Tilted-wire method for measuring resolution properties of CT images under extremely low-contrast and high-noise conditions

Chiaki Tominaga, Hiroki Azumi, Mitsunori Goto, Masaaki Taura, Noriyasu Homma, Issei Mori

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Edge methods are predominantly used for modulation transfer function (MTF) measurements in computed tomography (CT) images reconstructed using iterative methods. However, edge methods employ a relatively large and distinct test object, which is intended to simulate relatively large and distinct clinical organs. If one wants to assess the image quality of a small low-contrast object that is visually indistinct against a noisy background, a small and indistinct test object is desired. Another concern is that information related to the signal amount is discarded during MTF measurements. Choosing a weak impulse as the ultimately small test object, we have developed a tilted-wire method, which is a type of point spread function (PSF) method compatible with extremely low contrast-to-noise ratio (CNR) conditions. The signal amount is measured as the PSF volume. We used two commercial CT systems to evaluate the measurement accuracy of the tilted-wire method. When ensemble-averaged images are used, one can measure the MTF even when the wire is indiscernible from noise. The measurement error under such conditions is a few percent for both the MTF and signal amount. We also applied the tilted-wire method to two hybrid iterative reconstruction methods, namely AIDR-3D and ASiR. The results show that the MTF of ASiR is completely CNR-dependent, but that of AIDR-3D is noise-dependent. The signal amount obtained with ASiR is unchanged from that obtained through filtered back-projection (FBP). The signal amount obtained with AIDR-3D is less than that obtained through FBP, depending on the noise level.

Original languageEnglish
Pages (from-to)125-137
Number of pages13
JournalRadiological Physics and Technology
Issue number2
Publication statusPublished - 2018 Jun 1
Externally publishedYes


  • CT
  • Iterative reconstruction
  • Modulation transfer function
  • Nonlinear image
  • Signal amount

ASJC Scopus subject areas

  • Radiation
  • Physical Therapy, Sports Therapy and Rehabilitation
  • Radiology Nuclear Medicine and imaging

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