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Biomedical subjects

K Dietz

Publications and source records attributed to K Dietz.

At least 91 records · Page 5Linked to original sources
PubMed1997

Menstrual cycle and age: influence on parenchymal contrast medium enhancement in MR imaging of the breast.

PURPOSE: To evaluate the influence of menstrual cycle and age on parenchymal contrast medium enhancement in magnetic resonance (MR) imaging of the breast. MATERIALS AND METHODS: Dynamic gadolinium-enhanced fast low-angle shot, three-dimensional breast MR imaging was performed with high temporal and spatial resolution (eight measurements in 10 minutes). Menstrual cycle evaluations and age-influence studies were performed in 44 patients aged 27-55 years with a regular cycle (mean age, 41.5 years) and in 103 patients aged 15-79 years (mean age, 49.3 years), respectively. A region of interest was placed in each quadrant of the breast for evaluation of parenchymal enhancement. Quadrants with complete involution or lesions and patients who received hormonal therapy were excluded [corrected]. Analysis of variance was performed. RESULTS: Parenchymal contrast medium enhancement in cycle days 7-20 (geometric mean enhancement at minutes 1-10 = 0.12-0.47) was significantly lower than that in cycle days 21-6 (geometric mean, 0.17-0.98; P < or = .001). Contrast medium enhancement in patients aged 35-50 years (mean enhancement, 0.17-0.75) was significantly higher than that in patients aged younger than 35 years or older than 50 years (mean enhancement, 0.12-0.40; P < .01). CONCLUSION: Patients showed statistically significantly lower parenchymal enhancement in menstrual cycle days 7-20 than in days 21-6. Patients aged 35-50 years yielded higher parenchymal enhancement than did younger patients and older patients.

Adolescent↗
PubMed1997

Sonographic assessment of the fetal palpebral fissure slant--an additional tool in the prenatal diagnosis of syndromes.

Several syndromes and aneuploidies are associated with ocular abnormalities including up- and down-slanting palpebral fissures. We describes a technique for the sonographic assessment of the fetal palpebral fissure slant which was used in 70 normal pregnancies from 14 to 36 weeks of gestation. In a frontal view of the fetal face, the inferior angle between the palpebral fissure and the midline of the skull was determined. The median angle was 89 degrees, with a range from 87 degrees to 90 degrees. In selected cases, sonographic assessment of the fetal palpebral fissure slant may be a helpful additional tool in the prenatal diagnosis of syndromes, as demonstrated in a fetus with Seckel syndrome associated with downslanting palpebral fissures and in a fetus with Down's syndrome associated with upslanting palpebral fissures.

Craniofacial Abnormalities↗
PubMed1996

Eradication of poliomyelitis: when can one be sure that polio virus transmission has been terminated?

Most polio virus infections are silent. Vaccination reduces the incidence of infection, and the period between clinical cases of poliomyelitis becomes longer. As the point of eradication is approached, it becomes increasingly difficult to use the case-free period to determine whether silent infections have ceased. In this paper, the authors use stochastic computer simulations to relate case-free periods to the presence or absence of silent infections. After 2 years without paralytic cases in a population of 200,000 inhabitants, the probability for the presence of silent infections can still be as high as 38%. The case-free period must exceed 3 years before one can be 95% certain that there has been local extinction of the wild polio virus infection. Even after 5 years without cases, the probability of silent polio virus transmission can still be in the range of 0.1-1.0%.

Computer Simulation↗
PubMed1996

Immunogenicity and efficacy of a killed hepatitis A vaccine in day care center children.

The objective of this study was to characterize the immune response of children after the use of two different vaccine doses and to evaluate whether vaccination benefits children attending day care centers in areas with high anti-HAV seroprevalence. The study was conducted in a day care center with a stable population in São Paulo, Brazil. Two groups of 20 children, all seronegative for hepatitis A antibodies, were assigned randomly to receive three times 0.5 and 1.0 ml of the vaccine, the second and third dose 1 and 6 months after the first dose, respectively. There were 27 children in the control group. All children in both vaccinated groups had protective levels of antibodies in the serum after two inoculations, and serious adverse reactions were not observed. In the eighth month of follow-up, a hepatitis A outbreak occurred in the day care center. Five children in the control group had high titers of IgM class anti-HAV, four with clinical manifestations of acute hepatitis. None of the vaccinated children developed symptoms or signs of hepatitis (P = 0.0125), and the estimate of vaccine efficacy was 100%. Two nonstudy children from the center also had clinical and serological evidence of acute hepatitis A. It is concluded that vaccination represents an important method for prevention of hepatitis A transmission in day care centers. The results of this pilot study justify further testing in larger groups.

