2. Diffusion weighted magnetic
resonance imaging in diagnosis and
characterization of brain tumors in
correlation with conventional MRI
Essay
Submitted by
Mahmoud Abdou Mohammed Abdullah
M.B.B.Ch
For partial fulfillment of master degree in
Radio diagnosis
3. Supervised by
PROF. AHMED FARID YOSEF
Professor of radio diagnosis
Faculty of medicine - Banha University
DR. ISLAM MAHMOUD ELSHAZLY
Lecturer of radio diagnosis
Faculty of medicine – Banha University
Faculty of medicine
Banha University
2012
4. Introduction
The development of techniques capable of accurately depicting
tumor grades in vivo is important for determination of the most
appropriate treatment of tumors.
An unfortunate choice of biopsy site or insufficiently large samples
may result in an incorrect histological diagnosis. The diagnosis of
brain tumors by magnetic resonance imaging (MRI) is usually based
on basic unenhanced T1- and T2-weighted images and post contrast
T1-weighted images. Conventional MRI techniques are not sufficient
for the grading and specification of brain tumors.
5. ع ع ع ع ع عIn diffusion-weighted imaging (DWI), the image contrast is
determined by the random translational (Brownian) motion of water
molecules. The quantification of diffusion using DWI has been
attracting growing interest as an easy method to further characterize
the nature of brain tumors. Diffusion weighted imaging may help to
distinguish tumoral invasion from normal tissue or edema. This
distinction if possible, would be very important for planning surgical
resection, biopsies and radiation therapy.
6. BRAIN ANATOMY
The cerebrum
ع ع ع ع ع ع ع عThey are large, oval structures that superficially resemble the
surface of a shelled walnut. The midline longitudinal cerebral
fissure, occupied in life by the falx cerebri, incompletely separates
the two cerebral hemispheres from one another. The floor of the
cerebral fissure is formed by the corpus callosum, a large myelinated
fiber tract that forms an anatomical and functional connection
between the right and left hemispheres. Each cerebral hemisphere is
subdivided into five lobes: the frontal, parietal, temporal, and
occipital lobes, and the insula.
7. Additionally, the cortical constituents of the limbic system are also
considered to be a region of the cerebral hemisphere and some
consider it to be the sixth lobe, the limbic lobe. The temporal lobe is
separated from the parietal lobe by the lateral fissure (fissure of
Sylvius). The central sulcus (central sulcus of Rolando), separates the
frontal lobe from the parietal lobe. The division between the parietal
and occipital lobes is defined on the lateral aspect as the imaginary
line between the preoccipital notch and the parieto-occipital notch.
On the medial aspect, they are separated by the parieto-occipital
sulcus and its continuation, the calcarine fissure.
9. The Posterior fossa
The posterior fossa is divided into two compartments by the 4th
ventricle. Anteriorly the brain stem occupies about one third and
posteriorly the cerebellum occupies the posterior two thirds of the
posterior fossa. The brain stem has three anatomically recognizable
components; the midbrain, pons and medulla. The two cerebellar
hemispheres are joined by the
midline structures of the vermis.
10. The ventricular system
The ventricular system is composed of four fluid-filled cavities
(ventricles), which are located deep within the brain. The lateral
ventricles consist of central portion called the body and three
extensions: the anterior, occipital and temporal horns. The junction of
the body and occipital and temporal horns form the triangular area
termed the trigone (atria). The lateral ventricles open downward into
the third ventricle through the paired interventricular foramen
(foramen of Monro). The third ventricle is located midline just inferior
to the lateral ventricles.
11. The third ventricle communicates with the fourth ventricle via a
narrow passage way termed the cerebral aqueduct (aqueduct of
Sylvius). The fourth ventricle is a diamond-shaped cavity located
anterior to the cerebellum. The lateral angles of the fourth
ventricle extend to form the lateral apertures (foramina of
Luschka). The inferior angle of the fourth ventricle has an opening
called the median aperture (foramen of Magendie), which is
continuous with the central canal of the spinal cord. The apertures
allow passage of CSF between the ventricles and subarachnoid
space.
13. Axial T2 of the brain at the level of lateral ventricles
14. Pathology of Brain Tumors
Brain tumors may be primary (i.e. originating from brain itself), or
secondary (i.e. metastatic from another primary site of cancer). Both
primary and secondary brain tumors are capable of producing
neurological impairment according to their site. A benign tumor is
composed of slow-growing cells, but can be life threatening when
located in vital areas. Primary malignant tumors are usually invasive
and composed of fast growing cells. Primary tumors, whether
benign or malignant, rarely spread outside of the central nervous
system (CNS). Therefore, most symptoms tend to be neurologic in
origin.
