Analog interface amplifiers for sub-mm broadband polymer intravascular ultrasonic imaging

Intravascular ultrasound (IVUS) provides sufficient spatial resolution and penetration depth for use during radiological interventions and for detecting lesion morphology and pathology. Increased use of IVUS in peripheral arteries requires ever-smaller catheters with broader bandwidth to achieve microscopic resolution. This work advances the development of sub-mm IVUS catheters that have greatly improved resolution using broad-band polymer transducers. The high transducer impedance prevents direct attachment to standard 50-Ω micro-coaxial cables and requires high voltage excitation (50 - 100 V_PP typically). To enable broadbandwidth IVUS in a sub-mm catheter, a custom analog front end (AFE) ASIC was developed. The AFE used an active limiter with a regenerative clamping structure to safely withstand large voltages using low-V_T FETs. AFE characterization in series and shunt configurations demonstrated a typical signal-to-noise ratio of 33.3 dB over a 105 MHz imaging bandwidth. SNR was limited by the wide fractional bandwidth; AFEs demonstrated a 2.1 nV/√Hz noise floor. Pulse recovery to >230-Vpp excitation was measured between 325 - 450 ns, allowing imaging as close as 0.5 mm. The presented design achieves a broader imaging fractional bandwidth than previous interface amplifiers in a sub-millimeter form factor. Example images obtained from a 0.8-mm, 40 MHz transducer showed sufficient resolution for the detection of individual stent struts within a simulated artery with a wall thickness of 0.35 mm.