Which examination modality is most likely to have a high SPTA value?

Which examination modality is most likely to have a high SPTA value?

• A. CW Doppler
• B. PW Doppler
• C. Color flow Doppler
• D. M-mode

Answer: (B)

The main idea here is how SPTA (spatial peak temporal average intensity) tracks how much ultrasound energy is delivered over time. SPTA depends on both how strong the beam is at its peak and how long the beam is actually on. Continuous wave Doppler transmits without pauses, so its duty factor is essentially 1. That means the temporal average matches the peak intensity, giving the highest SPTA among the modalities listed. Pulsed wave Doppler sends short pulses repeatedly, so the beam is on only part of the time; the SPTA is reduced by the duty factor (pulse duration times repetition frequency). Color flow Doppler also uses pulsed sequences with a low duty cycle, lowering SPTA further. M-mode uses very brief, rapid pulses but with significant off time, resulting in a small duty factor and low SPTA. So, the modality most likely to have a high SPTA is continuous wave Doppler.

The main idea here is how SPTA (spatial peak temporal average intensity) tracks how much ultrasound energy is delivered over time. SPTA depends on both how strong the beam is at its peak and how long the beam is actually on. Continuous wave Doppler transmits without pauses, so its duty factor is essentially 1. That means the temporal average matches the peak intensity, giving the highest SPTA among the modalities listed. Pulsed wave Doppler sends short pulses repeatedly, so the beam is on only part of the time; the SPTA is reduced by the duty factor (pulse duration times repetition frequency). Color flow Doppler also uses pulsed sequences with a low duty cycle, lowering SPTA further. M-mode uses very brief, rapid pulses but with significant off time, resulting in a small duty factor and low SPTA. So, the modality most likely to have a high SPTA is continuous wave Doppler.