Normal & abnormal radiology of brain part ii

Normal and Abnormal
Radiology of CNS (Part II)
Mohammed Fathy Bayomy, MSc, MD
Lecturer
Clinical Oncology & Nuclear Medicine
Faculty of Medicine
Zagazig University

Role of Imaging
 Radiological diagnosis: tumor vs. non-tumor, determine a
certain subtype, grading.
 Take a biopsy to get histopathogical diagnosis.
 Detect squeal: parenchyma compromise, mass effects
 Treatment planning: extent of tumor >>> resection
 Localization for therapeutic modalities: RT, stereotaxic surgery:
tumor vs peritumoral edema.
Diagnosis
Treatment
 Evaluation of response: residual tumor vs treatment necrosis
Monitoring
 Tumor recurrence
Surveillance

Imaging of Brain Tumours
 Primarily of historical interest since the onset of CT in
1974.
 Rarely necessary.
 Useful in demonstrating calcification, erosion, or
hyperostosis.
 Most widely used for diagnosis of brain tumors.
 Will detect >90% of tumors, but might miss: Small
Tumors (<0.5 cm), Tumors Adjacent to bone (pituitary
adenomas, clival tumors, and vestibular schwannomas),
Brain Stem Tumors, Low Grade Astrocytomas.
 More sensitive than MRI for detecting acute
hemorrhage, calcification, and bony involvement.
SkullX-
rays
CT
 Preferred for follow-up of most brain tumors.
 More sensitive than CT scans.
 Can detect small tumors.
 Provides much greater anatomic detail.
 Especially useful for visualizing skull base, brain stem, &
posterior fossa tumors.
MRI

1- Density (CT number)
Structure/ Tissue Hounsfield units
Air -1000 to -600
Fat -100 to -60
Water 0
CSF +8 to 18
White matter +30 to 41
Gray matter +37 to 41
Acute blood +50 to 100
Calcification +140 to 200
Bone +600 to 2000
HYPERHYPOISO

(A) Hyperdense
5- Acute blood
6- Ocular
lens
4- Calcifications
2- Bone
1-Metal (bullets streak artifact)
Density>White/Gray matter
3- Contrast (dye)

(B) Isodense
Density=White/Gray matter
White matter
Gray matter
(cerebral cortex)
Gray matter
(basal ganglia)
White matter is less dense
than gray matter and
therefore: white matter is
darker than gray matter
High
attenuation
Low
attenuation
Bright Dark

(C) Hyodense
Density<White/Gray matter
CSF (water)
Fat
Air

Manipulation of image gray scale using image’s
CT numbers
* No additional or new information produced
2- Window

* Soft tissues
* Brain
* Dense structures
- Bone
Manipulation allows customization of visibility
2- Window

Window width (WW)
Window level (WL)
Range of CT number’s
imaged
Center or midpoint of
CT # range
WIDT
H
BON
E
MATERIAL
S
3095
-1000
0
LEVEL
LEVEL WIDT
SOFT
TISSUE
WATER
FAT
AIR
2- Window

• Pixels outside of window displayed as
Black or White
255
0
-1000 1000HU
CT Value
Window level
Grey
value Window width
2- Window

>200
151-200
101-150
51-100
1-50
(-49)-0
(-99)-(-50)
(-149)-(-100)
(-199)-(-150)
<(-199)
3000
-1000
0
1000
2000
Window: 400
Level: 0
2- Window

Small Window
Width
3000
0
-1000
Window: 400
Level: 0
Short gray scale
Small block of CT #’s
assigned gray levels
Small transition zone
of white to black
2- Window

3000
0
-1000
Window: 400
Level: 0
Used to display soft
tissues within
structures containing
different tissues of
similar densities.
Level centered near
average CT # of organ
of interest.
Small Window
Width
2- Window

