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Real-Time Visualization of Clot-Dissolution Using Doppler Ultrasound

Real-Time Visualization of Clot-Dissolution Using Doppler Ultrasound. Group 38: Taylor Tso , Vera Xiao and Debra Yen. Outline. Background Design Specifications Headset Probe Holder Head-Mount Imaging Probe Detection Algorithm Design Schedule Team Responsibilities. Background.

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Real-Time Visualization of Clot-Dissolution Using Doppler Ultrasound

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  1. Real-Time Visualization of Clot-Dissolution Using Doppler Ultrasound Group 38: Taylor Tso, Vera Xiao and Debra Yen

  2. Outline • Background • Design Specifications • Headset • Probe Holder • Head-Mount • Imaging Probe • Detection Algorithm • Design Schedule • Team Responsibilities

  3. Background • Client: Michael Sabo, Senior Director of R&D • Pulse Therapeutics, Inc. • Magnetite-Enhanced Diffusion Therapy for ischemic stroke • External magnetic field applied across the head • Sub-micron magnetite particles co-infused into bloodstream with thrombolytic (tPA) • Therapy targeted for use in Emergency Department

  4. Customer Needs • Imaging modality must be unaffected by weak magnetic fields • Must be used in the ER (portable, small, non-invasive, <30 sec start-up time) • Real-time visualization of lysis • Monitor and ensure successful lysis of clot • If therapy is failing, begin preparing for other clot interventions

  5. Headset Design

  6. Headset Design Specifications General: • cost: < $ 500 • weight : <200g • reusable • one person can attach to patient • no interference with the magnet therapy • no magnetic interference • no physical blockage of magnet access Probe Holding Mechanism: • adjustable probe insertion angle • fix probe at one location and angle for at least 90 minutes • allow operator to reapply gel on the tip of transducer • minimum interference on patient’s head • can easily attach and detach the probe within 2 minutes Head Fixture Mechanism: • have to be stable on patient’s head for 90 minutes with the weight of itself and probe • put on/remove from patient within 5 minutes • adjustable location for probe insertion • adjustable for different patient head size • no restriction on blood circulation on patient’s head

  7. Probe Holder Design Possibilities

  8. Track and Bar • Fast setup time ~2 min. • Fixed with three sets of screws or forked stop at desired location • Limited to cylindrical coordinates • Track friction US Patent: 409005

  9. Clap Holder • Limited to cylindrical coordinates • Fast set up time ~2 min. • Easy to operate (simple mechanics) • Long lasting • Arm sticks out, limiting patient movement during therapy RIMED

  10. Ball and Socket • 70° full range of motion (spherical coordinates) • Easily adjustable (only one stop) • Easy to setup ~2 min. • Medical grade plastic • Need a locking mechanism for intended angle of insonation http://lehmansbaseball.files.wordpress.com/2011/01/060710_joints_socket_02.jpg

  11. Adhesive-Collodion • Medical grade adhesive (used on ECG probes) • Strong normal stress, low shear stress • No adjustment after initial placement http://www.hellotrade.com/mavidon/product.html

  12. Probe Fixture PUGH Analysis • Ball and Socket provides best stability, ease of installation/removal and angle adjustability

  13. Head-Fixture Design Possibilities

  14. Elastic or Plastic Strap • Non-metal • More straps are heavier, but provide more stability • Solid • Have to use one band (bulky) • Would cover patient’s eye’s • Elastic • Needs at least two bands • Could be too tight • Light • Thin

  15. Open Helmet • Elastic material to accommodate various head sizes • Two holes over temporal window allow for probe placement • Easy set up • Circumferential Pressure

  16. Adhesive • A recommended location for maximum adhesion is over zygoma, squamous portion of the temporal bone (US Patent: 5070880). • Strong normal force, low shear force • Collodion

  17. Head-Fixture PUGH Analysis • We chose to incorporate the two highest scoring elements to account for decreased stability. • The adhesive and elastic strap are compatible.

