Multidetector Systems Research Articles

CT in musculoskeletal imaging: still helpful and for what?

Computed tomography (CT) is a common modality employed for musculoskeletal imaging. Conventional CT techniques are useful for the assessment of trauma in detection, characterization and surgical planning of complex fractures. CT arthrography can depict internal derangement lesions and impact medical decision making of orthopedic providers. In oncology, CT can have a role in the characterization of bone tumors and may elucidate soft tissue mineralization patterns. Several advances in CT technology have led to a variety of acquisition techniques with distinct clinical applications. These include four-dimensional CT, which allows examination of joints during motion; cone-beam CT, which allows examination during physiological weight-bearing conditions; dual-energy CT, which allows material decomposition useful in musculoskeletal deposition disorders (e.g., gout) and bone marrow edema detection; and photon-counting CT, which provides increased spatial resolution, decreased radiation, and material decomposition compared to standard multi-detector CT systems due to its ability to directly translate X-ray photon energies into electrical signals. Advanced acquisition techniques provide higher spatial resolution scans capable of enhanced bony microarchitecture and bone mineral density assessment. Together, these CT acquisition techniques will continue to play a substantial role in the practices of orthopedics, rheumatology, metabolic bone, oncology, and interventional radiology.

Calculation of efficiency and resolution of a hexagonal NaI(Tl) detector as a function of source position

Most gamma-ray scintillation detectors currently in use are made from inorganic materials that have a relatively high electron density. Quite often they are used to build multidetector systems that provide high scintillation light output. The performance of a gamma radiation detector (its detection efficiency) depends on the shape and size of the crystal, as well as on the source-to-detector geometry used. The NaI(Tl) gamma detector exhibits moderate energy resolution but relatively high gamma-ray detection efficiency and fast time response. In this work, the efficiency and resolution of a scintillation hexagonal detector are studied to optimize its response function. This type and size of scintillator were selected to construct a budget-friendly, reconfigurable, easy-to-maintain multidetector system for registering gamma-rays following fission, capture, and inelastic neutron scattering reactions, with reasonably good energy and time resolutions The research results made it possible to establish a geometric solid angle that increases the efficiency of recording gamma-ray radiation of the hexagonal NaI(Tl) scintillation probe under study.

A digital twin for parallel liquid-state nuclear magnetic resonance spectroscopy

One approach to increasing nuclear magnetic resonance measurement sample throughput is to implement multiple, independent detection sites. However, the presence of radio frequency interference poses a challenge in multi-detector systems, particularly in unshielded coil arrays lacking sufficient electrical isolation. This issue can lead to unwanted coupling of inductive coils, resulting in excitation pulse interference and signal transfer among multiple detection sites. Here we propose a theoretical framework that combines electromagnetic simulation with spin-dynamic calculations. This framework enables the evaluation of coil coupling effects, the design of parallel pulse sequences to mitigate inter-channel coupling, and the separation of composite free induction decays obtained from multiple detectors. The parallel pulse compensation scheme was validated by a 2-channel parallel spectroscopy experiment. These results provide valuable insights for the design of parallel nuclear magnetic resonance hardware and for exploring the limits of parallelization capacity within a fixed magnet system.

In situ build surface topography determination in electron beam powder bed fusion

Electron optical imaging is the most promising process monitoring method in electron beam powder bed fusion. State of the art in modern machines is the installation of a single detector in the top center of the build chamber. Exemplary applications are the reconstruction of digital twins of manufactured parts to compare their dimensional accuracy or analysing the top surface of each layer to identify surface features like pores or material transport. Multi-detector systems are currently under research and have shown great potential in reconstructing the surface topography in situ. A recently developed ray tracing model, describing the image formation process, allows to formulate design guide lines for multi-detector systems and provides a method for the computation of the normal vector field of the build surface. This work utilizes the recent progress and presents a newly developed four-detector system and an updated computation chain, which enable build surface topography reconstruction in situ in every layer of a build process. The computation chain contains a normal integration algorithm, which employs Tikhonov regularization to cope with measurement irregularities. The integration method is validated with ex situ measured as-built surfaces. Additionally, first applications are demonstrated and connections to process parameter changes illustrated.

