mansfield and lauterbur nobel prize 1978 first images
DESCRIPTION
MRI – Magnetic Resonance Imaging. Mansfield and Lauterbur nobel prize 1978 first images. 1 st published MRI images of abdomen. First brain MR. Modern T2 image. “Interesting images, but will never be as useful as CT” neuroradiologist, 1982. 3 Tesla MRI Scanner. MRI. - PowerPoint PPT PresentationTRANSCRIPT
Mansfield and Lauterbur nobel prize1978 first images
MRI – Magnetic Resonance Imaging
1st published MRI images of abdomen
3 Tesla MRI Scanner
“Interesting images, but will never be as useful as CT”neuroradiologist, 1982
First brain MR First brain MR Modern T2 imageModern T2 image
MRI
Advantages Disadvantagessafe expensivegreat soft tissue contrast long timemany contrast options bad for bones
mediocre resolution
CT versus MRI
CT
+Excellent bone imaging
+Excellent new acute hemorrhage detection
+Skull fracture, calcified lesion
+Short scan time, metal devices allowed
-Poor contrast and resolution
-Radiation
MRI
+Excellent grey/white matter contrast & spatial resolution
+Better for old hemorrhage (and new with Diffusion?)
-Long scan time
-Pts cannot have metal devices
-Claustrophobia, obesity problems
+No radiation
- expensive
Magnetic Field of a loop of Wire
SOLENOID
3 Tesla MagneticField (60,000 timesEarths field)
MRI
B0
B0
3
21
3 Tesla magnet field
B0
Protons (hydrogennuclei act like littlemagnets)
Not all the protonsline up – thermal energy
MRI
Collective MagneticMoment of Protons
Classical pictureof Quantum Phenomenon
B0
ModelofHeadCoil
B0
ModelofHeadCoil
collective spins
MRIexcite
B0
Radio Waves
Collective MagneticMoment of Protons
start
end
Why precession?
Just like a top on a table
spin
gravity
B0
magnetic moment
B0
ModelofHeadCoil
excite
3.0 T123 MHz
B0
ModelofHeadCoil
signalwe “hear”
LISTEN
3.0 T123 MHz
B0
Radio Waves 123 MHz
Body Coil - Gradients
MRIexcitewithslice
selection
Only excite One Slice
3.1 T127 MHz
3.0 T123 MHz
2.9 T119 MHz
excite
Like a swing. Got one of the 3 orthogonal spatial dimensions whenwe excite. z
B0
ModelofHeadCoil
LISTEN
signalwe “hear”
3.0 T123 MHz
B0
Image we get of water container
Imageshould be
3.1 T127 MHz
3.0 T123 MHz
2.9 T119 MHz
excite
Like a swing. Got one of the 3 orthogonal spatial dimensions whenwe excite. z
3.1 T127 MHz
3.0 T123 MHz
2.9 T119 MHz
LISTEN
Got second of the 3 orthogonal spatial dimensions whenwe listen.
fast
slow
regular
ModelofHeadCoil
x
signalwe “hear”
B0
Image we get of water container
Imageshould be
3.1 T127 MHz
3.0 T123 MHz
2.9 T119 MHz
excite
Like a swing. Got one of the 3 orthogonal spatial dimensions whenwe excite. z
3.1 T127 MHz
3.0 T123 MHz
2.9 T119 MHz
phase encode(after we excitebefore we listen)
Got second of the 3 orthogonal spatial dimensions whenwe listen.
fast
slow
regular
y
3.1 T127 MHz
3.0 T123 MHz
2.9 T119 MHz
LISTEN
Got second of the 3 orthogonal spatial dimensions whenwe listen.
fast
slow
regular
ModelofHeadCoil
x
signalwe “hear”
Repeat 256 times for a 256x256pixel image
Different phase each time
scan = 4 minutes
Image we get of water container
Imageshould be
180 Degree RF Pulse
correcting gradients
Excite
Z
Y
X
Listen
SPIN ECHO SEQUENCE
TE – echo time
TR – repeat time
Contrast
T1 weighted – (MPRAGE-anatomical)T2 weighted – (fmri)
Spin Relaxation• Spins do not continue to precess forever
• Longitudinal magnetization returns to equilibrium due to spin-lattice interactions – T1 decay
• Transverse magnetization is reduced due to both spin-lattice energy loss and local, random, spin dephasing – T2 decay
• Additional dephasing is introduced by magnetic field inhomogeneities within a voxel – T2' decay. This can be reversible, unlike T2 decay
T1 decay – “spins back down”
Collective MagneticMoment of Protons
end
start
B0
signalwe “hear”
V
Time
T1 Recovery
MRSignal
Time
Typical T1 Graph
T2 decay – separation (dephasing) of “collective magnetic moment”
sometime after RF excitationImmediately after RF excitation
=
collective magnecticmoment
individual spins
separation (dephasing)
a little time later
T2 Decay
MRSignal
Typical T2 Graph
Time
T2 Decay
MRSignal
T1 Recovery
MRSignal
50 ms50 ms 1 s1 s
Proton Density Contrast
TE – echo time TR – repeat time
Proton Density Weighted ImageProton Density Weighted Image
T2 Decay
MRSignal
T1 Recovery
MRSignal
50 ms50 ms 1 s1 s
T1 Contrast
time time
TE – echo time TR – repeat time
T1 Weighted ImageT1 Weighted Image
T2 Decay
MRSignal
T1 Recovery
MRSignal
50 ms50 ms 1 s1 s
T2* and T2 Contrast
TE – echo time TR – repeat time
T2 Weighted IMageT2 Weighted IMage
ProtonProtonDensityDensityWeightedWeightedImageImage
T1 T1 Weighted Weighted ImageImage
T2 T2 Weighted Weighted ImageImage
Properties of Body TissuesTissue T1 (ms) T2 (ms)
Grey Matter (GM) 950 100
White Matter (WM) 600 80
Muscle 900 50
Cerebrospinal Fluid (CSF) 4500 2200
Fat 250 60
Blood 1200 100-200
MRI has high contrast for different tissue types!