Speaker
Prof.
Wolfgang Treimer
(University of Applied Sciences - Beuth Hochschule für Technik Belin)
Description
One of the most important parameters in imaging (neutron, X-ray, etc,) is the determination of spatial resolution of the used system. Various methods may yield different results sometimes, mainly due to lack of agreement in standards of measurement. A simple and direct measurement can be achieved with the "Siemens star" [1]. Another, very commonly accepted method is the determination of the modulation transfer function (MTF) of an imaging system [2]. The MTF can be directly measured, as the image contrast as a function of spatial frequency of absorbing grids having increasing numbers of line pairs/unit length. Usually such absorbing grids are not easily available for thermal or cold neutrons. Moreover, they have different disadvantages, such as finite transparency or absorption and also they have to be adapted to the system under investigation, i.e. they do not cover the frequency range continuously.
Using polarized neutrons one can produce a fringe pattern due to path length-dependent depolarization of a neutron spin by traversing a magnetic field of a coil. Changing the current in a coil one can tune, i.e. increase or decrease the number of line pairs/unit length and thus measure the "magnetic" MTF (MMTF) of the imaging system [3]. We compared the MMTF - results of coils with different shapes (circle, quadratic, triangle, rhomboid) with the MTF yielded with straight edge measurements and with those, where a constant fringe pattern was moved vertically in steps of 50µm and the corresponding change of gray values in a pixel line was measured. Further, the spatial resolution was measured for different distances of a coil (110mm, 150mm and 170mm) from the detector. Thus, one get realistic values for the expected spatial resolution of a sample, measured at these distances.
References
[1] E.H. Lehmann, G. Frei, G. Kühne, P. Boillat, Nucl. Instr.& Meth. A 576 (2007) 389–396
[2] A. Kuhls-Gilcrist, A. Jain, D.l R. Bednarek, K. R. Hoffmann, S. Rudin , Med. Phys. 37, 2, p724-735 (2010)
[3] W. Treimer, O. Ebrahimi, N. Karakas, R Köhler, W. Vollmann, Nucl. Instr. & Meth. A, in preparation)
Primary author
Prof.
Wolfgang Treimer
(University of Applied Sciences - Beuth Hochschule für Technik Belin)
Co-authors
Dr
Indu Dhiman
(Helmholtz Zentrum Berlin Wannsee)
Mr
Köhler Ralf
(Univeristy of Applied Sciences- Beuth Hochschule für TechnikBerlin)
Mr
Nursel Karakas
(Univesity of Applied Sciences- Beuth Hochschule für Technik Berlin)
Mr
Omid Ebrahimi
(Helmholtz Zentrum Berlin Wannsee)
