EXAM #9 — PHYSICS UNIT 02 Flashcards
static magnetic field.
the main magnetic field- doesn’t change over space or time
fringe magnetic field.
the part of the static magnetic field that extends beyond the magnet bore
gradient magnetic field.
a magnetic field that changes linearly over a distance (slopes), used for spatial localization
magnetic field homogeneity.
the uniformity of the magnetic field
active magnet shielding.
confining and concentrating the main magnetic field with smaller; opposing magnetic fields
passive magnet shielding.
confining and concentrating the main magnetic field by placing large pieces of metal on the magnet, or lining the magnet room with steel
active magnet shimming.
improving the homogeneity of the main magnetic field by superimposing smaller magnetic fields
passive magnet shimming.
improving the homogeneity of the main magnetic field by placing pieces of iron around the magnet
body coil.
the RF transmitter/receiver that is built into the main magnet housing
RF coil.
a transmitter and/or receiver of RF
transceiver.
an RF coil that can transmit AND receiver RF
cryogen.
a naturally occurring gas that is compressed into liquid form
array processor.
the part of the MRI computer that reconstructs the MR images
slew rate.
the speed at which the gradients arrive at the peak amplitude
Faraday cage.
a complete box of copper and steel that surrounds the magnet room, shielding the room from outside RF
eddy currents.
electric currents that are induced in metal components of the MRI magnet housing
identify the 2 most important characteristics of an MRI computer.
speed and storage capacity
identify the notation used to represent the primary magnetic field.
Bo
list the 3 types of primary magnets used in MRI.
permanent, resistive, superconducting
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. ?
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
identify the maximum static magnetic field strength allowed by the FDA for clinical imaging of patients over 1 month old.
8T
explain the function of the yolk in a permanent MRI magnet.
to confine and concentrate the static field
state 3 advantages and 2 disadvantages of permanent MRI magnets.
advantages: low initial cost, low operating cost, small fringe field
disadvantages: low static field, very heavy
state 3 advantages and 3 disadvantages of resistive MRI magnets.
advantages: low initial cost, light weight, static field can be switched off
disadvantages: high power consumption, large fringe field, low static field
state 3 advantages and 3 disadvantages of superconducting MRI magnets.
advantages: high field strength, good field homogeneity, low power consumption
disadvantages: high initial cost, cryogen replacement, acoustic noise)
2 advantages of imaging with high static magnetic field strength.
faster scan times, better image quality
identify the superconducting metals most often used in MRI magnets.
niobium and titanium
identify the cryogen most often used in superconducting MRI magnets.
liquid helium
identify the 2 possible directions of the static magnetic field MRI magnets.
vertical or horizontal
identify the unit measurement of homogeneity of a magnetic field.
parts per million (PPM)
state the term used to identify the conductive bands that create a gradient magnetic field.
physical gradients
list the 3 letters used to identify the physical gradients.
X, Y, and Z
- 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. ?
- 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
- 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. ?
- 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
describe the direction of current flow in opposite loops of a gradient coil pair.
The current flows in opposite directions in each coil pair
identify the 2 properties used to compare gradient coil systems.
peak strength, slew rate
identify the unit of measurement of the slope or peak amplitude of a gradient magnetic field.
milliTesla per meter (mT/m)
identify the piece of system hardware that provides power to the gradient coils.
gradient amplifiers
identify the type of RF coil that can be used to receive and transmit RF.
volume RF coil
list the 3 categories of RF coils.
linear polarized (LP);
circular polarized (CP) or quadrature;
phased array
give an example of a common surface coil.
spine coil
list 3 examples of common volume coils.
body coil,
head coil,
extremity coil
describe the quadrature or circular polarized (CP) volume RF coil.
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
describe the quadrature or circular polarized (CP) surface RF coil.
a simple loop of wire is superimposed over a loop of wire that is in a figure-eight
describe the phased array RF coil.
4 or more simple loop coils that are slightly overlapped, providing increased signal and increased coverage
discuss the advantage and disadvantage of using smaller RF coils for MRI.
advantage: better signal
disadvantage: smaller area of coverage
- 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. ?
- 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
