Brain Functional Imaging Flashcards
Phrenology
Franz Joseph Gall (1758-1828) Pseudomedicine primarily focused on measurements of the human skull, based on the concept that the brain is the organ of the mind, and that certain brain areas have localized, specific functions or modules.
Brodmann’s areas
Neurons of a particular area are the same size, shape, and point in the same direction Used this basis to draw a map and number them I.e. Brodmann’s area 17 is the primary visual cortex, 18 visual association area, 19 color vision Area 3 (sensory), area 4 (motor)
Roy and Sherrington 1890
Sherrington received Nobel prize for defining monosynaptic reflexes Posited that blood flow in the brain will change if an area in the brain works Studies showed that with changes in function of the brain, there were changes in blood flow
Angelo Mosso 1880
Studied patients with skull defects to monitor the changes in brain volume or temperature that are produced by brain activity.
Kety and Schmidt 1945
Invented method for quantifying the flow of blood in the brain Inert gas i.e. Xe Obrist figured out how to do this without insertion of an arterial central line
Early brain mapping
Lassen and Ingvar developed the intra-arterial 85Krypton/133Xenon injection method for measurement of the regional CBF (1961) No anesthesia involved. Measurements in awake subjects: listening, speaking, reading aloud.
Reivich 1969
IAP, very lipid soluble molecule that passes the BBB quickly Rate of accumulation proportional to blood flow in brain Antipyrine would accumulate in the brain. 14C radioactive tag - take a brain section out and place onto radioactive film - higher intensity regions are regions of higher blood flow.
Sokoloff
2-DG autoradiography Applied the idea of 2-deoxyglucose to measure metabolism 2-deoxyglucose is like glucose except on the 2C there is a hydrogen instead of a hydroxyl (deoxy). Thus means it can’t go into glycolysis. Hexokinase and the Glut1 transporters don’t care, however. Transferred into the brain and metabolised by hexokinase. Instead of progressing further steps, it accumulates. Indicator of the rate of hexokinase activity. Hexokinase is rate-limiting for metabolism so it’s an indicator of glucose consumption.
“Coupling”
2-DG to see where metabolism was increasing, antipyrine to see where blood flow was increasing See where glucose utilization is proportional to blood flow Different areas of the brain have different metabolisms with proportional blood flow In activated brain, there is a proportional increase in blood flow and oxygen consumption
Structural methods
CAT: x-rays reconstituted to give a 3D image Quick and easy indicator of stroke, indicates if there is a bleed (determines whether or not to initiate anticoagulant therapy) PET: positron emitting tomography Positrons are positively charged e- (antimatter) They annihilate as soon as they meet an electron. Molecule is made a β emitter. Electron emitted from nucleus. β+ vs β- emissions differ in half life 11C = 20 min 13N = 10 min 15O = 2 min 18F = 110 min Attach fluorine to 2-deoxyglucose molecule = fluorodeoxyglucose. Positron travels a few mm then encounters an electron. Annihilates, transformed into photons. Travel 180° from each other. Looking for simultaneous events. Overlay on CT or MR scan. microPET PET scans: gives good quantitative information but poor temporal and spatial resolution, very expensive Also used for receptor identification in pharmacology MRI Diffusor Tensor Etc
MRI
Diffusor Tensor Etc
PET: positron emitting tomography
Positrons are positively charged e- (antimatter) They annihilate as soon as they meet an electron. Molecule is made a β emitter. Electron emitted from nucleus. β+ vs β- emissions differ in half life 11C = 20 min 13N = 10 min 15O = 2 min 18F = 110 min Attach fluorine to 2-deoxyglucose molecule = fluorodeoxyglucose. Positron travels a few mm then encounters an electron. Annihilates, transformed into photons. Travel 180° from each other. Looking for simultaneous events. Overlay on CT or MR scan. microPET PET scans: gives good quantitative information but poor temporal and spatial resolution, very expensive Also used for receptor identification in pharmacology
CAT: x-rays reconstituted to give a 3D image
Quick and easy indicator of stroke, indicates if there is a bleed (determines whether or not to initiate anticoagulant therapy)
Marcus Raichle
fMRI/BOLD Functional MRI Blood oxygen level dependent signal Looking at using MR, looking at deoxyhemoglobin Looks at amount of oxygen being delivered to an area of tissue
The origins of fMRI
Deoxygenated hemoglobin disrupts a magnetic field, but oxygenated hemoglobin does not. For this reason MRI images, which are obtained using an intense magnetic field, can exhibit darkening of the image in areas of draining veins owing to the loss of signal. If blood flow increases suddenly in the face of an increase in cellular activity and this increase is not accompanied by an increase in oxygen consumption of comparable magnitude, oxygenation in capillaries and veins is increased (i.e., supply increases more than demand). This would lead to an enhancement of the MRI signal that could be detected → BOLD contrast.
Coupling
Vasoneuronal Coupling
Vasoneuronal Coupling 2
Scan Times
Mathematical Models
The origins of fMRI
fMRI
Structure and Function
Study 1
Study 2
Images
The Brains Dark Energy
DTI
VN coupling
Fig 2
Fig 1
Mosso
Architectonics
Modern Phrenology
