ACCURACY OF CT NUMBERS OBTAINED BY DIRA AND MONOENERGETIC PLUS ALGORITHMS IN DUAL-ENERGY COMPUTED TOMOGRAPHY.

Maria Magnusson,Michael Sandborg,Gudrun Alm Carlsson,Alexandr Malusek,Åsa Carlsson Tedgren,Lilian Henriksson

doi:10.1093/rpd/ncab108

Abstract

Dual-energy computed tomography (CT) can be used in radiotherapy treatment planning for the calculation of absorbed dose distributions. The aim of this work is to evaluate whether there is room for improvement in the accuracy of the Monoenergetic Plus algorithm by Siemens Healthineers. A Siemens SOMATOM Force scanner was used to scan a cylindrical polymethyl methacrylate phantom with four rod-inserts made of different materials. Images were reconstructed using ADMIRE and processed with Monoenergetic Plus. The resulting CT numbers were compared with tabulated values and values simulated by the proof-of-a-concept algorithm DIRA developed by the authors. Both the Monoenergetic Plus and DIRA algorithms performed well; the accuracy of attenuation coefficients was better than about ±1% at the energy of 70 keV. Compared with DIRA, the worse performance of Monoenergetic Plus was caused by its (i) two-material decomposition to iodine and water and (ii) imperfect suppression of the beam hardening artifact in ADMIRE.

Highlights

The ability of computed tomography (CT) to produce information about photon attenuation of imaged objects is widely used in medical diagnostics and radiotherapy planning
This paper aims to evaluate whether there is room for improvement of the Monoenergetic Plus algorithm regarding the accuracy of reconstructed CT numbers
We recall that images reconstructed with ADMIRE at 80 kV and Sn150kV as input to Monoenergetic Plus, and artifacts introduced during the reconstruction process at this stage were further propagated to the virtual monoenergetic images

Summary

Introduction

The ability of computed tomography (CT) to produce information about photon attenuation of imaged objects is widely used in medical diagnostics and radiotherapy planning The latter requires accurate attenuation data to calculate doses delivered during radiotherapy treatments, proton therapy and low-energy brachytherapy. Dual-energy CT, which scans the patient using two different X-ray tube voltages, can suppress the beam hardening artifacts by performing material decomposition. In the Alvarez–Macovski method(4), the decomposition is performed on the projection data This method requires geometrically consistent rays from both low- and high-energy scans, and its use is currently limited to (i) the dual-layer DECT technique(5) available in the IQon Spectral CT (Philips Healthcare) and (ii) the fast kV switching technique(6) available for instance in the Revolution

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