The Effect of Patient Diameter on the Dual-Energy Ratio of Selected Contrast-Producing Elements.

OBJECTIVES: The aim of this study was to assess whether the low- to high-kVp computed tomography (CT) number ratio at dual-energy CT is affected by changes in patient diameter.

METHODS: Seven contrast-producing elements were housed sequentially within an abdomen phantom. Fat rings enlarged the phantom diameter from 26 to 44 cm. The phantom was scanned using single-energy CT at tube potentials of 80 and 140 kVp and rapid-kVp-switching dual-energy CT.

RESULTS: CT numbers decreased proportionally (∼20% CT number reduction for smallest to largest phantom diameters) for low- and high-energy acquisitions but resulted in consistent dual-energy ratios for each contrast element. For 17 of 21 material pair combinations, the dual-energy ratio ranges of the two elements did not overlap, implying that discrimination should remain possible for these material pairs at all patient sizes.

CONCLUSIONS: The dual-energy ratio for different contrast materials is largely unaffected by changes in phantom diameter. This should allow for robust separation of most contrast material combinations irrespective of patient size.