Advances in neuroimaging in CT and MRI.

1. Advances in Neuroimaging
Techniques
Dr Sreenivasa Raju N

2. Advances in Neuroimaging
Techniques
A. Advances of Computed
Tomography in neuroimaging
B. Advances of Magnetic Resonance
Imaging

3. Advances of computed
Tomography in Neuroimaging
Multidetector CT (MDCT)
 Latest techniques where multiple rows of detector are
used to acquire multiple slices per rotation through
interweaving (2,4,16 up to 320 slices)
 Advantages:
1. Increasing scan speed : Faster thinner sections , less
motion artifacts in critically ill patients & children.
2. Volume acquisition: Continuous volume acquisition
that ensures that no lesion are lost and improved 3D
capabilities.

5. Advances of computed
Tomography in Neuroimaging
Dual Source CT
 Uses two separate different energies X-ray sources
which are placed orthogonal to enhance the contrast
between adjacent structures which provides high
temporal resolution.
 Calcified plaques , surgical clips and bone can be
removed by processing.
 Has high diagnostic accuracy for the intracranial
aneurysm as compared with 3D DSA at low radiation
dose.

6. Dual Source CT

7. Advances of computed
Tomography in Neuroimaging
 Flat-panel Volume Computed Tomography:
 Allows coverage of large volume per rotation
 Advantages :
1. Ultra- high spatial resolution
2. Real time fluoroscopy
3. Dynamic imaging
4. Whole organ coverage in one rotation.
 Disadvantages :
1. Higher radiation dose
2. Longer scanning time
3. Lower contrast resolution.

8. Advances of computed
Tomography in Neuroimaging
 Dynamic CT angiography :
 Inability to provide dynamic information is resolved with
introduction of 320- detector row CT scanner
 Applications:
1. Capability of scanning the entire organs in a single
rotation as it provides large maximum detector area.
2. Visualization of dynamic flow and perfusion in stroke ,
steno-occlusive diseases, Av malformations and dural
shunts.

9. CT angiography
 Current non-invasive modality of choice for neuroangiography
overcomes disadvantages of MRA.
 Faster, cheaper , sensitive to calcium , displays bony landmarks and
can be used with aneurysmal clips.
 Technique:
1. 120-140kvp , 200-300mAs
2. 100ml if non-ionic contrast , right hand by pressure injector at
3ml/s
3. When ROI reaches 100hHU , the scan starts..
 Image processing by
1. MIP – vessel , calcium and thrombus are well delineated. Depth
information totally lost.
2. Surface shaded display(SSD) – preserves depth information ,
but does not in interior of vessels and underestimates stenosis.
3. VR- overcomes the problems seen with MIP and SSD.

10. CT angiography
 Image processing by
MIP SSD VR

11. CT angiography
 Applications :
A)Carotid artery stenosis:
1. Accurate estimation of eccentric and irregular stenosis ,
delineates mural calcium from luminal narrowing.
2. Has higher accuracy for assessing high grade stenosis and
distinguishing it from complete occlusion.
B)Carotid dissections:
1. Subadventitial dissections , presence of intramural
hematoma , stenosis, occlusions and pseudo aneurysms
can be picked up.

12. CT angiography
 Applications :
C)Intracranial aneurysm :
1. DSA is the gold standard.
2. Sensitivity is highest for the aneurysm > 5mm.
3. Aneurysmal sack morphology, neck, parent vessel calibre
4. Its spatial relationship and surrounding anatomy (bony and
soft tissue) for treatment options (surgical or minimally
invasive endovascular)
5. Also for the assessment of post operative status of
aneurysm.

