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Biomedical subjects

K Hahn

Publications and source records attributed to K Hahn.

At least 109 records · Page 6Linked to original sources
PubMed1999

Induction of an AP endonuclease activity in Streptococcus mutans during growth at low pH.

The oral microbe Streptococcus mutans uses adaptive mechanisms to withstand the fluctuating pH levels in its natural environment. The regulation of protein synthesis is part of the mechanism of acid adaptation and tolerance in S. mutans. Here, we demonstrate that the organism's acid-inducible protein repertoire includes an AP endonuclease activity. This abasic site-specific endonuclease activity is present at greater levels in cells grown at low pH than in cells grown at pH 7, and is apparently independent of the RecA protein. Experiments using tetrahydrofuran or alpha-deoxyadenosine-containing substrates indicate that the activity induced at low pH may be similar to the activity of exonuclease III from E. coli. Acid-adapted S. mutans also shows an increased survival rate after exposure to near-UV radiation in both the wild type and a recA strain. Far-UV radiation resistance is observed in the wild type only. The endonuclease activity was purified approximately 500-fold from an S. mutans recA mutant strain grown at pH 5. Initial characterization revealed a 3' to 5' exonuclease activity, and showed additional functional similarities to DNA repair enzymes from other organisms.

Calcium Chloride↗
PubMed1999

Use of three-phase bone scans and SPET in the follow-up of patients with allogenic vascularized femur transplants.

The vascularized allotransplantation of femoral diaphyses under immunosuppression is a novel approach in orthopaedic surgery. To evaluate which method provides the best information about microvascularity and viability of the transplant, we compared different diagnostic approaches used in transplant surgery. Three patients were investigated four times over a period of 1 month (on days 2, 7, 15 and 30 post-transplantation) and 6 and 12 months later with planar 99Tcm-MDP three-phase bone scintigraphy and SPET. The results were compared with duplex sonography, angiography and intraoperative biopsies. Rejection and thrombosis of the transplant were associated with decreased or missing perfusion detected by duplex sonography, angiography and blood pool scintigraphy. In these cases, late bone scans showed reduced or absent bone metabolism while biopsy revealed necrotic bone tissue. In cases without complications, blood pool scans revealed hyperaemia of the graft indicating excellent perfusion and patency of vascular anastomoses and transplant vessels. Late bone scans demonstrated increased bone metabolism. The corresponding biopsies showed viable bone cells. We conclude that bone scintigraphy is a valuable diagnostic tool in vascularized femur allotransplantation, since it provides reliable information on both viability and perfusion of the transplant within a single non-invasive investigation.

Adult↗
PubMed1999

Investigating one-dimensional diffusion by quasielastic neutron scattering: a theoretical approach.

Scattering functions and full widths at half maximum for quasielastic neutron scattering (QENS) are calculated for diffusion in systems of one-dimensional channels. The self-correlation function for diffusion in isotropically oriented channels is given and it is found that this function diverges at the origin. The calculations are carried out for both normal and single-file diffusion and the influence of the ballistic phase is investigated. It is found that the ballistic phase influences the scattering functions very strongly for large diffusion coefficients. QENS data from the literature are analyzed with respect to this influence. The influence of three different resolution functions (triangular, Gaussian, and Lorentzian) is considered.

Journal Article↗
PubMed1999

Normative volumetric data of the developing hippocampus in children based on magnetic resonance imaging.

PURPOSE: To acquire normative data of the hippocampus and its postnatal growth in 50 children (age, 1 month to 15 years) without epilepsy. METHODS: Morphometry of the hippocampus was carried out by using a spoiled FLASH 3D sequence (sagittal orientation), whereas the volume of the brain was assessed with a T2-weighted spin-echo sequence (transverse orientation). The volume of the hippocampus and the brain was determined by following Cavalieri's principle. Growth curves of the brain and hippocampus were fitted to a nonlinear Boltzmann sigmoidal equation. RESULTS: Intra-/interobserver coefficient of variation was 2.0/4.9% for hippocampal volume measurements and 2.0/2.1% for brain volumetry. A significant difference in volume was noted between the right and left hippocampus (p < 0.001), with the right side being larger on average by 0.10 cc. Correlation coefficients of growth curves ranged between 0.71 and 0.94. Growth curves demonstrated a faster development of the hippocampus in girls. A steeper slope of hippocampal growth as compared with brain growth was found in girls, whereas in boys, the slope of brain growth was steeper. CONCLUSIONS: Our findings will be of help in evaluating vulnerable phases of the hippocampal formation with accelerated growth, thereby leading to a better understanding of the development of hippocampal sclerosis in early childhood.

