Predictive analog to digital conversion of Doppler ultrasound signals.
Analog to digital conversion in multigate Doppler ultrasound systems for blood velocity measurements is a technological challenge. The echoes must be digitized at a rate determined by the system bandwidth (typically 2 MHz), and the dynamic range is large (16 bits or more) due to the presence of strong, low-frequency Doppler clutter echoes originating from slowly moving tissue. Off-the-shelf A/D converters do not meet these requirements with the transducer configuration employed by contemporary Doppler systems. Analysis reveals a 5-b reduction in required wordlength for an A/D converter in a predictive feedback loop when the maximum clutter frequency is about 1.5% of the pulse repetition frequency. The prediction error filter is recursive. Alternatively, first- and second-order DPCM (Differential Pulse Code Modulation) yield 4 and 6 b, respectively. With short input segments (from a high-resolution Color Flow Mapper), the results are, in the above order, 4, 4, and 5 b. The results are verified by processing an experimental Doppler signal.
Bøe
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S
Department of Informatics, University of Oslo, Norway.
Kristoffersen
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K
D000465:Algorithms; D000703:Analog-Digital Conversion; D001011:Aorta / Q000000981:diagnostic imaging; D001783:Blood Flow Velocity; D008955:Models, Cardiovascular; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D018608:Ultrasonography, Doppler / Q000379:methods*; D018615:Ultrasonography, Doppler, Color / Q000379:methods; D018617:Ultrasonography, Doppler, Pulsed / Q000379:methods