Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Simultaneous Reduction of Two Common Autocalibration Errors in GRAPPA
  EPI Time Series Data   The GRAPPA (GeneRalized Autocalibrating Partially Parallel Acquisitions)
method of parallel MRI makes use of an autocalibration scan (ACS) to determine
a set of synthesis coefficients to be used in the image reconstruction. For EPI
time series the ACS data is usually acquired once prior to the time series. In
this case the interleaved R-shot EPI trajectory, where R is the GRAPPA
reduction factor, offers advantages which we justify from a theoretical and
experimental perspective. Unfortunately, interleaved R-shot ACS can be
corrupted due to perturbations to the signal (such as direct and indirect
motion effects) occurring between the shots, and these perturbations may lead
to artifacts in GRAPPA-reconstructed images. Consequently we also present a
method of acquiring interleaved ACS data in a manner which can reduce the
effects of inter-shot signal perturbations. This method makes use of the phase
correction data, conveniently a part of many standard EPI sequences, to assess
the signal perturbations between the segments of R-shot EPI ACS scans. The
phase correction scans serve as navigator echoes, or more accurately a
perturbation-sensitive signal, to which a root-mean-square deviation
perturbation metric is applied for the determination of the best available
complete ACS data set among multiple complete sets of ACS data acquired prior
to the EPI time series. This best set (assumed to be that with the smallest
valued perturbation metric) is used in the GRAPPA autocalibration algorithm,
thereby permitting considerable improvement in both image quality and temporal
signal-to-noise ratio of the subsequent EPI time series at the expense of a
small increase in overall acquisition time.

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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: astro-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: alg-geom
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The categories of this paper are: stat
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The categories of this paper are: hep-lat
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The categories of this paper are: eess
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The categories of this paper are: math-ph
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The categories of this paper are: supr-con
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The categories of this paper are: econ
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The categories of this paper are: math
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The categories of this paper are: chem-ph