Both the morphological anatomy and functional parameters such as flow speed of the artery provide valuable information for the evaluation of cardiovascular diseases. Direct measurement of the arterial wall can be achieved by intravascular optical/ultrasound imaging methods, however no functional data are acquired with these methods. Fractional flow reserve (FFR) and Doppler wire have been used to assess the blood flow information, but do not provide cross-sectional images of the artery. This study is the first to design and fabricate a dual mode imaging catheter that contains a forward-looking ultrasonic transducer and a side-looking ultrasonic transducer together in one catheter. This dual-mode catheter not only provides morphological information about the artery, but also a precise measurement of functional flow. The data indicate that the proposed catheter can be used to acquire multiple parameters of the artery with a one-time procedure. This novel one-catheter approach could be used for the functional diagnosis of atherosclerotic arteries.
In this paper, we propose using magnesium alloy as the matching layer for the ultrasonic transducer made of 0.68 Pb(MgNb)O-0.32PbTiO (PMN-0.32PT) single crystal. The complete sets of elastic constants of AZ31B, GW83, and ZK60 magnesium alloys have been measured, which is practically a homogeneous material. The AZ31B magnesium alloy has an acoustic impedance of 10.36 MRayl, which is suitable for the development of high-performance ultrasonic transducers. A 3.5-MHz PMN-PT single crystal transducer has been designed and fabricated successfully using AZ31B magnesium alloy as the first quarter-wavelength matching layer. The -6-dB bandwidth and two-way insertion loss at the center frequency of the transducer are about 67% and 11.4 dB, respectively, much superior to the transducer fabricated using 0-3 composite matching layer. The high performance of this transducer indicates that the magnesium alloy is indeed an excellent matching layer material for ultrasonic transducer applications.
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