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Biomedical subjects

L K Wagner

Publications and source records attributed to L K Wagner.

At least 37 records · Page 2Linked to original sources
PubMed1994

Exposure rates during special procedures with C-arm type fluoroscopic systems.

PURPOSE: To test for regulatory compliance of free-in-air entrance air kerma rates (EAKR) in C-arm type fluoroscopic equipment, measurements are frequently made under minimum source-to-image receptor distance (SID) and at 300 mm from the image intensifier. However, this is not representative of normal patient geometry, and the automatic brightness controls on these units frequently increase tube output as SID increases. This study investigated effects of these circumstances on actual EAKRs. MATERIALS AND METHODS: Typical patient geometries were observed and recorded for 23 consecutive body vascular procedures. EAKRs were measured under compliance and normal patient geometries with use of five modern C-arm type systems for special procedures. RESULTS: SIDs of 1 m were typical when rapid film changers were employed and the patient's entrance skin surface was typically 500 mm from the image receptor. Actual EAKRs were found to be up to 2.5 times those measured under compliance geometry. CONCLUSION: Actual patient geometries should be used to ensure correct estimates of EAKRs.

Fluoroscopy↗
PubMed1994

Radiologic diagnosis of traumatic occipitovertebral dissociation: 1. Normal occipitovertebral relationships on lateral radiographs of supine subjects.

OBJECTIVE: The objective of this study was to establish a reliable method of determining the normal occipitovertebral relationship seen on lateral radiographs of the cervical spine in supine subjects in order to recognize alterations of normal that characterize occipitovertebral dissociation. MATERIALS AND METHODS: We define the rostral extension of the posterior cortex of the axis body as the posterior axial line, the distance between the basion (tip of the clivus) and the posterior axial line as the basion-axial interval, and the distance between the basion and the rostral tip of the dens as the basion-dental interval. The basion-axial interval was measured on horizontal-beam lateral radiographs of the cervical spine obtained at a 40-in. (1-m) target-film distance in 400 adults who had no occipitovertebral abnormalities. The basion-dental interval was measured in 374 (94%) of the same cohort of adults in whom the superior cortex of the dens could be identified. All radiographs were obtained with the subjects supine. The excursion of the basion referable to the posterior axial line was determined on lateral flexion and extension radiographs of 25 of the same cohort of adults. The basion-axial interval only was measured on radiographs of 50 children 2-13 years old who had no occipitovertebral abnormalities. RESULTS: In 392 (98%) of the 400 adults, the basion-axial interval did not exceed 12 mm. In eight adults (2%), the basion was situated 1-4 mm posterior to the posterior axial line. The excursion of the basion in flexion and extension ranged from 0 to 10 mm, but did not exceed the 12-mm limit of normal. The basion translated posterior to the posterior axial line in six (24%) of the 25 adults in whom excursion was measured. Of the 400 adults, the basion-dental interval ranged from 2 to 15 mm (mean, 7.5 +/- 4.3 mm [2 SD]); the 95% accuracy range was 11.8 mm. In all 50 children (100%), the basion was within the normal basion-axial interval of 12 mm, and in no instance was the basion posterior to the posterior axial line. CONCLUSION: In adults, the occipitovertebral junction can be considered normal when both the basion-axial interval and basion-dental interval are 12 mm or less. In children less than 13 years old, the basion-dental interval is not reliable because of the variable age at which complete ossification and fusion of the dens occur. The normal basion-axial interval in children did not exceed 12 mm. This simple, anatomically based method of recognizing normal occipitovertebral relationships facilitates identification of occipitovertebral dissociation.

Adult↗
PubMed1994

Radiologic diagnosis of traumatic occipitovertebral dissociation: 2. Comparison of three methods of detecting occipitovertebral relationships on lateral radiographs of supine subjects.

