Volumetric ultrasound imaging systems using capacitive micromachined ultrasonic transducer (CMUT) arrays [electronic resource]
Keywords: Electrical Engineering.

Medical imaging has become very important in the proper diagnosis of a disease. It has eliminated the need for invasive surgery for evaluation purposes, which can be painful to the patient. There are many modes of medical imaging, ultrasound being one of the most common. Ultrasound imaging provides various advantages compared to other modes that make it very attractive for diagnostic purposes. Conventional ultrasound systems provide real-time 2-D images of the human anatomy and have been used for decades. However, 4-D ultrasound imaging is becoming increasingly popular due to the additional information it provides over conventional 2-D imaging. It makes the imaging procedure less susceptible to the errors of the sonographer and 2-D image slices can be taken at various orientations with respect to the imaging probe allowing convenient offline analysis by the doctor. There are however, several challenges in building such a system. This is because of the requirement of the frontend electronics (typically consisting of LNAs) needing to be very close to the transducer array and the large number of elements that need to be interfaced to the backend system. Also, imaging a volume space requires image processing of a very large dataset that could eventually limit the imaging volume rate. The first part of this dissertation describes a 4-D ultrasound imaging system using Capacitive Micromachined Ultrasonic Transducer (CMUT) technology. Use of CMUTs enables us to address most of the challenges in building such a 4-D ultrasound system. Integrated circuits (IC) with a transmit beamformer and receive signal conditioning circuit were designed and fabricated, and were integrated tightly with the transducer array using flip-chip bonding technology. Different techniques of integration are demonstrated, and the choice between them is dictated by the targeted application. Multi-beam transmit functionality is incorporated in the IC that addresses the issue of limited imaging volume rate in a 4-D ultrasound system. Imaging experiments are presented that illustrate a true real-time volumetric imaging capability of the system. Two other ultrasound systems are also described. One is an extension of the work presented in the first part by incorporating capabilities of therapy using High Intensity Focused Ultrasound (HIFU), in the same 4-D ultrasound imaging system. This would allow physicians to use the same probe for imaging as well as therapy. This system uses an IC similar in design to that used for developing the 4-D ultrasound imaging system. It also consists of a switch network to allow external pulsers to provide a continuous wave sinusoidal excitation to the CMUT transducer. A new high-voltage switch circuit design is presented that is used in the switch network. Finally, a wearable ultrasound probe is presented that is capable of performing 2-D imaging in real-time. Such a probe is useful for applications that require constant or periodic monitoring of body functions and therefore can be worn by the patient at all times. Again, ICs were designed and integrated closely to a 1-D CMUT array. The assembly process is described and imaging results are presented.