Chapter 9 Flashcards
Instrumentation & equipment
Magnetic susceptibility refers to:
a. how easily something can become magnetized by an external factor
b. the Larmor Frequency
c. to the “spin-up” or “spin-down” state of an atom
d. the fringe fields of heavy magnets
a. how easily something can become magnetized by an external factor
In a typical superconducting magnet, what is the direction of the main magnetic field?
a. Vertical
b. Horizontal
c. Around the flux lines
d. As a slope in 3 directions
b. Horizontal
An active gradient coil, causes the following results on the main magnetic field?
a. The field becomes stronger throughout the main magnetic field.
b. The field becomes increasingly weaker away from isocenter.
c. The field becomes increasingly stronger away from isocenter.
d. The field becomes stronger at one end and weaker at the other.
d. The field becomes stronger at one end and weaker at the other.
What do diamagnetic materials do?
a. Strongly attract other materials.
b. Have unpaired electrons.
c. Have paired electrons that slightly repel magnetic fields.
d. They are used in permanent magnets.
c. Have paired electrons that slightly repel magnetic fields.
Alnico is used in what type of MRI system?
a. Solenoid electromagnet.
b. Permanent magnet.
c. Superconducting magnet.
d. Closed-bore magnet.
b. Permanent magnet.
What is the Slew Rate?
a. The speed and strength of the gradient.
b. The polarity of the gradient coil.
c. The time it takes an RF coil to transmit a signal.
d. Defines the steepness of the gradient slope.
a. The speed and strength of the gradient.
What type of material is used for RF shielding?
a. Nickel
b. Lead
c. Zinc
d. Copper
d. Copper
Which of the following is a limitation of a resistive electromagnet?
a. Resistance in the wires limits the magnetic field strength.
b. Weight of the magnet.
c. Cost of the magnet.
d. Requires extra shielding for high-fringe fields.
a. Resistance in the wires limits the magnetic field strength.
Which of the following are used as cryogens?
a. Liquid xenon
b. Liquid nitrogen
c. Liquid helium
d. Liquid aluminum
c. Liquid helium
What do shim coils do?
a. Receive the MR signal.
b. Allow for scanning in all three planes.
c. Produce the RF signal.
d. Correct the field inhomogeneities produced by the magnet or ferrous objects.
d. Correct the field inhomogeneities produced by the magnet or ferrous objects.
What types of coils are used for spatial encoding?
a. Gradient coils
b. RF coils
c. Transmit coils
d. Receiver coils
a. Gradient coils
Which of the following is a description of paramagnetism?
a. Half-filled electron shells that are easily magnetized
b. Paired electrons, not easily magnetized
c. Unpaired electrons, low positive magnetic susceptibility
d. Permanent Magnets
c. Unpaired electrons, low positive magnetic susceptibility
What do cryogens do?
a. Increase field strength with increased thermal energy.
b. Reduce electrical resistance in the magnetic coils.
c. Alter the magnetic field strength along a slope.
d. Change direction of the magnetic field from vertical to horizontal in a permanent magnet.
b. Reduce electrical resistance in the magnetic coils.
The wires in a superconducting magnet are made from which of the following materials?
I. Iron
II. Niobium
III. Cobalt
IV. Titanium
a. I only
b. I and III
c. II only
d. II and IV
d. II and IV- niobium & titanium
Where does the Fourier transformation take place?
a. RF source
b. image processor
c. field gradient system
d. array processor
d. array processor
Which type of magnet is made up of naturally ferromagnetic material?
a. Superconductive
b. Resistive
c. Permanent
d. Refrigerator
c. Permanent
Which type of magnetic coils are employed as a transmitter, receiver or as both?
a. Gradient coils
b. RF coils
c. Shim coils
b. RF coils
Magnetic fields have direction which are usually designated as north and south, therefore
they are described as:
a. vectors
b. dipoles
c. protons
d. axes
b. dipoles
Which type of electromagnetic coils can be found inside and outside of the housing of the
MRI magnet?
a. Gradient coils
b. RF coils
c. Shim coils
b. RF coils
Which type of magnet requires no electricity to maintain its magnetic field and can weigh more than 20,000 lbs?
a. Superconductive
b. Resistive
c. Permanent
c. Permanent
Which type of receiver RF coil is placed close to a patient’s body for the purpose of imaging
superficial anatomical structures?
a. Solenoid coils
b. Maxwell coils
c. Surface coils
d. Golay coils
c. Surface coils
Which type of magnet requires a steady current of electricity in coils of conductor wrapped
around an air or iron core?
a. Superconductive
b. Resistive
c. Permanent
b. Resistive
Which type of magnet has almost no discernible fringe field?
a. Superconductive
b. Resistive
c. Permanent
c. Permanent
What converts data into images?
a. RF source
b. computer system
c. field gradient system
d. image processor
d. image processor
Which materials have half-filled electron shells?
a. Diamagnetic
b. Paramagnetic
c. Superparamagnetic
d. Ferromagnetic
d. Ferromagnetic
Which magnet is created by passing current through many loops of wire to form a coil?
a. Solenoid
b. Rotating
c. Processional
d. Uneven
a. Solenoid
An electromagnet at room temperature is subject to Ohm’s law and is called a ____ magnet.
a. superconducting
b. natural
c. resistive
d. simple
c. resistive
What kind of shimming is performed by scanning a phantom and adjusting the position of the shim plates for optimum field homogeneity?
a. Passive
b. Active
c. Determined
d. Placement
a. Passive
The time it takes for a given gradient to reach its maximum amplitude is called:
a. slew rate
b. duty cycle
c. gradient strength
d. rise time
d. rise time
A cylindrical array of electrically conductive elements positioned around the inner circumference of the bore, is called a:
a. head coil
b. body coil
c. extremity coil
d. central coil
b. body coil
1.5T equals
a. 10,000 G
b. 15,000 G
c. 30,000 G
d. 5,000 G
b. 15,000 G
In a superconducting magnet, the magnetic field strength is increased by increasing the:
a. amount of cryogens
b. temperature
c. internal pressure
d. turns of wire
d. turns of wire
In a solenoid superconducting magnet, the direction of current flow affects the:
a. strength of the magnetic field
b. direction of the magnetic field
c. intensity of the magnetic field
d. homogeneity of the magnetic field
b. direction of the magnetic field
The percentage of time that the gradient is permitted to work is called the:
a. slew rate
b. duty cycle
c. gradient strength
d. rise time
b. duty cycle
If a coronal slice plane has been selected, the __________ is enabled to alter the magnetic field around the patient’s body.
a. X gradient
b. Y gradient
c. Z gradient
d. W gradient
b. Y gradient
The ________ the coil, the better the signal.
a. bigger
b. uglier
c. wider
d. smaller
d. smaller
The liquid cryogens are cooled in a superconducting magnet at a temperature of
_________?
a. 1 Celsius
b. 1 Fahrenheit
c. 4 Kelvin
d. 2 Kelvin
c. 4 Kelvin
Magnetic field gradients are generated by coils of wire ________ the magnet.
a. surrounding
b. on opposite ends outside
c. within the bore of
d. both inside and outside
c. within the bore of
Rise time is:
a. The time from one repetition to another
b. The time from the excitation pulse to the echo
c. The time it takes for the nuclei to reach equilibrium
d. The time required for a gradient to reach the correct slope
d. The time required for a gradient to reach the correct slope
What type of electromagnetic coils produce smaller magnetic fields, which allow spatial
localization to be performed?
a. Gradient coils
b. RF coils
c. Aneurysm coils
d. Shim coils
a. Gradient coils
