The document summarizes key points about brain imaging techniques used in detecting and characterizing various brain conditions like strokes and infections. It discusses CT and MRI findings and appearances of acute, subacute and chronic infarcts over time on imaging. It also covers imaging features of hemorrhagic strokes, ischemic penumbra, angiography techniques, hypoxic brain injuries, venous ischemia, CNS infections like meningitis, abscesses and neurocysticercosis.

1. A seminar on “Brain Imaging”
Presenter
Dr Ajay Tripathi JR3
Dept of Medicine
Guide
Dr Vimlesh Patidar
Sir
Professor
Dept of Medicine
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2. Overview of Talk
•  Orientation of Brain Anatomy
• CT/MRI imaging in different conditions
• Some special Sequences of MR
•  Recent advances
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4. 4

5. 5

6. 6

7. Imaging of Ischemic Infarct
• NCCT Brain
• Used for quick differentiation of ischemic
stroke from intracranial hemorrhage,
and to rule out other pathological processes,
such as tumors, which may present as stroke.
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8. Hyper Acute infarction changes
• In hyper acute stages of infarction, the changes
noticed on CT are the result of cytotoxic edema.
• The latter is seen as reduction in the density of
gray matter in the ischemic tissue and
obliteration of sulci and gray-white matter
differentiation.
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9. 9
Reduction in the density of gray matter in the ischemic
tissue and obliteration of sulci and gray-white matter
differentiation.
obscuration of lentiform nuclei due to acute ischemia of
lenticulostriate
territory

10. • In early stages, CT may
also be able to identify
the thrombus in the
affected vessel
• dense MCA sign can be
seen in up to 50% of
all cases.
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11. Hyperdense Artery
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12. Sub Acute Infarct
3 – 30 days
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13. Chronic Infarct
>30 days
13
In chronic stage;
encephalomalacia is
seen as area of low
density with
accompanying loss of
volume in the form of
dilated sulci and
adjacent ventricular
system

14. • Ultimately, however, the diagnosis of ischemic stroke
is clinical
• Moreover, even with sensitive MRI techniques,
imaging can be negative in cases of true ischemic
stroke, .
•
NCCT findings are time dependent and may be
normal or near normal even in the setting of
established or large infarct, particularly within the first
3 hours of stroke onset (the diagnostic sensitivity for
NCCT is approximately 50% even with modern CT scanners)
and increases by 15% with addition of CTA cuts for vessel and
territory localisation.
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15. Exclude Intracranial Hemorrhage
• Any acute Intracranial haemorrhage is contraindication for
reperfusion therapy
• This may be intracerebral hemorrhage, subarachnoid
hemorrhage, and subdural or extradural hematoma
The appearance of ICH on CT depends on the
time elapsed since the hemorrhage.
• Hyper-attenuation 30 to 60 HU
• Hounsfield units (HU) ( Relative and comparable to
chronic infraction attenuation)
• With next few hours as clot retaraction occurs this inc >60 and
mostly upto 100 HU
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16. 16

17. • MRI is considered equivalent to
CT for detection of intracranial
hemorrhage.
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18. MRI
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19. 19

20. 20

21. MRI Brain in suspected Stroke
• More Sn , >80 % infract detected within 24 hours
of insult
• DW Scan , can identify ischemic penumbra, acute
infract looks Bright in DWI
• T2 weighted Images are used as mostly as
Inflammation and Edema looks bright
• With Gandolium contrast T1 weighted images are
used, it enhances blood signal and site of
increased blood supply
• Inferior to CT in detection of bony injury
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22. MRI imaging in Stroke
• MRI findings of parenchymal FLAIR
and T2 hyper intensity and swelling
in a topographic distribution
concordant with the clinical symptoms
also confirm the clinical diagnosis of
stroke.
• MRI FLAIR may also be negative in 1st 3 hrs of
ischemic stroke, but detectable in DWI
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23. Ischemic Penumbra
• “Ischemic penumbra” a region that is ischemic
but still viable and may infarct if not treated.
• Mismatches between DW and PW images in
hyperacute stroke have been well recognized, and
it has been stated that subtraction of the area of
diffusion abnormality from the area
of perfusion (greater than diffusion) deficit can
provide an estimate of ischemic penumbra.
• DSC area substracted from DWI
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24. 24
Perfusion is reduced in greater
area in Perfusion weighted
sections while Diffusion weighted
images shows less , diffusion
deficiet
A difference in PWI-DWI shows
ischemic Penumbra at Risk
Perfusion weighted scan- (DSC, DCE,
ASL)
DSC- uses Contrast