13. CT angiography
 Intracranial aneurysm
Carotico –
Ophthalmic
aneurysm
A- MIP
B,C- VR
D- DSA
Carotid artery is
incorporated into
the aneurysm

14. CT Perfusion(CTP)
 CTP measures brain tissue blood perfusion using parameters such as
CBF,CBV and MTT.
 CBV is measured in units of millilitres of blood per 100 g of brain and is
defined as the volume of flowing blood for a given volume of brain.
 MTT is measured in seconds and defined as the average amount of time it
takes blood to transit through the given volume of brain.
 CBF is measured in units of millilitres of blood per 100 g of brain tissue per
minute and is defined as the volume of flowing blood moving through a given
volume of brain in a specific amount of time.
 CBF = CBV/MTT.
 In normal perfusion, there is symmetric perfusion with higher CBF and CBV in
gray matter compared with white matter, reflecting the physiologic hemodynamic
differences between these tissues

15. CT Perfusion(CTP)
 Normal :By convention, all color maps are coded RED for
higher values and BLUE for lower values.
NCCT (A)
CTP
parametric
maps,
CBF (B),
CBV (C),
MTT (D),
demonstrate
normal
symmetric
brain
perfusion.

16. CT Perfusion(CTP)
Acute stroke: Infarct .
NCCT shows some
micro vascular
ischemic changes
posteriorly.
B−D,CTP maps,
CBF (B),
CBV (C), and
MTT (D),
demonstrate a large
area of matched
deficit on CBV and
MTT maps,
indicative of core
infarct in the right
MCA territory.

17. CT Perfusion(CTP)
 Acute stroke with ischemic penumbra: Thrombolytic
therapy useful.
NCCT shows no evidence
of acute infarction. B, CT
perfusion CBF map shows
a region of decreased
perfusion within the
posterior segment of the
left MCA territory
(arrows). D, MTT map
shows a corresponding
prolongation within this
same region (arrows). C,
CBV map demonstrates
no abnormality, therefore,
representing a CBV/MTT
mismatch or ischemic
penumbra.

18. CT Venography(CTV)
 Allows visualization of the cerebral venous structures
and has sensitivity for depicting the cerebral veins and
sinus.
 The most commonly affect sinus are the superior
sagittal sinus , the transverse sinus and the sigmoid
sinus.
 MRV (MR Venography ) is the technique of choice.
 However , CTV overcomes flow related artifacts seen in
TOF MR, takes less time and can be done on patients
contra-indicated to MR.
 Technique : 100ml contrast at 3ml/sec , after a delay of
40sec , scan process is initiated.

19. CT Venography(CTV)
Shows
thrombosis in
the superior
sagittal sinus
and left
transverse
sinus

20. MDCT of Spine
 Isotropic resolutions , multiplanar reformations on
MDCT now enable diagnosis that are not apparent on
axial images.
 Clinical application:
1. Cervical trauma
2. Degenerative spine disease of the spine
3. Post operative patients with metallic hard ware (less
streak artifacts)
4. MDCT angiography of spinal vasculature provide the
details of perfusion and anatomy of Artery of
Adamkeiwicz

21. MDCT of Spine
Normal
appearing
Left and
Right facets
of the
cervical
spine from
MD
Computerize
d
Tomography
(MDCT)
scan.

22. MDCT of Spine
ARTICATS REDUCED ARTIFACTS

23. Advances of MRI in
Neuroimaging
1. Improvements in MR hardware and
Soft ware technology
2. Large ‘Field of Viewing’ imaging.
3. High Field strength MR imaging.
4. Efficient Data processing techniques.
5. Improvement in Pulse sequences.

24. Advances of MRI in
Neuroimaging
 Improvements in MR hardware and Software
technology:
1. Phased Array Coils:- Is the combination of Multiple
Surface coils significantly improving the image quality
through a higher SNR and parallel data generation.
2. Parallel Acquisition Techniques (PAT):- Use
decoupled receiver coils , separate channels to cover
sub –FOV in a parallel fashion, and the acquired data
is combined in K space to form an entire image using
reconstruction algorithm.
PAT uses two image reconstruction techniques
 SENSE(Sensitivity encoding )technique.
 SMASH(Simultaneous Acquisition of Spatial
Harmonics).

