Every voxel will contribute to the overall voltage by an amount, Sv tð Þ¼MT x; y ð Þe i ygGyt xgGxtþxgGx t t ð Þ ½ ð7:23Þ Hence, the contribution of all voxels in one XY slice will be: ST tð Þ¼ ð x,y MT x; y ð Þe i ygGyt xgGxtþxgGx t t ð Þ ½ dxdy ð7:24Þ The intensity of the field then is a function of the time. The maximum of the quantity obtained from Eq. (7.24) occurs for t ¼2t as shown in Fig. 7.15. The sequence that has been described is repeated many times with a repetition period TR. Repetition periods could be 128 or 256 to get the data necessary to reconstruct an image; every time that a time sequence is repeated the magnitude of Gx andGy are changed in equal steps. Fig. 7.15 Sequence of pulses to locate the position of a voxel in the XY plane Fig. 7.16 Detection of the phase of the magnetization vector in the frequency plane 7 Data Processing Techniques to Analyze Large 3-D Deformations of Cardiac Cycles 75
RkJQdWJsaXNoZXIy MTMzNzEzMQ==