25. Reduction in the density of gray matter in the ischemic tissue and obliteration of
sulci and gray-white matter differentiation.
obscuration of lentiform nuclei due to acute ischemia of lenticulostriate
territory
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26. Haemorrhagic Stroke
• Easily differentiated in NCCT and MR
• MR angiography is modality of choice to
identify culprit vessel
• Digital subtraction angiography (DSA) is the
modality of choice to visualize indolent
vascular malformation or aneurysm as the
cause of bleed.
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27. Angiography
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28. Magnetic Resonance Angiography
• MRA allows noninvasive assessment of neck vessels as well
as large intracranial vasculature. The reconstructed
images are similar to those of catheter angiography.
• A number of studies have shown the ability of MRA to
diagnose >70% carotid origin stenosis with a sensitivity of
85–98% and a specificity of 75–96% the spatial resolution
is still not adequate enough to assess small intracranial
vessels on 1.5T, & can be visualized with 3T
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29. 29

30. CT Angiography (CTA)
• CT angiography has emerged as the
alternative to the invasive cerebral digital
subtraction angiography (DSA)
• Pitfalls of CT angiography include lack of
visibility of small arteries
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31. CT Angiography
• Short scanning time 20-40 s
• Spatial resolution is not comparable to MR
and Catheter Angio but larger intracranial
vessels can be studied
• Extra Cranial vessels can also be studied
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32. Cerebral Digital Substraction
Angiography
• Cerebral Digital subtraction Angiography
• Invasive technique by catheter assisted angiography
• Small vessels can also be seen , unmatched resolution
Gold standard .
Identify the cause of bleed, define collateral circulation and assess
vasospasm.
Technically adequate angiography is essential.
Magnification, subtraction and stereoscopic techniques delineate the cause
of bleeding in most cases
Risk- Ischemic events occur in 1.3% of patients in the first 24 hours after
angiography.
Neurological deterioration occurs in 1.8% of patients between 18 and 72
hours of angiography. 32

33. 33

34. Hypoxic-Ischemic Injury
• Adults, cardiac arrest
with direct reduction
of blood flow to the
brain leads to primary
ischemic injury.
• “bilateral involvement
of gray matter,
in particular the
cortex and deep
nuclei”
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35. Venous Ischemia and Stroke
• Venous sinus
or cortical vein
thrombosis
leading to
stroke is rare
compared to
other types of
stroke.
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36. • CT Venography has high sensitivity for depicting
the cerebral veins and sinus.
• On CTV, a thrombosed dural sinus is seen as a
filling defect and is often associated with contrast
enhancement of the walls
• But MRV is modality of choice ,do not require
contrast, comparable sensitivity and specificity
• Especially useful when Contrast is Contra-
Indicated
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38. CNS Infections
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39. PYOGENIC MENINGITIS
• In early meningitis, the CT or MR findings may be normal.
• NCCT- Basal Inflammatory exudate and
brain swelling is obliteration of the basal subarachnoid
cisterns, fissures and cerebral and cerebellar sulci.
• On contrast enhanced CT scan, there is enhancement of the
inflammatory exudates
The abnormal leptomeningeal
contrast enhancement is typically more readily apparent and
more intense on MR imaging rather than on CT scanning.
For diagnosis MR+Contrast>CECT>MR>CT
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40. • TBM
• Detected more readily in Non Contarst MR
compared to Bacterial Meningitis
• A detection of Meningitis in Non Contrast MR
T1 is highly suggestive of TBM and warrents
early initiation of treatment
• Early detection due to Fibrin Exudates in TBM
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41. 41

