Tube Noise Research Articles

Evaluation of automatic tube current modulation in a CT scanner using a customised homogeneous phantom

Objective.The introduction of automatic tube current modulation (ATCM) has resulted in complex relationships between scanner parameters, patient body habitus, radiation dose, and image quality. ATCM adjusts tube current based on x-ray attenuation variations in the scan region, and overall patient dose depends on a combination of factors. This work aims to develop mathematical models that predict CT radiation dose and image noise in terms of attenuating diameter and all relevant scanner parameters.Approach.A homogenous phantom, equipped with the features to conduct discrete and continuous adaption tests, was developed to model ATCM in a Philips CT scanner. Scanner parameters were varied based on theoretical dose relationships, and a MATLAB script was developed to extract data from DICOM images. R statistical software was employed for data analysis, plotting, and regression modelling.Main Results.Phantom data provided the following insights: Median tube current decreased by 81% as tube potential varied from 80 kVp to 140 kVp. Doubling the DoseRight Index (DRI) from 12 to 24, at 24 cm diameter, produced a 294% increase in mA and a 46% decrease in noise. Mean mA increased by 53% whilst mean noise increased by 5.7% as helical pitch increased from 0.6 to 0.925. Changing rotation time from 0.33s to 0.75s gave a 56% reduction in mean mA and no change in image noise. Increasing detector collimation (n×T) resulted in higher tube currents and lower output image noise values, asnandTwere varied independently. Interpreting these results to apply transformations relevant to each independent variable produced models for tube current and noise with adjusted R-squared values of 0.965 and 0.912, respectively.Significance.The models developed more accurately predict radiation dose and image quality for specific patients and scanner settings. They provide imaging professionals with a practical tool to optimize scan protocols according to patient diameters and clinical objectives.

MCP-PMT quantum efficiency monitoring and operation status of the TOP counter at the Belle II experiment

The Belle II experiment is a high luminosity electron and positron collider experiment at SuperKEKB in Japan. The Time-Of-Propagation counter is a detector for particle identification in the barrel region. Micro-channel-plate photomultipliers are used as photodetectors and measure photon timing with a resolution of 30 ps; this leads to excellent particle identification performance. One of the issues is the photocathode lifetime of the photomultiplier tubes. Monitoring tools have been developed to measure the tube gain, accumulated output charge density and quantum efficiency during physics data taking. The gain was seen to decrease by about 10%. Although the accumulated output charge density is small compared to the tube expected lifetime, a quantum efficiency degradation was found larger than expected for 5% of the tubes after threshold efficiency calibration. Several causes for this degradation are being investigated. They can possibly be related to tube production and noise from the read-out system.

Technical Note: Assessment of Pulse Pileup on Single-Energy and Multienergy Images From a Clinical Photon-Counting Detector Computed Tomography.

Pulse pileup effects occur when pulses occur so close together that they fall on top of one another, resulting in count loss and errors in energy thresholding. To date, there has been little work systematically detailing the quantitative effects of pulse pileup on material decomposition accuracy for photon-counting detector (PCD) computed tomography (CT). Our aim in this work was to quantify the effects of pulse pileup on single-energy and multienergy CT images, including low-energy bin (BL), high-energy bin (BH), iodine map, and virtual noncontrast images from a commercial PCD-CT. Scans of a 20-cm diameter multienergy CT phantom with 10 solid inserts were acquired at a fixed tube potential as the tube current was varied across the available range. Four types of images (BL, BH, iodine map, and virtual noncontrast) were reconstructed using an iterative reconstruction algorithm at strength 2, a quantitative reconstruction kernel (Qr40), 2-/1-mm slice thickness/increment, and a 210-mm field-of-view. The mean and standard deviation of CT numbers were recorded and the ratios of CT number between BL and BH images were calculated and plotted, along with noise versus tube current and noise × versus tube current. As tube current was increased, the range of variations in CT numbers was less than 13.4 HU for all inserts and image types evaluated. Noise × versus tube current showed a small positive slope equal to a noise increase from 100 mA of 10% at 500 mA and 15% at 900 mA compared with what would be expected if the slope was zero. Minimal impact on single-energy and multienergy CT numbers and noise performance was observed for the evaluated clinical PCD-CT system.