15. WHO classification of tumors of the nervous system
grouped by their tissue of origin into the following
:major categories
I. Tumors of neuroepithelial tissue include:
Glial tumors.
Neuronal and mixed neuronal glial tumors.
Non-glial tumors.
II. Tumors of the sellar region:
Pituitary adenoma.
Pituitary carcinoma.
Craniopharyngioma.
III. Hematopoeitic tumors:
Primary malignant lymphoma.
16. IV. Germ cell tumors:
Germinoma.
Embryonal carcinoma.
Yolk sac tumor.
Choriocarcinoma.
Teratoma.
Mixed germ cell tumor.
V. Tumors of the meninges:
Menengioma.
Mesenchymal tumors (chondrosarcoma, Hemangiomapericytoma.).
Primary melanocytic lesions.
VI. Tumors of uncertain histogenesis
Hemangioblastoma
17. VII. Tumors of the peripheral nerves that affect the CNS:
Schwannoma.
Neurofibroma.
Malignant schwannoma.
VIII. Local extensions from regional tumors:
Paraganglioma (chemodectoma).
Chordoma.
Others.
IX. Metastatic tumors.
X. Cysts and tumor like lesions:
Arachnoid cyst.
Epidermoid cyst.
Dermoid cyst.
18. :Tumors of neuroepithelial tissue
:A- Glial tumors
Astrocytic tumors- 1
Oligodendroglial tumors- 2
Mixed gliomas- 3
Ependymal tumors- 4
:B- Neuronal and mixed neuronal glial tumors
.e.g gangilioglioma and central neurocytoma
:C- Non-glial tumors
(:Choroid plexus tumors (CPT- 1
:Pineal parenchymal tumors- 2
.Tumors with neuroblastic elements e.g: meduloblastoma and PNET- 3
19. Physical Principles of Diffusion–Weighted
Imaging
FICK'S LAW:
It which states that local differences in solute concentration
will give rise to a net flux of solute molecules from high
concentration regions to low concentration regions. However,
even with no concentration gradients the water molecules are
still in random motion. This is because; diffusion motions are
caused by the intrinsically possessed kinetic energy of the liquid
medium. The phenomenon of diffusion was named "Brownian
motion" after the person who first described it, Robert Brown.
20. :Free and restricted diffusion
In a glass of water, the motion of the water molecules is completely
random and is limited only by the boundaries of the container. In
biologic systems totally free diffusion generally does not occur due to
the presence of restrictions such as cell membranes or molecular
boundaries. The extent of translational diffusion of molecules
measured in a biologic system is therefore referred to as the apparent
diffusion coefficient (ADC). The intra-cellular diffusion coefficient is
lower than in the extra-cellular space due to intracellular barriers as
organelles, membranes and macromolecules.
21. DIFFUSION–WEIGHTED IMAGING USING
PULSED GRADIENT
In their fundamental study
Stejskal and Tanner described
an experimental method to
sensitively measure diffusion
with MRI. Stejskal and Tanner
used a pair of pulsed magnetic
field gradients, symmetrically
positioned around the 180°
refocusing spin echo pulse (as
shown in this figure).
22. The first gradient pulse induces a phase shift for all spins. The second
gradient pulse will invert this phase shift thus cancelling the phase shift
completely for static spins. Spins having completed a change of
location due to Brownian motion will however experience different
phase shifts by the two gradient pulses. Thus they are incompletely
refocused and consequently lead to a signal loss. According to Fick’s
law, true diffusion is the net movement of molecules due to a
concentration gradient. With MR imaging, molecular motion due to
concentration gradients cannot be differentiated from molecular
motion due to pressure gradients, thermal gradients, or ionic
interactions.
23. Disadvantages of pulsed gradient diffusion weighted imaging:
Measurement of diffusion properties requires an imaging
sequence sensitive for the detection of motion. However, such a
sequence will also have sensitivity to bulk motion as CSF
pulsations, involuntary twitches and cardiac cycling. Attempts to
minimize bulk motion include use of a head holder and cardiac
gating, but CSF pulsations remain problematic. To avoid these
non-diffusional motions, ultra-fast techniques are used.
These ultra-fast techniques are:
I- ECHOPLANAR IMAGING (EPI).
II- HASTE.
