MRI “Magnetic Resonance Imaging”. Nuclei with nuclear spin: elementary magnets Magnetic moment:  =magnetogyric ratio L=angular momentum.

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Presentation transcript:

MRI “Magnetic Resonance Imaging”

Nuclei with nuclear spin: elementary magnets Magnetic moment:  =magnetogyric ratio L=angular momentum

In absence of magnetic field: Random orientation of elementary magnets In magnetic field: elementary magnetsenergy levels orientsplit B0B0 parallel antiparallel EE B0B0 E B

Precession Precession or Larmor frequency:

B0B0 M Low energy state parallel in case of proton High energy state antiparallel in case of proton Net magnetization (M) due to spin excess in different energy states

Excitation using radio frequency (RF) radiation Resonance condition: Larmor frequency M Net magnetization

Spin-lattice relaxation T1 or longitudinal relaxation t MzMz T1 relaxation time: depends on interaction between elementary magnet (proton) and its environment

Spin-spin relaxation T2 or transverse relaxation M xy t “free induction decay” (FID) T2 relaxation time: depends on interaction between elementary magnets (protons)

1970: detection of lengthened relaxation times in cancerous tissues 1972: theoretical development of human in vivo 3D NMR 1977: first human MRI image Inventor of MRI: Raymond V. Damadian (1936-)

MRI: Net magnetization of the human body takes place “indomitable”

Paul C. Lauterbur (1929-) 1971: development of spatially resolved NMR

voxel: volume element pixel: picture element Image MRI imaging I: Spatial resolution

Definition and addressing of elementary 3D image points (voxels): by using gradient magnetic fields MRI imaging I: Spatial resolution ByBy BxBx BzBz

MRI imaging II: Color (grayscale) resolution (contrast) Based on relaxation times

MRI imaging II: Color (grayscale) resolution (contrast) Based on spin density and relaxation times T1-weighing T2-weighing Proton density- weighing

MRI technology Magnet: superconducting (liquid He) Resolution enhancement: with surface RF coils Excitation with pulse sequences 90˚ Detection and analysis: Fourier transform of temporal signal t

MRI: Image manipulation I Reslicing in perpendicular plane

MRI: Image manipulation II Spatial projection („volume rendering”)

Blood flow Image slice Saturated spins Unsaturated spins MRI: Non-invasive angiography

MRI: Non-invasive angiography arteria carotis Circulus arteriosus Willisii

MRI movie Based on high time resolution images Opening and closing of aorta valve

Functional MRI fMRI High time resolution image sequences recorded synchronously with physiological processes Effect of light pulses on visual cortex

ISOTOPE-BASED DIAGNOSTIC IMAGING TECHNIQUES Gamma camera SPECT PET

Gamma Camera Lead collimatorPMT matrixScintillation detector Kidney scintigram PROBLEM: Summation image

SPECT: Single Photon Emission Computed Tomography gamma camera The detector circles the body in the transaxial plane

PET: Positron emission tomography  photon (0.51 MeV) electron (e - ) positron (  + ) 18 F (positron emitter) Detector NB: annihilation radiation conservation of momentum Half life of isotopes: min. 1-2 mm

PET imaging Coincidence

PET: Tomographic imaging and 3D reconstruction Image slices Typical voxel (3D volume element): 8 mm x 8 mm x 14 mm

Studying brain glucose metabolism with PET

Superposition of different 3D image information 1. Based on common fiducial points 2. Simultaneus acquisition with two methods (PET&CT or PET&MRI) MRI PET + =

Superposed MRI and PET image sequence PET activity: during eye movement Volume rendering