Construction of U-Net++ pulmonary nodule intelligent analysis model based on feature weighted aggregation.

Lung cancer is a malignant tumor originating from the bronchial mucosa or glands of the lung. Early lung cancer patients often have no obvious symptoms, but early detection and treatment have an important clinical significance for prognostic effect. Computed tomography (CT) is one of the important means in the diagnosis of lung cancer. In order to better solve the problem of diagnosis efficiency, and reduce the rate of misdiagnosis and missed diagnosis, computer aided diagnosis are employed in the accurate localization and segmentation of pulmonary nodules through imaging diagnostics, image processing technology, and other clinical means. This present study was envisaged to establish an intelligent segmentation model of pulmonary nodules to improve the accuracy of early screening for lung cancer patients. Compared with the traditional segmentation model of fully convolutional neural network, the U-Net++ algorithm based on feature-weighted integration (WI-U-Net++) effectively utilized the feature weight information, adopted the adaptive weighted method for weighted integration, and performed an intelligent segmentation of the anatomical structure and image details, which was applied in the auxiliary diagnosis of pulmonary nodules in CT images. Standard chest X-ray phantom was selected as CT scanning objects, and 30 spherical and irregular simulated nodules were built into them, respectively. CT images were collected by setting different tube voltage and noise index, and randomly included into the training set, validation set and test set at a ratio of 8:1:1. The experimental results showed that the segmentation accuracy of WI-U-Net++ algorithm for spheroid nodules and irregular nodules was 98.75% and 83.47%, respectively, which was better than that of U-Net and U-Net++ algorithm. In the auxiliary diagnosis, the recall rate of the WI-U-Net++ algorithm for spheroid nodules and irregular nodules was 93.47% and 84.52%, respectively. The accuracy of the benign or malignant identification was 80.27%, and the AUC was 0.9342. U-Net++ algorithm based on feature-weighted integration could improve the segmentation effect of pulmonary nodules. Especially in the case of irregular nodules with malignant signs, the accuracy of clinical diagnosis was significantly improved, and the level of differential diagnosis between benign and malignant was improved.

A PHANTOM EVALUATION OF THE USE OF CT AUTOMATIC TUBE CURRENT MODULATION WITH LOW TUBE POTENTIALS FOR IODINATED CONTRAST STUDIES.

This paper aimed to investigate effects of different tube voltage and image quality settings on radiation dose and image quality for patients undergoing computed tomography iodinated contrast studies using automatic tube current modulation system and to recommend settings to achieve improved radiation dose and image quality values. A Pagoda phantom with an additional rod of iodine contrast was scanned using different tube voltages and noise index (NI) settings. Size-specific dose estimate (SSDE) and image quality (noise, contrast, contrast-to-noise ratio (CNR) and figure of merit (FOM)) were analysed. Values of SSDE were maintained with similar NI settings. Contrast and CNR were higher for lower tube voltage settings. Better FOM values can be achieved with higher NI settings with the lower kVs. To achieve better CNR and SSDE compared with the standard setting of 120kV, a 80kV with an NI setting of 15 was recommended.

An Approach to 1/f Noise Detection Based on Adaptive T-ATFPF Algorithm

The generation of 1/f noise is closely related to the quality defects of IGBT devices. In the process of detecting IGBT single tube noise, thermal noise and shot noise show obvious white noise characteristics in the low frequency band, which are detected under the background of strong white noise 1/f noise can characterize the performance of IGBT devices. Therefore, on the basis of the Time-Frequency Peak Filtering (TFPF) algorithm, a two-dimensional time-domain adaptive T-ATFPF algorithm is proposed, and the adaptive segmentation is realized by means of the confidence interval crossing criterion based on Chebyshev’s inequality. Variable window length,use a small window length to process the signal section, which retains more detailed information of the effective signal.Use a larger window length to process the buffer section to ensure a smooth transition.Use the large window length to process the noise section, which more effectively suppresses randomness for noise, apply T-ATFPF to artificial synthesis model and actual model. Experimental results indicate that compared with the conventional algorithm, the improved method can better recover 1/f noise, and the ratio of signal to noise is greatly improved by about 1.3dB.

