Overview of MRI Physics Flashcards
Magnetic Resonance Imaging (MRI) utilizes the behavior of ___ or ___, n the human body.
hydrogen nuclei, or protons,
Single charged spinning nucleon
Hydrogen
behave like tiny bar magnets.
Hydrogen nuclei
exhibits magnetism due to its angular momentum and magnetic moment.
hydrogen nucleus
Before entering the magnetic field (B0), proton
magnetic moments are randomly oriented.
*Upon exposure to the B0 magnetic field, some
proton _ with it.**
Magnetic Alignment
The alignment of proton magnetic moments creates _ in the patient. The Z-axis coincides with the axis of the static magnetic field (B0) in MRI systems.
Net Magnetization
The strength of the B0 magnetic field is measured in?
tesla (T).
There is no direct relationship between ___ and ___
magnetic field strength and ionizing radiation.
Though only a fraction of proton dipoles align with the magnetic field, the patient becomes ____
polarized
Polarized patients exhibits what?
north and south poles
is a phenomenon observed
when a patient is placed
in a static magnetic field
during MRI.
Precession
this phenomenon is crucial for
generating MRI signals used in imaging.
Precession
Relating the strength of
the static magnetic field (B0) to the precessional frequency (f).
Larmor equation
determines the precessional frequency and thus the resonance frequency in MRI.
Gyromagnetic Ratio
___ is akin to the disintegration
constant in radioactive decay, unique to each nuclear species.
Gyromagnetic ratio
The gyromagnetic ratio is expressed in ???
megahertz per tesla (MHz/T).
has a gyromagnetic ratio
of approximately 42 MHz/T.
Hydrogen
The Larmor frequency, also known as the ___
precessional frequency,
is a crucial aspect of MRI, representing the emission of radio signals by the net magnetization in the patient.
Free Induction Decay (FID)
represents the alignment of proton magnetic dipoles along the Z-axis after polarization in the static magnetic field (B0).
Net magnetization (MZ)
___ emitted at the ___, is transmitted into the patient via an RF coil to induce energy transfer and initiate imaging.
RF pulse, Larmor frequency,
is fundamental to MRI, analogous to the resonance of musical instruments or structural elements.
Resonance
must match the resonant frequency of the precessing hydrogen nuclei for efficient energy transfer and imaging to occur.
RF or Radio Frequency Pulse
When the RF signal is pulsed at resonance into the patient, the energy state of many protons is changed. The net magnetization, due to all of the protons, is said to “flip” toward the negative Z direction, while still precessing about the Z-axis
Phase Coherence
This precession is always perpendicular to Z, in the XY plane, and if initially all of the spins are aligned along the same direction in the XY plane
Phase Coherence
what relaxation times exist in MRI?
T1 and T2.
T2 are also known as?
transverse relaxation time
describes the decay of phase coherence and the FID signal over time.
T2 or transverse relaxation time
describes the rate of the magnetization increasing back to equilibrium.
T1
equilibrium magnetization state is also known as?
Normal State.