Adolescent↗
PubMed1999

MR angiography versus color Doppler sonography in the evaluation of renal vessels and the inferior vena cava in abdominal masses of pediatric patients.

OBJECTIVE: Involvement of renal vessels and the inferior vena cava (IVC) plays a decisive role during operative planning for removal of abdominal masses in pediatric patients. Advantages and limitations of MR angiography and color Doppler sonography for determining these factors were evaluated. MATERIALS AND METHODS: MR angiography and color Doppler sonography were performed preoperatively in 42 neonates, infants, and children with abdominal masses and were compared with spin-echo MR imaging and with surgical findings. Variables evaluated were anatomic variants, vessel displacement, patency of vessels, collateral circulation, and intravascular tumor extension. Quality of vessel visualization was assessed in vessels not affected by tumor. RESULTS: In 88% of unaffected renal vessels, the entire vessel course could be visualized on MR angiography compared with 58% on color Doppler sonography and 43% on spin-echo MR imaging. In four of nine cases, color Doppler sonography revealed an accessory renal artery, whereas MR angiography revealed these variants in seven of nine cases. MR angiography showed 79% and color Doppler sonography 66% of displaced vessels. Unlike MR angiography, color Doppler sonography did not reveal five stenotic renal veins because they could not be completely imaged. In two cases, however, MR angiography falsely indicated an occlusion of the IVC, whereas color Doppler sonography showed residual flow. CONCLUSION: Anatomic variants, vessel displacement, collateral circulation, and neoplastic vessel infiltration were revealed more accurately by MR angiography than by color Doppler sonography. In cases in which patency of the IVC is unclear on MR angiography, color Doppler sonography should also be performed.

Abdominal Neoplasms↗
PubMed1998

Regional differences in the metabolism of Tyr-MIF-1 and Tyr-W-MIF-1 by rat brain mitochondria.

Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH2) are endogenous neuropeptides with opiate modulating and other CNS effects. After incubation of the tritiated tetrapeptides with fractions of tissue from different areas of rat brain, formation of the metabolites was determined by HPLC. Marked regional differences in degradation were found for both peptides. The metabolism of Tyr-MIF-1, resulting in the formation of the biologically active MIF-1 (Pro-Leu-Gly-NH2), was greater in the mitochondrial than in the synaptosomal fractions. In the mitochondrial fraction, about twice as much MIF-1 was formed in brain cortex than in striatum, diencephalon, or midbrain/pons medulla. These results, showing differential metabolism in various areas of the brain, indicate another means for regulation of the concentrations of neuropeptides.

Animals↗
PubMed1998

Technetium-99m mercaptoacetyltriglycine clearance values in children with minimal renal disease: can a normal range be determined?

Use of technetium-99m labelled mercaptoacetyltriglycine (99mTc-MAG3) simplifies and improves the quantification of renal clearance in children by virtue of its permanent availability, good imaging properties and low radiation exposure. Due to the lack of reference values for 99mTc-MAG3 clearance in children, the Paediatric Task Group of the EANM initiated a multicentre study to evaluate 99mTc-MAG3 clearance values in children with minimal renal disease. One hundred and twenty-five children aged between 12 months and 17 years, classified as renally healthy using defined diagnostic criteria, were included in the study. 99mTc-MAG3 clearance was calculated using an algorithm on the basis of a single blood sample taken at any time between 30 and 40 min after tracer injection. In addition, the absolute 99m-Tc-MAG3 clearance values were normalized to body surface area. For further evaluation the children were classified into several groups according to age. There was a continuous increase in non-corrected 99mTc-MAG3 clearance values from the age of 1 year up to the age of 17 years (mean value <2 years: 98+/-57 ml/min; mean value >8 years: 208+/-66 ml/min). Normal clearance values for adults were achieved by the age of 8 years. Analysis of the relationship between non-corrected clearance and age yielded a correlation coefficient of r=0.7. When these absolute clearance values were normalized to body surface area, we found nearly constant clearance values for all age groups, with a mean clearance value of 315+/-114 ml/minx1.73 m2. The correlation coefficient for the relationship between normalized clearance and age was r=0.28. In conclusion, the clearance of 99mTc-MAG3 increases continuously throughout childhood into adolescence due to the maturation and growth of the kidney. After normalization of the absolute clearance to body surface area, no correlation between clearance and age could be proven.

Child↗
PubMed1998

ST segment elevation and the prediction of hospital life-threatening complications: the role of right ventricular and posterior leads.