Child Day Care Centers↗
PubMed1996

Subcellular distribution of glucose transporter (GLUT-1) during development of the blood-brain barrier in rats.

Electron microscopy was used to quantify the subcellular distribution of the GLUT-1 isoform of the glucose transporter in developing microvessels of the brain of embryonic rats from E (embryonic stage) 13 to E19 and in adult rats. Gold-conjugated secondary antibodies were used to localize, on ultrathin sections of brain, a rabbit polyclonal antiserum (anti-GLUT-1) raised against a synthetic peptide encoding 13 amino acids of the C-terminus of the human glucose transporter. Staining was weak at E13 but increased in density during development into adulthood. The increase represented an increase in the absolute amount of transporter per vessel profile, with a concomitant decrease in vessel size with the narrowing of the wall. At early stages, the percentages of total particles per profile of lumenal membrane, ablumenal membrane, and cytoplasm were approximately equivalent. The ratio of lumenal to ablumenal particle density then shifted from below 1 at E13 to above 2 at E19 and to 4 in the adult. In contrast, vessels of the choroid plexus were devoid of labeling, but the choroid plexus epithelium stained as early as E15. In the brain, no astrocytes, neurons, or pericytes were stained at any stage examined. Developmental upregulation of the GLUT-1 glucose transporter therefore seems to occur at the blood-brain barrier, and the modulation of the subcellular distribution of the transporter can be correlated with other observed changes in the microvessels as they develop the blood-brain barrier phenotype.

Animals↗
PubMed1996

CMV infection after allogeneic bone marrow transplantation is associated with the occurrence of various autoantibodies and monoclonal gammopathies.

Recent findings indicate that the kinetics of B-cell reconstitution after marrow transplantation mimic normal ontogeny. The early B-cell repertoire during ontogeny is characterized by a high degree of autoreactivity and interconnectivity. Therefore, in a prospective analysis, 95 consecutive recipients of an allogeneic marrow transplant were screened for the occurrence of various autoantibodies and 47 of these 95 were also screened for monoclonal gammopathies. None of the patients developed antibodies specific for systemic autoimmune disorders. In contrast, a high prevalence of natural antibodies (79/95) was found early post-transplant, with 58 of these 79 patients developing two or more autoantibodies. According to multiple regression, the mean number of natural antibodies (95% confidence limits in parentheses) depends significantly (P = 0.006) on the status of CMV infection: 0.9 (0.4; 1.6) CMV-negative: 2.0 (1.0; 3.3) asymptomatic CMV infection; 3.1 (1.7; 5.0) CMV disease. Sex, age, underlying disease, conditioning therapy, acute graft-versus-host disease and CMV serology of donor and recipient pretransplant did not affect the number of natural autoantibodies. Monoclonal gammopathies were detected in 12/47 patients with a predominance of the IgG-kappa subtype. All these 12 patients suffered from a viral infection (CMV, n = 11: influenza strain A, n = 1). The high degree of self-reactivity post-transplant further supports the hypothesis that B-cell reconstitution mimics ontogeny. Moreover, these data indicate nonspecific polyclonal, CMV-mediated, presumably T-cell independent B-cell stimulation and disturbed T-cell regulatory function following allogeneic BMT.

Adolescent↗
PubMed1995

The effect of household distribution on transmission and control of highly infectious diseases.

Two epidemic threshold parameters are derived for the spread of a highly infectious disease in a community of households, where a household is any group whose members have frequent contacts with each other. It is assumed that the infection of any member of a household results in the infection of all susceptible members of that household. The threshold parameters have simple expressions in terms of the mean household size and the mean and variance of the number of susceptibles per household. They provide a basic reproduction number R0 for the spread of infection from individual to individual and a basic reproduction number RH0 for the spread of infection from household to household. The threshold parameters are used to derive the levels of immunity required for the prevention of major epidemics in the community. They are also used to evaluate various vaccination strategies having the same vaccination coverage. For a community with households of equal size, it is found that random vaccination of individuals is better than immunizing all members of a corresponding fraction of households. In contrast, when households have varying sizes, immunizing all members of large households can be better than a corresponding vaccination coverage of randomly selected individuals. It is illustrated that these threshold parameters can also be used for a community of households with schools or day care centers. In particular, the effectiveness of immunizing all members of a school is quantified.

Child↗
PubMed1995

Threshold parameters for epidemics in different community settings.

Threshold parameters of epidemic models play a central role in the assessment of proposed control strategies for infectious diseases. They have been determined for numerous standard epidemic models. This paper points out, with several examples, that threshold parameters depend on the social setting of the community and the variations in the behavior of the members of the community. Specifically, communities are considered in which individuals have fixed patterns of behavior or random patterns of behavior as well as communities of households with fixed or random patterns of behavior. A threshold parameter is computed for each of the different settings. Some comparisons are made to provide insights into the effects that social settings and behavior changes have on the threshold parameters.

