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C A Beam

Publications and source records attributed to C A Beam.

16 recordsLinked to original sources
PubMed1992

Crypthecodinium and Tetrahymena: an exercise in comparative evolution.

Nucleotide sequences have been determined for the highly variable D2 region of the large rRNA molecule for over 60 strains of dinoflagellates. These strains were selected from a worldwide collection that represents all the known sibling species (compatibility groups, Mendelian species) in the sibling swarm referred to as Crypthecodinium cohnii. A phylogenetic tree has been constructed from an analysis of the variations in a length of about 180 bases, using PHYLOGEN string analysis programs. The Crypthecodinium tree is compared with the previously published but here augmented tree constructed upon the same rRNA region for the sibling species of a worldwide collection of ciliated protozoa related to the genus Tetrahymena. The first reported sequence of Lambornella clarki, the parasite of tree-hole mosquitoes, is included. The dinoflagellate species complex is much more homogeneous with respect to ribosomal variation. The mean number of differences among sequences from different Crypthecodinium species is about 7, in comparison with 22 differences among the ciliate species examined. Moreover, all the diversity in the dinoflagellates can be explained by base substitutions, whereas insertions and deletions are common in the ciliates. The dinoflagellates are also much more uniform with respect to nutritional and genetic economies. The two complexes differ also in the relationship between molecular variations and breeding compatibility. All tetrahymenine sibling species thus far examined are monomorphic in the D2 region, but several dinoflagellate species are polymorphic. Several different dinoflagellate species, moreover, have identical D2 regions. This kind of ribosomal identity of incompatible strains is found in these ciliates only in one tight cluster of species--Group C. The tetrahymenine swarm is apparently much older than the Crypthecodinium swarm, and the dinoflagellate species produce incompatible progeny species much more readily than do the ciliates, perhaps by the acquisition of mutations that potentiate incompatibility in sympatric populations.

Animals↗
PubMed1992

Aortoiliac angioplasty: is there a need for other types of percutaneous intervention?

In a retrospective study, the authors compared results in 81 patients who underwent 117 percutaneous transluminal angioplasty (PTA) procedures in the iliac arteries and 21 patients who underwent iliac artery atherectomy. Both groups were similar with respect to symptoms and risk factors. The overall technical success rates were 97.4% for PTA and 100% for atherectomy. The initial clinical success was 92.8% for PTA and 100% for atherectomy. Complications requiring surgery occurred in four of 117 (3.4%) PTA and one of 21 (4.8%) atherectomy procedures. The 2-year patency rate for PTA was similar to that achieved with atherectomy in a smaller patient population. These results indicate that atherectomy does not offer any definite advantage over conventional PTA for the routine management of iliac lesions and make it difficult to justify the additional expense and complexity of this technique.

Angioplasty, Balloon↗
PubMed1992

Threshold perception performance with computed and screen-film radiography: implications for chest radiography.

Images of a phantom obtained with computed radiography and standard screen-film imaging were compared to evaluate observer threshold perception performance with a modified contrast-detail technique. Optimum exposure necessary for performance with the imaging plate technique to match that with screen-film techniques was determined, as was comparative performance with variation in kilovoltages, plate type, spatial enhancement, and hard-copy interpolation method. It was found that computed radiography necessitates about 75%-100% more exposure than screen-film radiography to optimally match performance with Ortho-C film with Lanex regular or medium screens (Eastman Kodak, Rochester, NY) for detection of objects 0.05-2.0 cm in diameter. However, only minimal loss of detection performance (approximately 10% overall) was experienced if standard screen-film exposures were used with computed radiography. Little change in observer performance was found with variation in plate type, spatial enhancement, or method of hard-copy interpolation. However, perception performance with computed radiographic images was better at lower kilovoltages.

Humans↗
PubMed1992

Gastrointestinal bleeding: treatment with gastrointestinal arterial embolization.

Retrospective analysis of 36 embolization procedures in 29 patients with gastrointestinal bleeding was undertaken, and the presence or absence of coagulopathy was identified as a major factor affecting embolization outcome. Embolization was successful in 18 of 29 (62%) patients and unsuccessful in 11 (38%). Eight of 11 failures (73%) occurred in patients with a coagulopathy, whereas three patients (27%) in whom embolization was successful also had a coagulopathy. Embolization was 2.9 times more likely to be unsuccessful (P = .0463) and death from bleeding after embolization was 9.6 times more likely to occur (P = .0065) in patients with a coagulopathy than in those without. Because embolization was successful in six of 14 (43%) coagulopathy patients, the authors advocate embolization in patients with gastrointestinal bleeding and coagulopathy, while all efforts to correct the coagulopathy would be made as early as possible.

Adolescent↗
PubMed1992

Strategies for improving power in diagnostic radiology research.

