MRI (Magnetic resonance imaging)

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MRI (Magnetic resonance imaging)

• Introduction-MRI
• ?? ??????

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??

• soft tissue anatomy
• MRI
• ? ??? ???? ????? ???? ?? ?? ?? ???(proton)??
  ????? ?? ??? ??? ???? ?? ??
• Nuclei having odd number of neutrons, and odd
  number of protons, or both will have a net
  magnetic moment
• H or Proton NMR
• High concentration and high sensitivity

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MR? ?? ? ??

• ??
• 1964? Purcell? Bloch???? ?? ???? NMR??? ??
• 1967? Damadian? ?? ?? ???
• 1973? Laterbur? ??????? ??????? ????????? ??
• ?? ??????? ????? ??

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?? ????? MRI? ??

• ??
• ??? ???? ??
• ??? ??? ?? ? ??????? Parameter? ???? ????? ????.
• ???? ???? ???.(RF Electromagnetic Radiation?
  Magnetic Field? ??)
• MRS, MRA, fMRI?? ?? ??
• ??
• ????? ??
• ??? ???.
• ?? ???(Artifact)? ???.

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?? ??

• ?????? Magnetic Resonance Imaging(MRI), Nuclear
  Magnetic Resonance Computed Tomography, Spin
  Mapping, Hydrogen Mapping, Zeugmatography,
  Magnetic Resonance Imaging
• MRS Magnetic Resonance Spectroscopy
• MRA Magnetic Resonance Agiography
• fMRI functional MRI

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??(Magnetism)

• ??? ??? ??, ??? ??? ?? ??? ??
• ?????? ?? ??? ???? ??? ????? ??
• ????? ?? ??? ???? ??? ????? ??
• ??? ?? ???, ???, ???, ????
• ??? ??
• ????(Ferromagnetic material), ????(Paramagnetic
  material), ????(Diamagnetic material)
• ??? ??
• 1T(tesla)10,000 gauss1Kg/(sec2A), A),
  1gauss1wb/2

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Magnetization

• ??????? ??? ???? ??
• ????? ?? ??? ??? ?????? ??? ??? ??
• ?? ??? 1??? ??? ?? ??? ???? ??? ?? ???? ???? ??
  ??
• magnetic moments alignment
• Static magnetic field(B0)? ???? ??? ????? ?????
  ????
• ????? ?? ??? ???? M ?? ????.
• ?? 1??

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????

• ????
• ??? ?????(B0 )? ???? ??? ? ? ? ???? ???? ??

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?????

• ?????(?? B)
• ??? ???
• F?B0 , F(Larmor) ?????(MHz), B0 ?????(tesla),
  ??????
• ?????? ? nuclear ??? ?? ??
• ??? ?? ??? 42.57MHz
• ??? ????? ??? ???? ?? Oscillating magnetic (RF)
  field
• the spins will absorb energy and become excited
  excitation
• Tipping Magnetization, Induce a voltage in a
  nearby coil
• Figure 2.

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??????

• ???
• ????? ???? ??? ????(B0)? ???? ?? ??? ????(µ)?
  ???? ???? ???? ??? ?? ???
• ??? M? ? ???? ??? ???(µ)? ??? ??(MSµ)
• B0?? Mz(Z?)? ????? Mx(X?)My(Y?)0 ???
• B0? ?? ???? Z??? ????, ??? ????? X-Y??? ??
• M0?(Nr2B0/T)    ???, ???
•   (N ??? ?, r ?????,  B0 ????? ??, T
  ????)
• ???(Filp Angle) ?
• ??? ??? ??? Z????? ???? ???? ??? RF???? ?????
  ????(?? ???????)
• ??? ???? ?? ?(X,Y)?? ???? ?? ??? ?? ?? ???

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?? ?? ??RF pulse

• ?? ?? ??(FID Free Induction Decay)
• RF pulse? ???? ?????? ????? ?????? ?? ??? ????
  ??? ?? ????? X-Y???? ?? ??? ???? ??? ??? ?? ??
• ???? ??? ???? ???? ??? ?? ??? ?? ????? ??????
  ???? ???? ?? ????(?? A) ??? ??? ??? ??? ????????
• RF pulse(Radio Frequence Pulse)
• Hard pulse ??? ??????? ??? ??? ? ? ?? ????
• Soft pulse ??? ??????? ??? ??? ? ? ??? ????
• 0 RF pulse, 90 RF pulse, 180 RF pulse ? ??

?? A
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Relaxation(??)

