Dose optimization in pediatric cardiac x-ray imaging
Gislason-Lee, Amber J. Davies, A.G. Cowen, A.R.
Gislason-Lee, Amber J.
Davies, A.G.
Cowen, A.R.
Publication Date
2010-10
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2010-08-17
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Abstract
The aim of this research was to explore x-ray beam parameters with intent to optimize
pediatric x-ray settings in the cardiac catheterization laboratory. This study examined the effects of
peak x-ray tube voltage kVp and of copper Cu x-ray beam filtration independently on the image
quality to dose balance for pediatric patient sizes. The impact of antiscatter grid removal on the
image quality to dose balance was also investigated.
Methods: Image sequences of polymethyl methacrylate phantoms approximating chest sizes typical
of pediatric patients were captured using a modern flat-panel receptor based x-ray imaging system.
Tin was used to simulate iodine-based contrast medium used in clinical procedures. Measurements
of tin detail contrast and flat field image noise provided the contrast to noise ratio. Entrance surface
dose ESD and effective dose E measurements were obtained to calculate the figure of merit
FOM , CNR2 / dose, which evaluated the dose efficiency of the x-ray parameters investigated. The
kVp, tube current mA , and pulse duration were set manually by overriding the system’s automatic
dose control mechanisms. Images were captured with 0, 0.1, 0.25, 0.4, and 0.9 mm added Cu
filtration, for 50, 55, 60, 65, and 70 kVp with the antiscatter grid in place, and then with it removed.
Results: For a given phantom thickness, as the Cu filter thickness was increased, lower kVp was
favored. Examining kVp alone, lower values were generally favored, more so for thinner phantoms.
Considering ESD, the 8.5 cm phantom had the highest FOM at 50 kVp using 0.4 mm of Cu
filtration. The 12 cm phantom had the highest FOM at 55 kVp using 0.9 mm Cu, and the 16 cm
phantom had highest FOM at 55 kVp using 0.4 mm Cu. With regard to E, the 8.5 and 12 cm
phantoms had the highest FOM at 50 kVp using 0.4 mm of Cu filtration, and the 16 cm phantom
had the highest FOM at 50 kVp using 0.25 mm Cu. Antiscatter grid removal improved the FOM for
a given set of x-ray conditions. Under aforesaid optimal settings, the 8.5 cm phantom FOM improved
by 24% and 33% for ESD and E, respectively. Corresponding improvements were 26% and
24% for the 12 cm phantom and 6% and 15% for the 16 cm phantom.
Conclusions: For pediatric patients, using 0.25–0.9 mm Cu filtration in the x-ray beam while
maintaining 50–55 kVp, depending on patient size, provided optimal x-ray image quality to dose
ratios. These settings, adjusted for x-ray tube loading limits and clinically acceptable image quality,
should provide a useful strategy for optimizing iodine contrast agent based cardiac x-ray imaging.
Removing the antiscatter grid improved the FOM for the 8.5 and 12 cm phantoms, therefore grid
removal is recommended for younger children. Improvement for the 16 cm phantom declined into
the estimated margin of error for the FOM; the need for grid removal for older children would
depend on practical feasibility in the clinical environment.
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Gislason AJ, Davies AG and Cowen AR (2010) Dose optimization in pediatric cardiac x-ray imaging. Medical Physics. 37(10): 5258-5269.
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