Design of a selectable pinhole module for use in adaptive SPECT collimators

We present a module for the real-time control of gamma-camera pinhole apertures. The mechanical design includes the ability to rapidly select between an array of pinhole diameters and pinhole states (whether open or shuttered). This is achieved through the use of a wheel with multiple pinhole bores configured with the same entrance angles. Control of the module is via wireless Arduino using either Bluetooth or Wi-Fi to avoid wiring trailing from the system. Modulation of the aperture can either be done via manual control by the user, or through an automated routine integrated into the data acquisition code. Since we can control pinhole diameter, as well as the number and position of pinholes that are open in a multi-pinhole configuration, system resolution and sensitivity are dynamic variables that we can change for each individual acquisition (based on a priori information or a scout scan). The integration of these modules into the gamma ray camera is discussed, including the drive mechanism used to achieve the rotary motion and an opto-interrupter module used to obtain feedback for reproducible positioning. Two applications are discussed: apertures for clinical gamma cameras, and apertures for a dedicated brain imaging system.