A combined detector comprising a gamma radiation detector and an X-ray radiation detector ; the gamma radiation detector comprising: a gamma scintillator array (101 x,y ) comprising a plurality of first scintillator elements (101 1,1 , 101 2,1 ) for generating first scintillation light in response to received gamma quanta; an optical modulator ; and a first photodetector array (103 a,b ) for detecting the first scintillation light generated by the gamma scintillator array (101 x,y ); wherein the gamma scintillator array (101 x,y ), the optical modulator and the first photodetector array (103 a,b ) are arranged in a stacked configuration along a gamma radiation receiving direction ; and wherein the optical modulator is disposed between the gamma scintillator array (101 x,y ) and the first photodetector array (103 a,b ) for modulating a transmission of the first scintillation light between the gamma scintillator array (101 x,y ) and the first photodetector array (103 a,b ); wherein the optical modulator comprises at least one optical modulator pixel, the optical modulator pixel having a cross sectional area in a plane that is perpendicular to the gamma radiation receiving direction ; wherein the first photodetector array (103 a,b ) comprises a plurality of photodetector pixels (103 1,1 , 103 2,1 ), each photodetector pixel having a cross sectional area (103' a,b ) in the plane that is perpendicular to the gamma radiation receiving direction ; wherein the cross sectional area of each optical modulator pixel is greater than or equal to the cross sectional area of each photodetector pixel (103' a,b ); and wherein the X-ray radiation detector is disposed along the gamma radiation receiving direction and on the opposite side of the gamma scintillator array (101 x,y ) to the first photodetector array (103 a,b ). a gamma scintillator array (101 x,y ) comprising a plurality of first scintillator elements (101 1,1 , 101 2,1 ) for generating first scintillation light in response to received gamma quanta; an optical modulator ; and a first photodetector array (103 a,b ) for detecting the first scintillation light generated by the gamma scintillator array (101 x,y ); wherein the gamma scintillator array (101 x,y ), the optical modulator and the first photodetector array (103 a,b ) are arranged in a stacked configuration along a gamma radiation receiving direction ; and wherein the optical modulator is disposed between the gamma scintillator array (101 x,y ) and the first photodetector array (103 a,b ) for modulating a transmission of the first scintillation light between the gamma scintillator array (101 x,y ) and the first photodetector array (103 a,b ); wherein the optical modulator comprises at least one optical modulator pixel, the optical modulator pixel having a cross sectional area in a plane that is perpendicular to the gamma radiation receiving direction ; wherein the first photodetector array (103 a,b ) comprises a plurality of photodetector pixels (103 1,1 , 103 2,1 ), each photodetector pixel having a cross sectional area (103' a,b ) in the plane that is perpendicular to the gamma radiation receiving direction ; wherein the cross sectional area of each optical modulator pixel is greater than or equal to the cross sectional area of each photodetector pixel (103' a,b ); and wherein the X-ray radiation detector is disposed along the gamma radiation receiving direction and on the opposite side of the gamma scintillator array (101 x,y ) to the first photodetector array (103 a,b ). <EOS>