4 - History -The feasibility of diffusion images was demonstrated in the middle 1980sDemonstration on clinical studies is more recent ; it corresponds with the availability of EPI on MR system
5 Diffusion Weighted Image Core of infarct = irreversible damageSurrounding ischemic area may be salvagedDWI: open a window of opportunity during which treatment is beneficialDWI: images the random motion of water molecules as they diffuse through the extra-cellular spaceRegions of high mobility “rapid diffusion” darkRegions of low mobility “slow diffusion” bright
6 - Diffusion contrast -Diffusion gradients sensitize MR Image to motion of water moleculesMore motion = Darker imageFreely Diffusing Water = DarkRestricted 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
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 directionsIn brain white matter, diffusion’s value depends on the orientation of the myelin fiber tracts and on the gradient direction*
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 Metastasis 5.6.
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 Disequilibrium 1.2.
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 Metastasisthe 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 AssignmentTwo students will be selected for assignment.
30 QuestionDescribe the effect of b value upon diffusion sensitivity?