clinical imaging methods

matchmoaningAI and Robotics

Nov 17, 2013 (3 years and 11 months ago)

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Introduction to
different

brain

and
other

clinical

imaging

methods




Oury Monchi, Ph.D.

Parkinson Cognition Action &
Neuroimaging

(PCAN)
Laboratory


Centre de
Recherche
,
Institut

Universitaire

de
Gériatrie

de
Montréal

&
Universit
é

de Montréal

http://
unfweb.criugm.qc.ca/oury

Imaging Techniques

I.
Magnetic

Resonance

Imaging (MRI)


Brain

anatomy

techniques (
volumetry
, DTI)


Brain

function

technique (fMRI)


Vascular

and
heart

imaging

II.
Positron Emission
Tomography

(PET)

III.
Single Photon Emission
Computed

Tomography

(SPECT)

IV.
Application to
Exercise

Sciences

MRI Basic
Principles


Magnet:


Very powerful (1 to 7T) and homogeneous and static magnetic field, it
incites the hydrogen protons to align themselves.


Earth magnetic field 0.00005T!


Radiofrequency coils:


Generates and receive transient electromagnetic field, at the
frequency of resonance of hydrogen disrupting alignment of protons
from low to high energy state.


Energy released can be detected as they return to their base state


Speed to return to base states depends of the tissue they are part of,
this generate the T1 and T2 signals.


Gradient coils:



Gradual fields aligned in
x
,
y
,
z

axes


Allows us to place detected signals in a 3D volume


Anatomical

MRI (T1)

Morphological

variations


Large
variability

from

one
brain

to the
other


Can
we

make

inferences

based

on population
criteria

(
age
,
sex
,
health
) on
this

morphological

basis?
What

criteria

do
we

use?

Techniques


Volumetry


Voxel

Based

Morphometry

(VBM)


Diffusion
Tensor

Imaging (DTI)

Principles

of
volumetry


An anatomical image allows us to separate the grey and white matter


One can paint the region of interest on each subject’s scan


We can study the variation of this region compared with a specific
parameter (age, neuropsychological score, etc) or different groups
(Parkinson’s
vs

healthy controls)

Volumetry
:
example


Women

suffering

from

somatoform

disorders

compared

to
control participants


Significant

difference

in
caudate

nucleus volume

Hakala

et al.
(
2004)

Voxel

Based

Morphometry
:

principles


VBM consists in comparing
local grey matter density
between
two populations


This comparison is not dependent on:


any particular structure


the experimenter’s subjectivity (as in
volumetry
, where regions
are painted manually)


VBM is performed on the
entire brain

Voxel

Based

Morphometry
:

methods


Normalization

to a
template


Segmentation


Spatial
smoothing


Statistical

analysis

Voxel

Based

Morphometry
:

applications


22
Controls

and 56 MCI (13 have
evolved

into

dementia
) are
followed

over 22
months







Compared

with

stable
MCIs
, progressive
MCIs

exhibit

atrophy

in
different

regions

Hamalainen

et
al.
(
2007)

Diffusion
Tensor

Imaging:

principles


Allows to obtain images based on properties of water molecule
displacement in tissues


Reflects tissue properties (position, orientation, anisotropy),
especially of white matter


Reflects tissue degradation (axons, myelin, cell wall)


Made possible by an adequate acquisition sequence

Concept of Diffusion:

isotropy

and
anisotropy


Diffusion is isotropic if it is with the same amplitude in all
directions



Diffusion is anisotropic if it prefers one or more directions



Fractional anisotropy characterizes local diffusion

(1 > FA > 0)

Concept of
Mean

Diffusivity


Isotropy

is

not
enough

to
characterize

diffusion:

DTI: MRI
sequence


One or more images
at

b=0 (T2
contrast
)


As
many

image acquisitions as
there

are directions
at

b ~ 1000
sec/mm
2

DTI:
maps

obtained


Mean

diffusivity

map


high

signal in
ventricles

and
sulci


Fractional

anisotropy

map

DTI: FA and MD applications


Influence of
age

on
mean

diffusivity

in
grey

and white
matter


Correlation

of
both

measures

with

age

in
grey

matter
,
only

in
peak

height

in white
matter


Fibre reconstruction:
average

of
86 000km in
aged

participants
compared

with

118 000km in
young

Benedetti
et
al.
(
2006)

Study

of
anatomical

connectivity

a

b

c

f

e

g

DTI:
Fiber

tracking

Basic
Principles

of
fMRI


For a long time, a
relationship

between

brain

activity

and
deoxygenated

hemoglobin

(
which

is

paramagnetic
) in the
blood

has been
known


In the
early

90's
it

was

discovered

that

an MR pulse
sequence

could

measure

the rate of
deoxygenated

hemoglobin

(
Thulborn

et al.;
Ogawa

et al.)


