A Rotational Modulator (RM) gamma ray imager, consisting of a single grid of lead slats rotating above an array
of detectors with diameter equal to the slat spacing, has the capability of providing angular resolution significantly
better than the geometric resolution (i.e., the ratio of detector diameter to mask/detector separation). The
sensitivity, weight, and angular resolution are comparable to that of a coded aperture device, but with significantly
less complexity. As the grid rotates, the transmission from a source is modulated on each detector between 0 and
100%. The count profile is cross-correlated with precalculated modulation profiles to produce an approximate
source image. Deconvolution of this image with the known imager response can accurately resolve point sources
and complex emissions. The appropriate deconvolution technique can achieve angular resolution better than
the basic geometrical resolution of the instrument. A prototype RM developed at Louisiana State University
features high sensitivity and energy resolution, functional angular resolution of 15, and a simple readout system.
The detector array consists of 19 1.5 × 1 thick cerium-doped lanthanum bromide (LaBr<sub>3</sub>:Ce) crystals. LaBr3
produces significantly more light than other common scintillators, offering < 3% FWHM energy resolution at 662
keV. A grid spaced ~1.2 m from the detection plane with slat width 1.5 offers a 13.8° field of view. We present
our reconstruction technique, deconvolution algorithms, and simulated and experimental imaging results.