Dual energy iodine contrast CT with monochromatic X-rays

Computed tomography (CT) with monochromatic X-ray beams was used to image phantoms and a live rabbit using the preclinical multiple energy computed tomography (MECT) system at the National Synchrotron Light Source. MECT has a horizontal fan beam with a subject apparatus rotating about a vertical axis. Images were obtained at 43 keV for single-energy studies, and at energies immediately below and above the 33.17 keV iodine K-edge for dual-energy subtraction CT. Two CdWO₄ -photodiode array detectors were used. The high-resolution detector (0.5 mm pitch, uncollimated) provided 14 line pair/cm in-plane spatial resolution, with lower image noise than conventional CT. Images with the low-resolution detector (1.844-mm pitch, collimated to 0.922 mm detector elements) had a sensitivity for iodine of ≈60 μg/cc in 11-mm channels inside a 135 mm-diameter acrylic cylindrical phantom for a slice height of 2.5 mm and a surface dose of ≈4 cGy. The image noise was ≈1 Hounsfield Unit (HU); it was ≈3 HU for the same phantom imaged with conventional CT at approximately the same dose, slice height, and spatial resolution (≈7 1p/cm). These results show the potential advantage of MECT, despite present technical limitations