Does gantry rotation time influence accuracy of volume computed tomography dose index (CTDIvol) in modern CT?

Atsushi Fukuda; Nao Ichikawa; Yoshiharu Fujita; Pei-Jan Paul Lin; Kosuke Matsubara; Tosiaki Miyati

doi:10.1016/j.ejmp.2017.04.008

Does gantry rotation time influence accuracy of volume computed tomography dose index (CTDI_vol) in modern CT?

Phys Med. 2017 May:37:43-48. doi: 10.1016/j.ejmp.2017.04.008. Epub 2017 Apr 19.

Authors

Atsushi Fukuda¹, Nao Ichikawa², Yoshiharu Fujita², Pei-Jan Paul Lin³, Kosuke Matsubara⁴, Tosiaki Miyati⁵

Affiliations

¹ Division of PET Imaging, Shiga Medical Center Research Institute, 5-4-30 Moriyama, Moriyama, Shiga 524-8524, Japan. Electronic address: [email protected].
² Department of Radiology, Shiga Medical Center for Adults, 5-4-30 Moriyama, Moriyama, Shiga 524-0022, Japan.
³ Department of Radiology, Virginia Commonwealth University Medical Center, 1300 East Marshall Street, Richmond, VA 23298, USA.
⁴ Department of Quantum Medical Technology, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan.
⁵ Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan.

PMID: 28535914
DOI: 10.1016/j.ejmp.2017.04.008

Abstract

Purpose: The purpose of this study was to develop a gantry overrun corrected CTDI_vol (cCTDI_vol) dosimetry and evaluate the differences between the displayed CTDI_vol (dCTDI_vol), measured CTDI_vol (mCTDI_vol), and the cCTDI_vol.

Methods and materials: The each 8 rotation times between 275 and 1000ms of two CT scanners were investigated. Rotation time (T_rot) and the beam-on time (T_beam) in axial scanning were measured accurately to determine the gantry overrun time (T_over) as T_beam-T_rot. Subsequently, mCTDI_vol was measured by using a 100mm ionization chamber and CTDI phantoms. Furthermore, we introduced a gantry overrun correction factor (C_o=T_rot/T_beam) to obtain cCTDI_vol. Upon completion of the data acquisition, the dCTDI_vol and mCTDI_vol were compared with the cCTDI_vol.

Results: The discrepancies of T_rot were 0.2±0.2ms as compared to the preset rotation times, and T_over was machine-specific and almost constant (22.4±0.5ms or 45.1±0.3ms) irrespective of the preset rotation time. Both dCTDI_vol and mCTDI_vol were increasingly overestimated compared to cCTDI_vol as the faster the preset rotation time was selected (1.7-23.5%).

Conclusion: The rotation time influences the accuracy of CTDI_vol in modern CT, and should be taken into consideration when assessing the radiation output in modern CT.

Keywords: Beam-on time; CTDI; Gantry overrun time; Gantry rotation time; MDCT.

MeSH terms

Cone-Beam Computed Tomography*
Humans
Phantoms, Imaging
Radiation Dosage*
Rotation