3D Imaging Using 2D CMUT Arrays with Integrated Electronics
Our first 3D imaging results were reported in [1]. These results were obtained using a 2D CMUT array flip-chip bonded to a fan-out die used along with the PC-based data acquisition system designed for 1D CMUT arrays.
Real-time catheter-based ultrasound imaging tools are needed for diagnosis and image-guided procedures. The continued development of these tools is partially limited by the difficulty of fabricating two-dimensional array geometries of piezoelectric transducers. Using capacitive micromachined ultrasonic transducer (CMUT) technology, transducer arrays with widely varying geometries, high frequencies, and wide bandwidths can be fabricated.
Recently, we developed a volumetric ultrasound imaging system based on a 2D, 16x16-element, CMUT array for use in endoscopic applications (Fig. 1). Transducer arrays with operating frequencies ranging from 3 MHz to 7.5 MHz were fabricated for this system. The transducer array including DC bias pads measures 4 mm by 4.7 mm. The array pitch is 250 µm. The array is flip-chip bonded to a custom designed integrated circuit (IC) that comprises the front-end electronics (Fig. 2). Integrating the front-end electronics with the transducer array reduces the effects of cable capacitance on the transducer’s performance and provides a compact means of connecting to the transducer elements. The front-end IC provides a 27-V pulser and 10-MHz bandwidth amplifier for each element of the array. An FPGA-based data acquisition system is used for control and data acquisition. An output pressure of 230 kPa and a minimum detectable pressure of 1 mPa/√Hz were measured for the integrated prototype. Using this system, we obtained volumetric images of a wire phantom and a vessel phantom. Images of a wire phantom obtained with the described array are shown in Fig. 3. Although all elements have their dedicated pulsers and amplifiers, only a single element is selected at a time to simplify the initial implementation of the IC. Thus, classic synthetic aperture image reconstruction is used. For a 3-cm penetration depth, 10 ms is needed to acquire a single frame with no averaging. The images shown in Fig. 3 were obtained by averaging 16 acquisitions. Images of liquid filled polyethylene tubes in a tissue mimicking material are shown in Fig. 4. The presented volumetric ultrasound images were acquired in real-time using a fully-populated two-dimensional transducer array with integrated electronics. The system described here meets the challenges of catheter-based imaging. This prototype system proves the feasibility of a compact probe employing a 2D array with integrated electronics. These results are reported in [2-4]. This device is used for a number of projects in our group including work on photoacoustic imaging and acoustical cross-talk.
FIGURE 1. Basic architecture of the 3D endoscopic ultrasound imaging probe.
FIGURE 2. A 16x16 2D array integrated with frontend electronic circuits.
FIGURE 3. Images of a wire targets. (Top: 3D rendered image, bottom: cross-sections).
FIGURE 4. Two perpendicular cross-sectional mages of a vessel Phantom.
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Example video of 3D image of a fishing-line phantom acquired with a
5-MHz 16x16-Element CMUT Array
To save the file, please right-click on the link then "Save Target As" Download Here |
References
[1] Oralkan Ö, Ergun AS, Cheng CH, Johnson JA, Karaman M, Lee TH, and Khuri-Yakub BT, "Volumetric Ultrasound Imaging Using 2-D CMUT Arrays," IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, vol. 50, no. 11, pp. 1581-1594, Sep. 2003.
[2] Wygant IO, Zhuang X, Yeh DT, Nikoozadeh A, Oralkan Ö, Ergun AS, Karaman M, and Khuri-Yakub BT, “Integrated Ultrasonic Imaging Systems Based on cMUT Arrays : Recent Progress”, IEEE International Ultrasonics Symposium, Montreal, QC, Canada, Aug. 23-27, 2004, pp. 391-394.
[3] Wygant IO, Yeh DT, Zhuang X, Nikoozadeh A, Oralkan Ö, Ergun AS, Karaman M, and Khuri-Yakub BT, “A miniature real-time volumetric ultrasonic imaging system,” Proceedings of SPIE Medical Imaging Conference, pp. 26-36, 2005.
[4] Wygant IO, Zhuang X, Yeh DT, Vaithilingam S, Nikoozadeh A, Oralkan Ö, Ergun AS, Karaman M, and Khuri-Yakub BT, “An Endoscopic Imaging System Based on a Two-Dimensional CMUT Array: Real-Time Imaging Results,” presented at the 2005 IEEE International Ultrasonics Symposium, Rotterdam, The Netherlands, Sept. 18 - 21, 2005.
Acknowledgements
This project was funded by National Institutes of Health under grant CA99059.
