mt,cest,noe

Question 1

what is dipolar coupling

Answer 1

direct interaction between two magnetic dipoles

Question 2

why are NMR spectra of hydrogen atoms of water molecules narrow lines

Answer 2

dipole coupling is averaged due to chaotic molecular motion

Question 3

relationship of the magnetic field of the dipole with distance
and the force of its magnetic field on another dipole

Answer 3

the magnetic field goes as the inverse cube of internuclear distance

the force of its magnetic field on another dipole goes as the first derivative of the magnetic field

Question 4

why cant macromolecules be seen in conventional mri

Answer 4

not enough time for spatial encoding gradients to be played out between excitation and acquisition before the signal has completely decayed

Question 5

what allows the spin state of the macromolecular protons to influence the spin state of the liquid protons through exchange processes

Answer 5

coupling between the macromolecular protons and the mobile or ‘liquid’ protons

Question 6

what is k_AB

Answer 6

pseudo-first-order rate constant

Question 7

what is RM_0B

Answer 7

rate of transfer of spins from A to B

Question 8

what results in homogeneously broadened absorption lineshape in the bound pool

Answer 8

the protons in the macromolecules are strongly coupled to each other

Question 9

what is the effective saturation rate

Answer 9

the probability of absorption at the corresponding offset frequency times the average radio frequency (RF) power at the offset frequency (ref5,henkelman review)

Question 10

why is the effect of an off-resonance irradiation governed by the Bloch equations

Answer 10

the spins in the liquid pool are only weakly coupled

Question 11

what does the effective field B_eff consist of in the rf rotating reference frame

Answer 11

the vector sum of the transverse B1 field and a residual longitudinal field equal to delta/gamma, where delta = the resonant Larmor frequency (omega_0) - the rotating frequency of the RF (omega_RF)

(omega_0 - omega_RF)

Question 12

what are Rabi oscillations

Answer 12

transient oscillations of transverse magnetization leading from CW off-resonance irradiation which initially results in a precession of the liquid spins about the effective field

Question 13

what does transient mean

Answer 13

lasting for a short time

Question 14

what is T2_rho

Answer 14

the decay constant of the transient Rabi oscillations

Question 15

what is T1_rho

Answer 15

the decay constant of the magnetisation of B_eff

Question 16

how to suppress the transverse magnetisation

Answer 16

spoiler gradients or phase cycling

Question 17

why is supressing transverse magnetisation usually not an issue in MT imaging experiments

Answer 17

saturation pulses are sufficiently smooth that they are adiabatic or they are repeated sufficiently frequently that the transverse components are incoherently dephased

Question 18

why are CW better for characterising the mechanisms of the MT process

Answer 18

provide the cleanest separation between the amount of saturation in the two pools

Question 19

for practical imaging experiments, why are repetitive pulsed off resonance irradiation of shorter duration necessary

Answer 19

to allow time for the interleaved imaging experiment
to keep the SAR within reasonable limits
and because imaging RF transmitters are designed for pulsed RF and not CW operation

Question 20

how are off-res pulses usually delivered

Answer 20

with an amplitude modulation that varies smoothly in time, such as a Gaussian envelope

Question 21

how are spins exchanged in MT

Answer 21

]spin exchange can occur via dipolar coupling or via direct chemical exchange