14 April 2005 Evaluation of MRI DTI-tractography by tract-length histogram
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In the absence of ground truth, there are very few methods available to evaluate the accuracy of a specific tracking algorithm or the various data acquisition protocols for DTI-tractography. The objective of this work was to develop methodology, based on tract-length histograms, that could be used to evaluate whole-brain tractography with data acquired under different conditions for a given subject, for example six versus 25 gradient directions, or use of an 8-element phased array versus quadrature head-coil. Whole-brain DTI data were acquired from six healthy normal human volunteers on a 1.5 T GE scanner at TR=10.3s, field-of-view 26cm, 128x128 matrix, 28 contiguous 4mm thick slices from 25 isotropic gradient directions with b=1000s/mm2, one b=0 acquisition, and number of excitations (NEX)=1 for a total acquisition time of 3min 53s. Similarly, four sets of data were acquired from 6 non-colinear directions and combined with two b=0 acquisitions to equalize the time for 25 and 6-directions acquisitions. The tract-length histograms clearly show that at equal acquisition time, there are more long tracts in the 25-direction acquisition than the 6-direction acquisition, suggesting better estimation of the tensor with 25 directions. Tract-counts above a threshold provide an objective index to evaluate tractography. Also a comparison of the two coils shows a higher tract-count for long tracts with the 8-element coil, consistent with the demonstrated higher sensitivity and higher signal-to-noise ratio for EPI acquisitions by the 8-element coil.
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Manbir Singh, Manbir Singh, Darryl Hwang, Darryl Hwang, Witaya Sungkarat, Witaya Sungkarat, Karthic Veera, Karthic Veera, "Evaluation of MRI DTI-tractography by tract-length histogram", Proc. SPIE 5746, Medical Imaging 2005: Physiology, Function, and Structure from Medical Images, (14 April 2005); doi: 10.1117/12.594721; https://doi.org/10.1117/12.594721

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