The document discusses magnetic resonance diffusion weighted imaging (DWI). It begins by stating the learning objectives which are to identify the DWI hypothesis, meaning of B-value, applications of DWI, differential diagnoses of DWI appearances, and DWI pitfalls. It then proceeds to explain each topic in detail with examples. The key points are that DWI measures diffusion of water molecules in tissue, restricted diffusion appears bright on DWI and dark on ADC map while facilitated diffusion is dark on DWI and bright on ADC map. DWI can differentiate between cytotoxic and vasogenic edema and between restricted and freely mobile fluid. It has applications in assessing treatment response and performing tractography. Artifacts and mimics that can cause false appearances are

1. ‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬
‫العالمين‬ ‫رب‬ ‫والحمدهلل‬
‫المرسلين‬ ‫و‬ ‫األنبياء‬ ‫خاتم‬ ‫علي‬ ً‫ا‬‫سالم‬ ‫و‬ ً‫ة‬‫وصال‬
‫أجمعين‬ ‫صحبه‬ ‫و‬ ‫آله‬ ‫وعلي‬ ‫محمد‬ ‫سيدنا‬

2. MAGNETIC RESONANCE DIFFUSION
WEIGHTED IMAGING (DWI)

3. BY THE END OF THIS LECTURE YOU’LL
BE ABLE TO IDENTIFY:
1. DWI hypothesis.
2. B-value meaning.
3. DWI applications.
4. DDx of DWI appearances.
5. DWI pitfalls.

4. DWI HYPOTHESIS.

5. DWI HYPOTHESIS
To understand what is the diffusion and
effect of physical property on behavior
of substance diffusion let us see this
experiment at the following video:

7. Similarly, if we could put some “magic
ink" into the biological tissue and
follow its progress, we can gain
knowledge about the biological tissue
itself, as well as the kind of changes
that may occur in the biological tissue
when it is affected by various disease
processes.

8. Also MRI study of the diffusion in tissue
includes:
*Triggering the movement of water
molecules (represented by ink)
*Which normally present throughout the
intercellular spaces (represented by bucket
of water)
*By gradient force(represented by heater).

9. But the in vitro diffusion motion is
different than in biological tissues
because:

10. The free diffusion of the molecules in
normal biological tissue is restricted
by:
• The cell membranes,
• The intercellular bonds,

11. And another important difference is in
addition to the movement of molecules in
the intercellular spaces, the diffusion in
biological tissue also include perfusion of
some molecules intracellularly that is
affected by nuclear cytoplasmic ratio
(NCR).

13. 1-In neoplastic tissues the free diffusion
is more restricted than in normal
tissue by:
 Hypercellularity
 And increased the size of the nucleus
which in turn decrease the cytoplasmic
portion in which the perfusion part
occurs.

15. 1-While in normal tissue the diffusion
occur as follow.

17. This motion in biological tissues is
calculated by apparent diffusion
coefficient (ADC) that could be imagined
as measure of flow rate of water in
intercellular space.

19. B-VALUE MEANING.

20. B-VALUE MEANING
 To make DWI you need modern MR machine of
>1T and gradient coil.
 We remember the previous experiment of heater
and jars of water with the heater account for the
gradient coil.
 The b-value is a factor that reflects the strength and
timing of the gradient coil used to generate
diffusion-weighted images.

22. DWI APPLICATIONS

23. DWI APPLICATIONS
1. Differentiation between cytotoxic edema
(related to ischemic, inflammatory
pathology, active MS, CJD and CPM) and
vasogenic edema (related to SOL and PRES).

