Development of a phantom to simulate a wide range of body sizes

X-ray image quality is highly dependent on object size. Diagnostic image quality can be maintained while controlling dose to a patient with tube current modulation schemes. For PET attenuation correction, much lower requirements are placed on CT image quality, but the minimum technique is still likely to be body size dependent. To investigate tube current modulation and non-diagnostic CT image quality effects on PET attenuation correction, and to aid in the development of new body-size dependent CT protocols for CT and PET/CT, we have developed a water-equivalent phantom that simulates a wide range of body sizes. Design criteria for the phantom include cross-sectional dimensions, shape, taper rate and material. Cross sectional dimensions and shape were desired to closely resemble different sized human torsos. Taper rate was important to achieve a smooth edge to reduce edge artifacts and to prevent partial volume effects. The phantom material needed to be easily machined, but still be tissue equivalent for CT imaging. The finished phantom was made of cast acrylic. Twelve one-inch plates of acrylic were machined into ovals with continuously tapered edges. After fabrication, the plates were stacked and secured together. The tolerance between plate diameters is less than 1.0 mm. The final dimensions are 12.3 x 22.4 cm at the small end and 38.8 x 49.0 cm at the large end. The phantom has an overall length of 29.0 cm and a mass of 23.2 kg. Initial results from this phantom include evaluation of image quality when using tube current modulation and evaluation of low-dose CT techniques for accuracy in PET attenuation correction.