BASIC SCIENCE INVESTIGATIONS Performance Evaluation of a Modular Gamma Camera Using a Detectability Index

The performance of a modular gamma camera for the task of detecting signals in random noisy backgrounds was evaluated experimentally. The results were compared with a theoretical computer simulation. Methods: The camera uses a 10 10 cm thallium-doped sodium iodide crystal, a 2 2 array of 53 53 mm photomultiplier tubes, and a parallel-hole collimator (1.5-mm bore width, 23.6-mm bore length). The camera was positioned to look down into a 10-cm-deep water bath that filled its field of view (FOV). The top surface of the water was 5 cm from the front face of the camera. The camera has 3-mm intrinsic spatial resolution (SR) in the center of its FOV and 9-mm system SR for objects 5 cm below the top surface of the water. Uniform and nonuniform random background data were col-lected by imaging the bath containing 740 MBq (20 mCi) 99mTc. Nonuniformities were created by placing water-filled objects in the bath. Each signal dataset was collected by imaging a water-filled plastic sphere, injected with 99mTc and set at a specific depth (Z) in the bath. Data were collected for many signa