Large Window
Width
0
1000
Window:
2000
Level: 0
-1000
Long gray scale
Large block of CT #’s
assigned gray levels
Large transition zone
of white to black
2- Window

Large Window Width
0
1000
Window:
2000
Level: 0
-1000
Used where large
latitude required
Used to
simultaneously
display tissues of
greatly differing
attenuation.
2- Window

Example 1
WL =0
WW = 200
All pixels with CT #’s > 0
+(200/2) = 100: White
All pixels with CT #’s < 0 -
(200/2) = -100: Black
100
-100
200 0
2- Window

WL = 40
WW = 200
All pixels with CT #’s > 40 +
(200/2) = 140: White
All pixels with CT #’s < 40 -
(200/2) = -60: Black
140
-60
200 40
Example 2
2- Window

WL = 0
WW = 400
All pixels with CT #’s > 0
+ (400/2) = 200: White
All pixels with CT #’s < 0
- (400/2) = -200: Black
200
-200
400 0
Example 3
2- Window

Larger Window Means
Obscuring Small Differences in
Tissue Attenuation
One gray shade
encompasses larger
range of CT #’s
200
-200-100
100
20 - 40 40 - 8020 40
WW=200 WW=400
Range
2- Window

• As WW increases
– Contrast decreases
– Latitude (range of CT #’s imaged) increases
• As WW decreases
– Contrast increases
– Latitude decreases
• Clinical goal:
– Largest available contrast at
the latitude required by study
Window Width & Contrast
2- Window

• Large window width
– Different structures more likely to have same gray
shade
• Narrow window width
– Gray shade differences more likely visible
between structures
• Very narrow window width
– Small differences in attenuation seen as black &
white
Window Width & Image Contrast
2- Window

Common window
settings used when
interpreting a normal
CT Brain scan:
A: Brain window (WW
80, WL 40);
B: Bone window (WW
3000, WL 500);
C: Soft tissue window
(WW 260, WL 80);
D: Stroke window
(WW 40, WL 40).
2- Window

3- Multiplanar Reconstruction (MPR)
• Creates non-axial images from stack of
contiguous transverse axial scans
–stack contains 3 dimensional CT data
–pixels new cut identified & selected from
each axial image without scanning

• Coronal
• Sagittal
• Paraxial
• Oblique
Cuts

Coronal Reconstruction
Stack of
Axial Slices
Reconstructed
Slice

Stack of
Axial Slices
Reconstructed
Slice
Coronal Reconstruction

Stack of
Axial Slices
Reconstructed
Slice
Sagittal Reconstruction

Stack of
Axial Slices
Reconstructed
Slice
Oblique Reconstruction

• Enables visualization of specific
structures relative to surrounding
structures
• Aids in determining / localizing true
extent of
– Lesions
– Fractures
– Bone fragments
– Foreign bodies
Reformatting Advantages

Reformatting Disadvantages
• Image quality can be poorer than axial
images if plane thickness > pixel size
– Affects blurring
• Less problem in spiral scanning

Reformatting Disadvantages
• More prone to motion / breathing artifacts
– Reformatted image taken from many slices
– Reformatted image represents longer time
interval than single slice

4- Contrast
Physiological contrast enhancement
• Pituitary gland & its stalk.
• Dural structures.
• Arteries and veins especially deep veins and
sinuses.
• Choroid plexus

Magnetic Resonance
Imaging (MRI)

Advantage of MRI
 No ionizing radiation & no short/long-term effects demonstrated
 Variable thickness, any plane
 Better contrast resolution & tissue discrimination
 Various sequences to play with to characterize the abnormal
tissue
 Many details without I.V contrast
 No allergy (as with Iodine)
 Can be used in renal impairment
 Pregnancy is not a contraindication

