unit 3 Flashcards
what sequence suppresses fat
STIR
what does TE stand for
echo time
what does TI stand for
inversion time
what does TR stand for
repetition time
what sequence removes CSF signal
FLAIR
GRE stand for
gradient echo
FSE stands for
fast spin echo
PD stands for
proton density
NEX stands for
number of excitations
your planning scan is known as
scout / localizer
number of echos after an excitation pulse
echo train length (ETL)
time between excitation and the middle of the readout process
echo time (TE)
time between the inversion pulse and 90 degree pulse
inversion time (TI)
the slice region actually displayed
FOV
what does FS stand for
fat saturation
what sequence would best demonstrate MS plaques
T2 FLAIR
gadolinium is best seen on what type of weighted image
T1
it is required that the mri table/couch be able to be accurate within _____ of setting
+/- 1mm
measures coil sensitivity before the scan, usually very short & blurry image
pre calibration scan / asset
the coronal plane is associated with which axis
Y axis
coronal images typically start by using which localizer
sagittal , starting posterior & ending anterior
the sagittal plane is associated with which axis
x-axis
the sagittal image is typically plotted on which localizer
coronal , starting with patients left & ending right
the axial plane is associated with which axis
Z-axis
the axial image is typically plotted of which localizer
sagittal
inferior to superior - brain
superior to inferior - other studies
do thick or thin slices cover more of the patients body tissue
thick slices
what changes the voxel volume along the dimension of the slice
changes in the slice thickness
thicker slices give a ______ SNR, but a ______ spatial resolution
higher , lower
the distance between two slices
slice gap “aka skip”
RF could excite adjacent slices if too close, or overlap
crosstalk
you want a slice gap of at least ____ of the slice thickness to prevent cross talk
30%
a thin slice of gap
1mm/1mm to 4mm/1.5mm or less
a medium slice gap
5mm/ 2.5mm to 6mm/ 2.5mm
a large slice gap
8mm/2mm or more
the short axis of the image
phase matrix
phase matrix
coronal image = horizontal axis (X-axis)
sagittal image = vertical axis (Y-axis)
axial image = vertical axis (Y-axis)
-except head & brain image
* horizontal axis (X-axis)
the number of phase encodings determines the
number of lines in k-space that are filled to complete the scan
larger the number of a phase matrix =
the longer scan time
reducing the phase matrix =
reduces scan time
* assuming the field of view remains the same
the number of data points collected during the acquisition time
frequency matrix
the time between successive pulse sequences or excitation (RF) pulses for a particular slice
TR, repetition time
repetition time is measured in
ms
TE is always ______ than TR
shorter
determines the amount of T1 weighting used in the imaging contrast
TR , repetition time
longer TR =
longer scan time & vice versa
short TR is considered
under 500 ms
time between the excitation and the middle of the readout process
TE , echo time
the length of time from one 90 degree RF pulse to the next 90 degree RF pulse in a given slice
* determines the amount of T2 weighting for spin echo images
TE, echo time
number of times each k-space line if filled with data
NEX, number of excitations / number of signal averages
the higher the NEX/NSA number =
the more data that is stored in each line of k space
the higher the NEX =
more/longer scan time
image acquisition time is _______ to ETL (echo train length)
inversely proportional
the ____ is the voltage induced in the receiver coil , the intensity of the information
signal
the ____ is a random value depending on the area under examination
noise
the easiest way to increase SNR is to
increase NSA/NEX
what parameters changes can cause a decrease in SNR
increasing TE
increasing matrix
reducing slice thickness
typically a good _____ is the most important factor
SNR
as a technologist our goal is to achieve optimal images with
high SNR
good spatial image resolution
short acquisition/scan time
can decrease scan time by
using a short TR
a coarse phase matrix
the lowest NEX/NSA possible
sometimes the extremity coil is called a
“chimney coil”
if you are scanning a forefoot make sure to include all
toes in all imaging planes
where do you center for a fore foot exam
metatarsals
axial of the foot should be scanned
perpendicular to the long axis of the foot, should show metatarsals in cross section
axials of the foot are plotted
superior to inferior
coronals of the foot are scanned
with the short axis of the foot , angle parallel to the 2 & 3rd metatarsal heads
if you give contrast for a foot you are probably looking for
osteomyelitis or another infection
this condition is thought to be due to chronic entrapment of the nerve by the intermetstarsal ligament
morton’s neuroma
this condition is thought to be due to chronic entrapment of the nerve by the intermetstarsal ligament
morton’s neuroma
horizontal alignment light for the ankle
passes through the level of the malleoli
horizontal alignment light for the ankle
passes through the level of the malleoli
in the sagittal image of the ankle you should be able to visualize
the base of the 5th metatarsal
in which direction should you prescribe the axial slices in the ankle
superior to inferior
if scanning the entire lower leg (tib fib) what anatomy are you including
femoral condyles to the calcaneus
coronals & sagittals of the tib fib are
parallel to the shaft of the tibia
what coil type can be used for a knee MRI
phased array coil
proper centering of the knee in the coil is essential to avoid
drop off of signal
clear display of the ____ is essential in knee exams for pain , trauma, or suspected joint damage
ACL
sagittal images of the knee should include
both the lateral and medial collateral ligaments
coronals of the knee are aligned
parallel to the posterior surfaces of the femoral condyles
prevents anterior displacement of the tibia
ACL
when scanning a knee to visualize the ACL a slight ________ rotation of the knee is required
external , about 15 degrees
the most common mass in the popliteal fossa
bakers cyst , also termed popliteal cyst
MR arthrography of the knee is used for the diagnosis of
meniscal tears & chondral defects
what series of the foot is done pre and post contrast typically
T1 FS
for venous study of the lower leg, the axial slices should be set up going ______ to ______ due to the blood flow direction
superior, inferior
on an image that is proton dense and fat suppressed, the fracture would/ should appear
white
best views for the evaluation of the ACL include
sagittal & oblique
increasing NEX will increase
SNR
all ways to reduce metal artifact if a pat has a prosthetic hip
wider bandwidth
higher NEX/NSA
higher ETL
TSE/FSE
STIR
Mavric
patients with a hip replacement may experience ________ SAR and/or warmth of the body
higher
