TU‐A‐201B‐05: Radiation Dose Penalty in Axial Mode CT

K. Mathieu, M. Mcnitt‐gray, J. Hsieh, D. Cody

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Purpose: To determine whether a dose penalty exists when scanning patients in axial scan mode on General Electric (GE) Computed Tomography (CT) scanners. A 10‐millisecond‐long rise of the x‐ray tube output occurs immediately before image acquisition and is suspected to contribute additional dose near the start angle of the x‐ray tube. This dose penalty may exist for axial scanning because the rise time occurs for every 360° rotation of the x‐ray tube, whereas rise time only occurs once in helical scan mode. Method and Materials: 10‐, 15‐, and 32‐cm CTDI phantoms were scanned on a GE VCT scanner for a single axial rotation in service mode. Exposure was measured at a constant peripheral location (12:00) and recorded for various x‐ray tube start angles. These methods were repeated on the 32‐cm phantom, changing its vertical position in 2‐cm increments from 6‐cm below to 12‐cm above iso‐center. Results: Exposure, measured at the 12:00 peripheral chamber position, was 5.5%, 1.8%, and 1.0% higher in the 32‐, 15‐, and 10‐cm phantom, respectively, when a start angle of 0° was used versus a start angle of 270° (this start angle was used for comparison to avoid attenuation from the patient table). The exposure penalty ranged from 2.9% to 12.7% when the 32‐cm phantom was 6‐cm below and 12‐cm above iso‐center, respectively. Conclusion: In light of the dose penalty observed in this study, axial acquisitions should feature a start angle of 180° to avoid imparting this penalty on superficial radiosensitive organs (i.e. breast, testes, and thyroid), which are near the anterior side of patients. Also, dose is not consistent around the periphery of a phantom scanned in axial mode and contiguous helical scanning (pitch = 1.0) provides a dose advantage over axial scanning (all other technique factors being equal).

Original languageEnglish (US)
Number of pages1
JournalMedical physics
Volume37
Issue number6
DOIs
StatePublished - Jun 2010

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Tomography
X-Rays
Radiation
X-Ray Computed Tomography Scanners
Testis
Thyroid Gland
Breast

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

Cite this

TU‐A‐201B‐05 : Radiation Dose Penalty in Axial Mode CT. / Mathieu, K.; Mcnitt‐gray, M.; Hsieh, J.; Cody, D.

In: Medical physics, Vol. 37, No. 6, 06.2010.

Research output: Contribution to journalArticle

Mathieu, K. ; Mcnitt‐gray, M. ; Hsieh, J. ; Cody, D. / TU‐A‐201B‐05 : Radiation Dose Penalty in Axial Mode CT. In: Medical physics. 2010 ; Vol. 37, No. 6.
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abstract = "Purpose: To determine whether a dose penalty exists when scanning patients in axial scan mode on General Electric (GE) Computed Tomography (CT) scanners. A 10‐millisecond‐long rise of the x‐ray tube output occurs immediately before image acquisition and is suspected to contribute additional dose near the start angle of the x‐ray tube. This dose penalty may exist for axial scanning because the rise time occurs for every 360° rotation of the x‐ray tube, whereas rise time only occurs once in helical scan mode. Method and Materials: 10‐, 15‐, and 32‐cm CTDI phantoms were scanned on a GE VCT scanner for a single axial rotation in service mode. Exposure was measured at a constant peripheral location (12:00) and recorded for various x‐ray tube start angles. These methods were repeated on the 32‐cm phantom, changing its vertical position in 2‐cm increments from 6‐cm below to 12‐cm above iso‐center. Results: Exposure, measured at the 12:00 peripheral chamber position, was 5.5{\%}, 1.8{\%}, and 1.0{\%} higher in the 32‐, 15‐, and 10‐cm phantom, respectively, when a start angle of 0° was used versus a start angle of 270° (this start angle was used for comparison to avoid attenuation from the patient table). The exposure penalty ranged from 2.9{\%} to 12.7{\%} when the 32‐cm phantom was 6‐cm below and 12‐cm above iso‐center, respectively. Conclusion: In light of the dose penalty observed in this study, axial acquisitions should feature a start angle of 180° to avoid imparting this penalty on superficial radiosensitive organs (i.e. breast, testes, and thyroid), which are near the anterior side of patients. Also, dose is not consistent around the periphery of a phantom scanned in axial mode and contiguous helical scanning (pitch = 1.0) provides a dose advantage over axial scanning (all other technique factors being equal).",
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