OBJECTIVE: The purpose of this study was to describe a method for recognizing acute traumatic occipitoatlantal dissociation that uses the basion-axial interval and basion-dental interval and to compare the accuracy of this method with the accuracies of two other methods: the Powers ratio and the x-line method. MATERIALS AND METHODS: Lateral radiographs of the cervical spine of 37 patients in whom the diagnosis of occipitoatlantal dissociation had been made on the basis of the relationship of the basion to the tip of the dens, the Powers ratio, and/or the x-line method were reviewed. Retrospectively, the occipitoatlantal junction of each was reassessed by using the the Powers ratio, the x-line, and the basion-axial interval-basion-dental interval methods. Independently, the neurologic findings at admission and the final neurologic diagnosis at discharge were obtained from the hospital records and were compared with the radiologic findings to determine the degree of radiologic-clinical correlation. RESULTS: Three groups of patients were identified by analyzing the basion-axial and basion-dental intervals of the occipitovertebral junction and related clinical findings. Twenty-three patients (group 1) had frank occipitoatlantal dislocation. Eight patients (group 2) had incomplete occipitoatlantal dissociation, which was defined as occipitoatlantal subluxation. The remaining six patients (group 3) had normal radiologic and clinical findings. Four patterns of occipitovertebral dissociation were identified: purely anterior (4/31, 13%), purely distracted (6/31, 19%), concomitantly anterior and distracted (20/31, 65%), and purely posterior (1/31, 3%). Regardless of the magnitude or direction of occipitoatlantal dissociation, the basion-axial interval-basion-dental interval method correctly identified the abnormality and the type of each. Positive clinical correlation was found in 13 (57%) of the 23 patients in group 1 and in 100% of the eight and six patients in groups 2 and 3, respectively. Neither the Powers ratio nor the x-line method could be applied in 17 (46%) of 37 cases, either because the opisthion could not be detected on the radiographs or because fusion of the posterior arch of C1 had not occurred. In the remaining 20 patients in whom the Powers ratio and the x-line method were applicable, the type of occipitoatlantal dissociation was correctly identified by the Powers ratio in 12 (60%) and by the x-line method in four (20%). Neither the Powers ratio nor the x-line method was applicable in three (50%) of the six patients in whom analysis by the basion-axial interval-basion-dental interval method and clinical findings showed no occipitoatlantal abnormality. Normal occipitovertebral anatomy was correctly identified by the Powers ratio in the remaining three patients (50%) and by the x-line method in two (33%). CONCLUSION: Direct measurement of occipitovertebral skeletal relationships altered by occipitoatlantal dissociation using the basion-axial and basion-dental intervals provides the most accurate radiologic assessment of this injury.

Atlanto-Occipital Joint↗
PubMed1992

Radiation-induced micrencephaly in guinea pigs.

The effect of X rays on brain weight of guinea pig pups at birth was studied in 21-day-old embryos exposed in utero to doses of 75 and 100 mGy. When compared to controls and when corrected for body weight, gestation time, litter size, sex, and examiner differences, the brains of irradiated pups weighed approximately 46 mg less than those of controls (P < 0.001) for the 75-mGy group and about 55 mg less for the 100-mGy group. Brains of females weighed 51 mg less than those of males of the same body weight. Dam weight and caging conditions had no observed effect on brain weight.

Animals↗
PubMed1988

A modified x-ray spectra reconstruction technique.

We have previously reported on a four-parameter Laplace transform pair model that accurately reconstructs x-ray spectra from attenuation data. However, for some spectra, the model exhibits non-physical characteristics at the higher x-ray energies. This results when one of the fitted parameters, v, is less than or equal to 0.6. Simply limiting the parameter to values greater than 0.6 produces an unsatisfactory result. It is shown that improved accuracy is obtained when the model is applied to a more filtered segment of the attenuation curve. The resulting spectrum is satisfactory for the more filtered beam. One can then reliably construct the original spectrum by mathematically correcting for the additional filtration.

Models, Theoretical↗
PubMed1987

The impact-absorbing effects of facial fractures in closed-head injuries. An analysis of 210 patients.

A series of 210 patients with facial fractures sufficiently severe to require cranial computerized tomography (CT) to evaluate suspected closed-head injury (CHI) was studied. The injuries were separated into five grades of severity based on neurological examination, including cranial CT. The injuries were also grouped into three categories based on facial regional involvement, using chi-square contingency table analysis. The data demonstrated that patients with upper facial fractures were at greatest risk for serious CHI. Injuries to both the mandibular and the midfacial regions with no upper facial involvement more frequently resulted in mild CHI with a modest likelihood of no neurological deficits. Trauma to only the mandibular region or to only the midfacial region was least likely to involve CHI.

Adult↗
PubMed1986

Conceptus dose from two state-of-the-art CT scanners.

Two phantoms, constructed from plastic and water and appropriately proportioned to simulate the female pelvis, were used in the evaluation of the dose delivered to a conceptus from two widely used computed tomographic (CT) scanners. Doses were measured along the central axis and surface of each phantom while scanning 25 contiguous 1-cm sections. Ionization chambers were used for data acquisition. Methods for correcting for partial volume effects inside the chambers are examined. Formulas for calculating the dose to the conceptus in a wide variety of possible situations are presented. These data may be used to guide management of pregnant patients who require or have had CT examinations.

Fetus↗
PubMed1986

Hyperextension dislocation of the cervical spine.

