A data acquisition and control system for high-speed gamma-ray tomography

Abstract

A data acquisition and control system (DACS) for high-speed gamma-ray tomography based on the USB (Universal Serial Bus) and Ethernet communication protocols has been designed and implemented. The high-speed gamma-ray tomograph comprises five 500 mCi 241 Am 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 DACS design is based on Microchip's PIC18F4550 and PIC18F4620 microcontrollers, which facilitates an USB 2.0 interface protocol and an Ethernet (IEEE 802.3) interface protocol, respectively. By implementing the USB-and Ethernet-based DACS, a sufficiently high data acquisition rate is obtained and no dedicated hardware installation is required for the data acquisition computer, assuming that it is already equipped with a standard USB and/or Ethernet port. The API (Application Programming Interface) for the DACS is founded on the National Instrument's LabVIEW R graphical development tool, which provides a simple and robust foundation for further application 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 statistical measurement accuracy required for the specific application. The bandwidth of the DACS is 85 kBytes s −1 for the USB communication protocol and 28 kBytes s −1 for the Ethernet protocol. When using the iterative least square technique reconstruction algorithm with a 1 ms integration time, the USB-based DACS provides an online image update rate of 38 Hz, i.e. 38 frames per second, whereas 31 Hz for the Ethernet-based DACS. The off-line image update rate (storage to disk) for the USB-based DACS is 278 Hz using a 1 ms integration time. Initial characterization of the high-speed gamma-ray tomograph using the DACS on polypropylene phantoms is presented in the paper.

Dynamic characterization of a high speed gamma-ray tomograph

“…The output from the comparator of the SCA is further input to a digital counter circuit, which facilitates userprogrammable counting intervals via the data acquisition and control unit. This stage also includes the detector interface electronics for the data acquisition and control unit [6].…”

“…a tomogram, requires: 85 detectors * 24 bit per detector = 255 bytes, and the complete timing requirements of the HSGT DACS interface is presented in [6]. The dynamic characterization of the CompactRIO-based DACS system for the HSGT shows that the data acquisition and control time, i.e.…”

“…Characterization of the ILST reconstruction algorithm applied on polypropylene phantoms has demonstrated that the iterative calculation will have its minimum RMSE after approximately five to eight iterations, dependent on phantom geometry [6]. In this work the ILST algorithm has therefore been implemented using eight iterations.…”

“…The HSGT is therefore designed with focus on high temporal resolution rather than high spatial resolution. Considering the hydrocarbon gas-liquid flow application, significant measurement uncertainty can be tolerated, and the tomograph is not limited by a specific statistical measurement error [6].…”

“…This system is also based on FPGAs and has a reported data frame rate of up to 250 kHz [9]. Furthermore, a data acquisition and control interface based on the standard USB and Ethernet protocols has been developed for the HSGT at University of Bergen [6]. The design is based on Microchip microcontrollers, and the obtained data acquisition and control time of the USB and Ethernet interface is 3 ms and 9 ms, respectively.…”