UNLABELLED: Accurate prognosis in suspected acute myocardial infarction (AMI) is essential for appropriate use of thrombolytic therapy and primary angioplasty. However, previous models may be limited because the 12-lead electrocardiogram (ECG) does not examine the right ventricular (RV) and posterior myocardium. We evaluated ST segment elevation (STSE) in posterior (V7-V9) and RV (V4R-V6R) leads to determine their predictive value for hospital life-threatening complications (HLTCs). METHOD AND RESULTS: This prospective trial of seven Midwestern hospital emergency departments (EDs) had inclusion criteria of age 35 years, chest pain suggestive of ischemia, and coronary care unit (CCU) admission. ECG leads were test positive if STSE was > 0.1 mV. Patients were positive for HLTCs if ED or inpatient hospital course included: ventricular fibrillation or tachycardia, second- or third-degree block, shock, arrest, or death. Univariate and multivariate analyses were performed to test each lead's association with HLTCs. Of 533 patients, 64.7% (345/533) had AMI and 15.8% (85/533) had HLTCs. The sensitivity of 18 leads for HLTCS was increased by 5.8%, but specificity decreased by 8.2%. ECG subgroups by STSE were associated with the following HLTC rates: inferior/+RV (32.4%); anterior (29.5%), lateral (23.1%), inferior RV (17.9%), and posterior (16.2%). V1 (odds = 3.2) and V6R (odds = 3.1) were statistically significant independent predictors. CONCLUSION: Posterior and RV leads did not increase the ECG's overall prognostic value, but in the presence of inferior STSE, were associated with low and high complication rates, respectively. Right and left precordial leads were the best predictors of HTLCs.

Adult↗
PubMed1998

hpaA mutants of Xanthomonas campestris pv. vesicatoria are affected in pathogenicity but retain the ability to induce host-specific hypersensitive reaction.

Xanthomonas campestris pv. vesicatoria is the causal agent of bacterial spot disease on pepper and tomato plants. We reported previously that the main hrp (hypersensitive reaction and pathogenicity) gene cluster in X. c. pv. vesicatoria contains six transcription units, designated hrpA to hrpF. We present here the sequence of the hrpD operon and an analysis of non-polar mutants in each of the six genes. Three genes, hrcQ, hrcR and hrcS, are predicted to encode conserved components of type III protein secretion systems in plant and mammalian pathogenic bacteria. For hrpD5 and hrpD6, homologues have only been found in Ralstonia solanacearum. Interestingly, the hrpD operon contains one gene, hpaA (for hrp-associated), which is specifically required for disease development. hpaA mutants are affected in pathogenicity, but retain in part the ability to induce avirulence gene-mediated, host-specific hypersensitive reaction (HR). In addition, HpaA was found to contain two functional nuclear localization signals, which are important for the interaction with the plant. We propose that HpaA is an effector protein that may be translocated into the host cell via the Hrp secretion pathway.

Amino Acid Sequence↗
PubMed1998

[Dosimetry in conventional and spiral CT in 8 spiral CT scanners of the latest generation].

PURPOSE: Measurement of scanner-dependent differences in PCTDI for conventional and spiral CT and evaluation of PCTDI/100 mAs in eight spiral CT scanners of the latest generation. METHODS: Central PCTDI was evaluated in a PMMA phantom for different scan lengths of conventional and spiral CT in four scanners. Central and peripheral PCTDI/100 mAs, average dose and the quotient between peripheral and central PCTDI/100 mAs were measured with a dedicated 10 cm ionisation chamber positioned within a PMMA phantom using the parameters of a standardised liver protocol and a high-resolution inner ear protocol for eight spiral CT scanners. RESULTS: Depending on scanner type and scan length PCTDI for the spiral mode is in a range between 11.3% higher and 4.3% lower than that for the conventional mode. PCTDI/100 mAs varies considerably between different CT scanners. For the standardised liver protocol PCTDI/100 mAs varies up to a factor of 2, for the inner ear protocol up to a factor of 4. CONCLUSION: Even in comparable modern CT scanners there are considerable protocol and scanner-dependent differences in PCTDI/100 mAs. The values for his own scanner should be known to each CT user so that he can develop a dose-optimised, patient and problem-orientated examination strategy.

Ear, Inner↗
PubMed1998

Time resolving ionization monitor for microsecond radiation impulses.

The current induced in the outer circuit of a fast response ionization chamber exposed to pulsed radiation consists of two components, a fast one induced by free electrons and a slow one induced by ions. The fast electron component may be used for the representation of the shape of the ionizing pulse. In order to avoid interference with the slow ion current, the latter has to be removed from the signal. This is achieved by deriving a voltage course from the chamber signal which fits the shape of the ion component and subtracting this from the entire signal. The function of the electronic circuit used for this purpose is described. Some considerations about the time resolution of the chamber gas are to be found in the appendix.

