Real-Time Visualization of Clot-Dissolution Using Doppler

UltrasoundGroup 38: Taylor Tso, Vera Xiao and

Debra Yen

OutlineI. Background

II. Design Specifications1. Headset

a) Probe Holder

b) Head-Mount

2. Imaging Probe

3. Detection Algorithm

III. Design Schedule

IV. Team Responsibilities

Background

• Client: Michael Sabo, Senior Director of R&Do Pulse Therapeutics, Inc.

• Magnetite-Enhanced Diffusion Therapy for ischemic strokeo External magnetic field applied across the heado Sub-micron magnetite particles co-infused into bloodstream with thrombolytic (tPA)o Therapy targeted for use in Emergency Department

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

Headset Design

Headset Design Specifications

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

General:• cost: < $ 500• weight : <200g• reusable• one person can attach to patient• no interference with the magnet therapy

o no magnetic interferenceo 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

Probe Holder Design Possibilities

• Fast setup time ~2 min.• Fixed with three sets of

screws or forked stop at desired location

• Limited to cylindrical coordinates

• Track friction

Track and Bar

US Patent: 409005

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

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

Adhesive-Collodion

http://www.hellotrade.com/mavidon/product.html

• Medical grade adhesive (used on ECG probes)

• Strong normal stress, low shear stress

• No adjustment after initial placement

Probe Fixture PUGH Analysis

• Ball and Socket provides best stability, ease of installation/removal and angle adjustability

Head-Fixture Design Possibilities

Elastic or Plastic Strap• Non-metal• More straps are heavier, but

provide more stability• Solid

o Have to use one band (bulky)o Would cover patient’s eye’s

• Elastico Needs at least two bandso Could be too tighto Lighto Thin

Open Helmet

• Elastic material to accommodate various head sizes

• Two holes over temporal window allow for probe placement

• Easy set up• Circumferential Pressure

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

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.

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

Final Headset DesignBall 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

Probe Design

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

Single-element Transducer

• Crystal with “coated” electrodes on each side

• Backing material• Matching layer• Acoustic lens• Electrically insulated

casing

Types of Real-Time Ultrasound Probes

• Mechanical Sector• Linear Array• Phased Array• Matrix-phased (2D) Array

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

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

Phased Array• All crystals are excited

simultaneously• Electronic steering of beam

provides different lines of sighto 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

Matrix-phased (2D) Array

• Crystal elements in multiple rows forming rectangular plane

• Advantageso Allow electronic steering in three directions

without moving the transducer

• Disadvantageso Has 2000-9000 elementso Very high costo Transducer heating

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

Probe Resolution Field of ViewElectronic Focusing

Beam Divergence

Mechanical Wear

Mechanical Adjustments Physical Size Cost Total

Mechanical Sector 4 3 2 5 2 5 7 10 38Linear Array 7 5 7 9 9 5 5 6 53Phased Array 9 8 10 7 9 10 9 6 68Matrix-Phased (2D) Array 9 8 10 7 5 9 4 2 54

Phased Array Probe Design

Algorithm Design

Algorithm Design Specifications

Detect Clot-Dissolution:• Alert user at beginning of clot-dissolution

o Specificity: 80%o Selectivity: 80%

• Alert user when flow returns to normalo Specificity: 80%o Selectivity: 80%

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.”

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)

• 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

Interpreting TCD data

Algorithm Parameter PUGH Analysis

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

Algorithm Flow-Chart

Project Schedule September October # # # # # # # # # # # # # # # # # # # # 1 2 3 4 5 6 7 8 9 # # # # # # # # # # # # # # # # # # # # # #

Project Selection

Project Scope

Customer Needs gathering

Scope ✪

Preliminary Report

Literature/Prior Art Research

Oral Report ✪

Writen Report ✪

Progress Report

Transducer/Probe Search & Select ★

Fixture Assembly Design Concept ★

Alogrithm Concept Generation ★

Oral Report ✪

Writen Report ✪

Web Page

Web Page Initial Development ✪

Web Page Development

Lab Notebook

Check 1 ✪

Check 2

Weekly Report ✪ ✪ ✪ ✪ ✪ ✪ ✪

Project Schedule November December 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11

Final Report

Fixture Asembly Design

Alogrithm Development

Alogrithm Test with Data

Design Specification Evaluation

Oral Report ✪

Writen Report ✪

Design Safety Report ✪

Web Page

Web Page Initial Development

Web Page Development ✪

Poster ✪

Lab Notebook

Check 1

Check 2 ✪

Weekly Report ✪ ✪ ✪  

Team Responsibilities

• One Person in Charge of one component, other two assist

- Debra: Transducer- Vera: Headset- Taylor: algorithms/software

Questions ?