Fundamentals Flashcards
in the equation associated with LARMOR Equation, B(o)stand for
static magnetic field
in the equation associate with Larmor Equation, ω(o) stand for
frequency
in the equation associate with Larmor Equation, ϒ stand for
gyromagnetic ratio
a magnetic field strength of .05 T is equivalent to
5000 G
a condition whereby there are MORE spins in line with the magnetic field that opposed is knwn as
theralequilibrium
during thermal equalibrium there are
more spins in the low energy state
proton spins that are in line with the static magnetic field B(o) are referred to as all of the following
spin up
parallel
low energy spins
the microscopic magnetic field associated with the proton within the magnetic field is knwn as the
magnetic moment (µ)
during thermal equilibrium the vector taht represents the spn excess is known as the
net magnetization value (NMV)
the RF pulse is applied to acheive a condition known as
excitation
during excitation all of the following occur
low energy spins enter high energy state
spins begin to precess in phase
the NMV is transferred into the transverse plane
During relaxation all of the folloiwng occur
high energy spins return to a low energy state
spins begin to precess out of pahse or lose phase coherence
the NMV recovers longitudinally
T1 relaxation is also known as all of the following
T1 recovery
spin lattice
longitudinal recovery or relaxatoin
T2 relaxatoin is also known as
spin spin
T2 relaxatoin is also known as all of the following
T2 decay
spin spin
transverse relaxation
T1 relaxation time is defined as when
63% of the longitudinal magnetization has regrown
T2 relaxatoin time is defined as when
63% of the transverse magnetization has decayed
images acquired with a spin echo pulse sequence having a SHORT TR and TE valuse yield images known as
T1WI
images acquired with a spn echo pulse sequence having a LONG TR and TE valuses yield images known as
T2WI
images acquired with a spin echo pulse sequence having a LONG TR and SHORT TE valuse syield images known as
PDWI
spino density is another term for
proton density
spin density is determined by the
amount of excess spins in the low energy state at equilibrium
gradient echo (steady state) sequences acquired with short TR and flip angle combinations along with a moderately long TE yield images with
T2* contrast
T2 + T2’ equals
T2*
the LOGICAL gradient that is used for slice selection for the acquisition of an axial slice is the
z gradient
the PHSYICAL gradient that is used for slice selection for the acquisition of an aial slice is the
z gradient
the LOGICAL gradient that is used for slice selection for the acquisition of a sagittal slice is the
z gradient
the PHYSICAL gradient that is used for slice selection for the acquisition of a sagittal slice is the
x gradient
the LOGICAL gradient that is used for phsae encoding for the acquisition of an axial slice of the abdomen is the
y gradient
the LOGICAL gradient that is used for phase encoding for the acquisition of an axial slice of the head is the
y gradient
the PHYSICAL gradient that is used for phase encoding for the acquisition of an axial slice of the abdomen is the
y gradient
the PHYSICAL gradient taht is used for phase encoding for the acquisition of an axial slice of the head is the
x gradient
the receiver bandwidth is related to the slope of the
frequency encoding gradient
following a 90 RF pulse the signal that is created is called
free induction decay
T2* is a result of dephasing due to tissues T2 time and
susceptibility
inhomogeneities
chemical shift
the peak signal strength of a spin echo is less than the initial signal strength of the free induction decay because of
T2 relaxation
an example of a dipole is
hydrogen nucleus
bar magnet
earth
a vector has both direction and
magnatude
hydrogen nuclei have a magnetic moment because they possess a property called
spin
when placed in a large static magnetic field hygdrogen nuclei
align in either a parallel or anitparallel position
spins aligned in the antiparallel directino are in
high energy state
during thermal equilibrium the spin excesses of individual hydrogen nuclei add to form
a net magnetization vector
NMV
the formula that describes the relationship between the static magnetic field and the precessional frequency bo the hydrogen protons is the
larmor equation
o calculate the precessional frequencey the strength of the static magnetic field is multiplied by a constan knows as the
gyromagnetic ratio
the condition reached with a few seconds of hydrogen being placed in a magnetic field is described as
thermal equilibrium
during thermal equilibrium the individual protons precess
out of phase
in order for energy to transfer between systems the two systems must be at the same
resonant frequency
assuming a TR sufficient for full recovery of longitudinal magnetization maximum signal is produced in the receiver coil when the net magnetization is tipped
90 deg
in relatoin to the static magnetic field the RF field is oriented
perpendicular
the RF energy used in MRI is classified as
electromagnetic radiation
immediatly on the application of the 90 pulse the precessing protons
begin to precess in phase
the MR signal is produced by magnetization
in the transverse plane
frequency can be defined by the
rate of phase change per unit time
gradient magnetic fields are used to
spatially encode the data
slice thickness is controlled by
slope of the gradient
the physcial graient along with the bore of the superconducting magnet is the
z gradient
to produce a sagittal slice the physical gradient used during the excitation pulse is the
x gradient
the gyromagnetic ratio for hydrogen is
42.6 MHz/T
in a 0.5 T imager the precessional frequency of hydrogen is approximately
21.3 MHz
the amount of RF energy necessary to produce a 45ͦͦ° flip angle is determined by the
coil being used
ampl;itude and duratin of the RF pulse
strength of the external magnetic field
the gradient that varies in amplitude wtih each TR is the
phase encoding gradient
the gradient that is on during the sampling of the echo is the
frequency encoding gradient
K-space is
the raw data from which an MR image is created
multiple coil elements combined with multiple receive channels is a
phased array coil