Caveats of MRI
 Very sensitive to body movements
 Produces lots of noise during examination (The noise is due to
the rising electrical current in the wires of the gradient magnets
being opposed by the main magnetic field. The stronger the
main field, the louder the gradient noise)
 Time taking
 Difficult to perform in claustrophobic pts
 Expensive
 Less sensitive for SAH
 Less sensitive for detection of calcification
 Relatively insensitive to bony cortical abnormalities
 Peoples with metallic implants can not be scanned

Principle of MRI1- The Patient Is Placed In A Magnetic Field.
2- A Radio Frequency (RF) Wave Is Sent In.
3- The Radio Frequency Wave Is Turned Off.
4- The Patient Emits A Signal.
5- Which Is Received And Used For Reconstruction Of the
Picture

MRI Sequences
 CSF flow studies
 Diffusion weighted sequences (DWI): apparent diffusion coefficient (ADC), b-values, diffusion
tensor imaging (DTI)
 Echo-planar pulse sequences
 Fat-suppressed imaging sequences
 Gradient echo sequences: in-phase and out-of-phase, spoiled gradient echo MRI, steady-
state free precession
 Inversion recovery sequences: short tau inversion recovery (STIR), fluid attenuation inversion
recovery (FLAIR), turbo inversion recovery magnitude (TIRM), double inversion recovery (DIR)
 Metal artifact reduction sequence (MARS)
 Perfusion-weighted imaging (PWI): dynamic susceptibility contrast (DSC) MR perfusion,
dynamic contrast enhanced (DCE) MR perfusion, arterial spin labeling (ASL) MR perfusion,
cerebral blood flow (CBF), cerebral blood volume (CBV), k-trans, mean transit time (MTT),
negative enhancement integral (NEI), time to peak (TTP)
 Saturation recovery sequences
 Spin echo sequences: T1WI, T2WI, fast spin echo (FSE), proton density weighted image
 Spiral pulse sequences
 Susceptibility-weighted imaging (SWI)
 MR angiography (and venography): contrast-enhanced, non-contrast-enhanced MRA (phase
contrast imaging, time of flight angiography, TRICKS)
 MR spectroscopy (MRS)

Important MRI Sequences
• Conventional sequences: T1WI, T2WI, FLAIR,
Post contrast T1WI
• DWI.
• PWI.
• DTI.
• SWI.
• GRE.
• MRS.
• MRA.
• MRV.

 Short TE (echo time).
 Short TR (repetition time).
 Better anatomical details.
 Fluid: dark.
 Gray matter: gray.
 White matter: white.
T1WI sequence
Charactertics
 Most of pathologies are dark
(hypointense) in T1
 Bright (hyperintense) in T1
(see below)

T2WI sequence
 Long TE (echo time).
 Long TR (repetition time).
 Better pathological details.
 Fluid: bright.
 Gray matter: relatively bright.
 White matter: dark.
Charactertics
 Most of pathologies are bright
(hyperintense) in T2
 Dark (hypointense) in T2
(see below)

FLAIR* sequence
 Long TE (echo time).
 Long TR (repetition time).
 Better pathological details.
 Fluid: dark (free water suppression).
 Gray matter: relatively bright.
 White matter: dark.
Charactertics
 Most of pathologies are bright
(hyperintense) in FLAIR
 Good for lesions near ventricles of
sulci
* Fluid Attenuated Inversion Recovery Sequences
i.e. T2 except fluid inversion

T1WI vs T2WI vs FLAIR
T1WI T2WI FLAIR
TR Short Long Long
TE Short Long Long
CSF Low High Low
Fat High Low Medium
Brain Low High High
Edema Low High High

Contrast
 Principles of contrast uptake are same in CT and MRI i.e.
enhancement of CNS pathology due to disruption of blood
brain barrier.
 Unlike contrast agents used in CT which are directly visualized
those used in MRI produce local alteration in the magnetic
environment that influences the MRI signal intensity.
 It is the effect of proton relaxation that appears on MRI and not
the contrast itself.
 Gadolinium is a paramagnetic agent responsible for T1
shortening of MR images
 Shortening of T1 leads to higher signal intensity on a T1WI
hence areas of gad accumulation appear bright on T1
 Though it also shortens T2, effect is less as compared to T1
 Standard dose of Gad is 0.1 mmol/kg

Physiological contrast enhancement
• Pituitary gland & its stalk.
• Median eminence
• Dural structures.
• Arteries and veins especially deep veins and
sinuses.
• Choroid plexus
Contrast

Post contrast T1WI sequence
 Intravascular (vascular)
enhancement may reflect
neovascularity, vasodilatation or
hyperemia, shortened transit time or
shunting.
 Interstitial enhancement indicates
abnormal BBB.
Enhancement
Medulloblastoma

DWI* sequence
 Normally water protons have ability
to diffuse extracellularly & loose
signal.
 In most tumors there is no restricted
diffusion even in necrotic or cystic
components >>> This results in a
normal low signal on DWI.
Not Restricted
* Diffusion Weighted Image
 High intensity on DWI indicates
restriction of ability of water protons
to diffuse extracellularly (e.g.
Cytotoxic edema, abscess, acute
ischemia).
Restricted

ADC* sequence
* Apparent Diffusion Coefficient
 Calculated by software.
 Areas of restricted diffusion are dark
 True restricted diffusion, the region of increased DWI signal
will demonstrate low signal on ADC.
 T2 shine-through, ADC will be normal or high signal.
DWI AD
C
ADC map
RO
I

PWI* sequence
 Perfusion imaging can play
important role in determining
malignancy grade of CNS tumor.
 Perfusion depends on vascularity
of tumor & is not dependent on
breakdown of blood-brain barrier.
 Amount of perfusion shows a
better correlation with grade of
malignancy of tumor than amount
of contrast enhancement.
* Perfusion Weighted Image
Cerebral Blood Volume (CBV)
Cerebral blood flow (CBF)
Map
Time To Peak (TTP)
relative Cerebral Blood Volume (rCBV)
Mean Transit Time (MTT)

Axial MRI T1 showing hypointense mass in
right frontal lobe which appears hyperintense
on T2 and shows increased perfusion values
with elevated choline peak values confirming a
high grade glioma.
Left, Fluid-attenuated inversion recovery
(FLAIR) image demonstrates an area of
increased signal intensity in parietooccipital
region.
Right, Perfusion MRI demonstrates decreased
relative cerebral blood volume (rCBV),
consistent with a low-grade neoplasm.
The final pathologic diagnosis was a grade II
astrocytoma.
Low GradeHigh Grade
PWI* sequence

GRE* sequence
* Gradient Recalled Echo
FLAIR T1 GRE
 Generation of gradient echoes as a consequence of echo
refocusing. The initial slice selective RF pulse applied to the
tissue is less than 90° (typically rotation angles are between
10° and 90°). Immediately after this RF pulse, the spins
begin to dephase.

SWI* sequence
* Susceptibility weighted imaging
 Originally called BOLD venographic imaging
 MRI sequence that is exquisitely sensitive to venous blood,
hemorrhage and iron storage. SWI uses a fully flow
compensated, long echo, gradient recalled echo (GRE) pulse
sequence to acquire images.
Glioblastoma multiforme
(a) T1WI+C
(b, c) SWI

MRS*
* Magnetic Resonance Spectroscopy
 Non-invasive physiological imaging of brain that measure
relative of various tissue metabolites.
 Used to complement MRI in characterization of various
tissues
4 3 2 1 0
ppm
NAA
Glx
Cr
Cho
ml
Differentiate Neoplasms
from Nonneoplastic
Brain Masses
Radiation
Necrosis versus
Recurrent Tumor