  18. Final Headset Design • Probe Fixture: ball and Socket Mechanism • Head Fixture: adhesive and 3 straps

  19. Final Headset Design Ball and Socket: • Spherical coordinates angle of rotation to provide wider range of motion • One knot knockdown mechanism to simplify operation and minimize disturbance on probe positioning

  20. Probe Design

  21. Probe Design Specifications • Frequency: 2-4MHz • Resolution: 1 mm axial x 1 mm lateral • Scan Range: 30-80 mm • Field of View: 70-90 degrees • Diameter of transducer face = approximate diameter of temporal window • Weight: 20 grams • Cost: $5000

  22. Single-element Transducer • Crystal with “coated” electrodes on each side • Backing material • Matching layer • Acoustic lens • Electrically insulated casing

  23. Types of Real-Time Ultrasound Probes • Mechanical Sector • Linear Array • Phased Array • Matrix-phased (2D) Array

  24. Mechanical Sector • Crystals attached to stepping motor and move in an arc • Advantages • Physically small, can fit in tight areas • Low cost • Line density easily adjusted with speed of rotation of crystal • Disadvantages • Small size limits the field of view • Fixed focal length restricts lateral resolution to limited range of depths • Scan line density decreases with increasing distance from transducer face • Limited lifetime from mechanical wear

  25. Linear Array • Multiple rectangular crystals place in a row • Crystals are activated in sequential fashion in groups • Advantages • Can vary depth of focal zone • High spatial resolution • High frame rate (temporal resolution) • High line density • Can use electronic focusing techniques • Disadvantages • Flat transducer face -> difficulty maintaining transducer-patient contact • Field of view determined by physical length of array • Number of elements in array limits maximum number of scan lines • Radiating surface if transducer is large, prevents access to structures through narrow acoustic window

  26. Phased Array • All crystals are excited simultaneously • Electronic steering of beam provides different lines of sight • Alter timing of sequence of excitation pulses to angle the direction of transmitted beam • Advantages • Same as linear array (variable focal lengths, high resolution, high line density) • Field of view not limited to physical length of array (sector angle) • Electronic steering and focusing enhanced with delay times • Small size enables access through acoustic windows • Disadvantages • Lateral resolution deteriorates with large-angle beam steering

  27. Matrix-phased (2D) Array • Crystal elements in multiple rows forming rectangular plane • Advantages • Allow electronic steering in three directions without moving the transducer • Disadvantages • Has 2000-9000 elements • Very high cost • Transducer heating

  28. Probe Type PUGH Analysis • We chose the phased array because of its ability to produce high quality images, small physical size, and electronic focusing capabilities

  29. Phased Array Probe Design

  30. Algorithm Design

  31. Algorithm Design Specifications Detect Clot-Dissolution: • Alert user at beginning of clot-dissolution • Specificity: 80% • Selectivity: 80% • Alert user when flow returns to normal • Specificity: 80% • Selectivity: 80%

  32. Need for a “Return to Normal” • “Recovery did not occur if MV was less than 20 cm/sec or less than 50% of the unaffected side. With MV [mean velocity] between 20 and 40 cm/sec (50%-80% of unaffected side) the probability of recovery was about 25%, and above 40 cm/sec (about 80% of unaffected side), the probability of recovery was about 75%. Predictability based on absolute velocity was not much different the first 12 hr than on the second day. However, there were no recoveries if the velocity was less than 80% of the unaffected side after 12 hr.” –Halsey, J. and Tan, M. “Evaluation of Acute Stroke.”

  33. Mean Velocity vs. %Mean Velocity • Halsey, J and Tan, M. “Evaluation of Acute Stroke.” Transcranial Doppler. Raven Press NY, 1992. • MV% difference between recovered and nonrecovered strokes (see B) was significant (p=0.028), while the MV difference (See A) was marginal (p=0.068)

  34. Interpreting TCD data • Burgin, W. et al. “Transcranial Doppler Ultrasound Criteria for Recanalization After Thrombolysis for Middle Cerebral Artery Stroke.” Stroke. 2000;21:1128-1132. January 31, 2000. • Experiment with n=25, specificity=91% and selectivity=93% to detect complete recanalization

  35. Algorithm Parameter PUGH Analysis • All parameters can be incorporated into verification of algorithm results. • Measurement of ACA and PCA MFVs require readjustment of probe.

  36. Algorithm Flow-Chart

  37. Team Responsibilities • One Person in Charge of one component, other two assist - Debra: Transducer - Vera: Headset - Taylor: algorithms/software

  38. Questions ?

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