What control can assist in tissue differentiation or fill in fluid-filled structures in ultrasound imaging?

Harmonic imaging is the correct choice because it enhances tissue differentiation and improves the visualization of structures in ultrasound imaging. This technique works by using higher frequency sound waves, which can lead to clearer images with a better signal-to-noise ratio. As ultrasound waves travel through the body, they may generate harmonic frequencies that provide additional information about the tissue characteristics. This results in improved resolution of the images, making it easier to differentiate between various types of tissues and to more effectively visualize fluid-filled structures, such as cysts or vessels, within the body.

In contrast, color Doppler is primarily used to evaluate blood flow and does not specifically enhance tissue differentiation. Pulse width refers to the duration of the ultrasound pulse, which can influence temporal resolution but does not directly impact tissue differentiation. Gain control is utilized to adjust the overall brightness of the ultrasound image but does not inherently change the quality of tissue differentiation or visualization of specific structures.