Welcome to Day 26!
We’re now deep into the world of Doppler artifacts, and today we shift focus to Color Doppler imaging. Understanding these artifacts helps you interpret vascular and cardiac studies accurately — and score big on the SPI exam.
Let’s break down four key Color Doppler artifacts: Aliasing, Color Bleeding (Color Extending), Flash Artifact, and Color Noise.
🌈 1. Color Doppler Aliasing
Definition:
A color distortion caused when the Doppler shift exceeds the Nyquist limit, similar to PW Doppler aliasing.
Appearance:
- Abrupt color reversal across a vessel.
- Instead of smooth color gradation, you see wrap-around colors (e.g., red suddenly turning to blue).
Cause:
- High-velocity flow or low PRF setting.
✅ To reduce:
- Increase PRF (scale)
- Lower transducer frequency
- Decrease depth
- Shift color baseline
SPI Tip:
Aliasing in color Doppler shows a mosaic pattern — frequently tested in flow evaluation of stenosis.
💧 2. Color Bleeding (Color Extending)
Definition:
An artifact where color appears outside the vessel lumen or beyond the true area of flow.
Appearance:
The vessel seems to “bleed” color into surrounding tissues.
Cause:
- Excessive color gain
- Low wall filters
- Poor lateral resolution
SPI Tip:
Turn down the color gain just until color disappears, then increase slightly to find the optimal level.
⚡ 3. Flash Artifact (Motion Artifact)
Definition:
A burst of random color flow unrelated to actual blood movement.
Cause:
- Tissue motion
- Probe movement
- Breathing or pulsation of nearby organs
Appearance:
- Flickering colors over stationary structures
- Transient and non-anatomical
Example:
- Color appearing in the liver when the probe moves
- Flashing color in the bowel wall
✅ Solution:
- Stabilize the probe
- Increase wall filter
- Use motion suppression techniques
🌀 4. Color Noise (Speckle or Clutter)
Definition:
Random, weak color signals in areas where no flow is expected.
Cause:
- Excessive sensitivity or gain
- Electrical or machine noise
Appearance:
- Patchy, nonvascular color specks
- Occurs outside vessels or in anechoic spaces
✅ To reduce:
- Decrease color gain
- Use appropriate filtering
- Reposition transducer
🧠 Quick Summary Table
| Artifact | Appearance | Cause | Prevention Tip |
| Aliasing | Color wraps or reverses | High Doppler shift > Nyquist | Increase PRF, shift baseline |
| Color Bleeding | Color beyond vessel borders | High gain, poor resolution | Reduce color gain |
| Flash Artifact | Flickering unrelated to flow | Probe/tissue motion | Stabilize probe, increase wall filter |
| Color Noise | Random color speckles | Overgain, machine noise | Reduce gain, filter noise |
📘 SPI Exam Reminders
✅ Know Nyquist limit and how aliasing looks in color Doppler
✅ Flash and clutter artifacts result from motion or overgain
✅ Always optimize gain and PRF to avoid misinterpretation
✅ Expect diagram-based questions on aliasing and color bleeding
📝 Flashcard
Q: Which color Doppler artifact appears as speckled color outside vessels due to excessive gain?
A: Color Noise (Clutter)
🧭 Conclusion
Color Doppler artifacts can either enhance or hinder your ability to assess flow. Recognizing them is a critical skill for passing the SPI and practicing accurate sonography.