Torsten Diekhoff, Presenter: Nothing to Disclose

Kay-Geert A. Hermann MD, Abstract Co-Author: Nothing to Disclose

Dual energy computed tomography (DE-CT) is an emerging imaging technique in musculoskeletal radiology. However, until now it is restricted to dual source scanners. We used phantom measurements to prove the feasibility of single source DE-CT of the extremities using a volume scan mode in single source dual energy technique. In addition, we for the first time wanted to determine which concentrations of monosodium urate (MSU) in gout and calcium pyrophosphate (CP) in pseudogout are needed to detect or distinguish these soft tissue depositions.

We prepared a descending order of concentrations of MSU and CP in ultrasound gel to equip a hand shaped plastic phantom. Dual energy imaging was performed with a standard 320­row CT scanner (Aquilion ONE, Toshiba medical systems, Japan) in two volumes with 135 and 80 kV tube voltage, respectively. Scans were performed with 15 / 90 mA (lower dose) and 100 / 570 mA (higher dose). We calculated the dual energy gradient using linear regression analysis. 60 samples of MSU and CP in different concentrations were scored by three blinded readers with a proprietary dual energy software to determine specificity and sensitivity of this method. Receiver operating characteristics (ROC) analysis was done to determine the diagnostic power.

The DE gradient was calculated 1.020 ± 0.006 for MSU and 0.673 ± 0.001 for CP. The randomized phantom scans indicate a reliable detection of MSU at concentrations of 12.5 % or higher and of CP at 6.25 % or higher in a phantom scan. This corresponds to crystal depositions with 59.8 HU for MSU and 48.2 HU for CP, respectively. The sensitivity for MSU ranged from 83.3 to 97.3 at lower and from 86.7 to 97.3 at higher tube current. Specificity was 96.7% to 100% in lower and 100% in higher dose scans. In ROC analysis the area under the curve for MSU ranged from 0.867 to 0.947 at lower dose and from 0.867 to 0.919 at higher dose CT and for CP from 0.659 to 0.745 and 0.718 to 0.750, respectively.

This phantom study shows that single source DE-CT is capable to distinguish crystal depositions in soft tissues at relatively low concentrations.

Single source DECT may develop to a reasonable alternative for dual source systems. Further investigations have to prove its applicability in patients and its benefits in diagnostic imaging and therapy monitoring.

Diekhoff, T, Hermann, K, Single Source Dual Energy Computed Tomography in Soft Tissue Crystal Depositions - First Experience in a Phantom Study.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14010930.html