Scanning Detection Research Articles

Myelographic Techniques for the Localization of CSF-Venous Fistulas: Updates in 2024.

CSF-venous fistulas (CVFs) are a common cause of spontaneous intracranial hypotension. Despite their relatively frequent occurrence, they can be exceedingly difficult to detect on imaging. Since the initial description of CVFs in 2014, the recognition and diagnosis of this type of CSF leak has continually increased. As a result of multi-institutional efforts, a wide spectrum of imaging modalities and specialized techniques for CVF detection is now available. It is important for radiologists to be familiar with the multitude of available techniques, because each has unique advantages and drawbacks. In this article, we review the spectrum of imaging modalities available for the detection of CVFs, explain the advantages and disadvantages of each, provide typical imaging examples, and discuss provocative maneuvers that may improve the conspicuity of CVFs. Discussed modalities include conventional CT myelography, dynamic myelography, digital subtraction myelography, conebeam CT myelography, decubitus CT myelography by using conventional energy-integrating detector scanners, decubitus photon counting CT myelography, and intrathecal gadolinium MR myelography. Additional topics to be discussed include optimal patient positioning, respiratory techniques, and intrathecal pressure augmentation.

Ultra-fast Digital DPC Yielding High Spatio-temporal Resolution for Low-Dose Phase Characterization.

In the scanning transmission electron microscope, both phase imaging of beam-sensitive materials and characterization of a material's functional properties using in situ experiments are becoming more widely available. As the practicable scan speed of 4D-STEM detectors improves, so too does the temporal resolution achievable for both differential phase contrast (DPC) and ptychography. However, the read-out burden of pixelated detectors, and the size of the gigabyte to terabyte sized data sets, remain a challenge for both temporal resolution and their practical adoption. In this work, we combine ultra-fast scan coils and detector signal digitization to show that a high-fidelity DPC phase reconstruction can be achieved from an annular segmented detector. Unlike conventional analog data phase reconstructions from digitized DPC-segment images yield reliable data, even at the fastest scan speeds. Finally, dose fractionation by fast scanning and multi-framing allows for postprocess binning of frame streams to balance signal-to-noise ratio and temporal resolution for low-dose phase imaging for in situ experiments.

Optimizing Operando Electrochemical and X-Ray Diffraction Parameters for High-Resolution Measurements of Lithium-Based Battery Materials

Advances in lithium-based batteries depend on understanding the mechanisms behind electrode performance. Operando methods are very powerful and useful for decoupling thermodynamic and kinetic (e.g. diffusion) limitations, but impose challenges with data collection and analysis. Electrode composition changes as lithium is inserted or removed (according to the electrochemical conditions); composition resolution is defined by the current, (temperature-dependent) diffusion rate within the electrode, and the time to collect a diffraction pattern. Many material systems of interest require less than 1 atomic percent composition resolution to verify (or question) the expected crystalline phases, and separate composition gradients imposed by slow diffusion from the presence of solid solutions. Solid-solution ranges can be particularly challenging as the cell potential may change quickly over a very small composition range. Some advanced techniques use machine learning to optimize pattern collection time by comparing the measured diffraction pattern with references, and focusing on specific scattering angles to identify materials.1 Although powerful, this method is not well suited for materials with metastable or unidentified phases, e.g. metal alloys for advanced lithium-based batteries.Here we will describe a robust and low-cost platform for operando electrochemical and crystallographic measurements of lithium-based electrode materials. Electrode composition can be monitored at low to moderate rate electrochemical conditions using laboratory diffractometers and at high rates using some synchrotron-based diffractometers. Our test cell is based on Conflat-style vaccum flanges and a beryllium window;2 this design enables all standard two electrode electrochemical tests on e.g. lithium-based negative electrode materials with hermetic sealing and controlled pressure.Results from the electrochemical lithiation and delithiation of gold will be presented as a case study. Operando studies of lithium-gold reactivity are of interest since many lithium-gold phases have poorly defined unit cells and solid solution ranges,3 and gold electrodes are a common choice for in-situ / operando measurements in electron microscopes. A wide range of scattering angle is required to collect a sufficient number of peaks for unit cell indexing, which necessarily increases collection time and impacts composition resolution. We will discuss the influence of detector type and scan time (collection plus movement) on composition resolution as a function of electrochemical conditions (current, potential range, and temperature). Results from point, 1D, and 2D detectors on laboratory and synchrotron diffractometers will be provided, along with general strategies to optimize method resolution.

