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    Wyświetlanie 1-3 z 3
    Tytuł:
    Nuclear magnetic precession measured with SQUIDs
    Autorzy:
    Burghoff, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/156431.pdf
    Data publikacji:
    2007
    Wydawca:
    Stowarzyszenie Inżynierów i Techników Mechaników Polskich
    Tematy:
    SQUID
    nuclear magnetic precession
    low magnetic field measurement
    Opis:
    We have developed a superconducting quantum interference devices (SQUID) system measuring nuclear magnetic precession at very low magnetic fields with a spectral resolution beyond the natural line width of liquids. A coil system applies a magnetic polarization field and a perpendicular static detection field to the sample. The detection system for the very weak magnetic field generated by the processing nuclei consists of LTc-SQUID sensors in a liquid helium cryostat. We measured the 'H precession signal of benzene, distilled water and chloroform samples at various detection fields. With our set-up. broad band detection of the nuclear magnetic resonance of the investigated liquids with a very high resolution is possible. Benzene showed the narrowest natural resonance line width of 0.12 Hz followed by chloroform of about 0.17 Hz. The observed line widths increased linearly with the detection field with a slope independent of the investigated sample. This increase is attributed to the inhomogeneity of the detection field, rather than to intrinsic properties of the investigated liquids, and thus describes the properties of our measurement system. Reliable low field NMR and MRI depend strongly on field homogeneity of the detection field coils and the residual field inside the agnetically shielded room. At such low fields, high demands on the absolute homogeneity of the static field correspond to very moderate requirements on its relative homogeneity 111. Reduction of these system parameters and its influence is the prerequisite for a good frequency and spatial resolution. Here, we investigated our SQUID measurement system and estimated all main system parameters at very low fields below a microtesla.
    Źródło:
    Pomiary Automatyka Kontrola; 2007, R. 53, nr 9 bis, 9 bis; 17-20
    0032-4140
    Pojawia się w:
    Pomiary Automatyka Kontrola
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Measures to reduce the residual field and field gradient inside a magnetically shielded room by a factor of more than 10
    Autorzy:
    Voigt, J.
    Knappe-Grüneberg, S.
    Schnabel, A.
    Körber, R.
    Burghoff, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/220358.pdf
    Data publikacji:
    2013
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    magnetic shielding
    magnetic shielded room
    msr
    residual field
    residual field gradient
    degaussing
    demagnetization
    Opis:
    Very low residual magnetic field and field gradients are essential for a number of high resolution fundamental physical experiments and for further improvement of very sensitive magnetic measurement devices. The scope ranges from spin precession experiments, e.g. with 3He or neutrons, to biomagnetic measurements, like magnetoencephalograms, and to low field MR spectroscopy. One method of reducing environmental magnetic noise is to use a magnetically shielded room (MSR). Here, measures are demonstrated to improve residual field and field gradient inside a common MSR by a factor of more than 10 by a specific degaussing procedure, material selection of prefabricated parts and active shielding. The process is independent of the shielding factor and works also properly for heavily shielded rooms.
    Źródło:
    Metrology and Measurement Systems; 2013, 20, 2; 237-248
    0860-8229
    Pojawia się w:
    Metrology and Measurement Systems
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Improved contrast in ultra-low-field mri with time-dependent bipolar prepolarizing fields: theory and nmr demonstrations
    Autorzy:
    Nieminen, J. O.
    Voigt, J.
    Hartwig, S.
    Scheer, H. J.
    Burghoff, M.
    Trahms, L.
    Ilmoniemi, R. J.
    Powiązania:
    https://bibliotekanauki.pl/articles/220699.pdf
    Data publikacji:
    2013
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    T1 dispersion
    prepolarization
    polarizing field
    ultra-low-field MRI
    Opis:
    The spin-lattice (T1) relaxation rates of materials depend on the strength of the external magnetic field in which the relaxation occurs. This T1) dispersion has been suggested to offer a means to discriminate between healthy and cancerous tissue by performing magnetic resonance imaging (MRI) at low magnetic fields. In prepolarized ultra-low-field (ULF) MRI, spin precession is detected in fields of the order of 10-100 μT. To increase the signal strength, the sample is first magnetized with a relatively strong polarizing field. Typically, the polarizing field is kept constant during the polarization period. However, in ULF MRI, the polarizing-field strength can be easily varied to produce a desired time course. This paper describes how a novel variation of the polarizing-field strength and duration can optimize the contrast between two types of tissue having different T1) relaxation dispersions. In addition, NMR experiments showing that the principle works in practice are presented. The described procedure may become a key component for a promising new approach of MRI at ultra-low fields.
    Źródło:
    Metrology and Measurement Systems; 2013, 20, 3; 327-336
    0860-8229
    Pojawia się w:
    Metrology and Measurement Systems
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-3 z 3

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