Coils Flashcards
Electromagnetic components of RF System maybe provided by outside supplier and assemble by MRI manufacture
RF SYSTEM
2 Coils
SHIM COILS -MAKE MAGNETIC FIELD HOMOGENEOUS
RECEIVER COILS-DETECT THE RETERNING RADIOSIGNAL ARE ‘ANTENNA’ OF THE MRI SYSTEM THE BROADCAST
4 TYPES OF COILS
SURFACE COILS, PAIRED SADDLE COIL, HELMHORTZ PAIR COIL, BIRDCAGE COIL
use are the simply loop of wire either circular or RECTANGULAR
Surface coil
- Provide better homogeneity of RF in area of interest
PAIRED SADDLE COIL
consis of two circular coils parallel
HELMHORTZ PAIR COILS
- Transceiver coil for imaging of the head
BIRD CAGE COIL
What are the Power supply of MRI
2.4Kw, 5% voltage ripple, 1.5 Tesla commonly used
Use ALUMINUM, FORM OF SHEILD FARADAY CAGE, PRETECTION THE VERY WEAK RF SIGNAL
FARADAY CAGE
Is used in MRI to describe the relative contribution detected signal of background noise
SNR/SIGNAL NOISE RATIO
IF SNR WILL INCREASE
FACTOR AFFECTING SNR
BO,T1,T2,TE,TR,FOV,nex,matrix size, RF BANDWIDTH, PIXEL SIZE, SLICE THICKNESS
6 INCREASE IN FACTORS AFFECTING SNR
BO,TR,T2,FOV,RF BANDWIDTH,PIXEL SIZE, SICE THICKNESS
4DECREASE IN FACTORS AFFECTING SNR
T1,TE,NEX,MATRIX SIZE
Types of IF ALL PARAMETERS ARE CONSTANT/bandwidth
RF COIL,RF BANDWIDTH,THE RECEIVER (ACQUISITION)BANDWIDTH,THE TRANSMIT BANDWIDTH,PULSE SEQUENCE
IF ALL PARAMETERS ARE CONSTANT
- smaller sensitive volume of coil,local coil or better amd selected SLICE PLANE
RF COIL
- refers the frequencies associated either with RF excitation
RF BANDWIDTH
Range of frequencies accepted by the receiver to sample MR signal
THE RECEIVER (ACQUISITION)BANDWIDTH
Slice selection in pulse sequence, slice thickness, lowering the PULSE
THE TRANSMIT BANDWIDTH
- Acquire images with different tissue contrast mechanism
PULSE SEQUENCE
- MRI uses technology is called?
Pulse sequence
diffusion movement of molecules due to random motion
Diffusion weighted imaging(DWI)-
How many hours in DWI/Diffusion weighted imaging in prior scan
72HOURS prior scan
What will use in DWI?
used CVA/ CARDIOVASCULAR ACCIDENT and CNS/CENTRAL NERVOUS SYSTEM
In what signal diffusion values in DWI
T2
WHAT IS THE DWI REMAINS SENSITIVE ?
T1AND T2 RELAXATION
Most widely used start in 90pulse and ends of 180 degree pulse
SPIN ECHO
Refocus the spin gradient echo are more susceptible to blood flow 90° in additional TRand TE, Aka reverse the polarity of gradient
GRADIENT ECHO
How many flip angles of GRADIENT ECHO
LESS THAN 90°
2FAST PULSE SEQUENCE
Fast gradient echo(FGRE),FAST SPIN ECHO (FSE)
For turbulent blood flow
Fast gradient echo(FGRE)
is quicker because it is cover wide range of tissue used start in 90pulse and ends of 180 degree pulse
FAST SPIN ECHO(FSE)