The purpose of this report is to describe hyperextension dislocation of the cervical spine and to illustrate its often subtle radiographic features. An analysis of the lateral cervical spine radiographs in 20 patients with hyperextension dislocation of the cervical spine revealed the combination of diffuse prevertebral soft-tissue widening together with normally aligned cervical vertebrae in all patients with this injury. In six (30%) of 20 patients, this combination of findings was the only radiographic sign. The precise level of dislocation was indicated by a thin, transversely oriented avulsion fracture fragment arising from the anterior aspect of the inferior end-plate of the dislocated vertebra in 13 (65%) of 20 patients, by a vacuum defect in the intervertebral disk subjacent to the dislocated vertebra in three (15%), by a widened intervertebral disk space in three (15%), and by comminuted fracture of the spinous process in one (5%). Clinically, all 20 patients had facial trauma and all had some manifestation of the acute central cervical spinal cord syndrome.

Adolescent↗
PubMed1984

Dose efficiency of screen-film systems used in pediatric radiography.

Twenty-one screen-film systems were examined using contrast-detail-dose methods in order to determine which were most dose-efficient for use in pediatric radiography. With a given screen, dose efficiency in the noise-limited region (contrast approximately equal to 0.05) was more or less constant (within the range of experimental error) with changes in film speed. When screens with decreased phosphor thickness were used, dose efficiency deteriorated markedly. For a given speed of up to two times Par, rare-earth phosphors offered no advantage over calcium tungstate systems with regard to low-contrast dose efficiency; however, they did increase the speed of the system. Anti-crossover film proved to be an effective means of improving high-contrast detail while maintaining low-contrast dose efficiency.

Calcium Compounds↗
PubMed1982

Energy dependence of contrast-detail-dose and object-detectability-dose curves for CT scanners.

The energy dependence of contrast-detail-dose (CdD) and object-detectability-dose (OdD) curves for computed tomographic scanners is investigated. The effects of changes in beam energy on perceptibility are shown to be due to changes in signal-to-noise ratio resulting from changes in contrast and photon statistics. Energy-dependence analysis of OdD curves is shown to depend on the atomic composition of the phantom used to generate the curves, while such an analysis of CdD curves is independent of the atomic composition of the phantom. It is also shown that any OdD curve can be generated from CdD curves and that use of this fact rectifies any potential energy-dependent interpretation of CdD curves.

Dose-Response Relationship, Radiation↗
PubMed1982

Evaluation of a digital subtraction angiography unit.

The operating characteristics of a digital subtraction angiography unit were evaluated. Measurements included image intensifier and system linearity, uniformity, quantum and system noise, and iodine contrast. Various approaches to noise measurement were analyzed and tested, leading to the following conclusions: the video level should be maximized; changes in signal-to-noise ratio (SNR) due to changes in x-ray exposure do not necessarily reflect changes in quantum SNR alone, due to dependence of video levels on x-ray exposure; an understanding of the separate contributions of quantum and video SNRs to the total SNR guides proper selection of variables to minimize patient dose and x-ray tube heat loading.

Angiography↗
PubMed1981

Phosphatidylethanolamine synthesis in castor bean endosperm.

Phosphatidylethanolamine synthesis by CDP-ethanolamine:1,2-diacylglycerol ethanolaminephosphotransferase (EC 2.7.8.1) from the endoplasmic reticulum of castor bean (Ricinus communis L. var. Hale) endosperm was characterized. The Michaelis-Menten constant of the enzyme for CDP-ethanolamine was approximately 8.0 micromolar. The pH optimum was 6.5 and a divalent cation was an absolute requirement for activity, with Mg(2+) giving the greatest stimulation at 3 millimolar. Sulfhydryl reagents variously affected enzyme activity. No discernible differences were detected between the responses of the ethanolaminephosphotransferase and CDP-choline:1,2-diacylglycerol cholinephosphotransferase (EC 2.7.8.2) to a variety of treatments. CDP-choline and CDP-ethanolamine were competitive inhibitors of the ethanolaminephosphotransferase and cholinephosphotransferase reactions, respectively.

Journal Article↗
PubMed1981

Diabetes alters the myocardial cAMP-protein kinase cascade system.

An isolated perfused working rat heart preparation was used to assess the effect of alloxan-induced diabetes on the cAMP cascade system. Diabetes did not alter basal cAMP, cGMP content, or protein kinase or phosphorylase activities, but depressed (50%) isoproterenol-induced changes in cAMP content and protein kinase activity ratios. In contrast, phosphorylase activation and increased left ventricular pressure (LVP) were unaltered by diabetes. The relationship between cAMP and protein kinase activation is linear in hearts from both normal and diabetic rats. Diabetes did not alter this relationship. The relationship between protein kinase and phosphorylase activation or increases in LVP is also linear. An increase in the slopes obtained with diabetic hearts (P less than 0.05) was observed, suggesting an increased gain in the amplification cascade to protein kinase. The in vivo administration of insulin diminished this response. Thus, diabetes alters the ability of heart to accumulate cAMP and alters the gain of the amplification cascade system subsequent to protein kinase activation. This second effect may indicate an unmasking of a parallel regulatory pathway and in the beta-adrenergic regulation of phosphorylase activity and LVP.

Alloxan↗