Ultrahigh-Resolution K-Edge Imaging of Coronary Arteries With Prototype Deep-Silicon Photon-Counting CT: Initial Results in Phantoms.

Background Photon-counting CT (PCCT) represents a recent advancement in CT, offering improved spatial resolution and spectral separability. By using multiple adjustable energy bins, PCCT enables K-edge imaging, allowing mixed contrast agent distinction. Deep-silicon is a new type of photon-counting detector with different characteristics compared with cadmium photon-counting detectors. Purpose To evaluate the performance of a prototype deep-Si PCCT scanner and compare it with that of a state-of-the-art dual-energy energy-integrating detector (EID) scanner in imaging coronary artery plaques enhanced with iodine and K-edge contrast agents. Materials and Methods A series of 10 three-dimensional-printed inserts (diameter, 3.5 mm) was prepared, and materials mimicking soft and calcified plaques were added to simulate stenosed coronary arteries. Inserts filled with an iodine- or gadolinium-based contrast agent (GBCA) were scanned. Virtual monoenergetic images (VMIs) and iodine maps were generated using two- and eight-energy bin data from EID CT and PCCT, respectively. Gadolinium maps were calculated for PCCT. The CT numbers of VMIs and iodine maps were compared. Spatial resolution and blooming artifacts were compared on the 70-keV VMIs in plaque-free and calcified coronary arteries. Results No evidence of a significant difference in the CT number of 70-keV images was found except in inserts containing GBCAs. In the absence of a GBCA, excellent (r > 0.99) agreement for iodine was found. PCCT could quantify the GBCA within 0.2 mg Gd/mL ± 0.8 accuracy of the ground truth, whereas EID CT failed to detect the GBCA. Lumen measurements were more accurate for PCCT than for EID CT, with mean errors of 167 versus 442 µm (P < .001) compared with the 3.5-mm ground truth. Conclusion Deep-Si PCCT demonstrated good accuracy in iodine quantification and could accurately decompose mixtures of two contrast agents. Its improved spatial resolution resulted in sharper images with blooming artifacts reduced by 50% compared with a state-of-the-art dual-energy EID CT scanner. © RSNA, 2024.

Dual-Frequency Lidar for Compressed Sensing 3D Imaging Based on All-Phase Fast Fourier Transform

Lidar, with its advantages of high measurement accuracy, fine angular resolution, and strong anti-interference capability, plays a pivotal role in the field of scene depth information acquisition. Traditional approaches to achieving lateral spatial resolution in imaging include raster scanning and array detectors. The former necessitates frequent scanning to acquire depth maps, resulting in time consumption and instability. The latter encounters challenges such as high dark count rates, pixel crosstalk, and excessive costs for obtaining high-resolution images using array detectors. The introduction of compressed sensing (CS) offers a novel perspective on realizing non-scanning three-dimensional imaging. In this context, we propose a novel three-dimensional imaging system that combines CS with coherent dual-frequency continuous-wave lidar and utilizes the all-phase fast Fourier transform to extract both amplitude and phase information. This system requires only M measurements, and through a reconstruction algorithm, it achieves the inversion of depth information for N-pixel scenes (M &lt;&lt; N). Integrating cost-effective components such as digital micromirrors and single-point detectors, this affordable system accomplishes three-dimensional imaging of a single target. Notably, it significantly reduces the required number of measurements while concurrently ensuring enhanced eye safety and signal-to-noise ratio.

Encoding terahertz holographic bits with a computer-generated 3D-printed phase plate

A sub-terahertz holographic image of a two-dimensional 576-bit data code is produced using a diffractive phase-plate element. The phase plate was designed using a modified Gerchberg-Saxton iterative algorithm to encode a focused image of the data code into a phase modulation profile. The complex phase plate structure is fabricated from polylactic acid using fused deposition modeling, a common three-dimensional-printing technique. The design achieves a significantly simplified optical setup, consisting of a 0.14 THz diverging source, the holographic phase plate and a scanning detector, without the need for additional optical elements. The information stored in the data code is an example of a cryptographic private key. Specifically, the private key for a Bitcoin wallet address. Successful retrieval of the encoded information demonstrates a potential use case for terahertz holographic memory, using a storage medium that can be fabricated with consumer-level three-dimensional-printing techniques.