Research studies in diagnostic radiology often compare the diagnostic abilities of two imaging techniques. The "power" of such studies is the probability that they will detect a difference in abilities of a certain amount when, indeed, such a difference does exist. This article outlines several strategies that can be used to assess and improve the power of radiologic diagnostic studies. These strategies include selection of cases and controls, matching, use of one-tailed tests, selection of significance level, and choice of sample size.

Diagnostic Imaging↗
PubMed1991

Evaluation of acute renal failure with magnetic resonance imaging using gradient-echo and Gd-DTPA.

Detection of acute renal failure (ARF) using fast-scan magnetic resonance imaging (MRI) with Gd-DTPA was studied in a dog model. ARF was produced in five dogs by infusion of norepinephrine (0.75 micrograms/kg/min) into the renal arteries for 40 minutes. MRI was performed 1 hour later and compared with baseline (pre-ARF) MRI. There was no significant difference in the ratios of signal intensity-vs.-time curves from 0 to 35 seconds after injection of Gd-DTPA. However, a difference between the outer and inner medulla was significant in the time period of 5 to 20 minutes after Gd-DTPA injection. These later signal intensity differences by fast-scan (gradient-echo) technique may be useful in the evaluation of ARF.

Acute Kidney Injury↗
PubMed1991

Extravascular toxicity of two magnetic resonance contrast agents. Preliminary experience in the rat.

We compared the relative toxicities of standard concentrations of two magnetic resonance imaging (MRI) contrast agents, ionic gadolinium diethylenetriaminepentacetic acid (DTPA) and low-osmolar gadolinium-1, 4, 7 tris (carboxymethyl)-10-(2'-hydroxypropyl)-1, 4, 7, 10 tetra-azacyclododecane (HP-DO3A) with that of the conventional radiographic contrast medium meglumine diatrizoate, when extravasated into the deep dermal tissues of laboratory rats. Gadolinium-DTPA caused moderate necrosis, hemorrhage, and edema which was not statistically different than meglumine diatrizoate. In contrast, gadolinium HP-DO3A was significantly less toxic than meglumine diatrizoate. Additional experience will be needed in order to determine whether these laboratory results will be clinically relevant in humans.

Animals↗
PubMed1991

Cine phase-contrast magnetic resonance imaging for analysis of flow phenomena in experimental aortic dissection.

Using a 1.5 T magnetic resonance imaging (MRI) system, cine phase-contrast and magnitude images were obtained in three phantoms that simulated different anatomic configurations of aortic dissection. The dissection phantoms were made of compliant materials, and pulsatile flow was used in all experiments. Phantoms differed only in the location of the fenestration between the true and false lumens (I: an upstream "entry" only, II: both upstream "entry" and downstream "re-entry," and III: a downstream "entry" only). Flow jets, flap motion, and wave propagation were clearly visualized in cine MR images of each phantom, and quantitatively analyzed with reference to the stimulated cardiac cycle of the pump. Flow in the false lumen was always bidirectional. Upstream and downstream flow waves collided and dispersed within the false lumen. Flow through the false lumen was the same in phantoms I and II, and least in phantom III. The average area of the true lumen was largest in phantom III and smallest in I. Phantom I had the highest overall flow rate in the false lumen and greatest change in false lumen size during the cardiac cycle, while the downstream "entry" phantom had the lowest of both parameters. Flow phenomena in aortic dissections can be studied by cine phase-contrast MRI.

Aortic Dissection↗
PubMed1991

Status of clinical MR evaluations 1985-1988: baseline and design for further assessments.

The authors modified the methods used by Cooper et al (JAMA 1988; 259:3277-3280) to describe magnetic resonance (MR) clinical research during 1985-1988 in an objective manner. To avoid other shortcomings faced by Cooper et al, the authors randomly sampled 500 articles and obtained estimates of probable errors. Excluding case reports, all 40 of the studies with human subjects provided some evidence of prior research planning, which compares favorably with the 22% found by Cooper et al. Use of a standard for truth was similar between the data sets. Observer blinding, random ordering of procedures, and assessment of interobserver variability continued to be uncommon. Most studies provided only minimal statistical information. The work of these authors provides a study design and the baseline needed for future assessments of MR imaging evaluations.

Animals↗
PubMed1991

Measurement of force applied during mammography.

The discomfort that patients experience during mammography is probably related to a variety of factors, one of which might be the amount of compression used. The authors measured the amount of force applied to the breasts during mammography and the resulting breast thickness in 560 women and correlated these measurements with the patient's subjective impression of the examination. The amount of force applied ranged from 49 to 186.2 N (median, 122.5 N). Breast thickness ranged from 10 to 88 mm (median, 46.5 mm). Forty-seven women (8%) rated the examination as painful (ie, mammography was either "very uncomfortable" or "intolerable"). Logistic regression analysis revealed a highly significant relationship between probability of a painful response and ratio of force to thickness (P = .007). Current guidelines suggest that maximum available force be at least 160 N but not more than 200 N. However, because increasing force is associated with increasing likelihood of pain, technologists should be aware that these recommended maximum limits are not intended to be used routinely for all women. In this study, high-quality mammograms were obtained in a majority of women with forces less than the maximum available level.