A Ray Tracing Model for Electron Optical Imaging in Electron Beam Powder Bed Fusion

The recent success of the process monitoring method Electron Optical Imaging, applied in the additive manufacturing process Electron Beam Powder Bed Fusion, necessitates a clear understanding of the underlying image formation process. Newly developed multi-detector systems enable the reconstruction of the build surface topography in-situ but add complexity to the method. This work presents a physically based raytracing model, which rationalises the effect of detector positioning on image contrast development and masking. The model correctly describes the effect of multiple scattering events on vacuum chamber walls or heat shields and represents, therefore, a predictive tool for designing future detector systems. Most importantly, this work provides a validated method to compute build surface height gradients directly from experimentally recorded electron-optical images of a multi-detector system without any calibration steps. The computed surface height gradients can be used subsequently as input of normal integration algorithms aiming at the in-situ reconstruction of the build surface topography.

A VME: Versa Module Europa, crate controller for high speed data acquisition of heterogeneous, multi-detector systems.

Modern day complex experiments in physics demand highly efficient data acquisition (DAQ) systems capable of acquiring a large number of signals with a very high resolution and near zero dead time, without compromising on the event rate handling capability. To cater to the ever growing demands of the DAQ systems, an intelligent controller with a sequencer and an in-built busy logic has been developed. The heart of the controller is a field programmable gate array that provides (a) a sequencer engine, which holds a list of read-write commands that will be executed upon receiving a valid trigger, (b) a dual port random access memory divided into two blocks of 16 kbytes, each of which is configured in a ping-pong fashion to support data acquisition and data transfer functionalities simultaneously, thereby reducing the dead time, (c) a busy logic interface that validates the master strobe or trigger, a scalar for triggers received, and a time stamp engine for time stamping the events with 10ns interval, (d) the Versa Module Europa (VME) backplane interface for 32 bit data transfer standards of the VME, and (e) a superspeed universal serial bus communication interface to transfer the data to a computer/single board computer (SBC). The SBC is capable of booting locally or through net via a preboot execution environment from a netboot server, and it contains the driver, libraries, and data server for data collection. A throughput of 32 megabytes per second (MB/s) has been achieved with an event size of 288 signals at an event rate of 30 kiloevents per second with medium slow slave modules, which may further increase up to 45 MB/s with faster slave modules. The VME controller supports an event size (number of signals) of up to 1023 in a single VME crate. Thus, this sequencer engine based VME crate controller development facilitates collection of a high volume of data with a large number of signals at higher event rates and the least dead time; it is named as Readout Ordained Sequencer Engine.

Effective Dose Measurements of the Latest-Generation Angiographic System in Patients with Acute Stroke: A Comparison with the Newest Multidetector CT Generation.

Patients with acute ischemic stroke are increasingly triaged with one-stop management approaches, resulting in baseline imaging with a flat detector CT scanner. This study aimed to estimate the effective dose to a patient of a novel cervical and intracranial flat detector CT angiography and a flat detector CT perfusion protocol and to compare it with the effective dose of analogous multidetector row CT protocols. We estimated the effective dose to the patient according to the International Commission on Radiological Protection 103 using an anthropomorphic phantom with metal oxide semiconductor field effect transistor dosimeters. Placement was according to the organ map provided by the phantom manufacturer. We used 100 measurement points within the phantom, and 18 metal oxide semiconductor field effect transistor dosimeters were placed on the surface of the phantom. All protocols followed the manufacturer's specifications, and patient positioning and collimation were performed as in routine clinical practice. Measurements were obtained on the latest-generation angiography and multidetector row CT systems with identical placement of the metal oxide semiconductor field effect transistor dosimeters. The estimated effective doses of the investigated perfusion protocols were 4.52 mSv (flat detector CT perfusion without collimation), 2.88 mSv (flat detector CT perfusion with collimation), and 2.17 mSv (multidetector row CT perfusion). A novel protocol called portrait flat detector CT angiography that has a z-axis coverage area comparable with that of multidetector row CT angiography had an estimated effective dose of 0.91 mSv, while the dose from multidetector row CT was 1.35 mSv. The estimated effective dose to the patient for flat detector CT perfusion and angiography on a modern biplane angiography system does not deviate substantially from that of analogous multidetector row CT protocols.

