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Image Optimization for Critical Care Ultrasound

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Critical Care Ultrasound Training

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Image Optimization for Critical Care Ultrasound

  1. 1. Image optimization for critical care US <ul><li>Critical Care Ultrasound Course </li></ul><ul><li>SAH & RNSH 2011 </li></ul>
  2. 2. Summary <ul><li>Revision: basic image optimization </li></ul><ul><li>B- mode, M-mode, Doppler </li></ul><ul><li>LUNG </li></ul><ul><li>IVC </li></ul><ul><li>HEART </li></ul>
  3. 3. Revision: basic image optimisation
  4. 4. Revision: basic image optimisation <ul><li>Patient position (supine? left lateral?) </li></ul><ul><li>Lighting (dark) </li></ul><ul><li>Enough gel </li></ul><ul><li>Right probe </li></ul><ul><li>Right orientation </li></ul><ul><li>Right preset </li></ul><ul><li>Right depth </li></ul><ul><li>Overall gain </li></ul><ul><li>Individual TGC/DGC sliders </li></ul>
  5. 5. Revision: basic image optimisation <ul><li>Frequency </li></ul><ul><li>Focal Zones (how deep? how many?) </li></ul><ul><li>Cheat buttons - </li></ul><ul><ul><ul><ul><li>Auto –optimize </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Harmonics </li></ul></ul></ul></ul><ul><li>Change your angle & pressure </li></ul><ul><li>Zoom </li></ul>
  6. 6. Harmonics (THI) <ul><li>As a sound wave travels through tissue, the high pressure bit (compressing tissue) moves faster than the rarefactional component. </li></ul><ul><li>This distorts the wave! and generates higher frequency components ( harmonics ) deep in the tissues. </li></ul><ul><li>eg 3MHz wave creates 6MHz, 12 MHz harmonics </li></ul>
  7. 7. Harmonics (THI) <ul><li>Q: So what? </li></ul><ul><li>A: it turns out that aberrant/artefact signals are too weak to generate harmonic waves. </li></ul><ul><li>THI takes advantage of this: i.e. it displays only the harmonic signals. </li></ul><ul><li>THI images have: </li></ul><ul><ul><ul><li>reduced noise and clutter </li></ul></ul></ul><ul><ul><ul><li>improved spatial resolution (harmonic beams are narrower than the original) </li></ul></ul></ul>
  8. 8. Same Kidney, difficult patient No Harmonics With Harmonics
  9. 9. Top tip: Harmonics (THI) = another great button <ul><li>Don ’t use it for the lung </li></ul><ul><li>For other regions, give it a go </li></ul><ul><li>If it makes the image worse, press again to turn it off </li></ul><ul><li>Best for mid-depth images. </li></ul><ul><ul><li>harmonic generation does not take place near the skin, so THI no use there. </li></ul></ul><ul><ul><li>Also less useful in far field. </li></ul></ul>
  10. 10. M mode
  11. 11. M mode = motion mode <ul><li>Press ‘ M ’ button once & a line appears </li></ul><ul><li>Use touch pad / track ball to move the line to area of interest </li></ul><ul><li>Press ‘ M ’ again to plot a graph of what that line sees versus time </li></ul><ul><li>Stationary stuff = straight line </li></ul><ul><li>Moving things = curved/ dots </li></ul>
  12. 12. M-mode: what ’ s the point? <ul><li>CONS </li></ul><ul><li>If angles wrong, measurements wrong! </li></ul><ul><li>Easier to stuff up than B-mode </li></ul><ul><li>IF IN DOUBT, USE B MODE </li></ul><ul><li>PROS </li></ul><ul><li>M-mode (motion mode) = movement along a single line of info against time </li></ul><ul><li>Single line therefore much better sensitivity & resolution </li></ul><ul><li>More accurate dimensions </li></ul>
  13. 13. M mode: poorly contractile LV
  14. 14. M mode: IVC changing with respiration
  15. 15. Doppler
  16. 16. Doppler effect <ul><li>Probe sends a sound wave of known frequency </li></ul><ul><li>If it hits object moving towards probe, the returning sound wave is higher frequency </li></ul><ul><li>If object moving away, the returning wave is lower frequency </li></ul>
  17. 17. Today: we leave Doppler alone <ul><li>Master the basics first </li></ul><ul><li>Know your limitations </li></ul>
  18. 18. Sreening exam: scanning the lungs
