MRI basics Flashcards
Radio frequency (RF
– Radio waves that is introduced to disrupt the alignment of protons in water nuclei. One then measures the RF signals again after nuclei have returned to resting alignment.
Fourier transformation
– Converts the frequency information in the signal from each location of the imaged plane, to corresponding intensity levels.
Repetition time (TR)
The amount of time between successive pulse sequences applied to the same slice.
Time to Echo (TE)
is the time between the delivery of the RF pulse and the receipt of the echo signal.
T1
the time taken for the magnetic vector to return to its resting state
T2
the time needed for the axial spin to return to its resting state
T1-weighted images
: produced by using short TE and TR times. The contrast and brightness of the image are predominately determined by T1 properties of tissue.
T2-weighted images
produced by using longer TE and Tr times. In these images, the contrast and brightness are predominately determined by the T2 properties of tissue.
Flair acronym
Fluid Attenuated Inversion Recovery
Flair definition
Similar to a T2-weighted image, except that the TE and TR times are very long. By doing so, abnormalities remain bright, but normal CSF fluid is attenuated and made. Is very sensitive to pathology.
Diffusion weighted imaging (DWI)
Designed to detect the random movements of water protons. Water moleclules diffuse relateively freely in the extracellular space; their movement is significantly restricted in the intracellular space.
Field of View (FOV)
Defined as the size of the two or three dimensional spatial encoding area of the image. Usually defined in units of mm²
Flip angle,
the amount of rotation the net magnetization experiences during application of a RF pulse
Echo planar imaging (EPI)
a method to form a complete image from a single data sample, or a single “shot”.
Multi-echo fMRI
data is obtained by acquiring multiple echo times TEs for each MRI volume during data collection. Because the BOLD signal is known to decay at a set rate, collecting multiple echos allows us to assess non-BOLD.
