The Influence of Source-to-Image Distance on Effective Dose and Image Quality for Mobile Chest X-ray Imaging
Hauge, Ingrid Helen Ryste; Beecher, Donal; Ellermann, Anne; Hughan, Sophi; Nguyen, Thi; Parrone, Luca; Selboe, Silje; Soares, Flavio augusto; Van Wijngaarden, Stephan; Sanderud, Audun
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2017Metadata
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Original version
Hauge IHR, Beecher D, Ellermann A, Hughan S, Nguyen T, Parrone L, Selboe S, Soares Fa, Van Wijngaarden S, Sanderud A: The Influence of Source-to-Image Distance on Effective Dose and Image Quality for Mobile Chest X-ray Imaging. In: Hogg P, Hogg-Thompson, Buissink C. OPTIMAX 2016Optimising image quality for medical imaging, 2017. University of Salford p. 83-92Abstract
Aim:
To investigate the effect of source-to-image distance (SID) on effective dose
and image quality at a fixed mAs. Furthermore, to determine whether effective dose
varies as SID is varied after compensating mAs for the inverse square law.
Method:
A chest phantom with a simulated pathology was imaged at varying SIDs
at a fixed mAs and kV. Observers visually compared the experimental images with
a reference image using criteria divided into 3 categories: anatomy, noise and
nodule image quality. A 2AFC program was used to display the images. A 5-point
Likert scale was used ranging from ‘much worse’ to ‘much better’. PCXMC 2.0
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was used to estimate effective dose. At each SID, a new mAs was calculated using
inverse square law correction. Effective dose was estimated again.
Results:
Modal response for 2AFC visual evaluation of anatomy image quality was
‘equal’ for every SID, implying no observable change. Modal response for 2AFC
visual evaluation of noise changed from ‘better’ to ‘worse’ as SID increased. Modal
response for visual evaluation of nodule image quality was ‘worse’ at the smallest
SIDs and ‘better’ at the largest SIDs. Decreasing SID from 190-100 cm: increased
effective dose by 247%; compensating mAs reduced the effective dose by 36%.
Conclusion:
For variable SIDs used in this study, there is little perceived difference
in anatomical image quality. Nodule image quality may decrease at shorter SIDs
while effective dose increases. Therefore, when shorter SIDs are necessary due to
lack of space, practitioners must be aware of patient dose.