1. Intro to Neuroradiology
Jenna Ford, MD PGY 3 Neurology

2. Learning Objectives
Learn the fundamentals of common neuroimaging modalities
Review the pros and cons of different imaging modalities
Learn to identify common neurologic disease based on imaging characteristics
Learn the basic method of CT scan windowing

3. CT Scan
A series of XR images obtained at various angles and reformatted using software
Radiodensity measured in Hounsfield Units (HU)
related to how much the XR beam is weakened/attenuated by the material it is passing through
All relative to water which is 0 HU
CT Terminology (typically relative to brain)
White/Bright = Hyperdense
Black/Dark = Hypodense

4. CT Scan Indications Pros: Cons: Unstable patients, emergency room
Acute stroke
Looking for pathology that requires immediate intervention
Pros:
Fast!! Usually the first step
Cheap
Helpful for excluding large pathology (i.e. bleed, large ischemic stroke, mass, abscess, hydrocephalus)
Cons:
Less detail/information
Radiation (not ideal in young and pregnancy)
Low sensitivity in posterior fossa

5. CT Windowing Air -1000 Black Water Gray Cortical Bone +1000 White
Gray
Cortical Bone
+1000
White
Substance HU
CSF
+15
White Matter
+20-30
Grey Matter
+35-45
Acute Blood
+45-65
Fat
–100-(–15)
Bone

6. CT Windowing
W = Window
C = Center; L = Level (depending on the software) C
Air
-1000
Black
Water
Cortical Bone
+1000
White W

7. Window
Wide = >400
Lets you compare areas with different HU’s (bone)
+300
+700
Water
Black
White

8. Window
Narrow =
Lets you compare areas with similar HU’s (brain vs blood) 55
Water
Black
White 40

9. Center/Level
This is what you set to be the middle of your window (i.e. gray)
Dark Gray
Light Gray 50 L 45 55
Black
White
Gray

10. CT Scan: First Signs of Stroke
Hypodensity (edema)
Vasogenic – fluid leaking out of damaged blood vessels, integrity of BBB has been compromised.
Restricted to the white matter or highly vascular areas
Cytotoxic – induced by cytokines and inflammatory cells that are present when actual cell death/damage occurs.
Extends to the cortex, does not preferentially affect highly vascularized tissue (white and gray matter affected)

11. CT Scan: First Signs of Stroke
Sulcal Effacement
Loss of gray-white differentiation

12. CT Scan: First Signs of Stroke
Hyperdense MCA sign
Can be a soft call so be careful
If present will be the first thing to appear on imaging, if you get imaging early enough this may be the only thing you see

13. CT Scan: ASPECT Score Alberta Stroke Program Early CT Score
A 10-point pretreatment score that divides the MCA territory into 10 regions and identifies patients with stroke who are unlikely to have good outcome from thrombolysis
The ASPECTS value is calculated from two standard axial CT cuts, one at the level of the thalamus and basal ganglia, and one just rostral to the ganglionic structures.
10 = normal CT scan
0 = diffuse ischemic involvement throughout the complete MCA territory
A score of 7 or less predicts worse outcome at 3 months and symptomatic hemorrhage

15. CT Scan: ASPECTS Score

16. Case #1
ASPECTS 5

17. Case #2
ASPECTS 8

18. Case #3

19. Old Stroke vs New Stroke
Encephalomalacia
Abnormal tissue looks shriveled rather than plump
No mass effect, can see ex-vacuo hydrocephalus
Hypodense relative to new strokes; CSF is less dense than edema

20. CT Perfusion
Useful in acute stroke to determine how much salvageable tissue is left; i.e. the penumbra
CBV – Cerebral blood volume; amount of blood in that region
CBF – Cerebral blood flow; amount of blood passing through that region in a given period of time
TTP – Time to peak; MTT – Mean transit time (CBV/CBF); the amount of time that the blood spends in a give volume of circulation
Infarct – no blood flow, dead
Since blood is not really getting to this area the transit time will be very very long and MTT/TTP will be markedly increased
Ischemic penumbra – flow is less but the body is actively compensating to continue perfusion
Cerebral blood flow is only mildly diminished because cerebral blood volume is elevated to compensate for delayed collateral perfusion manifest as increased mean transit times. This pattern suggests robust collateral circulation at early stages of acute ischemic stroke.

21. CT Perfusion

22. CT Perfusion

23. MRI
Patient lies in a large magnet which aligns all the protons (i.e. Hydrogen or water molecules) in the body. Radiowaves are then shot through the patient and returning signals are converted into an image
MRI Terminology:
White/Bright = hyperintense
Black/Dark = Hypointense
Enhancing refers to contrast only!
Many different sequences and protocols depending on what you want to look at

24. MRI Indications Pros Cons: Acute stroke
Further evaluation of CT findings
Chronic/subacute symptoms
Tumors/masses
Infection (abscess, meningitis, encephalitis)
Aging of blood
Pros
More detailed
Safe in Pregnancy
Can obtain vessel imaging without contrast
Cons:
Slower
More contraindications (i.e. metal/implantable device, PPM, stents, AICD, bullet fragment)
Expensive
Patient must hold still, difficult if claustrophobic

25. T1 CSF – dark (hypointense) White Matter – bright (hyperintense)
Good image for anatomy

26. T2 FLAIR – Fluid Attenuated Inversion Recovery
CSF – bright (hyperintense)
White Matter – dark (hypointense)
T2 FLAIR – Fluid Attenuated Inversion Recovery
Removes CSF!
Great for looking at edema since that has a different protein make up than CSF and will remain bright
Also will show other fluids with increased protein content such as certain cysts and abscesses

28. DWI – Diffusion Weighted Image
Shows restricted diffusion of water molecules…i.e. ischemia!
Dying neurons will swell as their Na-K pumps stop working and water accumulates within the cell…diffusion of water is restricted intracellularly and this lights up on DWI
Bright spots on DWI are either:
Ischemia
“T2 shine-through”
Must compare to ADC and FLAIR

29. ADC – Apparent Diffusion Coefficient
Dark areas that are bright on DWI confirm ischemia
Very susceptible to artifact so this is never the first scan you look at when looking for ischemia
Areas bright on DWI that are not dark on ADC are most likely “T2 shine-through”, i.e. chronic
Look at T2 FLAIR sequence to confirm

31. SWI – Susceptibility Weighted Image
Shows hemosiderin deposits (old blood) and calcifications
Useful when looking for old hemorrhages that don’t show up on CT
Stroke with hemorrhagic conversion
Old hemorrhage of brain tumors
Cerebral amyloid angiopathy
Different institutions have different versions/names for this type of sequence
GRE (gradient echo), STIR, SPIN, SWAN

33. Post Contrast (Typically T1)
Contrast Study vs Angiogram…Not the same thing!
Contrast is to evaluate breakdown in the blood brain barrier and identify abnormal brain parenchyma or tissue
Angiograms are to evaluate the blood vessels
T1+C vs T1+C Fat sat
Fat sat just makes all of the fat tissue have decreased signal so that it doesn’t obscure any contrast enhancing lesions

34. CT w/wo contrast

35. CT Angiogram

36. MRI w/wo contrast

37. MRI w/wo contrast