Comprehensive and Detailed Explanation From Exact Extract:

Axial resolution depends on spatial pulse length (SPL), which is determined by the number of cycles per pulse. Fewer cycles per pulse shorten the SPL, thereby improving axial resolution and allowing better separation of closely spaced structures along the beam axis.

According to sonography instrumentation reference:

''Axial resolution improves with fewer cycles per pulse, which decreases the spatial pulse length and allows better discrimination of structures along the beam path.''

Therefore, the correct answer is B: Reducing the number of cycles per pulse.

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