unit 2 Flashcards
secondary coils around the magnet, used to contain, or reduce the main magnetic fringe field
active shielding
• adjusts the current on a certain sequence or patient
• helps achieve uniform fat suppression for images that call for it
• improves the magnet’s homogeneity
active shimming
• main static field of the MR system
- Z-axis , Longitudinal axis
B0 field
• alternating magnetic field created by the RF in a coil
- perpendicular to B0
B1 field
voltage created in the receiver coil , due to a change in the magnetic field
electromagnetic induction
uniformity of magnetic field, if you do not have it causes artifact on images
homogeneity
where the magnet bore assigns all the axis (X,Y,Z) =0
- the centering point of all the coordinates
- center of the bore and magnetic field
isocenter
magnetic forces running from a north and south pole to form a closed loop around the outside of the magnetic material
- has both strength and direction
- measured in tesla
magnetic field
lining around the MR room with steel or other type of ferromagnetic material
- reduces the scope and distance of the fringe field
passive shielding
placing metal sheets within the magnet to create a more homogeneous magnetic field
passive shimming
magnet that generates magnetic field with the use of ferromagnetic materials
- no super cooling or additional power source needed
- typically a lower field strength
permanent magnet
frequency band in the electromagnetic spectrum
radio frequency
can transmit, receive, or both of the RF signal
- create magnetic field opposite (B1) of the main magnet field (B0)
- responsible for detecting the MR signal
radio frequency coil
a magnet that can be turned on and off, uses electromagnetism to create the magnetic field
resistive magnet
exchange of energy between two sources at a specific frequency
resonance
coils that have a small current and provide localized magnetic fields, thus improving total field homogeneity
shim coils
process of improving homogeneity of the magnetic field
- active or passive
shimming
generates its magnetic field by using current in wires made of a superconducting material
- cooled with cryogens
- higher field systems
superconducting magnet
surface coil that both transmits and receives RF signal
transceiver coil
part of the MR scanner that produces the RF current and send it to the transmitting coil
transmit coil
3 main components of a MRI system / suite
- the gantry
- operating console
- the system electronics
high magnetic field is considered
1.5 T or higher
most common magnetic field strength
1.5 T
used when imaging the pituitary gland
dynamic contrast enhanced
important series for stroke imaging
DWI
reconstructed from diffusion weighted images, with multiple b-values, and corresponds to the distributed coefficients of the target tissues
ADC
movement of atoms or molecules from an area of high concentration to lower concentration
diffusion
a factor in diffusion weighted imaging the higher the number, the stronger the diffusion
b-value
inflammation of the fatty myelin sheaths around the axons of the brain and spinal cord
multiple sclerosis
tumor of greater than 1 cm in the pituitary gland
macro-adenoma
rupture of blood flow in the brain, causing a hemorrhage
cerebrovascular attack
temporary blockage of blood flow in the brain
transient ischemia attack
axial slices should be set up / plotted
inferior to superior
which series(s) can help reduce patient motion
propeller
blade
when plotting the sagittal images from the coronal localizer the slices should be plotted
left to right
the coronal slices, in a routine brain, need to cover through the ________ anteriorly
frontal sinuses
in a routine brain scan, the coronal slices should be set up / plotted
posterior to anterior
if you have to perform the oblique cervical spine images, what structure are you making the oblique slices perpendicular to?
lamina
in the lumbar spine, images acquired directly through the intervertebral disc spaces can be acquired in the ______ plane
axial
sagittal spine slices are prescribed in which direction
left to right
when setting up sagittal slices for the lumbar spine, the coverage should include
transverse process to transverse process
how often should imaging coils be inspected for safety
every time you use them
1 T is equal to _____ gauss
10,000
the liquid helium used to cool that magnet’s could has a temperature of
-452 degrees fahrenheit
5 gauss is equivalent to ___ T
0.0005 tesla
how many pairs of gradients are there
3
T/F: the localization light can possibly cause eye damage
true
the axial slices of the brain should be set up initially on the _________ localizer, then the remaining two of the localizer images
sagittal
the axial slices for the routine brain, should be set up
parallel to the inferior border of the genu of the corpus callosum and the splenium of the corpus callosum
the sagittal slices should be set up ______ to the midline of the brain
parallel
in an axial T2 image of the brain, fluids will appear
bright / white
the centering point for the localizer when doing a brain scan should be the patients
glabella / nasion
on a T1 weighted image, the CSF will appear
hypointense (dark) to the spinal cord
when imaging the t spine, how many blocks / sets of slices are typically set up when doing axials
two
T/F: contrast enhancement is good to visualize the MS plaques within the spinal cord canal
true
most inferior portion of the spinal cord
conus medullaris
spinal cords ends at the level of
L1-L2
anchors the spinal cord to the coccyx
filum terminale
spinal coil for lumbar spine
multi coil/ phased array
horizontal alignment light for L spine corresponds to the
third lumbar spine (L3)
scar tissue enhances ______ after contrast injection
immediately
when distance between the edges of the disc material is greater than the distance at the base
extrusion
horizontal light is centered where for t spine
level of 4th thoracic vertebra
SNR is dependent on the
quality of the coil
use ______ to minimize aliasing
oversampling
cancer that starts in the plasma cells in bone marrow
multiple myeloma
the medical term for a tumor that begins in the brain or spinal cord
glioma
pulse motion of the CSF within the spinal canal produces ________
phase ghosting
oval mass in spinal canal
spinal meningioma
coils located inside the bore of magnet, produces a magnet field that goes along the Z axis
gradient system
T1 weighted images are good for
anatomy identification
DWI is most often acquired using a _____ EPI sequence
T2 weighted
pathology will be bright on these images
axial T2 flair
demonstrates the most magnetic susceptibility, great at showing hemorrhage in a stroke patient
axial GRE
T1 , 3D / volume acquisition, helps see difference between white and gray matter
axial BRAVO
derived from multiple diffusion weighted series , multiple b values , usually done post processing
axial ADC
contrast is done with
T1 weighted sequences
less affected by chemical shift, good for microbleeds , 3D imaging
SWAN
FLAIR
fluid attenuated inversion recovery
* fluid suppression , CSF is nulled
suppresses fat signal
STIR