24. (I- ECHOPLANAR IMAGING (EPI
With the development of high-performance gradients, DWI can be
performed with an echo-planar spin-echo T2-weighted sequence. The
substitution of an echo-planar spin-echo T2-weighted sequence
markedly decreased imaging time and motion artifacts and increased
sensitivity to signal changes due to molecular motion. As a result, the
DW sequence became clinically feasible to perform. In EPI, multiple
lines of imaging data are acquired after a single RF excitation. Like a
conventional SE sequence, a SE EPI sequence begins with 90° and
180° RF pulses.
25. Conventional SE imaging. Within each TR period, the
pulse sequence is executed and one line of imaging data is
collected. The frequency-encoding gradient (Gx), phase-
encoding gradient (Gy), and section-selection gradient (Gz)
.are shown during one TR period. RF = radio frequency
26. Echo-planar imaging. Within each TR period, multiple lines of imaging
data are collected. Gx = frequency-encoding gradient, Gy = phase-
encoding gradient, Gz = section-selection gradient
27. Single-shot and multi-shot EPI
EPI can be performed by using single or multiple excitation
pulses ("shots"). The number of shots represents the number of
TR periods required to complete the image acquisition. In single-
shot (snapshot) EPI, all of the k-space data are acquired with
only one shot. Distortions and signal loss occur predominantly at
boundaries between tissue and air, due to the local change of
magnetic field strength. To achieve higher resolution and reduce
the image distortion and signal loss, multishot EPI can be
performed.
28. Comparison between single-shot and multishot echo-planar
imaging. Axial images were obtained with 1 shot (a), 8 shots (b),
16 shots (c), and 32 shots (d). The geometric distortion of the
anterior aspect of the brain (arrow) is reduced as the number of
.shots increases
29. :II- HASTE
Another non-EPI fast technique is diffusion weighted half-
Fourier single-shot turbo spin echo, in which only half of the k-
space is traversed and the other half constructed by mirroring,
with the advantage of reducing susceptibility artifacts. Images
covering the whole brain can be obtained in one minute and it
takes minutes to acquire data for calculation of the diffusion
coefficient. This technique can be implemented on most
conventional MRI systems
30. ISOTROPIC AND ANISOTROPIC
DIFFUSION
In isotropic diffusion, there is no preferred direction of water
motion. However, for white matter, consisting of dense fiber
bundles, water moves more easily parallel to the fibers than
across them. The anisotropic nature of diffusion in the brain can
be appreciated by comparing images obtained with DW gradients
applied in three orthogonal directions. The signal intensity
decreases when the white matter tracts run in the same direction
as the DW gradient because water protons move preferentially in
this direction.
31. Anisotropic nature of diffusion in the brain. Transverse DWI
with the diffusion gradients applied along the x (Gx, left), y (Gy,
.middle), and z (Gz, right) axes demonstrate anisotropy
Note that the corpus callosum (arrow on left image) is hypointense
when the gradient is applied in the x (right-to-left) direction, the
frontal and posterior white matter (arrowheads) are hypointense
when the gradient is applied in the y (anterior-to-posterior)
direction, and the corticospinal tracts (arrow on right image) are
hypointense when the gradient is applied in the z (superior-to-
.inferior) direction
32. CREATION OF ISOTROPIC DW IMAGE
DW gradient pulses are applied in one direction at a time. The resultant
image has information about both the direction and the magnitude of
the ADC. To create an image that is related only to the magnitude of the
ADC, at least three of these images must be combined. The simplest
method is to multiply the three images created with the DW gradient
pulses applied in three orthogonal directions. The cube root of this
product is the DW image.
33. b value
The magnitude of the diffusion weighting is referred to as the
b value. The b value increases with the strength of diffusion
gradient used, the duration of each gradient lobes, and the
time between the gradient lobes. At small b values, there is
minimal sensitivity to diffusional motions and T2 weighted
dominates. At high b-values the contrast is largely due to
diffusion properties. Unfortunately even with the maximal
currently applied b values, T2 component is still present in all
diffusion weighted images. As result of this,T2 shine through
effect occur. Increasing b values result in a progressive
decrease in the gray to white matter signal intensity ratio. Iso
intensity between gray and white matter results at b values
between 1000 and 2000 sec/mm2 (Typical b values in clinical use are
300-1000sec/mm2 ). At b values greater than 2000, the gray- white
pattern reverses relative to the usual b value 1000.
