Comments on congenital methemoglobinemia.
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Humans↗
Biomedical subjects
R D Thomas
Publications and source records attributed to R D Thomas.
Optimization of a fluoroscope to reduce radiation exposure in pediatric imaging.
BACKGROUND: A new children's hospital provided the impetus to investigate radiation dose and image quality in a fluoroscope that was specially engineered for pediatric fluoroscopy. Radiation protection management recommends radiation exposures that are as low as reasonably achievable, while still maintaining diagnostic image quality. OBJECTIVES: To obtain comparative phantom imaging data on radiation exposure and image quality from a newly installed fluoroscope before and after optimization for pediatric imaging. MATERIALS AND METHODS: Images were acquired from various thickness phantoms, simulating differing patient sizes. The images were evaluated for visualization of high- and low-contrast objects and for radiation exposure. Effects due to use of the image intensifier anti-scatter grid were also investigated. RESULTS: The optimization of the new fluoroscope for pediatric operation reduced radiation exposure by about 50% (compared to the originally installed fluoroscope), with very little loss of image quality. Pulsed fluoroscopy was able to lower radiation dose to less than 10% of continuous fluoroscopy, while still maintaining acceptable phantom image quality. CONCLUSION: Radiation exposure in pediatric fluoroscopy can be reduced to values well below the exposure settings that are typically found on unoptimized fluoroscopes. Pulsed fluoroscopy is considered a requisite for optimal pediatric fluoroscopy.
Adult↗
A multihospital survey of radiation exposure and image quality in pediatric fluoroscopy.
BACKGROUND: Traditionally, pediatric radiologists have been advocates of fluoroscopy systems that provide diagnostic images at the lowest possible radiation dose to the pediatric patient. Manufacturers of fluoroscopic equipment vary as to their claims of "low radiation" exposures. OBJECTIVES: To obtain comparative data on radiation exposure and image quality from four pediatric hospitals, across variants of fluoroscopic equipment (such as pulsed versus continuous fluoroscopy). MATERIALS AND METHODS: Images were acquired from phantoms that simulated the size of a 3-year-old child. Phantom results, both stationary and rotating dynamic, were evaluated for radiation exposure and for image resolution of high- and low-contrast objects. RESULTS: Radiation exposure from the four fluoro units varied widely; the lowest-dose selectable fluoro mode produced exposures varying between 34 and 590 mrads/min among the four fluoro units, and the highest-dose selectable fluoro mode produced 540-2,230 mrads/min. The lowest radiation exposures were produced by pulsed fluoro units, and the very lowest radiation exposure was produced by a fluoroscope that had been especially optimized for pediatric imaging. There was only a small variation in image quality among the hospitals for visualization of stationary objects. A wide variability was noted for detection of objects on the moving phantom. CONCLUSIONS: The variability in the number of detected objects was considerably smaller than the variability in radiation exposure. Pulsed fluoroscopy provides improved resolution for moving objects. Optimization of one hospital's fluoroscope especially for pediatric imaging produced the best ratio of image quality to radiation exposure.
Age Factors↗
Imaging of congenital and acquired gastric abnormalities in children.
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Adolescent↗
Assessing sensitivity in a multidimensional space: some problems and a definition of a general d'.
This article provides a formal definition for a sensivity measure, d'g between two multivariate stimuli. In recent attempts to assess perceptual representations using qualitative tests on response probabilities, the concept of a d' between two multidimensional stimuli has played a central role. For example, Kadlec and Townsend (1992a, 1992b) proposed several tests based on multidimensional signal detection theory that allow conclusions concerning the perceptual and/or decisional interactions of stimulus dimensions. One proposition, referred to as the diagonal d' test, relies on specific stimulus subsets of a feature-complete factorial identification task to infer perceptual separability. Also, Ashby and Townsend (1986), in a similar manner, attempted to relate perceptual independence to dimensional orthogonality in Tanner's (1956) model, which also involves d' between two multivariate signals. An analysis of the proposed d'g reveals shortcomings in the diagonal d' test and also demonstrates that the assumptions behind equating perceptual independence to dimensional orthogonality are too weak. This d'g can be related to a common measure of statistical distance, Mahalanobis distance, in the special case of equal covariance matrices.
Decision Making↗
The learning curve in vestibular schwannoma surgery.
