Joshua Grimes PhD, Presenter: Nothing to Disclose

Gregory James Michalak PhD, Abstract Co-Author: Nothing to Disclose

Ahmed Halaweish PhD, Abstract Co-Author: Employee, Siemens AG

Joel Garland Fletcher MD, Abstract Co-Author: Grant, Siemens AG

Cynthia H. McCollough PhD, Abstract Co-Author: Research Grant, Siemens AG

The purpose of this study was to a) determine the improvement in the maximum iodine CNR when images are processed with the Mono-energetic Plus (Mono+) algorithm compared to the previous mono-energetic algorithm (Mono), and b) compare the maximum achievable CNR with Mono+ with that obtained using single-energy (SE) scans.

Objects containing various concentrations of iodine and calcium hydroxyapatite were placed within torso-shaped water phantoms ranging in lateral width from 15 to 45 cm and scanned on a dual-source CT system (Siemens Somatom Force). Single energy scans were performed at x-ray tube potentials from 70-150 kV, and dual energy (DE) scans were performed using a tube potential paring of 90/150Sn kV. Mono-energetic images were generated using commercial software (syngo Via Dual Energy, VA30) at energies of 40-110 keV using both Mono and Mono+. Iodine contrast to noise ratio (CNR) was calculated using the mean (and standard deviation) of the CT numbers in iodine and water from respective regions-of-interest in 10 consecutive images.

Mono+ increased the maximum achievable CNR by an average of 45% as compared to Mono by causing an increase in CNR with a decrease in photon energy below 70 keV. However, the maximum CNR was achieved at 70 kV (SE) in the 15-35 cm phantoms, and 80 kV (SE) in the 45 cm phantom. Mono+ achieved the maximum CNR (30% higher than that of SE) in the 45 cm phantom. CNR obtained using Mono (DE) was on average 67% of that achieved with SE (range 53-91%), while the CNR achieved using Mono+ (DE) was on average 97% of that achieved with SE (range 78-130%).

The use of Mono+ greatly increased the CNR of mono-energetic images compared to Mono at each mono-energetic setting (keV value), but especially for settings below 70 keV. The maximum achievable CNR in DE images was improved such that it nearly matched that achievable in SE scanning.

Mono+ can be used to achieve a CNR that is comparable to optimized SE scanning, while allowing the flexibility to perform material discrimination or decomposition tasks.

Grimes, J, Michalak, G, Halaweish, A, Fletcher, J, McCollough, C, Contrast-to-Noise Ratio Comparison in Single and Dual-energy Mono-energetic CT Imaging.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045603.html