34. CREATION OF AN ADC MAP
An ADC map is an image whose signal intensity is equal to the
magnitude of the ADC. The ADC is calculated for each pixel of the
image and is displayed as a parametric map. By drawing regions of
interests on these maps, the ADCs of different tissues can be derived.
Areas of restricted diffusion show low ADC values compared with
higher ADC values in areas of free diffusion. Thus areas of restricted
diffusion will appear of high signal DW images, these areas will appear
as low-signal intensity areas (opposite to DW
images) on the ADC map.
35. Importance of ADC map
The residual T2 component on the DW image makes it
important to view the ADC map in conjunction with
the DW image. In lesions such as acute stroke, the T2-
and diffusion-WI effects both cause increased signal
intensity on the DW image.
The ADC maps are used to exclude "T2 shine through"
as the cause of increased signal intensity on DW
images. The ADC maps are useful for detecting areas of
increased diffusion that may be masked by T2 effects
on the DW image.
36. Conventional MRI findings of brain tumors
Gliomas
1-Astrocytomas : The common signal characteristics of the
tumors include low signal in T1 and high signal intensity T2
and appear more homogenous without central necrosis
a-Diffuse astrocytoma
they appear homogeneously hypointense on T1WI and hyper
intense on T2 WI. Contrast enhancement is absent on MRI in
diffuse low grade astrocytomas.
b. Glioblastoma multiforme(GBM) (WHO grade IV)
solitary deep heterogeneous ring enhancing lesion with extensive
surrounding vasogenic edema and mass effect. The most
common feature of the enhancing ring is irregularity, with a
wide ring that varies in thickness and has a shaggy inner
margin. The lesion usually extends through the corpus
callosum in most cases.
37. c. Juvenile pilocystic astrocytomas
The mural nodules appears homogenously hyperintense to grey matter
on T2 WI and hypointense on T1 WI. The associated cyst is even more
hyperintense on T2 weighted images and even more hypointense on T1
WI. Edema of the adjacent white matter is usually minimal.
Homogenous contrast enhancement of the tumor nodule is
characteristic although a calcific focus if present does not demonstrate
enhancement.
d. Pleomorphic xanthoastrocytoma (PXA)
A cystic supratenitorial mass containing an enhancing mural nodule.
e. Subependymal gaint cell astrocytoma(SEGA)
Occurs almost extensively in patients with tuberous sclerosis in their late
teens or 20s. Tumor appears as heterogonous sharply demarcated
intraventricular mass that is mildly hyperintense on T2 WI, hypo to iso
intense in T1 WI and appears as a markedly enhancing mass
38. GBM in the left frontal lobe. Axial gadolinium-
enhanced T1-weighted image demonstrates a mass with
thick, irregular, enhancing walls and areas of central
. necrosis
39. Pleomorphic xanthoastrocytoma (a) Axial T1-WI. Soft-
tissue (S) and cystic (C) components are noted. (b) Axial
T2-WI shows mild low signal intensity of the soft-tissue
portion of the mass, whereas the cystic portions are
hyperintense. Small “fingers” of vasogenic edema surround
the mass. (c) Contrast-enhanced axial T1-WI shows
intense enhancement of the soft-tissue portion of the mass
. with rim enhancement of the cystic margin
40. SEGA in a 16-year-old boy with a history of psychomotor
developmental delay. (a) Axial T1-weighted MR image shows
bilateral masses (arrows) near the foramen of Monro. The
masses are slightly hypointense compared with the white matter.
(b) On an axial T2-weighted MR image, the masses are slightly
hyperintense compared with the white matter (c) Contrast
enhanced axial T1-weighted MR image shows intense
enhancement of both masses
41. Oligodendrogliomas-2
Oligodendrogliomas appear heterogenous on both T1WI and T2
WI; on T1WI, the tumors appear predominantly hypointense to gray
matter and on T2WI, they are most often hyperintense, with small
intramural cysts, focal calcification and heterogenicity.
3- Ependymal cell tumors:
Most ependymomas arise in the floor of the fourth ventricle. They
have tendency to extend through the foramina of Luschka and
Magendi into the basal cisterns. The tumor is often calcified and
may demonstrate a large cystic component. Inhomogeneous
enhancement is usually seen.
42. :Tumors of Choroid plexus- 4
Most choroid plexus tumors occur as the benign, slowly growing
choroid plexus papilloma, (WHO grade I) tumor with a favorable
overall prognosis. The other 20% of cases manifest as a much more
biologically aggressive (WHO grade III) tumor, the choroid plexus
carcinoma, which is far more common in children than adults.