Fourier method for 3-dimensional data fusion of X-ray Computed Tomography and ultrasound

X-ray Computed Tomography (CT) is essential for nondestructive inspection of many manufactured components but is susceptible to various forms of artifacts and noise. In particular, multi-detector row cone-beam CT systems can suffer from so called “cone-beam” artifacts and partial volume effects, particularly on planar edges at the periphery of the field of view in the cone angle dimension. Uni-directional ultrasonic testing methods generally have extremely accurate in-plane depth resolution but poorer lateral resolution due to physical and geometric constraints. This paper presents a novel technique called Computed Tomographic Fusion (CT-F) which uses three-dimensional Fourier filtering to combine x-ray cone-beam CT reconstructions and ultrasound data in the frequency space. The result is a single image with improved accuracy and quality. CT-F mitigates artifacts while allowing for rapid, accurate characterization of large three-dimensional CT volumes. Using simulations and experiments, we demonstrate artifact reduction and edge contrast improvement in volumetric reconstructions.

High-Pressure Neutron Diffraction Study of the Crystal and Magnetic Structure of Materials at the Pulsed Reactor IBR-2: Current Opportunities and Prospects

The experimental capabilities and results of recent studies of the crystal and magnetic structure of functional materials on the diffractometers DN-12 and DN-6 of upgraded high-flux pulsed reactor IBR-2 in wide ranges of high pressures and temperatures are reviewed. The combination of high neutron flux on a sample, wide-aperture multidetector systems, and focusing devices has made it possible to implement diffraction experiments on samples with record-low volumes under ultrahigh pressures (up to 35 GPa) in the temperature range of 5–300 K. The results of recent studies of the structural and magnetic phase transitions in ferroelectrics, multiferroics, low-dimensional magnets, and other materials are presented.

Inclusion of quasi-vertex views in a brain-dedicated multi-pinhole SPECT system for improved imaging performance

With brain-dedicated multi-detector systems employing pinhole apertures the usage of detectors facing the top of the patient’s head (i.e. quasi-vertex (QV) views) can provide the advantage of additional viewing from close to the brain for improved detector coverage. In this paper, we report the results of simulation and reconstruction studies to investigate the impact of the QV views on the imaging performance of AdaptiSPECT-C, a brain-dedicated stationary SPECT system under development. In this design, both primary and scatter photons from regions located inferior to the brain can contribute to SPECT projections acquired by the QV views, and thus degrade AdaptiSPECT-C imaging performance. In this work, we determined the proportion, origin, and nature (i.e. primary, scatter, and multiple-scatter) of counts emitted from structures within the head and throughout the body contributing to projections from the different AdaptiSPECT-C detector rings, as well as from a true vertex view detector. We simulated phantoms used to assess different aspects of image quality (i.e. uniform activity concentration sphere, and Derenzo), as well as anthropomorphic phantoms with different count levels emulating clinical 123I activity distributions (i.e. DaTscan and perfusion). We determined that attenuation and scatter in the patient’s body greatly diminish the probability of the photons emitted outside the volume of interest reaching to detectors and being recorded within the 15% photopeak energy window. In addition, we demonstrated that the inclusion of the residual of such counts in the system acquisition does not degrade visual interpretation or quantitative analysis. The addition of the QV detectors improves volumetric sensitivity, angular sampling, and spatial resolution leading to significant enhancement in image quality, especially in the striato-thalamic and superior regions of the brain. Besides, the use of QV detectors improves the recovery of clinically relevant metrics such as the striatal binding ratio and mean activity in selected cerebral structures. Our findings proving the usefulness of the QV ring for brain imaging with 123I agents can be generalized to other commonly used SPECT imaging agents labelled with isotopes, such as 99mTc and likely 111In.

