Multidetector Systems Research Articles

Studies of Nuclear Reactions and Time Scale with the 4π Detector CHIMERA

With the discovery, in the early 1980s, of multifragmentation processes in heavy-ion induced nuclear reactions at medium energies, the design of multidetector systems capable of detecting most of the reaction products had attracted considerable efforts by a worldwide community of experimentalists [1].

Towards picosecond array detector for single-photon time-resolved multispot parallel analysis

Over the past few years there has been a growing interest in monolithic arrays of single photon avalanche diodes (SPADs) for parallel detection of faint ultrafast optical signals. SPADs implemented in CMOS-compatible planar technologies offer the typical advantages of microelectronic devices (small size, ruggedness, low voltage, low power, etc.). Furthermore, they have inherently higher photon detection efficiency than photomultiplier tubes and they are able to provide very high acquisition speeds. The development of fully-parallel multichannel systems is a challenge both for the detector (with new problems like optical and electrical crosstalk, isolation elements size reduction and the need for higher yields) and for the electronics. The development of a parallel detector must be accompanied by that of the time-to-amplitude converters and analysis electronics necessary in time-correlated single photon counting applications. In this paper we present the fundamental building blocks necessary to develop a parallel picosecond array detector: a new high-performance SPAD detector, compatible with the design of multi-detector systems with a large number of channels, and a new totally integrated system for time-to-amplitude conversion, to allow the simple integration of several channels on a single chip.

IRMM-3100a: A new certified isotopic reference material with equal abundances of 233U, 235U, 236U and 238U

The new so-called Quad-IRM (“Quadruple Isotope Reference Material”) was prepared from highly enriched 233U, 235U, 236U and 238U isotopic materials using an optimized combination of gravimetrical mixing and mass spectrometry. Within the mixing process the isotope ratios were adjusted to about n( 233U)/ n( 235U)/ n( 236U)/ n( 238U) = 1/1/1/1 and certified with expanded relative uncertainties of 0.0054% per mass unit (coverage factor k = 2). This new isotope reference material is ideal for verifying the inter-calibration of multi-detector systems in isotope mass spectrometry. The certified n( 233U)/ n( 236U) ratio of IRMM-3100a was derived from the mass metrology data of the gravimetrical mixing of highly enriched 233U and 236U materials. It was verified by thermal ionization mass spectrometry (TIMS) measurements using the classical total evaporation (TE) and modified total evaporation (MTE) methods. The n( 234U)/ n( 236U), n( 235U)/ n( 236U) and n( 238U)/ n( 236U) ratios were then determined by TIMS using the n( 233U)/ n( 236U) ratio for internal normalization and using a multi-dynamic measurement procedure in order to circumvent any possible influence and uncertainties from Faraday cup efficiencies and amplifier gain factors. The certified n( 235U)/ n( 236U) and n( 238U)/ n( 236U) ratios were additionally verified using the classical and modified total evaporation methods using two TIMS instruments at IRMM and one TIMS instrument at IAEA-SGAS. The verification data can be regarded as results obtained at three independent instruments at two different nuclear safeguards laboratories.

Development of a phoswich detector system for radioxenon monitoring

Measurement of radioactive xenon in the atmosphere is one of several techniques to detect nuclear weapons testing. For high sensitivity, some existing systems use beta/gamma coincidence detection to suppress background, which is very effective, but increases complexity due to separate beta and gamma detectors that require careful calibration and gain matching. In this paper, we will describe the development and evaluation of a simpler detector system, named PhosWatch, consisting of a CsI(Tl)/BC-404 phoswich well detector, digital readout electronics, and pulse shape analysis algorithms implemented in a digital signal processor on the electronics, and compare its performance to existing multi-detector systems.

Artefact misinterpretation on CT images of the head

In most radiology departments, axial computed tomography (CT) is the standard acquisition mode for routine head examinations. Historically, this practice involved the use of singledetector row machines, and has persisted even with the advent of helical and multidetector row CT systems. Artefacts seen using multidetector row CT systems have been shown to be substantially fewer than a single-detector row machines, and those that were identified were associated with helical scanning. However, artefacts can be seen if the axial scanning mode is used on a multidetector row CT system when one of the detector rows is faulty. It is important for radiologists, CT radiographers, and physicists to be aware of these as they can mimic disease and cause misinterpretation. We report the cases of three patients who underwent emergency head CT examinations that showed artefacts misinterpreted initially as pathological lesions by the radiologist, necessitating further investigations. Although there has been a report of an unknown substance on the collimator assembly causing hypoattenuating artefacts, prior to the present series, there have been no reports of contrast medium spill on the detector and optic assembly causing artefacts.

