What does spatial resolution depend on in ultrasound imaging?

Spatial resolution in ultrasound imaging refers to the ability to distinguish between two closely spaced structures. This ability is primarily influenced by both the frequency of the transducer and the depth of the tissue being imaged.

Higher frequency transducers provide better spatial resolution because they produce narrower pulses and, therefore, a smaller point spread function. This means that they can better differentiate structures that are close together. However, the depth at which the imaging is being performed also affects spatial resolution due to the phenomenon of beam divergence. As the ultrasound beam propagates deeper, it spreads out, which can lead to a loss in resolution. Therefore, the combination of frequency and depth is crucial in determining the overall spatial resolution of the image.

This makes option B the correct choice, as it accurately captures the two key factors influencing spatial resolution in ultrasound imaging.