EE PhD Oral Examination - Amin Nikoozadeh, Friday, June 4, 2010; 9:30 a.m.

Amin Nikoozadeh aminn at
Wed Jun 2 09:55:18 PDT 2010

Stanford University Oral Defense - Department of Electrical Engineering


Speaker: Amin Nikoozadeh


Title: Intracardiac Ultrasound Imaging Using Capacitive Micromachined
Ultrasonic Transducer (CMUT) Arrays


Advisor: Professor B. T. Khuri-Yakub


Date: Friday, June 04, 2010
Time: 09:30 AM (Refreshments at 9:15 AM) 

Location: Clark Center Auditorium (Basement, entrance across from Nexus)


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 fluoroscopic
guidance, which does not provide adequate soft-tissue resolution and exposes
the patient and the operator to harmful ionizing radiation. Intracardiac
echocardiography (ICE) provides real-time anatomical information that has
proven valuable in reducing the fluoroscopy time and enhancing procedural
success. Currently, piezoelectric transducer technology dominates the
ultrasound imaging market. For ICE catheters, however, the limited available
space and stringent packaging requirements challenge efforts to build a
piezoelectric transducer array at the tip of the catheter for
forward-looking imaging. This difficulty arises from the piezoelectric
transducer manufacturing process, which is based on meticulous and
labor-intensive steps.


I have developed two types of multi-functional forward-looking ICE catheters
using capacitive micromachined ultrasonic transducer (CMUT) technology:
MicroLinear (ML) and Ring catheters. The ML catheter enables real-time
forward-looking 2-D imaging using a 1-D CMUT array. The Ring catheter uses a
ring-shaped 2-D CMUT array that enables real-time forward-looking 3-D
imaging. Both of these catheters are equipped with custom-designed front-end
circuits that are integrated with the transducer at the catheter tip. 


In this talk, I will describe the main components of these catheters. I will
show how the integrated front-end IC improves the SNR by more than 20 dB. I
will explain how all the components are integrated in the tight space
available for full catheter construction with 100% yield. This task involved
numerous challenges, especially in the case of Ring catheter, wherein, I
successfully flip-chip bonded 8 IC’s (1.2 mm × 1 mm) and a Ring array (2.5
mm in diameter) to a flexible substrate with a total of 244 interconnects. I
will also present in-vivo imaging results obtained using these catheters. In
the last part of the talk, I will introduce a new CMUT structure that
exhibits ideal piston-like plate movement. Contrary to a conventional CMUT,
the top plate in the proposed structure does not need to be operated in
flexural mode. This results in significantly improved fill-factor, and thus,
a more efficient transducer.

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