Title: DIFFUSION & PERFUSION MRI IMAGING
1DIFFUSION PERFUSIONMRI IMAGING
Dr. Wael Darwish
2DIFFUSION MRI IMAGING
3- History -
- The feasibility of diffusion images was
demonstrated in the middle 1980s - Demonstration on clinical studies is more recent
it corresponds with the availability of EPI on
MR system - A single shot EPI sequence can freeze the
macroscopic pulsating motion of the brain or
motion of the patients head
4Diffusion Weighted Image
- Core of infarct irreversible damage
- Surrounding ischemic area ? may be salvaged
- DWI open a window of opportunity during which
ttt is beneficial - DWI images the random motion of water molecules
as they diffuse through the extra-cellular space - Regions of high mobility rapid diffusion ? dark
- Regions of low mobility slow diffusion ? bright
- Difficulty DWI is highly sensitive to all of
types of motion (blood flow, pulsatility, bulk
patient motion,).
5- Diffusion contrast -
- Diffusion gradients sensitize MR Image to motion
of water molecules - More motion Darker image
Freely Diffusing Water Dark
Restricted Diffusion Bright
6- Principles -Velocities and methods of
measurement
7- Principles -About the b factor
-
- b is a value that include all gradients effect
(imaging gradients diffusion gradients) - The b value can be regarded as analogous to the
TE for the T2 weighting
8Medium
High
Low
b 500
b 1000
b 5
9- Principles -About ADC
- The ADC value does not depend on the field
strength of the magnet or on the pulse sequence
used (which is different for T1 or T2) - The ADC obtained at different times in a
given patient or in different patients or in
different hospitals can be compared
10- Principles -Isotropic and Anisotropic diffusion
- Diffusion is a three dimensional process, but
molecular mobility may not be the same in all
directions - In brain white matter, diffusions value depends
on the orientation of the myelin fiber tracts and
on the gradient direction
11Anisotropic diffusion Individual
direction weighted
X Diffusion - Weighting
Y Diffusion - Weighting
Z Diffusion - Weighting
12Isotropic diffusion
Isotropic Diffusion- Weighted Image
Individual Diffusion Directions
Mathematical Combination (Sorensen et al., MGH)
- x /
13Diffusion weighted image
14Characteristics of diffusions contrast
Short TE DWI gives more SNR
TE100ms SR 120
TE75ms SR150
15Characteristics of diffusions contrast
Higher b value increases sensitivity
MS
Higher CNR helps distinguish active lesions
Stroke
Higher CNR
Vasogenic edema Cytotoxic Edema
Tumor
Vasogenic edema
b 1000 b 3000
16Mathematical Processing
Diffusion-weighted
ADC map
17Mathematical Processing
ADC map
Diffusion-weighted
Exponential ADC
18Diffusion Imaging Processing
Exponential ADC (ratio of Isotropic
DWI/T2) eliminates T2 shine through artifacts and
may distinguish subacute from acute stroke
19Arachnoid Cyst
b0
b1000
eADC
ADC
20Clinical Application
21 MR Images of 60-Year-Old Man with Glioblastoma
Multiforme
Figures 1, 2. On (1) T2-weighted fast spin-echo
and (2) contrast-enhanced T1-weighted spin-echo
images, the differential diagnosis between
glioblastoma and abscess is impossible.
22central hypointensity on diffusion-weighted image
and hyperintensity on ADC map, consistent with
the diagnosis of tumor.
23 MR Images of 57-Year-Old Woman with Cerebral
Metastasis
24 central hypointensity on diffusion-weighted image
and hyperintensity on ADC map, consistent with
the diagnosis of tumor.
25 MR Images of 70-Year-Old Man with History of
Recent Vertigo and Disequilibrium
26A brain abscess with Streptococcus anginosus was
found at surgery.
27 MR Images of 57-Year-Old Woman with Cerebral
Metastasis
the differential diagnosis between metastasis and
abscess is impossible.
28 Central hypointensity is seen on the
diffusion-weighted image and hyperintensity on
the ADC map, consistent with the diagnosis of
tumor.
