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Magnetic Resonance Imaging

Magnetic Resonance Imaging. I. Basic Concepts. Lorenz Mitschang Physikalisch-Technische Bundesanstalt, www.ptb.de 23 rd February 2009. Literature H. Morneburg (Ed.) “Bildgebende Systeme f ür die medizinische Diagnostik ” Siemens AG

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Magnetic Resonance Imaging

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  1. Magnetic Resonance Imaging I. Basic Concepts Lorenz Mitschang Physikalisch-Technische Bundesanstalt, www.ptb.de 23rd February 2009

  2. Literature H. Morneburg (Ed.) “Bildgebende Systeme für die medizinische Diagnostik” Siemens AG P. T. Callaghan “Principles of Nuclear Magnetic Resonance Microscopy” Oxford University Press R. A. de Graaf “In vivo NMR Spectroscopy” J. Wiley & Sons Radiology books Material partly courtesy of R. Brühl, F. Schubert, F. Seifert

  3. Morphology: 3D Structure magnetization density distribution

  4. Morphology: 2D Slices multiple sclerosis patient healthy test person gray matter white matter lesion T1 weighted tissue contrast T1 white matter < T1 gray matter intensity white matter > intensity gray matter

  5. Volume-selective in-vivo Spectroscopy multiple sclerosis patient metabolite identification by chemical shift quantification of metabolite concentration

  6. 3D Angiography contrast agent distribution

  7. Brain Function and Behavior: functional MRI visual stimulation activates visual cortex contrast by relaxation through enhanced blood flow

  8. Motion and Flow fast imaging enables motion detection blood flow velocity distribution

  9. Imaging Paradigm Application 3D, 2D morphology, lesions in-vivo spectroscopy, temperature Angiography, cancer cells, metabolism fMRI diffusion, flow, perfusion much more Parameter spin density,T1, T2 chemical shift contrast agent concentration (Gd, SPIO, 13C-labelling) T2* (stimulation) spin echo formation much more Effect tissue contrast metabolites, shifts tissue contrast, temporal evolution BOLD-effect signal attenuation much more local variation MR quantity bio-medical problem

  10. MR Imaging = localized determination of MR parameters signal out RF in I. Do we get sufficient signal from single voxel ? Yes, sometimes: signal-to-noise (next lecture)

  11. MRI = wave-like imaging attenuation in human tissue damaging high quality (hard tissue) resolution ~A harmless high quality (soft tissue) resolution ~m attenuation in human tissue harmless low quality resolution ~mm II. Can we get around the resolution limit ? Yes, we can: localization (next lecture)

  12. III. How do we obtain the image from the individual voxel signals ? image reconstruction algorithms, k-space (part of answer II.) IV. What spin manipulations are required for image formation ? pulse sequences (abound in the lectures) V. Are humans, animals, organisms well-doing in MRI ? let’s see now …

  13. MR Patient Treatment • noninvasive • nonionizing • homogeneous static fields are totally safe • limited time for investigation : animal (anesthetized) ~ 3 h test person ~ 1 h sick person ~ 15 min • noisy ~ 100 decibel • motion in inhomogeneous static field induces currents • conductivity of biological tissue causes absorption of radiation energy as heat “specific absorption rate”

  14. MR Safety at 3T wavelength < object, multi array coils 1 kW transmitted simulation experiment counter rotating hot spot cold spot Norm IEC 60601-2-33 "Particular requirements for the safety of magnetic resonance equipment for medical diagnosis“ local SAR < 10 W/kg

  15. MR Safety at 7T

  16. Next Lectures • basic signal-to-noise and resolution in MRI • basic localization methods (including reconstruction) • basic pulse sequences (2D, 3D morphology; in-vivo spectroscopy) • specific applications • visit of MRI scanner ???

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