Increasing the number of scan lines in an image will generally:

Increasing the number of scan lines in an image directly enhances the spatial resolution. Spatial resolution refers to the ability to distinguish between two closely spaced structures in the image. By increasing the number of scan lines, more detailed information is captured, allowing for finer distinctions between small structures in the area being imaged. This results in a clearer and more detailed representation of the anatomy, enabling better visualization of tissues and potential pathology.

While it is true that increasing scan lines can impact other aspects of imaging such as frame rate and field of view, the primary effect is seen on spatial resolution, making it the correct choice in this context. More scan lines mean that the ultrasound system can generate a more detailed image, which is crucial for accurate diagnosis and evaluation of anatomical structures.