29APPLICATIONS
30BENIGN VERSUS MALIGNANT FRACTURE
31- This finding indicates that the lack of signal
reduction in malignant vertebral fractures is
caused by tumor cell infiltration - Different diffusion effect is caused by more
restriction or hindrance in densely packed tumor
cells compared with more mobile water in
extracellular volume fractions in fractures
32- diffusion-weighted spin-echo sequences could
differentiate benign fracture edemas and
fractures caused by tumor infiltration due to
higher restriction of water mobility in tumor
cells.
33T2-weighted MR image shows ovoid hypointense mass
in spinal canal.
34T1-weighted sagittal MR image after infusion of
gadolinium contrast material shows diffuse signal
enhancement of mass.
35T1-weighted transverse MR image after infusion of
contrast material shows extent of tumor in spinal
canal and C4-C5 neural foramen
36Diffusion-weighted sagittal MR image using
peripheral pulse gating and navigator correction
shows signal intensity of mass (open arrows) to
be intermediate, less than that of brainstem
(large solid arrow) and greater than that of
vertebral bodies (small solid arrows).
37ADC map shows mass (arrows) as structure of
intermediate intensity.
MENINGIOMA
38- In that study, tumors with high cellularity had
low mean ADC values, and tumors with low
cellularity had high mean ADC values. - In addition, the relatively high ADC value seen
in our patient corresponded to a low degree of
cellularity, such as has been reported in
cerebral gliomas.
39Perfusion imaging
- Definitions
- Principles
- Some more definitions
- Perfusion technique
- Applications
- Future
40Definitions
- Perfusion is refer to the delivery of oxygen
and nutrients to the cells via capillaries - Perfusion is identified with blood flow
which is measured in milliliters per minute
per 100 g of tissue
41Principles
After injection of a contrast agent
- In normal brain, the paramagnetic contrast agent
remains enclosed within the cerebral
vasculature because of the blood brain barrier - The difference in magnetic susceptibility
between the tissue and the blood results in
local magnetic field ?finally to large signal loss
42Some more Definitions
- rCBF the rate of supply of Gd chelate to a
specified mass ( ml / 100g / min) - rCBV - the volume of distribution of the Gd
chelate during its first passage through the
brain ( or ml / 100g ) - MTT - the average time required for any given
particle to pass through the tissue, following an
idealised input function (min or s)
MTT rCBV / rCBF
43- Passage of Gd. can be followed by the changes in
the relaxation rates concentration of
local contrast.
- Linear relation bet. concentration and rates of
signal changes can be expressed as curve. - Tissue contrast concentration time curve can be
used to determine tissue micro vascularity,
volume and flow.
44At each voxel we observe
slice n
mean transit time
time
Integral cerebral blood volume
intensity
time
45Principles
- Each one of these effects is linearly
proportional to the concentration of the
paramagnetic agent - To date, this technique results in
non-quantitative perfusion parameters (like
rCBV,rCBF or MTT) because of the ignorance of
the arterial input function
46Principles
- Dynamic Susceptibility Contrast Imaging
Extract time-intensity curves
Perform mathematical manipulation
Generate functional maps
NEI
- x /
MTE
Negative Enhancement Integral Map(NEI) Qualitativ
e rCBV map
Mean Time to Enhance (MTE)Map Ischaemic Penumbra
First Pass Contrast bolus
47Dynamic MR perfusion
- Hemodynamics Bl. volume
- Bl. flow
- Aim 1. Diagnosis
- 2. Monitoring management
- 3. Understanding intracranial
lesions -
48rCBV
rCBV, processed with Negative Enhancement
Integral(NEI) is related to area under curve
49MTT
MTT is related to the time to peak and to the
width of the peak it is processed with Mean