25. Efficient Data processing
techniques.
T2 SE , 2MIN 3SEC T2 with PAT ,45SEC

26. Advances of MRI in
Neuroimaging
 Large ‘Field of Viewing’ imaging.
1. Development of sliding or rolling table platform or
phased array coils allows for unlimited FOV.
2. Fat saturated 3D gradient echo with isotropic
resolution have been employed for metastasis survey
and whole body angiography.
3. Distinct advantage is in evaluation of entire neural
axis at one go.
4. Use in angiography covering the area from the arch of
the aorta to the circle of Willis using a neurovascular
coil in patients with stroke.

27. Large ‘Field of Viewing’
imaging – Whole Body MRI
 Images are obtained in the coronal plane
only, which minimizes the number of
image acquisitions and enables fast
coverage of larger regions of the body.
 This plane also has an advantage in that
coronal images are also comparable to
those from other whole-body imaging
modalities.
 STIR sequences are used which show
lesions as region of high signal intensity.

28. Large ‘Field of Viewing’
imaging – Whole Body MRI
 Can reliably detect tumor spread to bone and
bone marrow as well as extra-skeletal
tissues.
 Well-suited to the evaluation of pediatric
patients with small round blue cell
neoplasms, such as neuroblastoma,
Ewing sarcoma family of tumors,
rhabdomyosarcoma, and lymphoma and
neurofibromatosis.
 Ability to detect osseous (both cortical and
medullary) and extraosseous disease in a
single imaging examination.

29. Whole Body MRI
STIR CT
LYMPHOMA
Normal NF

30. Advances of MRI in
Neuroimaging
 High Field strength MR imaging.
1. MR system of 3tesla (and higher).
2. Major advantage is improved SNR with increasing
the field strength.
3. Chemical shift increases in proportion to the magnetic
field and resultant increase in spectral separation of
resonance frequencies is used to the advantage in
Spectroscopy , Fat suppression.
4. Volumetric structural imaging , small lesion detection ,
i.e. multiple sclerosis evaluation of epilepsy ,
diffusion tensor imaging , MR angiography and
BOLD.

31. Advances of MRI in
Neuroimaging
 Efficient Data processing techniques.
The unprocessed 2D data set prior to
FT referred to as K-space is a
horizontal oriented phase views (Ky) ,
the vertical arm (Kx) being the
frequency axis.

32. Advances of MRI in
Neuroimaging
 Efficient Data processing techniques.
1. Multiple lines of K space in the same TR can be acquired by using
differently phase encoded echoes as in Fast Spine Echo(FSE)
2. Multiple lines of K space in the same TR can also be acquired by
use of oscillating gradients as in the single shot technique like
Echo Planar Imaging(EPI).
3. Two halves of the K space are symmetrical , hence less than full
data can be acquired and the remaining part interpolated from it
as is used in the HASTE(Half Acquisition Shot Turbo Spine
Echo) sequences.
4. The PROPELLER(Periodically rotated overlapping parallel
lines with enhanced reconstruction ) and BLADE reduce the
motion artifact and improve the image quality at high field ,
correcting the in-plane motion.

33. Efficient Data processing
techniques.
T2 FSE in an
uncooperative child
HASTE imaging in
spite of movements.

34. Advances of MRI in
Neuroimaging
 Useful Pulse sequences for neuroimaging.
1. Fast Spine Echo
2. Fluid Attenuated Inversion Recovery
3. Single Short Technique of FSE(HASTE, SS-FSE)
4. Gradient Echo Imaging (GRE ) and its variants
5. Susceptibility weighting Imaging (SWI).
6. Echoplanar Imaging (EPI)

35. Advances of MRI in
Neuroimaging
 Fast Spine Echo :
Originally Rapid Acquisition With Relaxation Enhancement (RARE)
by Henning.
A train of multiple spin echoes with different phase encoding steps
are generated from multiple closely applied 180degree RF
pulses to fill up the K space.
Characteristics:
The sequences is less sensitive to magnetic susceptibility effects ,
thus less prone for artifacts(This is a disadvantage in imaging
intracranial hemorrhage and calcification)
FSE has totally replaced the conventional SE and T2 weighted
images and gives exquisite images of brain and spine.

