A MATCHED-FILTER ECHO SUMMATION TECHNIQUE FOR MRI

A technique is presented to increase the signal-to-noise ratio (SNR) i n two-dimensional (2D), phase-encoded imaging at low SNR. The essence of this technique is to combine multiple echoes in the time domain. As analyzed in the paper, phase discrepancies exist among different echo es and may deteriorate the combined echo. In particular, extraneous ph ase shifts can be created if unshielded gradient coils are used. To ov ercome these phase discrepancies, a matched filter was derived from th e k = 0 component of image. This matched filter has the same phase dis crepancies among its echoes as the imaging signal and its magnitude de cays with an average T-2. In the echo summation with the matched filte r, the phase of the matched filter was subtracted from the imaging sig nal and the magnitude of the matched filter was used as the weighting function. We have shown that this matched filter echo summation techni que has better SNR than the case of 2D, phase-encoded imaging in both simulation and experiment. The SNR improvement is up to 60% in a phant om experiment. This technique is mostly useful in low SNR imaging that requires long imaging time, such as spectroscopic imaging and F-19 im aging.