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This really depends on the pulse sequence. Decreasing the BW by definition means that the time for each sample (Ts) increases. As a result, for the same number of samples (i.e., “ frequency encoding steps) the overall time to sample a line of k-space increases. This can impact the shortest achievable TE because the time between excitation and the center of the sampling time cannot be made as short as with a higher BW (i.e., shorter Ts). In most applications this does not impact overall acquisition time because the TE is so much shorter than TR. In very short TR scenarios, such as fast GRE, SSFP or single shot acquisitions, it is possible that the shortest achievable TR might increase with a decrease in BW. This is a matter of how much can be crammed into the time between one excitation and the next (I.e., TR).
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