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Improved wedge method for the measurement of sub-millimeter slice thicknesses in magnetic resonance imaging

Abstract

The standard method for measuring the slice thickness of magnetic resonance images uses the inclined surface of a wedge (wedge method); it is sensitive to small increases in noise because of the differentiation of the edge response function (ERF) required. The purpose of this study was to improve the wedge method by fitting a curve to the ERF. The curve-fit function was obtained by convolving an ideal ERF (a ramp function) with a Gaussian function to represent ERF blurring. Measurements of 5- and 3-mm slice thicknesses were performed on a 3T scanner using the conventional wedge method, the improved wedge method, and another standard method using an inclined slab (slab method). Subsequently, 0.5- and 0.25-mm slice thicknesses from multiple slices acquired using a three-dimensional sequence were measured using the improved wedge method. When measuring 5-mm slices, the differences in measurements obtained using the improved wedge method and the conventional slab and wedge methods were very small: <0.6% of the 5-mm slice thickness. The difference was ≤1.7% for 3-mm slices. For 0.5- and 0.25-mm slices, the mean values obtained using the improved wedge method were 0.543 ± 0.007 mm and 0.247 ± 0.015 mm, with a 1.2 and 5.9% coefficient of variation across slices, respectively. The improved wedge method is valid and potentially applicable to the measurement of sub-millimeter slice thicknesses.

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Acknowledgements

We thank Libby Cone, MD, MA, from Edanz Group Japan (www.edanzediting.com/ac) for editing drafts of this manuscript.

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Correspondence to Tsutomu Kanazawa.

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This article does not contain any studies with human or animal participants performed by any of the authors.

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The authors declare that they have no conflicts of interest.

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Kanazawa, T., Ohkubo, M., Kondo, T. et al. Improved wedge method for the measurement of sub-millimeter slice thicknesses in magnetic resonance imaging. Radiol Phys Technol 10, 446–453 (2017). https://doi.org/10.1007/s12194-017-0417-2

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Keywords

  • Magnetic resonance imaging/MT
  • Slice thickness
  • Wedge method
  • Slab method
  • Edge response function
  • Slice profile