Combined imaging detector for simultaneous detection of gamma and x-ray quanta; the combined imaging detector comprising: an x-ray anti-scatter grid; a layer of x-ray scintillator elements for generation of x-ray scintillation light signals in response to detected x-ray quanta; a first photodetector array configured to receive the x-ray scintillation light signals and to convert said x-ray scintillation light signals into a first group of electrical signals; a layer of gamma scintillator elements for generation of gamma scintillation light signals in response to detected gamma quanta; a second photodetector array configured to receive the gamma scintillation light signals and to convert said gamma scintillation light signals into a second group of electrical signals; wherein the x-ray anti-scatter grid, the layer of x-ray scintillator elements, the first photodetector array, the layer of gamma scintillator elements, and the second photodetector array are arranged in a stacked configuration along a radiation-receiving direction; wherein the x-ray anti-scatter grid comprises a plurality of septa (117 A, B, C) that define a plurality of apertures which are configured to collimate both x-ray quanta and gamma quanta received from the radiation receiving direction such that received gamma quanta are collimated only by the x-ray anti-scatter grid; characterised in that the combined imaging detector further comprises a reconstruction unit configured to generate a reconstructed nuclear scintigraphy image from a measured nuclear scintigraphy image comprising a plurality of pixel values, the measured nuclear scintigraphy image being generated based on the second group of electrical signals; and and in that the reconstruction unit is further configured to generate the reconstructed nuclear scintigraphy image by subtracting a reference pixel value from the pixel values in the measured nuclear scintigraphy image. an x-ray anti-scatter grid; a layer of x-ray scintillator elements for generation of x-ray scintillation light signals in response to detected x-ray quanta; a first photodetector array configured to receive the x-ray scintillation light signals and to convert said x-ray scintillation light signals into a first group of electrical signals; a layer of gamma scintillator elements for generation of gamma scintillation light signals in response to detected gamma quanta; a second photodetector array configured to receive the gamma scintillation light signals and to convert said gamma scintillation light signals into a second group of electrical signals; wherein the x-ray anti-scatter grid, the layer of x-ray scintillator elements, the first photodetector array, the layer of gamma scintillator elements, and the second photodetector array are arranged in a stacked configuration along a radiation-receiving direction; wherein the x-ray anti-scatter grid comprises a plurality of septa (117 A, B, C) that define a plurality of apertures which are configured to collimate both x-ray quanta and gamma quanta received from the radiation receiving direction such that received gamma quanta are collimated only by the x-ray anti-scatter grid; characterised in that the combined imaging detector further comprises a reconstruction unit configured to generate a reconstructed nuclear scintigraphy image from a measured nuclear scintigraphy image comprising a plurality of pixel values, the measured nuclear scintigraphy image being generated based on the second group of electrical signals; and and in that the reconstruction unit is further configured to generate the reconstructed nuclear scintigraphy image by subtracting a reference pixel value from the pixel values in the measured nuclear scintigraphy image.