36. Advances of MRI in
Neuroimaging
 Fast Spine Echo:
Characteristics (contd….) :
3D FSE-
 Isotropic coverage has become feasible by manipulating T2 decay b
variable flip angle non selective short refocusing pulses replacing
180degree pulses , thus allowing ultra long echo time and high
reduction factor in scan time.
 This technique is called SPACE(Sampling perfection with
application optimized contrasts).
 Allows one time acquisition of T1 , T2 , Proton and even FLAIR
contrast.
Uses : Multiple sclerosis , ear structures , sialogrpahy .

37. Fast Spine Echo : 3D FSE ,
with FLAIR
Isotropic voxels allow multiplanar free slicing with submillimeter resolution.

38. Advances of MRI in
Neuroimaging
 Fluid attenuated inversion recovery
(FLAIR):
1. Use a long TR and TE and an inversion
pulse designed to null the signal of
CSF.
2. Brain pathologies with intermediate T2
times are poorly visualized if they are
located near the CSF, FLAIR being
heavily T2 weighted improves
conspicuity of such lesion after

39. Advances of MRI in
Neuroimaging
 Fluid attenuated inversion recovery (FLAIR):
Major indications.
1. Evaluation of multiple sclerosis plaques particularly those situated
near the CSF interface
2. Superficial small infarcts are detected better & chronic infarcts
with hyperintense periphery can be differentiated from VR spaces.
3. Useful in neonatal hypoxia
4. Differentiate Arachnoid from epidermoid cyst.
5. Subarachnoid space disease – infections , tumors and
hemorrhage appear bright.

40. Fluid attenuated inversion
recovery (FLAIR):
 Brain MRI in Autoimmune Encephalitis Axial T2 and
FLAIR MRI of the brain . High signal intensity is
present in the right caudate nucleus and adjacent
anterior limb of the internal capsule.
T2 FSE FLAIR

41. Advances of MRI in
Neuroimaging
 Single shot Techniques of
FSE(HASTE , S-FSE):
It is a single shot FSE technique which
during one excitation uses multiple
echoes to fill slightly more than half K
space to obtain T2 images.
Use the concept of K space conjugate
symmetry , the images is reconstructed
with reduces scan time.

42. Advances of MRI in
Neuroimaging
 Single shot Techniques of FSE(HASTE ,
S-FSE): Indications:
1. Ideal for imaging claustrophobic /uncooperative
patients, inadequately sedated children.
2. In evaluating fetus – Fetal brain contains abundant
water, thus normal anatomy , development and
anomalies are well shown.(FISP and FIESTA also
used)
3. Reduce susceptibility effects , hence imaging
postoperative spine with metal hardware to show cord
anatomy can be done.

43. Single shot Techniques of
FSE(HASTE , S-FSE):
The fetal MRI (right)
shows a giant
omphalocele,
indicated by the
arrow.
The fetal MRI
(right) shows
Arnold Chiari II
malformation

44.  Magnetic Resonance Myelography(MRM):
MRM uses fat suppressed heavily T2 weighted
images and background suppression
Uses:
1. Fast non-invasive technique
2. Shows nerve roots and dorsal root ganglia
better thecal stenosis accurately
3. Arachnoid adhesion , syringomyelia and
perineural and arachnoid cysts.

