Evaluation of z -axis resolution and image noise for nonconstant velocity spiral CT data reconstructed using a weighted 3D filtered backprojection (WFBP) reconstruction algorithm

Jodie A. Christner, Karl Stierstorfer, Andrew N. Primak, Christian D. Eusemann, Thomas G. Flohr, Cynthia H McCollough

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Purpose: To determine the constancy of z -axis spatial resolution, CT number, image noise, and the potential for image artifacts for nonconstant velocity spiral CT data reconstructed using a flexibly weighted 3D filtered backprojection (WFBP) reconstruction algorithm. Methods: A WFBP reconstruction algorithm was used to reconstruct stationary (axial, pitch=0), constant velocity spiral (pitch=0.35-1.5) and nonconstant velocity spiral CT data acquired using a 128×0.6 mm acquisition mode (38.4 mm total detector length, z -flying focal spot technique), and a gantry rotation time of 0.30 s. Nonconstant velocity scans used the system's periodic spiral mode, where the table moved in and out of the gantry in a cyclical manner. For all scan types, the volume CTDI was 10 mGy. Measurements of CT number, image noise, and the slice sensitivity profile were made for all scan types as a function of the nominal slice width, table velocity, and position within the scan field of view. A thorax phantom was scanned using all modes and reconstructed transverse and coronal plane images were compared. Results: Negligible differences in slice thickness, CT number, noise, or artifacts were found between scan modes for data taken at two positions within the scan field of view. For nominal slices of 1.0-3.0 mm, FWHM values of the slice sensitivity profiles were essentially independent of the scan type. For periodic spiral scans, FWHM values measured at the center of the scan range were indistinguishable from those taken 5 mm from one end of the scan range. All CT numbers were within ±5 HU, and CT number and noise values were similar for all scan modes assessed. A slight increase in noise and artifact level was observed 5 mm from the start of the scan on the first pass of the periodic spiral. On subsequent passes, noise and artifact level in the transverse and coronal plane images were the same for all scan modes. Conclusions: Nonconstant velocity periodic spiral scans can achieve z -axis spatial resolution, CT number accuracy, image noise and artifact level equivalent to those for stationary (axial), and constant velocity spiral scans. Thus, periodic spiral scans are expected to allow assessment of four-dimensional CT data for scan lengths greater than the detector width without sacrificing image quality.

Original languageEnglish (US)
Pages (from-to)897-906
Number of pages10
JournalMedical Physics
Volume37
Issue number2
DOIs
StatePublished - 2010

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Spiral Computed Tomography
Artifacts
Noise
Four-Dimensional Computed Tomography
Thorax

Keywords

  • CT
  • CT image quality
  • Filtered backprojection
  • Reconstruction algorithm
  • Slice sensitivity profile
  • Spiral CT

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

Cite this

Evaluation of z -axis resolution and image noise for nonconstant velocity spiral CT data reconstructed using a weighted 3D filtered backprojection (WFBP) reconstruction algorithm. / Christner, Jodie A.; Stierstorfer, Karl; Primak, Andrew N.; Eusemann, Christian D.; Flohr, Thomas G.; McCollough, Cynthia H.

In: Medical Physics, Vol. 37, No. 2, 2010, p. 897-906.

Research output: Contribution to journalArticle

Christner, Jodie A. ; Stierstorfer, Karl ; Primak, Andrew N. ; Eusemann, Christian D. ; Flohr, Thomas G. ; McCollough, Cynthia H. / Evaluation of z -axis resolution and image noise for nonconstant velocity spiral CT data reconstructed using a weighted 3D filtered backprojection (WFBP) reconstruction algorithm. In: Medical Physics. 2010 ; Vol. 37, No. 2. pp. 897-906.
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AU - Primak, Andrew N.

AU - Eusemann, Christian D.

AU - Flohr, Thomas G.

AU - McCollough, Cynthia H

PY - 2010

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N2 - Purpose: To determine the constancy of z -axis spatial resolution, CT number, image noise, and the potential for image artifacts for nonconstant velocity spiral CT data reconstructed using a flexibly weighted 3D filtered backprojection (WFBP) reconstruction algorithm. Methods: A WFBP reconstruction algorithm was used to reconstruct stationary (axial, pitch=0), constant velocity spiral (pitch=0.35-1.5) and nonconstant velocity spiral CT data acquired using a 128×0.6 mm acquisition mode (38.4 mm total detector length, z -flying focal spot technique), and a gantry rotation time of 0.30 s. Nonconstant velocity scans used the system's periodic spiral mode, where the table moved in and out of the gantry in a cyclical manner. For all scan types, the volume CTDI was 10 mGy. Measurements of CT number, image noise, and the slice sensitivity profile were made for all scan types as a function of the nominal slice width, table velocity, and position within the scan field of view. A thorax phantom was scanned using all modes and reconstructed transverse and coronal plane images were compared. Results: Negligible differences in slice thickness, CT number, noise, or artifacts were found between scan modes for data taken at two positions within the scan field of view. For nominal slices of 1.0-3.0 mm, FWHM values of the slice sensitivity profiles were essentially independent of the scan type. For periodic spiral scans, FWHM values measured at the center of the scan range were indistinguishable from those taken 5 mm from one end of the scan range. All CT numbers were within ±5 HU, and CT number and noise values were similar for all scan modes assessed. A slight increase in noise and artifact level was observed 5 mm from the start of the scan on the first pass of the periodic spiral. On subsequent passes, noise and artifact level in the transverse and coronal plane images were the same for all scan modes. Conclusions: Nonconstant velocity periodic spiral scans can achieve z -axis spatial resolution, CT number accuracy, image noise and artifact level equivalent to those for stationary (axial), and constant velocity spiral scans. Thus, periodic spiral scans are expected to allow assessment of four-dimensional CT data for scan lengths greater than the detector width without sacrificing image quality.

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KW - Slice sensitivity profile

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