Communicable Diseases↗
PubMed1995

Modelling patterns of parasite aggregation in natural populations: trichostrongylid nematode-ruminant interactions as a case study.

The characteristically aggregated frequency distribution of macroparasites in their hosts is a key feature of host-parasite population biology. We begin with a brief review of the theoretical literature concerning parasite aggregation. Though this work has illustrated much about both the sources and impact of parasite aggregation, there is still no definite analysis of both these aspects. We then go on to illustrate the use of one approach to this problem--the construction of Moment Closure Equations (MCEs), which can be used to represent both the mean and second moments (variances and covariances) of the distribution of different parasite stages and phenomenological measures of host immunity. We apply these models to one of the best documented interactions involving free-living animal hosts--the interaction between trichostrongylid nematodes and ruminants. The analysis compares patterns of variability in experimental infections of Teladorsagia circumcincta in sheep with the equivalent wildlife situation--the epidemiology of T. circumcincta in a feral population of Soay sheep on St Kilda, Outer Hebrides. We focus on the relationship between mean parasite load and aggregation (inversely measured by the negative binomial parameter, k) for cohorts of hosts. The analysis and empirical data indicate that k tracks the increase and subsequent decline in the mean burden with host age. We discuss this result in terms of the degree of heterogeneity in the impact of host immunity or parasite-induced mortality required to shorten the tail of the parasite distribution (and therefore increase k) in older animals. The model is also used to analyse the relationship between estimated worm and egg counts (since only the latter are often available for wildlife hosts). Finally, we use these results to review directions for future work on the nature and impact of parasite aggregation.

Age Factors↗
PubMed1995

[A new miniaturized flicker test for detection of florid retrobulbar neuritis].

A new transportable miniaturized flicker test equipped with green LEDs is contrasted with the conventional Tübingen flicker test, based on brightness perception of intermittent white light. The results are compared with those of former studies. In this study we examined 45 eyes suffering from florid optic neuritis. Another group of 114 eyes were either normal (except minimal ametropia) or suffered from a non-inflammatory or non-refractive impairment of central visual function. In all groups only one eye of each subject was examined. Using the criteria of Trauzettel-Klosinski, the new miniaturized "green" flicker test for the detection of a florid optic neuritis showed a specificity of only 50.9% (83.3%) and a sensitivity of 91.1% (64.4%). (The corresponding results of the conventional Tübingen flicker test are shown in parentheses.) Alternatively, analyzing the data with the help of a logistic regression, the "green" flicker test turned out to have a specificity of 92.9% (93.8%) and a sensitivity of 60.5% (44.2%). For further examinations using the flicker test it is useful to consider the duration and reproducibility of each brightness match by repeating the test several times.

Adolescent↗
PubMed1994

On some formulas in a partnership model from the perspective of a semi-Markov process.

Many deterministic models of sexually transmitted diseases, as well as population models in general, contain elements of stochastic or statistical reasoning. An example of such a model is that of Dietz and Hadeler (1988) concerning sexually transmitted diseases in which there is partnership formation and dissolution. Among the interesting formulas in this paper, which enter into the analysis of the model, are those for the expected number of partners a male or female has during a lifetime. To a probabilist such formulas suggest the possibility that some stochastic process may be constructed so as to yield these formulas as well as others that may be of interest. The principal purpose of this paper is to demonstrate that such a stochastic process does indeed exist in the form of a three state semi-Markov process in continuous time with stationary laws of evolution and with a one-step density matrix determined by four parameters which were interpreted as constant latent risk functions in the classical theory of competing risks. This construction of a semi-Markov process not only provides a framework for the systematic derivation of the formulas of Dietz and Hadeler but also suggests pathways for extensions to the age-dependent case.

Female↗
PubMed1994

Some bounds on estimates for reproductive ratios derived from the age-specific force of infection.

In this paper we shall look at estimation of reproductive ratios for common childhood infections such as chickenpox, measles, mumps, and hepatitis A with and without a vaccination program. The paper starts with a survey of previous work in this area. We suppose that we are given data in the form of an age-related serological profile with a given vaccination program. This is used to estimate the reproductive ratio and evaluate vaccination campaigns. The effect of different mixing patterns, such as homogeneous mixing, assortative mixing, proportional mixing, and symmetric mixing are discussed. R phi denotes the reproductive ratio when a steady-state vaccination campaign phi is used. Assortative mixing maximizes the reproductive ratio R phi. A mixing pattern which minimizes R phi and a lower bound for R phi for the important symmetric mixing case are found. The most usual situation is that we are given the age-serological profile with no vaccination so that we have bounds for the basic reproductive ratio R0. These results are illustrated with an application to vaccination against hepatitis A in Bulgaria. Numerical evaluations of the effect of different elimination vaccination strategies are examined.

