ARDMS Ultrasound Physics & Instrumentation Practice Exam

What term describes the ability of the ultrasound system to distinguish parallel structures?

1. Lateral resolution

2. Axial resolution

3. Spatial resolution

4. Contrast resolution

The correct answer is: Axial resolution

The ability of the ultrasound system to distinguish parallel structures is best described by the term axial resolution. Axial resolution refers to the system's capability to separate two structures that lie along the axis or the beam's path. It is determined by the spatial pulse length (SPL) of the ultrasound beam, which is influenced by the frequency of the transducer; higher frequency transducers produce shorter wavelengths, resulting in better axial resolution. In this context, distinguishing parallel structures is specifically about the separation of structures located one behind the other in the direction of the ultrasound beam. Structures that are too close together in this axis may be perceived as a single echo. Therefore, axial resolution is crucial for imaging closely spaced anatomic features that are aligned with the direction of the sound wave. Other terms such as lateral resolution relate to the ability to separate structures that are side by side, spatial resolution encompasses both axial and lateral resolution regarding the overall clarity of the image, and contrast resolution denotes the system's ability to differentiate between tissues of similar echogenicity. Each of these plays a unique and important role in ultrasound imaging, but for distinguishing structures in a parallel arrangement along the axis of the beam, axial resolution is the most appropriate term.