Breast↗
PubMed1991

John Caffey Award. Determination of functional residual capacity from digital radiographs of the normal neonatal chest: studies in a rabbit model.

Spirometric measurement of lung volume in an infant or uncooperative child is often a difficult and time-consuming procedure. Previous investigators have successfully estimated total lung capacity in adults and older children by using chest radiography. The purpose of this study was to assess the accuracy of functional residual capacity (FRC) determination from chest radiographs in an animal model of the normal neonatal chest. FRC was determined with the helium dilution (HeD) method in 13 anesthetized, intubated, and paralyzed rabbits (weight range, 1.5-3.9 kg). FRC was then estimated from digital frontal and lateral chest radiographs. The radiographic estimate was made by applying measurements taken from the radiographic film pair to a geometric model of the chest. The best-fit model assumed an elliptical cross section for the intrathoracic cavity, heart, paraspinal structures, and diaphragm in the axial plane. Linear regression on independently determined HeD and radiographically determined FRC yielded a slope of 1.02 (p less than .001), an intercept of -3.02 cm3 (p = .565), and a correlation coefficient of 0.96 (p less than .001). We conclude that radiographic FRC estimates closely approximate HeD estimates in a rabbit model of the normal neonatal chest.

Algorithms↗
PubMed1991

A statistical method for the comparison of a discrete diagnostic test with several continuous diagnostic tests.

In this paper we study a statistic that is suitable for comparing a discrete diagnostic marker to one or more continuous diagnostic markers. Test procedures and confidence intervals are based on asymptotic normality. The statistic is applicable for correlated data in which all the markers are obtained for each subject. The statistic was studied for use in comparing two markers for rectal bleeding. Examples for this application and two more general applications are presented.

Analysis of Variance↗
PubMed1991

Iodine 131-labeled metaiodobenzylguanidine scintigraphy and biochemical analyses in suspected pheochromocytoma.

Detection of abnormal catecholamine levels and localization of tumor mass are important factors in the diagnosis and treatment of pheochromocytoma. Iodine 131-labeled metaiodobenzylguanidine scintigraphy was performed in 64 patients with suspected pheochromocytoma if their urinary catecholamine levels were borderline or elevated, or if the clinical suspicion for pheochromocytoma was high in spite of normal urinary catecholamine determinations. The 131I-metaiodobenzylguanidine scans were evaluated for abnormal localization of tracer. Twenty-four-hour urine collections were analyzed for vanillylmandelic acid, homovanillic acid, dopamine, epinephrine, and norepinephrine. Thirty of the 64 patients had pheochromocytomas. The 131I-metaiodobenzylguanidine scan had a sensitivity and a specificity of 88%. The 24-hour urine vanillylmandelic acid and norepinephrine measurements had the best sensitivity (97%), while the vanillylmandelic acid and homovanillic acid measurements had the best specificity (91%). In patients in whom the vanillylmandelic acid measurement and the 131I-metaiodobenzylguanidine scan were normal, no pheochromocytomas were found. In patients in whom the vanillylmandelic acid measurement and 131I-metaiodobenzylguanidine scan were abnormal, a pheochromocytoma was always present. The 131I-metaiodobenzylguanidine scan often documents the presence or absence of a pheochromocytoma and provides localization of the tumor in the preoperative evaluation of these patients.

3-Iodobenzylguanidine↗
PubMed1975

Genetic analysis in the dinoflagellate (Crypthecodinium (Gyrodinium) cohnii: evidence for unusual meiosis.

The atypical structure and behavior of dinoflagellate chromosomes suggests that the genetics of these organisms might show comparable peculiarities. We have begun genetic analysis of the neritic, marine heterotroph Crypthecodinium (Gyrodinium) cohnii by means of motility mutants that show complementation shortly after zygote formation, permitting identification of heterozygotes. Six mutations, conferring four microscopically distinguishable phenotypes, have been isolated and investigated. These "genes" were found to complement in double heterozygotes in all pairwise combinations, indicating that the lesions are recessive and non-allelic. Clones of all possible combinations of these factors have been established and each complements only those combinations expected on the assumption that there are six independent recessive mutant "genes." Tetrad analysis following isolation of over 200 complementing zygotes showed: (1) regular segregation with recovery of parental phenotypes and genotypes; (2) independent assortment, with one possible exception; (3) segregations that were always 1:1, that is, in all tetrads showing recombination, only the two reciprocal recombinant genotypes were found; there were no tetratypes. This behavior could result from centromere linkage or the absence of crossing over in an otherwise conventional meiosis, or it could result from an unusual one-division "meiosis." Some evidence is provided that favors the latter hypothesis.

Animals↗