Shuai Leng PhD, Presenter: Nothing to Disclose

Jodie A. Christner PhD, Abstract Co-Author: Nothing to Disclose

Lifeng Yu PhD, Abstract Co-Author: Nothing to Disclose

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

To assess the improvement in image quality of dual-energy virtual monoenergetic (VM) images using an energy domain noise reduction technique, and compare to single energy CT scans at optimal tube potentials (kV).

VM images at lower keV have been used in lesion detection due to the increased iodine contrast. However, image noise increases substantially for lower keV images, which reduces the contrast to noise ratio (CNR). In this study, a syringe filled with 10 mgI/ml contrast was placed into each of three water phantoms (30, 35 and 45cm wide) to simulate different body sizes. The phantoms were scanned on a dual source CT scanner (Definition Flash, Siemens) using both dual energy (80 and Sn140 kV) and single energy (80, 100, 120 and 140 kV) modes and the same dose levels. VM images from 40 to 110 keV were generated every 10 keV using commercial software (Syngo, VA40). An energy domain noise reduction algorithm (HYPR-LR) was applied to the VM images to reduce image noise by exploiting redundancies in the energy domain. The mean and standard deviation of CT numbers were measured in iodine and water. Iodine CNR was calculated for single energy CT images, and for VM images with and without HYPR-LR.

Using HYPR-LR, VM image noise was reduced by 25 to 59% at low keV images (40-60 keV) and iodine CNR improved. Optimal iodine CNR of original VM images (at 70 keV) were 18.6, 16.6, and 10.8 for 30, 35 and 45 cm phantoms, respectively, and 29.1 (at 80 kV), 21.2 (at 80 kV), and 11.5 (at 100 kV) with single energy CT images at the optimal kV. Using HYPR-LR, the optimal CNR of VM images increased to 30.6, 25.4, and 16.5 for the three phantoms, which were higher than the optimal CNR in single energy CT. After HYPR-LR processing, optimal keV of VM images with optimal CNR decreased from 70 keV to 40 keV.

Image noise was substantially reduced for VM images using HYPR-LR, resulting in improvement in iodine CNR at lower keV images. The optimal iodine CNR of VM images was similar to or better than the CNR of single energy CT images scanned with optimal kV.

Noise reduction and CNR improvement in VM images enhance its ability to improve lesion detection or reduce IV contrast dose.

Leng, S, Christner, J, Yu, L, McCollough, C, Application of an Energy Domain Noise Reduction Technique to Virtual Monoenergetic Images: Image Quality Assessment and Comparison with Single Energy CT.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12032998.html