Proc. SPIE. 7306, Optics and Photonics in Global Homeland Security V and Biometric Technology for Human Identification VI
KEYWORDS: Imaging systems, Sensors, Calibration, Crystals, Field programmable gate arrays, Personal digital assistants, Gamma radiation, Data communications, Signal detection, Global Positioning System
The GE Intelligent Personal Radiation Locator (IPRL) system consists of multiple hand held radiation detectors and a
base station. Each mobile unit has a CZT Compton camera radiation detector and can identify isotopes and determine the
direction from which the radiation is detected. Using GPS and internal orientation sensors, the system continuously
transforms all directional data into real-world coordinates. Detected radiation is wirelessly transmitted to the base station
for system-wide analysis and situational awareness. Data can also be exchanged wirelessly between peers to enhance the
overall detection efficiency of the system. The key design features and performance characteristics of the GE IPRL
system are described.
The output response characteristics of an X-ray photon counting detector are measured experimentally and
simulated using a Monte Carlo method in order to quantify the loss of statistical information due to pile-up. The
analysis is applied to idealize counting detector models, but is adaptable to realistic event processing that is not
amenable to analytic solution. In particular, the detective quantum efficiency (DQE) is calculated as a function of flux
rate and shown to have an intermediate zero for the paralyzable case at the maximum periodic rate. The progressive
degradation of the spectral response as a function of increasing flux rate is also modeled. Analogous metrics to DQE
are defined in regards to the detector's ability to resolve atomic number and enhance image contrast based on atomic
number differentiation. Analytic solutions are provided for the output and linearized response statistics and these
interpolate well across the Monte Carlo and experimental results.
A 4π direction-sensitive gamma imager is presented, using a 1 cm<sup>3</sup> 3D CZT detector from Yinnel
Tech and the RENA-3 readout ASIC from NOVA R&D. The measured readout system electronic noise is
around 4-5 keV FWHM for all anode channels. The measured timing resolution between two channels
within a single ASIC is around 10 ns and the resolution is 30 ns between two separate ASIC chips. After
3D material non-uniformity and charge trapping corrections, the measured single-pixel-event energy
resolution is around 1% for Cs-137 at 662 keV using a 1 cm<sup>3</sup> CZT detector from Yinnel Tech with an 8 x 8
anode pixel array at 1.15 mm pitch. The energy resolution for two pixel events is 2.9%. A 10 uCi Cs-137
point source was moved around the detector to test the image reconstruction algorithms and demonstrate
the source direction detection capability. Accurate source locations were reconstructed with around 200
two-pixel events within a total energy window ±10 keV around the 662 keV full energy peak. The angular
resolution FWHM at four of the five positions tested was between 0.05-0.07 steradians.
One of the results of the latest developments in x-ray tube and detector technology, is the enabling of computed tomography (CT) as a strong non-invasive imaging modality for a new set of clinical applications including cardiac and brain imaging. A common theme among the applications is an ability to have wide anatomical coverage in a single rotation. Large coverage in CT is expected to bring significant diagnostic value in clinical field, especially in cardiac, trauma, pediatric, neuro, angiography, Stroke WorkUp and pulmonary applications. This demand, in turn, creates a need for tile-able and scalable detector design. In this paper, we introduce the design of a new diode, a crucial part of the detector, discuss how it enables wide coverage, its performance in terms of cross-talk, light output response, maximized geometric efficiency, and other CT requirements, and compare it to the traditional design which is front-illuminated diode. We ran extensive simulation and measurement experiments to study the geometric efficiency and assess the cross talk and all other performance parameters Critical To Quality (CTQs) with both designs. We modeled x-ray scattering in the scintillator, light scattering through the septa and optical coupler, and electrical cross talk. We tested the design with phantoms and clinical experiments on a scanner (LightSpeed VCT, GE Healthcare Technologies, Waukesha, WI, USA). Our preliminary results indicate that the new diode design performs as well as the traditional in terms of cross talk and other CTQs. It, also, yields better geometric efficiency and enables tile-able detector design, which is crucial for the VCT. We introduced a new diode design, which is an essential enabler for VCT. We demonstrated the new design is superior to the traditional design for the clinically relevant performance measures.