45. Magnetic Resonance
Myelography(MRM):
a) Coronal and b)
sagittal single thick-
slice magnetic
resonance
myelograms show
simultaneous first
look detection of
significant lumbar
canal stenosis,
spinal arterio-
venous
malformation (a)
and synovial
neoarthrosis (b)
Baastrup’s disease

46.  Gradient echo imaging(GRE) and its variants.
Instead of using 180º pulse refocusing pulse , a gradient
echo is
formed , by using short flip angles that leads to build up
longitudinal magnetisation and persistence of transverse
relaxation – called FLASH (Fast Low Angle Shot)
Depending on whether transverse magnetisation is
spoiled or refocused,
1. Coherent (Steady state GRE): Provides accentuated
T1 contrast.
2. Incoherent (Spoiled GRE): Provides T2 contrast.

47. Gradient echo imaging(GRE)
and its variants.
T2* gradient echo sequence
showing multiple lobar brain
microbleeds as small black
dots, without any lesions in
the basal ganglia.
Spontaneous
Intracerebral
Haemorrhage

48.  Susceptibility weighting imaging:
Exploits the magnetic inhomogeneity where the tissues of higher
susceptibility distort the magnetic field and become out of phase and
show signal loss.
High resolution 3D gradient Echo sequences.
Uses:
1. Delineation of small vessels , particularly veins is exquisite
2. Evaluation of traumatic brain injuries , coagulopathic and
hemorrhagic brain disorders
3. Evaluation of neoplasm, cerebral infarction, vascular
malformations

49. Susceptibility weighting imaging:

50.  Echo planar imaging(EPI):
 Ultrafast technique , involves very rapid gradient
reversal , to acquire multiple phase encoding echoes
that form a complete image in one TR.
 Types – Blipped EPI , Spiral EPI.
 Clinical applications:
1. Brain scan of uncooperative patient
2. Breath hold imaging of the abdomen and heart
3. Functional task activation, perfusion imaging.

51.  DWI(Diffusion Weighted Imaging):
1. Diffusion contrast depends on molecular motion of water. The
directional movements of water in white matter tracts is depicted
as signal loss on images by application of gradients.
2. The b-value:
 Is a factor that reflects the strength and timing of the gradients
used to generate diffusion-weighted images.
 The higher the b-value, the stronger the diffusion effects. Value
> 1000sec/mm2 good DWI.
1. ADC :
 Measures impedance of water molecules diffusion.
 An Expressed in units of mm2/s.
 ADC values less than 1000-1100 x 10-6 mm2/s are generally
acknowledged in adults as indicating restriction,

52. DWI(Diffusion Weighted Imaging):
 Uses :
A) Ischemic Stroke:
1. Unique sensitivity for ischemic stroke
2. Infarct appear bright on DWI and dark on ADC
3. Diffusion changes are detectable within minutes
of ischemia which is vital for initiation of
therapy.
4. Reduced ADC persists variably (10 days) ,
returns to baseline and then remains elevated
subsequently due to brain softening and gliosis.
5. DWI pseudo normalize after reperfusion or
therapy within 1-2days.

53. DWI(Diffusion Weighted Imaging):
 Uses :
1. Helps differentiating stroke from multiple sclerosis
plaques
2. Differentiating from stroke mimics like vasogenic
edema syndromes (hypertensive encephalopathy
)which are not associated with diffusion restriction.
3. In diagnosing abscess , enchephalatides and diffuse
axonal injuries.
4. Characterization of hypercellular tumours, i.e.
lymphoma , malignant meningioma.
5. Differentiating radiation necrosis from recurrent
tumour.

