MRI INSTRUMENTATION Flashcards
What is the name of an electromagnet in the form of a current carrying wire coiled into a tightly packed Helix?
Solenoid
According to Faradays law, as the angle of interaction betweent he magnetic field and the conductor nears _______, the current produced within the conductor increase.
90 degrees
1st law of electrogmanetism
2nd law of electromagnetism
Faradays law 1st, Lenz Law 2nd
Lenz law states that an induced current sets up a _____________ opposing the magnetic field that produced the original current
Magnetic field
Lenz law states that another name for an induced magnetic field that opposes a current produced by an electromagnetic induction
Eddy Current
Unit that is used to represent magnet field homogeneity
PPM (parts per million)
The ferromagnet substance that commonly composes permanent magnets is :
ALNICO (Aluminum, nickel, and cobalt)
Which type of MRI magnet has the lowest operating cost?
Permanent magnet
What term describes the strength of the magnetic forces that act on substances exposed to external magnetic fields?
Magnetic Susceptibility
Substances with _________ magnetic susceptibility display no magnetic moment, and when in the presence of an external magnetic field they slightly repel it.
Diamagnetic - because they have paired orbital electrons
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.
Paramagnetic - because they have unpaired orbital electrons
Super-paramagnetic substances only display a magnetic moment when super paramagnetic molecules are grouped in bulk - which substance?
Iron Oxides - used in contrast ages for MRI
Ferromagnetic substances display a large positive magnetic moment because
They have half filled orbital electron shells
The RF field is oriented _________ to the magnetic field
Perpendicular
The RF Energy transmitted in MRI is considered :
Non Ionizing Radiation
Surface coils are only sensitive to tissue depths that are _____% of the coils diameter
50–75%
Surface coil that is 8” in diameter will only visualize tissues approx. 4 inches deep.
What type of volume coil is two coils that offset eachother by 90 degrees?
Quadrature coil
Another term for multi-channel coil is
Phased Array Coil
Transmit Bandwidth
Describes the entire range of frequencies that the system sends in an RF pulse
Transmit Bandwidth is indirectly controlled by selecting a
Slice Thickness
Receive Bandwidth
Entire range of frequencies that the system samples from
What is most affected by adjustments in receive bandwidth
SNR
Decreasing the receive bandwidth results in an _________ in SNR, and an ___________ in chemical shift artifact.
Increase/increase
What portion of an RF pulse profile is sampled during readout?
Central Portion
When performing a prescan, the center frequency of the transmitted RF pulse should be tuned to match the:
Larmor frequency of hydrogen protons
What energy field is used primarily to spatially encode data obtained during acquisition?
Gradient magnetic field
Abbreviation that represents the gradient magnetic field
TVMF (time varying magnetic field)
The time it takes for a gradient to achieve maximum gradient amplitude is called
Gradient Slew Rate
