ARDMS Sonography Principles and Instrumentation Exam Questions

The duty factor is the fraction of time that the ultrasound system is actively transmitting a signal. Continuous wave (CW) Doppler has the highest duty factor because it continuously transmits and receives ultrasound waves. Unlike pulsed wave Doppler, which alternates between sending and receiving signals, CW Doppler does not have a listening period, resulting in a duty factor of nearly 100%. Therefore, CW Doppler has the highest duty factor among the modes listed.

ARDMS Sonography Principles & Instrumentation Guidelines

Hedrick WR, Hykes DL, Starchman DE. Ultrasound Physics and Instrumentation. 4th ed. Philadelphia, PA: Elsevier Saunders; 2005.

The aperture of a transducer is the active area that emits and receives the ultrasound waves. In a linear array transducer, increasing the aperture (using more elements for transmission and reception) results in a deeper focus because the beam is more tightly focused over a longer distance. This improves lateral resolution at greater depths, as the ultrasound beam maintains a narrower width for a longer distance. It allows for better imaging of deeper structures without sacrificing resolution.

American Registry for Diagnostic Medical Sonography (ARDMS). Sonography Principles and Instrumentation (SPI) Examination Review Guide.

The image shown is typical of an abdominal ultrasound, which commonly utilizes a curvilinear transducer. Curvilinear transducers have a wider field of view at depth, making them ideal for imaging large structures within the abdomen. These transducers emit a curved beam, allowing for better penetration and a broader field of view, which is necessary for comprehensive abdominal examinations. The curvature of the image, the wide field of view, and the depth of penetration all suggest the use of a curvilinear transducer.

American Registry for Diagnostic Medical Sonography (ARDMS). Sonography Principles and Instrumentation (SPI) Examination Review Guide.

Lateral resolution describes the ability of an ultrasound system to distinguish between two structures that are side by side (perpendicular to the path of the ultrasound beam). This type of resolution depends on the beam width; narrower beams provide better lateral resolution. As the ultrasound beam travels deeper into the tissue, it generally widens, which can reduce lateral resolution. Techniques such as focusing the beam can help improve lateral resolution at specific depths by narrowing the beam width.

American Registry for Diagnostic Medical Sonography (ARDMS). Sonography Principles and Instrumentation (SPI) Examination Review Guide.

In ultrasound imaging, penetration refers to the ability of the ultrasound beam to travel deeper into the tissue. Lower frequency transducers produce sound waves with longer wavelengths, which are less attenuated by the tissues and therefore can penetrate deeper into the body. Conversely, higher frequency transducers produce sound waves with shorter wavelengths that provide better resolution but are more quickly attenuated, resulting in less penetration. Therefore, decreasing the frequency of the transducer improves penetration, allowing for better visualization of deeper structures.

American Registry for Diagnostic Medical Sonography (ARDMS). Sonography Principles and Instrumentation (SPI) Examination Review Guide.