ARDMS Ultrasound Physics & Instrumentation Practice Exam

What is the characteristic of axial resolution in ultrasound imaging?

1. Increases with frequency

2. Decreases with frequency

3. Unrelated to transducer frequency

4. Improved by the use of contrast agents

The correct answer is: Increases with frequency

Axial resolution in ultrasound imaging refers to the ability to distinguish two closely spaced structures along the axis of the ultrasound beam. This characteristic is primarily determined by the spatial pulse length, which is the distance over which one pulse of ultrasound is emitted. Higher frequencies produce shorter wavelengths and, consequently, shorter pulse lengths. Since axial resolution is directly related to the spatial pulse length, an increase in frequency leads to improved axial resolution. This means the ultrasound system can better differentiate between two closely located objects in the direction of the sound beam. Therefore, the choice indicating that axial resolution increases with frequency accurately captures the relationship between frequency and resolution in ultrasound imaging.