High-Resolution 2D Imaging Using High-Frequency 1D CMUT Arrays
Forward-viewing ultrasound volume images are desired for many intravascular and intracardiac applications such as guiding treatment of chronic total occlusion, helping stent deployment, and monitoring ablation procedures in the heart. Because of the requirements for a guide wire in catheters, an annular ring is the preferred geometry for transducer arrays. However, it is very challenging to implement this geometry in a very small scale (1-2 mm) using the existing piezoelectric transducer technology [1]. On the other hand, CMUT arrays can be made in any arbitrary geometry with very small dimensions using photolithographic techniques and standard microfabrication processes. We have recently demonstrated the first full synthetic phased array volumetric images from CMUT ring arrays with integrated electronics. A 64-element, 2-mm diameter ring array wire bonded to 64 transmit/receive channels in a bank of four custom designed integrated circuits has been used in the experiments (Fig. 1). An interesting feature of CMUT operation is the ability to change the operating frequency by changing the DC bias. In this experiment, the CMUT array has been operated in both conventional and collapse operating regimes by setting the DC bias voltage to 30 V and 100 V, respectively. The resulting operating frequencies in the conventional and collapse regimes are 8.5 MHz and 19 MHz, respectively. Potentially, this operating flexibility of CMUTs allows on-demand switching between its two modes of operation during the imaging procedure, thereby providing a choice between the low frequency conventional mode for navigation and the high frequency collapse mode for diagnosis. We have imaged several phantoms including a small metal spring and deployed and undeployed forms of a Palmaz-Schatz coronary stent. The 3D rendered images next to photographs are shown in Fig. 2. The details of this work can be found in [2, 3]].
FIGURE 1. (a) Several CMUT annular ring arrays. (b) Magnified view of a CMUT annular ring array. (c) CMUT annular ring array wire bonded to custom designed frontend integrated circuits.
FIGURE 2. 3-D rendered ultrasound images and some cross-sections of (a) a small metal spring; (b) an undeployed Palmaz-Schatz stent; and (c) a deployed Palmaz?Schatz stent.
References
[1] Wang Y, Stephens DN, and O’Donnell M, “Optimizing the beam pattern of a forward-viewing ring-annular ultrasound array for intravascular imaging,” IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, vol. 49, pp. 1652-1664, 2002.
[2] OralkanÖ, Hansen S, Bayram B, Yaralioglu GG, Ergun AS, and Khuri-Yakub BT, “ cMUT Ring Arrays for Forward-Looking Intravascular Imaging,” Proceedings of 2004 IEEE International Ultrasonics Symposium, Montréal, QC, Canada, pp. 403-406Aug. 23 - 27, 2004.
[3] Yeh DT, Oralkan Ö, Wygant IO, O'Donnell M, and Khuri-Yakub BT, "3D ultrasound imaging using a forward-looking CMUT ring array for intravascular/intracardiac applications,” IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, accepted for publication, 2006.
Acknowledgements
This project was funded by National Institutes of Health under grant HL67647.
