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Bioengineering Seminar Schedule
Summer, 2004 (For prior semesters, click here: Fall
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Thursday, June 10, 10:00 a.m. - 12:00 p.m., Room 210 Hallowell
Khaldon Saleh
Final Defense
"Design and Evaluation of Multi-Dimensional Ultrasound Phased Arrays for Thermal Treatment
of Prostate Diseases"
Abstract
The design and construction of multi-dimensional ultrasound phased arrays, to be used for the treatment of prostate
cancer and benign prostatic hyperplasia, present many challenges for design engineers. Many design issues, sometimes
contradicting each other, must be looked at in order to have a reliable design. The resonance frequency has to
be high enough in order to prevent cavitation and have a sharp focus, and low enough in order to be able to generate
a focus and go deep in tissue. A compromise resonance frequency of 1.2 MHz was chosen for the proposed designs.
The array must also have a lot of tiny elements in both directions in order to pin point the target, but at the
same time the elements must be large enough to be possible to manufacture. Electrical matching, acoustical matching
and appropriate cabling, must also be taken into consideration in order to efficiently deliver the required acoustical
energy to the target volume.
In this study, two multi-dimensional ultrasound phased array designs have been considered, a 64-element two-dimensional
and a 63-element 1.75-dimensional phased arrays. One l/4 silver epoxy matching layer
has been used for the first array, and two l/4 matching layers, the first being silver
epoxy and the second was SPURR-4, were used in the second one. The matching layer(s) ensured the delivery of maximum
acoustical power to tissue. Matching circuits and low capacitance coaxial cables have been used in both designs
to ensure delivering maximum electrical power to the arrays. Both designs were constructed, and then tested using
exposimetry and ex vivo bovine experiments.
Thursday, June 17, 9:00 a.m. - 12:00 p.m., Room 210 Hallowell
Jonathan Cannata
Final Defense
"High Frequency (>20 MHz) Ultrasonic Arrays for Medical Imaging Applications"
Abstract
High frequency (>20 MHz) ultrasound is currently used for various imaging applications in ophthalmology,
dermatology, and small animal studies. At present there are several commercial ultrasound systems available for
use in the 25 MHz to 50 MHz frequency range. These systems rely on single element transducers that are mechanically
scanned in a line or arc to form an image slice. Array systems, on the other hand, are desired because they use
electronic scanning to form an image slice. Arrays also lack movable parts the can be patient hazards, can be steered
and dynamically focused in the image plane, and can achieve higher frame rates. Unfortunately at the present time
array systems are not yet available at frequencies above 20 MHz due mainly to fabrication issues, as well as, a
lack of quality high frequency materials and electronics.
This presentation discusses the development of a 64 element 35 MHz ultrasonic array. This array was designed primarily
for ocular imaging applications, and features 2-2 composite elements mechanically diced out of a fine grain high
density Navy Type VI ceramic. Array elements were spaced at a 50 micron pitch, interconnected via a custom flexible
circuit and matched to the 50 Ohm system electronics via a 78 Ohm transmission line coaxial cable. Elevation, or
off axis, focusing was achieved using a cylindrical epoxy lens.
A finite element model was used to study the effects of array element geometry on performance. This model showed
that array element sub-dicing was required to suppress unwanted acoustic cross-talk between elements and improve
the angular response of the array. The final array design was based upon tradeoffs between the ease of fabrication,
level of array encapsulation, and performance.
Several prototype arrays were fabricated and tested, yielding promising results. An average center frequency of
35 MHz was achieved with and average -6 dB bandwidth of 55% and 20 dB pulse length of less than 110 ns. A maximum
combined electrical and acoustical crosstalk between adjacent or next adjacent elements was less than -23 dB. These
results indicate that the 35 MHz array developed is capable of resolving structures in the human body that are
smaller than 0.1 mm.
Tuesday, June 22, 10:00 a.m. - 12:00 p.m., Room 210 Hallowell
Seungjun Lee
Final Defense
"Ultrasound-Mediated Transdermal Insulin Delivery and Glucose Measurement Using the Cymbal
Array"
Abstract
Recent studies have shown that ultrasound mediated transdermal drug delivery offers a promising potential for noninvasive drug administration. The purpose of this study was to demonstrate ultrasonic transdermal delivery of insulin and glucose measurement with a novel, low profile two-by-two ultrasound array based on the cymbal transducer. As a practical device, the cymbal array (f = 20 kHz) was 37 x 37 x 7 mm3 in size and weighed less than 22g. To evaluate the efficacy of the array as a practical insulin delivery and glucose measurement device, one in vitro and three in vivo experiments have been designed for this study. For in vitro experiment, human cadaver skin from skin bank were used while hyperglycemic rats and rabbits were used for in vivo experiments. Human skin was placed in a Franz diffusion cell and exposed to the ultrasound for an hour. The increased concentration of insulin in the receiver chamber of a Franz diffusion cell was measured in a spectrophotometer. The concentration of insulin in the chamber after ultrasound exposure increased 10-fold. For an in vivo test, thirty Sprague Dawley rats were divided in six groups. Each animal was anesthetized with a combination of ketamine and xylazine. The abdominal area of the rats were shave and the array was placed on the surface of the shaved skin. With 5 minutes of ultrasound exposure (Isptp = 100 mW/cm2, 20% duty cycle), blood glucose level decreased 233.3 ± 22.2 mg/dL in 90 minutes compared to the glucose level of untreated control groups. To explore the efficacy of the array in larger animal, sixteen New Zealand White rabbit experiments were performed in three groups: two controls and one ultrasound with insulin exposure. The rabbits were anesthetized and their thigh area was shaved for the exposure area. After one hour of ultrasound and insulin exposure, the glucose level was decrease to -132.6 ± 35.7 mg/dL compared to the levels of glucose of control groups. For noninvasive glucose measurement, nine Sprague Dawley rats were used. The array was placed on the shaved abdominal skin of the rats and the skin was exposed to ultrasound for twenty minutes. The device was removed and the electrochemical glucose sensor was placed on the skin. The glucose level was measured by the electrochemical sensor and compare to the results from a commercial glucose meter. The difference between two results was about 11.9 ± 58.3 mg/dL. These results indicate the feasibility of the cymbal array for ultrasound enhanced transdermal insulin delivery and glucose measurement.
Friday, July 9, 12:00 - 1:00, Room 210 Hallowell
David Gough
University of California
"Bioengineering of the Implantable Glucose Sensor"
Abstract
The development of an implantable glucose sensor and automated insulin delivery system that would enable people with diabetes to better manage blood glucose has long been an important bioengineering objective. After considerable effort, sensors have been developed that are now being tested in human clinical trials, and the possibility of practical automatic control of blood glucose is in sight. Nevertheless, there are still many important issues to be addressed related to the sensors themselves, the control system, and the physiology of metabolic regulation.
For additional information, contact Ms. Doretta Garvey, Dept of Bioengineering, Tel: 814.865.1407
or E-Mail: bioe@psu.edu