An attenuation field network for dedicated cone beam breast CT with short scan and offset detector geometry

The feasibility of full-scan, offset-detector geometry cone-beam CT has been demonstrated for several clinical applications. For full-scan acquisition with offset-detector geometry, data redundancy from complementary views can be exploited during image reconstruction. Envisioning an upright breast CT system, we propose to acquire short-scan data in conjunction with offset-detector geometry. To tackle the resulting incomplete data, we have developed a self-supervised attenuation field network (AFN). AFN leverages the inherent redundancy of cone-beam CT data through coordinate-based representation and known imaging physics. A trained AFN can query attenuation coefficients using their respective coordinates or synthesize projection data including the missing projections. The AFN was evaluated using clinical cone-beam breast CT datasets (n = 50). While conventional analytical and iterative reconstruction methods failed to reconstruct the incomplete data, AFN reconstruction was not statistically different from the reference reconstruction obtained using full-scan, full-detector data in terms of image noise, image contrast, and the full width at half maximum of calcifications. This study indicates the feasibility of a simultaneous short-scan and offset-detector geometry for dedicated breast CT imaging. The proposed AFN technique can potentially be expanded to other cone-beam CT applications.

Wide-swath and high-resolution whisk-broom imaging and on-orbit performance of SDGSAT-1 thermal infrared spectrometer

Wide-swath and high-resolution Thermal infrared (TIR) data are limited by the mutual constraint between swath and resolution. In this paper, we propose a whisk-broom imaging method with the long-linear-array (LLA) 4-stage TDI detector (a total of 2048 pixels along splicing direction) and high-precision one-dimensional scanning mirror to achieve 30 m resolution and 300 km swath. And it is being implemented in the first SDGs satellite (SATSAT-1) thermal infrared spectrometer (TIS). Specially, the integration time of whisk-broom imaging system is limited by the speed of scanning mirror, and the shorter integration time is a huge challenge to meet the requirement of high sensitivity and dynamic range. The HgCdTe detector has been improved in its annealing process to reduce dark current and noise, and the opto-mechanical system has been regulated at 195 K to reduce instrument self-emission. To address the limitations of small satellite resources, TIS is equipped with a highly integrated and lightweight design, weighing 247.5 kg and consuming 248 watts respectively. As a result of the complexity of imaging mechanisms and the low frequency of deep space observations, positioning error and radiometric calibration resources have increased, and geometric and radiometric calibration methods have been improved. On-orbit test results show that TIS is capable of detecting temperature differences with a NEdT (noise equivalent differential temperature) less than 0.08 K@300 K, an absolute radiometric accuracy of less than 1 K @ 300 K, and MTF of greater than 0.125. Presently, a collection of more than 201,856 scenes covering land and marine and some precious TIR datasets of planes and naval vessels have been obtained and provided for United Nations for the realization of SDGs goals.

Diagnostic Performance of Decubitus Photon-Counting Detector CT Myelography for the Detection of CSF-Venous Fistulas.

