1. Computed tomography (CT) uses X-rays to produce images based on differential tissue absorption, with darker shades corresponding to less attenuation. Slice thickness is typically 5-10mm for head CTs. 2. Magnetic resonance imaging (MRI) utilizes the magnetic properties of hydrogen protons to produce images. Different sequences like T1-weighted, T2-weighted, and FLAIR provide contrast between tissues. Diffusion weighted imaging detects restricted diffusion seen in acute ischemia. 3. Neuroimaging techniques like CT, MRI, DWI, perfusion imaging, and MRS are used to evaluate conditions like stroke, tumors, infections, demyelinating diseases and more by visualizing anatomical structures and physiological properties

1. IMAGING IN NEUROLOGY
BASICS
Dr. Rahi Kiran.B
DM Resident
Dept. of Neurology
GMC Kota

2. COMPUTED TOMOGRAPHY (CT)
• Based on differential absorption of X-
ray by various tissues.
• Darker shades correspond to lesser
attenuation.
• Slice thickness may vary, but in general,
it is between 5 and 10 mm for a routine
Head CT.
Low
density
High density
CSF Bone
Fluid (Edema) Calcification
Air Blood
Fat Contrast
Metallic Foreign
Bodies

3. Pure water has an HU value of ‘0’.
DESCRIPTION Approx. HU DENSITY
Calcium > 1000 Hyperdense
Acute blood 60-80 Hyperdense
Grey matter 38 (32-42) Hyperdense
(light grey)
White matter 30 (22-32) Hyperdense
(dark grey)
CSF 0-10 ISODENSE
Fat -50 to - 80 Hypodense
Air - 1000 Hypodense

4. PHYSIOLOGIC CALCIFICATION

5. • MRI is based on the principle of NMR
1.Atoms with an odd number of protons have spin
2.A moving electric charge, be it positive or negative, produces a magnetic field
• Body has many such atoms that can act as good MR nuclei (1H, 13C, 19F, 23Na)
• MRI utilizes this magnetic spin property of protons of hydrogen to produce
images.
MRI

6. • TE (echo time) : time interval in which signals are measured after RF
excitation
• TR (repetition time) : the time between two excitations is called
repetition time.
• By varying the TR and TE one can obtain T1WI and T2WI.
• In general a short TR (<1000ms) and short TE (<45 ms) scan is T1WI.
• Long TR (>2000ms) and long TE (>45ms) scan is T2WI.
TR & TE

7. BASIC MR BRAIN SEQUENCES
• T1
• T2
• FLAIR
• DWI
• ADP
• MRS
• PERFUSION IMAGING

8. • Short TE
• Short TR
• Better anatomical details
• Fluid dark
• Gray matter gray
• White matter white
T1 W IMAGES

9. T1 W IMAGES
• Most pathologies dark on T1
• Bright on T1
– Fat
– Haemorrhage
– Melanin
– Early Calcification
– Protein Contents (Colloid cyst/ Rathke cyst)
– Posterior Pituitary appears BRIGHT ON T1
– Gadolinium

10. • Long TE
• Long TR
• Better pathological details
• Fluid bright
• Gray matter relatively bright
• White matter dark
T2 W IMAGES

11. • LONG TE, LONG TR
• to null the signal from CSF-Nulled tissue remains dark
• Similar to T2 except free water supression (inversion recovery)
• Most pathology is BRIGHT
• Especially good for lesions near ventricles or sulci or CSF spaces (eg MS, MTS, TS– for
detection of Hamartomatous lesions, neonates with perinatal HIE.
• less sensitive for lesions involving the brainstem & cerebellum, owing to CSF
pulsation artifacts
FLAIR
Fluid Attenuated Inversion Recovery Sequences

12. CT
FLAIRT2
T1

13. T1W T2W FLAIR(T2)
TR SHORT LONG LONG
TE SHORT LONG LONG
CSF LOW HIGH LOW
FAT HIGH LOW MEDIUM
BRAIN LOW HIGH HIGH
EDEMA LOW HIGH HIGH

14. Echoplanar Imaging
• fastest MR imaging
• serves as the basis for DWI, DTI, and dynamic contrast enhanced brain perfusion
studies, as well as BOLD imaging

