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

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

DIFFUSION MRI IMAGING

- 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

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

- 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

- 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

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

- 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

- 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*

Diffusion weighted image

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

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 = 1000 b= 3000

Mathematical Processing Diffusion-weighted ADC map

Mathematical Processing ADC map Diffusion-weighted

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

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.

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

MR Images of 57-Year-Old Woman with Cerebral Metastasis 5. 6.

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

MR Images of 70-Year-Old Man with History of Recent Vertigo and Disequilibrium 1. 2.

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

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

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

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?