CSF-venous fistulas are a common cause of spontaneous intracranial hypotension. Lateral decubitus digital subtraction myelography and CT myelography are the diagnostic imaging standards to identify these fistulas. Photon-counting CT myelography has technological advantages that might improve CSF-venous fistula detection, though no large studies have yet assessed its diagnostic performance. We sought to determine the diagnostic yield of photon-counting detector CT myelography for detection of CSF-venous fistulas in patients with spontaneous intracranial hypotension. We retrospectively searched our database for all decubitus photon-counting detector CT myelograms performed at our institution since the introduction of the technique in our practice. Per our institutional workflow, all patients had prior contrast-enhanced brain MR imaging and spine MR imaging showing no extradural CSF. Two neuroradiologists reviewed preprocedural brain MRIs, assessing previously described findings of intracranial hypotension (Bern score). Additionally, 2 different neuroradiologists assessed each myelogram for a definitive or equivocal CSF-venous fistula. The yield of photon-counting detector CT myelography was calculated and stratified by the Bern score using low-, intermediate-, and high-probability tiers. Fifty-seven consecutive photon-counting detector CT myelograms in 57 patients were included. A single CSF-venous fistula was definitively present in 38/57 patients. After we stratified by the Bern score, a definitive fistula was seen in 56.0%, 73.3%, and 76.5% of patients with low-, intermediate-, and high-probability brain MR imaging, respectively. Decubitus photon-counting detector CT myelography has an excellent diagnostic performance for the detection of CSF-venous fistulas. The yield for patients with intermediate- and high-probability Bern scores is at least as high as previously reported yields of decubitus digital subtraction myelography and CT myelography using energy-integrating detector scanners. The yield for patients with low-probability Bern scores appears to be greater compared with other modalities. Due to the retrospective nature of this study, future prospective work will be needed to compare the sensitivity of photon-counting detector CT myelography with other modalities.

A new promising new choice for modern medical CT scanners: Cerium-doped gadolinium yttrium gallium aluminum garnet ceramic scintillator

Cerium-doped gadolinium yttrium gallium aluminum garnet (GYGAG) ceramics show great promise as scintillators for modern medical CT scanners. They exhibit exceptional scintillation efficiency, fast decay, low afterglow, and high X-ray stopping power. However, the performance of GYGAG ceramic scintillators in modern medical CT scanners has not been thoroughly investigated, as previous research has primarily focused on optimizing material performance. To address this research gap, we prepared a high-quality GYGAG ceramic scintillator and compared its performance to that of a widely used commercial GOS ceramic scintillator in medical CT scanners. The GYGAG scintillator showed comparable afterglow intensity, but significantly higher light yields and faster scintillation decay. Additionally, we developed two-dimensional GYGAG scintillator arrays integrated into a CT detector and assessed their spatial resolution and low-contrast detectability. The successful acquisition of CT images of an adult head phantom demonstrates the promising potential of GYGAG ceramic scintillators as alternatives for modern medical CT scanner detectors.

Develop and Evaluate a Dose Calculation Strategy Using Electron Density Maps from Spectral CT

The conventional method of estimating relative electron density using Hounsfield Units (HUs) is prone to errors resulting from various factors such as energy spectrum, exposure, scanner/patient conditions, etc. Specific calibration is needed for each acquisition protocol. To overcome these limitations, dual energy CT has been extensively researched for its accuracy in dose calculation using tube potential switching techniques. A dual layer design offers a different approach to acquire spectral images using single data acquisitions. This study aims to develop and evaluate a dose calculation method using electron density maps generated directly from a dual layer detector scanner. A phantom with tissue equivalent inserts was scanned using different scanner configurations on a dual layer detector scanner. The electron density of 17 inserts ranged from 0.668 - 5.663 × 1023 m-23. The energy dependent attenuation curves were generated and translated into values of Compton and photoelectric components, which were used to calculate ED values. The ED values were compared to normal values provided by the vendor for each insert. The generated ED maps were normalized to the ED of water and used as the input for dose calculations without CT images. Dosimetry plans were generated on the phantom for two different field sizes (10 × 10 cm2 and 3 × 3 cm2) at gantry angles of 0 and 90 degrees using a 6 MV Monte Carlo engine. The dose distributions were compared between the conventional HU to ED calibration approach with CT images and the direct calculation using the calculated ED map. The results showed that compared to the conventional HU to ED map, the ED map generated from spectral CT had a relative ED that was about 0.02 lower and was more uniform, with smaller standard deviations. The ED map was closer to the nominal value in low-density regions, while the HU converted ED map was closer to the nominal value in high-density regions. The dose distributions between the two ED approaches were almost identical, with a maximum deviation of around 1% for both field sizes at deeper depths. In conclusion, a dual layer detector scanner can provide an accurate estimation of ED maps. We showed that the dose calculation using the generated ED map is highly accurate using a phantom. This method provides an alternative strategy for dose calculation that eliminates the need for HU to ED calibration and enables the use of the ED map directly.