• ?????
• ???? RF???? ???? ??? ??? ?????(???????) ?????
  ???? ???? ???? ????? ???? ??? ? ????? ??? ?? ??
• ?? ???????? ? ????? ???? ???? ?? ?? ?? ?? ? ???
  ???? ???? ??.
• ???(T1,longitudinal,spin-lattice relaxation)
• ???(T2, transverse, spin-spin relaxation)

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???(T1,longitudinal)

• ????? ?? ??? RF? ???? ???? ????? ???? RF? ???? ??
  ?? ??? RF? ???? ?? ??? ????? ?? ??? ???? ??
• ??? ?????? RF pulse? ????? ? ???? ?? ??? ?? ???
  63?? ???? ??? T1?? ??(?? A)
• ????? T1?? ?? ??(???)
• ???????????????????????? (?? B)
• T1 ??? ???? ???? ? ? ?? ??? ???? ????? ????? ????

?? A
?? B
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???(T2,transverse)

• ?????? ??? 90RF pulse? ???? ???? ???? ??? ????
  ???, ? ???? X-Y???? 360???? ??
• ?? ????? ??? ?? ??? ?? inphase ?????? ??
• ??? ??? ??? ?? ???? ???? ?? ????? X-Y???? ?? ????
  ???? ??
• 90RF pulse? ???? ?? ??? 37?? ???? ??? T2??????
  ?? (?? A)
• ????? T2???? ??(???)
• ??????????????????????????? (?? B)
• T2 ??? ???? ???? ? ? ?? ????? ???? ??? ?????
  ????.

?? A
?? B
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????

• 1?? ??
• 2?? ??
• 3?? ??

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1???? ?? ??

• ??? ????
• ????? ???? ??
• ????? ???? ?????
• B(x) B_0 G x
• F(x) gamma(B_0 G x)
• Frequency encoding

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Pulse ??

• RF pulse
• Frequency encoding
• Fourier transform
• Magnitude of a frequency represents
  magnetization(induced voltage) at a specific
  location
• Measure T2(signal decay) and T1(magnetization
  recovery)

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Phase encoding

• Same frequency
• Different phase gt phase encoding

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2?? ?? ??

• Two gradient is not working gt 45 degree gradient
• X direction frequency encoding
• Y direction phase encoding
• Frequency encoding -gt Phase encoding -gt frequency
  encoding
• Echo Planar Imaging(EPI) for fMRI

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K-space

• Data acquired form a continuous pathway through
  k-space

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K-space(2)

• K?? ??? ??? ??? ??? ??? ??, K?? ?? ??? ??? ???
  ??? ???? ?? ??? ??? ???
• Creating an MRI image by sampling 2D k-space
• Nyquist sampling theorem

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K-space(3)
(a)
(b)
(c)
(a) K space? ??? data? ??? ???? ??? ??? ?? ???
???? ???? ??? ? ???? ???. (b) K space? ??? data?
??? ???? ??? ??? ???? ????? ??? ????. (c) raw
data ??? ?? ??? ??? ??? ????.
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3?? ??(slice) ??

• Gradient in the Z-direction
• Resonant frequency varying as a function of z
• Resonant frequency at specific location
• Moving slice location
• Shifting the RF frequency up or down
• Shifting the overall magnetic field up or down
• Any oblique oriented slices by rotating x,y.z

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Pulse sequence

• MR ???? ??? ?? 4?? pulse sequence
• Partial saturation recovery(?? ?? ??)
• ??? ???? peak? ??? ?? ? ?? ??? ???? ??
• Spin echo
• Gradient echo
• Inversion recovery

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Spin echo

• ?? ?? ??? 90, 180??? ??? ??? ????? ???? ?? 90
  RF pulse? ??? ?? ??? ??? ??? ?? ??? 180 RF
  pulse? ??? ?? ?? ???? ????? ?? ???? ?? ??????? ??
  
• inphase ???(90RF pulse?? ?)
• Dephase ??? ??
• Rephase ??? ???
• TE(echo time) ?? 90 RF pulse? echo signal ??
  ??? ??.
• TR(time to repetition) ?? ???? RF pulse? ?? ???
  ???? ??.

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Spin echo

• Spin echo??
• T1 weighted(T1 ??) TE?, TR?gtT1WI ???? ??,
  ???? ??
• T2 weighted(T2??) TE?, TR?gtT2WI ???? ??.
• Spin density weighed(Proton Density, ???? ??,
  ???? ??) TE?, TR?gtPDWI(SDWI), ????

A TR2500, TE15(PDW1) B TR500,
TE15(T1W1) C TR2500, TE90(T2W1)
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Spin echo

• Pulse sequence ? ?? TR? TE
• ?) 800ms, 20ms gt T1? ???, 6000/200 gt T2 ,
  1600/20 gt PD? ??? , 1200/30 gt T1 and PD mixed
  image(??? ??? ?? ??)
• ? ???? ???? ?? ?? TE ?? TR??? ??? ???
• ?)1) ?2000/80   ?200/100
• gt?? ? ?? ??? ??
• ?2000/100  ?3000/100  ?4000/100
• gt?? ?? ??? ??(?, ????? ???)
• ?300/15  ?500/15  ?800/15
• gt?????? ??? ??(?? T1???? ????)

