Azadeh Moini

An integrated Ring CMUT array for endoscopic ultrasound and photoacoustic imaging

This work presents our preliminary results on developing an integrated quad-ring CMUT array for endoscopic ultrasound and photoacoustic imaging. We have designed and fabricated a ring capacitive micromachined ultrasonic transducer (CMUT) array composed of 512 elements distributed among four concentric rings each having 128 elements. The operational frequency of each ring was chosen to achieve a similar pressure beam profile for all the rings. The devices inner and outer diameters measure 5.0 and 10.1 mm, respectively. The CMUT array was integrated with custom front-end ICs using a quartz fan-out board. This bench-top assembly allowed connection to a single ring (i.e., 128 elements) at a time. Thus far, we have built assemblies with connections to the two outer rings. We have successfully demonstrated real-time volumetric imaging with these assemblies using nylon wire phantom and metal spring phantom.

Photoacoustic imaging using a 9F microLinear CMUT ICE catheter

This work presents our preliminary results on developing a multi-modality imaging catheter enabling combined ultrasound and photoacoustic imaging. We have developed an optical fiber ring catheter for use with our previously demonstrated 9F, real-time, forward-looking intracardiac ultrasound imaging catheter. Our custom software provides realtime ultrasound and photoacoustic imaging on a PC-based imaging platform. The promising phantom and in vivo imaging results presented here demonstrate the utility of a fully integrated catheter that provides both anatomical and functional information through co-registered ultrasound and photoacoustic imaging capabilities.

Dual-mode integrated circuit for imaging and HIFU with 2-D CMUT arrays

Successful high intensity focused ultrasound (HIFU) operation requires a reliable guidance and monitoring method such as magnetic resonance imaging (MRI) or ultrasound imaging. However, both widely used modalities are typically separate from the HIFU system, which makes co-registration of HIFU with cross-sectional imaging difficult. In this paper, we present a dual-mode integrated circuit (IC) that can perform both ultrasound imaging and HIFU with a single 2D capacitive micromachined ultrasonic transducer (CMUT) array, combining these two systems for ease of use. The dual-mode IC consists of pulsers, transmit beamforming circuitry, and low-noise amplifiers for imaging mode and switches for HIFU mode. By turning this switching network on and off, the system can alternately operate the imaging mode and HIFU mode on demand. The dual-mode IC was designed and fabricated in the 0.18-μm HV 4LM process provided by Maxim Inc. We fabricated a 32×32-element CMUT array that has a center frequency of 5 MHz using a sacrificial release process and flip-chip bonded this CMUT array to the IC. With the back-end system, real-time volumetric imaging on the wire phantom and HIFU ablation on ex-vivo tissue were performed respectively.

Volumetric intracardiac imaging using a fully integrated CMUT ring array: Recent developments

Atrial fibrillation, the most common type of cardiac arrhythmia, now affects more than 2.2 million adults in the US alone. Currently, electrophysiological interventions are performed under fluoroscopy guidance, a procedure that introduces harmful ionizing radiation without providing adequate soft-tissue resolution. Intracardiac echocardiography (ICE) provides real-time, high-resolution anatomical information, reduces fluoroscopy time, and enhances procedural success. We have previously developed a forward-looking, volumetric ICE catheter using a ring-shaped, 64-element capacitive micromachined ultrasonic transducer (CMUT) array with a 10MHz center frequency. The Ring array was flip-chip bonded to a flexible PCB along with 8 identical custom ASICs providing a total of 64 dedicated preamplifiers. The flex was then reshaped for integration with the catheter shaft. In the second-generation catheter, 72 micro-coaxial cables (reduced from 100) are terminated on a newly designed flex to provide the connection between the array electronics and the imaging system. The reduced number of cables enhances the catheters steerability. Furthermore, the new flex allows grounding of the top CMUT electrode through proper level-shifting of the ASIC supplies without additional circuitry. This feature enables complete ground shielding of the catheter, which improves its noise susceptibility and is an important safety measure for its clinical use. Beyond real-time, forward-looking imaging capability, the Ring catheter provides a continuous central lumen, enabling convenient delivery of other devices such as HIFU transducers, RF ablation catheters, etc. Using a PC-based imaging platform from Verasonics and a commercial Vivid7 imaging system from GE, we have demonstrated the in vivo, volumetric, real-time imaging capability of the finalized Ring catheter in a pig heart.

Capsule ultrasound device

We are developing a capsule ultrasound (CUS) device to serve as a wireless, portable, and ultrasonic pill for investigating the multiple layers of the complete gastrointestinal (GI) tract, in particular, the small intestine. This capsule will acquire ultrasound images with 360 degrees field-of-view (FOV) and a penetration depth of 5 cm using a 128-element and cylindrically-shaped capacitive micromachined ultrasonic transducer (CMUT) array, wrapped around the center of its body. Simulation results indicate that linear array imaging with a fixed focus of F#4 and 16 active elements produces valuable images. We have designed a CMUT for this application and the fabrication process to create cylindrical CMUT arrays has been established. We report our fabrication progress and show test devices that we successfully made and bent around a glass tube. In addition, the design of the application-specific integrated circuit (ASIC) and the wireless transmitter, responsible for the acquisition and wireless transmission of ultrasonic data respectively, is described.

