1. Diffusion-Weighted MR Imaging in Brain Tumor.
Dr/ ABD ALLAH NAZEER. MD.

2. Diffusion Weighted (DW) Imaging:
Diffusion-weighted MR imaging is the simplest form of
diffusion imaging. A diffusion weighted MR sequence is an
integral component of the MRI brain protocol for tumors. It
is a pulse sequence sensitized to the random motion of water
molecules (which is termed ' Brownian motion More Details').
Certain pathologies constrain the normal random motion of
water molecules in the brain tissue and this is referred to as
'restricted diffusion'. Diffusion weighting enables one to
distinguish between rapid diffusion of protons (unrestricted
diffusion) and slow diffusion of protons (restricted diffusion).
Lesions that have restricted diffusion appear hyperintense on
diffusion images and hypointense on the accompanying
apparent diffusion coefficient (ADC) maps. Using an ADC map
it is possible to quantify the diffusion in brain tissues.

3. DWI has been used to assess brain tumors and while it
has had limited success as a definitive prognostic tool,
its proponents suggest that in certain settings it can
increase both the sensitivity and specificity of MR
imaging.
DWI may be helpful is in distinguishing between brain
abscesses and necrotic and cystic neoplasms on MRI.
The abscesses have a high signal on DWI and a reduced
Apparent Diffusion Coefficient (ADC) within the cavity.
This restricted diffusion is thought to be related to the
characteristic of the pus in the cavity; this may in turn
lead to reduced water mobility, lower ADC, and bright
signal on DWI.

4. DWI is also an effective way of differentiating an arachnoid cyst
from epidermoid tumors. Both lesions present similar signal
intensity characteristic of cerebrospinal fluid (CSF) on T1 and T2
sequences. On DWI, epidermoid tumors are hyperintense – for
they are solidly composed –whereas arachnoid cysts are
hypointense, demonstrating high diffusivity. The ADC values of
epidermoid tumors are similar to those of the brain parenchyma,
whilst ADC values of arachnoid cysts are similar to those of CSF. In
certain settings diffusion-weighted imaging can increase both the
sensitivity and specificity of MR imaging in the evaluation of
brain tumors by providing information about tumor cellularity,
which may in turn improve prediction of tumor grade. The
mechanism in which DWI may help in the tumor grading is based
on the fact that free water molecule diffusivity is restricted by
cellularity increase in high-grade lesions. The reduction in
extracellular space caused by tumor cellularity causes a relative
reduction in the apparent diffusion coefficient (ADC) values.

5. Perhaps most helpfully, high grade tumors have in some studies
been found to have low ADC values, suggesting a correlation
between ADC values and tumor cellularity. In some studies,
however, ADC values found in high- and low-grade gliomas have
overlapped somewhat. It is well known that the brain tumors,
specially the gliomas, are heterogeneous. Usually within a same
neoplasm grade, mostly high grade, different histologic features
of grades II–IV are presented. This limitation may also be
explained by the fact that it is not only the tumor cellularity that
is responsible for reducing the diffusibility. Lymphoma, a highly
cellular tumor, has hyperintensity on DWI and reduced ADC
values. While meningiomas also have a restricted diffusion,
displaying low ADC values, they rarely present difficulty in
diagnosis. DWI can be somewhat helpful in distinguishing
medulloblastoma from other pediatric brain tumors, as it seems
to display restricted diffusion presumably because of the densely
packed tumor cells and high nuclear-to-cytoplasm ratio.

6. Diffusion-Tensor MR image
The movement of water occurs in all three directions, and is
assumed to behave in a manner physicists can describe using a
Gaussian approximation. When water molecules diffuse
equally in all directions, this is termed isotropic diffusion. In
the white matter, however, free water molecules diffuse
anisotropically, that is to say the water diffusion is not equal in
all three orthogonal directions. The fractional anisotropy (FA)
measures the fraction of the total magnitude of diffusion
anisotropy. In addition to assessment of the diffusion in a
single voxel, DTI has been used to attempt to map the white
matter fiber tracts. A color-coded map of fiber orientation can
also be determined by DTI. A different color has been
attributed to represent a different fiber orientation along the
three orthogonal spatial axes.