Choroid plexus tumors have long been associated with
hydrocephalus secondary to an increase in the production of CSF by
the tumor. It shows intense enhancement on contrast enhanced MRI
due to the marked vascularity of these tumors.
43. Choroid plexus carcinoma. (a) Axial T1-weighted MR image
shows the lobulated mass with heterogeneous signal intensity.
(b) On an axial T2-weighted MR image, the mass is slightly
hyperintense compared with the white matter. (c) Contrast
enhanced axial T1-weighted MR image shows intense but
heterogeneous enhancement within the mass. At surgery, the
ventricular wall was traversed by the mass, and histologic analysis
confirmed choroid plexus carcinoma.
44. : Primitive neuro ectdermal tumors
PNET of CNS can be divided into infratentorial tumors
(medulloblastoma) and supratentorial tumors PNET.
Supratentorial PNET : Their most common location is the frontal lobes.
They are often large tumors with lesser degrees of surrounding edema,
demonstrated heterogeniety of signal intensity on both T1WI and T2WI,
the solid portion of the tumor demonstrates strong contrast
enhancement.
Medulloblastomas: In children, medulloblastomas are usually at the
cerebellar vermis, but in adults they tend to be located more laterally in
the cerebellar hemispheres. The tumors are mildly hypointense to
isointense on T1WI, and isointense to hyperintense on T2WI.
45. Contrast enhancement of solid portion of the tumor is seen in more
than 90% of patients; it is typically intense and homogenous but may be
irregular and patchy.
Medulloblastoma (a) Axial T1-weighted MR image shows mild hyperintensity in
the hemorrhagic regions; otherwise the mass is predominantly hypointense. (b)
Axial T2-weighted MR image reveals marked hypointensity in the hemorrhagic
zones. These features are consistent with intracellular methemoglobin. (c)
Contrast-enhanced axial T1-weighted MR image demonstrates heterogeneous
.but intense enhancement of the nonhemorrhagic portions
46. :Dysembryoplastic neuroepithelial tumors
DNET commonly occur above the tentorium, mainly in the
temporal lobe or frontal lobe. They are lesions of long standing
duration that most frequently involve the convexity cortex and often
protrude beyond the adjacent cortical margin, eroding the overlying
inner table of the calvarium. Demonstrated as a mass centered in the
convexity cortex and bulging externally. It is hypointense to adjacent
brain on T1WI and hyperintense on T2WI with no surrounding
edema. The protruding external margin may present as (Soap bubble)
appearance, reflecting internal cystic changes. Contrast enhancement
is seen in only a minority of these lesions.
47. DNET: Axial T2-weighted image (a). Contrast-enhanced axial
T1-weighted image (b) showing no evidence of enhancement
within the mass. Note the protruding external margin.
48. Lymphoma
Most lymphomas occur in patients who are immunocompromised (such
as patients under chemotherapy and patients of (AIDS). Lymphomas
typically appear as homogeneous slightly high signal to isointense masses
deep within the brain on T2 weighted images. They are frequently found
in close proximity to the corpus callosum and have tendency to extend
across the corpus callosum into the opposite hemisphere. Multiple
lesions are presented in 50% of cases. They are associated with only a
mild or moderate amount of peritumoral edema. By time of presentation
they can be quite large and yet produce relatively little mass effect, most
lymphomas show homogeneous contrast enhancement.
49. Primary central nervous system lymphoma. Axial
postcontrast T1-weighted MR image (a) demonstrates a
homogeneously enhancing mass in the right frontal lobe,
which is isointense on the axial fluid-attenuated inversion-
recovery MR image (b), with extensive surrounding T2
hyperintensity.
50. Meningioma
Most commonly they are seen parasagittally (25%). Other locations
include the convexity (20%), sphenoid ridge (15-20%), olfactory groove
(5-10%), posterior fossa 10%, intraventricular region 2% and
extracranial region 1%. Meningiomas are more common in women than
men. They have predilection to occur from the third to sixth decades of
life. They are rare in patients younger than 20 years and if present
commonly are associated with neurofibromatosis type II. The WHO
classified meningiomas into the following three basic groups: benign
meningioma, atypical meningioma and malignant meningioma. Most
meningiomas are usually isointense with cortex on T1 and T2WI. On
non enhanced MRI the majority are of homogenous appearance.
51. The strong, often striking, homogenous contrast enhancement seen
in most meningiomas enables their accurate detection and location.
A thickened tapered extension of contrast enhancing dura is
commonly identified at the margin of the tumors.
