ARDMS SPI - Sonography Principles and Instrumentation

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.

Comprehensive and Detailed Explanation From Exact Extract:

Persistence averages multiple frames to smooth out random noise fluctuations, reducing the appearance of noise in the image and improving image quality.

According to sonography instrumentation reference:

“Persistence reduces noise by averaging data from consecutive frames, improving signal-to-noise ratio and producing a smoother image.”

Therefore, the correct answer is D: Increase persistence.

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Comprehensive and Detailed Explanation From Exact Extract:

Lateral resolution is the system’s ability to distinguish two structures side-by-side. It is directly determined by the beam width — the narrower the beam, the better the lateral resolution.

Principles and Instrumentation:

"Lateral resolution depends on beam width at a given depth. Narrower beams provide better lateral resolution."

Depth of penetration influences maximum imaging depth.

Propagation speed is largely constant in soft tissue.

Wavelength affects axial resolution.

Therefore, the correct answer is A: Beam width.

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Comprehensive and Detailed Explanation From Exact Extract:

Low PRF reduces the Nyquist limit, making the system more susceptible to aliasing when Doppler shift frequencies exceed this limit.

Principles and Instrumentation state:

"Aliasing occurs when Doppler shifts exceed half the PRF (Nyquist limit). Lowering PRF increases aliasing susceptibility."

Spectral broadening (A) results from turbulence or poor angle.

Range ambiguity (B) occurs at high PRF.

Dropout (D) refers to signal loss, not aliasing.

Therefore, the correct answer is C: Aliasing.

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The tissue-equivalent phantom image with the red oval indicates an area where axial resolution can be evaluated. Axial resolution refers to the ability to distinguish between two structures that are close together along the axis of the ultrasound beam. It is determined by the spatial pulse length (SPL) of the ultrasound wave. In phantoms, this is typically tested by observing the ability to separate closely spaced targets along the beam's path.

Attenuation refers to the reduction in the intensity of the ultrasound beam as it travels through tissue. Higher frequency ultrasound beams experience more attenuation because they are absorbed and scattered more than lower frequency beams. This is due to the fact that higher frequency waves have shorter wavelengths and interact more with the small particles in tissues, causing greater energy loss.

Comprehensive and Detailed Explanation From Exact Extract:

Spatial compounding acquires multiple frames from different angles and combines them into a single image. This technique reduces the appearance of artifacts such as shadowing and speckle noise, resulting in a smoother, more uniform image.

According to sonography instrumentation reference:

“Spatial compounding reduces artifacts like posterior shadowing and speckle by averaging data from multiple insonation angles.”

Therefore, the correct answer is D: Decreases shadowing.

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Comprehensive and Detailed Explanation From Exact Extract:

Color Doppler detects flow based on the Doppler shift, which is dependent on the cosine of the angle between the ultrasound beam and the direction of blood flow. At 90 degrees, the cosine value is zero, resulting in no Doppler shift and therefore no detectable color flow signal.

According to sonography instrumentation reference:

“When the insonation angle is 90 degrees, the Doppler frequency shift is zero because the cosine of 90 degrees equals zero. As a result, no flow is displayed.”

Therefore, the correct answer is D: 90 degrees.

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Sensitivity is the term for an ultrasound system's ability to display low-level echoes. It refers to the system's capacity to detect and accurately display weak echoes returning from tissues. High sensitivity allows the sonographer to visualize structures that produce faint echoes, such as small or low-contrast lesions. This parameter is critical for ensuring that subtle pathological changes are not missed during imaging.References:

ARDMS Sonography Principles and Instrumentation guidelines

"Sonography: Principles and Instruments" by Joan P. Baker and Marveen Craig

Comprehensive and Detailed Explanation From Exact Extract:

Color aliasing occurs when the Doppler shift exceeds the Nyquist limit, which is determined by the pulse repetition frequency (PRF). A low PRF reduces the Nyquist limit, making aliasing more likely.

According to sonography instrumentation reference:

“Aliasing occurs in color Doppler imaging when the Doppler shift frequency exceeds half of the PRF (Nyquist limit). A low PRF increases the likelihood of aliasing.”

Therefore, the correct answer is A: Low pulse repetition frequency.

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