EXAM #2 — MODULE 2 Flashcards
Human body composed mainly of _____
H atoms considered protons (subatomic particles with + charge)
Human body composed mainly of H2O
H atoms considered protons (subatomic particles with + charge)
Protons have spin
+ charged particle is moving: spinning
Moving charged particle (current) creates magnetic field called a spin (moment)
Magnetic vector _____ (wobbles), transcribes a _____
Protons have spin
+ charged particle is moving: spinning
Moving charged particle (current) creates magnetic field called a spin (moment)
Magnetic vector precesses (wobbles), transcribes a cone
Each proton has own _____ (ie: is a bar magnet)
Each proton has own magnetic field (ie: is a bar magnet)
Protons’ magnetic fields placed in _____ magnetic field of MRI magnet align with _____ magnetic field
_____ - requires less energy (walking on feet); preferred state; slight majority of protons in this orientation
_____ - requires more energy (walking on hands)
Protons’ magnetic fields placed in external magnetic field of MRI magnet align with external magnetic field
Parallel - requires less energy (walking on feet); preferred state; slight majority of protons in this orientation
Anti-parallel - requires more energy (walking on hands)
Protons _____ (wobble) along field lines of magnetic field (z axis)
Protons precess (wobble) along field lines of magnetic field (z axis)
Precession frequency calculated by the Larmor Equation:
ωo = γ βo
_____ = precession frequency (Hz or MHZ)
_____ = gyromagnetic ratio (42.5 MHZ for hydrogen protons)
_____ = external magnetic field strength in Tesla (T)
Precession frequency calculated by the Larmor Equation:
ωo = γ βo
ωo (omega) = precession frequency (Hz or MHZ)
γ (gamma) = gyromagnetic ratio (42.5 MHZ for hydrogen protons)
βo (beta) = external magnetic field strength in Tesla (T)
_____ magnetic field strength yields higher precessional frequency
Note: γ is unique and fixed for each element. ∴ precessional frequency is _____ for a given magnetic field strength
Higher magnetic field strength yields higher precessional frequency
Note: γ is unique and fixed for each element. ∴ precessional frequency is fixed for a given magnetic field strength
Magnetic field vector of protons precess around __ axis (form cone motion)
Each magnetic field vector has a z component which points either parallel (on feet) or antiparallel (on hands) along z axis
Antiparallel z axis components _____ out parallel z axis components, leaving a net of parallel z axis (up) components (parallel z axis magnetic field vectors which add up to form a new magnetic sum vector)
Magnetic field vector of protons precess around z axis (form cone motion)
Each magnetic field vector has a z component which points either parallel (on feet) or antiparallel (on hands) along z axis
Antiparallel z axis components cancel out parallel z axis components, leaving a net of parallel z axis (up) components (parallel z axis magnetic field vectors which add up to form a new magnetic sum vector)
Each magnetic field vector has __ axis and __ axis components
x and y axis components change from moment to moment with rapid precession of magnetic field vector
x and y axis components cancel each other, leaving no net magnetic field vector in the x, y plane
Each magnetic field vector has x axis and y axis components
x and y axis components change from moment to moment with rapid precession of magnetic field vector
x and y axis components cancel each other, leaving no net magnetic field vector in the x, y plane
Net result of all magnetic field vector component cancellations and additions:
A MAGNETIC SUM VECTOR PARALLEL TO Z AXIS (pg.13)
(along longitudinal direction within patient tissue)
Magnetic sum vector not measurable since it is in same direction as external magnetic field
Net result of all magnetic field vector component cancellations and additions:
A MAGNETIC SUM VECTOR PARALLEL TO Z AXIS (pg.13)
(along longitudinal direction within patient tissue)
Magnetic sum vector not measurable since it is in same direction as external magnetic field
Magnetic sum vector must be _____ to external magnetic field to be measured
Magnetic sum vector must be transverse to external magnetic field to be measured
A _____ _____ (__) pulse (radio wave) that can exchange energy with the protons is sent into the patient
A radio frequency (RF) pulse (radio wave) that can exchange energy with the protons is sent into the patient
