Transmission scanning: a useful adjunct to conventional emission scanning for accurately keying isotope deposition to radiographic anatomy.

In 1952 Mayneord (1) proposed the usefulness of a transmission counter for plotting outlines of organs. Later, he produced images of lead letters by recording the transmitted beam from a Tm170 (84 keV) source which was maintained in direct alignment with the aperture of a scintillation detector during scanning (2, 3). In 1963, Cameron and Sorenson reported use of Am241 (60 keV) and I125 (30 keV) sources to determine bone mineral content by measuring the change in intensity of a transmitted photon beam moved across a bone (4). No clinical application of transmission scanning for forming images of body structures was reported by these authors. We have explored transmission scanning as a means of improving the orientation of the radionuclide emission scan (5). Accurate evaluation of a radionuclide distribution in the body requires that the spatial relationships of emission scan data be oriented to the anatomy of the patient. Usually, data on the scan record are keyed to anatomy either by using reference mark...