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Biomedical subjects

F Thiele

Publications and source records attributed to F Thiele.

7 recordsLinked to original sources
PubMed1991

Appearance of poststenotic jets in MRI: dependence on flow velocity and on imaging parameters.

A flow model was used to study the appearance of poststenotic jets in MRI. Jets in CuSO4-doped water and bovine blood were imaged by spin-echo (SE) and fast-field-echo (FFE) pulse sequences at different degrees of stenosis and various flow rates. On flow-compensated FFE images, the jets were characterized by signal void if the mean flow velocity within the stenosis exceeded a limit, which was independent of the degree of the stenosis and the type of the fluid. On SE images and on FFE images without flow compensation, signal void occurred at significantly lower flow velocity. The extension of the poststenotic signal void on flow-compensated FFE images was increased by either reduction of the pixel diameter or by prolongation of the echo time. However, it was independent of the orientation of the imaging plane relative to the direction of flow. The results have an impact on attempts to use signal void for the assessment of turbulent jets with MRI.

Animals↗
PubMed1989

[Measurement of noise levels in MR tomography at 1.5 Tesla].

The noise levels at the isocentrum of an MR apparatus with a field strength of 1.5 Tesla was measured during various sequences. The rapid switching of the gradients exerts effects on the gradient coils, which result in the development of noise as from a loudspeaker. Measurements were carried out using gradients of 3 and 9.3 mT/m with head and body coils and a variety of sequences. The noise level depended largely on the type of sequence and, under extreme conditions, may attain 96 dB. Because of the short exposure times, we do not consider it necessary to use any form of protection. During the examination of patients with damaged hearing, some protection may be advisable.

Humans↗
PubMed1989

[Poststenotic flow in MRT: phantom measurements using spin-echo and gradient-echo sequences].

A flow model was used to study the appearance of poststenotic flow on spin-echo (SE) and fast-field-echo (FFE) images. On SE-images, extensive signal void distal to the stenosis was observed even with low flow velocities. FFE-sequences with short echo time and flow-compensated gradients demonstrated poststenotic loss of signal intensity only with high flow velocities. On FFE-images, the poststenotic signal loss increased with the severity of the stenosis, if total flow across the stenosis was maintained. The lower limit of the mean flow velocity within the stenosis, for which signal void was observed, appeared essentially independent of the degree of the stenosis. The results demonstrate the capability of flow-compensated FFE-sequences to assess poststenotic turbulent flow.

Arterial Occlusive Diseases↗
PubMed1987

[Vertical flow of germs in a building shaft: physical and microbiological measurements and development of an analogous mathematical model].

The air flow and the concentration of microorganisms have been measured in the stair shaft of a hospital. A diving bell-type of pressure-recording instrument and samplers for the microorganisms (impaction device) were used. With this experimental data the flow rate of microorganisms between the floors of the hospital was calculated. A physical model based on numerical calculations using simplified transport equations is proposed, which would be able to predict the flow field and the distribution of microorganisms in a staircase. The calculations have been executed up to a Reynolds number of 400 when the Schmidt number is 0.5 and 1.0. This numerical method can help to reduce the experimental work, as well as, to investigate unknown transport mechanisms of organic and inorganic substances including microorganisms.

Air Microbiology↗