The RF pulse must have same frequency (energy) as the protons’ _____ _____
The RF pulse must have same frequency (energy) as the protons’ precessing frequency
The frequency of the protons can be determined with the _____ _____ (since the gyromagnetic ratio for protons and the external magnetic field strength are known) (pg 19)
The frequency of the protons can be determined with the Larmor equation (since the gyromagnetic ratio for protons and the external magnetic field strength are known) (pg 19)
Larmor equation tells us the _____ of the RF pulse we must introduce in order for it to exchange energy with the protons and flip them into another _____
Only when protons and RF pulse have _____ frequency can protons pick up energy from the RF pulse (phenomenon called _____)
Larmor equation tells us the frequency of the RF pulse we must introduce in order for it to exchange energy with the protons and flip them into another plane
Only when protons and RF pulse have same frequency can protons pick up energy from the RF pulse (phenomenon called resonance)
RF pulse exchanging energy with protons’ magnetic vectors has 2 effects:
Some protons’ magnetic vectors _____ _____ from the lower energy state (on feet) to the higher energy state (on hands)
These now inverted magnetic vectors _____ out the same number of upright magnetic vectors, creating a _____ intense (shorter) magnetic sum vector in the longitudinal (z) axis pointing upward
(pg.18, fig 11)
RF pulse exchanging energy with protons’ magnetic vectors has 2 effects:
Some protons’ magnetic vectors flip 180° from the lower energy state (on feet) to the higher energy state (on hands)
These now inverted magnetic vectors cancel out the same number of upright magnetic vectors, creating a less intense (shorter) magnetic sum vector in the longitudinal (z) axis pointing upward
(pg.18, fig 11)
RF pulse gets the randomly precessing proton magnetic field vectors to precess in synch at the _____ _____ as the RF pulse.
Magnetic vectors precessing in synch (together) have x,y plane components which are now precessing in _____ (in _____) and add up to a magnetic sum vector in the x,y plane ( transverse plane) (fig13)
New magnetic sum vector in the x,y plane precesses with the same frequency as the RF pulse and the protons’ original magnetic vectors
RF pulse gets the randomly precessing proton magnetic field vectors to precess in synch at the same frequency as the RF pulse.
Magnetic vectors precessing in synch (together) have x,y plane components which are now precessing in synch (in phase) and add up to a magnetic sum vector in the x,y plane (transverse plane) (fig13)
New magnetic sum vector in the x,y plane precesses with the same frequency as the RF pulse and the protons’ original magnetic vectors
NET EFFECTS OF RF PULSE:
DECREASE IN LONGITUDINAL MAGNETIZATION (__ AXIS)
Depending on the RF pulse, longitudinal magnetization may disappear
ESTABLISHMENT OF TRANSVERSE MAGNETIZATION (__ PLANE) (pg 23, fig 15)
NET EFFECTS OF RF PULSE:
DECREASE IN LONGITUDINAL MAGNETIZATION (Z AXIS)
Depending on the RF pulse, longitudinal magnetization may disappear
ESTABLISHMENT OF TRANSVERSE MAGNETIZATION (X,Y PLANE) (pg 23, fig 15)
Precessing transverse magnetic vector is a moving magnetic field (can be measured)
This moving magnetic field induces an electrical current in a nearby antenna
Electrical current is the MRI _____ (pg. 24)
Magnetic vector precesses alternately toward and away from antenna, creating current (MR signal)
MR signal has precessing frequency of the magnetic vector (pg. 24)
Precessing transverse magnetic vector is a moving magnetic field (can be measured)
This moving magnetic field induces an electrical current in a nearby antenna
Electrical current is the MRI signal (pg. 24)
Magnetic vector precesses alternately toward and away from antenna, creating current (MR signal)
MR signal has precessing frequency of the magnetic vector (pg. 24)
Locating the MRI signal (determining the anatomic origin of the signal)
The patient (or anatomic part) is placed within a magnetic _____ (fields of incrementally increasing magnetic strength)
Locating the MRI signal (determining the anatomic origin of the signal)
The patient (or anatomic part) is placed within a magnetic gradient (fields of incrementally increasing magnetic strength)
