1 Seite 1 RUPRECHT-KARLS- UNIVERSITY HEIDELBERG Computer Assisted Clinical Medicine Andreas Lemke 12/22/2010 | Page 1 Basics of MRI Andreas Lemke and Prof. Dr. Lothar Schad MR Lab Rotation, Mannheim Chair in Computer Assisted Clinical Medicine Faculty of Medicine Mannheim University Heidelberg Theodor-Kutzer-Ufer 1-3 D-68167 Mannheim, Germany [email protected]www.ma.uni-heidelberg.de/inst/cbtm/ckm/ RUPRECHT-KARLS- UNIVERSITY HEIDELBERG Computer Assisted Clinical Medicine Andreas Lemke 12/22/2010 | Page 2 www.ma.uni-heidelberg.de/inst/cbtm/ckm/
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 1
Basics of MRI
Andreas Lemke and Prof. Dr. Lothar Schad
MR Lab Rotation, Mannheim
Chair in Computer Assisted Clinical MedicineFaculty of Medicine Mannheim University HeidelbergTheodor-Kutzer-Ufer 1-3D-68167 Mannheim, GermanyLothar.Schad@MedMa.Uni-Heidelberg.dewww.ma.uni-heidelberg.de/inst/cbtm/ckm/
12/22/2010 | Page 12Radio Frequency Coils: Coil Arrays II
102 seamlessly integrated coil elements at 32 receiving channels
matrix coils:
head
neck
stem
leg
courtesy: Siemens AG, Erlangen
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 13
transmitter
receiver
gradient
shimim
age
proc
esso
r350 MHz
control panel
computer
350 MHz
radio- gradients Gxyz static field B0frequency RF shim coils
MRI Components: Physical Parameters
static field B0 M0
radiofreq. RF signal
gradients Gxyz image
technicalcomponent
physicalparameter
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 14
Relaxation
Relaxation
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 15Magnetization: Mz and Mxy
longitudinal magnetization: Mz
transversal magnetization: Mxy
transversal magnetization: Mxy- phase synchronization after a 90°-pulse- the magnetic moments μ of the probe startto precede around B1 leading to a synchronizationof spin packages → Mxy
- after 90°-pulse Mxy = M0
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 16Movie: Mz and Mxy
source: Schlegel and Mahr. “3D Conformal Radiation Therapy: A Multimedia Introduction to Methods and Techniques" 2007
12/22/2010 | Page 59Exercise: Measurement of the ADC
)exp(0 bDSS −=
1. Calculate the apparent diffusion coefficient (ADC) from the DWI images in White Matter (WM), Grey Matter (GM), and Cerebrospinal Fluid (CF)
Experiment #1: 2 images were measured (DWI_b0.IMA, DWI_b1000.IMA, data at: http://www.ma.uni-heidelberg.de/inst/cbtm/ckm/lehre/„Medical Physics: Lab Rotation MR-Radiology“) with b = 0 and 1000 s/mm2. Plot signal intensity (= pixel mean value of ROI) semi-logarithm as a function of b-value and calculate ADC
- group 1: CF ( )
- group 2: WM ( )
- group 3: GM ( )
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 60Exercise: Measurement of the FA
23
22
21
321 )²()²()²(23
λλλ
λλλλλλ
++
−+−+−=FA
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛
zzyzxz
yzyyxy
xzxyxx
DDDDDDDDD
3λ1λ
2λ
2. Calculate the fractional anisotropy (FA) from the DTI images in White Matter (WM), Grey Matter (GM), and Cerebrospinal Fluid (CF)
Experiment #2: 6 images were measured (DTI_b1000_1.IMA … DTI_b1000_6.IMA, data at: http://www.ma.uni-heidelberg.de/inst/cbtm/ckm/lehre/„Medical Physics: Lab Rotation MR-Radiology“) with b = 1000 s/mm2 and 6 different directions. Evaluate signal intensity (= pixel mean value of ROI) for the different directions andcalculate FA
- group 2: CF ( )
- group 3: WM ( )
- group 1: GM ( )
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 61
Diffusion
Diffusion
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 62Free Diffusion
Dtx 6² =• mean diffusion length
(D = diffusion coefficient, t = time)
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 63Principle of DWI I
without diffusion weighting:
with diffusion weighting:
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 64Principle of DWI II
constant phase in the rotating reference frame
position of the spin in the rotating reference frame
after 90° pulse
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 65Principle of DWI III
1. gradient relative phase shift in the rotating frame
without diffusion:
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 66Principle of DWI IV
without diffusion:
2. gradient rephasing of the phase gradient echo
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 67Principle of DWI V
with diffusion:
1. gradient relative phase shift in the rotating frame
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 68Principle of DWI VI
with diffusion:
diffusion during the gradients spins on a different position
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 69Principle of DWI VII
2. gradient spins not completely rephased signal reduction
with diffusion:
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 70Dependence of the Signal Decay
)exp(0 bDSS −=( )3/222 δδγ −Δ= Gbstrength of the diffusion weighting:
signal decay:
• b-value can be calculated from the sequence• two DWIs are necessary to calculate D
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
12/22/2010 | Page 71Diffusion Measurement: Calculation of D
b-values = 0.5 – 1100 s/mm2
white matterD ~ 0.6 · 10-3 mm2/s
waterD ~ 2.4 · 10-3 mm2/s
Measurement of D in biological tissue is called ADC0 200 400 600 800 1000
Reference Manual for Magnetic Resonance Safety, Implants, and Devices: 2006 Edition.
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
| Page 92MR Safety Labeling
MR safe• an item which poses no known hazards in all MR environments
MR conditional• an item which has been demonstrated to pose no known hazards
in a specified MR environment with specified conditions of use. Field conditions that define the specified MR environment include
• field strength, • spatial gradient, • dB/dt (time rate of change of the magnetic field), • radio frequency (RF) fields, and • specific absorption rate (SAR).
• additional conditions, including specific configurations of the item, may be required
MR unsafe• an item which is known to pose hazards in all MR environments
ASTM International. Standard practice for marking medical devices and other items for safety in the magnetic resonance environment. F 2503-05
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
| Page 93Light Vizier
patient localizing and referencing• ask patient for closing eyes before
laser switch on
RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
| Page 94Danger of Crushing
couch movement• watch position of arms and fingers• save connections, ECG-wires, and
alarm ball• push “couch stop” – patient couch can
be moved manually
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RUPRECHT-KARLS-UNIVERSITY HEIDELBERG
Computer Assisted Clinical MedicineAndreas Lemke
| Page 95MR Safety Aspects: Summary
static magnetic field• missile effect• influencing equipments• physiological effects