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S7 EA
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introduction
Blood vessel localization and ablation
Highly potent therapeutic method for tumors
Employed to stop blood flow
Used in small arteries and target veins
Require two systems
1)imaging system -localizing blood vessels
2)therapeutic system-ablation treatment Synchronization between imaging and ablation
devices
Use single transducer
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hifu transducer
Focus range-55mm
Operating range-1.6 to 2.4MHz
Focus is in oval shape
Medium for acoustic wave conduction
Two modes of operation
1)Therapeutic mode
2)Imaging mode
Two tests
1)In vitro
2)In vivo
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Experimental setup
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Timing diagram
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In vitro test Test targeting ability
Performed on acryl amide phantoms
Acrylic tank
Albumin mixed into acryl amidephantoms
Water bath-acryl amide phantom
Degassed water preparation
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In vivo test
Test targeting and occluding ability
Performed by capping-
the HIFU transducer
Transducer mounted
on a stepper motor
Experimental setup for >
In vivo tests
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Imaging mode
Acoustic wave generation
Focus pressure estimation
Backscattered signal mixing with noise
Diplexer ,Digital oscilloscope ,A/D card
Customized lab view procedure
Doppler signal calculation
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Therapeutic mode Generate strong acoustic waves
Intensity averaged over space andtime
Acoustic power estimation
Operation mode switched back toimaging mode
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how useful the Doppler signal??
Determine target vessel
location in real time
HIFU transducer scanned the
vessel
Track centre of femoral artery
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Ultrasonic signal processing
Obtains Doppler frequency shift
Data for Doppler signals
Demodulated complex echo signal-nth firing
Doppler spectrum calculation
Doppler spectrum mean velocity
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Results for flow detection
a)Raw RF signals after firing 300 times with PRF 5KHzb)Doppler shifts-tube(diameter-2.9mm,flow rate-150ml/min)c)Comparison detected Doppler frequency &values from actual f low volume
for two pumping rates 150&75mL/min
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Doppler shifts peak amplitude & sum
Peak amplitude Doppler shift
Sum of Doppler shift
Change HIFU transducer focus
Velocity change
a)peak amplitude of Doppler shiftb)sum of Doppler shift
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Ablation in rabbit and rat
a &e:-pre-ablation setup and evaluationb &f:-Doppler signal before ablation(2-D ultrasound)c &g:-Doppler shifts with the HIFU transducer in the imaging mode
d &h:-Doppler signals were absent after ablation (2-D ultrasound)
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advantages
Single transducer for localization and ablation
Less complicated and cheaper
Smaller therapeutic window-easier to operate
Easier to tilt and focus on tissues behind ribs
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disadvantages
Cant provide 2-D ultrasound image
Setting range gate-Doppler signal calculation
Trade-off between good imaging quality and highablation efficiency
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conclusion
New system utilizes single HIFU transducer
In vivo and In vitro tests performed
Switching between imaging and therapeutic mode
Transducer movement-scanning target area
New system include function-stop blood flow
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reference
www.ieeexplore.com (IEEE transactions onUltrasonic ,Ferroelectrics and frequency
control)
www.seminarpaper.com
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