The purpose of this study was to substantiate the interdependency of image quality, radiation dose, and contrast
material dose in CT towards the patient-specific optimization of the imaging protocols. The study deployed two
phantom platforms. First, a variable sized phantom containing an iodinated insert was imaged on a representative CT
scanner at multiple CTDI values. The contrast and noise were measured from the reconstructed images for each
phantom diameter. Linearly related to iodine-concentration, contrast to noise ratio (CNR), was calculated for
different iodine-concentration levels. Second, the analysis was extended to a recently developed suit of 58 virtual
human models (5D-XCAT) with added contrast dynamics. Emulating a contrast-enhanced abdominal image
procedure and targeting a peak-enhancement in aorta, each XCAT phantom was “imaged” using a CT simulation
platform. 3D surfaces for each patient/size established the relationship between iodine-concentration, dose, and CNR.
The Sensitivity of Ratio (SR), defined as ratio of change in iodine-concentration versus dose to yield a constant
change in CNR was calculated and compared at high and low radiation dose for both phantom platforms. The results
show that sensitivity of CNR to iodine concentration is larger at high radiation dose (up to 73%). The SR results were
highly affected by radiation dose metric; CTDI or organ dose. Furthermore, results showed that the presence of
contrast material could have a profound impact on optimization results (up to 45%).