TANGRA multidetector systems for investigation of neutron-nuclear reactions at the JINR Frank Laboratory of Neutron Physics

In the framework of TANGRA-project at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear research in Dubna (Russia), two experimental setups (Fig. 1) have been designed and tested for investigation of 14-MeV neutron-induced nuclear reactions on a number of important for nuclear science and engineering isotopes. As a source of 14-MeV “tagged” neutrons we are using the VNIIA ING-27 steady-state portable neutron generator with embedded in its vacuum tube 64-pixel charge-particle detector. The “Romashka” system is an array of up-to 24 hexagonal NaI(Tl)-crystal scintillation probes, while the “Romasha” array consists of 18 cylindrical BGO-crystal detectors of neutrons and gamma-rays. In addition to these detectors there is a HPGe gamma-ray spectrometer and a number of Stilbene detectors that can be added for high-resolution gamma-ray spectrometry and neutron-gamma detection. The main characteristics of the neutron-induced nuclear reaction products can be investigated by commissioning the detectors in suitable for these experiments’ geometries. Both setups can be used for doing basic and applied scientific research, because they permit simultaneously to measure the energy, angle and multiplicity distributions of gamma-rays and neutrons, produced in the competitive neutron-induced nuclear reactions (n, n’γ), (n,2n), (n, xnγ) and (n, f) in pure or complex substances.

Fast stripe noise removal from hyperspectral image via multi-scale dilated unidirectional convolution

Hyperspectral images (HSIs) are often contaminated by noises due to the multi-detector imaging systems, which greatly affects the subsequent HSIs interpretation and application. The 3D HSIs deliver extra spectral information, which makes the most existing destriping algorithms hardly satisfied, and the complete stripes removal and less test time consuming remain to be overcome. To meet these challenges, we present a multi-scale dilated unidirectional convolution network (MsDUC) with the following contributions. First, the deep learning-based method can fully exploit and preserve spatial-spectral correlations in 3D HSIs while the conventional methods failed to realize it. Second, different dilated convolution learns different scale features, so the introduced multi-scale dilated convolution could get more contextual information for the final restoration. Third, the clear directional signature of stripe noise and the unidirectional total variation (UTV) model inspired us to put forward the unidirectional convolution to capture the directional signature of stripe, meanwhile, the less trainable parameters and the utilized residual strategy speed up the learning process. Experimental results have shown that our method outperforms many of the state-of-the-art methods in both image restoration performance and test running time. Our code can be download from .

A new image quality measure in CT: Feasibility of a contrast-detail measurement method

PurposeTo develop a new method of evaluating image quality in computed tomography (CT) using an objective measure of low contrast-detail (LCD). MethodTo achieve this aim a new LCD-CT (CDCT) phantom needed to be designed and developed. A CT inverse image quality figure (CT-IQFinv) value, based on the planar radiography LCD method, was also devised. Validation of the CDCT phantom design and CT-IQFinv calculations were undertaken using 67 observers and software methods. The CDCT phantom was scanned on three multi-detector CT systems using variable factors of kVp, mAs and slice thickness. ResultsThe results were compared to an a priori knowledge that image quality improves with increased photons reaching the detectors. Observer CT-IQFinv scores for the phantom's peripheral region were consistent with the a priori knowledge and generally consistent in the inner region, with one exception. The software CT-IQFinv scores for the phantom's peripheral region were also consistent with the a priori knowledge, however there were some inconsistencies. Software and observer CT-IQFinv score differed significantly (p < 0.05) however both were consistent with the a priori knowledge. ConclusionsThe work reported is designed as proof of concept of development of LCD measure in CT. CT-IQFinv can be used as a measure of LCD image quality in CT when evaluating CT parameter of mAs, kVp and slice thickness. The results demonstrate potential for use of CT IQFinv, however at present further work is needed to overcome design and technical issue encountered in this project.

Measurement of anthropogenic radionuclides in post-Fukushima Pacific seawater samples

Abstract Following the accident at the Daiichi Fukushima nuclear power plant in 2011, a vast number of Pacific seawater samples from many locations far from Fukushima have been collected by Japanese investigators. Due to dilution, the activities of radionuclides from North Pacific seawater samples are very low, which calls for extraordinary measures when being measured. This study focuses on the metrological aspects of the gamma-ray spectrometry measurements performed on such samples in two underground laboratories; at HADES (by JRC-IRMM in Belgium), and at Ogoya (by Kanazawa University in Japan). Due to many samples and long measurement times, all available HPGe detectors needed to be employed. In addition to single coaxial detectors, this involved multidetector systems and well detectors. Optimization of detection limits for different radionuclides and detectors was performed using Monte Carlo simulations.

