Cynthia H. McCollough, Ph.D.
Although state-of-the-art CT provides accurate sub-millimeter details of the size and location of renal stones, current routine clinical image analysis does not differentiate stone composition. Previous attempts to predict stone composition using spiral CT were based on the analysis of CT attenuation values. However, the CT value approach to predict stone composition is not yet robust or reliable enough to be used as a routine clinical application. An alternative is a dual-energy CT (DECT) technique, which is based on the difference in x-ray attenuation properties between stones of differing chemical compositions.
Dual-source CT allows simultaneous high spatial resolution acquisition of dual-energy CT data. Commercial three-material decomposition algorithms, as well as novel algorithms developed in our lab, have demonstrated the ability to discriminate, for example, between uric acid and non-uric acid stone types in an anthropomorphic phantom under clinical conditions. For stones larger than 3 mm in size, the evaluated dual-energy algorithm demonstrated 100% accuracy of UA vs. non-UA discrimination under all conditions. For stones smaller than 3 mm in size, the accuracy of the DECT approach was at least 92%. Thus, DECT fills an important clinical need for non-invasively identifying UA stones on abdominal CT scans, the predominant tool used to diagnose and stage renal stones.
The Imaging Core provides 4 key functions in support of this Urology O'Brien Center for Nephrolithiasis Research. These functions directly support Project 1 and Project 2, although they may also be of value for pilot projects initiated during later years of the Center's activities:
- Dual-energy CT scanning of ex-vivo specimens in or patients;
- Dual-energy material decomposition analysis to determine stone type;
- High-spatial resolution image reconstruction and analysis to determine stone volume; and
- Coordination of micro-CT scanning and data analysis with Dr. Jim Williams, of Indiana University.