Elsevier

Academic Radiology

Volume 16, Issue 9, September 2009, Pages 1134-1141.e1
Academic Radiology

Technical report
An Airway Phantom to Standardize CT Acquisition in Multicenter Clinical Trials

https://doi.org/10.1016/j.acra.2009.02.018Get rights and content

Rationale and objectives

The purpose of this study was to demonstrate the use of a phantom to standardize low-dose chest computed tomographic (CT) protocols in children with cystic fibrosis.

Materials and Methods

Spiral chest CT scans of a Plexiglas phantom simulating airway sizes (internal diameter, 1.1–16.4 mm; wall thickness, 0.4–4.6 mm) in children with cystic fibrosis were obtained using two multidetector CT (MDCT) scanners (GE VCT and Siemens Sensation 64). Quantitative airway measurements from both scanners were compared with micro-CT airway measurements over a range of doses (0.2–1.8 mSv) to evaluate bias and variance of measurements. The effective doses for CT protocols were estimated using the ImPACT CT Patient Dosimetry Calculator.

Results

Both MDCT scanners were able to accurately measure airway sizes down to 3 mm internal diameter and 1.3 mm airway wall thickness, with errors of <3.5%. ImPACT estimates of effective dose were different for the MDCT scanners for a given peak tube voltage and product of tube current and exposure time. Accuracy and precision were not found to be associated with dose parameters for either machine. Bias in all measurements was strongly associated with airway diameter (P values < .00001), but the magnitude of bias was small (mean, 0.07 mm; maximum, 0.21 mm). Differences between machines in error components were on the order of a few micrometers.

Conclusions

The use of a standard airway phantom confirms that different MDCT scanners have similar results within dose ranges planned for potential future clinical trials. Standardized protocols can be developed that adjust for differences in radiation exposure for different MDCT scanners.

Section snippets

Materials and methods

A Plexiglas airway phantom was manufactured by Phantom Laboratory, Inc (Salem, NY), modeled after the Plexiglas phantom developed by Reinhardt et al (8) (Fig 1). The phantom models tracheobronchial airway sizes in children and adolescents with CF that are seen with inspiratory chest CT imaging. The airway phantom consists of eight Plexiglas tubes that are encased in a larger Plexiglas cylinder (Fig 1). The sizes of the tubes simulate tracheal, bronchial, and bronchiolar airway sizes encountered

Results

The actual simulated airway sizes for the eight Plexiglas tubes measured by the micro-CT scanner are provided in Supplement Table 1. To provide a means of comparison with actual quantitative CT airway morphology obtained from previous obtained contiguous CT scans in children with CF (aged 6–18 years), additional examples of airway sizes are provided in this table as well.

Discussion

In principle, the guideline for determining the technique for CT scanning protocols should be the “as low as reasonably achievable” principle. When applied to research studies, the dose should be chosen to be as low as possible while providing the information necessary to adequately address the research question. The determination of this adequacy may be difficult but will likely be easier when quantitative measures are used, because a level of error can be ascertained and then used to

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