OBJECTIVE: This study aimed to examine the effect of surgical team experience on facial nerve function and complication rate in vestibular schwannoma surgery. STUDY DESIGN: The study design was a retrospective analysis of a case series. SETTING: The study was conducted at a tertiary referral center. PATIENTS: One hundred sixty consecutive patients undergoing vestibular schwannoma excision participated. INTERVENTION: Surgical excision of vestibular schwannoma via a translabyrinthine, middle cranial fossa, suboccipital, or combined approach was performed. MAIN OUTCOME MEASURES: Facial nerve function (House-Brackmann score) and complication rates including cerebrospinal fluid leak and meningitis compared by groups of 20 patients were measured. RESULTS: There was a statistically significant improvement in the number of patients achieving a House-Brackmann grade I result between the first 20 patients (35% House-Brackmann grade 1) and the ensuing 7 groups of 20 patients (74% House-Brackmann grade 1) by chi2 analysis. When considering House grades I and II together, there was no statistically significant difference in facial nerve function in the first 20 patients (80%) compared to the last 7 groups of 20 patients (88%) by Tukey's pairwise comparisons (p = 0.245). Mean tumor size was not significantly different in the groups studied (p = 0.54). The total cost of patient care declined over the study period; however, the wide case-to-case variance made it so that this trend was not statistically significant (p = 0.448). CONCLUSIONS: A learning curve of 20 patients was demonstrated by this study to have been necessary for attaining acceptable standards in the surgical removal of vestibular schwannomas by a new surgical team. The findings of this study may have implications for patient care and surgeon training.
Adolescent↗
Biliary cystadenoma in a child: CT and MR appearances.
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Adenoma, Bile Duct↗
Langerhans cell histiocytosis: unusual skeletal manifestations observed in thirty-four cases.
OBJECTIVE: Unusual manifestations are occasionally encountered in Langerhans cell histiocytosis and may be a source of confusion. The objective of this study was to determine the frequency of occurrence of the unusual manifestations in our case material. DESIGN AND PATIENTS: Thirty-four children, average age 4.4 years (range 3 months to 16 years) with 262 skeletal lesions of biopsy-proven Langerhans cell histiocytosis (LCH) were retrospectively reviewed to determine the frequency of occurrence of unusual manifestations defined either as an atypical location of a skeletal lesion or an atypical radiographic appearance of the lesion. RESULTS: Twenty-four unusual lesions were found in this retrospective review. Among these were epiphyseal lesions, transphyseal lesions, extracranial 'button' sequestra, posterior vertebral arch lesions, dural extension of vertebral lesions, and fluid-fluid levels. The finding of fluid-fluid levels has not previously been described in the radiologic literature. Involvement of unusual sites included clavicles and small bones of the hands and feet. CONCLUSIONS: Radiographic, computed tomographic, and magnetic resonance imaging of LCH yield a variety of unusual manifestations. Recognition of these varied appearances of LCH may prevent confusion of such appearances with other pathologic processes. When the unusual manifestation occurs as the initial finding of the disease, LCH should be included in the differential diagnosis.
Adolescent↗
Learning correlations in categorization tasks using large, ill-defined categories.
The experiments revealed whether individual participants are sensitive to exemplar information in the form of within-category correlations between stimulus dimensions after training on large overlapping categories. Participants were trained in 1 of 2 categorization conditions. The sign of the correlation between dimensions differed across conditions, but the categorization rules that best separated the categories were identical. An unannounced attribute-prediction task followed categorization training. Several participants produced predictions consistent with the correct correlation between the dimensions. For other participants, the predictions reflected the correlation only within the region they had associated with the given category, even though the categories overlapped, suggesting that the decision boundary was explicitly represented in memory. Finally, for other participants, no correlational information appeared to be accessible for the prediction task.
Humans↗
Tuberous sclerosis complex and Wolff-Parkinson-White syndrome.
This report highlights the association between tuberous sclerosis and Wolff-Parkinson-White syndrome. Ten patients with concurrent diagnoses of Wolff-Parkinson-White syndrome and tuberous sclerosis were identified. Wolff-Parkinson-White syndrome presented early in life, nine cases being diagnosed in the first year. Eight of the 10 cases were male. In eight cases, the syndrome was associated with supraventricular tachycardias, and in nine with cardiac rhabdomyomata. One child died from cardiac failure secondary to obstruction of the left ventricular outflow tract by a rhabdomyoma. Five of nine survivors showed resolution of Wolff-Parkinson-White syndrome on follow up. The accessory pathway was localised in nine patients from surface electrocardiograms: six children had left sided pathways and three had right sided pathways.