A correction method for mitigating inter-instrumental absorbance drift in grating-based near-infrared spectrometers

In near-infrared spectroscopy analysis, the accuracy of instrument wavelength and breadth is crucial as it forms the foundation for transferring different instrument models. Wavelength and absorbance drift in grating-based scanning instruments result from differences in the grating, detector, and wavelength scanning system. Spectral wavelength drift can be corrected using materials such as polyethylene and polystyrene, which have absorption peaks in the near-infrared region. To reduce absorbance drift in spectra at different wavelength points, this article proposes a point-by-point linear correction method for near-infrared spectra using a small number of typical agricultural product samples. The method constructs a linear relationship model for the absorbance of each wavelength point between the main instrument and slave instruments. The study used seven S450 grating-based diffuse reflection near-infrared spectroscopy instruments, one serving as the main instrument and the remaining six as slave instruments. The point-by-point linear correction method was used to correct wheat spectra collected by the slave instruments, and a crude protein content model for wheat was established for prediction. The results showed that the method reduces spectral differences between different instruments, improves spectral consistency, and reduces prediction errors, achieving better model sharing between instruments. After correcting, the average normalized variation coefficient of wheat spectra decreased by 95.12%, from 7.78% to 0.38%, and the average standard deviation of the predicted results decreased by 78.18%, from 0.5321 to 0.1161. The correction effect of the method combined with traditional pre-processing methods was better than using pre-processing methods alone. Overall, the point-by-point correction method based on a small number of typical agricultural product samples has a significant effect on improving the accuracy of near-infrared spectroscopy analysis.

Search for the singlet vector-like top quark in T → tZ channel with [formula omitted] at the 14 TeV LHC

The vector-like top quark T is an important new fermion beyond the Standard Model. In the framework of a simplified model, we study the possibility of detecting the T through the single production of T decaying into tZ with Z decaying to neutrinos at the 14 TeV Large Hadron Collider (LHC). This simplified model includes three free parameters, that is the coupling constant g⁎, the T quark mass mT and the mixing parameter RL. In order to investigate the observability of the single T production, we make a detailed detector simulation and scan the parameter space. Corresponding to an integrated luminosity of 3000 fb−1, the correlated regions g⁎∈[0.14,0.5]([0.2,0.5]) with mT∈[1200GeV,1900GeV]([1200GeV,1660GeV]) can be excluded (discovered) for RL=0 and the correlated regions g⁎∈[0.1,0.5] with mT∈[1600GeV,2520GeV]([1320GeV,2220GeV]) can be excluded (discovered) for RL=0.5.

A virtual-pinhole PET device for improving contrast recovery and enhancing lesion detectability of a one-meter-long PET scanner: a simulation study

This paper presents a simulation study to demonstrate that the contrast recovery coefficients (CRC) and detectability of small lesions of a one-meter-long positron emission tomography (PET) scanner can be further enhanced by the integration of high resolution virtual-pinhole (VP) PET devices. The scanner under investigation is a Siemens Biograph Vision Quadra which has an axial field-of-view (FOV) of 106 cm. The VP-PET devices contain two high-resolution flat panel detectors, each composed of 2 × 8 detector modules each of which consists of 32 × 64 lutetium-oxyorthosilicate crystals (1.0 × 1.0 × 10.0 mm3 each). Two configurations for the VP-PET device placement were evaluated: (1) place the two flat-panel detectors at the center of the scanner’s axial FOV below the patient bed; (2) place one flat-panel detector at the center of the first and the last quarter of the scanner’s axial FOV below the patient bed. Sensitivity profiles were measured by moving a point 22Na source stepwise across the scanner’s FOV axially at different locations. To assess the improvement in CRC and lesion detectability by the VP-PET devices, an elliptical torso phantom (31.6 × 22.8 × 106 cm3) was first imaged by the native scanner then subsequently by the two VP-PET geometry configurations. Spherical lesions (4 mm in diameter) having 5:1 lesion-to-background radioactivity concentration ratio were grouped and placed at nine regions in the phantom to analyze the dependence of the improvement in plane. Average CRCs and their standard deviations of the 7 tumors in each group were computed and the receiver operating characteristic (ROC) curves were drawn to evaluate the improvement in lesion detectability by the VP-PET device over the native long axial PET scanner. The fraction of coincidence events between the inserts and the scanner detectors was 13%–16% (out of the total number of coincidences) for VP-PET configuration 1 and 2, respectively. The VP-PET systems provide higher CRCs for lesions in all regions in the torso, with more significant enhancement at regions closer to the inserts, than the native scanner does. For any given false positive fraction, the VP-PET systems offer higher true positive fraction compared to the native scanner. This work provides a potential solution to further enhance the image resolution of a long axial FOV PET scanner to maximize its lesion detectability afforded by its super high effective sensitivity.

