Abstract: An apparatus for measuring the nonuniform attenuation caused by a patient's body in scintillation cameras is disclosed. The apparatus comprises a gantry having an annular support, a radiation source mounted on the annular support for emitting a radiation which is incident on the patients body, a dedicated radiation detector mounted on the annular support in opposed relation to the radiation source for detecting the radiation transmitted through the patient's body and a mechanism for rotating the annular support around the patient's body. The annular support defines at the center a cylindrical space where the patient's body is located along the longitudinal axis of the cylindrical space. The radiation source and radiation detector are rotated by 180 degrees around the longitudinal direction of the patients body while the radiation source scans the patient in the transversal direction such that the radiation attenuation in all directions around the patient's body can be measured.