SPI Exam Dumps - Sonography Principles and Instrumentation

Comprehensive and Detailed Explanation From Exact Extract:

Axial resolution depends on spatial pulse length (SPL), which is determined by the number of cycles per pulse. Fewer cycles per pulse shorten the SPL, thereby improving axial resolution and allowing better separation of closely spaced structures along the beam axis.

According to sonography instrumentation reference:

“Axial resolution improves with fewer cycles per pulse, which decreases the spatial pulse length and allows better discrimination of structures along the beam path.”

Therefore, the correct answer is B: Reducing the number of cycles per pulse.

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Comprehensive and Detailed Explanation From Exact Extract:

At greater depths, pulse repetition frequency (PRF) is automatically reduced due to longer pulse travel times, lowering the Nyquist limit and increasing the likelihood of aliasing.

Principles and Instrumentation state:

"As sample depth increases, PRF decreases, lowering the Nyquist limit and increasing the risk of aliasing in pulsed-wave Doppler."

Doppler shift depends on flow velocity and angle, not depth.

Actual velocity measurements do not increase with depth.

Signal strength typically decreases (not increases) due to attenuation.

Therefore, the correct answer is A: Increased aliasing.

The Doppler shift is directly related to the cosine of the angle between the ultrasound beam and the direction of blood flow. As the angle increases from 30 degrees to 60 degrees, the cosine of the angle decreases (cosine of 30 degrees is approximately 0.87, while cosine of 60 degrees is 0.5). Since the Doppler shift is proportional to the cosine of the angle, increasing the angle results in a decreased Doppler shift. This means the measured blood flow velocities will appear lower at a 60-degree angle compared to a 30-degree angle.

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.

Comprehensive and Detailed Explanation From Exact Extract:

Aliasing occurs in pulsed-wave Doppler imaging when the Doppler shift frequency exceeds the Nyquist limit (which is half the pulse repetition frequency, PRF). This results in a wrap-around of the Doppler signal, which appears as a reversal of flow direction (aliasing artifact).

According to standard Principles and Instrumentation references in sonography:

“To eliminate aliasing, the Doppler PRF (scale) should be increased. Increasing the PRF raises the Nyquist limit and therefore allows for higher measurable velocities without aliasing.”

The correct adjustment to correct this aliasing artifact isC: Increase the Doppler pulse repetition frequency. This effectively increases the Nyquist limit and resolves the wrap-around aliasing appearance.

Options A and B (adjusting the spectral Doppler gain) would only change the appearance of the Doppler waveform (i.e., its amplitude and brightness) but would not affect aliasing. Option D (decreasing the PRF) would actually worsen the aliasing by lowering the Nyquist limit.

Therefore, the correct choice is toincrease the Doppler PRF.

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.

A string phantom is designed to evaluate the accuracy of Doppler ultrasound systems, specifically in measuring flow velocity. It consists of a moving string or filament that mimics blood flow within a vessel. By using this phantom, sonographers can assess how accurately the ultrasound system can detect and measure the speed of the moving target. This helps in calibrating and verifying the performance of Doppler systems, ensuring they provide accurate flow velocity readings in clinical practice.

American Registry for Diagnostic Medical Sonography (ARDMS) Sonography Principles and Instrumentation study materials.

Textbook of Diagnostic Sonography by Hagen-Ansert, S. L. (latest edition).

Comprehensive and Detailed Explanation From Exact Extract:

Temporal resolution reflects how quickly frames are updated (frame rate). Reducing the number of scan lines per frame (low line density) decreases acquisition time, thus increasing frame rate and improving temporal resolution.

According to sonography instrumentation reference:

“Lower line density allows for faster frame rates, improving temporal resolution at the expense of spatial resolution.”

Therefore, the correct answer is D: Low line density.