs 6.34%).

Adipose Tissue↗
PubMed1991

Creation of a feline model of obstructive uropathy.

The aim of this project was to create a reproducible, quantifiable feline model of obstructive uropathy. Seventy-three adult female cats of comparable age were evaluated to obtain the normal control urodynamic data base. Twenty-four cats had a silastic cuff installed around the urethra to induce bladder outlet obstruction, and eight underwent a sham operation. Repeated urodynamic evaluations were performed at predetermined postoperative intervals. The obstructed and normal cats inhibited detrusor contractility by reflex striated urethral sphincter activity. Measurements of voiding pressure to verify the presence, and to assess the degree of induced outlet obstruction, required paralysis of the sphincter by curare. Following cuff implantation, voiding pressure increased from a mean normal of 17.2 cm./H2O to 31.6 to 42.5 cm./H2O in animals designated as moderately obstructed, and to 101.7-125.0 cm./H2O in animals designated as severely obstructed. 84.6% of the high pressure bladders developed vesicoureteral reflux. Analysis of resting, low bladder volume, urethral pressure profile (UPP) data and voiding pressures indicate a compensatory sphincteric response to filling in non-curarized animals, and a lack of that response in curarized animals. It appears that implantation of a silastic cuff to prevent full opening of the urethra during voiding, without actually compressing it, is a reasonable model of obstructive uropathy. The observation that the relationship between striated urethral sphincter activity and inhibition of detrusor contractility is influenced by administration of curare was unexpected, and may have clinical implications.

Animals↗
PubMed1991

Interaction of somatotropin and genotype on the requirement for energy in two lines of finishing pigs.

Eighty barrows were used in a 2 x 2 x 4 factorial experiment to examine the effects of genetic line (Hampshire x Yorkshire, H x Y, and Yorkshire x Landrace, Y x L), somatotropin (dose, 0 and 5 mg/d) and energy intake (ad libitum, 93%, 86% and 80%) on growth performance and energy requirements for lean gain over the finishing phase of growth. Four diets were formulated to maintain equal intakes of protein, vitamins and minerals at different energy intakes. Somatotropin increased growth rate 30 to 35% across diets despite an 8 to 12% reduction in ad libitum feed intake. Lean growth rate (kg/d) was increased preferentially by ST in the faster-growing H x Y barrows, which showed a 2.8-fold greater maximum rate increase than the slower-growing Y x L barrows. In control barrows, 10% reductions in energy intake had no effect on lean gain and improved feed/lean gain about 10%. In somatotropin-treated barrows, lean gain was reduced with each energy restriction in H x Y; energy intake had no effect on lean gain in Y x L barrows. Feed/lean gain was improved 22% in Y x L barrows at the lowest energy intake. Data indicate that somatotropin accentuates breed differences in lean gain and energy requirements. Pigs with low lean-growth potential will benefit from restricted feeding, whereas strategies to increase energy intake in pigs with high lean-growth potential may be desirable.

Animal Feed↗
PubMed1991

The effects of recombinant porcine somatotropin on reproductive function in gilts treated during the finishing phase.

The objective of this study was to determine the effects of recombinant porcine somatotropin (rpST) treatment during the finishing phase on subsequent reproductive function in crossbred gilts. Forty gilts weighing 50 kg and housed in a swine finishing facility were randomly assigned to control or rpST treatment. Four control and four rpST-treated gilts were allotted per pen. Twenty rpST-treated gilts received 6 mg of rpST.gilt-1.d-1 in 1 ml of buffered carrier and 20 control gilts received 1 ml of buffered carrier.gilt-1.d-1. Injections were administered daily at 1400 in the extensor muscle of the neck. All gilts received an 18% CP diet containing 1.2% lysine. Treatment was terminated when the average weight in each pen reached 110 kg. Gilts treated with rpST gained more weight (P less than .05) than control gilts (59.8 +/- 1.0 vs 53.5 +/- 1.0 kg). Age at puberty was not different (rpST, 182.2 +/- 3.3; control 181.4 +/- 3.1 d). Prior treatment with rpST did not significantly affect length of estrus (rpST, 1.9 +/- .1; control, 1.8 +/- .1 d) or estrous cycle length (rpST, 20.6 +/- .4; control, 20.4 +/- .4 d). Ovulation rates at second estrus were similar for rpST gilts (15.1 +/- .5) and control gilts (14.4 +/- .5). More embryos (P = .10) were recovered on d 9 to 12 of gestation from rpST-treated gilts than from control gilts (13.1 +/- .9 vs 10.7 +/- .9).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Short term functional effects of bladder outlet obstruction in the cat.

