The disclosure provides improvements of resolution and contrast in the field of x-ray imaging by using a line emitting, quasi-monochromatic x-ray source for x-ray fluorescence computed tomography. A particular type of x-ray source suitable for this is a line emitting liquid-jet-anode x-ray source. X-ray fluorescence is obtained using nanoparticles, preferably coated nanoparticles with a metallic core. The x-ray radiation from the x-ray source is shaped and filtered using energy dispersive optics before being delivered to the nanoparticles.