What is the axial resolution of an ultrasound system?

Axial resolution refers to the system's ability to distinguish two closely spaced structures in the direction of the ultrasound beam. It is determined by the spatial pulse length (SPL), which is the product of the number of cycles in a pulse and the wavelength of the ultrasound waves.

To achieve enhanced axial resolution, it is essential to have a shorter spatial pulse length. Since the axial resolution is defined as the ability to differentiate two points that are aligned with the ultrasound beam, it can be mathematically represented as one half of the spatial pulse length. Therefore, the correct understanding of axial resolution leads to the conclusion that it is equal to one half of the SPL.

The other options do not accurately reflect the concept of axial resolution. Wavelength relates to the spatial dimension of the sound wave itself, but it does not directly equate to axial resolution measures. Similarly, frequency is a fundamental characteristic of sound waves and influences imaging resolution indirectly through wavelength, but it does not define axial resolution directly. The distance between the transducer and a reflector does not represent axial resolution; instead, it relates to the measurement of the echo timing and is unrelated to the resolution capability of the imaging system.