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BASICS OF CT AND MRI
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By DR A K SINGH LECTURER PG DEPT OF MEDICINE
BASICS OF NEUROIMAGING
What We Need to Know
• Air is very black (less than -300 HU)• Water/CSF is black (near 0 HU)• Bone is very dense/white (500-3000 HU)• Blood is white (60-80 HU)• Brain is gray 35-50 HU
Normal CT of brain
• Ventricles are normal sized, the grey versus white distinctionis clear.
• Midline is straight.• Sulci are symmetrical on
bothsides.• Skull is intact with no
scalp edema.
Systemic Approach to Head CT Interpretation
• Symmetry – Compare left and right side of the cranium
• Midline – Look for midline shift• Cross-sectional anatomy – Review anatomical landmark for
each slide– Brain tissue : gray matter, white matter , intracerebral lesions– CSF space : ventricle, basal cistern, cortical sulci, fissure– Skull and soft tissue : scalp swelling, fractures, sinuses, orbit
• Subdural windows : Look for blood collection adjacent to the skull
• Bone windows : Skull, orbit and sinuses, intracranial air
Lateral View of Brain
Cross-sectional Anatomy
• Grey/White interface, Subcortical white matter
Cross-sectional Anatomy
• Paired of crescent-shape = Twin bananas
Cross-sectional Anatomy
Basal ganglia
Cross-sectional Anatomy
• Third ventricle, Basal ganglia, Superior cerebellar cistern
Physiologic Calcification
Cross-sectional Anatomy
• Third ventricle, Smiley face
Cross-sectional Anatomy
• Midbrain, Interpeduncular cistern
Cross-sectional Anatomy
• Star shape ~ Circle of Willis, • Fourth ventricle, Temporal horn ~ slit
Cross-sectional Anatomy
• Base of skull, Midline bony prominence, • Prepontine cistern, Pretrous bone, Frontal
sinus
Cross-sectional Anatomy
• Orbits, Ethmoid air cell
GREEN IS TEMPORAL LOBE
RED DENOTES FRONTAL LOBE
GREEN DENOTES TEMPORAL LOBE
RED DENOTES FRONTAL LOBE
GREEN-TEMPORAL LOBE
RED- FRONTAL LOBE
GREEN-TEMPORAL LOBE
RED-FRONTAL LOBEGREEN-TEMPORAL LOBEYELLOW-OCCIPITAL LOBE
RED- FRONTAL LOBEGREEN- TEMPORAL LOBEYELLOW-OCCIPITAL LOBE
RED-FRONTAL LOBEGREEN-TEMPORAL LOBEYELLOW-OCCIPITAL LOBE
RED –FRONTAL LOBEBLUE-PARIETAL LOBEGREEN-TEMPORAL LOBEYELLOW-OCCIPITAL LOBE
RED-FRONTAL LOBEBLUE-PARIETAL LOBEYELLOW- OCCIPITAL LOBE
RED –FRONTAL LOBEBLUE- PARIETAL LOBEYELLOW- OCCIPITAL LOBE
RED –FRONTAL LOBEBLUE-PARIETAL LOBEYELLOW-OCCIPITAL LOBE
FRONTAL LOBE –RED
PARIETAL LOBE - BLUE
RED – FRONTAL LOBE
BLUE-TEMPORAL LOBE
RED – FRONTAL LOBE
BLUE – TEMPORAL LOBE
ThalmusAqueduct of sylviusS
Cerebellum
Fourth ventricle
Corpus callosum
Midbrain
Pons
Medulla
Corpus callosum Thalamus Aqueduct of SylviusFourth Ven. Mid-brain Pons Cerebellum Medulla oblongata
SECTION AT MID-SAGITTAL PLANE
MRI
• Based on the absorption and emission of radiofrequency energy – so there is NO ionizing radiation.
• Uses magnets ranging in strength from 0.3 to 1.5 Tesla to create a magnetic field around the patient.
• Magnetic field causes protons in the body to align and then pulsed radiowaves are directed at the patient causing a disturbance of the proton alignment.
