Mri brain anatomy

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


Fat supression Liquid supression


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


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Post Contrast sagittal T1 Wtd M.R.I.

Section at the level of medulla

Answers

6. Medulla

7. Sigmoid Sinus


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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


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Section at the level of Mid Brain

Answers18. Aqueduct of Sylvius

19. Midbrain

20. Orbits

21. Posterior Cerebral Artery

22. Middle Cerebral Artery


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Section at the level of theIII Ventricle

Answers23. Occipital Lobe

24. III Ventricle

25. Frontal Lobe

26. Temporal Lobe

27. Sylvian Fissure


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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


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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


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Section at the level of Body of Corpus Callosum

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42. Parietal Lobe

43. Body of the Corpus Callosum

44. Frontal Lobe


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Section above the Corpus Callosum

Answers

45. Parietal Lobe

46. Frontal Lobe

Normal anatomical structure of head on MRI

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 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

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

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

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

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


T2WI T1WI Contrast T1WI

Mri brain anatomy

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