54. DWI(Diffusion Weighted
Imaging):
Acute infarct (left MCA)
Bright on DWI Dark on ADC

55. DWI(Diffusion Weighted
Imaging):

56. DWI(Diffusion Weighted
Imaging):
 Confusion and disturbed conscious level after surgical
correction of TOF.
Left temporal intra axial
cystic space occupying
lesion surrounded by
moderate perifocal
edema. It has thick
capsule that displays
low signal in T2, bright
signal in T1 and avidly
enhancing post contrast.
The cyst content shows
diffusion restriction
being bright signal in
DWI and low signal in
ADC.
Diagnosis: Left temporal
lobe abscess
T2 FLAIR DWI ADC
T1 + C

57. Diffusion Tensor Imaging
 Is an extension of DWI that allows data profiling
based upon white matter tract orientation.
 Within cerebral white matter, water molecules
tend to diffuse more freely along the direction of
axonal fascicles than across them. Such
directional dependence of diffusivity is termed
anisotropy..
 Color coding:
1. red for fibres crossing from left to right
2. green for fibres traversing in anterior-posterior
direction
3. blue for fibres going from superior to inferior

58. Diffusion Tensor Imaging
 FA reflects the directionality of
molecular displacement by diffusion
and vary between 0 (isotropic
diffusion) and 1 (infinite anisotropic
diffusion). FA value of CSF is 0.
 MD reflects the average magnitude of
molecular displacement by
diffusion. The more the MD value, the
more the isotropic is the medium

59. Diffusion Tensor Imaging
T2 MD map FA map FA fused with MD

60. Diffusion Tensor Imaging
Color-encoded
maps
Red: left to right;
Blue: Cranial to
caudal
Green: Anterior
to posterior.
MD map FA Map

61. Diffusion Tensor Imaging
 Uses:
1. Assess the deformation of white matter
by tumours - deviation, infiltration,
destruction of white matter and in Pre-
surgical planning
2. Delineate the anatomy of immature
brains
3. Alzheimer disease - detection of early
disease
4. Schizophrenia- Disturbances in
anisotropy.
5. Focal cortical dysplasia

62. Diffusion Tensor Imaging
Amyotrophic lateral sclerosis Healthy subject.
Descending fibre tracts connecting the cortex and brainstem are
shown in purple and the corticospinal tract is shown in green.
The ratio of the number of fibre tracts in corticospinal tract to the
total number fibre tracts is decreased in amyotrophic lateral
sclerosis

63. Color-encoded DT images (red,-left to right; blue- cranial to caudal;
green,-anterior to posterior) demonstrate
•DISPLACEMENT (A–C),
•INFILTRATION (D–E)
•DESTRUCTION (F) of white matter tracts (arrow) by tumor

64. Perfusion weighted Imaging
 Measures signal reduction induced in the brain during passage of
paramagnetic contrast agents which induce magnetic susceptibility
effects.
 It measures
1. rCBV is measured in units of millilitres of blood per 100 g of brain
and is defined as the volume of flowing blood for a given volume
of brain.
2. MTT is measured in seconds and defined as the average amount
of time it takes blood to transit through the given volume of brain.
3. rCBF is measured in units of millilitres of blood per 100 g of brain
tissue per minute and is defined as the volume of flowing blood
moving through a given volume of brain in a specific amount of
time.
rCBF = rCBV/MTT.

65. Perfusion weighted Imaging
 In Stroke:
Ischemic brain after acute vascular occlusion shows
reduced rCBV and elevated MTT , as a lack of signal
drop after contrast arrival.
Interpretation:
 PWI > DWI i.e. mismatch – Denoted viable tissues at
risk.
 PWI=DWI, or PWI < DWI – Infarct is presumed or
already perfused.
Thus MRI stroke protocol should include T2 FSE, FLAIR
followed by DWI, PWI and GRE sequence for
haemorrhage.

66. Perfusion weighted Imaging
 In cerebral tumors:
1. Tumor angiogenesis and vascularity
2. Useful for differentiating tumor necrosis
from recurrent tumors (Necrosis will be
avascular)
3. Assesses response by chemotherapeutic
agents(reduced rCBF)
4. Guide in heterogeneous tumors for biopsy
from aggressive areas for appropriate
staging.

67. Perfusion weighted Imaging

68. Perfusion weighted Imaging
NCCT DWI PWI
There is match of PWI = DWI