Spectral anomaly methods for aerial detection using KUT nuisance rejection

This work discusses the application and optimization of a spectral anomaly method for the real-time detection of gamma radiation sources from an aerial helicopter platform. Aerial detection presents several key challenges over ground-based detection. For one, larger and more rapid background fluctuations are typical due to higher speeds, larger field of view, and geographically induced background changes. As well, the possible large altitude or stand-off distance variations cause significant steps in background count rate as well as spectral changes due to increased gamma-ray scatter with detection at higher altitudes. The work here details the adaptation and optimization of the PNNL-developed algorithm Nuisance-Rejecting Spectral Comparison Ratios for Anomaly Detection (NSCRAD), a spectral anomaly method previously developed for ground-based applications, for an aerial platform. The algorithm has been optimized for two multi-detector systems; a NaI(Tl)-detector-based system and a CsI detector array. The optimization here details the adaptation of the spectral windows for a particular set of target sources to aerial detection and the tailoring for the specific detectors. As well, the methodology and results for background rejection methods optimized for the aerial gamma-ray detection using Potassium, Uranium and Thorium (KUT) nuisance rejection are shown. Results indicate that use of a realistic KUT nuisance rejection may eliminate metric rises due to background magnitude and spectral steps encountered in aerial detection due to altitude changes and geographically induced steps such as at land–water interfaces.

Potential of full pattern fit methods for the texture analysis of geological materials: implications from texture measurements at the recently upgraded neutron time-of-flight diffractometer SKAT

The application of Rietveld texture analysis (RTA) to time-of-flight (TOF) neutron diffraction data allows complex materials with many diffraction peaks to be investigated, for example, rocks composed of different minerals. At the recently upgraded SKAT texture diffractometer at the JINR in Dubna (Russia), which provides three alternative multidetector systems, resolution and accessible range of latticedspacings can be adapted to sample requirements. In order to infer the optimum experimental setup and the reliability of texture estimates from complicated TOF patterns, the influence of counting statistics and various spectral resolutions on texture deconvolution was investigated. Comparing the results obtained at different resolutions and from different sections of thedpatterns indicates that the textures of a four-phase sample can be determined, but using a section at smalldspacings with a larger number of peak overlaps leads to smoother textures. A complex seven-phase sample shows orientation differences in addition to the smoothing effect. Weak textures and textures of the minor rock constituents are inaccurate owing to multiple peak overlaps. Consequently, good resolution is essential for RTA on such samples. Grid thinning tests confirmed that no more than 150 diffraction spectra are needed to characterize the texture of a monomineralic sample, and approximately 350 spectra are sufficient for a four-phase sample. The irregular grid point arrangement caused by the SKAT geometry has no negative consequences.

Computed tomography angiography of lower extremities in the emergency room for evaluation of patients with gunshot wounds.

To assess the role of CT angiography in the evaluation of patients with lower extremity gunshot wounds in the emergency room. Eighty patients (73 male, 7 female, mean age 26 years) underwent CT angiography for the evaluation of lower extremity gunshot injuries. Imaging was conducted on the basis of standardized protocols utilizing 16-slice and 64-slice multidetector systems and images were qualitatively graded and assessed for various forms of arterial injury. CT angiography findings indicative of arterial injury were observed in 24 patients (30%) and a total of 43 arterial injuries were noted; the most common form was focal narrowing/spasm (n = 16, 37.2%); the most common artery involved was the superficial femoral artery (n = 12, 50%). In qualitative assessment of images based on a 4-point grading system, both readers considered CT angiography diagnostically excellent (grade 4) in most cases. Surgical findings were consistent with CT angiography and follow-up of patients' medical records showed no arterial injuries in patients with normal findings on initial imaging. Our findings demonstrate that CT angiography is an effective imaging modality for evaluation of lower extremity gunshot wounds and could help limit more invasive procedures such as catheter angiography to a select group of patients. • CT angiography efficiently evaluates lower extremity gunshot wounds. • CT angiography provides image quality sufficiently reliable for assessment of gunshot injuries. • CT angiography could help limit invasive procedures to select patients.

