A spatial registration apparatus comprising: a probe comprising a gamma-ray probe or an imaging gamma-ray camera; a camera rigidly connected with and spatially registered to the probe; a fiducial marker with well-defined measurement affixed to an object of interest; and at least one processor operatively coupled with a memory and the camera, the memory having instructions for execution by the at least one processor configured to: identify the fiducial marker in a field of view of the camera by using an image of the fiducial marker captured by the camera; use an apparent shape of the fiducial marker to determine a first spatial position and orientation of the camera with respect to the fiducial marker, transform the first spatial position and orientation of the camera with respect to the fiducial marker into a first position and orientation of the probe with respect to the fiducial marker, as the camera is spatially registered to the probe, associate first radiation count data from the probe with the first spatial position and orientation of the probe with respect to the fiducial marker to create first spatially registered radiation count data, use the apparent shape of the fiducial marker to determine a second spatial position and orientation of the camera with respect to the fiducial marker, transform the second spatial position and orientation of the camera with respect to the fiducial marker into a second position and orientation of the probe with respect to the fiducial marker, as the camera is spatially registered to the probe, associate second radiation count data from the probe with the second spatial position and orientation of the probe with respect to the fiducial marker to create second spatially registered radiation count data, and construct a three-dimensional distribution of a source inducing radiation count data in the probe with respect to the fiducial marker using the first spatially registered radiation count data and the second spatially registered radiation count data. a probe comprising a gamma-ray probe or an imaging gamma-ray camera; a camera rigidly connected with and spatially registered to the probe; a fiducial marker with well-defined measurement affixed to an object of interest; and at least one processor operatively coupled with a memory and the camera, the memory having instructions for execution by the at least one processor configured to: identify the fiducial marker in a field of view of the camera by using an image of the fiducial marker captured by the camera; use an apparent shape of the fiducial marker to determine a first spatial position and orientation of the camera with respect to the fiducial marker, transform the first spatial position and orientation of the camera with respect to the fiducial marker into a first position and orientation of the probe with respect to the fiducial marker, as the camera is spatially registered to the probe, associate first radiation count data from the probe with the first spatial position and identify the fiducial marker in a field of view of the camera by using an image of the fiducial marker captured by the camera; use an apparent shape of the fiducial marker to determine a first spatial position and orientation of the camera with respect to the fiducial marker, transform the first spatial position and orientation of the camera with respect to the fiducial marker into a first position and orientation of the probe with respect to the fiducial marker, as the camera is spatially registered to the probe, associate first radiation count data from the probe with the first spatial position and orientation of the probe with respect to the fiducial marker to create first spatially registered radiation count data, use the apparent shape of the fiducial marker to determine a second spatial position and orientation of the camera with respect to the fiducial marker, transform the second spatial position and orientation of the camera with respect to the fiducial marker into a second position and orientation of the probe with respect to the fiducial marker, as the camera is spatially registered to the probe, associate second radiation count data from the probe with the second spatial position and orientation of the probe with respect to the fiducial marker to create second spatially registered radiation count data, and construct a three-dimensional distribution of a source inducing radiation count data in the probe with respect to the fiducial marker using the first spatially registered radiation count data and use the apparent shape of the fiducial marker to determine a second spatial position and orientation of the camera with respect to the fiducial marker, transform the second spatial position and orientation of the camera with respect to the fiducial marker into a second position and orientation of the probe with respect to the fiducial marker, as the camera is spatially registered to the probe, associate second radiation count data from the probe with the second spatial position and orientation of the probe with respect to the fiducial marker to create second spatially registered radiation count data, and construct a three-dimensional distribution of a source inducing radiation count data in the probe with respect to the fiducial marker using the first spatially registered radiation count data and the second spatially registered radiation count data.