A rectilinear scanner is an imaging device, used to capture emission from radiopharmaceuticals in nuclear medicine.

Before then hand-held detectors had been used to locate radioactive materials in patients, but the Cassen system (designed for Iodine-131) combined a motor driven photomultiplier tube and printing mechanism.

This could be a simple light source over photographic film, dot matrix printer, oscilloscope or television screen.

The detector moves in a raster pattern over studied area of the patient, making a constant count rate.

[11][12] Disadvantages include the very long imaging time (several minutes) due to the need to separately cover each target area, unlike a gamma camera which has a much larger field of view, and the motion artefacts this can result in.