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001 MRI > EXAM #9 — PHYSICS UNIT 02 > Flashcards

EXAM #9 — PHYSICS UNIT 02 Flashcards

1
Q

static magnetic field.

A

the main magnetic field- doesn’t change over space or time

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2
Q

fringe magnetic field.

A

the part of the static magnetic field that extends beyond the magnet bore

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3
Q

gradient magnetic field.

A

a magnetic field that changes linearly over a distance (slopes), used for spatial localization

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4
Q

magnetic field homogeneity.

A

the uniformity of the magnetic field

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5
Q

active magnet shielding.

A

confining and concentrating the main magnetic field with smaller; opposing magnetic fields

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6
Q

passive magnet shielding.

A

confining and concentrating the main magnetic field by placing large pieces of metal on the magnet, or lining the magnet room with steel

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7
Q

active magnet shimming.

A

improving the homogeneity of the main magnetic field by superimposing smaller magnetic fields

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8
Q

passive magnet shimming.

A

improving the homogeneity of the main magnetic field by placing pieces of iron around the magnet

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9
Q

body coil.

A

the RF transmitter/receiver that is built into the main magnet housing

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10
Q

RF coil.

A

a transmitter and/or receiver of RF

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11
Q

transceiver.

A

an RF coil that can transmit AND receiver RF

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12
Q

cryogen.

A

a naturally occurring gas that is compressed into liquid form

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13
Q

array processor.

A

the part of the MRI computer that reconstructs the MR images

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14
Q

slew rate.

A

the speed at which the gradients arrive at the peak amplitude

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15
Q

Faraday cage.

A

a complete box of copper and steel that surrounds the magnet room, shielding the room from outside RF

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16
Q

eddy currents.

A

electric currents that are induced in metal components of the MRI magnet housing

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17
Q

identify the 2 most important characteristics of an MRI computer.

A

speed and storage capacity

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18
Q

identify the notation used to represent the primary magnetic field.

A

Bo

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19
Q

list the 3 types of primary magnets used in MRI.

A

permanent, resistive, superconducting

20
Q

identify the field strengths in Tesla that are usually associated with the:

a. permanent MRI magnet. ?
b. resistive MRI magnet. ?
c. whole-body superconducting MRI magnet. ?

A

identify the field strengths in Tesla that are usually associated with the:

a. permanent MRI magnet. less than . 3 T
b. resistive MRI magnet. less than .3 T
c. whole-body superconducting MRI magnet. .5- 3T or above

21
Q

identify the maximum static magnetic field strength allowed by the FDA for clinical imaging of patients over 1 month old.

A

8T

22
Q

explain the function of the yolk in a permanent MRI magnet.

A

to confine and concentrate the static field

23
Q

state 3 advantages and 2 disadvantages of permanent MRI magnets.

A

advantages: low initial cost, low operating cost, small fringe field
disadvantages: low static field, very heavy

24
Q

state 3 advantages and 3 disadvantages of resistive MRI magnets.

A

advantages: low initial cost, light weight, static field can be switched off
disadvantages: high power consumption, large fringe field, low static field

25
Q

state 3 advantages and 3 disadvantages of superconducting MRI magnets.

A

advantages: high field strength, good field homogeneity, low power consumption
disadvantages: high initial cost, cryogen replacement, acoustic noise)

26
Q

2 advantages of imaging with high static magnetic field strength.

A

faster scan times, better image quality

27
Q

identify the superconducting metals most often used in MRI magnets.

A

niobium and titanium

28
Q

identify the cryogen most often used in superconducting MRI magnets.

A

liquid helium

29
Q

identify the 2 possible directions of the static magnetic field MRI magnets.

A

vertical or horizontal

30
Q

identify the unit measurement of homogeneity of a magnetic field.

A

parts per million (PPM)

31
Q

state the term used to identify the conductive bands that create a gradient magnetic field.

A

physical gradients

32
Q

list the 3 letters used to identify the physical gradients.

A

X, Y, and Z

33
Q
  1. for a superconducting MRI electromagnet, identify the location of the:
    a. X gradient coil pair. ?
    b. Y gradient coil pair. ?
    c. Z gradient coil pair. ?
A
  1. for a superconducting MRI electromagnet, identify the location of the:
    a. X gradient coil pair. sides of the bore
    b. Y gradient coil pair. top and bottom of the bore
    c. Z gradient coil pair. circular bands at the head and foot of the bore
34
Q
  1. for a superconducting MRI electromagnet, identify the direction of the gradient magnetic field induced by the:
    a. X gradient coil pair. ?
    b. Y gradient coil pair. ?
    c. Z gradient coil pair. ?
A
  1. for a superconducting MRI electromagnet, identify the direction of the gradient magnetic field induced by the:
    a. X gradient coil pair. from one side of the bore to the other
    b. Y gradient coil pair. from the top of the bore to the bottom or vice versa
    c. Z gradient coil pair. from one end of the bore to the other
35
Q

describe the direction of current flow in opposite loops of a gradient coil pair.

A

The current flows in opposite directions in each coil pair

36
Q

identify the 2 properties used to compare gradient coil systems.

A

peak strength, slew rate

37
Q

identify the unit of measurement of the slope or peak amplitude of a gradient magnetic field.

A

milliTesla per meter (mT/m)

38
Q

identify the piece of system hardware that provides power to the gradient coils.

A

gradient amplifiers

39
Q

identify the type of RF coil that can be used to receive and transmit RF.

A

volume RF coil

40
Q

list the 3 categories of RF coils.

A

linear polarized (LP);

circular polarized (CP) or quadrature;

phased array

41
Q

give an example of a common surface coil.

A

spine coil

42
Q

list 3 examples of common volume coils.

A

body coil,

head coil,

extremity coil

43
Q

describe the quadrature or circular polarized (CP) volume RF coil.

A

two loops of wire are arranged opposite each other, then another 2 loops are arranged opposite each other, and 90° offset from the first pair

44
Q

describe the quadrature or circular polarized (CP) surface RF coil.

A

a simple loop of wire is superimposed over a loop of wire that is in a figure-eight

45
Q

describe the phased array RF coil.

A

4 or more simple loop coils that are slightly overlapped, providing increased signal and increased coverage

46
Q

discuss the advantage and disadvantage of using smaller RF coils for MRI.

A

advantage: better signal
disadvantage: smaller area of coverage

47
Q
  1. identify the type of electric power used to create magnetic fields · in the:
    a. active shim coils. ?
    b. active shielding coils. ?
    c. primary magnet coils. ?
    d. gradient coils. ?
    e. RF transmitter coils. ?
A
  1. identify the type of electric power used to create magnetic fields · in the:
    a. active shim coils. DC
    b. active shielding coils. DC
    c. primary magnet coils. DC
    d. gradient coils. DC
    e. RF transmitter coils. AC

001 MRI (15 decks)

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