Consider the excitation of a slice of thickness Az = 4 mm, by a bandlimited rf...

 

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Consider the excitation of a slice of thickness Az = 4 mm, by a bandlimited rf pulse on for a time duration T,f = 4ms. Assume that the flip angles of the spins are dominated by the exact (time) center of the rf pulse. If the applied gradient strength is given as 10 mT/m: a) Find the difference in accumulated phase between two spins on opposite sides of the slice (i.e., at z = 20 + Az/2) at the end of the rf pulse. b) Show that, in general, o = 0 for all spins at the end of the rephase gradient lobe, under the constraint (10.26). c) How long must the rephasing gradient be applied, for complete refocusing, if Grephase = -G and the two gradients are boxcar pulses? What is the duration of the total slice select process, including the time that both Gss and Grephase are applied? refocusing. For a symmetric slice select gradient with |G, Grephasel total area under Grephase S dtGrephase S dtG ss 50% (10.26) %3D total area under Gss including the possibility of arbitrary time dependence for each gradient lobe. The signs of Consider the excitation of a slice of thickness Az = 4 mm, by a bandlimited rf pulse on for a time duration T,f = 4ms. Assume that the flip angles of the spins are dominated by the exact (time) center of the rf pulse. If the applied gradient strength is given as 10 mT/m: a) Find the difference in accumulated phase between two spins on opposite sides of the slice (i.e., at z = 20 + Az/2) at the end of the rf pulse. b) Show that, in general, o = 0 for all spins at the end of the rephase gradient lobe, under the constraint (10.26). c) How long must the rephasing gradient be applied, for complete refocusing, if Grephase = -G and the two gradients are boxcar pulses? What is the duration of the total slice select process, including the time that both Gss and Grephase are applied? refocusing. For a symmetric slice select gradient with |G, Grephasel total area under Grephase S dtGrephase S dtG ss 50% (10.26) %3D total area under Gss including the possibility of arbitrary time dependence for each gradient lobe. The signs of

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given Z 4mm T rf 4 ... View the full answer