Efficiency of background suppression by tagged neutron technology

The possibility of background suppression by spatial and time discrimination of events stipulates the potentialities of the nanosecond tagged neutron technology (NTNT) for neutron analysis. For practical application of NTNT, the multi-detector systems and high intensity (up to 1×1081/s) neutron generator should be used. The total intensity of signals can exceed 1×1061/s from all gamma-detectors and 1×1071/s from all alpha-detectors. A preliminary “on-line” data processing by hardware sufficiently facilitates the data transmission interface and computer equipment. The basic criteria of processing (selection of useful events) are the presence of signals from alpha- and gamma-detectors in the certain time interval (tracking interval), range of gamma-ray energy and absence of foldover of the signals. The suggested architecture of data acquisition and control system is discussed. The basic components of background and factors affecting the total time resolution are examined. The preliminary results demonstrate high efficiency of NTNT for suppression of background by spatial and time discrimination of events.

Quantification of global left ventricular function: comparison of multidetector computed tomography and magnetic resonance imaging. a meta-analysis and review of the current literature

Cardiac morbidity and mortality are closely related to cardiac volumes and global left ventricular (LV) function, expressed as left ventricular ejection fraction. Accurate assessment of these parameters is required for the prediction of prognosis in individual patients as well as in entire cohorts. The current standard of reference for left ventricular function is analysis by short-axis magnetic resonance imaging. In recent years, major extensive technological improvements have been achieved in computed tomography. The most marked development has been the introduction of the multidetector CT (MDCT), which has significantly improved temporal and spatial resolutions. In order to assess the current status of MDCT for analysis of LV function, the current available literature on this subject was reviewed. The data presented in this review indicate that the global left ventricular functional parameters measured by contemporary multi-detector row systems combined with adequate reconstruction algorithms and post-processing tools show a narrow diagnostic window and are interchangeable with those obtained by MRI.

Advances in imaging of the paranasal sinuses

Imaging technology has played a significant role in the diagnosis and management of sinonasal disorders. Plain sinus films are almost exclusively replaced by CT in the work-up for inflammatory sinus disease. MRI provides complementary information to CT in cases of sinonasal and skull-base neoplasms. The evolution of endoscopic surgical techniques for the paranasal sinuses and skull base is made possible by the parallel advancement of imaging technologies. Recent advances that are currently in clinical use have included multidetector row CT scanners and computer image-guidance systems for surgery. Three-dimensional CT angiography, image-guided CT-MR fusion, and intraoperative image-guidance are new techniques that are currently being evaluated. As imaging technology continues to advance, so does the capability to treat diseases beyond the sinuses and skull base with minimally invasive, endoscopic approaches.

Dose Reduction in CT while Maintaining Diagnostic Confidence: Diagnostic Reference Levels at Routine Head, Chest, and Abdominal CT—IAEA-coordinated Research Project

To measure radiation doses for computed tomography (CT) of the head, chest, and abdomen and compare them with the diagnostic reference levels, as part of the International Atomic Energy Agency Research coordination project. The local ethics committees of all participating institutions approved the study protocol. Written informed consent was obtained from all patients. All scanners were helical single-section or multi-detector row CT systems. Six hundred thirty-three patients undergoing head (n = 97), chest (n = 243), or abdominal (n = 293) CT were included. Collected data included patient height, weight, sex, and age; tube voltage and tube current-time product settings; pitch; section thickness; number of sections; weighted or volumetric CT dose index; and dose-length product (DLP). The effective dose was also estimated and served as collective dose estimation data. Mean volumetric CT dose index and DLP values were below the European diagnostic reference levels: 39 mGy and 544 mGy . cm, respectively, at head CT; 9.3 mGy and 348 mGy . cm, respectively, at chest CT; and 10.4 mGy and 549 mGy . cm, respectively, at abdominal CT. Estimated effective doses were 1.2, 5.9, and 8.2 mSv, respectively. Comparison of CT results with diagnostic reference levels revealed the need for revisions, partly because the newer scanners have improved technology that facilitates lower patient doses.

