An apparatus for detection of radiation comprising: - at least a first collimator arranged to transmit radiation, emitted from a radiation source, through a first and at least a second slit (104, 105) in a z-direction and prevent radiation in said z-direction apart from through said first and at least second slit, characterised in - a first and at least a second array (101, 102) of at least two radiation detecting elements, the arrays extending in an x-direction, - said radiation detecting elements being semiconductor elements, - each of said radiation detecting elements having a width α in said x-direction, - each of said radiation detecting elements having a length β in a γ-direction, wherein the x-, y-, and z-directions are substantially orthogonal, - said first and at least second slit, for letting through radiation in the z-direction, having a length in said x-direction which is at least as long as the total length of said arrays of radiation detecting elements, - said first and at least second slit having a length in said y-direction which is substantially shorter than said length β of said radiation detecting elements, - said first and at least second array being arranged to be displaced in relation to each other substantially only in the y-direction with a distance substantially equal to β, - said first and at least second slit being arranged to be displaced in relation to each other substantially only in the y-direction with a distance substantially equal to β, and - displacement means arranged to move said collimator and/or said arrays of radiation detecting elements at least in said y-direction. - at least a first collimator arranged to transmit radiation, emitted from a radiation source, through a first and at least a second slit (104, 105) in a z-direction and prevent radiation in said z-direction apart from through said first and at least second slit, characterised in - a first and at least a second array (101, 102) of at least two radiation detecting elements, the arrays extending in an x-direction, - said radiation detecting elements being semiconductor elements, - each of said radiation detecting elements having a width α in said x-direction, - each of said radiation detecting elements having a length β in a γ-direction, wherein the x-, y-, and z-directions are substantially orthogonal, - said first and at least second slit, for letting through radiation in the z-direction, having a length in said x-direction which is at least as long as the total length of said arrays of radiation detecting elements, - said first and at least second slit having a length in said y-direction which is substantially shorter than said length β of said radiation detecting elements, - said first and at least second array being arranged to be displaced in relation to each other substantially only in the y-direction with a distance substantially equal to β, - said first and at least second slit being arranged to be displaced in relation to each other substantially only in the y-direction with a distance substantially equal to β, and - displacement means arranged to move said collimator and/or said arrays of radiation detecting elements at least in said y-direction.