Technical Note: SpekPy v2.0-a software toolkit for modelling x-ray tube spectra.

Abstract

PURPOSE\nSpekPy is a free toolkit for modelling x-ray tube spectra with the Python programming language. In this article, the advances in version 2.0 (v2) of the software are described, including additional target materials and more accurate modelling of the heel effect. Use of the toolkit is also demonstrated.\n\n\nMETHODS\nThe predictions of SpekPy are illustrated in comparison to experimentally determined spectra: three radiation quality reference (RQR) series tungsten spectra and one mammography spectrum with a molybdenum target. The capability of the software to correctly model changes in tube output with tube potential is also assessed, using the example of a GE RevolutionTM CT scanner (GE Healthcare, Waukesha, WI, USA) and specifications in the system s Technical Reference Manual. Further, we note that there are several physics models available in SpekPy. These are compared on and off the central axis, to illustrate the differences.\n\n\nRESULTS\nSpekPy agrees closely with the experimental spectra over a wide range of tube potentials, both visually and in terms of first and second half-value-layers (within 2% here). The CT scanner spectrum output (normalized to 120 kV tube potential) agreed within 4% over the range of 70 to 140 kV. The default physics model (casim) is adequate in most situations. The advanced option (kqp) should be used if high accuracy is desired for modelling the anode heel-effect, as it it fully includes the effects of bremsstrahlung anisotropy.\n\n\nCONCLUSIONS\nSpekPy v2 can reliably predict on- and off-axis spectra for tungsten and molybdenum targets. SpekPy s open-source MIT license allows users the freedom to incorporate this powerful toolkit into their own projects.