Electrocardiography↗
Management of an infected hematometrocolpos in a patient with congenital adrenal hyperplasia and vaginal stenosis.
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Adrenal Hyperplasia, Congenital↗
Biochemical and molecular changes at the cellular level in response to exposure to environmental estrogen-like chemicals.
Estrogen-like chemicals are unique compared to nonestrogenic xenobiotics, because in addition to their chemical properties, the estrogenic property of these compounds allows them to act like sex hormones. Whether weak or strong, the estrogenic response of a chemical, if not overcome, will add extra estrogenic burden to the system. At elevated doses, natural estrogens and environmental estrogen-like chemicals are known to produce adverse effects. The source of extra or elevated concentration of estrogen could be either endogenous or exogenous. The potential of exposure for humans and animals to environmental estrogen-like chemicals is high. Only a limited number of estrogen-like compounds, such as diethylstilbestrol (DES), bisphenol A, nonylphenol, polychlorinated biphenyls (PCBs), and dichlorodiphenyltrichloroethane (DDT), have been used to assess the biochemical and molecular changes at the cellular level. Among them, DES is the most extensively studied estrogen-like chemical, and therefore this article is focused mainly on DES-related observations. In addition to estrogenic effects, environmental estrogen-like chemicals produce multiple and multitype genetic and/or nongenetic hits. Exposure of Syrian hamsters to stilbene estrogen (DES) produces several changes in the nuclei of target organ for carcinogenesis (kidney): (1) Products of nuclear redox reactions of DES modify transcription regulating proteins and DNA; (2) transcription is inhibited; (3) tyrosine phosphorylation of nuclear proteins, including RNA polymerase II, p53, and nuclear insulin-like growth factor-1 receptor, is altered; and (4) DNA repair gene DNA polymerase beta transcripts are decreased and mutated. Exposure of Noble rats to DES also produces several changes in the mammary gland: proliferative activity is drastically altered; the cell cycle of mammary epithelial cells is perturbed; telomeric length is attenuated; etc. It appears that some other estrogenic compounds, such as bisphenol A and nonylphenol, may also follow a similar pattern of effects to DES, because we have recently shown that these compounds alter cell cycle kinetics, produce telomeric associations, and produce chromosomal aberrations. Like DES, bisphenol A after metabolic activation is capable of binding to DNA. However, it should be noted that a particular or multitype hit(s) will depend upon the nature of the environmental estrogen-like chemical. The role of individual attack leading to a particular change is not clear at this stage. Consequences of these multitypes of attack on the nuclei of cells could be (1) nuclear toxicity/cell death; (2) repair of all the hits and then acting as normal cells; or (3) sustaining most of the hits and acting as unstable cells. Proliferation of the last type of cell is expected to result in transformed cells.
Animals↗
Runaway in a modern "soft top" pacemaker.
Although runaway pacemaker was a relatively common occurrence, modern pacemaker design has made it extremely rare. We report a case occurring with a modern "soft-top" pacemaker that resulted from a loss of hermeticity. Although the different treatment options are discussed, the definitive maneuvre is explantation of the faulty pacemakers
Aged↗
Wessex regional radiology audit: barium enema in colo-rectal carcinoma.
In the first Wessex regional radiology audit, a retrospective comparison of pathology and radiology reports was made to determine rates of demonstration and reporting of colo-rectal carcinoma on barium enema. Barium enema films were analysed by peer review in cases of discrepancy. The standard set was 100% demonstration and 100% diagnosis of colo-rectal carcinoma on a barium enema undertaken in the 12 months preceding histological diagnosis. The carcinoma demonstration rate was 97% and carcinoma reporting rate 85%. Of 1351 patients with carcinoma, 557 had a barium enema in the preceding 12 months. Four hundred and seventy-one enema reports satisfactorily recorded the malignant lesion (85%). The reasons for non-reporting of a carcinoma were failure to demonstrate the lesion (18 cases, 3%), failure to perceive a demonstrated lesion (23 cases, 4%) and failure to analyse a perceived lesion (45 cases, 8%). Any improvement in demonstration cannot be estimated, but 94% of carcinomas should be reported when improved reporting techniques are instituted and the audit loop is closed.
