Baiyu Chen, Presenter: Nothing to Disclose

Ehsan Samei PhD, Abstract Co-Author: Advisory Board, Ion Beam Applications, SA Consultant, Siemens AG

Samuel Richard PhD, BSC, Abstract Co-Author: Nothing to Disclose

Daniela Barbara Husarik MD, Abstract Co-Author: Nothing to Disclose

Daniele Marin MD, Abstract Co-Author: Fellowship funded, Bracco Group

Rendon C. Nelson MD, Abstract Co-Author: Consultant, General Electric Company Research support, Bracco Group Research support, Becton, Dickinson and Company Speakers Bureau, Siemens AG

The estimation of iodine concentration in contrast enhanced abdominal CT can be affected by scan and reconstruction parameters. Our purpose is to study the dependence of iodine concentration measurement on reconstruction algorithm and dose.

An anthropomorphic hepatic phantom consisting of iodine enhanced lesions was scanned using a Discovery CT750 HD scanner(GE Healthcare). The scan parameters were chosen based on a routine abdominal protocol for small patients in Duke Hospital: 40 mm beam collimation, 120 kVp, 1.375:1 pitch, 0.5 s gantry rotation time, and 150mA. Four more dose levels were investigated by changing the mA setting to 115, 75, 40 and 15. Each protocol was repeated 10 times for assessing reproducibility and reconstructed into 2.5mm slices using Filtered Back-projection(FBP), Adaptive Statistical Iterative Reconstruction(ASiR), and Model Based Iterative Reconstruction(MBiR). For each image dataset, multiple ROIs of 11x11 pixels were placed on muscle(iodine concentration 0mg/mL), uniform liver background(2.3mg/mL), low contrast lesion(3.2mg/mL) and high contrast lesion(3.7mg/mL). The concentration of iodine in tissues was quantified in terms of mean HU values within each ROI, averaging over repeats. The reproducibility of measurements was assessed via repeatability coefficient.

Mean HU values appeared independent of reconstruction algorithm and dose, while being linearly related to the designed iodine concentration of the phantom (muscle: 28.70+/-0.33; liver: 74.64+/-1.55; low contrast lesion: 80.72+/-1.27; high contrast lesion: 92.97+/-0.68). The repeatability coefficient of HU measurements, however, showed a significantly better reproducibility at higher dose and slightly better result with ASiR reconstruction algorithm (FBP: 3.01-10.18; ASiR: 2.89-9.19), thus showing a certain dose level requirement for the confidence of HU measurement, and a preference for ASiR over FBP. More MBiR data analysis is ongoing and is expected to advance this result.

This study provides a framework for the evaluation of effects of imaging parameters on iodine concentration assessment, thus providing possible guidelines for protocol optimization of quantitative CT tasks.

Knowledge of the dependence of HU on imaging parameters helps determining the true uptake of iodine. It also provides possible guidelines for protocol optimization in terms of quantitative capacity.

Chen, B, Samei, E, Richard, S, Husarik, D, Marin, D, Nelson, R, Quantification of Iodine Concentration in Abdominal CT: Effects of Reconstruction (FBP, ASiR, and MBiR) and Dose.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9012900.html