Download Diffusion contrast

DIFFUSION & PERFUSION
MRI IMAGING
Dr. Mohamed El Safwany, MD.
1
Intended learning outcome
• The student should learn at the end of this
lecture principles of Diffusion and
Perfusion MRI studies.
.
DIFFUSION MRI IMAGING
3
- History • The feasibility of diffusion images was
demonstrated in the middle 1980s
• Demonstration on clinical studies is more
recent ; it corresponds with the availability
of EPI on MR system
4
Diffusion Weighted Image
• Core of infarct = irreversible damage
• Surrounding ischemic area  may be salvaged
• DWI: open a window of opportunity during which
treatment is beneficial
• DWI: images the random motion of water molecules as
they diffuse through the extra-cellular space
• Regions of high mobility “rapid diffusion”  dark
• Regions of low mobility “slow diffusion”  bright
5
- Diffusion contrast 

Diffusion gradients sensitize MR Image to
motion of water molecules
More motion = Darker image
Freely Diffusing Water = Dark
Restricted Diffusion = Bright
- Principles Velocities and methods of
measurement
Fast Flow
Arteries
~ 1000mm/ s
“Phase Contrast”
Slow Flow
Veins
~ 100mm/ s
“Phase Contrast”
Perfusion
Capillaries
~ 1mm/ s
Contrast Wash out
Diffusion
I ntercellular
space
~ 0,001mm/ s
Diffusion weighting
7
- Principles About the b factor
• b is a value that include all gradients effect
(imaging gradients + diffusion gradients)
• The b value can be regarded as analogous to
the TE for the T2 weighting
8
Low
Medium
High
“b = 5”
“b = 500”
“b = 1000”
- Principles About ADC
The ADC value does not depend on the field strength
of the magnet or on the pulse sequence used (which is
different for T1 or T2)
The ADC obtained at different times in a given patient
10
- Principles Isotropic and Anisotropic diffusion
• Diffusion is a three dimensional process, but
molecular mobility may not be the same in all
directions
• In brain white matter, diffusion’s value
depends on the orientation of the myelin fiber
tracts and on the gradient direction*
11
Diffusion weighted image
12
Characteristics of diffusion’s contrast
Short TE DWI gives more SNR
TE=100ms
SR 120
b = 1000 s/mm
2
TE=75ms
SR150
Characteristics of diffusion’s contrast
Higher b value increases sensitivity
Higher CNR helps
distinguish active lesions
MS
Higher CNR
Stroke
Vasogenic edema
Tumor
Cytotoxic Edema
Vasogenic edema
b = 1000
b= 3000
Mathematical Processing
Diffusion-weighted
ADC
map
Mathematical Processing
Diffusion-weighted
ADC
map
Diffusion Imaging Processing
Exponential ADC (ratio of Isotropic DWI/T2)
eliminates T2 shine through artifacts and may
distinguish subacute from acute stroke
Arachnoid Cyst
b=0
b=1000
ADC
eADC
Clinical
Application
19
MR Images of 60-Year-Old Man
with Glioblastoma Multiforme
.
2.
Figures 1, 2. On (1) T2-weighted fast spin-echo and (2) contrastenhanced T1-weighted spin-echo images, the differential diagnosis
between glioblastoma and abscess is impossible.
20
.
3.
4.
central hypointensity on diffusion-weighted image and
hyperintensity on ADC map, consistent with the diagnosis
of tumor.
21
MR Images of 57-Year-Old
Woman with Cerebral Metastasis
5.
6.
22
7.
8.
central hypointensity on diffusion-weighted image and
hyperintensity on ADC map, consistent with the diagnosis of tumor.
23
MR Images of 70-Year-Old Man with History of Recent Vertigo and
Disequilibrium
1.
2.
24
3.
4.
A brain abscess with Streptococcus anginosus was found at surgery.
25
MR Images of 57-Year-Old Woman with Cerebral Metastasis
5.
6.
the differential diagnosis between metastasis and abscess is
impossible.
26
7.
8.
Central hypointensity is seen on the diffusion-weighted image and
hyperintensity on the ADC map, consistent with the diagnosis of
tumor.
27
Text Book
• David Sutton’s Radiology
• Clark’s Radiographic positioning and
techniques
Assignment
• Two students will be selected for
assignment.
Question
• Describe the effect of b value upon
diffusion sensitivity?