Biological research has been accelerated by the development of noninvasive imaging techniques and by use of genetically engineered mice to model human diseases and normal development. Because these mice can be expensive, noninvasive imaging techniques, such as high-resolution positron emission tomography (PET), that permit longitudinal studies of the same animals are very attractive. Such studies reduce the number of animals used, reduce intersubject variability, and improve the accuracy of biological models. PET provides quantitative measurements of the spatiotemporal distribution of radiotracers and is an extremely powerful tool in using molecular imaging to study biology, to monitor disease intervention, and to establish pharmacokinetics for new drugs. The design of animal PET scanners has improved significantly in the past decade and can provide adequate image resolution and sensitivity to study transgenic mice. This article reviews the fundamental and technical challenges of small-animal PET imaging, with a particular focus on the latest developments and future directions of detector technologies and system design.

https://www.annualreviews.org/doi/pdf/10.1146/annurev.bioeng.6.040803.140021

Instrumentation aspects of animal PET.

The response of Cd(Zn)Te Schottky and resistive detectors to intense x-rays is investigated in a commercial computed tomography (CT) system to assess their potential for medical diagnostics. To describe their signal height, responsivity, signal-to-noise ratio (SNR), and detective quantum efficiency the devices are modeled as solid-state ionization chambers with spatially varying electric field and charge collection efficiency. The thicknesses and pixel areas of the discrete detector elements are 0.5-2 mm and a few mm2, respectively. The incident spectrum extends from 26 to 120 keV and comprises 10(10) quanta/s cm2. It photogenerates a carrier concentration in the semiconductor that is two to three orders of magnitude above the intrinsic concentration, but remains to a similar extent below the charge densities on the device electrodes. Stable linear operation is achieved with the Schottky-type devices under high bias. Their behavior can be modeled well if negatively charged near-midgap bulk defects with a concentration of 10(11)-10(13) cm-3 are assumed. The bulk defects explain the amount and time constant (about 100 ms) of the detrapping current measured after x-ray pulses (afterglow). To avoid screening by the trapped space charge the bias voltage should exceed 100(V) x [detector thickness/mm]2. Dark currents are of the order of the generation-recombination current, i.e., 300 pA/mm3 detector volume. With proper device design the signal height approaches the theoretical maximum of 0.2 A/W. This high responsivity, however, is not exploited in CT since the SNR is determined here by the incident quantum noise. As a consequence of the detrapping current, the response speed does not meet CT requirements. A medium-term effort for crystal growth appears necessary to achieve the required reduction of the trap density by an order of magnitude. Scintillation based detectors are, therefore, still preferred in fast operating medical diagnostic systems.

Signal formation and decay in CdTe x-ray detectors under intense irradiation

The invention is directed to a system and method for detecting substances, such as explosives and/or drugs, using, in part, short bursts of energy light from a relatively low energy strobe. Embodiments include coupling the strobe with a detector for use in a portable hand-held unit, or a unit capable of being carried as a backpack. Embodiments further include placement of one or more stroboscopic desorption units and detectors in luggage conveyors systems, carry-on X-ray machines, and check-in counter locations.

Stroboscopic liberation and methods of use

The invention is directed to a system and method for detecting substances, such as high boiling and low vapor pressure materials, using high energy radiation imparted by a suitable radiation source, such as a strobe or laser over a short time period. The radiation source causes the materials to vaporize. A system handling system is used in conjunction with a detector to detect the presence of the materials including explosives, explosive-related compounds, chemical warfare agents, drugs, toxic industrial compounds, and derivatives thereof.

Strobe desorption method for high boiling point materials

We report on recent three-dimensional imaging performance and detection efficiency measurements obtained with 5 mm thick prototype CdZnTe detectors fabricated with orthogonal coplanar anode strips. In previous work, we have shown that detectors fabricated using this design achieve both very good energy resolution and sub-millimeter spatial resolution with fewer electronic channels than are required for pixel detectors. As electron-only devices, like pixel detectors, coplanar anode strip detectors can be fabricated in the thickness required to be effective imagers for photons with energies in excess of 500 keV. Unlike conventional double-sided strip detectors, the coplanar anode strip detectors require segmented contacts and signal processing electronics on only one surface. The signals can be processed to measure the total energy deposit and the photon interaction location in three dimensions. The measurements reported here provide a quantitative assessment of the detection capabilities of orthogonal coplanar anode strip detectors.

/pdf/three-dimensional-imaging-and-detection-efficiency-49j8mfzabw.pdf

Three-dimensional imaging and detection efficiency performance of orthogonal coplanar CZT strip detectors

The authors report progress in ongoing measurements of the performance of a sub-millimeter pitch CdZnTe strip detector developed as a prototype for astronomical instruments. Strip detectors can be used to provide two-dimensional position resolution with fewer electronic channels than pixellated arrays. Arrays of this type are under development for the position-sensitive image plane detector for a coded-aperture telescope operating in the hard x-ray range of 20--200 keV. The prototype is a 1.5 mm thick, 64 x 64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, approximately one square inch of sensitive area. In addition to energy and spatial resolution capabilities, as reported last year, the authors demonstrate the imaging capabilities and discuss uniformity of response across an 8 x 8 stripe, 64 pixel, segment of detector. A technique for determination of the depth of photon interaction is discussed and initial results related to depth determination are presented. Issues related to the design and development of readout electronics, the packaging and production of strip detectors and the production of compact strip detector modules, including detector and readout electronics, are also discussed.

Progress in the development of large area sub-millimeter resolution CdZnTe strip detectors

We report /spl gamma/-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for /spl gamma/-ray astronomy measurements in the range of 20-200 keV. The prototype is a 1.5 mm thick, 64/spl times/64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8/spl times/8 strip region of the prototype we measured good spectroscopic uniformity and sub-pitch (/spl sim/0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals, and the photon detection efficiency. We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results to the data. The data indicate that the cathode signal-as well as the anode signal-arises primarily from the conduction electrons rather than the holes. This presents a detection efficiency limitation which must be considered in the design of strip detector systems.

Performance and simulation of CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

We report /spl gamma/-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for /spl gamma/-ray astronomy measurements in the range of 20-200 keV. The prototype is a 1.5 mm thick, 64/spl times/64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8/spl times/8 stripe region of the prototype we measured good spectroscopic uniformity and sub-pitch (/spl sim/0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals, and the photon detection efficiency. We also present a technique for determining the location of the event in the third dimension (depth). We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results with the data. The data indicate that the cathode signal-as well as the anode signal-arises more strongly from the conduction electrons rather than the holes.

/pdf/performance-of-cdznte-strip-detectors-as-sub-millimeter-1tb1jrg2ys.pdf

Performance of CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

We report /spl gamma/-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for /spl gamma/-ray measurements in the range of 20-600 keV. The prototype is a 1.5 mm thick, 64/spl times/64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8/spl times/8 stripe region of the prototype we measured good spectroscopic uniformity and sub-pitch (/spl sim/0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals. We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results with the data. The data indicate that cathode signal-as well as the anode signal-arises more strongly from the conduction electrons rather than the holes.

/pdf/cdznte-strip-detectors-as-sub-millimeter-resolution-imaging-4mzh7nqf7a.pdf

CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

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Progress in the development of large area sub-millimeter resolution CdZnTe strip detectors

Performance and simulation of CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

Performance of CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers