mri brain anatomy
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MR IMAGING OF BRAIN
Muhammad Bin Zulfiqar PGR II SIMS/SHL
New Radiology Department
Basics of MR
• MR sequences
• MR signal characteristic
MRI----conventional sequences
• SE sequence ( spin echo )– T1-weighted,T1-WI
TR: 200-800ms TE:15-30ms
– T2-weighted,T2-WI
TR:1500-2000ms TE:60-150ms
– Proton Density,N(H) ) TR:1500-2500ms TE:15-30ms
• IR sequence ( inversion recovery sequence ) TR ( short ) TE ( short ) TI ( short )
MR signal characteristics
• SE sequences :– T1-WI: highest signal on fat tissue ,better for showing
anatomical structures
– T2-WI: highest signal in liquid, better for detecting lesions
– N ( H ) Density(H): for characteristics of lesions
• GRE sequence : flip angle , fast scan• IR sequence : separation between of fat and
liquid
T2WI T1WI
MR signal characteristics
Fat supression Liquid supression
MR signal characteristics
THREE DIMENSIONAL BRAIN ANATOMY
Fig. 1.1 Post Contrast Axial MR Image of the brain
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Post Contrast sagittal T1 Weighted M.R.I.
Section at the level of Foramen Magnum
Answers1. Cisterna Magna
2. Cervical Cord
3. Nasopharynx
4. Mandible
5. Maxillary Sinus
Fig. 1.2 Post Contrast Axial MR Image of the brain
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Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of medulla
Answers
6. Medulla
7. Sigmoid Sinus
Fig. 1.3 Post Contrast Axial MR Image of the brain
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Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of Pons
Answers
8. Cerebellar Hemisphere
9. Vermis
10. IV Ventricle
11. Pons
12. Basilar Artery
13. Internal Carotid Artery
14. Cavernous Sinus
15. Middle Cerebellar Peduncle
16. Internal Auditory Canal
17. Temporal Lobe
Fig. 1.4 Post Contrast Axial MR Image of the brain
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Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of Mid Brain
Answers18. Aqueduct of Sylvius
19. Midbrain
20. Orbits
21. Posterior Cerebral Artery
22. Middle Cerebral Artery
Fig. 1.5 Post Contrast Axial MR Image of the brain
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Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of theIII Ventricle
Answers23. Occipital Lobe
24. III Ventricle
25. Frontal Lobe
26. Temporal Lobe
27. Sylvian Fissure
Fig. 1.6 Post Contrast Axial MR Image of the brain
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Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of Thalamus
Answers
28. Superior Sagittal Sinus
29. Occipital Lobe
30. Choroid Plexus within the
occipital horn
31. Internal Cerebral Vein
32. Frontal Horn
33. Thalamus
34. Temporal Lobe
35. Internal Capsule
36. Putamen
37. Caudate Nucleus
38. Frontal Lobe
Fig. 1.7 Post Contrast Axial MR Image of the brain
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Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of Corpus Callosum
Answers39. Splenium of corpus callosum
40. Choroid plexus within the
body of lateral ventricle
41. Genu of corpus callosum
Fig. 1.8 Post Contrast Axial MR Image of the brain
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Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of Body of Corpus Callosum
Answers
42. Parietal Lobe
43. Body of the Corpus Callosum
44. Frontal Lobe
Fig. 1.9 Post Contrast Axial MR Image of the brain
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Post Contrast sagittal T1 Wtd M.R.I.
Section above the Corpus Callosum
Answers
45. Parietal Lobe
46. Frontal Lobe
Normal anatomical structure of head on MRI
T2WI
T1WI
Flair sequence
T2WI(coronal section )
T1WI ( sagittal section )
Corpus callosum; optic chiasm; pituitary gland; medulla oblongata
MRI diagnosis of brain vascular diseases
• Intra cerebral Hemorrhage
• Cerebral Infarction
• Intracranial Aneurysm
Brain bleed (hemorrhage)
• Causes : high blood pressure, vascular malformation and tumor
• Stage : acute, sub acute, chronic
MRI appearances of hemorrhage at different stage
• Acute hemorrhage MRI - iso-intensity on T1WI, slightly low or low intensity on T2WI( ideally MR was poor than CT for Acute hemorrhage ).
• Sub acute hemorrhage MRI - iso- or high signal intensity on T1WI, iso- or slightly high signal intensity on T2WI.• Chronic hemorrhage MRI - high signal intensity both on T1WI/T2WI.
acute/subacute hemorrhage
acute
subacute T2WI T1WI
Chronic intracranial hemorrhage
MRI diagnosis of cerebral infarction
MR appearances of cerebral infarction
• High signal intensity at Acute , subacute and chronic stage on T2WI because of increment of fluid at infarction.
• Iso-intensity at acute stage , iso- or slightly low intensity at subacute stage, low intensity at chronic stage on T1WI.
• Flair and DWI sequences are more sensitive for detecting acute infarction.
MR:44396
MR&CT appearances of acute MR&CT appearances of acute cerebral infarctioncerebral infarction
T2WI T1WI Flair
MR:44396
MR&CT appearances of acute cerebral MR&CT appearances of acute cerebral infarctioninfarction
Flair T1WIT2WI
Acute infarction
Acute infarction
Acute infarction DWI
Subacute/chronic infarction—T2WI
T2WI--Coronal
Chronic infarction at brain stem and cerebellum—T2WI
Chronic infarction at brain stem and cerebellum—T1WI
MRI diagnosis of head trauma
The types of head trauma
Skull fracture traumatic cerebral swelling brain contusions Intracranial bleed of trauma
– Epidural hematoma– Subdural hematoma– Subarachnoid hemorrhage– Intracerebral hematoma
MR diagnosis of cranial trauma
Epidural hematoma:direct violence on skull ٭
skull fracture and deformation٭
direct laceration or tearing of meningeal arteries٭
local hematoma ,not across cranial suture ٭
shape of duple convex mirror٭
MR appearances
shape of hematoma is biconvex ٭ signal intensity of hematoma varies greatly depending ٭
on times. at acute stage ٭ ( 0~2 days ), iso-intensity on T1WI ,
low intensity on T2WI.at subacute stage٭ ( 3~14 days ), becoming high
signal intensity from rim to center on T1WI, still low signal intensity at 6~8 days and high signal intensity after 8 day on T2WI.
at chronic stage (14 days later) , high signal intensity on ٭both T1WI and T2WI for quite long times (may be several months)
Subacute hematoma at left frontal lobe
Subacute hematoma at left frontal lobe
Subdural hematoma
.Location: supratentorial convexity٭ .Caused by stretching and tearing of bridging veins ٭ Hematoma is located between dura mater and ٭
arachnoid. Often quite large extent , across cranial suture.
MR appearances ٭ : shape of hematoma semilunar , signal changes of hematoma similar to epidural hematoma at different stages.
Subacute Subdural Hematoma
Axial T1-weighted magnetic resonance imaging demonstrates bilateral subacute subdural hematomas with increased signal intensity. Areas of intermediate intensity represent more acute hemorrhage into the subacute collections.
T2-weighted magnetic resonance imaging in a patient with subdural hematoma shows blood products of differing ages.
Subacute subdural hematoma at left frontal-temporal area
Subacute subdural hematoma at left frontal-temporal area
MR Features of brain contusion
.Often involve the temporal and frontal lobe ٭
• Temporal lobe lesions tend to lie just above the petrous bone or posterior to the greater sphenoid wing.
• Frontal lobe lesions occur just above the cribriform plate, orbit, planum sphnoidale, and lesser sphenoid wing.
MR appearances
MR is more sensitive than CT to find small contusion ٭ because of easy to find edema caused by contusion.
hemorrhagic foci appear petechia or multiple confluent٭regions with high signal intensity.
.easy to find contusion at brain stem ٭
Contusion and epidural hemorrhage at both temporal lobe and frontal lobe
Contusion and epidural hemorrhage at both temporal lobe and frontal lobe
Multiple contusions at both sides of frontal and temporal lobes
Multiple contusions at both sides of frontal and temporal lobes
INTRACRANIAL TUMORS
,primary (80%) :originating from cranial bone ٭
cranial meninges, brain tissues,
vessels, cranial nerves, pituitary
gland, etc.
glioma(50%) , meningioma(14%) , pituitary
tumor (11%) , acoustic neuroma(7%)
secondary (20%) : metastasis , involved by tumor٭
from near structures.
The types of intracranial tumors
• Intraaxial brain tumors : 1.glioma( astrocytoma and oligodendroglioma)
2.ependymoma
3.medulloblastoma
4.hemangioblastoma
5.papilloma choroideum
6.metastases
The types of intracranial tumors
• Extraaxial brain tumors 1.meningioma 2.craniopharyngioma 3.pituitary tumor 4.nerve sheath tumors-acoustic schwannoma 5.epidermorid cyst, dermoid cyst and hamartomas
Direct signs 1. tumor or occupying lesion. 2. abnormal density or signal. 3. enhancement in different degree on enhanced scan.
CT and MRI Signs for diagnosis
of intracranial tumors
、、
Indirect signs
1. shift of near structures 2. edema in brain tissue near tumor 3. Intratumoral bleed 4. Intratumoral calcification 5. bone changes
Astrocytoma
lower grading of astrocytoma , grading I or II .
• Often in adult (20~40years ) -- more occult in cerebral hemisphere , grading II , solid
• child– less seen , more in cerebellum , grading I, cyst
Astrocytoma MR : Isointensity on T1WI , unclear border , high or slightly high signal intensity on T2WI no or slight occupying effect , no or slight enhancement.
Grade I Astrocytoma
T1WI T2WI
Grade II astrocytoma
T2W Gd+ Gd+
MR:39547
Astrocytomahigh grading ( grading III or IV)
• Fast growing
• Occur in any age
Imaging appearances of high grading astrocytoma
• Obvious occupying effects ,infiltrating growing with unclear margin , growing across lobe and hemisphere.
• Necrosis, cyst , bleed. • Obvious brain edema around tumor.• Obvious uneven or ring-like enhancement.
Grade IV astrocytoma
MR:39985
T2W T1W Gd+
Grade IV
astrocytoma
MR:39985
T2W Gd+
T2W Gd+
MR : 53847
Grading IV astrocytoma
Brain metastasis
• Old age• Single or multiple • Multiple appearances on CT or MR, but often
shown in nodule • Heterogeneous density or signal, central
necrosis with lower density or signal on T1WI.• Ring-like or even enhancement• Obviously finger-like peritumoral edema
Multiple metastases
Metastasis from lung cancer
uncontrast contrast
Metastasis from lung cancer
uncontrast contrast
Imaging of meningioma
• Round or hemishere mass occur mostly in convexity of brain , especially sagittal sinus.
• Mass with clear margin which was encysted with cerebral spinal fluid and/or vessels.
• Iso- or slightly high density on plain CT and low signal on T1WI, iso- or slightly high signal on T2WI, which was enhanced obviously and evenly.
• A broad thickened dural-based margin which was called “tail sign” .
• Edema may be not or obvious.• Local bone changes including destruction, thin or
thickness.
Right parietal meningioma
Plain T1WI
Contrast T1WI
T2WI AND contrast T1WI
Meningioma
T2WI
T1WI
Gd-T1W
Acoustic schwannoma• Benign tumor, occur mostly at middle age people,
approximately 7 ~8 of all primary intracranial neoplasms.﹪ ﹪• Ovoid or tubular tumors may occur in the internal auditory canal
and cerebellopontine angle cistern .• Tumor may be part of solid and cystic . • On Plain CT, solid part of tumor was iso-density ,and cystic part
was low density.• Iso-intensity or low signal intensity were seen in solid or cystic
part of tumor on T1WI, but high or very high signal intensity on T2WI,.
• Obvious enhancement was seen on solid tumor.• Enlargement of internal auditory canal.
Left acoustic schwannoma
Left acoustic schwannoma
T2WI T1WI Contrast T1WI
Left acoustic schwannoma
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