Wade Alleman MD, Presenter: Nothing to Disclose

Kale Dean Bodily MD, Abstract Co-Author: Nothing to Disclose

James E. Huprich MD, Abstract Co-Author: Nothing to Disclose

Joel Garland Fletcher MD, Abstract Co-Author: Research grant, Siemens AG Grant, E-Z-EM, Inc License agreement, General Electric Company

Shawna L. Rego BS, Abstract Co-Author: Nothing to Disclose

Cynthia H. McCollough PhD, Abstract Co-Author: Research grant, Siemens AG Research grant, RTI Electronics AB

Jeff Lynn Fidler MD, Abstract Co-Author: Grant, E-Z-EM, Inc, Lake Success, NY

et al, Abstract Co-Author: Nothing to Disclose

et al, Abstract Co-Author: Nothing to Disclose

CT enteroclysis is highly accurate in the identification of small bowel polyps in patients with polyposis, but surveillance demands reducing radiation dose. Our purpose was to examine the complex inter-relationship of oral contrast CT number, x-ray tube current and energy, slice thickness, polyp size and conspicuity in order to determine techniques which minimize dose yet permit polyp detection.

An anthropomorphic small bowel phantom containing polyps of various sizes (2, 5, 10, and 20mm) was imaged using 64-slice MDCT and 8 combinations of tube energies & currents (80 or 120 kV, CTDIvol range 2.3 – 18.3 mGy) for 8 oral contrast agents of varying CT number (water; Smoothie; low contrast barium solution (LCBS); LCBS mixed with 3%, 5%, 10%, 20%, and 30% Omnipaque 300) using 1 and 3 mm slice thicknesses. For each oral agent and across all combinations of parameters, two radiologists determined the lowest doses at which 2 and 5 mm polyps could be confidently identified and graded polyp conspicuity. Additionally, artifact type and severity, shape distortion and attenuation heterogeneity were graded.

2 mm polyps were more conspicuous using 1 mm slices (p=0.006). The minimal dose at which a 5mm polyp was confidently identified was identical using either 80 or 120 kV. However, using oral contrast agents with mid-range CT numbers (ie, Smoothie and LCBS + 3–5% Omnipaque, 218 to 335 HU @ 120 kV), 2mm polyps were more confidently identified at lower doses (2.3 – 4.6 mGy) with 80 kV. Using oral agents with 20% or more Omnipaque resulted in beam hardening artifacts, which were worse at 80 kV, resulting in polyp conspicuity being greater at 120 kV with these agents.

1)Polyp conspicuity can be maximized and dose minimized using a combination of oral contrast agents of mid-range CT number and lower tube energy (80 kV), or higher CT number and higher tube energy (120 kV). 2) To avoid artifacts, large patients should be imaged with high tube energies and oral contrast agents having higher CT numbers.

Our phantom experiment suggests that radiation doses can be dramatically lowered using positive contrast CT enteroclysis for surveillance of small bowel polyps.

Alleman, W, Bodily, K, Huprich, J, Fletcher, J, Rego, S, McCollough, C, Fidler, J, et al, , et al, , Reducing Dose and Increasing Conspicuity of Small Bowel Polyps at CT Enteroclysis: A Phantom Study.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5012079.html