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.
4. 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.
5. Dual Source CT
6. 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.
7. 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.
8. 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.
9. CT angiography Image processing by MIP SSD VR
10. 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.
11. 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.
12. CT angiography Intracranial aneurysm Carotico Ophthalmic
aneurysm A- MIP B,C- VR D- DSA Carotid artery is incorporated into
the aneurysm
13. 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
14. 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.
15. CT Perfusion(CTP) Acute stroke: Infarct . NCCT shows some
micro vascular ischemic changes posteriorly. BD,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.
16. 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.
17. 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.
18. CT Venography(CTV) Shows thrombosis in the superior
sagittal sinus and left transverse sinus
19. 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
20. MDCT of Spine Normal appearing Left and Right facets of the
cervical spine from MD Computerize d Tomography (MDCT) scan.
21. MDCT of Spine ARTICATS REDUCED ARTIFACTS
22. 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.
23. 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).
24. Efficient Data processing techniques. T2 SE , 2MIN 3SEC T2
with PAT ,45SEC
25. 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.
26. 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.
27. 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.
28. Whole Body MRI STIR CT LYMPHOMA Normal NF
29. 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.
30. 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.
31. 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.
32. Efficient Data processing techniques. T2 FSE in an
uncooperative child HASTE imaging in spite of movements.
33. 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)
34. 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.
35. 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 .
36. Fast Spine Echo : 3D FSE , with FLAIR Isotropic voxels
allow multiplanar free slicing with submillimeter resolution.
37. 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
38. 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.
39. 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
40. 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.
41. 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.
42. 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
43. 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.
44. 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) Baastrups disease
45. Gradient echo imaging(GRE) and its variants. Instead of
using 180 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.
46. 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
47. 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
48. Susceptibility weighting imaging:
49. 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.
50. 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,
51. 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.
52. 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.
53. DWI(Diffusion Weighted Imaging): Acute infarct (left MCA)
Bright on DWI Dark on ADC
54. DWI(Diffusion Weighted Imaging):
55. 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
56. 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
57. 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
58. Diffusion Tensor Imaging T2 MD map FA map FA fused with
MD
59. Diffusion Tensor Imaging Color-encoded maps Red: left to
right; Blue: Cranial to caudal Green: Anterior to posterior. MD map
FA Map
60. 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
61. 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
62. Color-encoded DT images (red,-left to right; blue- cranial
to caudal; green,-anterior to posterior) demonstrate DISPLACEMENT
(AC), INFILTRATION (DE) DESTRUCTION (F) of white matter tracts
(arrow) by tumor
63. 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.
64. 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.
65. 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.
66. Perfusion weighted Imaging
67. Perfusion weighted Imaging NCCT DWI PWI There is match of
PWI = DWI