Influence of CT acquisition and reconstruction parameters on radiomic feature reproducibility.

High-dimensional imaging features extracted from diagnostic imaging, called radiomics, are increasingly reported for diagnosis, prognosis, and response to therapy. Establishing the sensitivity of radiomic features to variation in scan protocols is necessary because acquisition and reconstruction parameters can vary widely across and within institutions. Our objective was to assess the reproducibility of radiomic features derived from computed tomography (CT) images by varying tube current (mA), noise index, and reconstruction [adaptive statistical iterative reconstruction (ASiR)], parameters increasingly varied by institutions seeking to reduce radiation dose in their patients. We extracted radiomic features from CT images of a uniform water phantom, anthropomorphic phantom, and a human scan. Scans were acquired from the phantoms with six tube currents (50, 100, 200, 300, 400, and 500mA) and five noise index levels (12, 14, 16, 18, and 20), respectively. Scans of the phantoms and patient were reconstructed from 0% ASiR (i.e., filtered back projection) to 100% ASiR in increments of 10%. Two hundred and forty-eight well-known radiomic features were extracted from all scans. The concordance correlation coefficient was used to assess agreement of features. Our analysis suggests that image acquisition parameters (tube current, noise index) as well as the reconstruction technique strongly influence radiomic feature reproducibility and demonstrate a subset of reproducible features potentially usable in clinical practice.

TC Protocol optimization: A quantitative approach

Introduction Every year the number of performed CT scans is dramatically increasing, so that protocol optimization in terms of dose and image quality is mandatory. Purpose To evaluate the efficacy of a novel objective method to compare different CT protocols based on a functional (F) encompassing signal to noise ratio (SNR), low contrast resolution (LCR) and CTDI. Materials and methods Catphan 600 was scanned with a Discovery 750 (GE healthcare) 64 slices CT scanner varying tube voltage (kV = 100, 120, 140) and noise index (NI = 8, 12). Images were reconstructed using the standard FBP algorithm. LCR was assessed with CTP515 analysis, SNR was evaluated for every CTP404 insert And CTDI was recorded from consolle. An F value was calculated for each protocol as follows: F prot ( α ) = ( 1 - α ) ∑ w ins SNR ins prot SNR ins ‾ + LCR ‾ LCR prot + α CTDI ‾ CTDI prot where average values were computed over all the protocols used and α is weighting factor which was varied between 0 and 1 to differently balance dose and quality aspects. For each selected α higher F values are associated with a better trade-off between image quality and dose. Results For α values between 0 and 0.6 higher F values were obtained for 120 kV/8 NI; for 0.7 ⩽ α ⩽ 1 the best trade-off was found for 100 kV/12 NI. Conclusion The proposed CT protocol optimization approach provided an objective way to balance between dose and image quality in phantom. Further studies are in progress to assess the performances of the method in vivo. Disclosure Authors disclose any relationship that may bias their presentation.

A prediction method for the general corrosion behavior of Alloy 690 steam generator tube using eddy current testing

The purpose of this work is to develop an eddy current testing method to predict the general corrosion behavior of Alloy 690 steam generator tubes. A corrosion test was conducted for tubes with different levels of eddy current noise in simulated primary water at 330°C, and their corrosion behavior was correlated with the tube noise measured using bobbin and rotating probes. The corrosion behavior was closely correlated with the tube noise measured using a rotating probe. However, there was no correlation between the corrosion behavior and the tube noise measured using a bobbin probe. The tube noise value measured using a rotating pancake coil probe is suggested to be a significant parameter in estimating the general corrosion behavior of tubes.