Adult↗
PubMed1994

On the antigenic diversity threshold model for AIDS.

In this paper stochastic simulations of a model for AIDS pathogenesis developed by Nowak and coworkers are presented. The results reveal a strong dependency on initial conditions, and the model predicts a nonmonotonic hazard rate for the transition to AIDS. Doubts are raised concerning the significance of the "antigenic diversity threshold," since it only partially characterizes the model dynamics.

Acquired Immunodeficiency Syndrome↗
PubMed1994

[The chemoembolization of hepatocellular carcinoma: the computed tomographic findings and clinical results in prospective repetitive therapy].

Between April 1989 and March 1993 162 transarterial chemoembolizations (TACE) were performed repeatedly (mean interval: 2.9 months) in 52 patients with hepatocellular carcinoma (HCC): An emulsion of Lipiodol and epirubicin was injected as selectively as possible in a dosage proportional to liver function and tumour size. Before and after each TACE the size of tumours and ratio of tumour volume containing Lipiodol (RTVCL) were determined in CT and the grade of tumour vascularisation was assessed angiographically. The RTVCL increased from 58% after the first treatment to 73% after the third treatment. RTVCL and Lipiodol retention were higher in responders than in non-responders. Tumours with expansive growth pattern showed a higher response rate (56%) than infiltrating tumours (20%). Mean survival of these patients was different (19 and 8 months; p < 0.01), respectively. Survival rates of all patients were 54, 22, and 11% after 1, 2 and 3 years, respectively. Repeated TACE shows local effectiveness. Three treatments during a period of one year are recommended for patients with Child-Pugh class A cirrhosis.

Adult↗
PubMed1994

[The value of the supine chest x-ray with digital luminescence radiography in relation to the experience of the observer. A ROC analysis in CT-validated cases].

The aim of the present study was to evaluate supine chest radiographs obtained by DLR for the diagnosis of pleural and parenchymatous changes and to compare the accuracy of observers in relation to their experience. 50 examinations, which had been checked by CT, were chosen. The images were examined by 7 doctors (2 non-radiologists, 5 radiologists). Our experience indicates that DLR has high specificity but low sensitivity for the diagnosis of a pneumothorax but relatively high sensitivity and low specificity for other changes (pleural effusions, atelectases and other intrapulmonary opacities). The area under the ROC curve averaged over the 7 rater was similar for these 4 entities. There were marked differences between the observers; the radiologists were considerably better than the non-radiologists. Altogether, the diagnostic value of single DLR examinations was relatively low. In indeterminate cases, additional diagnostic methods should, therefore, be used.

Adolescent↗
PubMed1994

Promotion of preneoplastic foci in rat liver with 2,3,7,8-tetrachlorodibenzo-p-dioxin, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin and a defined mixture of 49 polychlorinated dibenzo-p-dioxins.

In a two-stage initiation-promotion experiment the hypothesis was investigated that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents (TE), calculated from data of CYP1A induction in hepatocytes in primary culture, or international TCDD equivalents (ITE) are useful for evaluating the tumor-promoting potency of 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD) and of a defined mixture (M2) of 49 polychlorinated dibenzo-p-dioxins (PCDDs) in comparison with TCDD. Therefore, female Wistar rats were treated with an initiating dose of N-nitrosomorpholine, and subsequently received daily doses of 2, 20 and 200 ng TCDD/kg or equivalent doses of HpCDD or M2, based on TE values. After a promotion phase of 13 weeks, hepatic PCDD levels, CYP1A activity and the relative hepatic volume of adenosinetriphosphatase-negative or glutathione S-transferase P-positive preneoplastic foci were determined. After logarithmic transformation, linear PCDD level-response relationships were obtained for induction of CYP1A activity with TCDD, HpCDD or M2. Based on TE values, inducing potencies of both HpCDD and M2 were over-estimated at higher doses, whereas induction was approximately equivalent at the lowest dose. The best fit of PCDD level-response relationships of relative hepatic volumes of preneoplastic lesions was achieved using a four-parameter logistic model. Significantly different functions were calculated for promotion with TCDD or HpCDD. It is concluded that (i) different PCDD level-response relationships exist for the induction of hepatic CYP1A activity and the promotion of preneoplastic liver foci, and (ii) that TE or ITE factors provide only a rough estimate of the tumor-promoting potency of a PCDD mixture but may overestimate the risk from exposure to higher-chlorinated 2,3,7,8-substituted congeners such as HpCDD.

Animals↗