Question

Aliasing is seen while scanning the femoral artery at a 3O-degree angle.

Which step will correct this artifact?
a. Reduce the angle of incidence.
b. Increase the frequency of the transducer.
c. Find a window that is deeper.
d. Increase the pulse repetition frequency (PRF)

Answer 1

To correct femoral artery scanning aliasing, one should increase the pulse repetition frequency (PRF). Echo time differences and minimum ultrasound frequencies relate to a system's resolving power and must conform to diagnostic norms.

Step-by-step explanation:

The question involves aliasing in diagnostic ultrasound, specifically when scanning the femoral artery. Aliasing is an artifact that occurs when the velocity of blood or tissue motion exceeds the Nyquist limit of the ultrasound system, which is half the pulse repetition frequency (PRF). In the given scenario, the correct step to correct this artifact is to increase the pulse repetition frequency (PRF). By increasing the PRF, the Nyquist limit is also increased, which allows the system to accurately measure higher velocities without the occurrence of aliasing. Adjusting the angle of incidence, changing the transducer frequency, or finding a deeper window do not address the fundamental issue of the Nyquist limit being exceeded.

Regarding the echo times, the difference in echo times for tissues located at 3.50 and 3.60 cm would be representative of the scanner's ability to resolve structures that are 0.100 cm apart. The period (T) of the ultrasound waves must indeed be shorter than this minimum time resolution to distinguish between these tissues. The minimum frequency required can be calculated based on the inverse of the period, and it must fall within the typical range used for diagnostic ultrasounds, which can vary from 2 to 15 MHz for most clinical applications.

Answer 2

To correct aliasing observed while scanning the femoral artery at a 30-degree angle, the best option is to increase the pulse repetition frequency (PRF). Increasing PRF provides an expanded range of velocities that can be measured correctly, thus reducing the artifact of aliasing.

Step-by-step explanation:

Aliasing is an artifact that occurs in Doppler ultrasound when the frequency shift exceeds half the pulse repetition frequency (PRF). To correct aliasing seen while scanning the femoral artery at a 30-degree angle, one should increase the pulse repetition frequency (PRF). This adjustment will allow the system to correctly measure higher velocity blood flow without the ambiguity that causes aliasing.

As for option (a), reducing the angle of incidence may also help, but this might not be practical or possible due to anatomical constraints. Option (b), increasing the frequency of the transducer does not address aliasing directly. While option (c), finding a window that is deeper, might not tackle the issue of aliasing and can result in a lower quality image due to increased attenuation of the ultrasound signal.

Thus, the mentioned correct option for correcting aliasing is to increase the PRF, which will provide an adequate range of measured velocities before aliasing occurs again.