Development of a 3 French Dual-Frequency Intravascular Ultrasound Catheter.

Coronary plaque morphology, including plaque size and fibrous cap thickness, is thought to contribute to the risk of plaque rupture and future cardiac events. Dual-frequency intravascular ultrasound has been proposed as a possible technique to visualize both large-scale features and superficial detail of coronary plaque; however, it has not been found to be feasible within the constraints of a clinically functional intravascular ultrasound catheter. In this study, we describe the design and fabrication of a dual-frequency catheter using a bidirectional transducer stack with center frequencies of approximately 30 and 80 MHz. We describe how the high-frequency transducer achieves significantly improved axial and lateral resolution (16 and 120 µm, respectively, vs. 50 and 220 µm) at the expense of penetration depth. Finally, imaging of ex vivo human coronary artery segments reveals that the catheter can provide complementary images of the deeper arterial wall and superficial plaque features.

Symmetric miniaturized heating system for active microelectronic devices.

To qualify interconnect technologies such as microelectronic fine wire bonds for mass production of integrated circuit (IC) packages, it is necessary to perform accelerated aging tests, e.g., to age a device at an elevated temperature or to subject the device to thermal cycling and measure the decrease of interconnect quality. There are downsides to using conventional ovens for this as they are relatively large and have relatively slow temperature change rates, and if electrical connections are required between monitoring equipment and the device being heated, they must be located inside the oven and may be aged by the high temperatures. Addressing these downsides, a miniaturized heating system (minioven) is presented, which can heat individual IC packages containing the interconnects to be tested. The core of this system is a piece of copper cut from a square shaped tube with high resistance heating wire looped around it. Ceramic dual in-line packages are clamped against either open end of the core. One package contains a Pt100 temperature sensor and the other package contains the device to be aged placed in symmetry to the temperature sensor. According to the temperature detected by the Pt100, a proportional-integral-derivative controller adjusts the power supplied to the heating wire. The system maintains a dynamic temperature balance with the core hot and the two symmetric sides with electrical connections to the device under test at a cooler temperature. Only the face of the package containing the device is heated, while the socket holding it remains below 75 degrees C when the oven operates at 200 degrees C. The minioven can heat packages from room temperature up to 200 degrees C in less than 5 min and maintain this temperature at 28 W power. During long term aging, a temperature of 200 degrees C was maintained for 1120 h with negligible resistance change of the heating wires after 900 h (heating wire resistance increased 0.2% over the final 220 h). The device is also subjected to 5700 thermal cycles between 55 and 195 degrees C, demonstrating reliability under thermal cycling.