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62 Cards in this Set

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Spoiled GE acronyms
What is the effective TE
The contrast in fast spin echo is modified in relation to a standard spin echo sequence. As the echoes are received at different echo times, the echoes corresponding to the central k-space lines are the ones that will determine image contrast. The moment at which theses echoes are acquired is called effective TE
What limits the echo train length in T1 sequences
In T1 weighted sequences, the need to choose a short TR limits echo train length
When is fast spin echo commonly used
This type of sequence is very commonly used in T2 weighting, namely in pelvic imagery.
Why does fast spin echo cause fat to be brighter than standard T2 sequences
Within lipid molecules a spin-spin coupling (J coupling) occurs between the atomic nuclei. This coupling shortens relaxation time T2. Fast repetition of 180° pulses in fast spin echo sequences will perturb J coupling, causing fat T2 to lengthen.
Thus, fat has a higher T2 signal in fast spin echo than in standard spin echo, the latter respecting J coupling.
What is a delayed interval echo train used for
A DIET (Delayed Interval Echo Train) sequence is a fast SE sequence where the delays between 180° pulses are designed to respect J coupling: as a result, the fat maintains an appearance closer to that observed in a standard SE sequence
How fast is fast SE sequences
fast around 10 seconds
Are fast SE susceptible to magnetic susceptibility and magnetic field heterogeneities
less than normal T2
Why are the parameters (TR, effective TE, echo train length) of fast SE sequences limitied
The risk of artifacts and the large quantity of radiofrequency energy deposited by 180° pulses
Fast spin echo can be combined with the technique developed for multi-echo sequences to obtain images faster with different contrasts in the same zone of interes
yes
What are the acronymns for ultrafast SE
What does a generic diagram of ultrafast spin echo look like
What is awseme about ultrafast echo sequences
The echo train technique can be pushed to the limit to fill the entire Fourier plane with a single 90° pulse
How long is TR in ultrafast echosequences
as long as is needed
Why are ultrafast spin echo sequences sometimes called single shot
These so-called « single-shot » sequences require the successive application of as many 180° pulses as there are k-space lines to fill.
What is the arrangement of the phase encoding gradients before and after the 180 pulses
Are the latest echos (ones that create K spaces at the bottom) in an ultrafast spin echo alway acquired
no, The sequence can be further accelerated, avoiding the need to register the latest echoes (whose signal is much reduced by T2 relaxation) by partial k-space acquisition
How many K space lines are actually aquired in an ultrafast spin echo
Just over half the k-space lines are actually acquired
How are the remaining K spaces filled in
the missing lines are calculated using k-space symmetry properties.
What is the consequence of calculating the K space properties in the bottom half
increased signal to noise in ultrafast spin echo
Are ultrafast spin echo sequences highly T2 weighted
yes
How long does it take to make a slice with an ultrafast spin echo sequence
under 1 second
What is effective TE
this is when the echos corresponding to the signals that make up the central K space are acquired
What is effective TE
What is TE time
(TE) The echo time represents the time in milliseconds between the application of the 90° pulse and the peak of the echo signal in spin echo and inversion recovery pulse sequences.
Does ultrafast spin echo sequences image moving body parts well
These sequences are well adapted to imaging non-circulating liquid structures appearing as a T2-weighted hypersignal
What to areas of the body does a ultrafast spin echo image well
cholangio MRI
Uro MRI
What is a negative impact of a long echo time
The negative impact of very long echo trains is a decay in signal to noise ratio
What are two reasons for a decay in the signal to noise ratio
weak signal from later echos

very high effective TE
Does ultrafast imaging have a low spatial resolution and blurring in the phase encoding direction
yes
If you see the acrynomn "ss" what are they talking about
ultrafast spin echo
If you see HASTE what is it
ultrafast spin echo
What are the acronymns of IR, STIR and FLAIR
Do all acroynms of IR have the word 'IR' or TIRM
yes
Do all acryonyms of STIR have the word STIR
yes
Do all acrynomn of flair have the word flair
yes
What is the TI
between the initial 180 pulse and first 90 RF pulse
What is the purpose of the first 180 pulse in inversion recovery
The sequence starts with a 180° RF inversion wave which flips longitudinal magnetization Mz in the opposite direction (negative)
What occurs after the magnetization is in the negative longitudinal direction
Due to longitudinal relaxation, longitudinal magnetization will increase to return to its initial value, passing through null value
What is the TI time
The delay between the 180° RF inversion wave and the 90° RF excitation wave is referred to as the inversion time TI.
What are inversion recovery sequences weighted in
T1
Does inversion recovery increase the T1 weighting of spin echo
yes
What types of sequences can an inversion recovery sequence be used
Spin Echo and Gradient echo
How does inversion recovery work
first 180 degree pulse
then once the longitudinal relaxation of the tissue you are trying to null reaches the transverse plane so a 90 pulse occurs
What does the 90 degree pulse do
flips the protons into the transverse plane
What causes the signal in an inversion recovery sequence
A second 180 degree pulse at time TE/2 produces an echo at time TE, which is the
detected signal intensity.
What is the inversion recovery dependent on T1 or T2 changes
The size of the signal obtained with the readout pulse is strongly dependent on the
value of T1 and TI.
Important: When does inverstion recovery occur
the begining of the sequence
After inversion recovery occurs what type of sequence is if followed by
Spin echo (standard but sometimes gradient echo)
Once all the tissue types are a hit with the 90 pulse which one does not give a signal
the one that was already at 90 degrees and therefore did not move.
In an inversion recovery are you measuring T1 or T2
this is confusing because spin echo is typically a T2 sequence but this is actually T1 since the signal that is being measure is because of longitudinal relaxation
What are the 2 ways that a IR sequences is gray scalled
Either signal magnitude (amplitude in relation to 0) used for gray scale display: the more absolute the value of the tissue signal (positive or négative), the stronger it will be.
Or the gray levels will be distributed from the negative signal values to the positive values (with a null signal background that will be gray rather than black): this is the « true » display type.
In the magnitude type of gray scale what is black
where the signal is null
In the magnitude type of gray scale what is more gray
the higher the magnitude of the signals (negative or positive)
What is the other scale
gray levels will be distributed from the negative signal values to the positive values (with a null signal background that will be gray rather than black): this is the « true » display type.
Is the null gray or black in the true display type
gray
What is more black in the true display type
negative
Why cant a null tisue emit a signal
absence of transverse magnetization due to the absence of longitudinal magnetization (dont understand just memorize)
If a photon undergoes a 180 pulse and is exactly at the transverse plane can it emit a signal if a 90 degree pulse occurs
no
How do you make a tissue null
by adjusting the TI
In order to save time can IR sequences be combined with fast spine echo sequences
yes
What is emphasized in IR sequences
IR emphasizes T1 differences, and tissues with short T1 values produce high-in-
tensity signals.