Jia Wang PhD, Presenter: Nothing to Disclose

Xinhui Duan PhD, Abstract Co-Author: Nothing to Disclose

Shuai Leng PhD, Abstract Co-Author: Nothing to Disclose

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

Kidney stone differentiation is possible with DECT due to differences in the effective atomic number(Zeff) of different stone types. The purpose of this work is to explore the potential of maximizing the ability to distinguish a range of clinically important stone types by using photon-counting(PC) CT detectors.

A virtual 30-cm water phantom was created containing five cylindrical objects (diameter and length=1cm) with Zeff matched to five stone types: uric acid(UA), struvite(STR), cystine(CYS), calcium oxalate monohydrate(COM) and hydroxyapatite(APA). A DECT scanner with energy-integrating detectors was simulated based on a clinical CT system(Definition Flash, Siemens Healthcare) for three DECT scans: 80/140kV, 80/140Sn and 100/140Sn (140Sn indicates tin filtration of the 140kV beam). PC detectors were simulated based on a prototype system design using 1.6mm-thick CdTe detectors and a tube voltage of 140kV. In PC CT, energy bins were selected that resulted in an equal number of photons in each bin. A two-bin ([25-61],[61-140keV]) and four-bin ([25-53],[53-61],[61-77],[77-140keV]) scan were simulated. Images were reconstructed of the linear attenuation coefficients for each tube potential or energy bin. An increase in image noise due to use of fewer photons per bin in PC scan was avoided using a previously published method. The ratio of linear attenuation coefficients (DER) between low and high energy images was calculated for each cylinder. In PC scans, DER was calculated using both bins for the two-bin mode and the two bins with furthest energy separation ([25-53keV] and [77-140keV]) for the four-bin mode.  

For 80/140kV, DERs were 1.13, 1.23, 1.3, 1.46 and 1.6 for UA, STR, CYS, COM and APA, respectively. Adding tin filtration increased the difference between adjacent DERs values (DERs=1.2, 1.34, 1.44, 1.7 and 1.93). In PC CT, the two-bin scan gave similar DER separation as the 80/140Sn conventional detector scan. Using the lowest and highest bins from the four-bin scan, DER separation was increased by 275%-350% between stone types (DERs=1.31, 1.59, 1.8, 2.31 and 2.8). 

PC CT can significantly improve the ability to differentiate multiple types of clinically relevant kidney stones. 

Technological advances to increase spectral separation, whether a tin filter or photon counting detectors, improve the ability to differentiate materials with similar atomic numbers.

Wang, J, Duan, X, Leng, S, McCollough, C, Improved Kidney Stone Differentiation with Use of a Photon-counting Detector-based CT System Relative to an Energy-integrating Detector-based Dual-Energy CT (DECT) System.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043926.html