1. DIFFUSION & PERFUSION MRI IMAGING Dr. Mohamed El Safwany, MD.

2. Intended learning outcome
The student should learn at the end of this lecture principles of Diffusion and Perfusion MRI studies. .

3. DIFFUSION MRI IMAGING

4. - 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

5. 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

6. - Diffusion contrast -
Diffusion gradients sensitize MR Image to motion of water molecules
More motion = Darker image
Freely Diffusing Water = Dark
Restricted Diffusion = Bright

7. - Principles - Velocities and methods of measurement

8. - 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

9. Medium
High
Low
“b = 500”
“b = 1000”
“b = 5”

10. - 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

11. - 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*

12. Diffusion weighted image

13. Short TE DWI gives more SNR
Characteristics of diffusion’s contrast
Short TE DWI gives more SNR
TE=100ms
SR 120
b = 1000 s/mm 2
TE=75ms
SR150

14. Characteristics of diffusion’s contrast
Higher b value increases sensitivity MS
Higher CNR helps
distinguish active lesions
Stroke
Higher CNR
Vasogenic edema
Cytotoxic Edema
Tumor
Vasogenic edema
b = b= 3000

15. Mathematical Processing
Diffusion-weighted
ADC
map

16. Mathematical Processing
ADC
map
Diffusion-weighted

17. Diffusion Imaging Processing
Exponential ADC (ratio of Isotropic DWI/T2)
eliminates T2 shine through artifacts and may
distinguish subacute from acute stroke

18. Arachnoid Cyst
b=0
b=1000
ADC
eADC

19. Clinical Application

20. MR Images of 60-Year-Old Man with Glioblastoma Multiforme. 2.
Figures 1, 2. On (1) T2-weighted fast spin-echo and (2) contrast-enhanced T1-weighted spin-echo images, the differential diagnosis between glioblastoma and abscess is impossible.

21. 3. 4. .
central hypointensity on diffusion-weighted image and hyperintensity on ADC map, consistent with the diagnosis of tumor.

22. MR Images of 57-Year-Old Woman with Cerebral Metastasis5. 6.

23. 7. 8.
central hypointensity on diffusion-weighted image and hyperintensity on ADC map, consistent with the diagnosis of tumor.

24. MR Images of 70-Year-Old Man with History of Recent Vertigo and Disequilibrium1. 2.

25. 3. 4.
A brain abscess with Streptococcus anginosus was found at surgery.

26. 5. 6.
MR Images of 57-Year-Old Woman with Cerebral Metastasis
the differential diagnosis between metastasis and abscess is impossible.

27. 7. 8.
Central hypointensity is seen on the diffusion-weighted image and hyperintensity on the ADC map, consistent with the diagnosis of tumor.

28. Text Book David Sutton’s Radiology
Clark’s Radiographic positioning and techniques

29. Assignment
Two students will be selected for assignment.

30. Question
Describe the effect of b value upon diffusion sensitivity?