Microwave imaging offers associated benefits, namely, nonionizing exposures and relatively low cost. In these applications, the technique exploits the considerable dielectric property contrast between normal and diseased tissues’ ( Joines et al., 1994 Chaudhary et al., 1984 Surowiec et al., 1988 Lazebnik et al., 2007a 2007b Sugitani et al., 2014 Meaney et al., 2012a Semenov et al., 2002 Persson et al., 2014 and Gabriel et al., 1996a) and property variation as a function of temperature ( Duck, 1990 Lazebnik et al., 2006 and Ohlsson and Bengtsson, 1975). Microwave imaging has been investigated for several decades as a potential medical tool for detecting/diagnosing a variety of indications including breast cancer ( Poplack et al., 2007 Meaney et al., 2013 and Klemm et al., 2008a), cardiac conditions ( Semenov et al., 2000), stroke ( Persson et al., 2014), bone health ( Meaney et al., 2012a), and temperature during thermal therapy ( Meaney et al., 2003b 2003a and Haynes et al., 2014). In a larger channel configuration, the approach is expected to provide performance comparable to commercial vector network analyzers at a fraction of the cost and in a more compact footprint. Our design exploits the rapidly evolving technology being developed for the telecommunications environment for test and measurement tasks with the higher performance specifications required in medical microwave imaging applications. Consequently, we have configured an external reference that overcame these limitations in a compact and robust package. For our system, N-series SDRs were less suitable because they are not amenable to RF shielding required for the cross-channel isolation necessary for an integrated microwave imaging system.
While B210 units are capable of being synchronized with each other via coherent reference signals, they are somewhat unreliable in this configuration and the manufacturer recommends using N200 or N210 models instead.
The system utilizes the B210 USRP SDR developed by Ettus Research that operates over a 70 MHz–6 GHz bandwidth.
We have implemented a prototype 4-channel transmission-based, microwave measurement system built on innovative software defined radio (SDR) technology.
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