Modeling of a slanted-hole collimator in a compact endo-cavity gamma camera.

Abstract

Having the ability to take an accurate 3D image of a tumor greatly helps doctors diagnose it and then create a treatment plan for a patient. One way to accomplish molecular imaging is to inject a radioactive tracer into a patient and then measure the gamma rays emitted from regions with high-uptake of the tracer, viz., the cancerous tissues. In large, expensive PET- or SPECT-imaging systems, the 3D imaging easily is accomplished by rotating the gamma-ray detectors and then employing software to reconstruct the 3D images from the multiple 2D projections at different angles of view. However, this method is impractical in a very compact imaging system due to anatomical considerations, e.g., the transrectal gamma camera under development at Brookhaven National Laboratory (BNL) for detection of intra-prostatic tumors. The camera uses pixilated cadmium zinc telluride (CdZnTe or CZT) detectors with matched parallel-hole collimator. Our research investigated the possibility of using a collimator with slanted holes to create 3D pictures of a radioactive source. The underlying concept is to take 2D projection images at different angles of view by adjusting the slant angle of the collimator, then using the 2D projection images to reconstruct the 3D image. To do this, we first simulated the response of a pixilated CZT detector to radiation sources placed in the field of view of the camera. Then, we formulated an algorithm to use the simulation results as prior knowledge and estimate the distribution of a shaped source from its 2D projection images. From the results of the simulation, we measured the spatial resolution of the camera as ~7-mm at a depth of 13.85-mm when using a detector with 2.46-mm pixel pitch and a collimator with 60° slant angle.