A Nonuniformity Correction Method Based on 1D Guided Filtering and Linear Fitting for High-Resolution Infrared Scan Images

During imaging, each infrared focal plane linear array scan detector detection unit determines a row of pixels in the image output. This sensor’s nonuniformity appears as horizontal stripes. Correcting nonuniformity in high-resolution images without destroying delicate details is challenging. In this paper, a single-frame-based nonuniformity correction algorithm is proposed. A portion of a single-frame picture is intercepted initially. The 1D column guided filter is applied to smooth the captured image in the vertical direction. Then, the smooth image and high-frequency component with horizontal stripes and texture information are obtained. The subsequent step is to use the smooth portion of the image as the guided image and the high-frequency portion of the image as the input, so that the estimated nonuniformity noise of the image may be extracted using a 1D row guided filter. The segment of the corrected image is then obtained by subtracting the estimated nonuniformity noise from the segment of the raw image. The correction coefficients could be obtained by performing a linear regression fit on the pre- and post-guided filtering image segments. With the correction coefficients, the entire image could be corrected. Based on qualitative and quantitative analysis, the proposed algorithm outperforms other current advanced algorithms in terms of nonuniformity correction and real-time performance.

Optical link acquisition for the LISA mission with in-field pointing architecture

We present a comprehensive simulation of the spatial acquisition of optical links for the LISA mission in the in-field pointing architecture, where a fast pointing mirror is used to move the line-of-sight of the optical transceiver, which was studied as an alternative scheme to the baselined telescope pointing architecture. The simulation includes a representative model of the far-field intensity distribution and the beam detection process using a realistic detector model, and a model of the expected platform jitter for two alternative control modes with different associated jitter spectra. For optimally adjusted detector settings and accounting for the actual far-field beam profile, we investigate the dependency of acquisition performance on the jitter spectrum and the track-width of the search spiral, while scan speed and detector integration time are varied over several orders of magnitude. Results show a strong dependency of the probability for acquisition failure on the width of the auto-correlation function of the jitter spectrum, which we compare to predictions of analytical models. Depending on the choice of scan speed, three different regimes may be entered which differ in failure probability by several orders of magnitude. We then use these results to optimize the acquisition architecture for the given jitter spectra with respect to failure rate and overall duration, concluding that the full constellation could be acquired on average in less than one minute. Our method and findings can be applied to any other space mission using a fine-steering mirror for link acquisition.

Evaluation of scanning resolution, detector choice and detector orientation to be used for accurate and time-efficient commissioning of a 6MV clinical linear accelerator