Multidetector-row computed tomography for noninvasive coronary imaging

Computed tomography (CT) permits cross-sectional imaging of the heart. Temporal and spatial resolutions of the technique have been insufficient to cover the heart without motion artefacts until the recent advent of multidetector systems with more than 16 detector rows. The modality is now suited for noninvasive imaging of the coronary arteries, producing detailed morphologic images of the entire coronary tree with upto 0.4 mm of spatial resolution, within a single short breath-hold duration. CT imaging goes beyond the delineation of the coronary lumen as provided by selective invasive angiography; the plaque burden of the coronary artery wall can be visualized directly, utilizing soft-tissue contrast and a high sensitivity even for the small calcifications that are present in hard plaque formations. Therefore, CT combines elements of catheterization angiography for lumen imaging and of intravascular ultrasound imaging for coronary wall imaging. However current CT technology is not yet able to compete with the temporal or spatial resolution of catheterization angiography nor does it provide the detailed spatial or contrast resolution of intravascular ultrasound imaging. At present, its use is therefore restricted to complementing the invasive modalities in appropriate indications. Although CT entails significantly less risk than the invasive procedures, the risks of radiation dose exposure and contrast agent application are not negligible. In the foreseeable future, if the current rate of technological advancement continues, CT may replace the invasive modalities in routine care for diagnostic purposes.

SPECT Imaging for Radioaerosol Deposition and Clearance Studies

Planar gamma camera scintigraphy is well established for measuring the deposition and clearance of radioaerosols. Single photon emission computed tomography (SPECT) provides threedimensional (3D) reconstructions of the radioactivity distribution, thus avoiding the compression of 3D data into two-dimensional (2D) images and potentially offering superior assessment of aerosol deposition patterns. However, SPECT has traditionally been associated with long imaging times, making it unsuitable for measuring deposition and clearance of radioaerosols with fast clearance. Multi-detector SPECT systems can collect complete SPECT studies in <1 min, allowing both initial deposition and clearance over time to be assessed by dynamic SPECT. Simultaneous transmission measurement with an external source provides attenuation correction for absolute activity quantification as well as aiding in the definition of the lung volume of interest. A dynamic SPECT imaging protocol has been developed to allow fast imaging from the oropharynx to the abdomen using gamma cameras with limited axial field of views. This allows activity quantification not only in the lungs, but also in areas outside the thorax. However, fast dynamic SPECT imaging is technically and computationally more demanding and provides less scope for reducing the radioactivity administered to the subjects. It has been shown that dynamic SPECT, compared to planar imaging, is more sensitive in detecting changes in deposition as measured by the Penetration Index (PI). Thus, SPECT can better differentiate between large and small airways, which is important for lung regional analysis.

Recent developments in semiconductor gamma-ray detectors

The successful development of lithium-drifted Ge detectors in the 1960s marked the beginning of the significant use of semiconductor crystals for direct detection and spectroscopy of gamma-rays. In the 1970s, high-purity Ge became available, which enabled the production of complex detectors and multi-detector systems. In the following decades, the technology of semiconductor gamma-ray detectors continued to advance, with significant developments not only in Ge detectors but also in Si detectors and room-temperature compound-semiconductor detectors. In recent years, our group at Lawrence Berkeley National Laboratory has developed a variety of gamma-ray detectors based on these semiconductor materials. Examples include Ge strip detectors, lithium-drifted Si strip detectors, and coplanar-grid CdZnTe detectors. These advances provide new capabilities in the measurement of gamma-rays, such as the ability to perform imaging and the realization of highly compact spectroscopy systems.

Linear or branched structure? Probing molecular architectures of fullerene–styrene copolymers by size exclusion chromatographs with online right-angle laser-light scattering and differential viscometric detectors

The poly(C 60- co-styrene)s prepared by radical copolymerizations of C 60 and styrene in bulk were characterized by multiple-detector size-exclusion chromatographs consisting of a refractometer, a differential viscometer, and/or a right-angle laser-light scattering photometer. The multidetector systems enabled the determinations of reliable, absolute molecular weights of the copolymers. The plots of intrinsic viscosity vs. molecular weight and radius of gyration vs. molecular weight offered valuable information about the molecular architectures of the copolymers. The slopes of the plots reveal that the structure of the copolymer changes with its C 60 content: the copolymer with a low C 60 content of 0.58 wt% possesses a linear structure, whereas its conger with a high C 60 content of 1.14 wt% possesses a branched structure.

