Gin-Shin Chen

High intensity focused ultrasound, HIFU has been used to non-invasively treat human tumors, such as uterine fibroids, prostate cancer, breast cancer, liver tumor, and brain tumor. However, the tumor in some organs can be moved by human breathing and heart beat, which may cause the ablation and damage of normal tissues during the sonication of HIFU. The purpose of this study was to develop a HIFU phased array for tracking the moving tumors. In the initial design, the array had a center frequency of 1.0 MHz and 512 elements that allowed symmetric control. PZT-4 1-3 composites were formed via the ldquodice and fillrdquo technology and then shaped into a cylindrical structure. The results simulated by Field II demonstrated that the array in water had a dynamic focusing range from 145 mm to 175 mm in Depth and a steering range from -15 mm to 15 mm in azimuthal direction with respect to the center of the array. A prototype of the array was fabricated. The aperture of the array was 15 cm by 12 cm and the radius of curvature was 15 cm. The impedance of each channel (a pair of elements) was measured and the average was 1500 Ohm. Surface acoustic intensity up to 12.6 W/cm2 was applied to one piece of cylindrical PZT4-composite consisting of 22 elements for 50 minutes, and the temperature of the composite was not observed to rise appreciably. A 256-channel amplifier was utilized to drive the array without impedance matching in water and the water spring was observed at the natural focus of the array when the driving signal to each channel was zero-phase at 0.9 MHz. The phase control and impedance matching circuits for each channel are being designed.

In HIFU treatment applications, the annular array transducer is a feasible solution for the clinical/engineering requirements which are as follows: ablation of tumors deep inside body, electronic dynamic focusing in the depth direction, simple configuration/operation, and lower cost due to fewer elements/channels of amplifier. A 12 cm-diameter, 12 cm-radius-of-curvature annular array transducer has been developed in this study. The pseudo-inverse method was adopted to calculate the desired phase of each element for focusing, and the Rayleigh-Summerfield integral was used to obtain the ultrasonic pressure field. In the simulation, the operating frequency was 0.9 MHz, and the acoustic medium was water. A piece of 1-3 piezocomposite was fabricated using the dice and fill technique for the pilot test. The dimension of the sample was 4×2 cm, and it was thermally shaped using a spherical mold of 12 cm in radius. The results of the simulation showed that the focus could not be moved electronically in the depth direction until the number of elements (annuli) was equal to or higher than 5, and the dynamic focusing range increased as the number of elements increased. The intensity at the acoustic window or skin was also estimated from the simulated results and was only 0.03% of the intensity at focus. The curved composite sample was tested using an impedance analyser and a radiation force balance. The resonant frequency and electro-acoustic efficiency were measured to be 0.914 MHz and 65%, respectively. The results of the simulation can provide a design guideline for the development of different-size HIFU annular array transducers. A prototype of the HIFU annular array transducer designed is being fabricated in-house.

A dual-curvature focused ultrasound phased-array transducer with a symmetric control has been developed for noninvasive ablative treatment of tumors. The 1.5-D array was constructed in-house and the electro-acoustic conversion efficiency was measured to be approximately 65%. In vitro experiments demonstrated that the array uses 256 independent elements to achieve 2-D wide-range high-intensity electronic focusing.

A novel active surface Laplacian electroencephalogram (LEEG) sensor for the real-time mu rhythms detection has been developed in our study. Analog LEEG signals with high signal to noise ratio obtained directly by using the active sensor can reduce the duration and quantum error of digital signal processing and computation for the quick and precise control of brain-computer interface (BCI) systems. The portable active surface LEEG sensor comprises five gold electrodes integrated to a cross-shaped structure and a battery-powered, low-noise amplifier with the following specification: gain of 10,000, band-pass filtering from 2.5 Hz to 55 Hz, input impedance of 10 GΩ, common mode rejection ratio (CMRR) of 110 dB. The clinical experiments showed that the amplitude suppression of mu waves detected directly by active surface LEEG sensors was obvious as the normal subject was asked to imagine grasping something with his right hand. Furthermore, the distribution of mu waves captured real time in the un-shielded room by active surface LEEG sensor was similar to that acquired in the shielded room of hospital through EEG data collection by an EEG instrument, and then offline analyses. Real-time mu rhythms obtained by the active surface LEEG sensor will be utilized to control a device or system via the BCI in real time.

Flexible polymer heart valves are promising clinical prostheses for replacement of diseased or malfunctioned natural heart valves. However, the flexible polymer leaflets are prone to fatigue fracture, which hinders their practicality in clinical applications. In this study, microstrain sensor (gauge) for strain measurement is designed in the polyurethane (PU) thin film to measure the stress/strain in situ. In our design, the strain gauge is embedded in PU, which is different than the commercial strain gauge of sticking to the sample. The metal layer of strain gauge used in this study is gold. The overall size of the designed strain gauge is 1 mm × 1 mm × 0.1 µm, and the resistance value was measured to be 200 ±30Ω. The static test of strain gauge without damp proof shows that gauge sensitivity G was measured to be 4 and 1.8, when strain range is less than 1% and between 1–1.5%, respectively, while the static test of strain gauge with damp proof shows that gauge sensitivity G was measured to be 2.6 when strain range is less than 1.2%. The dynamic test of strain gauge was also applied in this study.

A concept regarding DNA fragments electrophoretic analyses by directly detecting electrical charges is proposed. The arrival time and voltage of charged DNA fragments with different charge-to-mass ratio could be detected using the custom-made micro electronic circuits. These time and voltage information imply the size and intensity information acquired from the conventional slab gel image by fluorescent labeling. A prototype of the portable electrophoresis device consists of a flow channel with the dimension of 35 mm (length) × 0.5 mm (width) × 0.2 mm (depth) on an acrylic substrate, and the detection circuit with amplification gain of 10,000 and analogous filter bandwidth between 0.1 Hz and 10 Hz has been developed. A simple experiment was carried out to demonstrate the feasibility of proposed idea. The volume of 2μl of the DNA ladder (1 Kb Plus DNA ladder, Invitrogen, U.S.A.) with the diluted concentration of 0.1μg/μl was loaded into the reservoir when applying the electrical field of 12.5 V/cm to both end of the flow channel, which was only filled with TBE solution. The preliminary results showed that the developed electrophoresis device can pick up the electrical signals of un-separated DNA fragments with total mass of 0.2 μg , and the magnitude is 0.6 V . Micro flow channels fabricated by an excimer-laser machine and low-noise amplifier with high gain, e.g. 100,000 are being processed. Moreover, HEC (hydroxyethylcellulose) solution will be utilized as the media in the micro channels for DNA fragments separation.