24. DWI APPLICATIONS
Vasogenic edemaCytotoxic edema
Dysfunction of BBB fluid
shift from blood to
intercellular space.
Tumor, early venous
infarction, abscess, PRES
Finger like
facilitated
Dysfunction of Na-K
channels in cell
membrane intracellular
fluid shift cell swelling
Ischemic, inflammatory,
metabolic & toxic
Regular outline
restricted
• Mechanism
• Pathology
• FLAIR
• DWI

26. DWI APPLICATIONS
2. Differentiation between freely mobile simple
fluid (related to simple cyst, CSF
encephalomalacia and necrotic tumor) and
restricted mobility of highly proteinaceous
material (related to abscess, TB and
epidermoid).

29. DWI APPLICATIONS
3. Differentiation between malignant and benign
tissue.

30. As the malignant tissue have:
 Hypercellularity,
 More nuclear to cytoplasmic ratio,
 More macromolecular proteins
 And more cell membranes which represent
restriction to diffusion and, consequently, a
lower ADC.

32. On the other hand, benign tissue have a
decrease in the restrictive cell membranes
with less of restriction to diffusion and a
consequently higher ADC.

34. DWI APPLICATIONS
4. Assess the response to Cth and Rth.

35. *Soon after initiation of necrosis induced
therapy, cell swelling occurs, which can lead
to decrease in tumor ADC. This is followed
by cell necrosis and lysis, resulting in rise in
ADC.
*While apoptosis induced therapy resulting in
direct cell shrinkage and immediate
increased ADC.

37. DWI APPLICATIONS
5. Tractography.
water molecules tend to
diffuse more freely along the
direction of axonal fascicles
rather than across
them. Such directional
dependence of diffusivity is
termed anisotropy.

39. DDX OF DWI APPEARANCES.

40. BRIGHT DWI & BLACK ADC
i.e. Restricted diffusion
 Means that the lesion/area preserves its bright signal till the
highest b-value used and turned low signal on ADC map.
 DDx:-
1. Cytotoxic edema.
2. CPM
3. CJD
4. Epidermoid.
5. Abscess/caseous material.
6. Hypercellular tissue as meningioma and lymphoma.
7. Cholesteatoma.

42. BLACK DWI & BRIGHT ADC
i.e. Facilitated diffusion
 Means that the lesion/area get low signal as the b-value
increased and turned high signal on ADC map.
 DDx:-
1. Vasogenic edema.
2. Necrotic tumor.
3. Hypocellular tissue.
4. Simple cyst.
5. Encephalomalacia.

44. BRIGHT DWI & BRIGHT ADC
i.e. T2 shine through
 Means that as the diffusion image is diffusion weighted that
means in most it contains diffusion criteria but also contains
but to much lesser extent T2 criteria, so when the T2 of the
lesion is very long, T2 will spill over into the DWI, making it
appear bright and thus mimicking restricted diffusion.
 DDx:-
1. Vasogenic edema.
2. Hemangioma.

46. BLACK DWI & BLACK ADC
i.e. T2 blackout
 Means that as the diffusion image is diffusion weighted that
means in most it contains diffusion criteria but also contain to
much lesser extent T2* criteria, so when the T2* of the lesion
is very short, T2* will spill over into the DWI, making it
appear dark and thus mimicking facilitated diffusion.
 DDx:-
1. Hemorrhage.
2. Fibrous tissue.
3. Uterine fibroid.

48. DWI PITFALLS

49. DWI PITFALLS
 DWI should not be interpreted in isolation but in
association with other sequences.
 Sometimes restriction is attributed to marked
fibrosis due to chronic granulomatous disease
(benign) or post Rth fibrosis or due to high fat
content of the tissue which cause restriction due
to tight binding of water molecules to fat
molecules leading to restriction.

50. LAST MESSAGE

51. EDGAR DALE’S PYRAMID OF LEARNING
PEOPLE GENERALLY REMEMBER:-

52. THANK YOU
‫اليك‬ ‫اتوب‬ ‫و‬ ‫استغفرك‬ ‫أنت‬ ‫إال‬ ‫إله‬ ‫ال‬ ‫ان‬ ‫أشهد‬ ‫وبحمدك‬ ‫اللهم‬ ‫سبحانك‬