10. Glioblastoma in the right temporal lobe.
A, T2-weighted image showing tumor of mixed intensity
(from low to high) with peritumoral edema.
B, The tumor shows heterogeneous enhancement after
intravenous injection of contrast medium.
C, On DWI, a solid portion of the tumor is isointense to
moderately high in intensity, and edema is isointense.
D, The ADC map calculated from DWI. Small circles from
1 to 12 in the right medial temporal lobe indicate the
regions of interest (which are too small to be seen).

11. A–C, Gadolinium-enhanced T1-weighted MR
image (400/14) (A), FLAIR MR image
(10,002/175/22000) (B), and ADC map from
DW image (b = 0, 1000 s/mm2) (C) obtained at
7-month follow-up after radiation treatment
show a left parietotemporal mass with
surrounding T2 prolongation. D–F, Gadolinium-enhanced
T1-weighted MR image (400/14) (D),
FLAIR MR image (10,002/175/22000 (E), and
ADC map from DW image (b = 0, 1000 s/mm2)
(F) show a new focus of enhancement in the left
basal ganglia at 7-month follow-up after
radiation treatment. Further follow-up imaging
(not shown) revealed marked progression of
enhancement and T2 prolongation. Patient had
progressive functional deterioration in clinical
course. This patient from the recurrence group
exhibited a mean ADC in the enhancing lesion
of 1.13 × 10−3 mm/s2, a mean ADC in T2
prolongation of 1.64 × 10−3 mm/s2, and a
normalized ADC ratio of the enhancing region
of 1.35. X indicates ROI of the enhancing lesion.
ROI in T2 prolongation was drawn in a different
section.

12. Images in a patient with
glioblastoma multiforme.
A, Contrast-enhanced T1-
weighted MR image
demonstrates an enhancing mass
in the left temporal lobe that is
not clearly high-grade glioma nor
clearly metastasis on this
conventional MR image.
B, ROIs are placed within the
hyperintense vasogenic edema
on a T2-weighted MR image and
within the corresponding
contralateral white matter.
C, MD overlay map renders a
mean MD of 0.603 × 10−3 mm2/s.
D, FA overlay map renders a
mean FA of 0.301. The
peritumoral DTI metrics are
consistent with glioblastoma
multiforme.

14. Grade II astrocytoma in the left insular portion.
A, Tumor shows high intensity on a T2-weighted
image.
B, No enhancement is seen on a T2-weighted
image.
C, On DWI, the tumor is isointense to mildly
hyperintense.
D, On the ADC map, representative regions of
interest are shown (small circles).

15. ADC and astrocytoma grade.
WHO grade II (top row),
grade III (middle row), and
grade IV (bottom row)
astrocytomas. Axial
postcontrast T1-weighted
images (left column), FLAIR
images (middle column), and
ADC maps (right column)
demonstrate typical
examples of 3 different
grades of astrocytoma. With
increasing tumor grade, the
tumor ADC value of grade III
astrocytoma is lower (black
arrows) than that of grade II
and the grade IV
astrocytoma has the lowest
(white arrow).

21. Decreased diffusion in tumours with high cellularity(Medulloblastoma).

24. Diffusion-weighted Imaging
of Metastatic Brain Tumors:
The SI on DWI may predict the histology of brain
metastases. On DWI, the enhancing areas of
metastatic brain tumors of different histologic types
demonstrated different SI. Well differentiated
adenocarcinomas tended to be hypointense; their SI
was significantly lower than that of tumors with a
different histology. Our 3 small-cell carcinomas and 1
large-cell neuroendocrine carcinoma manifested
hyperintensity on DWI. Their ADC values reflected the
cellularity of metastatic brain tumors.

25. Tumor in the right occipital lobe,
metastasized from the lung. A, On a
T2-weighted image, the solid
portion of the tumor is mildly
hyperintense, and peritumoral
edema is present anterior to the
tumor. B, Tumor shows relatively
homogeneous enhancement after
injection of contrast medium. C, On
DWI, the solid portion of the tumor
is isointense to mildly high in
intensity. D, Regions of interest are
shown (small circles) on the ADC
map. The ADC values are 0.80, 0.74,
0.68, and 0.67, and the averaged
ADC value is 0.72. Apparent
restricted diffusion (high signal) in
the tumor periphery appears to
reflect T2 shine through effect,
although peripheral high intensity is
not seen on the T2-weighted image.

