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Lecture 23: 1. MRI noise processes. MP574. Dipole Moments from Entire Sample. Magnetic Field (B 0 ). Magnetic Field (B 0 ). m. m. Positive Orientation. Negative Orientation. Source of Signal. Proton or Water MRI B o Magnetic Field Proton Nucleus S = ±ħ/2. rg. 2. 2. h. D E.

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slide2

Dipole Moments from Entire Sample

Magnetic

Field (B0)

Magnetic

Field (B0)

m

m

Positive

Orientation

Negative

Orientation

source of signal
Source of Signal
  • Proton or Water MRI
    • Bo Magnetic Field
    • Proton Nucleus
      • S = ±ħ/2

rg

2

2

h

DE

D

µ

=

E

M

B

z

o

4

kT

detected signal

z

B1(t)

F

=

w

AB

g

cos(

t

)

1

L

g

2

w

Ah

B

Ah

=

µ

w

w

=

w

o

L

V

(

t

)

S

(

t

)

g

sin(

t

)

g

sin(

t

)

y

L

L

L

kT

kT

x

Detected Signal
brownian motion
Brownian Motion
  • Brownian Motion Conditions:
  • x0= 0
  • x(t) is a continuous random variable
  • Increments x(t1) and x(t2) are statistically independent and normally distributed

http://en.wikipedia.org/wiki/Wiener_process

johnson or thermal noise

Rp

Rc

Johnson or “Thermal” Noise

Electrical Resistance of Coil

Patient Resistance

Thermal noise in patient dominant at high field strengths

johnson or thermal noise on both i and q channels
Johnson or “Thermal” Noise on both I and Q channels

I = “in phase”

Q = “quadrature” or 90o out of phase

Imaginary

Real

background noise
Background noise

Imaginary

Real

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