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T Meindl

Publications and source records attributed to T Meindl.

12 recordsLinked to original sources
PubMed2006

Dose reduction in multidetector CT of the urinary tract. Studies in a phantom model.

A novel ureter phantom was developed for investigations of image quality and dose in CT urography. The ureter phantom consisted of a water box (14 cm x 32 cm x 42 cm) with five parallel plastic tubes (diameter 2.7 mm) filled with different concentrations of contrast media (1.88-30 mg iodine/ml). CT density of the tubes and noise of the surrounding water were determined using two multidetector scanners (Philips MX8000 with four rows, Siemens Sensation 16 with 16 rows) with varying tube current-time product (15-100 mAs per slice), voltage (90 kV, 100 kV, 120 kV), pitch (0.875-1.75), and slice thickness (1 mm, 2 mm, 3.2 mm). Contrast-to-noise ratio as a parameter of image quality was correlated with dose (CTDI) and was compared with image evaluation by two radiologists. The CT densities of different concentrations of contrast media and contrast-to-noise ratio were significantly higher when low voltages (90 kV versus 120 kV, 100 kV versus 120 kV) were applied. Smaller slice thickness (1 mm versus 2 mm) did not change CT density but decreased contrast-to-noise ratio due to increased noise. Contrast phantom studies showed favourable effects of low tube voltage on image quality in the low dose range. This may facilitate substantial dose reduction in CT urography.

Phantoms, Imaging↗
PubMed2006

Functional connectivity of the fusiform gyrus during a face-matching task in subjects with mild cognitive impairment.

Cognitive function requires a high level of functional interaction between regions of a network supporting cognition. Assuming that brain activation changes denote an advanced state of disease progression, changes in functional connectivity may precede changes in brain activation. The objective of this study was to investigate changes in functional connectivity of the right middle fusiform gyrus (FG) in subjects with mild cognitive impairment (MCI) during performance of a face-matching task. The right middle FG is a key area for processing face stimuli. Brain activity was measured using functional MRI. There were 16 MCI subjects and 19 age-matched healthy controls. The linear correlation coefficient was utilized as a measure of functional connectivity between the right middle FG and all other voxels in the brain. There were no statistical differences found in task performance or activation between groups. The right middle FG of the healthy control and MCI groups showed strong bilateral positive linear correlation with the visual cortex, inferior and superior parietal lobules, dorsolateral prefrontal cortex (DLPFC) and anterior cingulate. The healthy controls showed higher positive linear correlation of the right middle FG to the visual cortex, parietal lobes and right DLPFC than the MCI group, whereas the latter had higher positive linear correlation in the left cuneus. In the healthy controls, the right middle FG had negative linear correlation with right medial frontal gyrus and superior temporal gyrus and with left inferior parietal lobule (IPL), angular gyrus, superior frontal gyrus and anterior cingulate gyrus, but the MCI group had negative linear correlation with the left IPL, angular gyrus, precuneus, anterior cingulate, and to right middle temporal gyrus and posterior cingulate gyrus. In the negatively linearly correlated regions, the MCI group had reduced functional connectivity to the frontal areas, right superior temporal gyrus and left IPL. Different regions of the cuneus and IPL had increased functional connectivity in either group. The putative presence of Alzheimer's disease neuropathology in MCI affects functional connectivity from the right middle FG to the visual areas and medial frontal areas. In addition, higher linear correlation in the MCI group in the parietal lobe may indicate the initial appearance of compensatory processes. The results demonstrate that functional connectivity can be an effective marker for the detection of changes in brain function in MCI subjects.

Aged↗
PubMed2005

Task difficulty in a simultaneous face matching task modulates activity in face fusiform area.

