FMRI: Biological Basis and Experiment Design Lecture 12: Signal-to-Noise Ratio Things that determine signal strength –voxel size –RF coil Things that determine.
Post on 21-Dec-2015
217 Views
Preview:
Transcript
fMRI: Biological Basis and Experiment DesignLecture 12: Signal-to-Noise Ratio
• Things that determine signal strength– voxel size– RF coil
• Things that determine noise contribution– Bandwidth (thermal noise)– Brains (physiological noise)
• Averaging
antwrp.gsfc.nasa.gov/apod/ap041008.html
1 light year = 5,913,000,000,000 miles?
Broad definitions
• Thermal noise– Assumed white
– Fluctuations in RF path (coupling to sample, amplifiers ...)
• Physiological noise– Probably colored
– Vasoreactivity
– Motion
– Respiration
– Cardiac
– ...
– Uncontrolled cognitive processes
SNR maps, 2 definitions
Definition 1: mean through time divided by standard deviation through time
Definition 2: static signal intensity divided by background noise
SNR maps in water phantoms
New category of noise: inanimate processes?
Siemen’s implementation of SENSERegular EPI
SNR – dependence on coil properties
(These are just static images, not SNR maps.)
Body coil transmit,body coil receive
Body coil transmit,8-channel coil receive
Pulse sequence diagram: Spoiling in FLASH/GRASS/RAGE ...
Nrep = 256
256 points
RF
GSS
GPE
GRO
DAC
Flip angle = 7 deg. TR = 10ms
TE ~ 5ms
Goal: obliterate any remaining transverse magnetization before next excitation.
top related