Comparison of impulse peak insertion loss measured with gunshot and shock tube noise sources

The National Institute for Occupational Safety and Health in cooperation with scientists from 3M and the U.S. Army Aeromedical Research Laboratory conducted a series of Impulse peak insertion loss (IPIL) tests of the acoustic test fixtures from the Institute de Saint Louis (ISL) with a 0.223 caliber rifle and two different acoustic shock tubes. The Etymotic Research ETYPlugs™ earplug, 3M™ TacticalPro™ communication headset and the dual protector combination were tested with all three impulse noise sources. The spectra, IPIL, and the reduction of different damage risk criteria will be presented. The spectra from the noise sources vary considerably with the rifle having peak energy at about 1000 Hz. The shock tubes had peak levels around 125 and 250 Hz. The IPIL values for the rifle were greater than those measured with the two shock tubes. The shock tubes had comparable IPIL results except at 150 dB for the dual protector condition. The treatment of the double protection condition is complicated because the earmuff reduces the shock wave and reduces the effective level experienced by the earplug. For the double protection conditions, bone conduction presents a potential limiting factor for the effective attenuation that can be achieved by hearing protection.

Comparison of different phantom designs for CT scanner automatic tube current modulation system tests

Modern CT scanners modulate tube current during scans according to patient size, shape and attenuation. However, the ATCM (automatic tube current modulation) systems for different CT manufacturers work on different principles. Although the systems are used for the majority of patients and examinations, there is no standard phantom for routine quality control of CT scanner ATCM operation. The ideal phantom for testing these systems should be capable of evaluating how tube current and image quality as well as dose vary according to changes in patient size and shape. For this study, a conical phantom designed by ImPACT has been compared with two phantoms made from elliptical sections with varying dimensions. The concept of the designs is to reflect the ATCM performance for the varying shapes and dimensions along the length of the human body. The first phantom comprises five elliptical sections with a wide range of different dimensions and the second has three sections that are more similar in size. The phantoms have been used to test ATCM systems for Philips, Siemens, GE and Toshiba scanners. Although the results of the tube current modulation patterns were similar for all CT scanners, the abrupt changes in attenuation for the first sectional phantom provoked an abnormal ATCM response for the GE and Toshiba scanners. The second sectional phantom was developed from the results of the first, and was more effective for ATCM system testing and could be used for dose and image quality assessment in standard positions. However, the ImPACT conical phantom provided the best overall assessment of performance in terms of tube current modulations and noise pattern.

Comparison of deuterated and normal liquid scintillators for fast-neutron detection

Liquid organic scintillators have long been used for fast-neutron detection due to their fast response and the ability to use pulse-shape discrimination (PSD) to distinguish between neutron and γ-ray interactions. Deuterated liquid organic scintillators have, in addition to the aforementioned properties, structure on their pulse-height spectra due to the different characteristics of n–d vs. n–p scattering.We report on the direct comparison of two small-volume liquid scintillator detectors with exactly the same geometries (11.43cm diameter and 2.54cm thickness); the first based on NE213 produced by Nuclear Enterprise, and the second based on EJ-315 produced by Eljen Technologies, the latter being a deuterated scintillator. A variety of photomultiplier tubes (PMTs) were used, but the quality of the data was determined to be independent of the PMT type.It is shown that, while the light output of the deuterated detector is lower than for the conventional non-deuterated detector, it is possible to detect 60keV neutrons. The PSD capabilities of the deuterated detector match and surpass those of the NE213 detector. Its efficiency is comparable to that of the NE213 detector at neutron energies above 2MeV; below that energy its relative efficiency suffers from the significantly lower n–d scattering cross-section. For very low neutron energies (<200keV), the relative efficiency of the deuterated detector increases again, due to the lower noise level for our particular detectors, showing the importance of low photomultiplier tube noise for the detection of low-energy neutrons.

