Dose reduction in helical CT: Dynamically adjustable z-axis x-ray beam collimation

Jodie A. Christner, Vanessa A. Zavaletta, Christian D. Eusemann, Alisa I. Walz-Flannigan, Cynthia H McCollough

Research output: Contribution to journalArticle

71 Citations (Scopus)

Abstract

OBJECTIVE. The purpose of this study was to measure the dose reduction achieved with dynamically adjustable z-axis collimation. MATERIALS AND METHODS. A commercial CT system was used to acquire CT scans with and without dynamic z-axis collimation. Dose reduction was measured as a function of pitch, scan length, and position for total incident radiation in air at isocenter, accumulated dose to the center of the scan volume, and accumulated dose to a point at varying distances from a scan volume of fixed length. Image noise was measured at the beginning and center of the scan. RESULTS. The reduction in total incident radiation in air at isocenter varied between 27% and 3% (pitch, 0.5) and 46% and 8% (pitch, 1.5) for scan lengths of 20 and 500 mm, respectively. Reductions in accumulated dose to the center of the scan were 15% and 29% for pitches of 0.5 and 1.5 for 20-mm scans. For scan lengths greater than 300 mm, dose savings were less than 3% for all pitches. Dose reductions 80 mm or farther from a 100-mm scan range were 15% and 40% for pitches of 0.5 and 1.5. With dynamic z-axis collimation, noise at the extremes of a helical scan was unchanged relative to noise at the center. Estimated reductions in effective dose were 16% (0.4 mSv) for the head, 10% (0.8 and 1.4 mSv) for the chest and liver, 6% (0.8 mSv) for the abdomen and pelvis, and 4% (0.4 mSv) and 55% (1.0 mSv) for coronary CT angiography at pitches of 0.2 and 3.4. CONCLUSION. Use of dynamic z-axis collimation reduces dose in helical CT by minimizing overscanning. Percentage dose reductions are larger for shorter scan lengths and greater pitch values.

Original languageEnglish (US)
JournalAmerican Journal of Roentgenology
Volume194
Issue number1
DOIs
StatePublished - Jan 2010

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Spiral Computed Tomography
Noise
Air
X-Rays
Radiation
Coronary Angiography
Pelvis
Abdomen
Thorax
Head
Liver
Computed Tomography Angiography

Keywords

  • CT
  • Dose efficiency
  • Helical CT
  • Overscanning
  • Radiation dose

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

Cite this

Dose reduction in helical CT : Dynamically adjustable z-axis x-ray beam collimation. / Christner, Jodie A.; Zavaletta, Vanessa A.; Eusemann, Christian D.; Walz-Flannigan, Alisa I.; McCollough, Cynthia H.

In: American Journal of Roentgenology, Vol. 194, No. 1, 01.2010.

Research output: Contribution to journalArticle

Christner, Jodie A. ; Zavaletta, Vanessa A. ; Eusemann, Christian D. ; Walz-Flannigan, Alisa I. ; McCollough, Cynthia H. / Dose reduction in helical CT : Dynamically adjustable z-axis x-ray beam collimation. In: American Journal of Roentgenology. 2010 ; Vol. 194, No. 1.
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abstract = "OBJECTIVE. The purpose of this study was to measure the dose reduction achieved with dynamically adjustable z-axis collimation. MATERIALS AND METHODS. A commercial CT system was used to acquire CT scans with and without dynamic z-axis collimation. Dose reduction was measured as a function of pitch, scan length, and position for total incident radiation in air at isocenter, accumulated dose to the center of the scan volume, and accumulated dose to a point at varying distances from a scan volume of fixed length. Image noise was measured at the beginning and center of the scan. RESULTS. The reduction in total incident radiation in air at isocenter varied between 27{\%} and 3{\%} (pitch, 0.5) and 46{\%} and 8{\%} (pitch, 1.5) for scan lengths of 20 and 500 mm, respectively. Reductions in accumulated dose to the center of the scan were 15{\%} and 29{\%} for pitches of 0.5 and 1.5 for 20-mm scans. For scan lengths greater than 300 mm, dose savings were less than 3{\%} for all pitches. Dose reductions 80 mm or farther from a 100-mm scan range were 15{\%} and 40{\%} for pitches of 0.5 and 1.5. With dynamic z-axis collimation, noise at the extremes of a helical scan was unchanged relative to noise at the center. Estimated reductions in effective dose were 16{\%} (0.4 mSv) for the head, 10{\%} (0.8 and 1.4 mSv) for the chest and liver, 6{\%} (0.8 mSv) for the abdomen and pelvis, and 4{\%} (0.4 mSv) and 55{\%} (1.0 mSv) for coronary CT angiography at pitches of 0.2 and 3.4. CONCLUSION. Use of dynamic z-axis collimation reduces dose in helical CT by minimizing overscanning. Percentage dose reductions are larger for shorter scan lengths and greater pitch values.",
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AU - Walz-Flannigan, Alisa I.