Each sectional slice of anatomy is in a different magnetic field strength along the _____ (the location of the anatomy within each magnetic field strength in the gradient is known)
Protons within different slices of anatomy precess at different frequencies which are proportional to the magnetic field strength of their slice
These differing precessional frequencies generate differing MRI signal frequencies which are equal to the magnetic vector precessing frequencies and are directly proportional to to the magnetic field strength of the slice
An MRI signal can be located by linking its frequency to the known anatomic location of its associated magnetic field strength
Each sectional slice of anatomy is in a different magnetic field strength along the gradient (the location of the anatomy within each magnetic field strength in the gradient is known)
Protons within different slices of anatomy precess at different frequencies which are proportional to the magnetic field strength of their slice
These differing precessional frequencies generate differing MRI signal frequencies which are equal to the magnetic vector precessing frequencies and are directly proportional to to the magnetic field strength of the slice
An MRI signal can be located by linking its frequency to the known anatomic location of its associated magnetic field strength
[The Basics: MRI]
is an imaging modality that uses strong _____ fields and _____ pulses (no radiation used)
[The Basics: MRI]
is an imaging modality that uses strong magnetic fields and radiofrequency pulses (no radiation used)
[The Basics: MRI]
provides excellent _____ _____ contrast between varying anatomic structures
[The Basics: MRI]
provides excellent soft tissue contrast between varying anatomic structures
[The Basics: MRI]
produces sectional images in various orthogonal planes (_____, _____, _____)
Image data acquired in one _____ _____ can be used to generated additional images in any other _____ _____ without rescanning the patient
[The Basics: MRI]
produces sectional images in various orthogonal planes (transverse, sagittal, coronal)
Image data acquired in one orthogonal plane can be used to generated additional images in any other orthogonal plane without rescanning the patient
[MRI uses: ]
transmitted _____ _____ (__) to disrupt the alignment of the hydrogen protons in water and fat molecules.
[MRI uses:]
transmitted radio frequencies (RF) to disrupt the alignment of the hydrogen protons in water and fat molecules.
[MRI uses:]
Received radio frequency signals from the hydrogen protons as they return (relax) to their magnetically induced alignment.
[MRI uses:]
Received radio frequency signals from the hydrogen protons as they return (relax) to their magnetically induced alignment.
[Hydrogen protons (H+) ]
_____: wobble like spinning top
H+ magnetic fields outside of magnet bore: _____ _____
H+ magnetic fields within magnet bore: Align _____ or _____ to Bo
Result: Net magnetic tissue vector (Mo) aligned with external magnetic field (Bo).
Mo precesses around __ axis.
[Hydrogen protons (H+)]
Precession: wobble like spinning top
H+ magnetic fields outside of magnet bore: Random orientation
H+ magnetic fields within magnet bore: Align parallel or antiparallel to Bo
Result: Net magnetic tissue vector (Mo) aligned with external magnetic field (Bo).
Mo precesses around z axis.
What is the Larmor Equation?
ωo = γ Bo
Describe the Larmor Equation
The precessional frequency of hydrogen protons is directly proportional to the magnetic field into which they are placed
RF pulse application net affects:
_____ (_) magnetization degeneration
RF pulse energy flips many parallel magnetic vector to antiparallel (parallel # = antiparallel #)
_____ (__) magnetization generation
RF pulse puts all transverse magnetic vectors into phase
RF pulse application net affects:
Longitudinal (z) magnetization degeneration
RF pulse energy flips many parallel magnetic vector to antiparallel (parallel # = antiparallel #)
Transverse (XY) magnetization generation
RF pulse puts all transverse magnetic vectors into phase
Degeneration of _____ magnetization: parallel = antiparallel
Generation of _____ magnetization: all H+ magnetic vectors in phase
Degeneration of longitudinal magnetization: parallel = antiparallel
Generation of transverse magnetization: all H+ magnetic vectors in phase
What does M represent?
M represents net magnetization within patient tissues
