introduction to different brain and other clinical imaging methods
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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. - PowerPoint PPT PresentationTRANSCRIPT
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 & Université de Montréal
http://unfweb.criugm.qc.ca/oury
Imaging TechniquesI. 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 PrinciplesMagnet:
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 variationsLarge variability from one brain to the otherCan we make inferences based on population criteria
(age, sex, health) on this morphological basis? What criteria do we use?
TechniquesVolumetry
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: exampleWomen suffering from somatoform disorders compared
to control participantsSignificant 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 templateSegmentationSpatial smoothingStatistical 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 sequenceOne or more images at b=0 (T2 contrast)As many image acquisitions as there are directions at b
~ 1000 sec/mm2
DTI: maps obtainedMean diffusivity map
high signal in ventricles and sulci
Fractional anisotropy map
DTI: FA and MD applicationsInfluence 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
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DTI: Fiber tracking
Basic Principles of fMRIFor 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 PET18FDG (Fludeoxyglucose): glucose metabolismH215O : regional blood flow (cerebral or myocardial)18FDOPA : Dopa uptake (dopamine precurser)[11C]raclopride : Dopamine D2 antagonist18FP-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)
SPECTSimilar 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
AknowledgementsKristina Martinu, BScRick Hoge, PhDJean-Paul Soucy, MD/MScAntonio P. Stradella, MD/PhDLouis Bherer, PhD
The slides will be available on:unfweb.criugm.qc.ca/oury/downloads.html