Experimental test-object study of electronically collimated SPECT.

The imaging performance of a prototype electronically collimated single-photon emission computed tomography (SPECT) camera comprising a unique 4 x 4 germanium detector backed by an uncollimated scintillation camera has been evaluated. Three-dimensional images of cylindrical test-objects containing either 99mTc (140 keV) or 137Cs (662 keV) are reported. Electronically collimated counts were acquired from the objects rotated to 20 or 40 angular positions in front of the germanium detector to simulate a cylindrical scanning system. For comparison, mechanically collimated data were also acquired from the test-objects. The SPECT images show a slightly better resolution for mechanical over electronical collimation (1.3 +/- 0.25 cm mechanical, 1.5 +/- 0.25 cm electronical at 140 keV; 1.5 +/- 0.25 cm mechanical, 1.7 +/- 0.25 cm electronical at 662 keV). The equi-resolution sensitivity, however, was deduced to be approximately an order of magnitude higher with electronic collimation to image a head-sized object using 99mTc. In addition, the sensitivity gain increases with increasing energy, suggesting the unique potential of electronic collimation in high-energy SPECT.