Gy 90 180 rf Sig T2 contrast 2-D Imaging 4. Above is a pulse sequence in MRI (Fi
ID: 1885070 • Letter: G
Question
Gy 90 180 rf Sig T2 contrast 2-D Imaging 4. Above is a pulse sequence in MRI (Fig 2b in Magnetic Resonance in Medicine, 39:941-949, 1998). a) This pulse sequence has two segments, divided as "T2 contrast" and 2-D Imaging". Let's first focus on the pulses labeled as "2-D Imaging" 1) What should the horizontal axes be labeled as and in what unit? 2) Explain what 'rf,", "G2 Gy" G and "Sig" mean? Which of the gradients is the slice/phase7read gradient in the usual MRI terminology? 3) What do "90" and "180" mean? What is the purpose of each? 4) What is the ratio of the area of the first Gz pulse over the area of the 5) What is the ratio of the area of the first positive G pulse over the area 6) What is the squiggle in the last channel Sig? What causes the center of second Gz pulse? (Hint: the two G2 pulses are not drawn to scale.) of the negative Gx pulse this squiggle to sit as it is? How can the center of the squiggle be forward and backward? b) What do the three rf pulses above the horizontal line "T2 contrast" do? c) Bonus: What is the purpose of the last gradient in G,?Explanation / Answer
a.1 The horizontal axes should be labelled as TIME axis and the unit should be in mili-second.
a.2 "rf" is the RF excitation field. "Gz", "Gy" and "Gx" are magnetic field gradients that modulate resonant frequency. "Gz" is the Slice Selection. "Gy" is the Phase Encode. "Gx" is the Read Out or Frequency Encode.
a.3 "90" is the excitation RF pulse that selects one slice, "180" is the Spin Echo pulse responsible for Refocusing.
a.4 Area of the first Gz pulse over the second of the same is 0.5. Because the area of first and second pulse, before the signal peak happens, should be same.
a.5 The area ratio of first and second Gx pulse is 2.
c. Gx pulse is responsible for transversal imaging.
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