Izuru Matsuda MD, Presenter: Nothing to Disclose

Masaaki Akahane MD, Abstract Co-Author: Nothing to Disclose

Jiro Sato MD, Abstract Co-Author: Nothing to Disclose

Akira Kunimatsu MD, Abstract Co-Author: Nothing to Disclose

Kosuke Sasaki MS, Abstract Co-Author: Employee, General Electric Company

Koji Segawa RT, Abstract Co-Author: Employee, General Electric Company

Kuni Ohtomo MD, Abstract Co-Author: Nothing to Disclose

To compare dual energy computed tomography (CT) spectral imaging and conventional CT imaging in terms of precision of the measurement of CT numbers by a phantom study.

A 15 cm circular phantom (CP) with circularly arranged drill-holes of 1 cm in diameter and a 33 x 22 cm elliptic phantom (EP) with 2 drill-holes positioned at the center and 15cm-periphery along the long axis were used. The drill-holes were filled with iodine contrast media solutions at concentrations of 0, 1.875, 3.75, 7.5, 15 mgI/ml. Scans were acquired with a 64 slice CT system (Discovery CT 750HD; GE Healthcare, Milwaukee, Wisconsin). Conventional CT examination was performed with 120 kVp tube voltage. Simulated monochromatic images at 65 keV were obtained by dual energy CT spectral imaging with fast kVp switching between 80 kVp and 140 kVp. Each CT number for the iodine solutions was measured by placing a round region of interest. Linear regression model was used to evaluate linearity. Variability of the CT numbers associated with phantom shape in each imaging method was investigated with analysis of covariance.

All the correlation coefficients of linear regression between iodine concentration levels and CT numbers measured in each condition were above 0.999. While CT numbers for water density were approximately 0 HU (Mean and standard deviation were 0.50 +- 2.27), those for 15mgI/ml iodine solution were 406.79 HU, 328.66 HU, 345.99 HU, 431.85 HU, 405.83 HU and 413.55 HU for conventional imaging of CP, EP center, EP periphery, simulated monochromatic imaging of CP, EP center and EP periphery, respectively. With conventional imaging, slopes of the regression lines for CT numbers measured in EP center and EP periphery were significantly lower than that of CP (p < 0.0001 for both EP center vs CP and EP periphery vs CP). The slopes were not significantly different among each other with dual energy imaging.

CT numbers considerably varied depending on the shape of the phantoms in conventional CT imaging, whereas dual energy CT spectral imaging provided consistent CT numbers in any phantoms.

Dual energy CT spectral imaging may achieve accurate CT number measurement without any harmful effect from shape and distribution of surroundings in vivo.

Matsuda, I, Akahane, M, Sato, J, Kunimatsu, A, Sasaki, K, Segawa, K, Ohtomo, K, Precision of the Measurement of CT Numbers: Comparison of Dual-Energy CT Spectral Imaging with Fast kVp Switching and Conventional CT.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9005869.html