Meningioma: Axial post contrast T1 WI showing intense
homogenous enhancement with tapered enhancing extension of the
related dura (dural tail).
52. Schwannoma
This tumor arises from the Schwann cells of the nerve sheath of the
cranial nerves. Most common site of intracranial involvement is the
superior vestibular division of the eighth cranial nerve. On axial
images, the tumor often has a comma-like shape with a globular
cisternal mass medially and a short tapered fusiform extension laterally
into the internal auditory canal. Contrast enhancement is seen in
nearly all Schwannomas; and may be homogenous in two thirds of
cases. On T1WI it appears as homogenous mild hypointense or
isointense to adjacent brain; on T2WI, it appears mildly to markedly
hyperintense and may be obscured by the similarity in signal intensity
to that of the surrounding CSF.
53. Schwannoma (acoustic neuroma_ Contrast enhanced
axial T1-weighted MR image shows a homogeneously
.enhanced, coma-shaped right cerebello-pontine lesion
54. Brain metastasis
Most metastasis is round well-demarcated lesions located at the junction
of gray and white matter. Leaky tumor vessels result in an extensive zone
of edema surrounding the tumor. Most intra-cerebral metastatic lesions
are hypo intense on T1WI and hyper intense on T2WI. Signal intensity
depends on cellularity of the lesion, the extent of intratumoral necrosis,
the presence and age of hemorrhage, the presence and extent of
calcification. Contrast administration facilitate delineation of the tumor
margin. Melanoma has somewhat characteristic appearance if there has
not been previous hemorrhage, the lesion is hyperintense in T1WI and
isointense T2WI most likely because of free radical content of melanin.
55. Dermoid tumors and Epidermoid tumors
Dermoid tumors are thought to arise at the site of neural tube closue at
the midline. This may explain the frequent midline location of dermoid
tumors. In contrast, epidermoid tumors are often located lateral to the
midline of the cranium. Intracranial dermoid tumors usually present in
patients up to 20 years of age. In contrast, epidermoid tumors are most
often first diagnosed in patients aged 40-50 years. Most epidermoid cysts
show a distinctive MR imaging appearance consisting of an irregularly
shaped lesion having slightly higher signal intensity than CSF on T1, T2
and proton density weighted images. Dermoid without fat or calcification
within them may be indistinguishable from epidermoid or arachnoid cysts.
56. Epidermoid cyst To the left: Axial T1-weighted MR
image shows an epidermoid cyst with characteristic focal
marbling in the left CPA (arrow). To the right: Axial T2-
weighted MR image shows the lobulated margins of the
cyst impinging on the pons (arrowhead).
57. Diffusion MRI and Brain Tumors
Diffusion of water molecules.
a) Restricted diffusion: high cellularity and intact cell membranes. Note water )
molecules (black circles with arrows) within extracellular space, intracellular space, and
intravascular space, all of which contribute to measured MR signal. In this highly
cellular environment, water diffusion is restricted because of reduced extracellular
space and by cell membranes, which act as barrier to water movement. (b) Free
diffusion: low cellularity and defective cell membranes. In less cellular environment,
relative increase in extracellular space allows free water diffusion than more cellular
environment would. Defective cell membranes also allow movement of water
.molecules between extracellular and intracellular spaces
58. Role of Diffusion MRI in glioma
Exact differentiation and grading of malignant brain tumors are essential
for proper treatment planning. Although conventional MRI can detect the
location and extent of the tumor, it is sometimes insufficient for
differentiation and grading of malignant brain tumors. Also often some
low-grade tumors may demonstrate peritumoral edema, strong
enhancement, central necrosis, or mass effect. The enhancing pattern of a
tumor is not always reliable for distinguishing high-grade and low-grade
tumors because tumoral enhancement is mainly due to disruption of the
blood brain barrier rather than from tumoral vascular proliferation itself
and these two entities are usually independent of each other.
59. Furthermore, the peritumoral abnormal high signal intensity on T2-
weighted images, is not specific for the tumor because it may reflect
vasogenic edema, the tumoral infiltration, or frequently both, and its
exact nature is indistinguishable by conventional MRI .
Diffusion criteria of gliomas: The signal intensity of cerebral
gliomas on DWI is variable (hyper, iso or hypointense). In high grade
cerebral gliomas, areas of tumors that show significant enhancement on
T1WI obtained after injection of contrast material has lower ADC value
than the ADC of non enhancing tumor and peirtumoral edema. Cystic
or necrotic portions of tumor show the highest ADC value.