• Atoms then realign and in doing so, emit the absorbed radiofrequency
• The time it takes the protons to regain their equilibrium state = • RELAXATION TIME. �• 2 types of relaxation time: T1 – Longitudinal (parallel to the magnetic
field) and T2 –transverse (perpendicular to the mag field). �• Relaxation Time and Proton Density are the main determinants of
signal strength. �• The main determinants of contrast or the weighting are: � 1)Repetition Time (TR) – the time between successive RF pulses
2)Echo Time (TE) – time between the arrival of the RF pulse that excites
and the arrival of the return signal at the detector.
Short TR + Short TE = T1 weighted
•Dark– CSF– Increased Water –
edema, – tumor, infarct,
inflammation, – infection, hemorrhage (hyperacute or
chronic)– Low proton density, calcification– Flow Void
•Bright– Fat– Subacute hemorrhage– Melanin– Protein-rich Fluid– Slowly flowing blood– Gadolinium– Laminar necrosis of
an infarct
Long TR + Long TE= T2 weighted
• Dark– Low Proton Density, – calcification, fibrous
tissue– Paramagnetic
substances - • deoxyhemoglobin, • methemoglobin
(intracellular), • iron, hemosiderin,
melanin – Protein-rich fluid– Flow Void
• Bright– CSF– Increased Water –
edema, – tumor, infarct,
inflammation, – infection, subdural
collection– Methemoglobin – (extracellular) in
subacute – hemorrhage
Fluid-Attenuated Inversion Recovery
FLAIR
• Basically T2 without CSF brightness
• TE>80 and TR>10,000
• Edema and Gliosis are hyperintense
T1W / T2W / FLAIR
T1W T2W FLAIR
Fig. 1.1 Post Contrast Axial MR Image of the brain
1
2
3
4
5
Post Contrast sagittal T1 Weighted M.R.I.
Section at the level of Foramen MagnumAnswers
1. Cisterna Magna2. Cervical Cord3. Nasopharynx4. Mandible5. Maxillary Sinus
Fig. 1.2 Post Contrast Axial MR Image of the brain
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6
Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of medullaAnswers
6. Medulla7. Sigmoid Sinus
Fig. 1.3 Post Contrast Axial MR Image of the brain
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8
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1213
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16
17Post Contrast sagittal
T1 Wtd M.R.I. Section at the level of
PonsAnswers8. Cerebellar Hemisphere9. Vermis10. IV Ventricle11. Pons12. Basilar Artery
13. Internal Carotid Artery14. Cavernous Sinus15. Middle Cerebellar Peduncle16. Internal Auditory Canal17. Temporal Lobe
Fig. 1.4 Post Contrast Axial MR Image of the brain
18
19
20
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22
Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of Mid Brain
Answers18. Aqueduct of Sylvius19. Midbrain20. Orbits21. Posterior Cerebral Artery22. Middle Cerebral Artery
Fig. 1.5 Post Contrast Axial MR Image of the brain
23
24
25
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27
Post Contrast sagital T1 Wtd M.R.I.
Section at the level of theIII Ventricle
Answers23. Occipital Lobe24. III Ventricle25. Frontal Lobe26. Temporal Lobe27. Sylvian Fissure
Fig. 1.6 Post Contrast Axial MR Image of the brain
28
29
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31
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38
33
34
36
35
37
Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of Thalamus
Answers28. Superior Sagittal Sinus29. Occipital Lobe30. Choroid Plexus within the occipital horn31. Internal Cerebral Vein32. Frontal Horn
33. Thalamus34. Temporal Lobe35. Internal Capsule36. Putamen37. Caudate Nucleus38. Frontal Lobe
Fig. 1.7 Post Contrast Axial MR Image of the brain
39
40
41
Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of Corpus Callosum
Answers39. Splenium of corpus callosum40. Choroid plexus within the body of lateral ventricle41. Genu of corpus callosum
Fig. 1.8 Post Contrast Axial MR Image of the brain
42
43
44
Post Contrast sagittal T1 Wtd M.R.I.
Section at the level of Body of Corpus
CallosumAnswers42. Parietal Lobe43. Body of the Corpus Callosum44. Frontal Lobe
T1W T2W FLAIR
acute/subacute hemorrhage
acute
SUBACUTE T2WI T1WI
Strokes show up faster on MRI than CT
MRI and CAT views of the same whole R. hemispherical infarct
Some very big strokes settle down and don’t require surgical decompression. This man opens his eyes to verbal on nasal cannula and follows on the right side 10 days post stroke.
MR:44396
MRI appearances of acute cerebral infarction
T2WI T1WI Flair
The End…
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