  19. 19. LUNGS: probe & preset <ul><li>PROBE </li></ul><ul><li>Not the linear array (too much fine detail!) </li></ul><ul><ul><li>… False neg PTX (movement) </li></ul></ul><ul><ul><li>… False pos PTX (pain) </li></ul></ul><ul><li>The curved probe is best </li></ul><ul><ul><li>Image quality </li></ul></ul><ul><ul><li>Anatomy </li></ul></ul><ul><li>The phased array probe fits b/w ribs & gets round the back </li></ul><ul><li>PRESET </li></ul><ul><li>One with plenty of greyscale/ dynamic range </li></ul><ul><li>Abdo preset (abdo > FAST) </li></ul><ul><li>NOT cardiac preset </li></ul><ul><li>Turn off the fancy filters: THI, compounding/MB etc- they make the artefacts harder to see! </li></ul>
  20. 20. Depth & alignment <ul><li>DEPTH </li></ul><ul><li>5cm: just for pleura eg sliding </li></ul><ul><li>10cm: to confirm true B lines </li></ul><ul><li>15cm: anatomical relations, diaphragm, effusions </li></ul><ul><li>PROBE ALIGNMENT </li></ul><ul><li>Surprisingly, stay sagittal (perpendicular to ribs) </li></ul><ul><li>Only turn parallel if interrogating structures further eg solid areas </li></ul>
  21. 21. Screening exam: the IVC
  22. 22. Probe & preset <ul><li>PROBE </li></ul><ul><li>C urved probe is best </li></ul><ul><ul><li>Image quality </li></ul></ul><ul><ul><li>Anatomy </li></ul></ul><ul><li>Phased array probe if already on TTE </li></ul><ul><li>PRESET </li></ul><ul><li>Whatever preset you’re on is fine </li></ul>
  23. 23. Screening exam: single view heart Keep it simple Same probe & preset
  24. 24. Trans thoracic echocardiogram (TTE) We ’re not in Kansas any more
  25. 25. B-mode top tips for cardiac scan <ul><li>Roll the patient to the left </li></ul><ul><li>Sector /phased probe </li></ul><ul><li>Cardiac preset (image ‘ round the wrong way ’ ) </li></ul><ul><li>‘ Jerky ’ image (less averaging) </li></ul><ul><li>Dynamic range decreased (more contrast) </li></ul><ul><li>Line density decreased </li></ul><ul><li>Sector width narrowed </li></ul><ul><li>ECG leads can help but we rarely have time! </li></ul><ul><li>What does all this mean? </li></ul>
  26. 26. The bottom line <ul><li>The heart beats very quickly </li></ul><ul><li>We need to capture this movement accurately </li></ul><ul><li>So we maximise ‘ temporal resolution ’ = increased frame rate </li></ul><ul><li>And we turn off averaging = only ‘ true ’ images are seen </li></ul><ul><li>But we sacrifice something to achieve this: mainly spatial resolution </li></ul><ul><li>i.e. the image has less anatomical detail = lower ‘ line density ’ </li></ul><ul><li>And less greyscale /dynamic range (ie it ’ s a more ‘ black & white ’ picture) </li></ul><ul><ul><li>So we need to try certain ‘ tricks ’ to improve our image within these limits e.g: </li></ul></ul><ul><ul><ul><li>- decrease depth </li></ul></ul></ul><ul><ul><ul><li>- zoom the image </li></ul></ul></ul><ul><ul><ul><li>- decrease sector width </li></ul></ul></ul>
  27. 27. Why the jerky image? <ul><li>Image not as smooth </li></ul><ul><li>No averaging = no ‘ fudging ’ </li></ul><ul><li>What you see on screen is really there </li></ul>
  28. 28. What ’ s Line Density? <ul><li>How many lines per frame </li></ul><ul><li>A high line density is desirable for high resolution imaging of small parts (thyroid, breast testes…), </li></ul><ul><li>A lower line density is useful in cardiac applications as it allows significantly higher frame rates. </li></ul><ul><li>Reference: LOGIQ 9 Basic User Manual, Direction 5140804 -100 Rev.3 5-24 </li></ul>
  29. 29. Sector Width (Scan Area) <ul><li>Allows you to widen or narrow the sector angle to maximise the region of interest (ROI), and maximise frame rate. </li></ul><ul><li>You can usually steer the narrowed sector as well, useful for looking in corners! </li></ul><ul><li>Top tip: keep sector as narrow as possible </li></ul>
  30. 30. Summary <ul><li>Critical care echo is where it ’ s at </li></ul><ul><li>TTE i s tricky! </li></ul><ul><li>But screening exam is simple </li></ul>
  31. 31. References <ul><li>Roger Gent: Applied Physics & Technology of Diagnostic Ultrasound </li></ul><ul><li>1997 </li></ul><ul><li>Sam Kaddoura: Echo Made Easy </li></ul><ul><li>Cindy Lucas, senior sonographer Liverpool Hospital </li></ul>

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