60. Glioblastoma multiforme. (a) Contrast-enhanced T1-, (b)
diffusion-weighted images, and (c) ADC map. The necrotic
components are hypo intense on DWI, while the non necrotic
components are slightly hyper intense. The peritumoral
vasogenic edema is isointense to the white matter because the
effect of increased diffusion (dark) is compensated for by the
increased T2 value of edema (bright). The peritumoral edema
,CSF, and necrotic component of the tumor are hyper intense
(high diffusion) on ADC map.
61. Grading of gliomas
Tumor cellularity (and histologic tumor grading) is inversely correlated
with tumor ADC value in various grades of astrocytomas. Glioblastoma
multiforme had the lowest ADC; anaplastic astrocytoma had intermediate
ADC and low-grade astrocytoma had the highest ADC. Although the
ADCs of grade II astrocytoma and glioblastoma overlapped somewhat, the
combination of routine image interpretation and ADC had a higher
predictive value. The lower ADC suggesting malignant glioma, whereas
higher ADCs suggest low-grade astrocytoma. The ADC of anaplastic
astrocytoma (grade III astrocytoma) is intermediate between those of
glioblastoma and grade II astrocytoma.
62. Delineation of gliomas
In malignant gliomas, peritumoral edema, which can be depicted with
either CT or conventional MR imaging, often has been reported to have
infiltrating neoplastic cells. Therefore, the tumor border is still inaccurately
depicted even with imaging techniques. Areas that showed marked signal
suppression with a higher ADC, most likely representing areas of
predominantly peritumoral edema, and areas that showed a lesser degree of
signal suppression with similar but slightly lower ADCs than those of
edema, most likely representing areas of predominantly nonenhancing
tumor. So DWI is a useful technique to distinguish areas of predominantly
nonenhancing tumor from areas of predominantly peritumoral edema.
63. Role of diffusion MRI in cystic brain tumors
Differentiation between brain abscesses and cystic brain tumors such as
high-grade gliomas and metastases is often difficult with conventional
MRI. Diffusion MRI study provides tremendous contribution to
differential diagnosis of these lesions when conventional approaches fail.
The abscess cavity viscosity is highly restricting the microscopic diffusional
movements of water molecules . High signal intensity on DWI and low
ADC value in brain abscesses, in contrast to low signal intensity on DWI
and high ADC value in most tumors or high signal intensity on DWI for
cystic or necrotic tumors is due to T2 shine-through.
64. Cerebral abscess. (a) Transverse contrast-enhanced
T1WI showing rim enhancement of the abscess wall,
(b) DWI showing high signal of the abscess cavity, and
(c) ADC map showing low signal of the abscess cavity
.matching with restricted diffusion
65. Glioblastoma multiforme. (a) Contrast
enhanced T1WI showing rim enhancement of
the solid component, (b) DWI showing low
signal of the necrotic center and (c) ADC map
showing high signal of the necrotic center
matching with free diffusion.
66. Role of Diffusion MRI in meningioma
It is useful to distinguish among benign, malignant and atypical
meningiomas before resection, because it would aid in the surgical and
treatment planning. Atypical and recurrent meningiomas have more
tendency for recurrence. This distinction is neither easily nor reliably
accomplished with conventional MRI. Using diffusion-weighted MR
imaging, atypical and malignant meningiomas tend to be markedly
hyperintense on DWI and exhibit marked decreases in ADC values
when compared to normal brain parenchyma on routine MRI.
Although benign meningiomas have variable appearances on DWI,
. they tend to have higher ADC values compared to the normal brain
67. Left frontal benign meningioma. Hypointense in T1 WIs (a), isointense
in T2 WIs (b), FLAIR (c), uniform contrast enhancement in axial T1WI
(d), hypointense in DWI (e), and iso to hyperintense in ADC (f)
68. Right parietal malignant meningioma. Isointense in T1WI (a),
hyperintense in T2 WI (b), hyperintense in FLAIR (c), uniform contrast
enhancement in axial T1WI (d), markedly hyperintense in DWI (e), and
isointense in ADC (f).