Electronics↗
PubMed1998

Limited value of scintimammography and contrast-enhanced MRI in the evaluation of microcalcification detected by mammography.

The aim of this study was to evaluate whether scintimammography using 99Tc(m)-sestamibi or contrast-enhanced magnetic resonance imaging (MRI) can improve the specificity of mammography for the differentiation of benign and malignant breast microcalcification. From 156 consecutive patients studied with SMM, 44 patients with microcalcification on mammograms were selected for this study. Forty patients in this group also had contrast-enhanced MRI of the breast. The intensity and patterns of sestamibi uptake for scintimammography and contrast enhancement for MRI were visually determined and graded on a 5-point scale for malignancy. The results of both techniques were compared and correlated with final histopathologic diagnoses. The sensitivity and specificity of scintimammography were 63% and 85% respectively, if only those cases classified as probable or definite malignancy were considered positive. If indeterminate findings were also considered positive, the sensitivity and specificity of scintimammography were 79% and 80% respectively. Using the latter classification for MRI revealed a comparable sensitivity of 82% but a markedly lower specificity of 56%. Excluding indeterminate findings from the group of positive MRI diagnoses resulted in a specificity of 94% and a sensitivity of 64%. In conclusion, scintimammography of the breast had a comparable sensitivity but a higher specificity than MRI. The sensitivity of both techniques, however, is probably too low for routine use in the evaluation of microcalcification detected by mammography.

Adult↗
PubMed1998

Radiation dose and image quality in spiral computed tomography: multicentre evaluation at six institutions.

The purpose of this study was to evaluate the correlation of radiation dose with image quality in spiral CT. Seven clinical protocols were measured in six different radiological departments provided with four different types of high specification spiral CT scanners. Central and surface absorbed doses were measured in acrylic. The practical CT dose index (PCTDI) was calculated for seven clinical examination protocols and one standardized protocol using identical parameters on four different spiral CT scanners with a dedicated ionization chamber inserted into PMMA phantoms. For low contrast measurements, a cylindrical three-dimensional (3D) phantom (different sized spheres of defined contrast) was used. Image noise was measured with a cylindrical water phantom and high contrast resolution with a Perspex hole phantom. Image quality phantoms were scanned using the parameters of the clinical protocols. Images were randomized, blinded and read by six radiologists (one from each institution). PCTDI values for four different scanners varied up to a factor between 1.5 (centre) and 2.2 (surface) for the standardized protocol. A greater degree of variation was observed for seven clinical examination protocols of the six radiological departments. For example, PCTDI varied up to a factor between 1.7 (cerebrum protocol) and 8.3 (abdomen paediatric protocol). Low contrast resolution correlates closely with dose. An improvement in detection from 8 mm to 4 mm sized spheres needs approximately a ten-fold increase in dose. Noise shows a moderate correlation with PCTDI. High contrast resolution of clinical protocols is independent of PCTDI within a certain range. Differences in modern CT scanner technology seem to be of less importance for radiation exposure than selection of protocol parameters in different radiological institutes. Future discussion on guidelines regarding optimal (patient adapted) tube current for clinical protocols is desirable.

Brain↗
PubMed1998

Prospective evaluation of MR arthrography performed with high-volume intraarticular saline enhancement in patients with recurrent anterior dislocations of the shoulder.

OBJECTIVE: The purpose of this study was to evaluate the accuracy of high-volume saline-enhanced MR arthrography in assessing the labrum, the ligaments, and the bony components of the glenohumeral joint. SUBJECTS AND METHODS: Forty-four patients with recurrent anterior dislocations of the shoulder underwent MR arthrography after intraarticular injection of 15-40 ml of saline solution. Two-dimensional fast low-angle shot and T1-weighted spin-echo sequences were prospectively evaluated by two observers. Anterior (Bankart) lesions, superior labral lesions extending from anterior to posterior, and Hill-Sachs lesions were diagnosed. Glenohumeral ligaments (GHLs) were identified and classified using a standard system. MR imaging results were compared with those of arthroscopy (n = 32) or open surgery (n = 12), either of which was the gold standard. RESULTS: Bankart lesions and superior labral lesions extending from anterior to posterior were revealed with a sensitivity of 93% and 89%, respectively, and a specificity of 80% and 89%, respectively. Diagnostic accuracy was 89% for both types of lesions. All six patients with bony Bankart lesions had high fat-marrow signal intensity within the fragment on T1-weighted MR images. For GHLs, MR imaging results and arthroscopy correlated in 25 of the 31 patients. In three patients all three GHLs were visible on MR imaging, but only two GHLs were detected with arthroscopy. In three patients two GHLs were detected on MR imaging but all three were visible on arthroscopy. Hill-Sachs lesions were revealed with a sensitivity of 95%, a specificity of 50%, and an accuracy of 81%. CONCLUSION: High-volume saline-enhanced MR arthrography is accurate in revealing the labrum, the ligaments, and the bony components of the glenohumeral joint Saline solution is inert and inexpensive, two advantages over gadopentetate dimeglumine.