Adenocarcinoma↗
Mitochondrial enzyme-catalyzed oxidation and reduction reactions of stilbene estrogen.
We have demonstrated for the first time that mitoplasts (i.e. mitochondria without outer membrane) were able to convert stilbene estrogen (diethylstilbestrol, DES) to reactive metabolites, which covalently bind to mitochondrial (mt)DNA. Depending on the cofactor used, mitochondrial enzymes catalyzed the oxidation and/or reduction of DES. DES was oxidized to DES quinone by peroxide-supported mitochondrial enzyme. A Lineweaver-Burk plot of rate of formation of DES quinone at various substrate concentrations yielded a Km of 33 microM and Vmax of 39 nmol/mg protein/min. The oxidation of DES to DES quinone by mitochondria was drastically decreased by known inhibitors of cytochrome P450. DES quinone was reduced to DES by mitoplasts in the presence of NADH. The Km and Vmax for the DES quinone reduction in the absence of mitoplasts and NADH were 3.2 microM and 5.6 nmol respectively. The reduction of DES quinone to DES by mitoplasts was significantly inhibited by inhibitors of cytochrome b5 reductase and diaphorase. DES quinone was also reduced to DES by pure diaphorase, a mitochondrial reducing enzyme, in the presence of NADH. The Km and Vmax for the DES quinone reduction by diaphorase were 9.0 microM and 4.3 nmol respectively. Under reaction conditions similar to oxidation of DES to DES quinone by mitoplasts, it was observed that mitochondrial metabolic products of DES were able to covalently bind to mtDNA. These data provide direct evidence of mitochondrial enzyme-catalyzed oxidation and reduction reactions of DES. In the cell, activation of DES in the mitochondria (the organelle in which mtDNA synthesis, mtDNA repair and transcription systems are localized) is of utmost importance, because an analogous in vivo mitochondrial metabolism of DES through covalent modifications in mitochondrial genome may produce instability in the mitochondrial genome of the cells. These modifications may in turn play a role in the development of DES-induced hepatocarcinogenicity.
Animals↗
Age-specific carcinogenesis: environmental exposure and susceptibility.
Environmental exposures in children may occur through many routes, including diet, air, and the ingestion of various nonfood items such as medications and household materials. This article focuses on dietary exposure, but it does highlight the importance of considering other routes of exposure when assessing exposure in children. It presents many of the findings in the two recent reports, Pesticides in the Diets of Infants and Children and Science and Judgment in Risk Assessment of the National Academy of Sciences (NAS)/National Research Council (NRC). Diet is an important source of exposure for children to potential carcinogens. The trace quantities of chemicals present on or in foodstuffs are termed residues. In addition, there are substances that children may be exposed to in air and water that should be considered in a total exposure analysis. To minimize exposure of the general population to chemical residues in food, water, and air, the U.S. government has instituted regulatory controls. These are intended to limit exposures to residues while ensuring an abundant and nutritious food supply, and safe drinking water and air. The legislative framework for these controls was established by the Congress through various local and state laws and such federal laws as the Insecticide, Fungicide, and Rodenticide Act (FIFRA), the Federal Food, Drug, and Cosmetic Act (FFDCA), the Safe Drinking Water Act (SDWA), and the Clean Air Act (CAA). This article summarizes current approaches to assessing exposure and susceptibility in children.
Air Pollution↗
Asymptomatic mediastinal mass in an elderly man.
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Aged↗
'To bead or not to bead?'.
In subcuticular wound closure, the use of anchorage beads or knots to maintain opposition of wound edges is a common practice, but can lead to complications. One hundred and one abdominal subcuticular wound closures (44 vertical and 57 transverse) were prospectively studied and assessment of wound swelling was made by measuring the length of exposed suture at both ends of the wound, on successive days postoperatively. Results showed progressive reduction in the exposed suture length. We would suggest that if anchorage beads are used with subcuticular sutures then they should not be pulled tight as postoperative wound swelling will cause the beads to be drawn into the wound often resulting in a troublesome ulcer(s) at the end(s) of the wound.
Abdominal Muscles↗