Characterization of atherosclerotic plaque: a contrast‐detail study using multidetector and cone‐beam computed tomography

A Hindmarsh‐Rose model perceptibility phantom containing inserts with various in vitro atherosclerotic plaque compositions was constructed and imaged on a clinical 64 slice multidetector (MDCT) system using 80 and 120 kVp settings and two other cone‐beam (CBCT) systems at 80 kVp. Perceptibility of the simulated lipid‐fibrotic plaque solutions in the images was evaluated by six observers. The effective doses of the protocols employed were estimated using phantom CTDI‐vol measurements placed at identical settings. The CBCT system allowed reduction in effective dose in comparison with the conventional MDCT system for imaging of the carotid plaque phantoms without degrading image quality. The CBCT dose was less than MDCT, with a mean dose of 1.14±0.01 mSv and 1.11±0.02 mSv for MDCT using two measuring techniques vs. 0.35±0.01 mSv for CBCT. The image quality analysis showed no significant differences in the contrast‐detail (C‐D) curves of the best performing CBCT vs. clinical MDCT (p>0.05) using a Mann‐Whitney U test. Results indicate that low‐tube‐potential CBCT may produce comparable C‐D resolution for phantom‐based representations of soft plaque types with respect to MDCT systems. This study suggests that the utility of low kVp CT techniques for evaluating carotid vulnerable atherosclerotic plaque merits further study.PACS numbers: 87.53.Bn, 87.57.N‐, 87.57.Q‐, 87.57.cj

Avalanche current read‐out circuit for low‐jitter parallel photon timing

We propose a novel circuit for single photon avalanche diode (SPAD) current read-out, for photon timing applications. The circuit consists of a single transistor trans-impedance amplifier with a GHz bandwidth: the feedback loop fixes the SPAD anode voltage and allows us to obtain a high time resolution with a very high equivalent current threshold (almost 700 μA). The trans-impedance stage is followed by a low pass filter that reduces the crosstalk of other on-chip detectors and makes the designed structure suitable for multi-detector systems. The discrete components prototype presented in this letter achieves a state-of-art resolution of 34.4 ps FWHM, presents negligible crosstalk between the different pixels and opens the way for the development of an integrated structure with a large number of channels.

VSHEC—A program for the automatic spectrum calibration

Calibration is the transformation of the output channels of a measuring device into the physical values (energies, times, angles, etc.). If dealt with manually, it is a labor- and time-consuming procedure even if only a few detectors are used. However, the situation changes appreciably if a calibration of multi-detector systems is required, where the number of registering devices extends to hundreds (Tsyganov et al. (2004) [1]). The calibration is aggravated by the fact that needed pivotal channel numbers should be determined from peak-like distributions. But peak distribution is an informal pattern so that a procedure of pattern recognition should be employed to discard the operator interference. The automatic calibration is the determination of the calibration curve parameters on the basis of reference quantity list and the data which partially are characterized by these quantities (energies, angles, etc).The program allows the physicist to perform the calibration of the spectrometric detectors for both the cases: that of one tract and that of many. Program summaryProgram title: VSHECCatalogue identifier: AENN_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AENN_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 6403No. of bytes in distributed program, including test data, etc.: 325847Distribution format: tar.gzProgramming language: DELPHI-5 and higher.Computer: Any IBM PC compatible.Operating system: Windows XX.Classification: 2.3, 4.9.Nature of problem:Automatic conversion of detector channels into their energy equivalents.Solution method:Automatic decomposition of a spectrum into geometric figures such as peaks and an envelope of peaks from below, estimation of peak centers and search for the maximum peak center subsequence which matches the reference energies in the statistically most plausible way.Running time:On Celeron (R) (CPU 2.66 GHh) it is the time needed for the dialog via the visual interface. Pure computation—less than 1 s for the test run.