Resonating Normal function Change
Lipids 0.9 & 1.3 Cell membrane  High grade
neoplasia
Metabolite
Lactate 1.3 Anaerobic
glycolysis
 Neoplasia,
necrosis
Alanine 1.5 Amino acid  Meningioma
Acetate 1.9 Anabolic
precursor
 Neoplasia
NAA 2 Neural marker  Neoplasia,
necrosis
Creatine 3.03 Cell energy marker  Neoplasia
Choline 3.2 Marker of cell
memb. turnover
 Neoplasia
MRS

Normal
NAA/Cr 2.0
Metabolite Ratios
NAA/Cho 1.6
Cho/Cr 1.2
Cho/NAA 0.8
Myo/NAA 0.5
Abnormal
<1.6
<1.2
>1.5
>0.9
>0.8
 Cho/Cr
 Myo/NAA
 Cho/NAA
 NAA/Cr
 Lipid/lactate
Indicate
Malignancy
MRS

MRA*
* Magnetic Resonance Angiography

MRV*
* Magnetic Resonance Venography

Normal Radiology
of Brain
Mohammed Fathy Bayomy
Assistant Lecturer of Clinical
Oncology Zagazig University

1- Skull Bones and Sutures
Bone windows
Bones of the skull are assessed viewing the
'bone window' CT images
Note that no detail of brain structure is provided
on these window settings

Tentorium cerebelli
3- Meninges & Dural folds

Falx cerebri

Falx and tentorium

4- CSF spaces
The brain is surrounded by cerebrospinal
fluid (CSF) within Subarachnoid spaces,
Cisterns. CSF is also found centrally within
the ventricles.

4- CSF spaces
1- Subarachnoid spaces,
2- Cisterns,
3- Ventricles.
Together form the 'CSF spaces', also known
as the 'extra-axial spaces'.

• CSF is of lower density than the grey or
white matter of the brain, and therefore
appears darker on CT images.
• An appreciation of the normal
appearances of the CSF spaces is
required to allow assessment of brain
4- CSF spaces

Lateral Ventricles
4- CSF spaces

Fourth Ventricle
4- CSF spaces

Subarachnoid spaces
4- CSF spaces

Cisterns
4- CSF spaces
Pentagon Cistern
Basal
Cistern Perimesencephalic
cistern

Cisterns
4- CSF spaces
Sylvian
cistern
Lamina terminalis
cistern
Interpeduncular
cistern
Pentagon Cisterns

Cisterns
4- CSF spaces
Perimesencephalic Cisterns

Cisterns
4- CSF spaces
Pericallosal cistern

Cisterns
4- CSF spaces
Lamina terminalis cistern

Cisterns
4- CSF spaces
Suprasellar (Chiasmatic) cistern

Cisterns
4- CSF spaces
Interpeduncular Cistern

Cisterns
4- CSF spaces
Pontine Cistern

Cisterns
4- CSF spaces
Crual Cistern

Cisterns
4- CSF spaces
Ambient Cistern

Cisterns
4- CSF spaces
Sylvian Cistern

Cisterns
4- CSF spaces
Supracerebellar Cistern

Cisterns
4- CSF spaces
Quadrigeminal Cistern
**

Cisterns
4- CSF spaces
Cisterna Magna (Cerebellomedullary cistern)
*

Grey matter vs white matter
5- Brain parenchyma

Brain lobes
5- Brain parenchyma

Lobes vs regions
5- Brain parenchyma
• CT does not clearly show the anatomical borders of the
lobes of the brain. For this reason radiologists often refer
to 'regions', such as the 'parietal region' or 'temporal
region', rather than lobes.
• If more than one adjacent region needs to be described
then conjoined terms can be used such as 'temporo-
parietal region' or 'parieto-occipital region'

Lobes vs regions
5- Brain parenchyma

Cerebral cortex
6- Gray Matter structures

Insula

Basal ganglia and thalamus

Internal Capsules & Corpus Callosum
6- White Matter structures

Corpus Callosum

Corpus Callosum & Corona Radiata
Corpus callosum - clinical
significance
 Malignant lesions of the
brain can grow from one
brain hemisphere to the
other via the corpus
callosum
 Elsewhere the falx acts
as a relative barrier to
direct invasion