The level of difficulty of a task can alter the neural network that activates for performance of the task. Previous studies have shown increased activation with task difficulty in the frontal lobes while the effects in the extrastriate visual areas have been unclear. We hypothesized that the face fusiform area (FFA), an area specialized for face processing, would increase activation as task difficulty increased in a face matching task. The difficulty level was increased by degrading the quality of the images. The degradation levels were 10%, 20%, 40% and 60%. Based on the correct response rate, the data were divided into a baseline level (composed of non-degraded and 10% degraded images) and a difficult level (composed of the 20%, 40% and 60% degraded images). Brain activation was measured using functional magnetic resonance imaging. The baseline face matching task activated a wide network of regions that included bilaterally the occipital, temporal and parietal lobes and the right frontal lobe. A novel behavioral finding was that task difficulty did not linearly increase with image degradation. The novel brain imaging finding was that the FFA is modulated by task difficulty and performance in the task was linearly correlated to activation in FFA. In addition, we found that activation in the dorsolateral prefrontal cortex (DLPFC) had increased activation as task difficulty increased. When adding the response time as a covariate, the differences in the DLPFC did not remain statistically significant. Increased task difficulty also led to a decrease in activation of visual areas in the extrastriate cortex. Task difficulty increased activation in the FFA to enhance the face processing and suppressed activation in visual extrastriate areas that processed low level properties of the stimuli. Task difficulty led to enhanced response in the FFA and suppressed response in other visual areas.

Adult↗
PubMed2004

[Low-dose spiral CT of the lung in the follow-up of non-malignant lung disease].

PURPOSE: To assess image quality of chest CT with an 80 to 90 percent dose reduction in follow-up studies of patients with lung disease, dose and image quality of a low-dose protocol was investigated. MATERIALS AND METHODS: A follow-up low-dose CT (ND-CT, 120 kV, 10 mAs/slice, 3 mm slice thickness) was performed on 35 patients with non-malignant lung disease and compared with the initial standard dose CT (= SD-CT, 100 mAs/slice, 3 or 5 mm slice thickness). The dose was measured by thermo-luminescence in an Alderson phantom. Image quality was assessed by four independent radiologists in six perihilar, central and peripheral lung regions using a 4-point-scale ("very good", "good", "moderate", and "poor"). RESULTS: Effective dose was 0.5 mSv for ND-CT and 4.0 - 5.0 mSv for SD-CT. The ratings "very good"/"good" were given in the perihilar regions in ND-CT 97.5 % versus SD-CT 99.3 % (n. s.), in the central regions in ND-CT 96.4 % versus SD-CT 94.6 % (n. s.), and in the peripheral regions in ND-CT 70.0 % versus SD-CT 88.2 % (p < 0.01). CONCLUSION: Follow-up CT of pulmonary structures in patients with chronic lung disease can be performed with substantial dose reduction. A decrease of image quality may result in peripheral lung regions.

Adolescent↗
PubMed2003

[Volumetric MRI for evaluation of regional pattern and progressin of neocortical degeneration in Alzheimer's disease].

PURPOSE: Volumetric analysis of the corpus callosum and hippocampus using MRI in Alzheimer's disease (AD) to evaluate the regional pattern and progression of neocortical neurodegeneration. METHODS: In subsequent studies we investigated patients with AD and healthy controls. Volumetry was based on MRI-data from a sagittal 3D T1w-gradient echo sequence. The corpus callosum (CC) was measured in a midsagittal slice, and subdivided into 5 subregions. Volumetry of the hippocampus/amygdala-formation (HAF) was performed by segmentation in coronary reoriented slices. RESULTS: In AD patients we found a significant atrophy in the rostrum und splenium of CC. The atrophy was correlated with the severity of dementia, but no correlation was found with the load of white matter lesions. In comparison with (18)FDG-PET, we found a significant correlation of regional CC-atrophy with the regional decline of cortical glucose metabolism. A ROC-analysis demonstrated no significant differences in the diagnostic accuracy of HAF volumetry and regional CC volumetry of the splenium (region C5) even in mild stages of dementia. CONCLUSION: Regional atrophy of CC can be used as a marker of neocortical degeneration even in early stages of dementia in AD.

Alzheimer Disease↗
PubMed2003

[Cost-utility analysis of contrast-enhanced MR angiography with automated table-translation for diagnosis and therapy planning in patients with peripheral vascular disease].

