MIDTERMS Flashcards
_________ coils acts as an antenna to produce or transmit and detect or receive radiowaves that are referred to as the MRI signal
radiofrequency coils
a typical _____ coil is enclosed in the gantry of the magnet
radiofrequency coil
most homegenous coils are of a ______ design
birdcage
coil that is integrated into the scanner bore and cannot be seen by the patient
this completely surrounds the patient
acts as transceivers
body coils
it is a head coil
acts as transceivers
provides best radiofrequency homogeneity
volume/birdcage coils
a coil that has simple loop designs, either circular or rectangular and have excellent SNR close to the coil but the sensitivity drops off rapidly with distance from the coil
these are only used as receivers, the body coil will act as transmitter
surface/local coils
coil used for imaging anatomy near the coil
the depth of the image of a _____ coil is generally limited to about one radius
surface/local coils
coil commonly used for the knee
these coils provide better homogeneity of the RF in the area of interest and are used as volume coils, unlike surface coils
also used for the x and y gradient coils
paired saddle coils
this is required to protect the environment from the effects of fringe fields which surround magnet
radiofrequency shielding
to maintain magnetic field homogeneity, ______ is necessary for the field to be protected from being distorted by the external environment
shielding
magnetic field outside the patient aperture
fringe magnetic field
an advance technique used to acquire images from moving body parts like chest, abdomen, cardiac and blood vessels studies reducing motion artifacts
gating
3 types of gating
cardiac gating
respiratory gating
breath holding
carding gating acquisition is generally triggered by an _______, this eliminate the blurring and artifact problem inherent
electrocardiogram
cardiac gating uses programmed ____ __ ______ (TR) to deliver RF pulse and to monitor the cardiac cycle to determine which signal it uses for reconstruction
time of repetition
this suppress breathing motion
acquisition takes place only during the gate when respiratory is minimal
respiratory gating
respiratory gating is effective in minimizing _____ motion but increases imaging time and resolution
breathing
gatings used in MRI of the chest, abdomen, liver perfusion and dynamics, kidneys, spleen, adrenals and MRCP
respiratory gating
breath holding
gating where image acquisition every breath holds after exhalation
breath holding
is a provrammed set of changing magnetic gradients
defined by multiple parameters
pulse sequences
time required for the external magnetic field to go to two third of its original value
gives informatjon about the thermal conductivity of the surrounding tissue
anatomy
T1 weighted images
time required for the transverse magnetic field to decay to a third of its original value
gives information about the homogeneity of the surrounding atoms
pathology
T2 weighted images
is commonly used in MRI to suppress the signal from adipose tissue or detect adipose tissue
it can be applied to both T1 and T2 weighted sequences
fat suppression pulse sequence
areas contain adipose tissues appear ____ on T2 weighted fat saturated images
dark
due to added fat suppression, pathological processes are usually very bright
T2 fatsat
water has low signal and appears dark
fat will appear bright
T1 weighted images
water appears bright and fat will appear intermediate bright
T2 weighted images
