Which of the following determines the number of scan lines per frame?

The number of scan lines per frame is determined by the Pulse Repetition Frequency (PRF). PRF refers to the frequency at which ultrasound pulses are emitted and is measured in hertz (Hz), indicating how many pulses are sent out per second. A higher PRF leads to more scan lines being acquired per frame, as the system can fire multiple pulses and receive their echoes within the same time period.

This is directly related to temporal resolution, which is the ability to accurately depict moving structures over time; however, temporal resolution itself is not the determinant of the number of scan lines. Instead, it is the PRF that sets the potential for acquiring multiple scan lines in quick succession, thereby affecting the temporal resolution as a secondary factor. The contrast resolution is determined by how distinguishable different tissue characteristics are, and the operating frequency specifically affects image quality and depth of penetration, not the number of scan lines per frame.

Therefore, understanding the role of PRF in determining scan lines per frame is crucial for optimizing imaging performance in ultrasound.