departments.weber.edu/chfam/2570/Neurology.html

Central sulcus

Susceptibility0Negative: repelled Positive: attracted

Fer

rom

agne

tic

Par

amag

netic

Dia

mag

netic

-1

Water-910-6

Air (oxygen)+0.36 10-6

Deoxyg. Blood-6.52 10-6

Permanent magnets106

Superconductors-1

Magnetic forces

Special dissociation curves

CO stop haemoglobin giving up oxygen

Fetal blood preferentially takes up oxygen in placenta

1/T2* against % dHb for blood at 7T

Active cortexBlood flow

Blood volume

Blood oxygenation

Arteriole VenuleCapillary Bed

Glucose and O2

Glucose and O2

Lightson

Lightson

Lightsonaa

bb

Time (s)

00 3030 6060

Boldsignal

8 s

Time (s)

Stim

ulus

Initial dipPost stimulus undershoot

Boldsignal

Heamodynamic response function

EPI pulse sequence

RF

Gslice

Gphase

Gread

Time

Repeat 128 times

A B C

A

B C

kx

ky

EPI k-space trajectory

0.98

1

1.02

1.04

1.06

1.08

0 50 100 150time (s)

norm

alise

d s

ign

al i

nte

nsi

ty

7 T

3 T

1.5 T

B

0.98

1

1.02

1.04

1.06

1.08

1.1

0 5 10 15 20 25 30

time (s)

norm

alis

ed s

ignal

inte

nsi

ty

7 T3 T1.5T

C

stimulus

Time course of signal change at optimum TE for each field strength averaged over subjects

Cycle average for each field strength.

Rising edge of response intersects base-line earlier at higher field.

BOLD timecourses

Image registration (From Welcome Functional Imaging Lab)

1 0 0 Xtrans

0 1 0 Ytrans

0 0 1 Ztrans

0 0 0 1

1 0 0 0

0 cos() sin() 0

0 sin() cos() 0

0 0 0 1

cos() 0 sin() 0

0 1 0 0

sin() 0 cos() 0

0 0 0 1

cos() sin() 0 0

sin() cos() 0 0

0 0 1 0

0 0 0 1

Translations Pitch Roll Yaw

Rigid body transformations parameterised by:

Squared Error

Somatotopic mapping

Response to fat

Correlation of BOLD response with all attributes of oral fat delivery’

Areas with a positive correlation of BOLD response with fat concentration

Different fat levels

Supertaster effect

Cochlear implant & Cochlear StimulationCochlear implant & Cochlear Stimulation

fMRI & Cochlear StimulationfMRI & Cochlear Stimulation

LLRR

Collaboration with C. Ludman (Radiology), S. Mason (Medical Physics), G. O’Donoghue (Otolaryngology)Collaboration with C. Ludman (Radiology), S. Mason (Medical Physics), G. O’Donoghue (Otolaryngology)

250 Hz, biphasic right cochlear stimulation (9V)250 Hz, biphasic right cochlear stimulation (9V)

ARTERIAL SPIN LABELLING

Possible labelling scheme

• Could measure perfusion like this:

Blood flow

INVERSION PULSE

Magnetization transfer• Could measure perfusion like this:

• The inversion pulse is off-resonance to slice– Might expect it to have no effect on slice– It does because of magnetization transfer

• Exchange between bound and free protons

Blood flow

INVERSION PULSE

INVERSION PULSETAG

EPISTAR

Blood flow

Compare TAG and CONTROL conditionsTAG: tag arterial blood that will exchange with tissueCONTROL: tag venous blood

INVERSION PULSECONTROL

Perfusion• Brain signal comes from mixture of tissue and

blood• Water assumed to be freely diffusible tracer

exchanging between capillary and tissue– Exchange time assumed to be zero

• Not quite true

IN OUT

Blood brain partition coefficient• There are

– 80.5 g water /100g blood– 84.0 g tissue /100g grey matter

• Blood flowing in has more magnetization per unit volume than tissue

• Blood brain partition coefficient = water content of brain = ~ 0.98

water content of blood

Transit time• It takes the labelled blood a finite time to

reach the voxel– And the even longer to reach the capillary

• This must be taken account of in models

Blood flow

TransitTime

Kinetic model

• IF Mz is equal at start of tag and control conditions is same

• Then different signal is given convolution:

DifferenceMz

TagControl

Kinetic model

Arterial input functionDepends on tagging scheme

Timeafter tag applied

Transit time

Transit time

Kinetic model

Residue FunctionAmount of contrast remaining after a time t

r(t)

Inputfunction

Time

Kinetic model

r(t)

Time

Time

r(t)

Magnetization decay functionDescribes T1 relaxation of tag

Labelling schemesFAIR (flow alternating inversion recovery)

Blood in slice follows inversion recoveryBlood outside slice alternates between

• following inversion recovery and • being at equilibrium (Mo)

Blood flow

SE-EPI FAIR, 3x3x5 mm3, 96x96 matrix, TE = 23 ms

Free-breathe. PW-average (40 dynamics, realigned).

Kidney ASL