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Spin echo

• ??? ??
• ????? ???? ?? ???? ????? ? ??? ??? ???? ?? ?? ??
  ? ?? ??? ?? ? ???? ?? ?? ??? ? ?? ??, 4?? ?? ??
  ???
• ? TR?? ??? ??? ?? ? ??.
• Slice(??)? ?? ? ?? ???? TR? ???? TE? ?????
• number of sliceTR(TE?)

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TR(Repetition time)

• TR? 90 pulse? 180 pulse? ??? 1?? signal? ??, ??
  signal? ?? ?? ? ?? 90 pulse ? ?????, ??? 90
  pulse?? ?? 90 pulse ??? ??
• TR? ??? ?????? ???? ???? ??
• TR? ??? ??? ??
• TR ??? SNR? ?????, ???? Scan time? ??
• ??? ????? ????? ?? ??? ?? ??

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TE(Echo time)

• ????? ??? signal? ?? ???? ?? ??? ???? ?? T1W,
  T2W, PDW? ??? ????.
• TE ??? ??? ???? ????? ??? ??

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T1 weighted Image

• Fat ? water??? T1 ??? ?? ?? ?? ??? ??? ??
• ?? ?? ??? ????? ??
• T2 Contrast ??? ?? ???? ??? ?? (TR ? TE ??)
• TR ? ?? fat? water? ?? ???? T1 ????? ?? ?? ??? ??
  T1 ?? ??? ?? ?? (?? TR, ?? TE)
• ????? T1?? ?? ??
• ????????????????????????

(?) ? ?? T1 ?? ?? ?? ? ? ?? ??? TR? ??? ?? (?)
?? TR ???? RF pulse? ?? , ? ???? T1??? ??? ??
??. ?? ?? ??? signal? ??? T1 weighted image?
????. ?? TE? ?? ? ??? Signal ??? ???? T1 contrast
??? ????.
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T2 weighted Image

• TR? TE? ?? T2??? ??? ???
• TR? ?? ?? T1 contrast? ??
• ????? T2???? ??
• ???????????????????????????

(?) RF pulse? ?? ?? ??? ??? ??? ?? ???? T2
weighted image? ?? ? ???? (?)? ???? TE? ???
??. TE? ??? ? ???? ???? ??? Proton density
weighted image? ???, TE? ?? ??? ???? ??? ??? ????
??? ? ??.
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Proton density weighted Image

• ??? ?? ???? ???? ???? ?? ???? ?? ?? ???? ??? ??
• Signal intensity? ?? ??, ?? ??? ????? ??
• T1, T2 contrast? ???? ?, Proton density weighted
  image? ?? ? ??.
• Long TR? Short TE? ??
• ??? contrast? ??? ????? , signal? ?? TR? ????? ??
  slice? ?? ? ??.

(?) long TR??? ? ??? ?? ? ????? ??? T1
contrast? ??? ???. ??? Long TR? ?? (?) TE? ??
?? ???? ? T2 contrast? ???? signal? ??, ?? TE ?
?? T2 contrast ??? ?? ??? signal? ???. ???? TE?
?? ???? Signal? ??? ??.
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Gradient echo(???? ??)

• ???? ????? ????? ???
• ??? ???? ?? 180 RF pulse??? ????? ?? ???? ???
  FID??? ???
• 90 RF pulse?? 5-30? ?? ???? RF pulse? ????
• TR? TE? ?? ?? ??
• ???? ?? ?? 
• T1?? gradient echo?? ??? FA?(30? ???)
• T2?? gradient echo ?? ??? FA?(5? ???)
• PD?? gradient echo ?? ??? ??? ??
• ?? scan time? ??
• ?? ??? ????.(??? ???.)

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Gradient echo(???? ??)

• Gradient echo(GE, GRE, field echo) ?????
  Cardiac imaging, MR angiography, 3-dimensional
  imaging(3?? ??), EPI(echo planar imaging, ???
  ??), dynamic contrast technique ?? ?? fast scan??
  ???? ???? ???? SE? ?? ??? ?? ??? ?? ????.
• GE? ???? ???? ??? ??? ???? ?? ???? ???? ????, ???
  ???, ??? ???? ?? ???? ??? SE pulse sequence? ??
  echo ??? ???? ??? ???
• ???? ??? ??? ??? ??? ?? artifact? ????.
• ?? ???(B0)? ???? ??? ???? ??? ????? ???? ??? ???
  ???? ??? ????? ??? ????? ??? ???? ???? ??
• ???? GE??? ??? ??? ?? ??? ??? ??? ?????

