SU‐F‐J‐75: Accuracy and Stability of Electron Density Measurements Across Patient Size Using Dual Energy CT

Abstract

Purpose:Dual energy (DE) CT can be used to characterize tissue composition. One application of DE CT is to measure electron density (ED, rho) and atomic number (Z) for use in radiation therapy treatment planning. This work evaluated the accuracy and stability of ED estimation as patient size varied for both single‐energy (SE) and DE CT.Methods:An ED phantom (CIRS) and four torso‐shaped water tanks (lateral widths 15, 25, 35 and 45 cm) containing 8 tissue‐simulating cylinders of known ED were scanned on a dual‐source CT system (Siemens Somatom Force) in SE (120 kV) and DE (90/150Sn) modes. Additional scans were performed on the 15 and 25 cm water tanks using DE techniques of 70/150Sn and 80/150Sn, respectively. CTDIvol was matched for all SE and DE scans for a given phantom size. Images were reconstructed using quantitative kernels to preserve CT number accuracy. ED was estimated in each test cylinder and in solid and liquid water using calibration measurements acquired in the CIRS phantom (SE) and a Rho‐Z algorithm (DE).Results:ED estimates showed good agreement with the nominal ED values when using Rho‐Z (slope = 1.0051, R2 = 0.9982). Mean percent error was similar between SE (1.21%) and DE (1.28%). Mean deviation across patient size decreased 34% (1.43% with SE, 0.95% with DE). When compared to 90/150Sn, DE techniques of 70/150Sn and 80/150Sn showed mean differences in ED of 0.43% and 0.15%, respectively.Conclusion:While both DE Rho‐Z and SE CT number calibration methods are both accurate for estimating ED, Rho‐Z offers the advantages of having less variability across patient size, not requiring a phantom calibration, and being able to distinguish between materials of similar attenuation, but different chemical composition. Low kV DE pairs are an option in small patients due to lack of effect on ED accuracy.This research was supported by Siemens Healthcare