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Biomedical subjects

C A Beam

Publications and source records attributed to C A Beam.

36 records · Page 2Linked to original sources
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↗
PubMedDate not supplied

Evaluation of the quality of clinical research studies of magnetic resonance angiography: 1991-1994.

To evaluate the quality of clinical research studies of magnetic resonance angiography (MRA), the authors reviewed studies of carotid, renal, and lower extremity MRA published in English during 1991-1994. The purpose, design, and implementation of the study, and the type of statistical information presented, were evaluated. The results were compared with those of previous studies that assessed the quality of MRI research. Fifty-nine studies of renal (n = 10), carotid (n = 29), and lower extremity (n = 20) MRA were identified; 30 met the inclusion criteria for the analysis. In these papers, presentation of a reference standard was routine, observer blinding was usual, information often was given about patient selection and exclusion, sample sizes were always given, and parameter estimates and statistical analyses were common. However, evidence of research planning was not routine, measurement of interobserver variability was occasional, variability of parameter estimates was usually not estimated, and validation of statistical assumptions was uncommon. On balance the authors conclude that the scientific quality of recent investigations of MRA is better than that of older studies of MRI.

Arteries↗
PubMedDate not supplied

Ribosomal RNA sequencing of members of the Crypthecodinium cohnii (Dinophyceae) species complex; comparison with soluble enzyme studies.

Sixty-five members of the Crypthecodinium cohnii species complex were analyzed for sequence differences within the D2 region of the 23S ribosomal RNA molecule. On the basis of 46 sequence differences the strains fell into 19 distinct ribosets (strains of identical sequence), some with many members. Members of four of the seven major sibling species (widespread breeding groups) were each found within single ribosets. Members of three other major sibling species were each, however, divided into two ribosets by a single sequence difference correlated with geographic separation and with previously reported electrophoretic polymorphisms of soluble enzymes within the sibling species. In addition to members of major sibling species, some ribosets include many minor sibling species (each represented by only one strain). Of 38 minor sibling species, 22 shared sequence with a major sibling species. Of these 22, 14 were identical in soluble enzymes to their related major sibling species or differed by only one of three enzymes. Other minor sibling species appear to have diverged extensively from any others in both rRNA sequence and electrophoretic profile. As a group, major sibling species differ markedly in the number of minor sibling species associated with them, suggesting differences in frequency of sexually isolating events in their past histories. These findings are discussed in the context of the previously proposed model of sympatric speciation.

Animals↗