42. Subdural Abscess (Empyema)
• Ten to fifteen percent of empyemas are due to complication
of meningitis.
• The most common locations of subdural empyema are the
cerebral convexities and the interhemispheric fissure.
• Unenhanced CT scanning reveals a crescentic or
lentiform extra-axial fluid collection that is slightly denser
than cerebrospinal fluid.
• On CT scan, after intravenous contrast administration, an
overlying peripheral rim of enhancement of varying
thickness is identified.
• This rim represents an inflammatory chnages.
• Hypodensity or contrast enhancement of the adjacent brain
parenchyma may also be seen secondary to thrombophlebitis42

43. 43

44. 44

45. Cerebritis and Brain Abscess
• Cerebritis and abscess formation constitute a
continuum.
• The majority of patients with brain abscess
demonstrate a contiguous focus of infection
usually sinusitis or otitis media
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46. • Cerebral abscesses as a result of dental sepsis often
containmixed mouth flora with a predominance of anaerobic
bacteria.
• Hematogenous brain abscesses have the following
characteristics
• (i) a distant focus of infection (ii) location in the
distribution of the middle cerebral artery (iii) initial location at
the gray-white matter junction (iv) poor encapsulation (v)
high mortality.
• These abscesses are more commonly multiple
and multiloculated as compared to those that have an origin
in foci of contiguous infection.
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47. 47
Typically the center of a mature abscess contains necrotic
material hypointense on T1-weighted images and
hyperintense to brain on T2-weighted images.
Edema surrounding an abscess may be greater in volume
than the abscess itself and causes much of the associated
mass effect

48. 48

49. NEUROCYSTICERCOSIS
• Cysticercosis is a disease transmitted by the ingestion
of the eggs of the worm Taenia solium.
• The initial host is the pig.
• Cysticercosis may involve any tissue and any
organ in the body, most symptoms are due to invasion
of the central nervous system (CNS)
• Clinical presentations include seizures,
headaches, syncope, focal neurological deficits
•
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50. • Parenchymal cysticercosis 4 stages
• A) Vesicular- In the vesicular stage, a clearly marginated cyst with
thin cyst wall that is usually not identifiable is seen. The cyst
fluid is similar to cerebrospinal fluid in signal intensity.
• A discrete, eccentrically located scolex completes the image
of a parenchymal cyst in the vesicular stage.
• No contrast enhancement of the cyst wall is seen in this stage
because the cyst is alive; there is no immune response by the host
at this stage and no surrounding edema is seen.
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Contrast Enhanced Axial CT

52. • b) In the next stage (colloidal vesicular stage), the larva
begins to degenerate .
• There is associated surrounding white matter edema The
capsule becomes visible on T1-weighted or FLAIR
• The cyst fluid is slightly hyperintense on T1-weighted
images and markedly hyperintense on T2-weighted
• Contrast enhancement is seen involving the cyst wall which
is a result of an inflammatory reaction caused by the
degenerating
parasite.
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53. 53

54. • In the third stage (granular nodular stage),
the cyst undergoes retraction, the wall of the
cyst thickens and the scolex is transformed
into a coarse mineralized granule.
•
Surrounding edema regresses gradually.
• nodular or a thick, small, ring-like
enhancement
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56. 56

57. CENTRAL NERVOUS SYSTEM
TOXOPLASMOSIS
• Toxoplasma gondii is a parasite
• The definitive host is the cat
• H/o of contact with Cats, or unwashed salad/vegetable
consumption
• Most toxoplasmosis infections in immunocompetent
individuals are subclinical or mildly symptomatic.
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58. Imaging Findings
• On noncontrast CT, toxoplasma encephalitis characteristically
appears as multiple areas of hypodensity.
• There is a predilection for the basal ganglia (in 75–88%) and
the corticomedullary junction and lesions may involve the
posterior fossa.
•
• Lesions vary in size from less than 1 cm to over 3 cm and there
is surrounding mass effect and edema of variable degree.
Postcontrast CT demonstrates ring or nodularenhancement.
• Ring enhancement is more common with central hypodensity.
• The rings are usually thin and smooth 58