15. • Free water diffusion in the images is Dark (Normal)
• Acute stroke, cytotoxic edema causes decreased rate of water diffusion within the
tissue i.e. Restricted Diffusion (due to inactivation of Na K Pump )
• Increased intracellular water causes cell swelling
DIFFUSION WEIGHTED IMAGES (DWI)

16. • Areas of restricted diffusion are BRIGHT.
• Restricted diffusion occurs in
– Cytotoxic edema
– Ischemia (within minutes)
– Abscess
Other Causes of Positive DWI
Bacterial abscess,
Acute demyelination
Epidermoid cysts
Lymphoma, some meningiomas
T2 shine through ( High ADC)

17. • Areas of restricted diffusion are dark - Negative of DWI
• Nonischemic causes for decreased ADC
• Abscess
• Lymphoma and other tumors
• Multiple sclerosis
• Seizures
• Metabolic (Canavans Disease)
APPARENT DIFFUSION COEFFICIENT Sequences (ADC MAP)

18. Clinical Uses of DWI & ADC in Ischemic Stroke
• Hyperacute Stage:- within one hour - minimal hyperintensity seen in DWI and ADC value
decrease 30% or more below normal
• Acute Stage:- Hyperintensity in DWI and ADC value low but after 5-7days of episode ADC
values increase and return to normal value (Pseudonormalization)
• Subacute to Chronic Stage:- ADC value are increased but hyperintensity still seen on DWI
(T2 shine effect)

19. DIFFUSION TENSOR IMAGING (DTI) - TRACTOGRAPHY
• more advanced type of diffusion imaging - quantifying anisotropy of diffusion in
white matter.
• isotropic -same intensity in all directions
• anisotropic – occurs preferentially in one direction
• greatest current application-direction/course of the given white matter tract
• shows degenerating white matter tracts that appear normal on conventional MRI.

20. • Post contrast images are always T1 W images
• Sensitive to presence of vascular or extravascular Gd
• Useful for visualization of:
– Normal vessels
– Vascular changes
– Disruption of blood-brain barrier
POST CONTRAST (GADOLINIUM ENHANCED)

21. Magnetization Transfer Contrast Imaging
• produces increased contrast within an MR image, specifically on T1-weighted
gadolinium-enhanced images and in MRA
• White matter appears darker, CSF and blood does not lose signal
• Background becomes dark – so target structures (Gd enhanced lesions/ blood
vessel) better visualised
• “normal appearing white matter” of MS on conventional images – can be detected

22. • Form of T2-weighted image which is susceptible
to iron, calcium or blood.
• Blood, bone, calcium appear dark
• Areas of blood often appears much larger than
reality (BLOOMING)
• Useful for:
– Identification of haemorrhage / calcification
Look for: DARK only
GRE Sequences (GRADIENT RECALLED ECHO)

23. • Non-invasive physiologic imaging of brain that measures relative levels of
various tissue metabolites.
• Used to complement MRI in characterization of various tissues.
MR SPECTROSCOPY

24. MRS
Dec NAA/Cr
Inc acetate, succinate,
amino acid, lactate
Neuodegenerative
Alzheimer
Dec NAA/Cr
Dec NAA/ Cho
Inc Myo/NAA
Slightly inc Cho/ Cr
Cho/NAA
Normal Myo/NAA
± lipid/lactate
Inc Cho/Cr
Myo/NAA
Cho/NAA
Dec NAA/Cr
± lipid/lactate
Malignancy Demyelinating disease
Pyogenic abscess

25.  Stroke
Detection and assessment
of ischemic stroke
(Lower perfusion )
 Tumors
Diagnosis, staging, assessment of
tumour grade and prognosis
Treatment response
Post treatment evaluation
Prognosis of therapy effectiveness
(Higher perfusion)
PERFUSION IMAGING- ? ASL-arterial spin labelling

26. SUSCEPTIBILITY-WEIGHTED IMAGING
• contrast achieved by this sequence distinguishes the
magnetic susceptibility difference between oxygenated and
deoxygenated hemoglobin
• is very sensitive for intravascular venous deoxygenated
blood as well as extravascular blood products.
• evaluating any lesion (e.g., stroke, AVM, cavernoma or
neoplasm microbleeds associated with traumatic brain
injury, diffuse axonal injury, or cerebral amyloid
angiopathy.)
FLAIR SWI
Patient with DAI

27. THANK YOU