Control System for ImageGuided Treatment of Uterine Fibroids using Phased Array High Intensity Focus

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Control System for Image-Guided Treatment of
Uterine Fibroids using
Phased Array High Intensity Focused Ultrasound
By 1,2Robert T. Held and 1,2Shahram Vaezy, Ph.D.
1 Department of Bioengineering, University of
Washington, Seattle, WA 2 Center for Industrial
and Medical Ultrasound, Applied Physics
Laboratory, University of Washington, Seattle, WA
How Does the Phased Array HIFU Transducer Work?
The 3 MHz transducer built by Imasonic (Lyons,
France) employs an annular array of 11 elements
Hardware
In a phased-array transducer, high-frequency
sine waves excite multiple piezoceramic elements
(11 here). Electronic stimulation makes the
elements vibrate, thereby producing mechanical
waves. If a specific phase delay is assigned to
each elements driving signal, then the point
where the waves constructively interfere may be
changed. The Imasonic transducers focal length
may be set to any distance between 30 and 60 mm.
Its natural focal length is 50 mm.
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What is HIFU? High Intensity Focused
Ultrasound (HIFU) stands as a viable,
non-invasive alternative to surgery. When a
HIFU
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The absence of phase delays produces a focal
point at the center of curvature of the
transducer. (Note that all 11 channels are not
represented below)
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treatment is applied, ultrasound waves are
focused at a 1-by-10 mm region (approximately the
size of a grain of rice), which experiences a
70C temperature increase in less than one
second.
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By changing the phase delays, one may
electronically alter the transducers focal
length.
A Dell Latitude laptop (1) controls the Advanced
Surgical Systems Phased Array Driving System (2),
which powers the Imasonic HIFU transducer (11
elements, 3 MHz) (3). The HIFU transducer is
mechanically coupled to a Philips C9-5 ultrasound
imaging probe(4). A Philips HDI-3000 ultrasound
imaging units video output is simultaneously
captured and conditioned by the laptop to remove
any noise introduced by HIFU waves.
Uterine Fibroids Uterine fibroids occur in
approximately 25 of women over the age of 351.
Uterine fibroids are benign tumors that vary in
diameter from 1-20 cm and can cause excessive
bleeding and discomfort. If they cause pain or
grow rapidly, a woman may need a hysterectomy to
completely remove the uterus, which is not a
desirable option.
Testing/Future Work
Tissue-mimicking gel phantoms3, turkey
breast, and beef samples were treated in a
water tank to test HIFU lesion formation. Total
power levels of 110 and 165 W were used at focal
depths ranging from 30 to 60 mm, spaced 5 mm
apart. Exposure times varied between 10 and 20
seconds per focal depth. Gel Phantoms
Noise Reduction Algorithm When HIFU is applied,
it creates noise on the ultrasound image. In
order to maintain clear visualization, a duty
cycle is applied to the HIFU signal. The result
is a band of interference that sweeps across the
ultrasound image. The software monitors the
position of the band and, once it has swept
across the entire screen, crops and combines
several frames to create one, interference-free
image that is displayed on the screen.
Gel lesion images (A) 110W, focal depth moved
from 60 to 30mm. (B) Same as A, but with 165 W.
(C) 110W, focal depth moved from 30 to 60mm. (D)
Same as C, but with 165W.
User-friendly software can optimize the
application of ultrasound image-guided HIFU for
the treatment of uterine fibroids. Why use
HIFU? HIFU has been proposed as a viable means
for destroying uterine fibroids without
hysterectomy. Our lab previously demonstrated
that HIFU effectively treated uterine fibroids in
nude mice2. In that study, a 90 reduction in
fibroids was noted after three months. This led
to the development of an ultrasound image-guided
device designed for treating fibroids.
Previously, the only methods for determining the
HIFU focal point on an ultrasound image were to
visually assess the distance or actually apply
treatment. A targeting system provides an
accurate visualization of the focal location
prior to treatment.
The trials that progressed from 60 to 30 mm
produced lesions that were at least 60 longer
and at least 15 thinner than those that
progressed from 30 to 60 mm. As reported by Chen
et al., previously-formed lesions raised the
attenuation of the treatment area, facilitating
subsequent HIFU energy absorption and lesion
formation3. This was apparent when no initial
lesions could be formed at 30 mm, unless the 35
mm distance had already been treated. Turkey and
Beef Samples
Several raw video frames are assembled into one
clear image
Interface used to monitor and control HIFU
treatment
Tissue lesion images turkey breast (A through D)
and beef (E through H). Scale bars represent 1
cm. The HIFU transducer was located to the left
of each lesion as they are displayed here. Each
tissue lesion was created using 165W of power and
formed from 60mm back to 30mm.
HIFU Control System The computer communicates
with the ultrasound driving system via RS-232
connection, thereby alleviating the user from
manually entering commands to designate power and
phase values. The user sets the power and
duration values and then indicates the desired
HIFU focal points by typing them in or clicking
directly on the ultrasound image. The program
then calculates each channels phase values for
those focal lengths. After Start Treatment is
pressed, the driving systems channels deliver
power to the HIFU transducer.
Thermal lesions were produced in the first ex
vivo tests. Further work will include the
quantitative assessment of lesions formed with
vary- ing power levels at different focal
locations. Analysis of the re- sulting
lesion volumes will facilitate treatment
planning.
Acknowledgements
Terry
Myntti, Jennifer Flexman, Blake Miller, Tim
Soper, and Vesna Zderic
1. Stewart, E. A., Lancet, 2001. 357(9252) p.
293-8. 2. Vaezy, S., Fujimoto, V. Y., Walker, C.,
Martin, R. W., Chi, E. Y., Crum, L. A., Am J
Obstet Gynecol, 2000. 183(1) pp. 6-11. 3.
Lafon, C., Kaczkowski, P., Vaezy, S., Noble, M.,
Martin, R., Crum, L., International Congress on
Acoustics, Rome, Italy, 2001. 4. Chen, L., G.
ter Haar, and C.R. Hill, Ultrasound Med Biol,
1997. 23(6) pp. 921-31.