59. • On MRI T2-weighted images, depict active lesions as
variable signal intensity
• Godolinium reveals ring or nodular enhancement
in active lesions are clearly distinguishable from the
surrounding edema
• Magnetic resonance has a greater sensitivity than CT
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60. 60
T2W and T1W image Post contrast
Target sign
Surrounding Edema
FLAIR hyperintensity due to local edema

61. HYDATID DISEASE
• Hydatid disease is caused by Echinococcus
granulosus and less frequently by
Echinococcus multilocularis.
• H/o contacts with Dogs and Sheep, or
unwashed salad/vegetable consumption
•
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62. Imaging
• Imaging Findings
• T2-weighted MR images, the better of the two
sequences for imaging these lesions, shows a
thin low signal intensity rim representing the
capsule surrounding a hyperintense lesion.
• Rim enhancement or edema is uncommon
unless the cyst becomes superinfected
.
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63. 63

64. HERPES SIMPLEX VIRUS
• Herpes simplex virus (HSV) types 1 and 2 most
commonly manifest as reactivated latent
infections.
• HSV-1 is nonsexually transmitted and
commonly produces skin lesions and
encephalitis.
• HSV-2 is sexually transmitted and is associated
with genital lesions
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65. • CT scan and MR imaging findings are nonspecific early in
the course of CNS HSV infection and scans may even appear
normal
• Initial CT scans show subtle hypodense lesions in the
periventricular white matter with relative sparing of the
basal ganglia, thalami and posterior fossa structures
• Finger-like areas of increased
attenuation within the cortical gray matter
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66. 66

67. • MR imaging can demonstrate the early
edematous changes of herpes encephalitis
seen as
• hyperintensity on T2-weighted images with
characteristic involvement of the temporal
lobes and inferior frontal lobes
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68. 68
DWI and FLAIR sequences

69. White Matter disease
• Multiple sclerosis
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70. • Diagnostic criteria proposed for establishing the
diagnosis of MS, have been based on three main
principles:
•
Demonstration of demyelinating lesions disseminated
in space (DIS)
Demonstration of demyelinating lesion demonstrated
in time (DIT)
Exclusion of alternative explanation for the clinical
presentation.
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71. • The MR appearance of MS is widely variable depending on the
acuity and extent of the disease.
• The characteristic lesion is a T2 hyperintense lesion that
occurs throughout the CNS. It shows a typical distribution
in the PV (touching ventricle surface) location more so than
the peripheral white matter .
• Within the white matter, the lesion may be discrete or juxtacortical.
• Rarely the lesion may lie entirely within the gray matter (cortical)
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74. 74
Corpus callosum lesions are frequent and lie within the
inner or deep surfaces.18 The corpus callosum is a region that
is especially vulnerable to demyelination in MS,

75. fMRI
• Functional MRI
• Based on BOLD technique
• Blood oxygenation level dependent (BOLD)
imaging is the standard technique used to
generate images in functional MRI (fMRI) studies,
and relies on regional differences in cerebral
blood flow to delineate regional activity.
• “specific region of the cortex increases its activity
in response to a task”
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76. Recent Advances
• MRI sequence developed that can aid in
identification of Neoplastic tissue in body
• (Alexander wong et al March 2022 )
• MR sequence “synthetic correlated diffusion
imaging (CDIss)”
• DWI concept , restricted diffusion coefficient due
to abnormal microstructure of Neoplasm
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77. References
1) AIIMS-MAMC-PGI
diagnostic book of Radiology
2) CT-MRI of Whole Body 6th
Ed Jhon s. Hagga et all
3) Radiopedia.org
4) Internet
Thank you
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