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

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Presentation on theme: "Magnetic Resonance Imaging Lorenz Mitschang Physikalisch-Technische Bundesanstalt, www.ptb.de 23 rd February 2009 I. Basic Concepts."— Presentation transcript:

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

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 healthy test person multiple sclerosis patient white matter gray matter lesion T1 weighted tissue contrast T1 white matter < T1 gray matter intensity white matter > intensity gray matter

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

6 3D Angiography contrast agent distribution

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

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

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

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

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

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  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”  noninvasive  nonionizing  homogeneous static fields are totally safe

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

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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