Aleksandr Kivenson PhD, Presenter: Employee, Gamma Medica, Inc

Timothy Garcia PhD, Abstract Co-Author: Employee, Gamma Medica, Inc

Haris Kudrolli PhD, Abstract Co-Author: Employee, Gamma Medica, Inc

Available scientific literature on collimator design for gamma cameras generally presupposes that the camera functions by means of scintillating crystals and photodetectors. However, recent advances in direct-conversion detectors using semiconductors like cadmium-zinc-telluride (CZT) have made it desireable to design collimators specifically for cameras built from such detectors. These detectors present new constraints on collimator design; specifically, they consist of fixed-size pixels in a square array. Here we present algorithms for designing collimators registered to an array of pixels, the results of computer simulations of various collimator designs, and examples of real-world performance for registered collimators.

Computer simulations were guided by first-order calculations and carried out using custom software as well as the GATE and Geant4 software packages. Collimators were fabricated from tungsten by electrical discharge machining and also by photochemical etching. Gamma cameras from a LumaGEM DC-MBI system were used for imaging experiments.

We have derived equations defining the set of optimal collimators given a pixel size and the collimator material. These collimators have the maximal sensitivity for their resolution while obeying the University of Chicago Penetration Criterion for septal thickness. A collimator has been designed and fabricated in accordance with these equations. We have also investigated the effect of septal penetration on image quality in simulations and in experiments, in order to determine whether a collimator with thinner septa than those called for by the University of Chicago Penetration Criterion may be used in order to obtain improved sensitivity without a significant loss of image quality.

The collimator we have designed has resolution and sensitivity in agreement with our equations. We expect that it will be better than existing collimators for clinical applications. We have quantified septal penetration in this collimator and compared it to values predicted by simulations; future collimators with thinner septa may be possible.

Imaging devices using pixellated direct-conversion gamma ray cameras are poorly served by conventional hexagonal collimators. Lower patient dose is possible with registered square-hole collimators.

Kivenson, A, Garcia, T, Kudrolli, H, Registered Collimator Design for Direct-Conversion Gamma Cameras.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14014494.html