Performance of longitudinal and volumetric tube current modulation in a 64-slice CT with different choices of acquisition and reconstruction parameters

Aim of the study was to evaluate the performance of a tube current modulation (TCM) system (SUREExposure 3D).On a 64 detector-row CT scanner (Aquilion 64, Toshiba), performance of fixed tube current, longitudinal TCM, and volumetric TCM acquisitions were assessed. A homogeneous cone-shaped phantom and an anthropomorphic phantom were used. Tube current and noise profiles were quantitatively analysed by box and whisker plots when phantom size, acquisition, and reconstruction parameters were varied.At similar median noise, fixed tube current scanning showed a noise range of 16.8–38.3 HU, while longitudinal TCM showed a range of 19.4–31.4 HU and volumetric TCM showed an even lower range of 20.7–28.7 HU. When acquisitions resulting in similar image quality (noise) were compared, the use of volumetric compared to longitudinal TCM resulted in a variable radiation dose reduction up to 6.6%.In conclusion, SUREExposure 3D resulted in more uniform image quality at a lower dose. Volumetric TCM shows improved results over longitudinal TCM.

Fluctuations of electroluminescence intensity of single CdSe nanocrystals excited by scanning tunneling microscope current

Electroluminescence from single CdSe nanocrystals (NCs) excited by tunneling current of scanning tunneling microscope (STM) has been measured. Two types of samples with low and high concentration of CdSe NCs deposited on the gold substrate have been prepared. Both types of samples had no plasmon emission. It enabled one to detect pure electroluminescence from single CdSe NCs. Samples with low concentration of NCs exhibit an intensive short-term luminescence of NCs for several seconds. Samples with high concentration of NCs exhibit a weak fluctuating long-term luminescence for thousand seconds. Fluctuations of NC electroluminescence differ considerably from those detected recently in photoluminescence of CdSe NCs embedded in polymer films. The difference in fluctuations results from the difference in physical conditions existing in electro- and photoluminescence. The distribution of photons w(N, T) emitted in time interval T has been found from statistical treating of fluctuating luminescence. Due to weakness of the pure signal, we paid a special attention to allowing for photomultiplier tube noise while treating these fluctuations. The photon distribution in pure signal is one of super-Poisson type, i.e. it is broader than Poisson distribution. A dynamical model for an absorber–emitter excited by tunneling current of STM has been offered. The model takes into account the thermal drift of STM tip.

Relationship between chest lateral width, tube current, image noise, and radiation exposure associated with coronary artery calcium scanning on 320-detector row CT

The relationship between chest lateral width, tube current, image noise, and radiation exposure on 320-detector row CT has not been reported. We investigated the relationships between chest lateral width, estimated radiation exposure (DLPe), and image noise in 300 patients undergoing clinical coronary calcium scanning. Patients undergoing coronary calcium scanning with 320-detector row CT (prospective, volumetric mode, 120 kV of tube voltage, 100-550 mA of tube current, 0.5-mm detector width) were grouped by chest lateral width (small, medium, and large) from anteroposterior topograms and 100 consecutive patients were selected from each group (n = 300). Tube current, DLPe, and noise were compared among groups with Kruskal-Wallis or one-way ANOVA. Phantom experiments were performed to evaluate the accuracy of calcium quantification as a function of size and tube current. Median tube current in small, medium, and large patients was 130, 200, and 250 mA, respectively (P < 0.0001). Despite the use of higher tube current settings, noise levels also increased with size (20.2 ± 4.5 HU, 22.0 ± 3.9 HU, and 25.1 ± 4.9 HU, respectively; global P < 0.001). DLPe was significantly higher with increasing size (54, 83, and 104 mGy · cm, respectively; P < 0.0001). Phantom experiments showed that 50-100 mA, 150-200 mA, and approximately 300 mA in small, medium, and large phantoms were associated with stable estimate of calcium. Increasing chest lateral width is associated with increasing radiation exposure and image noise. The use of 50-100 mA in small and 150-200 mA in medium patients is associated with acceptable noise and stable estimate of coronary artery calcium. In large patients, precise identification of individual calcified lesions remains difficult despite increasing tube current and radiation exposure.

