Excitation and Relaxation Flashcards
What is the direction of low energy and spin up?
parallel to B0
What represents direction and magnitude?
vector
What is the direction of low energy and spin up?
parallel to B0
What is the direction of high energy and spin down?
antiparallel to B0
What is the speed of the wobble called?
precessional frequency
What is the Larmor Equation?
w0 = yB0
What is the phenomenon when an RF cause resonance to occur?
excitation
What is the term for the position of each magnetic moment on the precessional path around B0?
phase
What is the sum of the magnetic effects of all the protons exposed to the main B0?
Net Magnetic Moment (Net Magnetization Vector)
What is 1 Tesla equal to in Gauss?
10,000 gauss
What’s the gyromagnetic ratio for hydrogen?
42.57 mHz/T
What’s the phenomenon that permits the efficient transfer of energy from one object or system to another?
resonance
What’s the plane which is perpendicular to the longitudinal direction?
transverse plane
What are the 2 factors Flip Angle depend on?
- RF amplitude
- RF pulse duration
What’s the angle between the starting position of the NMV and the resultant position after the delivery of the RF energy?
RF Flip Angle
What is the Flip Angle most often used with spin echo?
90 degree
What is the Flip Angle most often used with gradient echo?
less than 90 degree
What’s the process by which energy is lost to the environment?
relaxation
What is the recovery of longitudinal magnetization caused by?
T1 recovery
What is the decay of transverse magnetization caused by?
T2 decay
What are the 2 types of relaxation?
- T1 or spin-lattice
- T2 or spin-spin
Is T1 dependent on T2?
No. both occur simultaneously, but completely independent of one another
What’s T1 relaxation?
the time required for the net magnetization to grow to 63% of its final amplitude
What’s the signal decay due to the transverse dephasing called?
free induction decay (FID)
What’s T2 relaxation?
the time at which the transverse magnetization has decayed to 37% of its full value due to spin-spin interactions
What lines up with the main B0 along the longitudinal direction?
the net magnetization of protons
What caused the magnetization to move into the transverse plane?
90 degree RF pulse
What caused the magnetization to rephrase and form an echo?
180 degree RF pulse
What contains the contrast information to differentiate the appearance of the soft tissues of the body in the resulting MR image?
the echo
What’s the time from one 90 degree pulse to the next 90 degree pulse called?
TR (repetition time)
What’s the time from the 90 degree pulse to the peak of the signal called?
TE (echo time)
Which sequence parameters is great for demonstrating anatomy?
T1 weighting
Which sequence parameters is great for demonstrating pathology?
T2 weighting
What is the term for small dipole magnet associated with hydrogen?
magnetic moment
What causes the motion of magnetic moment to exist?
isotope protium