26. A 67-year-old man with a well differentiated adenocarcinoma from the lung.
A, T2-weighted fast spin-echo image shows a parietotemporal lesion (arrow) near
the trigone of the left lateral ventricle. It is hypointense relative to the normal-appearing
white matter. The CNR of the solid lesion was 12. B, On contract-enhanced
T1-weighted image, the lesion is enhanced (arrow). C, On DWI, the lesion is
hypointense relative to the normal-appearing white matter (arrow). It was graded as
−2. D, On ADC map, the nADC of the lesion was calculated as 1.95.

27. A 69-year-old man with small-cell carcinoma from the lung.
A, On T2-weighted fast spin-echo image, the solid portion of a right parietal mass
lesion (arrow) is hyperintense relative to the normal-appearing white matter. The
CNR of the enhancing lesion was 45. B, On contract-enhanced T1-weighted image,
the peripheral region of the lesion is enhanced (arrow). C, On DWI, the lesion is
hyperintense relative to the normal-appearing cortical gray matter (arrow). The
lesion was graded as +2. D, On ADC map, the solid lesion is slightly hyperintense. Its
nADC was calculated as 0.57.

28. A 63-year-old man with large cell neuroendocrine carcinoma from the lung.
A, On T2-weighted fast spin-echo image, the solid portion of left occipital lesion
(arrow) is hyperintense relative to the normal-appearing white matter. The CNR of
the enhancing lesion was 56. B, On contrast-enhanced T1-weighted image, the
posterior part of the lesion is enhanced (arrow). There are multiple enhancing
areas (arrowheads) in the left frontal lobe indicative of subacute infarction. C, On
DWI, the solid lesion is hyperintense relative to the normal-appearing cortical gray
matter (arrow). The lesion was ranked as grade +2. D, On ADC map, the solid
lesion is hypointense; its nADC was calculated as 1.04.

29. Axial postcontrast T1-weighted with DWI of brain stem metastasis.

30. Images in a patient with lung
carcinoma. A, Contrast-enhanced
T1-weighted MR
image demonstrates an
enhancing mass adjacent to the
central sulcus on the right side.
B, ROIs are placed within the
hyperintense vasogenic edema
on this T2-weighted MR image
and within the corresponding
contralateral white matter. C,
MD overlay map renders a
mean MD of 0.908 × 10−3
mm2/s. D, FA overlay map
renders a mean FA of 0.114. The
peritumoral DTI metrics are
consistent with lung metastasis.

31. Meningothelial
meningioma in the left
high frontal convexity.
A, On a T2-weighted
image, tumor is mildly
high in intensity.
B, Tumor enhances
homogeneously on
a T2-weighted image.
C, The tumor is of high
intensity on DWI.
D, Regions of interest
are shown on the ADC
map. The ADC values
are 0.76, 0.63, and 0.55,
and the averaged ADC
value is 0.65. Restricted
diffusion in the tumor
probably is caused by
high tumor cellularity.

32. Fibrous meningioma in the left
convexity. A, On a T2-weighted
image, tumor intensity is mildly high
and edema is present anterior to the
tumor. B, The tumor enhances
homogeneously. C, On DWI, the
peripheral portion of the
tumor is moderately hyperintense
and the central portion is isointense.
Peritumoral edema is mildly high in
intensity. D, Regions of interest are
shown on the ADC map. The ADC
values are 0.83, 0.74, 0.71, 0.67, and
0.57, and the averaged ADC value is
0.70. Some areas of apparent
restricted diffusion in the tumor
probably reflect T2 shine-through
effect, because ADC values in these
areas are not low and the signals in
those areas show high intensity on
the T2-weighted image.

33. Prebulbar meningioma in a 10-year-old girl with history of torticollis. Sagittal,
T1WI, Axial T2 & GRE T2* image shows an heterogeneous extra-axial mass (b)
apparent diffusion coefficient (ADC) map show no restricted diffusion within mass.

40. Thank You.