Lecture 23: 1. MRI noise processes

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# Lecture 23: 1. MRI noise processes - PowerPoint PPT Presentation

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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### Lecture 23: 1. MRI noise processes

MP574

Dipole Moments from Entire Sample

Magnetic

Field (B0)

Magnetic

Field (B0)

m

m

Positive

Orientation

Negative

Orientation

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

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 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

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

I = “in phase”

Q = “quadrature” or 90o out of phase

Imaginary

Real

Background noise

Imaginary

Real