SEC Molecular-Weight-Sensitive Detection

In addition to an updated view of the basic principles of viscometry and elastic light scattering molecular-weight-sensitive detectors for size-exclusion chromatography (SEC), this review also examines many of the specific applications described in publications since 2001. These include the use of multidetector systems for validating SEC fractionation, examining polymer conformation, quantifying many forms of polymer topology (e.g., branching), physiochemical studies (e.g., phase separation and aggregation), analyzing oligomers, assessing polymer optical anisotropy, and estimating second virial coefficients. Although multidetector SEC is not without sources of error and uncertainty, it has developed into an extremely powerful analytical method that is increasingly used to accomplish diverse and difficult polymer analyses.

Computed tomography angiography: principles and clinical applications.

Clinical applications of computed tomography (CT) angiography have increased with the improved technology of multidetector CT systems. Adequate contrast enhancement and the timing of image acquisition are key elements in producing technically adequate CT angiograms. This review article provides guidelines and protocols for four-, eight- and 16-channel multidetector systems in studies of the thoracoabdominal aorta, aortoiliac, and abdominal visceral vasculature, abdominal and extremity run-off studies, and carotid/cerebral CT angiography.

Longitudinal diffusion in size-exclusion chromatography: a stop-flow size-exclusion chromatography study

Band broadening in size-exclusion chromatography (SEC) has an adverse effect upon calculated molecular mass averages, distributions, and dilute solution data generated using single- and multi-detector systems. In the past, the longitudinal diffusion contribution to band broadening in SEC has been considered negligible. This assumption has been investigated by using a stop-flow methodology (SF-SEC) that maximizes the potential for longitudinal diffusion while minimizing that for mass transfer. Under the given experimental conditions, the effects of B-term band broadening were manifest only below 30 KDa, irrespective of chemical functionality or molecular mass polydispersity. This type of broadening was found to be flow rate-independent for a representative high molecular mass polymer.

CT and bowel disease.

CT has now come of age in the detection and demonstration of bowel pathology and is likely to supplant traditional imaging techniques further in the future. Its role here has been greatly aided by the advent of fast spiral CT sequences and, with the development of even faster multidetector CT systems, this can only increase.

Statistical interpretation of the correlation between intermediate mass fragment multiplicity and transverse energy

Multifragment emission following Xe+Au collisions at 30, 40, 50 and 60 AMeV has been studied with multidetector systems covering nearly 4-pi in solid angle. The correlations of both the intermediate mass fragment and light charged particle multiplicities with the transverse energy are explored. A comparison is made with results from a similar system, Xe+Bi at 28 AMeV. The experimental trends are compared to statistical model predictions.

Signal linearity in XPS counting systems

Abstract Inadequate design, deterioration through ageing and poor setting-up procedures may cause the intensity measuring systems in XPS instruments, and very possibly in all simple particle counting systems, to show non-linearities. Even in correctly designed and used equipment smaller non-linearities occur but these, being predictable, may be corrected to a high level of accuracy. Non-linearities are shown for both the high and low count rate regimes for both single channel and multidetector systems. To monitor these defects for XPS systems three simple methods are described which require no additional equipment. The first two, for assessing the effects at high count rates, make use of `ratio plots' which involve the ratios of intensities measured at two X-ray source emission currents. The first of these methods uses the survey spectrum from a copper or stainless steel sample measured in either the constant ΔE/E or constant ΔE mode. The second method uses the Cu 2p3/2 peak to diagnose other effects. For very low count rates a signal generator simulating the detector pulses, but with pulses evenly spaced in time, may be used for checking the electronic part of the circuit. Using these methods, non-linearities of up to 50% are illustrated for commercial equipment for electron counting in common analytical use.

Method for determining the signal linearity in single and multidetector counting systems in X-ray photoelectron spectroscopy

Both predictable and unpredictable non-linearities occur in the electron counting systems which provide the intensity scales of different X-ray photoelectron spectrometers. The predictable effects are inherent in good system design and may be accurately corrected as they are both stable and repeatable. Unpredictable effects occur due to inadequate design, deterioration in service or poor setting-up procedures. We have therefore, devised a method to measure this non-linearity in X-ray photoelectron spectroscopy (XPS). A widescan (survey) spectrum is recorded from a copper or stainless steel sample at both high and low X-ray source emission currents. The ratio of these spectra, at each emission energy, allows non-linearities to be easily measured. We show results for one example of a predictable system exhibiting only dead time effects which can be corrected to give 1% accuracy up to 5 Mc/s. We also show results for an unpredictable multichannel detector system where the non-linearity exceeds 5% at counting rates below 20 kc/s and reaches 50% at 500 kc/s.