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Gradient echo(???? ??)

• ????? ??
• Z gradient ???
• Y gradient ???
• X gradient ???

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Gradient echo(???? ??)

• ????? ??
• 1gauss/cm 10mT/m
• ???? ??
• ???? ?? ??? ???? ??? ?? ??? ????? ?? ?? ???? RF
  pulse? ??? ? ??? ???? ??? ??? ?? ?? ?? ??? ???
  ??? ?? ? ??
• 20mT/m? 10mT/m? ??
• 20mT/m 2gauss/cm 1gauss/0.5cm gt 0.5cm? ???
  ???
• 10mT/m 1gauss/cm 1gauss/1cm   gt 1cm? ??? ???
• ?, ????? ?? ???? ??? ????
• ?? ?? ??? ? ? ????? ??? ???? ? ??? ????? ????
  ???? ?? ??? ?? ?? ?? ???? ???? ??
• ????? ? ??
• ??? ???/(?????????? ??)slice??

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Inversion recovery(????)

• 180RF pulse? ?? ??? Z??? ?? ?? ??? (MzM0)?
  -Z??? ??(Mz-M0)??? ??
• STIR(short TI inversion recovery) ??? ???? ??. 

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Inversion recovery(????)

• FAIR(Fluid attenuated inversion recovery) ?????
  ??? ???? ?? ??.

(a)
(b)
?? ?????? ??? ??? ????. (a)? T2 ??????. (b)?
FLAIR(TR/TE 1000/119, T1 2500)? ?????? ????? ??
???? ?????
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MR Parameter
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MRI? ??

• Gantry
• Operating Console
• Computer

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Gantry

• Gantry ? ??
• ???? ? ?? ???? ??(secondary magnetic field)? ??
• ?? ??? ??? ?? ??? ??
• ????, ????, ????

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Gantry

• Secondary Magnetic Fields
• Shimming coil
• ?????? ??? ??? static Magnetic Field? ????? ????
  ?? ?? ??? ??? ??.
• Shimming ? ??? ???? ???? ??? ??? ???? Shim Drift?
  ??? ?? Subject??? ?? ???? ??? ??? ??? ??.
• Gradient coil, Gradient amplifier, ????
• ????? ??? ?? ???? ???? ??? FOV(Field of view)? X,
  Y, Z???? Gradient coil? ??? ????.
• Gradient? ??? ????? ??? ???.
• ??? ????? ??? ???? ?? ????? ??.
• Radio Frequency system
• ??? ???? RF Pulse? Modulation?????, ??? MR
  Signal? Demodulation?? ?? High Precision
  Waveform? ???.
• RF Coil
• ????? ??? ??? ??? Radiowave? ??????? ?? ???? RF
  coil? ?? ??
• RF Coil? ?? ?? ???? ???? ?? ????? ?? ??? Signal?
  ???? Proton? ??

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Operation Console Computer

• Operation
• MR??? ???? Monitor? Keyboard ??? Scan ??? Scan
  ??? ???? Monitor? Keyboard? ??
• ??? CT? Console? ???? ??
• Computer
• ??? ?? ????? ?? Minicomputer
• 128128Pixel? 50 Image?1.6MB
• 256256 Pixel? 31Slice, 4 Echo? Spin Echo Image?
  3D? ???? ?????8.1MB

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MRI ??? ????
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Artifacts, ????, ???

• motion and ghost artifact
• ?? ???, ??? ?? ???, ????? ??? pulsation? ?? ????
  ????? ??? ?? ??? ??? ????? ??? ??.
• chemical shift artifact(??? ?? ??)
• ???? ??? ??? ??? ???? ???? ??
• black boundary artifact(out-of-phase artifact)
• ??? ??? ?? ?? ??? ?? ??? ??? ???? ?? ???? ?
• eddy current artifact
• ???? ??? ??? blurring ?? ??? ????? ???? ?
• truncation artifact(ringing, gibbs, spectral
  leakage artifact)
• ?? ?? ?? ??? ?? ??? ?? ???? ???? ??? ????.(????
  ?? ????? ???)
• aliasing(wrap around) artifact
• ??? FOV? ???? ????? ??? ?? ? ???? ??? ??? ??? ???
  ?? ??? ???? ??

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Artifacts, ????, ???

• susceptibility artifact(???)
• ???? ??? ?? ???(?? ??, ??? ??, ?? ??) ?? ???? ??
  ?? ??(clips, plate, screw)? ??? ???? ??? ???
  ????? ????? ??? ???? ?????
• zipperlike artifact
• ??? ????? ??? ?? ??.
• partial voluming artifact
• voxel? ?? ?? ??? ?? ??? ??