USB-based Data Acquisition and Control System for High Speed Gamma-ray Tomography

B.T. Hjertaker, R. Maad, O.A. Almås and G.A. Johansen

Department of Physics and Technology, University of Bergen, Allégaten 55, N-5007 Bergen, Norway.

E-mail: bjorn.hjertaker@ift.uib.no

ABSTRACT

A USB-based data acquisition and control (DAC) system for high speed gamma-ray tomography has been designed and implemented at the Department of Physics and Technology, University of Bergen (UoB). The high speed gamma-ray tomograph at UoB comprises five 500 mCi 241Am gamma-ray sources, each at a principal energy of 59.5 keV, which corresponds to five detector modules, each consisting of 17 CdZnTe detectors. The USB-based DAC is designed using the Microchip PIC18F4455 microcontroller, which has a USB (Universal Serial Bus) interface controller incorporated. Previously the DAC for this tomograph was based on a conventional digital I/O-board using the PCI interface bus. By implementing a USB-based DAC, a higher data acquisition rate is obtained, but most importantly, no dedicated hardware installation is required for the data acquisition computer, assuming it is already equipped with a standard USB port. In addition, the USB-based DAC improves computer platform versatility, thereby simplifying tomograph research software developments. The API (Application Programming Interface) of the USB-based DAC is founded on the National Instrument’s LabVIEW graphical development tool. A dedicated LabVIEW data acquisition VI (Virtual Instrument) has been developed which includes readout of high speed gamma-ray tomograph measurement data. The availability of the LabVIEW API VI provides a simple and robust foundation for further software developments for the tomograph. The data acquisition interval, i.e. the integration time, of the high speed gamma-ray tomograph is user selectable, and is a function of the required statistical measurement accuracy. Using the USB-based DAC, the shortest data acquisition interval, i.e. the time to measure and communicate one tomograph measurement frame through to the reconstruction unit, is 7 ms when a 5 ms integration time is used. Initial results using the high speed gamma-ray tomograph equipped with the USB-based DAC on a polypropylene phantom, is presented in the paper.

Keywords High speed gamma-ray tomograph, data acquisition and control, USB interface protocol, LabVIEW API