MRI INSTRUMENTATION

Question 1

What is the name of an electromagnet in the form of a current carrying wire coiled into a tightly packed Helix?

Answer 1

Solenoid

Question 2

According to Faradays law, as the angle of interaction betweent he magnetic field and the conductor nears _______, the current produced within the conductor increase.

Answer 2

90 degrees

Question 3

1st law of electrogmanetism
2nd law of electromagnetism

Answer 3

Faradays law 1st, Lenz Law 2nd

Question 4

Lenz law states that an induced current sets up a _____________ opposing the magnetic field that produced the original current

Answer 4

Magnetic field

Question 5

Lenz law states that another name for an induced magnetic field that opposes a current produced by an electromagnetic induction

Answer 5

Eddy Current

Question 6

Unit that is used to represent magnet field homogeneity

Answer 6

PPM (parts per million)

Question 7

The ferromagnet substance that commonly composes permanent magnets is :

Answer 7

ALNICO (Aluminum, nickel, and cobalt)

Question 8

Which type of MRI magnet has the lowest operating cost?

Answer 8

Permanent magnet

Question 9

What term describes the strength of the magnetic forces that act on substances exposed to external magnetic fields?

Answer 9

Magnetic Susceptibility

Question 10

Substances with _________ magnetic susceptibility display no magnetic moment, and when in the presence of an external magnetic field they slightly repel it.

Answer 10

Diamagnetic - because they have paired orbital electrons

Question 11

Substances with ___________ magnetic susceptibility display a small positive magnetic moment, and when in the presence of an external magnetic field, they are slightly attracted to it.

Answer 11

Paramagnetic - because they have unpaired orbital electrons

Question 12

Super-paramagnetic substances only display a magnetic moment when super paramagnetic molecules are grouped in bulk - which substance?

Answer 12

Iron Oxides - used in contrast ages for MRI

Question 13

Ferromagnetic substances display a large positive magnetic moment because

Answer 13

They have half filled orbital electron shells

Question 14

The RF field is oriented _________ to the magnetic field

Answer 14

Perpendicular

Question 15

The RF Energy transmitted in MRI is considered :

Answer 15

Non Ionizing Radiation

Question 16

Surface coils are only sensitive to tissue depths that are _____% of the coils diameter

Answer 16

50–75%

Surface coil that is 8” in diameter will only visualize tissues approx. 4 inches deep.

Question 17

What type of volume coil is two coils that offset eachother by 90 degrees?

Answer 17

Quadrature coil

Question 18

Another term for multi-channel coil is

Answer 18

Phased Array Coil

Question 19

Transmit Bandwidth

Answer 19

Describes the entire range of frequencies that the system sends in an RF pulse

Question 20

Transmit Bandwidth is indirectly controlled by selecting a

Answer 20

Slice Thickness

Question 21

Receive Bandwidth

Answer 21

Entire range of frequencies that the system samples from

Question 22

What is most affected by adjustments in receive bandwidth

Answer 22

SNR

Question 23

Decreasing the receive bandwidth results in an _________ in SNR, and an ___________ in chemical shift artifact.

Answer 23

Increase/increase

Question 24

What portion of an RF pulse profile is sampled during readout?

Answer 24

Central Portion

Question 25

When performing a prescan, the center frequency of the transmitted RF pulse should be tuned to match the:

Answer 25

Larmor frequency of hydrogen protons

Question 26

What energy field is used primarily to spatially encode data obtained during acquisition?

Answer 26

Gradient magnetic field

Question 27

Abbreviation that represents the gradient magnetic field

Answer 27

TVMF (time varying magnetic field)

Question 28

The time it takes for a gradient to achieve maximum gradient amplitude is called

Answer 28

Gradient Slew Rate