Adult↗
PubMed1998

Technetium-99m-sestamibi scintimammography for the detection of breast carcinoma: comparison between planar and SPECT imaging.

UNLABELLED: The purpose of our study was to compare the results of planar and SPECT scintimammography for the detection of breast carcinoma. In addition, our goal was to determine whether SPECT reconstructed with filtered backprojection (FBP) or with iterative algorithms (ISA) can improve the sensitivity and specificity of planar scintimammography (SMM). METHODS: One hundred thirteen patients with suspicious physical examinations and/or mammography underwent planar lateral and anterior breast imaging as well as SPECT imaging after injection of 99mTc-sestamibi. We used a blind evaluation, both separately and combined, for planar SMM, ISA-SPECT and FBP-SPECT. Scintigraphic findings were correlated with the final histopathological diagnoses. RESULTS: The sensitivity of planar SMM was 80% with a specificity of 83%. All ISA-SPECT studies were of diagnostic quality, while FBP-SPECT was considered nondiagnostic in 14 that were excluded for statistical calculation. Sensitivity of ISA-SPECT and FBP-SPECT were 71% and 69%, respectively. Specificity was 70% for ISA-SPECT and 66% for FBP-SPECT. Combined planar SMM plus ISA-SPECT sensitivity was 85% (81% for planar SMM plus FBP-SPECT) with a specificity of 72%. Three carcinomas indeterminate on planar SMM were correctly identified by combined planar SMM plus ISA-SPECT. ISA-SPECT and FBP-SPECT provided additional information to planar SMM with respect to localization of sestamibi uptake, tumor extent, improved diagnostic certainty and detection of axillary nodes in 40 and 14 patients, respectively. CONCLUSION: ISA reconstruction is the preferable approach to SPECT data. Combined with planar SMM, ISA-SPECT can improve sensitivity. SPECT is useful in cases of indeterminate and positive planar SMM.

Algorithms↗
PubMed1998

Iodine-123-iodobenzamide SPECT assessment of dopamine D2 receptor occupancy in riperidone-treated schizophrenic patients.

UNLABELLED: The recently introduced neuroleptic, risperidone, was expected to block fewer dopamine D2 receptors than typical neuroleptics (e.g., haloperidol), but at comparable potency. The aim of this study was to evaluate the degree of dopamine D2 receptor occupancy in relation to the neuroleptic dosage and to correlate the findings with the presence of extrapyramidal symptoms (EPS). Additionally, the data were compared to previous iodobenzamide (IBZM) SPECT findings in patients treated with other neuroleptics, haloperidol and clozapine. METHODS: In 20 patients with schizophrenia [Diagnostic and Statistical Manual of Mental Disorders (Third Edition-Revised)] treated with mean daily doses of risperidone ranging from 0.029 to 0.128 mg/kg body weight, SPECT was performed 2 hr after intravenous injection of 185 MBq 123I-IBZM, a selective dopamine D2 receptor ligand. Striatal IBZM binding was assessed by calculating a striatal/frontal cortex ratio, expressed as a percentage of the control value. RESULTS: Selective dopamine D2 receptor binding of the ligand was reduced in all treated patients, with binding values ranging from 7% to 68%. The degree of occupancy displayed an exponential dose-response relationship (r = -0.86; p < 0.0001). The slope of the curve was between those of haloperidol and clozapine but was closer and more similar in shape to the curve of haloperidol. Extrapyramidal symptoms were observed in 8 of 20 patients with binding values between 7% and 47%. However, there was no clear relationship between the degree of receptor occupancy and the presence of EPS. CONCLUSION: The findings suggest an exponential dose-response relationship between the daily dosage of risperidone and the dopamine D2 receptor occupancy. The blockade of specific striatal IBZM binding found under therapy with risperidone is between those of haloperidol and clozapine. The dose-response curve for risperidone, however, shows greater similarity to that of haloperidol.

Adult↗