69. Recurrent malignant meningioma. (a) Axial
post-contrast T1WI shows intense enhancement
of meningioma, (b) DWI shows hyper intense
signal, and (c) ADC map shows hypo intense
signal reflecting restricted diffusion due to high
.cellularity
70. Role of Diffusion MRI in lymphoma
The rate of water diffusion in CNS lymphoma, as represented by
ADC value is significantly lower than that of high grade
astrocytoma. The cellularity of lymphoma, as represented by
nuclear to cytoplasmic (N/C) ratio, is significantly higher than
that of astrocytoma. Lymphomas are generally hyperintense to
gray mater on DWI and iso to hypointense on ADC maps,
findings that are consistent with lower diffusivity. In contrast,
high grade astrocytomas are generally hypo- or hyperintense to
. the gray matter
71. Primary CNS lymphoma. (a) Axial contrast-enhanced
T1-, (b) Axial FLAIR shows perilesional edema. (c) ADC
map shows low signal intensity within the enhancing tumor
and high signal intensity in peritumoral edema. This is
denoting restricted diffusion at the tumor and facilitated
diffusion at the peri-lesional edema du to high N/C ratio.
72. Role of Diffusion MRI in metastasis
The signal intensity of non-necrotic component of cerebral metastasis
on DWI is variable (generally iso or hypointense, occasionally hyper
intense). The necrotic component of metastasis shows marked signal
suppression on DWI and increased ADC values. The signal intensity
of the solid component depend on the tumor cellularity. Metastasis
from well differentiated adenocarcinomas has significantly higher
ADC values than in poorly differentiated adenocarcinomas and lesions
other than adenocarcinoma. The signal intensity of the necrotic
component is related to increased free water.
73. Multiple metastases. Axial contrast-enhanced T1- (a)
diffusion (b) weighted images, and corresponding
ADC map (c). Free diffusion of the necrotic
component is noted with low signal in DWI and high
.signal in ADC map
74. Role of Diffusion MRI in Differential diagnosis of
cyst like tumor lesions
Epidermoid tumors appear sharply hyperintense on DWI relative to the
brain and CSF; however, have higher signal intensity on ADC maps than
that of the brain. Apparently, this hyperintensity on DWI should not be
attributed to a decrease in ADC, but should be attributed to the T2 shine-
through effect, meaning that the T2 properties dominated the
contributions to DW signal intensity and even overwhelmed the effect of
signal attenuation resulting from the increase in ADC. The differential
diagnosis of epidermoid and arachnoid cyst is straightforward on DWI.
(The epidermoid cyst is bright, while the arachnoid cyst is dark on DWI).
75. Arachnoid cyst (a) Axial T1 post contrast image, (b) Axial T2
WI, (c) DWI showing low signal and (d) ADC map showing high
signal due to free diffusion.
76. Epidermoid cyst (a) T1 WI , (b) T2 WI , (c) FLAIR, (d) DWI
showing high signal due to T2 shine through effect and (e)
ADC map showing that epidermoid cyst has diffusion rate
relatively more than normal brain parenchyma.
77. Role of Diffusion MRI in differentiation of Cerebellar
Tumors in Children
ADC values and ratios are simple and readily available
techniques for evaluation of pediatric cerebellar neoplasms
that may accurately differentiate the 2 most common tumors,
JPA and medulloblastoma. Proposed cutoff values of (>1.4
× 10−3 mm2/s) for JPA and (<0.9 × 10−3 mm2/s) for
medulloblastoma seem to reliably provide the diagnosis,
which may affect further diagnostic studies, treatment plan,
and prognosis. Ependymomas are also significantly different
from other tumor types, and in most of cases show ADC
values (1.00–1.30 × 10−3 mm2/s).
78. Scatter diagram of average ADC tumor values for all pilocytic
astrocytomas (JPA), ependymomas (Epend) and medulloblastomas
(Medullo) (open circles) along with their respective mean (full circles)
and standard deviation (bars) values. ADC values are expressed in
10−3 mm2/s.
79. Fifteen-year-old girl with cerebellar JPA. ADC map in
axial plane at level of middle cerebellar peduncles shows
well defined, oval mass in right paramedian location with
increased diffusion
80. Sixteen-year-old boy with ependymoma
A, Axial T2-weighted image at level of middle cerebellar peduncles
shows a very heterogeneous abnormality (arrows) within the fourth
. ventricle
B, Corresponding contrast-enhanced T1-weighted image
demonstrates enhancement of the solid portion of this mass
(. (arrows
C, ADC map at a level similar to that of A and B shows that
diffusion within the solid portion of the tumor (arrows) is slightly
. higher compared with normal cerebellum
81. 22-year-old woman with desmoplastic cerebellar
medulloblastoma. Axial ADC map at level of middle
cerebellar peduncles reveals lesion of decreased
diffusion in left cerebellar hemisphere (arrow). No
significant surrounding edema is seen.