Singulation for imaging ring arrays of capacitive micromachined ultrasonic transducers

Singulation of MEMS is a critical step in the transition from wafer-level to die-level devices. As is the case for capacitive micromachined ultrasound transducer (CMUT) ring arrays, an ideal singulation must protect the fragile membranes from the processing environment while maintaining a ring array geometry. The singulation process presented in this paper involves bonding a trench-patterned CMUT wafer onto a support wafer, deep reactive ion etching (DRIE) of the trenches, separating the CMUT wafer from the support wafer and de-tethering the CMUT device from the CMUT wafer. The CMUT arrays fabricated and singulated in this process were ring-shaped arrays, with inner and outer diameters of 5 mm and 10 mm, respectively. The fabricated CMUT ring arrays demonstrate the ability of this method to successfully and safely singulate the ring arrays and is applicable to any arbitrary 2D shaped MEMS device with uspended microstructures, taking advantage of the inherent planar attributes of DRIE.

Fabrication, Packaging, and Catheter Assembly of 2D CMUT Arrays for Endoscopic Ultrasound and Cardiac Imaging

Ultrasound is increasingly in demand as a medical imaging tool and can be particularly beneficial in the field of intracardiac echocardiography (ICE). However, many challenges remain in the development of a 3D ultrasound imaging system.We have designed and fabricated a quad-ring capacitive micromachined ultrasound transducer (CMUT) for real-time, volumetric medical imaging. Each CMUT array is composed of four concentric, independent ring arrays, each operating at a different frequency, with 128 elements per ring. In this project, one ring will be used for imaging. A large (5mm diameter) lumen is available for delivering other devices, including high intensity focused ultrasound transducers for therapeutic applications or optical fibers for photoacoustic imaging.We address several challenges in developing a 3D imaging system. Through wafer vias are incorporated in the fabrication process for producing 2D CMUT arrays. Device integration with electronics is achieved through solder bumping the arrays, designing a flexible PCB, and flip chip bonding CMUT and ASICs to the flexible substrate. Finally, we describe a method for integrating the flex assembly into a catheter shaft. The package, once assembled, will be used for in-vivo open chest experiments.Copyright

Capsule ultrasound device: Further developments

We are developing a capsule ultrasound (CUS) device - a pill with the capability to scan the gastrointestinal (GI) tract through ultrasound. In this paper, we discuss the design and fabrication of the main components of the CUS device including the CMUT array, front-end electronics, and the wireless transmitter. We demonstrate a successfully fabricated 128-element CMUT array with polydimethylsiloxane (PDMS)-filled trenches and show their input impedance in air. The front-end electronics, measuring 6 mm by 6 mm and the high-data rate wireless transmitter, measuring 1 mm by 1.76 mm, have been fabricated. Our preliminary power analysis indicates that our total power consumption is less than 20 mW for the CUS device. Our future work involves integrating these core components for imaging experiments.

Integration of a dual-mode catheter for ultrasound image guidance and HIFU ablation using a 2-D CMUT array

Image-guided high-intensity focused ultrasound (HIFU) is widely used not only for non-invasive therapy but also for a precise approach for tissue ablation. Most HIFU systems use piezoelectric transducers, which are typically bulky due to active cooling, and separate imaging and HIFU transducers, and are therefore impractical for catheter-based applications. Taking advantage of a single 2-D capacitive micromachined ultrasonic transducer (CMUT) array, we developed a dual-mode catheter that can switch between ultrasound imaging mode and HIFU ablation mode. The catheter is equipped with an application-specific integrated circuit (ASIC) and a 32 × 32-element 2-D CMUT array. Both ASIC and CMUT are flip-chip bonded to a custom-designed flexible printed circuit board (flex PCB) via 100-μm and 80-μm solder balls. Then, the flex legs are folded and terminated with pads for a micro zero insertion force (μZIF) connector, allowing easy assembly replacement without the extra cost of coaxial cable assembly. Next, the micro-coaxial cables are assembled at the end of the μZIF connectors. After integration with a 3-D printed tip and encapsulating with polydimethylsiloxane (PDMS), the catheter is finalized in a 22-mm diameter shaft. We successfully validated the functionality of both modes of the dual-mode catheter in oil. We are currently preparing the test for an animal study.

Integration of percutaneous cardiac catheter for HIFU ablation and image guidance

Image-guided high intensity focused ultrasound (HIFU) is widely used not only for non-invasive therapy but also as a precise approach for cardiac tissue ablation. However, most HIFU systems use piezoelectric transducers, which are typically bulky due to active cooling, and separate imaging and HIFU transducers, and therefore impractical for catheter-based applications. Taking advantage of a single 2-D capacitive micromachined ultrasonic transducer (CMUT) array, we developed a percutaneous cardiac catheter that can switch between ultrasound imaging mode and HIFU ablation mode.