8- Calcified Structures
Calcified choroid plexus

Calcified pineal gland

Calcified basal ganglia

Calcified falx cerebri

Level of above Corpus Callosum
Axial

CT-Axial

Level of body Corpus Callosum
CT-Axial

Level of Mid-ventricle
CT-Axial

Level of Third ventricle
CT-Axial

Level of Medulla
CT-Axial
External Auditory
canal
Fourth
Ventricle

Level of foramen magnum
CT-Axial

T1WI – Axial
Frontal Lobe
Parietal
Lobe

T2WI – Axial
Frontal Lobe
Parietal
Lobe

Level of Body of Corpus Callosum
T1WI – Axial
Body of
corpus
callosum
Frontal Lobe
Parietal
Lobe

Level of Body of Corpus Callosum
T2WI – Axial
Body of
corpus
callosum
Frontal Lobe
Parietal
Lobe

T1WI – Axial
Genu of corpus
callosum
Splenium of
corpus
callosum
Choroid plexus
éin body of lateral
ventricle
Septum
Pallicidum

T2WI – Axial
Genu of corpus
callosum
Splenium of
corpus
callosum
Choroid plexus
éin body of lateral
ventricle
Septum
Pallicidum

Level of Thalamus
T1WI – Axial
Frontal horn
Frontal Lobe
Caudate
nucleus
Putamen
Internal
capsule
Thalamus
Choroid
plexus éin
occipital horn
Temporal
Lobe
Superior
Sagittal Sinus

Level of Thalamus
T2WI – Axial
Frontal horn
Frontal Lobe
Caudate
nucleus
Putamen
Internal
capsule
Thalamus
Choroid
plexus éin
occipital horn
Temporal
Lobe
Superior
Sagittal Sinus
Retrothalamic
Cistern
Supracerebellar
Cistern

Level of Third Ventricle
T1WI – Axial
Frontal Lobe
Sylvian fissure
Insular Cortex
Temporal Lobe
Occipital Lobe
Third ventricle
Occipital
hornSupracerebellar
cistern

Level of Third Ventricle
T2WI – Axial
Frontal Lobe
Sylvian fissure
Insular Cortex
Temporal Lobe
Occipital Lobe
Third ventricle
Occipital
hornSup. cerebellar
cistern

Level of Midbrain
T1WI – Axial
Orbit
Optic chiasma
Infundibulum Suprasellar
cistern
Midbrain
Aqueduct of
Sylvius
Ambient
cistern
Quadrigeminal
cistern
Cerebellum
Sup. cerebellar
cistern
Hippocampus

Level of Midbrain
T2WI – Axial
Orbit
Optic chiasma
Infundibulum Suprasellar
cistern
Midbrain
Ambient
cistern
Quadrigeminal
cisternCerebellum
Sup. cerebellar
cistern
Temporal
horn
Hippocampus

Level of Pons
Vermis
IV Ventricle
Pons
Basilar A.
ICACavernous
sins
Middle cerebellar
peduncle
Internal Auditory
canal
Temporal lobe
T1WI – Axial

Level of Pons
Vermis
IV Ventricle
Pons
Basilar A.
ICACavernous
sins
Middle cerebellar
peduncle
Temporal lobe
T2WI – Axial

Level of Medulla
T1WI – Axial
Maxillary
Sinus
Flow void of
vertebral A.Medulla
oblongata
Cerebellum

Level of Medulla
T2WI – Axial
Flow void of
vertebral A.Medulla
oblongata
Cerebellum

Level of Forman Magnum
T1WI – Axial
Cisterna
Magna
Cervical
cord
MandibleNasopharynx
Maxillary
Sinus

Normal & abnormal radiology of brain part ii

Normal & abnormal radiology of brain part ii

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