This gave
rise

to Blood
Oxygenation

Level

Dependent

(BOLD)
fMRI or T2*
sequence
,
which

provides

us
with

an indirect
measure

of
brain

activity
.

Preprocessing

Belin
,
et al.
(2000)
Nature

Functional MRI: Voice recognition

Functional

Connectivity

studies

Physiological Studies: Spectroscopy

MRI of the
heart

MR
-
measurement

of
aortic

compliance


Compliance

of
aorta

is

highly

predictive

of
overall

vascular

health


Flow
velocity

imaging

allows

measurement

of
pressure
-
wave

propagation in
aorta


Vessel

wall

imaging

allows

measurement

of
distensibility

Flow
velocity

imaging

of
aorta

Vessel

wall

imaging

of
aorta


Brain

vascular

images

Positron Emission
Tomography

(PET)

Positron Emission
Tomography

principles


PET
depends

on the injection of a radioactive isotope
produced

by a cyclotron


From

the time of
their

injection,
these

radio
-
isotopes
decay

and
emit

positrons,
which

collide

with

electrons
.
These

collisions
produce

opposit

γ
-
rays

that

are
captured

the
coincidence

detectors of the PET scanner


Depending

on the
molecules

that

these

isotopes
bind

with
,
we

can

get

information on
metabolism
,
blood

flow, or the release
of
neurotransmitter

(
eg
. 11C
raclopride

which

binds

to striatal
D2
receptors
)

Radioactive tracers for PET


18FDG (
Fludeoxyglucose
)
: glucose metabolism


H215O : regional blood flow (cerebral or myocardial)


18FDOPA :
Dopa

uptake (dopamine
precurser
)


[11C]raclopride : Dopamine D2 antagonist


18FP
-
TZTP :
muscarinic

agonist (acetylcholine)


PHNO, FLB 457, WAY, ……….

FDG PET


FDG
-
PET scan in a boy with left parietal
-
temporal epilepsy showing
decreased glucose metabolism in the left parietal and temporal lobes

FDG
-
PET in the
detection

of
tumor

Water PET


Regional cerebral blood flow
(
rCBF
) is related to glucose and
oxygen consumption.


Very sensitive to acute changes…


E.g., patients with Parkinson’s
disease who received DBS on
STN perform a joystick task while
OFF
-

or ON
-
DBS.


Similar task
-
induced
rCBF

changes in the M1 in both
condition, but greater changes in
SMA.


Normalizing effect of DBS.

Single Photon Emission
Computed

Tomography

(SPECT)

SPECT


Similar

to PET, SPECT
makes

use of radioactive tracer.
However

the gamma radiation
is

mesured

directly

(not
following

positrons
which

annihilate

with

electrons

like

in PET).


A PET
allows

for
higher

resolution

images
than

SPECT
be

cause of the
coincidence

detection
.


But SPECT
can

use
longer
-
lived
, more
easily
-
obtained

radioisotopes

than

PET


Important if no cyclotron





Inferior infarctus without other perfusion anomaly

What

are the
effects

of
physical

training
that

can

explain

improvement

in cognition?


Direct
effects

on cognition:


Aerobic

exercise

has an impact on
cerebral

functions



Indirect
effects
:


Aerobic

exercise

acts

on
moderators

of cognitive
aging



Effect

of
physical

fitness training on
brain

structures and
functions


VBM: better
cardiorespiratory

fitness level (VO2max) was
associated with a reduced loss in grey and white matter in the
frontal, prefrontal and temporal regions in older adults

Colcombe

et al., 2003

Effect

of
physical

fitness training on
brain

structures and
functions


Functional brain imaging studies (fMRI) showed that enhanced
cardiovascular functions after aerobic training are associated
to greater task
-
relevant activity in brain areas recruited in an
attentional control task


Flanker

task

Colcombe

et al., 2004


Caffeine

decreases exercise
-
induced hyperaemic myocardial
blood flow


Most prominent in coronary artery disease patients


Caffeine decreases myocardial perfusion reserves


Most pronounced in coronary artery disease patients

Aknowledgements



Kristina Martinu,
BSc


Rick
Hoge
,
PhD


Jean
-
Paul
Soucy
, MD/
MSc


Antonio P. Stradella,
MD
/
PhD


Louis
Bherer
,
PhD

The slides will be available on:

unfweb.criugm.qc.ca/oury/downloads.html