Lukas Havla, Presenter: Nothing to Disclose

Michael Peller DPhil, Abstract Co-Author: Nothing to Disclose

Konstantin Nikolaou MD, Abstract Co-Author: Speakers Bureau, Siemens AG Speakers Bureau, Bracco Group Speakers Bureau, Bayer AG

Maximilian F. Reiser MD, Abstract Co-Author: Nothing to Disclose

Olaf Dietrich PhD, Abstract Co-Author: Nothing to Disclose

The transformation of DECT attenuation data into polar coordinates exhibits the potential to improve tissue visualization and material decomposition.

Dual-energy computed-tomography (DECT) allows for patient examination with two different x-ray spectra at the same time. Thereby, independent data on material-specific attenuation properties are obtained. The separate evaluation of both datasets can be difficult and non-conclusive; particularly, for DECT data with contrast media enhancement, material decomposition in the relevant scale of ±200 HU is challenging due to similar attenuation coefficients of calcium and iodine. We hypothesize that the transformation of dual-energy data into polar coordinates can ease analysis and help to distinguish between concentration and kind of matter.

Given two corresponding DECT images, first, the attenuation values (ai(U1), ai(U2)) in Hounsfield units (HU) of both energies (U1, U2) are displayed as scatter plot in Cartesian coordinates for all voxels i. Then, the polar coordinate transformation is applied; i. e., the distance, ri, of every data point (ai(U1), ai(U2)) to the coordinate origin and the angle, φi, to the abscissa is calculated. Depending on the examined tissues and/or materials, different characteristic polar angles can be observed in the spectrum-like scatter plot of (ri, φi). For example, typical polar angles for fat, calcium, and iodine-based contrast agent are -125°, 62°, and 71°, respectively. Alternatively, it is possible to display the parameter map φ(x,y) (x,y: coordinates in image space) which allows assessing the spatial distribution of specific materials in an image with preserved anatomic and morphologic structure and details.  

The advantage of our method is the possibility to display the energy dependence of the attenuation coefficient in a function of a single variable (polar angle φ) which contains the additional relevant information on material attenuation. Material decomposition becomes possible by selecting only data corresponding to certain polar angles.

Havla, L, Peller, M, Nikolaou, K, Reiser, M, Dietrich, O, Material Decomposition of Dual-energy Computed-tomography Data Using Polar Coordinates.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13044202.html