Virtual contouring for transmission scanning in spect and pet studies

A method of diagnostic imaging using a nuclear medicine gamma camera, the method comprising:

• (a) placing a subject in a subject receiving aperture;
• (b) injecting the subject with a radiopharmaceutical;
• (c) positioning a plurality of radiation sources and corresponding radiation detector heads about the subject receiving aperture such that the radiation sources are across the subject receiving aperture from their corresponding radiation detector heads;
• (d) obtaining a contour of the subject disposed in the subject receiving aperture;
• (e) detecting radiation emitted by the injected radiopharmaceutical using the plurality of radiation detector heads;
• (f) calculating the position of virtual lines extending from each radiation source to an edge of a radiation receiving face disposed on each corresponding radiation detector head;
• (g) shifting the detector heads laterally such that the virtual lines are tangent to the contour of the subject;
• (h) transmitting radiation from the radiation sources toward the corresponding radiation detector heads positioned across the subject receiving aperture;
• (i) detecting radiation transmitted by the radiation sources using one of the plurality of radiation detectors;
• and
• (j) reconstructing the detected transmission and emission radiation into a volumetric image representation.

A nuclear camera system comprising:

• a rotating gantry which defines a subject receiving aperture;
• a plurality of real radiation detector heads movably attached to the rotating gantry, said real detector heads rotating about the subject receiving aperture with rotation of the rotating gantry about an axis of rotation;
• a plurality of radiation sources mounted to the plurality of real detector heads for rotation with the rotating gantry, such that transmission radiation from the radiation sources is directed toward and received by the corresponding real detector heads positioned across the subject receiving aperture from the plurality of radiation sources;
• a plurality of virtual detector heads, said virtual detector heads imposing shift restrictions on the real detectors heads during rotation about the subject receiving aperture;
• a rotational drive which rotates the real detector heads around the subject receiving aperture;
• a plurality of translational drives which translate independently the plurality of real detector heads at least one of laterally and radially with respect to the subject receiving aperture;
• an orbit memory which stores a predefined contour of a subject disposed in the subject receiving aperture;
• a shift calculator which calculates shifts in the real detector heads according to the predefined contour of the subject and the shift restrictions imposed by the virtual detector heads;
• and
• a motor orbit controller which controls the translational and rotational drives in response to commands from the shift calculator.

A method of controlling a nuclear camera which includes a rotating gantry on which at least first and second detector heads are mounted, the first detector head carrying an offset transmission radiation source that projects a fan beam of transmission radiation to the second detector head, the fan beam extending between edge rays, a rotating drive which rotates the rotating gantry continuously or in steps, a radial drive which moves the detector heads in a radially inward direction toward a center of rotation of the rotating gantry and a radially outward direction away from the center of rotation, and a lateral drive which moves the detector heads with a component of motion orthogonal to the radially inward and outward directions, the method comprising:

• positioning a subject on a subject support with a region of interest at the center of rotation;
• calculating a clearance offset orbit around and displaced from the subject and the subject support;
• calculating a subject orbit around the region of interest;
• injecting the subject with a radiopharmaceutical;
• controlling the rotating drive and the radial drive such that the detector heads are maintained tangent to the clearance offset orbit as the detector heads are rotated around the subject;
• and
• controlling the lateral drive such that one of the fan beam edge rays is maintained tangent to the subject orbit as the detector heads rotate.