The present study is aimed at exploring different scanning parameters, detectors and their orientations for time-efficient and accurate commissioning of a 6 MV clinical linear accelerator (LINAC). Beam profiles and percentage depth dose (PDD) curves were measured with a PTW dosimetry diode, a PTW Semiflex and a PinPoint ion chamber in different orientations. To acquire beam data, equidistant (step size of 0.5mm, 1mm, 2mm and 3mm) and fanline (step size of 2-0.5mm, 2-1mm, 3-0.5mm and 3-1mm) scanning modes were employed and data measurement time was recorded. Scan time per measurement point was also varied (0.2s, 0.5s and 1.0s) to investigate its effect on the accuracy and acquisition time of beam data. Accuracy of the measured data was analyzed on the basis of the variation between measured data and data modeled by a treatment planning system. Beam profiles (particularly in penumbra region) were found to be sensitive to variation in scanning resolution and showed an improved accuracy with decrease in step size, while PDD curves were affected negligibly. The accuracy of beam data obtained with the PTW dosimetry diode and the PinPoint ion chamber was higher than those obtained with the PTW Semiflex ion chamber for small fields (2 × 2cm2 and 3 × 3cm2). However, the response of the PTW diode and the PinPoint ion chamber was significantly indifferent in these fields. Furthermore, axial orientation of the PTW Semiflex ion chamber improved accuracy of profiles and PDDs as compared to radial orientation, while such a difference was not significant for the PinPoint ion chamber. It is concluded that a scan time of 0.2s/point with a fanline scanning resolution of 2-1mm for beam profiles and 3mm for PDDs are most favorable in terms of accuracy and time efficiency. For small fields (2 × 2cm2 and 3 × 3cm2), a PinPoint ion chamber in radial orientation or a dosimetry diode in axial orientation are recommended for both beam profiles and PDDs. If a PinPoint ion chamber and a PTW dosimetry diode are not available, a Semiflex ion chamber in axial orientation may be used for small fields.

Secondary electron count imaging in SEM

Scanning electron microscopy (SEM) is a versatile technique used to image samples at the nanoscale. Conventional imaging by this technique relies on finding the average intensity of the signal generated on a detector by secondary electrons (SEs) emitted from the sample and is subject to noise due to variations in the voltage signal from the detector. This noise can result in degradation of the SEM image quality for a given imaging dose. SE count imaging, which uses the direct count of SEs detected from the sample instead of the average signal intensity, would overcome this limitation and lead to improvement in SEM image quality. In this paper, we implement an SE count imaging scheme by synchronously outcoupling the detector and beam scan signals from the microscope and using custom code to count detected SEs. We demonstrate a ∼30% increase in the image signal-to-noise-ratio due to SE counting compared to conventional imaging. The only external hardware requirement for this imaging scheme is an oscilloscope fast enough to accurately sample the detector signal for SE counting, making the scheme easily implementable on any SEM.

Experiment analysis of non-uniformity measurement by array detector scanning system

Solar simulator is used to analysis characteristic of the solar cells. The non-uniformity is its major performance. The traditional non-uniformity measurement calls single detector method. The paper’s objective is to design and construct an array detector scanning system and to determine the optimal scanning time to achieve the lowest uncertainty. To investigate the non-uniformity by our proposed method and the traditional method, our detector consisted of eight photodiodes mounted on an arm of a linear motion lead screw to guide the detector scaning onto the lighting area. A microcontroller applied for controling and measuring light irradiance in 64 points corresponding to IEC 60904-9 standard. The results showed that the array detector scanned at a speed of 33.33 mm/s to obtain the non-uniformity with the lowest uncertainty, less than 0.6%. Analysis results of the non-uniformity obtained from our system on the test areas of (mm×mm) 156×156, 166×166 and 200×200 compared with the single detector. It showed that the mean absolute error was 1.27. Our system provided a lower uncertainty than the traditional method. The measurement accuracy was acceptable. The advantage is for testing on different test areas within a single device. The measurement time is around 1/32 of the traditional method.

Prevalence of Artifacts in Cone-Beam Computed Tomography

Introduction: In dentistry, cone-beam computed tomography (CBCT) is an essential diagnostic technique. To use CBCT imaging technology efficiently, it is vital to understand its benefits and limits. Artifacts are discrepancies between the reconstructed visual image and the actual content of the subject that can reduce anatomic accuracy. Aims and Objectives: This study aimed to assess the prevalence of artifacts in CBCT images. Materials and Methods: Three hundred sixty-five CBCT images were retrospectively studied to identify artifacts, and the prevalence of different artifacts was recorded. Frequency and percentages are used for descriptive statistics. The Chi-square test was used for interventional statistics. Results: Artifacts were observed in two hundred forty-five images examined. The most prevalent image artifact recorded was the beam hardening artifact that falls under the physics-based category. Conclusion: Physics-based and scanner-based artifacts may be avoided by concentrating on X-ray parameters and scanner detector state, respectively. To limit the frequency of patient-based artifacts in CBCT images, patients should be instructed to remove any metallic jewelry and be stabilized appropriately. Scan time should be maintained to a minimum.