| 摘要 |
In Fourier transform NMR imaging, magnified images free of aliasing artifacts are achieved by band limiting the NMR signal in the X- and Y-axes directions thereby avoiding under-sampling. Band limiting in the X-axis direction is accomplished by reducing the signal bandwith by a low-pass filter before A/D conversion. In the Y-axis direction, the signal is band limited by providing selective excitation of the spin isochromats, such that only spins in a selected Y region of the object are available to contribute to the signal. When the region of interest is not centered, offsets in the X- and Y-axes directions are obtained by shifting the receiver frequency by an amount DELTA fR, and causing the selective RF pulse to have a complex amplitude. |