PURPOSE: To analyze the cost-utility of contrast-enhanced MR angiography (ceMRA) in the diagnosis and the planning of surgical or interventional treatment in patients with peripheral arterial occlusive disease. MATERIALS AND METHODS: Additional costs and incremental costs per quality-adjusted life-year for ceMRA were calculated by a decision model. The costs of ceMRA and conventional angiography were compared. Treatment was either surgery or PTA. A retrospective analysis of 24 patients provided the data for the diagnostic accuracy of ceMRA. The data about quality of life assessment were taken from the literature. Costs were calculated in Euro using the current fee schedule. The influence of the individual parameters on the model was estimated from a sensitivity analysis. RESULTS: Per quality-adjusted life-year, ceMRA added euro; 24,408.60 in cases undergoing radiologic intervention and euro; 24,191.32 in cases treated surgically. CONCLUSION: Despite its high costs, ceMRA is an effective diagnostic procedure considering patient benefits. Additional costs do not exceed an acceptable range.

Adult↗
PubMed2003

Successful treatment of muscle sarcoidosis with thalidomide.

A 36-year-old male patient suffered from therapy resistant sarcoidosis with long-standing contractures, myopathy, skin lesions and pulmonary changes. Low-dose therapy with thalidomide (50 mg/day) was well tolerated, and the patient rapidly improved. Thalidomide was effective for muscular, cutaneous, and pulmonary involvement in our patient. This is the first report on the efficacy of thalidomide in muscle sarcoidosis. Therefore, thalidomide may become a second-line agent in patients with severe muscle and skin involvement, but further studies are warranted.

Adult↗
PubMed2000

The bacterial elicitor flagellin activates its receptor in tomato cells according to the address-message concept.

flg22, a peptide corresponding to the most conserved domain of bacterial flagellin, acts as a potent elicitor in plants. Here, we have used an iodinated derivative of flg22 ((125)I-labeled Tyr-flg22) as a molecular probe for the flagellin receptor in tomato cells. This radioligand showed rapid binding to a single class of specific, saturable, high-affinity receptor sites in intact cells and membrane preparations. Binding, although essentially nonreversible under physiological conditions, was not covalent, and chemical cross-linking was required to specifically label a single polypeptide of 115 kD. Intact flagellin and elicitor-active flagellin peptides but not biologically inactive analogs efficiently competed for binding of radioligand. Peptides lacking the C terminus of the conserved domain, previously found to act as competitive antagonists of elicitor action in tomato cells, also competed for binding of radioligand. Thus, this novel, high-affinity binding site exhibited all the characteristics expected of a functional receptor of bacterial flagellin. For a model of receptor activation, we propose a two-step mechanism according to the address-message concept, in which binding of the N terminus (address) is the first step and activation of responses with the C terminus (message) is the second step.

Alkalies↗
PubMed1998

The plant wound hormone systemin binds with the N-terminal part to its receptor but needs the C-terminal part to activate it.

Suspension-cultured cells of Lycopersicon peruvianum respond with rapid medium alkalinization and a strong increase of a MAP kinase-like activity when treated with subnanomolar concentrations of the plant wound hormone systemin. Systemin fragments comprising the N-terminal 14 amino acids (syst1-14) or the C-terminal four amino acids (syst15-18), added singly or in combination, were inactive as inducers of these responses. Syst1-14 but not syst15-18 antagonized activity of intact systemin in a competitive manner. Likewise, intact systemin showed stimulatory, syst1-14 antagonistic activity, and syst15-18 showed no activity in leaf pieces of tomato (L. esculentum) plants assayed for the induction of ethylene biosynthesis. To study the molecular basis of perception, we extended the C-terminal end of systemin by a tyrosine residue and radioiodinated it to yield systemin-125I-iodotyrosine. In membrane preparations of L. peruvianum, this radioligand exhibited rapid, saturable, and reversible binding to a single class of binding sites. Binding showed a dissociation constant of approximately 1 nM, and binding of radioligand was efficiently competed by unlabeled systemin but not by syst15-18 or structurally unrelated peptides. Binding was also competed by the systemin antagonists syst1-14 and syst-Ala-17 (IC50 of 500 and 1000 nM, respectively). Thus, this binding site exhibits the characteristics expected for a functional systemin receptor. Based on these results, we propose a two-step mechanism for systemin action, with binding of the N-terminal part to the receptor as the first step and activation of responses with the C-terminal part as the second step.

Amino Acid Sequence↗