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Automatic exposure control in CT: the effect of patient size, anatomical region and prescribed modulation strength on tube current and image quality

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Abstract

Objectives

To study the effect of patient size, body region and modulation strength on tube current and image quality on CT examinations that use automatic tube current modulation (ATCM).

Methods

Ten physical anthropomorphic phantoms that simulate an individual as neonate, 1-, 5-, 10-year-old and adult at various body habitus were employed. CT acquisition of head, neck, thorax and abdomen/pelvis was performed with ATCM activated at weak, average and strong modulation strength. The mean modulated mAs (mAsmod) values were recorded. Image noise was measured at selected anatomical sites.

Results

The mAsmod recorded for neonate compared to 10-year-old increased by 30 %, 14 %, 6 % and 53 % for head, neck, thorax and abdomen/pelvis, respectively, (P < 0.05). The mAsmod was lower than the preselected mAs with the exception of the 10-year-old phantom. In paediatric and adult phantoms, the mAsmod ranged from 44 and 53 for weak to 117 and 93 for strong modulation strength, respectively. At the same exposure parameters image noise increased with body size (P < 0.05).

Conclusions

The ATCM system studied here may affect dose differently for different patient habitus. Dose may decrease for overweight adults but increase for children older than 5 years old. Care should be taken when implementing ATCM protocols to ensure that image quality is maintained.

Key Points

• ATCM efficiency is related to the size of the patient’s body.

• ATCM should be activated without caution in overweight adult individuals.

• ATCM may increase radiation dose in children older than 5 years old.

• ATCM efficiency depends on the protocol selected for a specific anatomical region.

• Modulation strength may be appropriately tuned to enhance ATCM efficiency.

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Abbreviations

ATCM:

Automatic tube current modulation

CIR:

Circumference

CT:

Computed tomography

HU:

Hounsfield unit

mAsmod :

Mean modulated mAs

ROI:

Region of interest

SD:

Standard deviation

ROI:

Region of interest

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Acknowledgements

The scientific guarantor of this publication is Antonios E Papadakis. The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article. The authors state that this work has not received any funding. No complex statistical methods were necessary for this paper. Institutional review board approval was not required because this study was performed on anthropomorphic phantoms. Methodology: experimental, performed at one institution.

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Authors and Affiliations

  1. Department of Medical Physics, University Hospital of Heraklion, Stavrakia, P.O. Box 1352, Heraklion, 71110, Crete, Greece

    Antonios E. Papadakis

  2. Faculty of Medicine, Department of Medical Physics, University of Crete, P.O. Box 2208, Heraklion, 71003, Crete, Greece

    Kostas Perisinakis & John Damilakis

Authors
  1. Antonios E. Papadakis
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  2. Kostas Perisinakis
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  3. John Damilakis
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Correspondence to Antonios E. Papadakis.

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Papadakis, A.E., Perisinakis, K. & Damilakis, J. Automatic exposure control in CT: the effect of patient size, anatomical region and prescribed modulation strength on tube current and image quality. Eur Radiol 24, 2520–2531 (2014). https://doi.org/10.1007/s00330-014-3309-4

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  • DOI: https://doi.org/10.1007/s00330-014-3309-4

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