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Individual A-lines of the rf signal through the needle, demonstrating the nature of the comet-tail artifact. Though the images appear similar, the underlying signals are not. (a) PA A-line, the comet-tail artifact appears to be a continuous signal that diminishes over time, and (b) US A-line at the same location. The comet-tail artifact in the US image appears as a discontinuous train of signal bursts that decrease in amplitude over time.
