1st part chapter 9

Question 1

Homogeneity

Answer 1

Uniform was of magnetic field measured in parts per million

Question 2

Faradays law

Answer 2

When there is a current running through closed loop of wire an magnetic filed will be generated

Question 3

Ferromagnetic

Answer 3

Strong attraction to magnetic field and can become a projectile
High and positive
Can become permanent magnetized

Question 4

Magnetism and types

Answer 4

Ability to be affected by magnetic field
Paramagnetic
Diamagnetic
Ferromagnetic
Super paramagnetic

Question 5

Paramagnetic

Answer 5

Affects a MF by local increase in strength

Low and positive

Question 6

Diamagnetic

Answer 6

Affects MD by local decrease in strength

Low and negative

Question 7

3 primary magnets

Answer 7

Permanent
Resistive
Superconductive

Question 8

Advantages and disadvantages of permanent magnet

Answer 8

Adv- low cost, negligent able fringe field

Dis- limited field strength, fixed field strength and very heavy

Question 9

Adv and disadv of resistive

Answer 9

Adv- low cost, easy maintence and negligible fringe field

Dis- high power consumption, water cooling necessary and potential field instability

Question 10

Adv and disadv of superconductive magnet

Answer 10

Adv- high FS, high homogeneity and low power consumption

Dis- high cost, high cryogenic cost and intense fringe filed

Question 11

RF system perform 2 primary task

Answer 11

Excited tissue and converts signal to image

Question 12

Rf receiver and preamplifiers

Answer 12

Receiver amplifies signal

Preamp strengthens the entire signal

Question 13

Characteristics of surface coils large

Answer 13

More uniform
Lower SNR
Not suitable for small FOV
Applications are torso hips and long bones

Question 14

Characteristics SUrface coils small

Answer 14

Sensitive only near body
High SNR
Small FIV
High resolution

Question 15

Local coils - 5

Answer 15

Linear - single loop
Helmholtz- two parallel loops
Flexible- 1 or more linear loops around roi
Quadrature- bird cage
Phased array- multiple coils

Question 16

Gradient coils

Answer 16

Slope created by electromagnetic coils
Number of loops in coil
Current passing thru
Diameter and spacing of loops

Xyz

Question 17

Steps to begin scan

Answer 17

Light markers all centered for homogeneity
Adjust automatic tuning least path of resistance
Frequency
Transmitter adjustment
Receiver adjustment - analog to digital

Question 18

What type of magnetism is gadolinium?

Answer 18

Paramagnetic

Question 19

Measurement of magnetism

Answer 19

Tesla

1T = 10000 gauss

Question 20

Magnetic fields of low to ultra high Ts

Answer 20

Low- .2-.35
Midfield- .5-.7
High- 1.-1.5
Ultra high- 3t

Question 21

What is purpose of RF coils? Body coils? Surface coil?

Answer 21

RF to transmit and receive
Body to transmit
Surface to receive

Question 22

Permanent open system used for?

Answer 22

Claustrophobic
Kinematic
Interventional studies

Question 23

Shin coils provide?

Answer 23

MF homogeneity

Question 24

Magnetic susceptibility

Answer 24

Way material behaves in external MF

Question 25

Active shielding

Answer 25

Use of solenoid electromagnets around outside of the main magnet at each end of the bore

Located inside cryostat and superconducting

5 G threshold few ft from isocentre

Question 26

Passive shielding

Answer 26

Surround the magnet and lining of room with steel and copper plates.

Use for high field