Multi-detector row spiral CT angiography of the thoracic outlet: dose reduction with anatomically adapted online tube current modulation and preset dose savings.

To evaluate image quality obtained with anatomically adapted online tube current modulation and preset minimum dose savings at multi-detector row spiral computed tomographic (CT) angiography of the thoracic outlet. A total of 100 patients were evaluated for thoracic outlet arterial syndrome with spiral CT angiography (collimation, 4 x 1 mm; pitch, 1.75) both with and without dose reduction by means of anatomically adapted online tube current modulation and preset minimum dose savings. Preset minimum savings of 20% and of 32% were applied in two groups of 50 patients (groups 1 and 2). In each group, low-dose scanning was performed in 25 patients in the neutral position and in 25 patients after postural maneuver. Tube current-time product, noise, presence and quality of graininess and of linear streak artifacts on transverse CT scans, and diagnostic value of sagittal reformations and volume-rendered images were evaluated and recorded for each data set. chi2 test was used to compare frequencies; paired Wilcoxon rank test, to compare subjective and objective image quality scores. P <.05 indicated a significant difference. In group 1, mean tube current-time product was 3225 mAs for reference scans and 2101 mAs for low-dose scans (mean reduction, 35%; range, 27%-47%). In group 2, mean was 3070 mAs for reference scans and 2068 mAs for low-dose scans (mean reduction, 33%; range, 17%-38%). In group 1, no differences in frequencies of graininess and linear streaking or in noise level were found between images acquired with or without dose reduction. In group 2, no difference was found in noise level between low-dose and reference scans. On low-dose scans, moderate linear streaking was observed with lower frequency and moderate graininess was observed with higher frequency, but artifacts did not compromise image quality or prevent confident assessment of arterial diameter in the three compartments of the thoracic outlet. Online tube current modulation with a preset minimum dose saving of 20% allowed 35% reduction in mean tube current-time product, with no loss in image quality.

Vacuum photodetectors for e +e − collider detectors in BINP

The test results of vacuum phototriodes (VPT) and PMT with microchannel plates (MCPT) are described. About 3000 VPTs now operate successfully in the BINP collider detector. Some recent results on MCPT are presented, in particular tube counting rate capability and the effect of a thin Al film on tube noise. The first measurements of the hybrid PMT with a silicon diode were performed.

X‐ray tube noise and vibration reduction

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Tritium monitoring system for near ambient measurements

The authors describe the current status of research on an improved tritium measurement system at the Oak Ridge National Laboratory (ORNL) for the US Navy. Present tritium-in-air monitoring systems installed by the Navy can reliably measure to less than 10 mu Ci/m/sup 3/, but medical and safety issues are pushing measurement needs to below 1 mu Ci/m/sup 3/, which is equivalent to 1-10 mu Ci/ml in liquid samples, using calcium metal converter. A significant effort has been expended over the past 10 years by the Navy RADIAC development program at ORNL on various schemes to improve the detection of tritium in both air and liquid at near ambient levels. One such scheme includes a liquid flowthrough system based on an NE 102 sponge scintillator with dual photomultiplier tubes for tube noise rejection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A New Technique for the Characterization of Cesium Beam Tube Performance

Abstract : Cesium beam tube atomic standards tend to exhibit a decreasing beam tube current with time. This report describes a technique to measure noninvasively the product of electron multiplier gain and noise figure, as well as tube signal and noise performance, thus providing information to discriminate between possible causes of decreasing beam tube current. The technique characterizes cesium beam tube performance without measuring clock frequency stability. Consequently, no extensive analysis of long term data is required. The technique is also applicable to a simular evaluation of photomultiplier tubes. Keywords: Atomic clocks; Cesium beam tubes; Electron multiplier gain; Electron multiplier noise.