How do I use Power Doppler on a Voluson S8 USG (Ultrasound) machine?

How to Use Power Doppler on a Voluson S8 Ultrasound Machine

Power Doppler should be used as an adjunct to grayscale imaging on the Voluson S8, with careful attention to gain, pulse repetition frequency (PRF), and wall motion filter (WMF) settings to optimize detection of low-velocity flow in small vessels.

Initial Setup and Machine Configuration

Starting the Examination

• Begin with conventional B-mode imaging to identify your target structure before switching to Power Doppler mode 1
• Use a dual-screen format showing B-mode alongside the Power Doppler display for improved anatomic guidance, especially for small lesions 1
• Hold the transducer motionless once the target is identified to maintain consistent imaging 1

Transducer Selection

• Use linear probes (7-15 MHz) for superficial structures like salivary glands or superficial vessels 1
• Use sector or convex probes for deeper structures 1
• Higher frequencies (≥15 MHz) provide better resolution but limited penetration 1, 2
• Lower frequencies provide greater tissue penetration but reduced resolution, suitable for deeper structures and obese patients 2

Critical Machine Settings

Pulse Repetition Frequency (PRF)

• For vascular imaging: Set PRF between 0.3-1.3 kHz for detecting slow flow in small vessels 3, 4
• For temporal arteries: Use PRF of 2-3.5 kHz 1, 2
• For extracranial arteries: Use PRF of 3-4 kHz 1, 2
• PRF has the second-most profound effect on Power Doppler signal after gain 5
• Using PRF lower than 1.3 kHz can cause aliasing artifacts, but Power Doppler is generally less susceptible to aliasing than Color Doppler 6, 3

Gain Settings

• Gain has the greatest effect on Power Doppler signal - adjust carefully to avoid underfilling or overfilling of the vessel lumen 1, 5
• Use low signal gain initially, then increase gradually until flow is visible without excessive background noise 1
• At lowest gain settings, no Doppler signals will be detected; at maximum settings, you'll get the highest recordable indices but also excessive noise 5
• Adjust gain to avoid anechoic appearance of the artery wall in B-mode 1

Wall Motion Filter (WMF)

• WMF cutoff frequency profoundly influences Power Doppler magnitude 3
• Use minimal WMF settings (50-100 Hz) when detecting slow flow 4
• Higher WMF settings (up to 250 Hz) may be needed to eliminate motion artifacts from vessel walls 3
• The effect of WMF varies with PRF, so these settings must be optimized together 3

Additional Technical Parameters

• Set image depth to 10-20 mm for superficial structures, 30-40 mm for deeper vessels 1
• Position the focus at the level of the target artery or structure 1
• Maintain the angle between sound waves and artery ≤60° 1
• Use tissue harmonic imaging to improve sensitivity and specificity in differentiating blood from tissue 1

Clinical Applications and Advantages

When Power Doppler Excels Over Color Doppler

• Detecting flow in solid components: Power Doppler differentiates true solid components from debris within cysts 1
• Confirming vascular origin: Use the "bridging-vessel sign" to confirm whether an adnexal mass originates from the uterus versus ovary 1
• Assessing indeterminate masses: Power Doppler is essential for evaluating any indeterminate or solid adnexal mass 1
• Slow flow detection: Power Doppler has higher sensitivity for detecting slow flow in small vessels compared to Color Doppler 6, 7
• Better edge definition: Power Doppler provides superior depiction of vessel continuity and vascular detailing 7

Specific Clinical Scenarios

• Adnexal masses: Combine grayscale morphologic assessment with Power Doppler to detect flow within solid areas 1
• 3D Power Doppler: May help reduce false-negative rates in benign indeterminate cystic masses, though not considered standard 1
• Inflammatory conditions: Power Doppler depicts increased flow in dilated vessels due to inflammatory response 7
• Tumor vascularity: Power Doppler improves detection of intratumoral vessels in tortuous and irregular patterns 7

Common Pitfalls and How to Avoid Them

Setting-Related Errors

• Overestimation of blood volume: Power Doppler can overestimate moving blood volume up to 44 times in small vessels due to limited spatial resolution 4
• Inconsistent settings: Maintain identical Doppler settings for any meaningful comparisons within and between subjects 5
• Speed of acquisition: Fast acquisition mode reduces vascular indices, particularly the vascularization flow index 5

Technical Limitations

• Angle independence is relative: While Power Doppler is more angle-independent than Color Doppler, maintaining proper angle alignment still improves signal quality 6
• Background noise: Power Doppler displays background noise differently, which can increase usable dynamic range but requires careful gain adjustment 6
• Flow velocity limitations: At PRF of 0.3 kHz, flow velocities below 2 cm/s may not be registered 4

Interpretation Cautions

• Spectral Doppler parameters (resistive index, pulsatility index) do not significantly improve morphologic assessment - use spectral Doppler primarily to differentiate motion artifacts from true flow 1
• Power Doppler does not alias like Color Doppler, but aliasing can still affect quantification at very low PRF settings (<1.3 kHz) 6, 3
• The presence of "very strong flow" on Power Doppler is one of the IOTA Simple Rules malignant features for adnexal masses 1

Optimization Algorithm

1. Start with B-mode to identify target structure 1
2. Select appropriate transducer based on depth and resolution requirements 1, 2
3. Set PRF based on expected flow velocity (0.3-1.3 kHz for slow flow, 2-4 kHz for arterial flow) 1, 2, 3, 4
4. Adjust gain from low to moderate, avoiding underfilling or overfilling 1, 5
5. Set WMF to minimum initially, increase only if motion artifacts are problematic 3, 4
6. Optimize focus at the level of the target vessel 1
7. Maintain consistent settings throughout the examination for valid comparisons 5