Time to Enhance(MTE)
50Cerebral blood perfusion by bolus tracking
Requires very high speed imaging
power injector - Gadolium 5ml/sec
Procedure 1 - Start Imaging 2 - Inject
Contrast 3 - Continue Imaging
10 slices - 50 images of each slice - TOTAL
time 134 min
Push Gadolinium with 20 cc of saline flush
51Applications of Perfusion MRI
- Neurology
- Gerontology
- Neuro-oncology
- Neurophysiology
- Neuropharmacology
52Perfusion Imaging Findings in Infarction
Stroke
- CBV
- regional perfusion deficit
- compensatory increased volume
- MTT
- regional prolongation of transit time
53Head Trauma
54Head traumaHypo-perfusion
55E.g. 1 Left hemisphere stroke, 4.5 hrs after
onset of symptoms
56Same patient with DWI and FLAIR
4.5 hrs
57Apparent diffusion coefficient ADC
ADC map
Isotropic diffusion image b800
58Contrast enhanced perfusion imaging
24 slices 3 seconds/acquisition
Time/intensity graph
59Mean Time To Enhance
delayed compensatory hyperperfusion
delayed hypoperfusion
60EPI Diffusion and Perfusion mapping
EPI Diffusion
EPI Perfusion
61Findings with Perfusion Imaging for Infarction
- Changes seen almost immediately after the
induction of ischemia - more sensitive than conventional MRI
- Perfusion findings often more extensive than
those on DW-EPI in early stroke - more accurately reflects the amount of tissue
under ischemic conditions in the hyperacute
period than DW EPI - Abnormal results correlate with an increased risk
of stroke - PerfEPI - DWEPI tissue at risk
62Alzheimers disease
Findings with Perfusion imaging for Gerontology
- FDG PET
- marked temporo-parietal hypometabolism
- Tc-HMPAO SPECT
- marked temporo-parietal hypoperfusion
- DSC MRI
- correlates well with SPECT
63Findings with Perfusion imaging for
Neurophysiology and pharmacology
- Traumatic brain injury
- focal rCBV deficits that correlate with cognitive
impairment - Schizophrenia
- decreased frontal lobe rCBV
- HIV/ AIDS
- multiple discrete foci of decreased CBV
- Polysubstance abuse
- multiple discrete foci of decreased CBV
New Jersey Neuroscience Institute
64Findings with Perfusion imaging for Neuro-oncology
- Critical imaging to BBBB imaging of neoplasm
- many tumors have high rCBV
- regions of increased rCBV correlate with areas of
active tumor. - heterogeneous patterns of perfusion suggest high
grade - radiation necrosis typically demonstrates low
rCBV - Lesion characterization may be possible
- meningiomas have very high CBV in contrast to
schwannomas
New Jersey Neuroscience Institute
65Dynamic MR perfusion
- Clinical applications-
- Intracranial neoplasm
- N.B angiogenesis usually aggressiveness
- Exceptions- 1. Meningioma
- 2.Choroid plexus papilloma
- 1.Glioma Grading
- Biopsy
- D.D recurrence from radiation
necrosis
662.Metastasis Can differentiate solitary
metastasis from 1ry brain neoplasm (glioma) by
measuring the peritumoral relative blood
volume. 3.1ry cerebral lymphoma Can help in
differentiating lymphoma from glioma as lymphoma
is much less vascular
674. Meningioma Hypervascular
Extra axial Has leaky and permeable capillaries
causing no recovery of T2 signal to basline. 5.
Tumor mimicking lesions e.g.
cerebral infections tumefactive
demyelinating lesions less
commonly infarcts
686.Tumefactive demyelinating lesions No
neo-vascularization in demyelinating lesions To
conclude MR perfusion should be included in
routine evaluation of brain tumor as it improve
diagnostic accuracy.
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73Neuro-oncology
rCBV maps
-
- low rCBV in tumour infers low grade glioma
74Eg2 Diffused tumorAbnormal capillary density
Glioblastoma multiform
Hyper perfusion
Excised region
Before surgery MTSE shows blood brain / barrier
breakdown (bbbb)
After surgery rCBV map shows diffuse disease in
right frontal lobe
75 Eg3 tumor vs.radiation necrosis
CBV
Conventional T2
Recurrent Tumor
Non specific changes