Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Discovery of Two Types of Twinkling Can Explain Contradictory
  Observations among Twinkling Artifact Investigators in Ultrasound Imaging   Twinkling Artifact is a valuable tool in detecting dense objects such as
kidney stones, calculi etc., especially when there is no acoustic shadowing and
presence of hyperechogenic tissues obstructs visualization. This phenomenon is
not completely understood. Different scientific groups have contradictory
findings concerning its properties: some of them observed a decrease in
Twinkling intensity at elevated pulse repetition frequencies (PRF), while
others found Twinkling to be independent from PRF, etc. In this paper we
hypothesize that this kind of contradictions can be partially resolved on an
assumption that there are two types of Twinkling. The 1st type presumably is
produced by random-phased reflections from microcavitation and can be
registered even at PRF high enough to suppress blood flow. The 2nd is
originated from elastic vibrations as the object under investigation swings
like a pendulum in the field of ultrasound. These vibrations can be associated
with an external source such as a muscles contraction, etc. or the acoustic
radiation force from signals emitted by the transducer. The 2nd type of
Twinkling disappears at high PRF and can be regularly observed in silicone and
polyurethane phantoms where the occurrence of cavitation microbubbles is highly
unlikely. Key Words: Ultrasound Imaging, Twinkling Artifact, Stone Detection,
Doppler Effect, Color Frame Mapping, Acoustic Radiation Force, Elastic
Vibration, Ultrasound Phantom, Cavitation, Microbubbles.

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The categories of this paper are: plasm-ph
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The categories of this paper are: supr-con
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The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: dg-ga
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The categories of this paper are: cs
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The categories of this paper are: cond-mat
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: cmp-lg
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph