A Dual Modality Gamma Camera Using ${\rm LaCl}_{3}({\rm Ce})$ Scintillator

Portable gamma-ray imaging devices capable of responding to a broad energy range while providing reasonable angular resolution and efficiency are useful in a number of applications, including environmental remediation and industrial surveys. Due to this, a dual radiation imaging system that combines the advantages of a multi-aperture mechanical collimator with electronic-collimation has been designed, built, and tested. The combination of these two disparate imaging modalities offers both efficiency and good angular resolution, and is unique since a single gamma ray can contribute information to both modalities simultaneously. The dual modality gamma camera (DMGC) combines a high-resolution uniformly redundant array (URA) coded aperture with a Compton scatter camera to provide a broader range of energy response suitable for a wider range of industrial applications. The LaCl₃(Ce) in the first detector module has 22times22 voxels, each voxel having a dimension of 2times2times5 mm³. The LaCl₃(Ce) in the second detector module has 6times6 voxels having dimensions of 4times4times10 mm³. Both scintillators are coupled to position-sensitive photomultiplier tubes (PSPMT). The front-end, peak detection and coincident circuits of the DMGC are custom-designed for simplicity and compactness. Point and simulated ring radiation sources at intermediate energies (356 and 662 keV) are measured for mechanical, electronic and dual collimation and the reconstructed images are compared. The results show that the combined dual collimation image, using the maximum likelihood method for image reconstruction, yields better images than either a mechanical or an electronic collimation image at intermediate energies.