Experimental bladder outlet obstruction in cats was produced by surgical placement of a silastic cuff around the urethra. Two sizes of cuff were used to produce either moderate or severe obstruction. The following is a summary of the short-term effects on bladder function. Obstruction induced a significant increase in the in vivo voiding pressure, in proportion to severity of the obstruction. There were no significant differences between control and obstructed cats in bladder mass, response of the isolated whole bladder to field stimulation or bethanechol, response of isolated bladder strips to field stimulation, bethanechol and ATP, or muscarinic receptor density in the bladder body. Although there were no differences in bladder mass between control and obstructed bladders, the hydroxyproline concentration of the severely obstructed bladders was significantly reduced. Creatine phosphate concentration was also significantly reduced in obstructed bladders. Although all whole cat bladder preparations displayed spontaneous contractile activity during in vitro cystometry, the obstructed bladders had a greater amplitude and frequency of spontaneous contractions with a lower volume threshold. In addition, the obstructed bladders had a greater tetrodotoxin-resistant contractile response to field stimulation. These results suggest that the obstructed cat bladder can compensate for increased outlet resistance without induction of bladder hypertrophy or significant functional changes, as seen in both rat and rabbit.

Adenosine Triphosphate↗
PubMed1990

Intramuscular collagen and serum hydroxyproline as related to implanted testosterone, dihydrotestosterone and estradiol-17 beta in growing wethers.

Relationships of implanted testosterone, dihydrotestosterone and estradiol-17 beta to collagen degradation and intramuscular collagen concentration and stability were determined. Intramuscular collagen content, solubility and shrinkage temperature and serum hydroxyproline were analyzed in groups of six rams, wethers, and wethers implanted with various levels of testosterone or dihydrotestosterone and groups of 10 rams, wethers and wethers implanted with estradiol-17 beta, dihydrotestosterone or a combination of these two steroids. Intramuscular collagen content in both experiments was higher (P less than .05) in muscles of rams than in muscles of wethers. Administration of the highest level of testosterone to wethers raised (P less than .05) total and insoluble intramuscular collagen to concentrations noted in rams. Administration of the testosterone metabolite, dihydrotestosterone, to wethers had no effect on intramuscular collagen. Administration of estradiol-17 beta to wethers tended to raise concentrations of intramuscular collagen so that they were no longer lower (P less than .05) than those in rams. Collagen stability as measured by solubility and thermal shrinkage temperature did not differ among rams, wethers or implanted wethers (P greater than .05). Increases in collagen accretion due to hormone administration were observed to be the result of increases in the insoluble portion of the intramuscular collagen (P less than .05).

Animals↗
PubMed1990

Remarriage among women in the United States: 1985.

"This paper has presented a description of recent trends in remarriage for women in the United States.... The focus has been on who is most likely to remarry among women whose first marriage ends in divorce or widowhood.... The major findings in the paper indicate that remarriage is much more likely after divorce than after widowhood and that while characteristics like age, race, Hispanic origin, education, and presence of children have some role in determining remarriage prospects, age at divorce or widowhood exerts an overriding influence on the likelihood of remarriage."

Age Factors↗
PubMed1989

Relationships among intramuscular collagen, serum hydroxyproline and serum testosterone in growing rams and wethers.

Concentration and maturation of collagen and serum concentrations of hydroxyproline and testosterone were determined in growing rams and wethers to characterize developmental changes in collagen associated with a representative testicular steroid. Groups of eight rams and eight wethers were slaughtered at 12, 18, 24 and 30 wk of age. Concentrations of collagen in longissimus, supraspinatus and infraspinatus muscles and serum hydroxyproline were greater (P less than .05) in rams than in wethers at all ages. Collagen stability, as measured by collagen solubility and thermal shrinkage temperature, was greater (P less than .05) in wethers than in rams. Differences in collagen stability and serum hydroxyproline concentration indicated that collagen synthesis and turnover were more rapid in rams than in wethers. Serum hydroxyproline decreased (P less than .05) and collagen solubility decreased (P less than .05) with age, indicating that collagen turnover was occurring most rapidly in 12-wk-old lambs and that collagen maturation was predominant in 24- to 30-wk old lambs. Testosterone parameters measured in rams were unrelated within groups to collagen characteristics, possibly reflecting the high variability in testosterone secretion and the slow development of collagen. However, rams as young as 12 wk of age were under the influence of testosterone, and differences in collagen between rams and wethers were apparent at that time.

Animals↗
PubMed1977

Nitrones. 7. alpha-Quinoxalinyl-N-substituted nitrone 1,4-dioxides.

A series of alpha-quinoxalinyl-N-substitute nitrone 1,4-dioxides has been synthesize and evaluated as antibacterial and antiprotozoal agents. Structure-activity relationships are discussed. Of the compounds tested, alpha-(3-methyl-2-quinoxalinyl)-N-methylnitrone 1,4-dioxide (2) was the most active agent in vivo against the gram-negative and the gram-positive organisms.

Animals↗