AU - McCollough, Cynthia H

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N2 - OBJECTIVE. The purpose of this study was to measure the dose reduction achieved with dynamically adjustable z-axis collimation. MATERIALS AND METHODS. A commercial CT system was used to acquire CT scans with and without dynamic z-axis collimation. Dose reduction was measured as a function of pitch, scan length, and position for total incident radiation in air at isocenter, accumulated dose to the center of the scan volume, and accumulated dose to a point at varying distances from a scan volume of fixed length. Image noise was measured at the beginning and center of the scan. RESULTS. The reduction in total incident radiation in air at isocenter varied between 27% and 3% (pitch, 0.5) and 46% and 8% (pitch, 1.5) for scan lengths of 20 and 500 mm, respectively. Reductions in accumulated dose to the center of the scan were 15% and 29% for pitches of 0.5 and 1.5 for 20-mm scans. For scan lengths greater than 300 mm, dose savings were less than 3% for all pitches. Dose reductions 80 mm or farther from a 100-mm scan range were 15% and 40% for pitches of 0.5 and 1.5. With dynamic z-axis collimation, noise at the extremes of a helical scan was unchanged relative to noise at the center. Estimated reductions in effective dose were 16% (0.4 mSv) for the head, 10% (0.8 and 1.4 mSv) for the chest and liver, 6% (0.8 mSv) for the abdomen and pelvis, and 4% (0.4 mSv) and 55% (1.0 mSv) for coronary CT angiography at pitches of 0.2 and 3.4. CONCLUSION. Use of dynamic z-axis collimation reduces dose in helical CT by minimizing overscanning. Percentage dose reductions are larger for shorter scan lengths and greater pitch values.

AB - OBJECTIVE. The purpose of this study was to measure the dose reduction achieved with dynamically adjustable z-axis collimation. MATERIALS AND METHODS. A commercial CT system was used to acquire CT scans with and without dynamic z-axis collimation. Dose reduction was measured as a function of pitch, scan length, and position for total incident radiation in air at isocenter, accumulated dose to the center of the scan volume, and accumulated dose to a point at varying distances from a scan volume of fixed length. Image noise was measured at the beginning and center of the scan. RESULTS. The reduction in total incident radiation in air at isocenter varied between 27% and 3% (pitch, 0.5) and 46% and 8% (pitch, 1.5) for scan lengths of 20 and 500 mm, respectively. Reductions in accumulated dose to the center of the scan were 15% and 29% for pitches of 0.5 and 1.5 for 20-mm scans. For scan lengths greater than 300 mm, dose savings were less than 3% for all pitches. Dose reductions 80 mm or farther from a 100-mm scan range were 15% and 40% for pitches of 0.5 and 1.5. With dynamic z-axis collimation, noise at the extremes of a helical scan was unchanged relative to noise at the center. Estimated reductions in effective dose were 16% (0.4 mSv) for the head, 10% (0.8 and 1.4 mSv) for the chest and liver, 6% (0.8 mSv) for the abdomen and pelvis, and 4% (0.4 mSv) and 55% (1.0 mSv) for coronary CT angiography at pitches of 0.2 and 3.4. CONCLUSION. Use of dynamic z-axis collimation reduces dose in helical CT by minimizing overscanning. Percentage dose reductions are larger for shorter scan lengths and greater pitch values.

KW - CT

KW - Dose efficiency

KW - Helical CT

KW - Overscanning

KW - Radiation dose

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