PULSE SEQUENCES AND CONTRAST Flashcards
What is the process called when the spins (protons) return to thermal equilibrium?
Relaxation
The decay of transverse magnetization results from what?
T2 relaxation
What is T2 Relaxation?
An exchange of energy among the spins (protons)
The recovery of longitudinal magnetization results from what?
T1 Relaxation
T1 relaxation results from what?
A loss of energy from the spins (protons)
What is another term for T2 relaxation?
Spin spin
What is the T2 relaxation time?
63% of transverse has decayed
What has the shortest T2 relaxation time?
Fat
T2 relaxation times of tissues are expressed in units of:
Milliseconds
Which has the longest T2 relaxation time?
CSF
The T1 relaxation time is:
63% of longitudinal magnetization to recover
Which has the longest T1 relaxation time?
CSF
T1 relaxation times are affected by what?
Tissue type, temperature and field strength
Increasing the strength of the magnetic field will result in T1 times of tissue to what?
Increasing (lengthening)
The signal induced in a receiver coil followed by RF pulse is known as:
FID
Dephasing the spins results in:
Reduction of detectable signal
Dephasing due to inhomogeneties and chemical shift can be referred to as:
Off resonance effects
T2* is a transverse decay due to:
T2 plus effects of inhomogeneties and chemical shift
The pulse sequence that begins with a 90 followed by 180 degree pulse is called:
Spin echo
Increasing the flip angle from 90 to 180 degree requires how much of an increase in RF power?
4 times
In a spin echo the time between 90 RF pulse and 180 refocusing pulse is:
1/2 the TE
Which sequence is the most sensitive to hemorrhage in the brain?
Gradient echo
The excitation pulse in a gradient echo is also known as:
The alpha pulse
In gradient the echo is formed by the reversal of:
The readout gradient
In a gradient echo sequence the duration of the rephrasing lobe is:
Twice
Which controls T1 Weighting?
TR (Repetition time)
Which controls T2 Weighting
TE (Echo time)
In a spin echo sequence the following parameters TR=550MSEC TE=15MSEC would be:
T1 weighted
TR=4550 MSEC AND TE=15MSEC:
PD (Proton density)
TR=3500MSEC AND TE=80MSEC:
T2 weighted
An inversion recovery pulse sequence begins with a:
180 degree pulse
In an inversion recovery the time between initial and the 90 degree pulse is known as:
TI (Inversion time)
Selecting an inversion time, what percent of a tissues T1 recovery time will null the signal from that tissue?
69%
When an IR sequence is used to null CSF, it is referred to as:
FLAIR
To obtain a TE which is out of phase which type of pulse sequence would be selected?
Gradient echo
The common clinical application of acquiring both an in phase and out of phase TE is:
Characterizing adrenal adenomas
In a gradient echo sequence T1 is controlled by:
Flip angle and TR
To produce a T1 weighted image using a short TR which of the following gradient sequences would be selected?
Spoiled
In a balanced gradient echo, the contrast weighting is based on:
The ratio between a tissues T1 and T2 relaxation times
