Abstract: A diagnostic imaging scanner system is provided which includes an arm structure mounted to a support structure for pivotal motion about a substantially horizontal arm axis. A source of radiation directs radiation along a beam path. A detector is mounted on the arm structure in alignment with the beam path and is spaced from the source to accommodate placement of a subject under examination therebetween. During pivotal motion the detector thus moves along an arcuate path which lies in a substantially vertical plane. Means are provided for compensating the gravitational torque experienced about the arm axis during scanning motion. The compensating means includes means for producing a predetermined force and a cam mounted for pivotal motion about a substantially horizontal cam axis which is operatively coupled to the force means for converting the predetermined force to a first torque about the cam axis.