Three energy computed tomography with synchrotron radiation

Preliminary experiments for digital subtraction computed tomography (CT) at the K-edge of iodine (33.1 keV) were carried out at SMERF (Synchrotron Medical Research Facility X17B2) at the National Synchrotron Light Source, Brookhaven National Laboratory. The major goal was to evaluate the availability of this kind of imaging for in vivo neurological studies. Using the transvenous coronary angiography system, CT images of various samples and phantoms were taken simultaneously at two slightly different energies bracketing the K-absorption edge of iodine. The logarithmic subtraction of the two images resulted in the contrast enhancement of iodine filled structures. An additional CT image was taken at 99.57 keV (second harmonic of the fundamental wave). The third energy allowed the calculation of absolute iodine, tissue and bone images by means of a matrix inversion. A spatial resolution of 0.8 LP/mm was measured in single energy images and iodine concentrations down to 0.082 mg/ml in a 1/4 diameter detail were visible in the reconstructed subtraction image