Using MRI to peer inside the
brain at NIAAA
Chris Kaldahl
Physics Teacher
Yorktown High School
Arlington, VA
NIAAA, Section of BEI
National Institute on Alcohol Abuse and
Alcoholism, Section of Brain
Electrophysiology and Imaging
Dr. Dan Hommer, Senior Investigator
Dr. Jim Bjork, Prat Fellow
NIAAA Mission Statement
To conduct investigations on…
the effects of acute and chronic alcohol consumption
and withdrawal on the brain’s electrical activity.
in vivo brain structure and function such that cerebral
physiology is referenced to brain morphology
supplemented with other measures of brain electrical
activity and behavior.
the brain’s physiological responses to drugs and
cognitive challenges that are associated with
behavioral control and dyscontrol mechanisms.
Personal Goals
Gain better understanding of physics
underlying use of Magnetic Resonance
Imaging (MRI)
Learn about research methodology from
current practitioners
Connect abstract particle physics
concepts to concrete applications
MRI
Magnetic
Resonance
Imaging
2 Types
Structural
Functional
Structural vs. Functional MRI
Just like it sounds
Structural – uses MR imaging techniques to
look at soft tissues of the body in a non-
invasive fashion
Functional – uses MR imaging to locate
activity in soft tissues of body
fMRI uses a BOLD technique
Blood Oxygenation Level Dependent
Difference in magnetic properties of
oxygenated versus deoxygenated blood
Assuming brain activity requires
oxygenated blood, fMRI uses BOLD to
map regions of brain activated in
response to various stimuli
BOLD
How does MRI work?
Protons have a Magnetic
property called spin Field Bo
Moving charge
creates a magnetic
field
Each proton (spin)
has its own magnetic A spinning proton
field (or spin)
Am I a magnet?
Billions upon billions of spins
Each oriented in a slightly different way
Magnetic fields are vectors
Components cancel out in all directions
You don’t stick to your refrigerator door
Precession
Spins placed in Precession about Bo
external magnetic
field precess
Think about a
External
spinning top magnetic
wobbling under the field Bo
influence of gravity
Larmor Equation
Spins precess at a frequency that
depends on two variables
the type of nucleus the spin is a part
of (we are interested in H+ nuclei)
the strength of the magnetic field B
Larmor Equation
=B
- angular precessional frequency of the
proton (measured in Hz)
- gyromagnetic ratio – this is a value that
differs for different nuclei - for H+ it is
42.6 MHz / T
B - magnetic field intensity (in Tesla)
Dial M for Magnet
Spins placed in Quantum physics
external magnetic tells us that there
field assume one of are always slightly
two energy states more spins parallel
Parallel to external than anti parallel
field – spin up This results in a net
Anti parallel to magnetization in
external field – spin
positive z-axis
down
Longitudinal Magnetization
Bo Mo
A sample of randomly External magnetic field Bo
oriented spins before a creates net magnetic field
magnetic field is Mo in parallel direction
introduced (spin up or low energy)
A dead end?
Longitudinal magnetization does not
change in a fixed magnetic field
No measurement possible
Need to do 2 things to make an image…
Create changing magnetic field
Create a component of that field in a
direction other than the z-axis
Resonance
Shake any object back and forth
At certain frequencies, the object
vibrates more energetically than others
Energy can be transferred from one
object to another if it is “pushed” at
these resonant frequencies
R stands for Resonance
Spins precessing at frequency as given
by the Larmor Equation
Frequencies are in the part of the
electromagnetic spectrum called radio
waves
Send in a radio frequency (RF) pulse at
same frequency – pushing spins at right
frequency to give them more energy
One effect of RF pulse
Causes some of parallel / spin up / low
energy spins to transition into higher
energy state
This causes a change in the longitudinal
magnetization
Longitudinal magnetization can go to zero,
or become larger in the negative z
direction, depending on duration and
intensity of RF pulse
A second effect of RF pulse
Causes initially out of phase spins to
precess in phase
This causes a magnetization in the xy
plane to form
This is called transverse magnetization
Effect of RF pulse on spins
Voila!
Transverse
magnetization is a
changing magnetic
field
Changing magnetic
fields induce
alternating current in
nearby coils of wire
This signal is turned
into an image
Current Research
Uses fMRI to explore the brain function
of incentive motivation
Seeks to compare adolescent children
of alcoholics (COA’s) with children
without family risk or history of
alcoholism
Hypothesis
Parts of Nucleus Accumbens (Nacc) will
show increased activation during
periods of anticipating reward as
compared to no reward
This activation will be greater during
anticipation of greater reward and
smaller for small reward
COA’s exhibit less BOLD activation
during anticipation of working for
reward
Experimental Design
Monetary Incentive Delay (MID) task
Participants see cues that indicate whether
they will win or lose money in varying
amounts
Wait for a variable anticipatory delay
Respond to rapidly presented target in
order to win or avoid losing money
Results
Study still ongoing
Preliminary results indicate similarities
in brain function between adults and
non-alcoholic adolescents
Probably greater activation in adults than
non-alcoholic adolescents
Potentially significant lack of BOLD
activation in COA in anticipation of
reward
Anticipation of Reward Images
Adult
Non-
Alcoholic
Adolescent COA
Reward Feedback Images
Adult
Non-
Alcoholic
Adolescent COA
Applications to the Classroom
MRI for HS Students text
Presentation
Class website
Numerous science fair topic ideas
Greater understanding of research
methodology
Contact Information
E-mail
c_kaldahl@yahoo.com
Web address
http://yhspatriot.yorktown.arlington.k12.va.us/~ckaldahl